SYSTEM AND METHOD FOR PREPARING PURE METALLIC NANOPARTICLES USING A DIRECT ELECTRIC ARC

Abstract

A method for synthesizing pure metallic nanoparticles (MNPs) uses a direct electric arc process. The method involves arranging a pair of tungsten filament electrodes within a reaction chamber, connected via a graphite rod passed through a quartz tube. An aqueous solution of a metal nitrate precursor, preferably Fe(NO.sub.3).sub.3.Math.9H.sub.2O, is introduced into the quartz tube. An inert gas, preferably argon, is supplied to maintain an oxygen-free atmosphere. A high voltage is applied across the electrodes to generate an electric arc, which creates a localized plasma, vaporizing the metal ions in the solution. The vaporized metallic species are rapidly cooled and condensed in the inert atmosphere, forming metallic nanoparticles with high purity. The resulting nanoparticles are then collected and washed with water to remove residual contaminants. This method provides a scalable, efficient, and environmentally friendly approach to produce MNPs with controlled size and morphology, suitable for various industrial and scientific applications.

Claims

1. A method for preparing pure metallic nanoparticles using a direct electric arc, comprising: arranging a pair of electrodes within a reaction chamber, wherein at least one of the electrodes is a filament connected to a graphite rod and passed through a quartz tube, wherein said electrodes comprise tungsten filaments; introducing an aqueous solution of a metallic precursor into the quartz tube within the reaction chamber, wherein said metallic precursor is a metal nitrate salt preferably 0.05-0.25 M Fe(NO.sub.3).sub.3.Math.9H.sub.2O is prepared using deionized water; introducing an inert gas into the reaction chamber at a flow rate of approximately 10-15 mL/min; applying a high voltage between the electrodes to generate an electric arc, and creating a plasma by applying a high voltage across the electrodes to vaporise the metal ions and to convert them into MNPs and maintaining the electric arc with a continuous electric current, thereby localized vaporizing the aqueous solution, wherein the electric arc is initiated with a breakdown voltage of approximately 240 V and is maintained with a sustaining voltage of approximately 80-90 V; cooling and condensing vaporized metallic components escaping the electric arc into an inert atmosphere upon subjecting the vapor to rapid thermal quenching in a cooler argon-filled region, thereby inducing homogeneous nucleation, thereby forming metallic nanoparticles, wherein said inert gas is argon; and collecting the formed metallic nanoparticles and washing the nanoparticles with water to remove any residual contaminants, wherein the tungsten filament electrodes are arranged such that the inter-electrode gap is precisely maintained at 2.00.2 mm using a micrometer-controlled actuator coupled with a servo motor, the actuator being automatically regulated through a closed-loop feedback system receiving real-time arc length measurements from a laser displacement sensor, wherein adjustments are made every 0.2 seconds during discharge to counter electrode erosion, thereby ensuring plasma column stability, uniform arc temperature of 4800-5200 K, and reproducible vaporization of the aqueous precursor droplets; and wherein the Fe(NO.sub.3).sub.3.Math.9H.sub.2O solution of 0.05-0.25 M concentration is introduced via a peristaltic pump at a controlled rate of 0.35-0.45 mL/min into the quartz tube through a stainless-steel nozzle having a bore diameter of 0.300.02 mm and positioned at an angle of 422 relative to the electrode axis, the nozzle being heated externally by a nichrome coil maintained at 90-95 C. to achieve partial evaporation, thereby reducing droplet diameter to below 20 m prior to entry into the arc discharge zone.

2. The method of claim 1, further comprising: cleaning the collected metallic nanoparticles multiple times with water; wherein the electric arc is generated for a duration of approximately 20 minutes; and adjusting at least one parameter selected from the group consisting of: the cooling rate, the electric arc parameters (current, voltage, duration), the composition of the aqueous solution, and the inert gas flow rate, to control the average diameter of the synthesized Fe NPs.

3. The method of claim 2, wherein initiation of the electric arc is accomplished by applying a high-voltage pulse of 240-250 V for 0.2-0.4 seconds to achieve breakdown, followed by stabilization of the discharge at a sustaining voltage of 80-90 V with a current of 85-95 A, wherein the current is modulated by a pulse-width modulation driver operating at 7010 Hz with a duty cycle of 50-60%; and wherein the discharge chamber is operated at 0.9-1.1 atm pressure regulated by a back-pressure control valve connected to a downstream vacuum pump, wherein synchronization between precursor feed rate, arc current, and argon flow is achieved by a programmable logic controller that dynamically tunes these parameters every 500 ms, thereby maintaining steady vaporization conditions and preventing incomplete decomposition of precursor droplets.

4. The method of claim 1, wherein the argon carrier gas having 99.999% purity is introduced into the chamber at a flow rate of 121 mL/min using a digital mass flow controller with 1% accuracy, said gas being preconditioned by sequential passage through a silica gel dryer, a 3 molecular sieve, and a 0.2 m PTFE particulate filter, wherein a stainless-steel diffuser plate installed at the inlet ensures laminar distribution across the plasma region.

5. The method of claim 1, wherein vaporized metallic species are quenched in a double-jacketed quartz condensation chamber with inner wall water circulation at 15-20 C. regulated by a PID-controlled chiller, wherein the residence time of vapor within the cooling zone is adjusted to 160-180 ms by maintaining argon velocity at 0.12-0.14 m/s, and wherein the chamber incorporates a conical expansion section angled at 18+2; and wherein the condensation chamber inner surface is lined with fused quartz polished to Ra<0.2 m to minimize heterogeneous nucleation, and wherein the expansion geometry prevents stagnation zones by gradually reducing flow velocity.

6. The method of claim 1, wherein nanoparticle collection is performed by directing the cooled argon-nanoparticle stream onto a stainless-steel mesh collector having pore size 50-70 m, the mesh being maintained at 5-10 C. using a thermoelectric Peltier cooler.

7. The method of claim 2, wherein the collected nanoparticles are subjected to sequential washing cycles comprising dispersion in deionized water at a ratio of 0.1 g per 100 mL, ultrasonication at 40 kHz for 10-15 minutes to break soft agglomerates, and centrifugation at 8500500 rpm for 10 minutes to separate metallic nanoparticles from ionic residues, said cycle being repeated at least three times until residual conductivity of wash supernatant is less than 10 S/cm; and wherein the washed nanoparticles are redispersed in ethanol containing 0.05 wt. % polyvinylpyrrolidone (PVP), the dispersion being rotary evaporated at 50-55 C. under 100-150 mbar vacuum until dryness, followed by vacuum drying at 60 C. for 8-10 hours in a desiccator.

8. The method of claim 1, wherein the electrodes are coated prior to use with a graphite film of 50-100 m thickness deposited by brushing colloidal graphite suspension followed by drying at 80 C. for 2 hours, the coating reducing tungsten sputtering and preventing incorporation of tungsten impurities in the nanoparticles; and wherein the reaction chamber incorporates a dual-zone cooling jacket, the upstream loop maintaining electrode temperature at 40-50 C. using hot water circulation, and the downstream loop providing quenching at 10-15 C. using chilled water, each loop being independently PID-controlled to 0.5 C. stability.

9. The method of claim 2, wherein precursor solution is degassed by ultrasonication at 40 kHz for 15 minutes followed by vacuum evacuation at 100 mbar for 5 minutes prior to introduction, said degassing eliminating entrapped bubbles that otherwise destabilize atomization and arc stability; and wherein nanoparticles are washed alternately with ethanol and acetone, each cycle comprising 5 minutes ultrasonication and 10 minutes centrifugation at 10,000 rpm, the alternating polar-nonpolar solvent washing improving removal of carbonaceous impurities and enhancing nanoparticle surface passivation.

10. The method of claim 1, wherein droplet injection into the arc zone is synchronized with plasma oscillations using a phase-locked loop control system that detects plasma light intensity via photodiodes and modulates peristaltic pump speed in-phase with high-energy intervals; and wherein nucleated nanoparticles are passed through a cyclone separator operated at inlet velocity 12-14 m/s and cut size of 15-20 nm, wherein oversized agglomerates are separated into the underflow, while primary nanoparticles are collected in the overflow stream.

11. The method of claim 1, wherein a capping step is employed by dispersing washed nanoparticles in 0.1 wt. % sodium citrate aqueous solution followed by ultrasonication for 20 minutes at 50 kHz, said citrate molecules binding via carboxylate groups to nanoparticle surfaces, imparting electrostatic stabilization and preventing agglomeration in suspension; and wherein the stabilized suspension is freeze-dried by pre-freezing at 40 C. for 6 hours and sublimation under vacuum of 10.sup.3 mbar for 24 hours.

12. The method of claim 1, wherein the final nanoparticle powder is sieved through a 325-mesh stainless steel sieve to eliminate agglomerates>45 m, and wherein the sieved powder is packaged in vacuum-sealed laminated aluminum pouches containing oxygen scavenger sachets rated at 50 mL O.sub.2/g, thereby ensuring stable storage with minimized oxidation; and wherein the condensation chamber is equipped with an acoustic standing-wave generator operating at 20-25 kHz and 0.5-1 W/cm.sup.2, wherein the acoustic field enhances Brownian dispersion, prevents chain-like agglomerate formation, and promotes spherical nanoparticle morphology.

13. The method of claim 2, wherein the arc chamber walls are periodically passivated by flushing with 0.1 M nitric acid, rinsing with deionized water, and drying at 120 C. for 2 hours, such maintenance preventing contamination by deposited metallic residues and preserving nanoparticle purity over repeated runs; and wherein a neodymium permanent magnet of 0.8-1.0 T is applied externally to the washed nanoparticle suspension in ethanol, thereby magnetically retaining metallic particles while non-magnetic impurities are decanted, and wherein retained particles are re-dispersed and washed, yielding purified metallic nanoparticles with minimal oxide inclusions.

14. The method of claim 1, wherein precursor concentration is dynamically varied between 0.05 M and 0.25 M by blending two reservoirs through a computer-controlled manifold, thereby producing oscillatory supersaturation within the plasma, inducing repeated nucleation pulses, and yielding narrower particle size distribution; and wherein nanoparticle formation is monitored in situ using a laser scattering probe positioned at the condensation outlet, said probe operating at 532 nm with multi-ange detection, wherein scattering signals are fed to a control algorithm that adjusts argon flow and precursor feed in real time, thereby maintaining targeted nanoparticle size distribution within 10% of set value.

15. The method of claim 1, wherein the annealed nanoparticles are transferred into an inert-atmosphere glove box having oxygen concentration less than 1 ppm and water vapor concentration less than 1 ppm, sealed in borosilicate ampoules under vacuum of 10.sup.3 mbar, and flame-sealed using a micro-oxygen torch while monitoring internal pressure with a Pirani gauge, thereby ensuring oxygen-free long-term storage; and wherein the plasma discharge is stabilized by introducing a secondary shielding flow of argon gas injected coaxially around the quartz tube at 2-3 mL/min, wherein the shielding flow prevents infiltration of atmospheric oxygen through micro-leaks, reduces convective losses at the plasma boundary.

16. The method of claim 2, wherein the electrodes are cooled by an integrated water-cooled copper jacket surrounding the electrode holders, the cooling water being circulated at 200-250 mL/min and maintained at 251 C., wherein said cooling prevents thermal deformation of tungsten filaments during sustained discharge; and wherein an auxiliary hydrogen-containing reducing gas consisting of 95% argon and 5% hydrogen is introduced downstream of the plasma zone at 1-2 mL/min, wherein said reducing gas scavenges oxygen residues during condensation.

17. The method of claim 1, wherein in-situ optical emission spectroscopy is performed during arc discharge by placing a fiber optic probe at 45 inclination to the plasma column, said probe transmitting real-time emission data to a spectrometer calibrated at 200-800 nm, wherein spectral line intensity ratios are monitored to estimate plasma temperature, and wherein precursor feed rate is dynamically adjusted based on said spectral data to maintain vaporization efficiency above 95%; and wherein nanoparticle growth suppression is further achieved by pulsing the precursor feed with an on-off cycle of 2-3 seconds at constant flow rate of 0.35-0.45 mL/min, wherein during the off interval, supersaturation in the plasma reduces.

18. The method of claim 1, wherein the condensation chamber is configured with an internal helical flow-guiding insert fabricated from quartz with pitch of 20-25 mm, said insert imparting controlled swirl to the argon flow at Reynolds number below 2000.

19. The method of claim 1, wherein the collected nanoparticles are subjected to low-energy plasma cleaning in a downstream RF plasma chamber operated at 13.56 MHz and 30-40 W power under argon pressure of 0.5-1.0 Torr for 5-10 minutes, wherein such treatment removes surface-bound organic contaminants and enhances metallic surface purity without altering nanoparticle size; and wherein nanoparticle collection efficiency is increased by applying an electrostatic field of 2-4 kV/cm across the condensation chamber, said field being generated by electrodes embedded along the chamber walls, wherein the charged metallic nanoparticles experience electrophoretic migration toward the collection substrate, thereby increasing deposition yield by 20-30%; and wherein prior to initiation of the electric arc, the entire reaction chamber is purged with argon at a high flow rate of 50-60 mL/min for 10-15 minutes, followed by stabilization at 121 mL/min during synthesis.

Description

BRIEF DESCRIPTION OF FIGURES

[0024] These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read concerning the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0025] FIG. 1 illustrates a block diagram of a system for preparing pure metallic nanoparticles in accordance with an embodiment of the present disclosure;

[0026] FIG. 2 illustrates a flow chart of a method for preparing pure metallic nanoparticles using a direct electric arc in accordance with an embodiment of the present disclosure;

[0027] FIG. 3 (a) illustrates Designed experimental set-up for the fabrication of MNPs using electric arc;

[0028] FIG. 3(b) Mechanism involved during the formation of MNPs from metal ions in electric arc generated plasma in accordance with an embodiment of the present disclosure;

[0029] FIG. 4 (a) illustrates The Captured photo of the designed electric arc setup during the formation of MNPs;

[0030] FIG. 4 (b) illustrates the Fe(NO.sub.3).sub.3.Math.9H.sub.2O salt paste;

[0031] FIG. 4 (c) illustrates Collected Fe NPs after the completion of electric arc treatment on Fe(NO.sub.3).sub.3.Math.9H.sub.2O solution;

[0032] FIG. 5 (a) illustrates SEM pictures at 500 nm;

[0033] FIG. 5 (b) illustrates SEM pictures at 150 nm; and

[0034] FIG. 5 (c) illustrates EDX spectrum of the prepared Fe NPs using direct electric arc approach in accordance with an embodiment of the present disclosure.

[0035] Further, skilled artisans will appreciate those elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION

[0036] To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0037] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

[0038] Reference throughout this specification to an aspect, another aspect or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase in an embodiment, in another embodiment and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0039] The terms comprises, comprising, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by comprises . . . a does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0041] Embodiments of the present disclosure will be described below in detail concerning the accompanying drawings.

[0042] Referring to FIG. 1, a block diagram of a system for preparing pure metallic nanoparticles is illustrated in accordance with an embodiment of the present disclosure. The system (100) includes a quartz tube reaction chamber (102) configured to contain an aqueous solution of a metallic precursor, wherein said metallic preferably 0.05-0.25 M Fe(NO.sub.3).sub.3.Math.9H.sub.2O is prepared using deionized water.

[0043] In an embodiment, a pair of electrodes (104) are positioned within the reaction chamber (102) and configured to generate an electric arc therebetween for a duration of 20 minutes, wherein at least one of the electrodes (104) is a filament connected to a graphite rod (106). These electrodes were fixed with the assistance of engineers. As can be observed in the figure, they placed the electrodes in the holders consisting of quartz tubes, and then they covered the electrodes with quartz tubes.

[0044] In an embodiment, a power supply (108) is coupled to the electrodes (104) and configured to provide a high voltage and a continuous electric current to maintain the electric arc.

[0045] In an embodiment, an inert gas inlet (110) is configured to introduce an inert gas into the reaction chamber (102) for maintaining an inert atmosphere, wherein said inert gas is argon.

[0046] In an embodiment, a vaporization zone (112) is within the arc region for inducing localized plasma-assisted evaporation of metal ions from the aqueous solution.

[0047] In an embodiment, a cooling and condensation chamber (114) downstream of the arc region is used for cooling vaporized metallic species and condensing them into nanoparticles.

[0048] In an embodiment, a collection mechanism (116) is configured to retrieve condensed metallic nanoparticles and wash the nanoparticles with water to remove any residual contaminants.

[0049] In another embodiment, the electrodes (104) comprise tungsten filaments, wherein the pair of electrodes are separated by a gap of 2-5 mm, with one electrode tip positioned to be in direct contact with or in close proximity to the aqueous solution.

[0050] In a further embodiment, inducing localized plasma-assisted evaporation comprises positioning at least one electrode in direct contact with or in close proximity to the aqueous solution. Then, initiating and stabilizing the direct electric arc to generate a localized, high-temperature plasma zone at the interface with the aqueous solution. Then, transferring thermal energy from the localized plasma to the aqueous solution, causing superheating of the solution. Then, nucleating and rapidly expanding microbubbles within the superheated solution, leading to the ejection of water molecules and dissolved metal ions into the plasma phase. Thereafter, atomizing and ionizing the ejected metal ions within the plasma.

[0051] In some embodiments, the electric arc is maintained by a constant current power supply that provides a stable current to the electrodes, wherein the inert gas is supplied at a flow rate of approximately 10-15 mL/min.

[0052] The system (100) further comprising a high-purity graphite rod with an erosion rate that is managed by regular reshaping or replacement.

[0053] In some embodiments, the cooling and condensation chamber further comprises a closed-loop water cooling system to maintain the temperature of the vaporized metallic species below 25 C.

[0054] FIG. 2 illustrates a flow chart of a method for preparing pure metallic nanoparticles using a direct electric arc in accordance with an embodiment of the present disclosure. At step (202), method (200) includes arranging a pair of electrodes within a reaction chamber, wherein at least one of the electrodes is a filament connected to a graphite rod and passed through a quartz tube, wherein said electrodes comprise tungsten filaments, wherein the pair of electrodes are separated by a gap of 2-5 mm, with one electrode tip positioned to be in direct contact with or in close proximity to the aqueous solution.

[0055] At step (204), method (200) includes introducing an aqueous solution of a metallic precursor into the quartz tube within the reaction chamber, wherein said metallic precursor is a metal nitrate salt preferably 0.05-0.25 M Fe(NO.sub.3).sub.3.Math.9H.sub.2O is prepared using deionized water.

[0056] At step (206), method (200) includes introducing an inert gas into the reaction chamber at a flow rate of approximately 10-15 mL/min.

[0057] At step (208), method (200) includes applying a high voltage between the electrodes to generate an electric arc thereby creating a plasma by applying a high voltage across the electrodes to vaporise the metal ions and to convert them into MNPs and maintaining the electric arc with a continuous electric current, thereby localized vaporizing the aqueous solution, wherein the electric arc is initiated with a breakdown voltage of approximately 240 V and is maintained with a sustaining voltage of approximately 80-90 V.

[0058] At step (210), method (200) includes cooling and condensing vaporized metallic components escaping the electric arc into an inert atmosphere upon subjecting the vapor to rapid thermal quenching in a cooler argon-filled region, thereby inducing homogeneous nucleation, thereby forming metallic nanoparticles, wherein said inert gas is argon.

[0059] At step (212), method (200) includes collecting the formed metallic nanoparticles and washing the nanoparticles with water to remove any residual contaminants.

[0060] The method (200) further comprising cleaning the collected metallic nanoparticles multiple times with water.

[0061] In another embodiment, the electric arc is generated for a duration of approximately 20 minutes.

[0062] The method (200) further comprising adjusting at least one parameter selected from the group consisting of: the cooling rate, the electric arc parameters (current, voltage, duration), the composition of the aqueous solution, and the inert gas flow rate, to control the average diameter of the synthesized Fe NPs.

[0063] In an embodiment, the tungsten filament electrodes are arranged such that the inter-electrode gap is precisely maintained at 2.00.2 mm using a micrometer-controlled actuator coupled with a servo motor, the actuator being automatically regulated through a closed-loop feedback system receiving real-time arc length measurements from a laser displacement sensor, wherein adjustments are made every 0.2 seconds during discharge to counter electrode erosion, thereby ensuring plasma column stability, uniform arc temperature of 4800-5200 K, and reproducible vaporization of the aqueous precursor droplets; and wherein the Fe(NO.sub.3).sub.3.9H.sub.2O solution of 0.05-0.25 M concentration is introduced via a peristaltic pump at a controlled rate of 0.35-0.45 mL/min into the quartz tube through a stainless-steel nozzle having a bore diameter of 0.300.02 mm and positioned at an angle of 422 relative to the electrode axis, the nozzle being heated externally by a nichrome coil maintained at 90-95 C. to achieve partial evaporation, thereby reducing droplet diameter to below 20 m prior to entry into the arc discharge zone.

[0064] In this embodiment, the process achieves high stability and reproducibility in nanoparticle synthesis through a dual-control strategy that simultaneously regulates the arc plasma conditions and the precursor droplet delivery. The tungsten filament electrodes are spaced at a narrow tolerance of 2.00.2 mm, but instead of relying on static positioning, a micrometer-controlled actuator coupled with a servo motor ensures active compensation for electrode wear during continuous discharge. Real-time arc length is monitored by a laser displacement sensor, and corrections are applied automatically every 0.2 seconds, which effectively counteracts gradual erosion of tungsten tips. This continuous correction eliminates fluctuations in the plasma column length that would otherwise destabilize arc temperature. By maintaining arc stability, the plasma consistently operates at 4800-5200 K, a range suitable for complete and reproducible vaporization of the precursor solution.

[0065] The precursor delivery system further ensures uniform feed into the plasma. The aqueous Fe(NO.sub.3).sub.3.Math.9H.sub.2O solution, within a concentration window of 0.05-0.25 M, is pumped using a peristaltic pump that delivers a steady and pulsation-free flow rate of 0.35-0.45 mL/min. The nozzle, engineered from stainless steel with a bore diameter precisely controlled to 0.300.02 mm, provides consistent droplet formation and directional control. Its angular positioning at 422 relative to the electrode axis optimizes droplet interception with the plasma core, avoiding direct electrode impingement that could disturb arc stability. To further enhance vaporization efficiency, the nozzle is externally heated by a nichrome coil maintained at 90-95 C., which partially evaporates solvent from the droplets before they enter the discharge zone. This thermal preconditioning reduces droplet diameters to below 20 m, ensuring that they completely vaporize within the plasma without producing unreacted residues or causing localized quenching.

[0066] The synergy between precise electrode regulation and pre-conditioned precursor injection provides a reproducible balance of plasma stability and feed uniformity. The closed-loop electrode adjustment guarantees a constant high-temperature environment, while droplet size reduction ensures consistent interaction with the plasma, preventing variability in particle nucleation. Together, these controls lead to uniform vapor-phase formation of metallic species, enabling the downstream production of nanoparticles with narrow size distributions and high purity.

[0067] In an embodiment, initiation of the electric arc is accomplished by applying a high-voltage pulse of 240-250 V for 0.2-0.4 seconds to achieve breakdown, followed by stabilization of the discharge at a sustaining voltage of 80-90 V with a current of 85-95 A, wherein the current is modulated by a pulse-width modulation driver operating at 7010 Hz with a duty cycle of 50-60%, thereby damping arc instabilities, reducing temperature oscillations, and enabling consistent vapor-phase formation of metallic species; and wherein the discharge chamber is operated at 0.9-1.1 atm pressure regulated by a back-pressure control valve connected to a downstream vacuum pump, wherein synchronization between precursor feed rate, arc current, and argon flow is achieved by a programmable logic controller that dynamically tunes these parameters every 500 ms, thereby maintaining steady vaporization conditions and preventing incomplete decomposition of precursor droplets.

[0068] In this embodiment, the operation of the plasma discharge is carefully engineered through a combination of staged arc initiation, real-time electrical modulation, and synchronized process control, each element contributing to stability and reproducibility of nanoparticle formation. The discharge begins with a controlled high-voltage pulse in the range of 240-250 V applied for 0.2-0.4 seconds, which provides sufficient energy to overcome the dielectric breakdown of the inter-electrode gap and transition from non-conductive to plasma-conductive state. This staged ignition step avoids prolonged unstable glow discharge phases that typically cause electrode pitting and arc wandering. Once the arc column is established, the sustaining conditions are immediately switched to a lower but stable operating voltage of 80-90 V, supported by a high current of 85-95 A. These values are chosen to maintain plasma temperatures in the range required for complete decomposition and vapor-phase generation of metallic species from the precursor feed.

[0069] To further refine arc stability, the discharge current is not supplied in a constant DC mode but rather modulated using a pulse-width modulation (PWM) driver operating at 7010 Hz. By controlling the duty cycle at 50-60%, the plasma is periodically relaxed and re-energized, which damps out oscillations that arise from turbulence or electrode erosion. This prevents thermal overshooting and reduces temperature fluctuations within the plasma column, resulting in more consistent conditions for precursor vaporization. The overall effect is that metallic species generated from the decomposition of the precursor are produced in a stable vapor-phase form, without large fluctuations in concentration or plasma chemistry.

[0070] Equally critical is the regulation of the discharge chamber pressure, which is maintained within the narrow window of 0.9-1.1 atm using a back-pressure control valve connected to a downstream vacuum pump. Operating in this slightly controlled atmosphere suppresses turbulence and prevents plasma flickering caused by uncontrolled pressure fluctuations, while ensuring that vaporized metallic species experience a predictable residence time before quenching. Synchronization of all input parametersprecursor feed, arc current, and argon flowis achieved through a programmable logic controller (PLC). The PLC continuously monitors process variables and dynamically adjusts them every 500 ms, ensuring that fluctuations in one subsystem are compensated for in the others. For example, if precursor feed rate momentarily increases, the PLC proportionally adjusts argon flow and modulates current to prevent incomplete decomposition or oversaturation.

[0071] The synergy between staged ignition, PWM modulation, pressure stabilization, and PLC synchronization enables the system to achieve steady-state plasma conditions that are highly reproducible across multiple runs. The technical efficacy of this configuration is demonstrated by the consistent vapor-phase formation of metallic species, which translates into nanoparticles with controlled size distribution and high purity. Without such coordinated control, arc instabilities would lead to intermittent vaporization, incomplete decomposition of precursor droplets, and broad polydispersity in the resulting nanoparticles.

[0072] In an embodiment, the argon carrier gas having 99.999% purity is introduced into the chamber at a flow rate of 121 mL/min using a digital mass flow controller with 1% accuracy, said gas being preconditioned by sequential passage through a silica gel dryer, a 3 molecular sieve, and a 0.2 m PTFE particulate filter, wherein a stainless-steel diffuser plate installed at the inlet ensures laminar distribution across the plasma region, thereby preventing turbulence-driven inhomogeneities during nucleation.

[0073] In this embodiment, the role of the carrier gas is not limited to merely transporting precursor vapors and nanoparticles but is actively engineered to create a highly controlled reaction environment that directly governs nucleation uniformity and particle quality. Argon of ultra-high purity (99.999%) is chosen because even trace levels of oxygen, nitrogen, or water vapor can react with the vaporized metallic species to form oxides or nitrides, leading to contamination and irregular nucleation. To ensure such contaminants are completely removed, the argon is sequentially purified through a three-stage preconditioning system: first, a silica gel dryer removes moisture to sub-ppm levels; second, a 3 molecular sieve adsorbs any residual water molecules and light gases such as CO.sub.2; and finally, a 0.2 m PTFE particulate filter eliminates micro-particulates that could otherwise serve as unintended nucleation sites. Each stage progressively eliminates a different class of impurities, ensuring the gas entering the chamber is chemically inert and particle-free.

[0074] The flow rate of argon is regulated with exceptional precision at 121 mL/min using a digital mass flow controller with 1% accuracy, ensuring that the volume of gas introduced into the plasma zone is consistent across runs. This precision is critical because even small deviations in flow rate can alter residence times of vaporized metallic atoms, leading to shifts in particle size distribution. A stainless-steel diffuser plate is installed at the inlet to distribute the conditioned gas evenly into the plasma region. The diffuser forces the incoming argon into multiple finely distributed channels, creating a laminar flow field as it enters the discharge zone. By eliminating eddies and turbulence, the laminar flow ensures that vaporized metallic atoms and precursor decomposition products are uniformly carried through the plasma, reducing the formation of localized concentration gradients.

[0075] This combination of ultra-pure gas, stringent flow control, and laminar distribution directly impacts the nucleation step. Inhomogeneous flow conditions typically cause uneven cooling and clustering of metallic species, leading to broad size distributions and irregular morphologies. By contrast, the carefully conditioned and distributed argon environment maintains uniform supersaturation levels throughout the plasma, thereby promoting homogeneous nucleation. The technical efficacy of this approach is evident in the production of nanoparticles with narrow size distributions and reduced defect densities, while the synergistic action of chemical purification, flow precision, and hydrodynamic stabilization ensures reproducibility and scalability of the synthesis.

[0076] In an embodiment, vaporized metallic species are quenched in a double-jacketed quartz condensation chamber with inner wall water circulation at 15-20 C. regulated by a PID-controlled chiller, wherein the residence time of vapor within the cooling zone is adjusted to 160-180 ms by maintaining argon velocity at 0.12-0.14 m/s, and wherein the chamber incorporates a conical expansion section angled at 182, thereby promoting homogeneous nucleation and producing nanoparticles of 8-12 nm with geometric standard deviation below 1.3; and wherein the condensation chamber inner surface is lined with fused quartz polished to Ra<0.2 m to minimize heterogeneous nucleation, and wherein the expansion geometry prevents stagnation zones by gradually reducing flow velocity, thereby suppressing wall deposition and ensuring that nucleation occurs predominantly within the gas phase.

[0077] In this embodiment, the transition from vaporized metallic species to solid nanoparticles is carefully controlled through a condensation chamber design that integrates thermal management, flow dynamics, and surface engineering to achieve uniform nucleation and size control. The chamber is constructed from double-jacketed quartz, with the inner jacket circulating chilled water maintained at 15-20 C. under the control of a proportional-integral-derivative (PID) feedback loop. This tight regulation ensures that the cooling profile remains consistent across synthesis runs, avoiding fluctuations that would otherwise alter supersaturation dynamics. As vaporized metallic atoms enter the chamber, the rapid but uniform cooling induces supersaturation, which drives nucleation of nanoparticles.

[0078] The residence time of the vapor in the cooling zone is fixed in the narrow range of 160-180 milliseconds by precisely adjusting the argon flow velocity to 0.12-0.14 m/s. This control ensures that vaporized species experience sufficient time in the cooling zone to nucleate, but not so long as to allow excessive growth or secondary aggregation. To further refine nucleation, the chamber geometry includes a conical expansion section angled at 182. This gradual widening of the flow path reduces velocity in a controlled manner, suppressing the formation of stagnation pockets while maintaining homogeneous mixing of vapor with carrier gas. The expansion geometry promotes uniform supersaturation across the chamber volume, resulting in nanoparticles of consistent size within the 8-12 nm range and a geometric standard deviation below 1.3.

[0079] A further critical feature is the inner surface of the condensation chamber, which is fabricated from fused quartz polished to a surface roughness of less than 0.2 m. Such a smooth surface minimizes the number of nucleation-active defects that would otherwise promote heterogeneous nucleation at the walls. By suppressing wall-induced deposition, nucleation occurs predominantly in the gas phase where conditions are uniform, leading to high-purity nanoparticles with spherical morphology. This gas-phase nucleation, combined with controlled residence time and cooling, ensures that nanoparticles form consistently in the desired size range, free from contamination caused by wall interactions.

[0080] The technical efficacy of this embodiment lies in the synergy between PID-regulated thermal control, hydrodynamically optimized flow residence, and surface-engineered chamber walls. Without this integration, cooling would be non-uniform, leading to wide particle size distributions, or wall deposition would dominate, reducing yield and purity. By orchestrating these parameters together, the system achieves reproducible nanoparticle production with narrow size distributions and minimal agglomeration, directly addressing challenges of consistency and scalability in plasma-based nanoparticle synthesis.

[0081] In an embodiment, nanoparticle collection is performed by directing the cooled argon-nanoparticle stream onto a stainless-steel mesh collector having pore size 50-70 m, the mesh being maintained at 5-10 C. using a thermoelectric Peltier cooler, thereby enhancing thermophoretic deposition efficiency and preventing re-evaporation or sintering of collected particles.

[0082] In this embodiment, the process of nanoparticle collection is engineered to maximize deposition efficiency while preserving the fine size and morphology of the particles synthesized in the plasma discharge. After quenching in the condensation chamber, the argon-nanoparticle stream is directed onto a stainless-steel mesh collector with a pore size of 50-70 m. The pore size is selected to allow unhindered passage of the carrier gas while simultaneously providing sufficient surface area for nanoparticle capture. Unlike solid plates, which can create pressure build-up or flow disturbances, the mesh allows continuous flow-through while maintaining high surface-particle interaction, thereby improving deposition uniformity.

[0083] The stainless-steel mesh is maintained at a temperature of 5-10 C. by employing a thermoelectric Peltier cooling system directly mounted onto the collector assembly. This active cooling generates a strong thermal gradient between the incoming particle-laden gas stream and the collector surface. The resulting thermophoretic force drives nanoparticles from the warmer bulk gas toward the cooler mesh, significantly enhancing deposition efficiency beyond that achievable by inertial impaction alone. By exploiting this thermophoretic effect, even nanoparticles as small as 8-12 nm, which otherwise tend to remain suspended due to Brownian motion, are effectively captured.

[0084] Maintaining the collector surface at sub-ambient temperatures also serves an additional protective role. If the collector were at or near room temperature, nanoparticles could undergo localized re-evaporation or surface sintering, especially if residual thermal energy remained in the stream. At 5-10 C., however, the collector surface acts as a heat sink, rapidly dissipating the energy of incoming nanoparticles and preventing them from coalescing. This preserves their discrete morphology and prevents the formation of fused aggregates that would compromise powder dispersibility.

[0085] The technical efficacy of this embodiment thus arises from the synergy of three carefully integrated elements: the permeable mesh geometry for gas flow compatibility, the thermoelectric cooling system to create strong thermal gradients for thermophoresis, and the low collector temperature to suppress re-evaporation and sintering. Together, these measures ensure high-efficiency collection of nanoparticles while retaining their designed nanoscale characteristics and surface integrity, which are critical for downstream applications.

[0086] In an embodiment, the collected nanoparticles are subjected to sequential washing cycles comprising dispersion in deionized water (0.1 g per 100 mL), ultrasonication at 40 kHz for 10-15 minutes to break soft agglomerates, and centrifugation at 8500500 rpm for 10 minutes to separate metallic nanoparticles from ionic residues, said cycle being repeated at least three times until residual conductivity of wash supernatant is less than 10 S/cm; and wherein the washed nanoparticles are redispersed in ethanol containing 0.05 wt. % polyvinylpyrrolidone (PVP), the dispersion being rotary evaporated at 50-55 C. under 100-150 mbar vacuum until dryness, followed by vacuum drying at 60 C. for 8-10 hours in a desiccator, thereby yielding free-flowing metallic nanopowder with suppressed surface oxidation.

[0087] In this embodiment, the post-synthesis purification and stabilization of the nanoparticles are achieved through a multi-stage process designed to remove ionic impurities, disperse agglomerates, and impart a protective surface layer that enhances storage stability. Immediately after collection, the nanoparticles are prone to carrying residual ionic by-products from precursor decomposition, such as nitrate ions from Fe(NO.sub.3).sub.3.Math.9H.sub.2O, which, if left unremoved, can cause unwanted surface reactions and limit long-term stability. To address this, the nanoparticles are dispersed in deionized water at a controlled loading of 0.1 g per 100 mL, a concentration selected to maintain colloidal stability during processing. The dispersion is then subjected to ultrasonication at 40 kHz for 10-15 minutes. This acoustic treatment generates cavitation bubbles that collapse and release microjets, which impart localized shear forces capable of breaking apart weakly bound soft agglomerates without damaging the crystalline integrity of individual nanoparticles.

[0088] Following dispersion, the suspension undergoes centrifugation at 8500500 rpm for 10 minutes. At this centrifugal force, the nanoparticles sediment efficiently, while dissolved ionic residues remain in the supernatant. The supernatant is discarded, and the sediment is redispersed in fresh deionized water. This cycle is repeated at least three times, ensuring progressive reduction of ionic impurities. The efficiency of purification is confirmed when the conductivity of the final wash supernatant is less than 10 S/cm, a level indicative of near-complete removal of soluble residues. Such stringent washing is essential to ensure that the final nanopowder does not undergo surface reactions or uncontrolled charging effects that would destabilize dispersions in subsequent applications.

[0089] After purification, the nanoparticles are redispersed in ethanol containing 0.05 wt. % polyvinylpyrrolidone (PVP). PVP molecules adsorb strongly to the metallic nanoparticle surfaces through coordination of their carbonyl groups, forming a steric barrier that prevents particle-particle contact. This surface modification suppresses both agglomeration and oxidation by reducing direct exposure of the metallic surface to oxygen and moisture. The PVP-stabilized ethanol dispersion is then concentrated by rotary evaporation at 50-55 C. under reduced pressure (100-150 mbar), which removes ethanol efficiently without thermal degradation of the PVP or oxidation of the nanoparticles. To ensure complete solvent removal and powder stabilization, the material is finally vacuum-dried at 60 C. for 8-10 hours in a desiccator, resulting in a dry, free-flowing metallic nanopowder.

[0090] The technical efficacy of this embodiment is demonstrated by the synergistic interplay between the sequential washing cycles and the PVP surface functionalization. Washing ensures that ionic residues are fully eliminated, preventing surface corrosion or conductivity anomalies, while ultrasonication disperses weak aggregates to preserve nanoscale particle size. PVP coating then provides steric and partial chemical stabilization, suppressing surface oxidation and enabling the powder to remain free-flowing rather than forming hard cakes during storage. Collectively, this integrated purification-stabilization strategy ensures that the nanoparticles retain both their purity and nanoscale properties over extended periods, making them suitable for high-performance applications.

[0091] In an embodiment, the electrodes are coated prior to use with a graphite film of 50-100 m thickness deposited by brushing colloidal graphite suspension followed by drying at 80 C. for 2 hours, the coating reducing tungsten sputtering and preventing incorporation of tungsten impurities in the nanoparticles; and wherein the reaction chamber incorporates a dual-zone cooling jacket, the upstream loop maintaining electrode temperature at 40-50 C. using hot water circulation, and the downstream loop providing quenching at 10-15 C. using chilled water, each loop being independently PID-controlled to 0.5 C. stability, thereby creating a controlled thermal gradient conducive to uniform nucleation.

[0092] In this embodiment, two distinct yet complementary measures are employed to improve both the purity of the nanoparticles and the consistency of nucleation during plasma-assisted synthesis: electrode surface protection and dual-zone thermal management of the reaction chamber. Prior to arc initiation, the tungsten filament electrodes are coated with a uniform graphite film of 50-100 m thickness. This coating is applied by brushing a colloidal graphite suspension onto the electrode surface and subsequently drying it at 80 C. for two hours to ensure adhesion and solvent removal. The presence of this graphite layer serves as a sacrificial barrier during high-energy discharge, significantly reducing tungsten sputtering into the plasma zone. Since tungsten atoms sputtered from bare electrodes could incorporate into the growing nanoparticles and alter their composition, the graphite film effectively prevents such contamination, thereby preserving the chemical purity of the synthesized particles. Moreover, graphite itself is chemically inert under the selected arc conditions, so it neither destabilizes the plasma nor introduces reactive contaminants.

[0093] The second element of this embodiment focuses on thermal control of the reaction chamber through a dual-zone cooling jacket. The upstream loop, positioned near the electrode assembly, circulates hot water at 40-50 C. to maintain electrode temperature within a controlled window. This prevents excessive cooling of the electrode tips, which could destabilize the arc discharge, while simultaneously minimizing thermal stress on the graphite coating. The downstream loop, positioned in the region where vaporized metallic species condense, circulates chilled water at 10-15 C. to create a strong cooling gradient. This quenching zone rapidly reduces the temperature of the vaporized metallic species, inducing supersaturation and promoting uniform nucleation of nanoparticles.

[0094] Each loop is independently controlled by a proportional-integral-derivative (PID) regulator with stability of +0.5 C. This high-precision control allows the upstream and downstream zones to function in a coordinated but independent manner. The upstream zone ensures arc stability by maintaining electrode integrity, while the downstream zone ensures nucleation uniformity by enforcing reproducible cooling conditions. The controlled thermal gradient across the chamber not only maintains plasma stability but also ensures that the transition from vapor phase to nucleated nanoparticles occurs under well-defined conditions, thereby minimizing broad particle size distributions and preventing uncontrolled agglomeration.

[0095] The technical efficacy of this embodiment arises from the synergy between the graphite coating and the dual-zone cooling system. The graphite film ensures chemical purity by preventing tungsten incorporation, while the thermal gradient ensures physical uniformity of nanoparticle formation. Together, these measures create a synthesis environment where both compositional integrity and morphological control are preserved, enabling the reproducible production of high-quality metallic nanoparticles.

[0096] In an embodiment, precursor solution is degassed by ultrasonication at 40 kHz for 15 minutes followed by vacuum evacuation at 100 mbar for 5 minutes prior to introduction, said degassing eliminating entrapped bubbles that otherwise destabilize atomization and arc stability, thereby improving reproducibility of nanoparticle synthesis; and wherein nanoparticles are washed alternately with ethanol and acetone, each cycle comprising 5 minutes ultrasonication and 10 minutes centrifugation at 10,000 rpm, the alternating polar-nonpolar solvent washing improving removal of carbonaceous impurities and enhancing nanoparticle surface passivation.

[0097] In this embodiment, the focus is on ensuring stability during precursor introduction and on achieving high-purity nanoparticles through a carefully designed washing sequence. Before being introduced into the plasma discharge, the aqueous precursor solution undergoes a two-step degassing treatment. First, it is subjected to ultrasonication at 40 kHz for 15 minutes, which generates microscopic cavitation bubbles that collapse and expel dissolved gases, thereby destabilizing gas pockets within the liquid. This is followed by vacuum evacuation at 100 mbar for 5 minutes, which physically removes the liberated gases and residual entrapped air. By eliminating bubbles, the precursor enters the atomization system as a homogeneous liquid, free of gas inclusions that would otherwise cause erratic spray dynamics. Such bubbles, if present, can destabilize droplet formation, disrupt the flow through the nozzle, and create local impedance changes in the plasma discharge, ultimately leading to fluctuations in arc stability. The degassing step therefore ensures reproducibility of both atomization and plasma behavior, directly improving the reliability of nanoparticle synthesis.

[0098] Once nanoparticles are collected, they undergo an alternating solvent washing sequence specifically designed to address carbonaceous impurities, which often arise from decomposition of solvent residues or electrode coatings. The nanoparticles are dispersed alternately in ethanol and acetone, with each solvent providing complementary cleaning properties. Ethanol, being polar, solubilizes ionic residues and hydrophilic organic fragments, while acetone, being less polar, dissolves hydrophobic and carbonaceous contaminants. Each washing step includes 5 minutes of ultrasonication at 40 kHz, which disrupts weakly bound aggregates and enhances solvent penetration into particle clusters. This is followed by centrifugation at 10,000 rpm for 10 minutes, which separates purified nanoparticles from the supernatant carrying dissolved impurities. By alternating the solvents over successive cycles, the process achieves deeper cleaning than possible with a single solvent alone, as each cycle targets different classes of contaminants.

[0099] The technical efficacy of this embodiment lies in the synergistic combination of pre-introduction degassing and alternating solvent washing. Degassing stabilizes the atomization-plasma interface, producing reproducible vaporization of the precursor, while alternating solvent cycles ensure that carbonaceous residues are comprehensively removed from the nanoparticle surface. Furthermore, the removal of such residues enhances nanoparticle surface passivation, as clean surfaces are more effectively stabilized by adsorbed solvent molecules or subsequent capping agents. Together, these measures ensure that the nanoparticles not only form reproducibly in the plasma but also maintain high purity and stability in their post-synthesis state, with suppressed tendencies toward uncontrolled oxidation or aggregation.

[0100] In an embodiment, droplet injection into the arc zone is synchronized with plasma oscillations using a phase-locked loop control system that detects plasma light intensity via photodiodes and modulates peristaltic pump speed in-phase with high-energy intervals, thereby achieving consistent vaporization of droplets and reducing partially decomposed residues; and wherein nucleated nanoparticles are passed through a cyclone separator operated at inlet velocity 12-14 m/s and cut size of 15-20 nm, wherein oversized agglomerates are separated into the underflow, while primary nanoparticles are collected in the overflow stream, thereby enhancing size uniformity prior to collection.

[0101] In this embodiment, the process integrates real-time plasma monitoring with intelligent feed control and aerodynamic size classification to achieve highly uniform nanoparticle formation. The first part of the system addresses synchronization between precursor droplet injection and plasma energy oscillations. The plasma column inherently exhibits oscillatory behavior due to current modulation and localized instabilities, resulting in alternating high- and low-energy intervals. If droplets enter during low-energy intervals, they may undergo incomplete vaporization, generating partially decomposed residues and broadening the nanoparticle size distribution. To prevent this, a phase-locked loop (PLL) control system is employed. Photodiodes are positioned to detect plasma light intensity fluctuations, which directly correlate with instantaneous plasma energy states. The PLL system processes this signal and dynamically adjusts the peristaltic pump speed, ensuring that droplets are introduced only during high-energy intervals of the plasma oscillation cycle. This synchronization guarantees complete and consistent vaporization of each droplet, improving reproducibility and reducing the fraction of unreacted residues.

[0102] Following vaporization and nucleation, the nanoparticle stream is subjected to acrodynamic classification using a cyclone separator. The separator is operated at an inlet velocity of 12-14 m/s, which creates a centrifugal field that separates particles based on their aerodynamic diameter. The design is tuned for a cut size of 15-20 nm, meaning that particles larger than this threshold experience sufficient centrifugal force to be directed toward the underflow, where they are separated out as agglomerates or oversized clusters. Meanwhile, primary nanoparticles within the desired size range remain entrained in the gas stream and are carried into the overflow, where they are collected for further processing. This step not only removes unwanted agglomerates but also improves the overall monodispersity of the nanoparticle product.

[0103] The synergy of synchronized injection and cyclone classification provides a two-level control over nanoparticle uniformity. Synchronization ensures that droplets entering the plasma are consistently vaporized, producing nucleated nanoparticles of predictable primary size. The cyclone separator then acts as a post-formation filter, eliminating agglomerates that would otherwise degrade size distribution and performance. Together, these measures result in nanoparticles with tighter size control, improved purity, and reduced variability between synthesis runs. The technical efficacy of this embodiment is thus derived from coupling real-time plasma-phase feedback with acrodynamic downstream processing, enabling a more deterministic synthesis pathway compared to unsynchronized or unclassified systems.

[0104] In an embodiment, a capping step is employed by dispersing washed nanoparticles in 0.1 wt. % sodium citrate aqueous solution followed by ultrasonication for 20 minutes at 50 kHz, said citrate molecules binding via carboxylate groups to nanoparticle surfaces, imparting electrostatic stabilization and preventing agglomeration in suspension; and wherein the stabilized suspension is freeze-dried by pre-freezing at 40 C. for 6 hours and sublimation under vacuum of 10.sup.3 mbar for 24 hours, thereby retaining dispersion state and preventing irreversible hard agglomeration that occurs during oven drying.

[0105] In this embodiment, the stabilization and long-term preservation of nanoparticles are achieved through a surface functionalization and drying strategy specifically designed to prevent agglomeration while maintaining colloidal dispersibility. After washing, the nanoparticles are dispersed in a 0.1 wt. % aqueous sodium citrate solution, where citrate molecules act as capping agents. The citrate anions bind to the metallic nanoparticle surfaces via their carboxylate groups, creating a negatively charged layer around each particle. This electrostatic repulsion between similarly charged surfaces prevents particle-particle contact, thereby suppressing aggregation in the suspension. To ensure uniform adsorption of citrate molecules, the suspension undergoes ultrasonication at 50 kHz for 20 minutes. The acoustic energy from ultrasonication breaks apart weakly bound clusters, exposes fresh surface sites, and allows citrate molecules to effectively cover the particle surfaces, thereby maximizing stabilization efficiency.

[0106] Once stabilized in suspension, the nanoparticles are subjected to freeze-drying to convert them into a stable, free-flowing dry powder while retaining the dispersed state achieved in solution. The process begins with pre-freezing the citrate-stabilized suspension at 40 C. for six hours, which immobilizes nanoparticles in their dispersed configuration by trapping them within the ice matrix. Subsequent sublimation is carried out under high vacuum at 10.sup.3 mbar for 24 hours, where water is removed directly from solid to vapor phase without passing through the liquid state. This bypassing of the liquid phase is critical, as it eliminates capillary forces that typically draw particles together during conventional oven drying, which leads to irreversible hard agglomeration. The freeze-drying process therefore preserves the nanoscale spacing maintained by citrate stabilization, ensuring that the dry powder can be readily redispersed in aqueous or other compatible media without significant loss of colloidal stability.

[0107] The technical efficacy of this embodiment derives from the synergy of surface chemistry and physical drying method. Sodium citrate provides electrostatic stabilization by modifying particle surface charge, while freeze-drying preserves this stabilization during transition from liquid suspension to dry powder. Oven drying or vacuum drying without freezing would collapse the interparticle distances maintained in suspension, producing aggregates that cannot be readily redispersed. By combining molecular-level surface passivation with phase-controlled drying, this embodiment ensures nanoparticles remain discrete, stable, and usable for extended storage and downstream applications where high surface area and controlled dispersion are essential.

[0108] In an embodiment, the final nanoparticle powder is sieved through a 325-mesh stainless steel sieve to eliminate agglomerates>45 m, and wherein the sieved powder is packaged in vacuum-scaled laminated aluminum pouches containing oxygen scavenger sachets rated at 50 mL O.sub.2/g, thereby ensuring stable storage with minimized oxidation; and wherein the condensation chamber is equipped with an acoustic standing-wave generator operating at 20-25 kHz and 0.5-1 W/cm.sup.2, wherein the acoustic field enhances Brownian dispersion, prevents chain-like agglomerate formation, and promotes spherical nanoparticle morphology.

[0109] In this embodiment, the focus is on post-synthesis refinement, storage stabilization, and in-situ morphological control to ensure that the nanoparticles retain their purity, uniformity, and functional integrity over extended timeframes. Once the nanoparticles have been collected and dried, they are passed through a 325-mesh stainless steel sieve, corresponding to a pore size of approximately 45 m. This sieving step removes large agglomerates or mechanically fused clusters that may have formed during handling or drying, ensuring that the final nanopowder consists predominantly of nanoscale particles with only minimal presence of oversized debris. By eliminating such agglomerates, the powder achieves improved homogeneity, higher surface-to-volume ratio, and more predictable re-dispersibility in downstream applications.

[0110] Following sieving, the nanopowder is packaged under vacuum in laminated aluminum pouches, which provide both a physical and chemical barrier against environmental oxygen and moisture ingress. To further minimize oxidative degradation, oxygen scavenger sachets rated at 50 mL O.sub.2 per gram of scavenger are included in each pouch. These sachets actively absorb residual oxygen within the sealed package, reducing the effective oxygen concentration around the nanoparticles to near-zero levels. The combination of vacuum scaling and oxygen scavenging ensures that metallic nanoparticles are preserved in their pristine state, with minimal oxide shell growth even after prolonged storage, thereby retaining their high reactivity and surface area for future applications.

[0111] In parallel with these post-processing and storage strategies, the condensation chamber is equipped with an acoustic standing-wave generator operating at a frequency of 20-25 kHz and a power density of 0.5-1 W/cm.sup.2. The acoustic waves generate alternating pressure nodes and antinodes within the chamber, imparting mechanical agitation at the nanoscale to the vapor-particle system. This acoustic field enhances Brownian dispersion by preventing freshly nucleated nanoparticles from aligning or clustering into chain-like agglomerates under attractive van der Waals forces. The oscillatory energy disrupts such tendencies and promotes spherical symmetry during particle growth, resulting in nanoparticles with more uniform morphology. By reducing anisotropic aggregation, the acoustic field ensures that nucleation and early growth stages proceed in a well-dispersed environment, yielding spherical, monodisperse particles with improved stability.

[0112] The technical efficacy of this embodiment arises from the synergy of three distinct yet complementary measures: (i) sieving removes macroscopic agglomerates, ensuring physical uniformity of the powder, (ii) vacuum-sealed packaging with oxygen scavengers guarantees long-term chemical stability by suppressing oxidation, and (iii) acoustic field-assisted nucleation prevents chain-like structures and promotes spherical morphology during synthesis. Together, these approaches provide a closed loop of control extending from synthesis through packaging, ensuring that nanoparticles not only form with desirable characteristics but also retain those characteristics until the point of use.

[0113] In an embodiment, the arc chamber walls are periodically passivated by flushing with 0.1 M nitric acid, rinsing with deionized water, and drying at 120 C. for 2 hours, such maintenance preventing contamination by deposited metallic residues and preserving nanoparticle purity over repeated runs; and wherein a neodymium permanent magnet of 0.8-1.0 T is applied externally to the washed nanoparticle suspension in ethanol, thereby magnetically retaining metallic particles while non-magnetic impurities are decanted, and wherein retained particles are re-dispersed and washed, yielding purified metallic nanoparticles with minimal oxide inclusions.

[0114] In this embodiment, both the integrity of the synthesis environment and the post-synthesis purity of nanoparticles are ensured by integrating chamber passivation procedures with a selective magnetic purification strategy. During repeated synthesis runs, metallic vapors and partially condensed particles inevitably deposit on the walls of the arc chamber, where they can later flake off or re-entrain into the plasma, leading to contamination of subsequent nanoparticle batches. To counter this, the chamber walls are periodically subjected to a passivation cycle. First, the inner surfaces are flushed with a 0.1 M nitric acid solution, which dissolves and removes metallic residues by oxidizing them into soluble nitrate species. This is followed by thorough rinsing with deionized water to eliminate residual acid and dissolved contaminants, ensuring that no acidic traces remain to destabilize future plasma runs. Finally, the chamber is dried at 120 C. for two hours to remove all moisture, preventing oxidation of freshly generated nanoparticles during subsequent operation. This maintenance cycle restores the chamber's inert surface condition, ensuring that each synthesis run begins in a contamination-free environment, thereby preserving the chemical purity and reproducibility of the nanoparticles.

[0115] After synthesis and collection, an additional purification step is employed to refine the nanoparticle product. The nanoparticles are first dispersed in ethanol, where a neodymium permanent magnet of 0.8-1.0 T is externally applied to the container. The strong magnetic field selectively retains the metallic nanoparticles within the suspension by aligning their induced or permanent magnetic moments, while non-magnetic impurities, such as oxide fragments, organic residues, or by-products, remain suspended and are decanted with the supernatant. The magnetically retained metallic nanoparticles are then re-dispersed in fresh ethanol and washed to remove any weakly bound impurities. By repeating this cycle, nanoparticles with minimal oxide inclusions and enhanced metallic core purity are obtained.

[0116] The technical efficacy of this embodiment arises from the complementary action of chamber passivation and magnetic purification. Chamber passivation ensures that nanoparticles synthesized in subsequent runs are not contaminated by legacy deposits, providing consistency across production cycles. Magnetic purification, on the other hand, leverages the inherent difference in magnetic response between metallic nanoparticles and non-metallic impurities to achieve selective separation without the need for harsh chemical treatments. Together, these processes establish a closed-loop quality control framework that maintains both environmental cleanliness during synthesis and high-purity output during product refinement. The synergistic effect is evident in nanoparticles that are not only compositionally uniform but also exhibit suppressed oxide shell formation, thereby retaining their desirable nanoscale properties and functionality for advanced applications.

[0117] In an embodiment, precursor concentration is dynamically varied between 0.05 M and 0.25 M by blending two reservoirs through a computer-controlled manifold, thereby producing oscillatory supersaturation within the plasma, inducing repeated nucleation pulses, and yielding narrower particle size distribution; and wherein nanoparticle formation is monitored in situ using a laser scattering probe positioned at the condensation outlet, said probe operating at 532 nm with multi-ange detection, wherein scattering signals are fed to a control algorithm that adjusts argon flow and precursor feed in real time, thereby maintaining targeted nanoparticle size distribution within 10% of set value.

[0118] In this embodiment, dynamic precursor blending and real-time optical monitoring arc combined to create a feedback-controlled synthesis environment that actively shapes nanoparticle size distribution. Instead of supplying a constant precursor concentration, two reservoirs containing solutions of different molarities0.05 M and 0.25 Mare connected to a computer-controlled manifold that continuously varies the blending ratio. By modulating the feed composition during operation, the system induces oscillatory supersaturation conditions in the plasma. These oscillations trigger repeated bursts of nucleation rather than a single continuous growth process. Each nucleation pulse consumes available vapor-phase metallic species, suppressing overgrowth of existing particles and leading to the formation of fresh nuclei in subsequent cycles. As a result, the overall particle size distribution narrows, with fewer oversized particles and reduced polydispersity compared to steady-state feeding.

[0119] To ensure these dynamic conditions remain within a controlled window, nanoparticle formation is simultaneously monitored in situ using a laser scattering probe positioned at the condensation chamber outlet. The probe operates at 532 nm with multi-angle detection, allowing it to capture scattering intensity profiles that are sensitive to particle size and distribution. This data stream is continuously analyzed by a control algorithm, which interprets deviations from the target size distribution. Based on real-time feedback, the algorithm adjusts argon flow rate and precursor feed composition via the manifold and digital mass flow controllers. For instance, if scattering signals indicate particle growth beyond the target, the algorithm may increase the proportion of low-concentration precursor or raise argon flow to dilute supersaturation. Conversely, if particle sizes trend smaller, higher concentration feed can be blended in to promote more robust growth.

[0120] The technical efficacy of this embodiment lies in the synergy between oscillatory precursor feeding and adaptive feedback control. Oscillatory supersaturation inherently narrows size distribution by enforcing periodic nucleation, while laser-based monitoring ensures that any drift from the desired particle size window is corrected in real time. Together, these approaches provide a deterministic method to maintain nanoparticle size distribution within 10% of the set value, significantly improving reproducibility and scalability. Without this integration, static precursor feeding would lead to broad polydispersity, and offline size monitoring would fail to provide the rapid corrections necessary to stabilize the synthesis process.

[0121] In an embodiment, the annealed nanoparticles are transferred into an inert-atmosphere glove box (<1 ppm O.sub.2 and <1 ppm H.sub.2O), sealed in borosilicate ampoules under vacuum of 10.sup.3 mbar, and flame-sealed using a micro-oxygen torch while monitoring internal pressure with a Pirani gauge, thereby ensuring oxygen-free long-term storage; and wherein the plasma discharge is stabilized by introducing a secondary shielding flow of argon gas injected coaxially around the quartz tube at 2-3 mL/min, wherein the shielding flow prevents infiltration of atmospheric oxygen through micro-leaks, reduces convective losses at the plasma boundary, and thereby ensures consistent metallic nanoparticle formation with suppressed oxide contamination.

[0122] In this embodiment, both storage stability and plasma stability are addressed through a combination of controlled encapsulation and gas-flow engineering. Once the nanoparticles are synthesized and, if required, annealed, they are handled entirely within an inert-atmosphere glove box, where oxygen and moisture levels are maintained below 1 ppm. This stringent environment prevents any oxidation or hydrolysis of the highly reactive metallic surfaces during handling. The nanoparticles are then transferred into borosilicate ampoules, which offer low gas permeability and mechanical durability. Inside the glove box, the ampoules are evacuated to 10.sup.3 mbar using a high-vacuum system, with a Pirani gauge continuously monitoring internal pressure to ensure that the desired vacuum level is reached. Each ampoule is then flame-sealed using a micro-oxygen torch while still under inert conditions, creating a permanent, oxygen-free encapsulation. This method ensures that the nanoparticles are stored in a chemically stable state over long durations without forming oxide shells or aggregating due to atmospheric contamination, a key requirement for applications demanding metallic purity.

[0123] Parallel to the storage strategy, the plasma discharge itself is stabilized during synthesis through the introduction of a secondary coaxial shielding flow of argon gas at 2-3 mL/min around the quartz tube. Although the primary plasma is maintained within a sealed reaction chamber, minor micro-leaks or convective instabilities at the plasma boundary can allow infiltration of atmospheric oxygen, leading to partial oxidation of the vaporized metallic species and the formation of oxide-rich nanoparticles. By injecting a coaxial argon flow, a protective buffer layer is created around the plasma, which prevents oxygen ingress and shields the plasma-wall interface. This flow also reduces convective heat losses at the boundary, maintaining a more thermally stable discharge column. The net effect is a more consistent plasma environment where metallic nanoparticles are formed with minimal oxide contamination.

[0124] The technical efficacy of this embodiment lies in the synergistic link between storage and synthesis stabilization. Oxygen exclusion is enforced at both ends of the process: during synthesis, the shielding flow maintains a clean plasma environment, and during storage, inert glove box handling with vacuum-sealed ampoules ensures long-term chemical integrity. Without such measures, nanoparticles would exhibit oxide shells even during synthesis or degrade rapidly during storage, compromising their functional properties. By addressing both plasma-phase contamination and long-term oxidation risks, this embodiment ensures that metallic nanoparticles retain their pristine structure, composition, and nanoscale stability until the point of application.

[0125] In an embodiment, the electrodes are cooled by an integrated water-cooled copper jacket surrounding the electrode holders, the cooling water being circulated at 200-250 mL/min and maintained at 251 C., wherein said cooling prevents thermal deformation of tungsten filaments during sustained discharge, thereby ensuring constant electrode geometry and repeatable plasma arc shape; and wherein an auxiliary hydrogen-containing reducing gas (95% Ar+5% H.sub.2) is introduced downstream of the plasma zone at 1-2 mL/min, wherein said reducing gas scavenges oxygen residues during condensation, thereby reducing oxide shell formation on metallic nanoparticles and increasing metallic core fraction by at least 15% compared to pure argon quenching.

[0126] In this embodiment, two complementary strategies are employed to enhance both the structural stability of the discharge system and the chemical purity of the nanoparticles: electrode cooling with a copper jacket and controlled downstream introduction of a reducing gas. The tungsten filament electrodes, being subjected to intense thermal loads during sustained arc discharge, are vulnerable to thermal softening and deformation if left unregulated. To counter this, each electrode holder is surrounded by an integrated water-cooled copper jacket. Copper, with its high thermal conductivity, efficiently transfers heat away from the electrode body, while cooling water circulated at 200-250 mL/min and maintained at 251 C. ensures rapid and continuous thermal dissipation. By maintaining the electrodes at this stable temperature, thermal expansion and filament warping are prevented, which preserves the electrode geometry across extended runs. As a result, the plasma arc retains a consistent shape and length, ensuring reproducible discharge conditions and uniform precursor vaporization. Without this cooling system, electrode wear and deformation would progressively distort the plasma column, leading to unstable temperatures, inconsistent vapor-phase formation, and increased variability in nanoparticle characteristics.

[0127] Alongside thermal stabilization, the embodiment also addresses chemical purity during nanoparticle formation. After vaporization in the plasma, metallic species condense into nanoparticles in the downstream cooling zone. Residual oxygen in the chamber, even at trace levels, can react with the freshly nucleated nanoparticles to form oxide shells, thereby reducing the metallic content and altering functional properties. To mitigate this, an auxiliary reducing gas mixture comprising 95% argon and 5% hydrogen is introduced downstream at a controlled flow of 1-2 mL/min. The hydrogen component reacts preferentially with residual oxygen or oxygen-containing radicals, effectively scavenging them from the environment before they can interact with metallic nanoparticles. This reduces oxide shell formation during condensation and stabilizes the nanoparticles in a more metallic state. Experimental results demonstrate that this approach increases the metallic core fraction by at least 15% compared to conventional quenching in pure argon.

[0128] The technical efficacy of this embodiment stems from the synergy between physical and chemical stabilization. The water-cooled copper jacket ensures that the plasma discharge remains geometrically and thermally stable, directly improving the reproducibility of vaporization and nucleation. The hydrogen-enriched reducing gas, on the other hand, preserves chemical purity by eliminating oxygen-induced oxidation during condensation. Together, these measures ensure that the nanoparticles produced are both structurally uniform and compositionally pure, overcoming two major limitationselectrode instability and oxide contaminationthat often compromise plasma-based nanoparticle synthesis.

[0129] In an embodiment, in-situ optical emission spectroscopy is performed during arc discharge by placing a fiber optic probe at 45 inclination to the plasma column, said probe transmitting real-time emission data to a spectrometer calibrated at 200-800 nm, wherein spectral line intensity ratios are monitored to estimate plasma temperature, and wherein precursor feed rate is dynamically adjusted based on said spectral data to maintain vaporization efficiency above 95%; and wherein nanoparticle growth suppression is further achieved by pulsing the precursor feed with an on-off cycle of 2-3 seconds at constant flow rate of 0.35-0.45 mL/min, wherein during the off interval, supersaturation in the plasma reduces, thereby interrupting growth and limiting agglomeration, resulting in smaller and more monodisperse nanoparticles compared to continuous feeding.

[0130] In this embodiment, real-time plasma diagnostics and dynamic precursor feeding strategies are combined to ensure precise vaporization efficiency and to suppress excessive nanoparticle growth. Optical emission spectroscopy (OES) is performed in situ by positioning a fiber optic probe at a 45 inclination to the plasma column. This geometry allows for stable light capture without interfering with the discharge while minimizing background reflections. The probe transmits the collected emission data to a spectrometer calibrated across the range of 200-800 nm, which covers the characteristic emission lines of both tungsten electrode species and precursor-derived metallic species. By continuously monitoring spectral line intensity ratios, the plasma temperature can be estimated with high temporal resolution. Since vaporization efficiency is strongly dependent on plasma temperature, this diagnostic provides a direct feedback mechanism: if the plasma begins to cool below the optimal temperature range, the control system reduces the precursor feed rate; conversely, if excess energy is available, the feed rate is increased. Through this closed-loop regulation, vaporization efficiency is maintained consistently above 95%, preventing unvaporized droplets from entering the condensation stage and ensuring stable nucleation conditions.

[0131] In addition to regulating vaporization efficiency, this embodiment introduces a pulsed feeding strategy to actively suppress uncontrolled nanoparticle growth. Instead of continuously supplying precursor solution, the feed is pulsed with an on-off cycle of 2-3 seconds, while maintaining the same flow rate of 0.35-0.45 mL/min during the on intervals. During each on phase, supersaturation in the plasma reaches a peak, triggering rapid nucleation events and formation of primary nanoparticles. When the feed is switched off, supersaturation in the plasma drops, thereby interrupting particle growth and preventing further accretion onto existing nuclei. This periodic modulation ensures that particles are nucleated in multiple short bursts rather than undergoing prolonged continuous growth, which typically results in broad size distributions and agglomeration. By limiting growth in this way, the resulting nanoparticles are smaller, more uniform, and more monodisperse compared to those obtained with a constant precursor supply.

[0132] The technical efficacy of this embodiment lies in the synergy between real-time diagnostics and pulsed process control. The OES feedback loop ensures that every droplet entering the plasma is fully vaporized, thereby eliminating variability caused by incomplete decomposition. The pulsed feeding strategy complements this by structuring the nucleation-growth dynamics to favor multiple, controlled nucleation bursts rather than uncontrolled particle growth. Together, these measures result in nanoparticles that are both chemically pure and structurally uniform, overcoming common challenges in plasma-based synthesis such as droplet residues, oversized clusters, and broad size distributions.

[0133] In an embodiment, the condensation chamber is configured with an internal helical flow-guiding insert fabricated from quartz with pitch of 20-25 mm, said insert imparting controlled swirl to the argon flow at Reynolds number below 2000, thereby ensuring uniform residence time of vaporized metal atoms and minimizing local concentration gradients during nucleation.

[0134] In this embodiment, hydrodynamic engineering of the condensation chamber is used to create a highly controlled flow environment that enhances uniformity in nanoparticle nucleation. The chamber incorporates an internal helical flow-guiding insert fabricated from quartz, with a carefully designed pitch of 20-25 mm. When the argon carrier gas passes through this insert, it acquires a controlled swirling motion that distributes the vaporized metal atoms evenly across the chamber cross-section. The flow is maintained at a Reynolds number below 2000, ensuring laminar swirl rather than turbulent mixing. This controlled swirling effect lengthens and equalizes the residence time of the vaporized species within the cooling zone, preventing some particles from experiencing premature condensation while others remain in the vapor phase for too long.

[0135] By enforcing uniform residence time, the insert minimizes local supersaturation gradients, which are one of the primary causes of broad particle size distributions in plasma-based nanoparticle synthesis. In the absence of such control, metal atoms near the walls or in stagnant flow zones tend to nucleate earlier, while those in faster-moving central streams may remain uncondensed until much later, leading to variability in particle sizes and morphologies. The helical insert eliminates these disparities by redistributing vapor and gas flow into a homogenized swirling pattern. Furthermore, quartz is selected as the fabrication material because of its thermal stability, chemical inertness, and low surface roughness, ensuring that the insert itself does not act as a nucleation site or introduce contaminants into the system. The technical efficacy of this embodiment arises from the synergy between geometrically induced flow control and laminar hydrodynamics. The swirling flow promotes homogeneous mixing and synchronized cooling, while the low Reynolds number ensures that the flow remains stable and predictable. Together, these factors suppress localized concentration gradients and create a nucleation environment where all vaporized atoms experience comparable thermal and temporal conditions. The result is a narrower nanoparticle size distribution, reduced likelihood of agglomeration, and improved reproducibility across multiple synthesis runs.

[0136] FIG. 3 illustrates (a) Designed experimental set-up for the fabrication of MNPs using electric arc, and (b) Mechanism involved during the formation of MNPs from metal ions in electric arc generated plasma in accordance with an embodiment of the present disclosure. FIG. 3 (a) illustrates Designed experimental set-up for the fabrication of MNPs using electric arc; FIG. 3(b) Mechanism involved during the formation of MNPs from metal ions in electric arc generated plasma in accordance with an embodiment of the present disclosure;

[0137] This present invention offers the application of electric arc, which can directly apply on the metal ions to convert them into metal atoms, forming tiny and pure MNPs. In this invention, we applied the electric arc between two electrodes, which were connected through a graphite rode which was passed through a metal ion's solution filled in a quartz chamber, in a controlled inert atmosphere wherein the material was vaporised and subsequently condensed into MNPs (FIG. 3a). The simplicity, efficiency, and ability to create MNPs with regulated size and shape set this approach apart. The mechanism of the formation of MNPs from metal ions is shown in FIG. 3b.

[0138] FIG. 4 illustrates (a) The Captured photo of the designed electric arc setup during the formation of MNPs, (b) Fe(NO.sub.3).sub.3.Math.9H.sub.2O salt paste, and (c) Collected Fe NPs after the completion of electric arc treatment on Fe(NO.sub.3).sub.3.Math.9H.sub.2O solution in accordance with an embodiment of the present disclosure. FIG. 4 (a) illustrates The Captured photo of the designed electric arc setup during the formation of MNPs; FIG. 4 (b) illustrates the Fe(NO.sub.3).sub.3.Math.9H.sub.2O salt paste; and FIG. 4 (c) illustrates Collected Fe NPs after the completion of electric arc treatment on Fe(NO.sub.3).sub.3.Math.9H.sub.2O solution.

[0139] The adopted approach for the preparation of MNPs is shown in FIG. 4, involving the following steps:

[0140] 1. Electrodes Arrangement: First of all, we connected two electric filaments as electrodes with a graphite rode, which was passed through a quartz tube (FIG. 4a).

[0141] 2. Arc Generation: Additionally, the aqueous solution of Fe(NO.sub.3).sub.3.Math.9H.sub.2O was (FIG. 4b) introduced into the quartz tube, and argon gas was introduced into the chamber. A high voltage was applied between the electrodes, resulting in the generation of an electric arc and a substantial discharge of energy. This arc was maintained by a continuous electric current, resulting in localised vaporisation of the solution.

[0142] 3. Cooling and Condensation: As it escaped the arc, the vaporised metallic components cooled and condensed as it swiftly spread into the surrounding inert air. MNPs were formed during the cooling process.

[0143] 4. Collection of Nanoparticles: The synthesised MNPs are subsequently collected after condensation and thoroughly cleaned with water multiple times (FIG. 4c). The acquired MNPs were subsequently subjected to characterization processes.

[0144] 5. Control of Particle Size and Morphology: MNPs size and shape can be controlled by adjusting electric arc parameters such applied current, voltage, electrode material, cooling rate, and gas composition in the surrounding environment.

[0145] FIG. 5 illustrates (a-b) SEM pictures, (b) EDX spectrum of the prepared Fe NPs using direct electric arc approach in accordance with an embodiment of the present disclosure. FIG. 5 (a) illustrates SEM pictures at 500 nm, FIG. 5 (b) illustrates SEM pictures at 150 nm, FIG. 5 (c) illustrates EDX spectrum of the prepared Fe NPs using direct electric arc approach in accordance with an embodiment of the present disclosure.

[0146] A preferred method utilised a 50 A electric arc at 40 V in an argon atmosphere between two tungsten filaments, connected by a graphite rod immersed in a 1 M aqueous solution of Fe(NO.sub.3).sub.3.Math.9H.sub.2O for 20 minutes, facilitating plasma-assisted evaporation of Fe3+ ions and resulting in the formation of Fe NPs upon cooling. The SEM characterization results demonstrated that the synthesized MNPs have an average diameter of 40-50 nm (FIG. 5(a-b)), which can be further adjusted by altering the cooling rate, electric arc, solution composition, and gas flow rate. Moreover, the FE-SEM EDX analysis clearly indicated high purity of the fabricated Fe NPs (FIG. 5(c)).

[0147] The present invention offers several significant advantages for the production of metallic nanoparticles (MNPs). Firstly, its efficiency is remarkable; the direct electric arc method provides a rapid and energy-efficient means of creating MNPs, circumventing the need for intricate chemical precursors or high-energy techniques like lasers. Secondly, the method boasts impressive scalability, making it highly suitable for industrial-scale MNP fabrication. Thirdly, it enables controlled particle size and shape, as these characteristics can be precisely managed by adjusting electric arc parameters such as applied current, voltage, electrode material, cooling rate, and the composition of the surrounding gas. Furthermore, the versatility of this approach allows for the creation of a diverse range of nanomaterials, including various MNPs and nanocomposites. Lastly, this invention has a low environmental impact compared to conventional nanoparticle synthesis methods, as it eliminates the use of harmful chemicals and significantly reduces byproduct generation.

[0148] The disclosed invention provides a method and system for manufacturing metallic nanoparticles (MNPs) that involves three key steps: first, establishing a direct electric arc between two electrodes; second, applying a high voltage to these electrodes to generate a plasma that vaporizes metal ions and converts them into MNPs; and finally, condensing this vaporized material into MNPs. Crucially, the size and morphology of these nanoparticles can be precisely controlled by fine-tuning parameters such as voltage, current, electrode material, cooling rate, and the composition of the surrounding gas. Furthermore, the chemical composition of the nanoparticles can be modified by introducing additional precursor materials directly into the arc. The versatility of this method allows for the production of a wide range of nanoparticles, including metallic, semiconductor, or composite nanoparticles.

[0149] On account of their resistance to high temperatures and relatively low erosion rates in comparison to metallic alternatives, we decided to employ graphite electrodes of high purity.

[0150] After each synthesis cycle, the length of the electrode and the shape of the tip were examined on a regular basis. Electrodes were either reshaped (via the process of mechanical grinding) or replaced, depending on the degree of degradation that had occurred. Depending on arc duration and current load that was being applied at the time, reshaping was required generally every 2-3 runs, while full replacement was performed approximately every five to seven runs.

[0151] The arc gap is standardized and ensured uniform electrode geometry. This was done to ensure that the creation of nanoparticles was consistent. Through the application of this approach, a stable arc and reproducible synthesis conditions were effectively maintained.

[0152] In order to ensure an adequate mechanical fit, the tungsten filament is either twisted tightly around the graphite rod or inserted into a drilled recess at the end of the rod. After that, a metallic clamp made of stainless steel that is resistant to high temperatures is used to secure this junction. This clamp delivers consistent pressure to maintain contact. The metallic clamp also functions as the point of contact for the electrical current, which enables current to flow from the power source to the tungsten filament and finally to the graphite rod with a minimal amount of resistance.

[0153] Around regions that are close to the arc zone, a water jacket is placed around the quartz tube and the electrode holders. A closed-loop water cooling system incorporates this jacket as an integral component.

[0154] The flow rate of the chiller unit, which is typically 2-4 L/min, is used to supply the circulating water, which ensures that the temperature is maintained consistently.

[0155] This setup allows the arc to initiate and sustain between the submerged cathode and the tip of the anode that is just above the liquid. This setup enables efficient vaporization of precursors and generates nanoparticles in a precise manner.

[0156] Within the context of this discussion, the term close proximity refers to the gap of 2-5 mm gap that exists between the anode tip and the solution surface. This gap was designed to ensure that the arc remains stable without generating splashing or uncontrolled boiling.

[0157] Intense thermal energy is transferred to the surface of the liquid when the plasma arc comes into contact with the aqueous solution or is in extremely close proximity to it.

[0158] This results in the liquid to get superheated in a microscopic volume close to the contact, which causes the temperature to rise locally over the boiling point before nucleation can take place.

[0159] This unstable state induces explosive evaporation, which results in the formation of microbubbles, which are typically comprised of water vapor and volatile species and have a diameter ranging from 1 to 10 m.

[0160] As a result of collisions with high-energy electrons and other species, water molecules (H2O) are energetically unstable in the plasma environment and undergo thermal dissociation extremely quickly.

[0161] In most cases, the voltage that is required to initiate the arc is about 240 volts. During stable operation, the sustaining arc voltage declines drastically to lower levels (80-90 V) after the breakdown has occurred. The constant current power supply that we employ in our arc discharge setup maintains the continuous electric current. This power supply also ensures that the electrodes receive a consistent current when the setup is in operation.

[0162] The electric arc of our apparatus remains stable due to several fundamental mechanisms. (i) Inert atmosphere; (ii) Design and arrangement of electrodes; (iii) Constant Current Power Supply; and (iv) Thermal management and cooling. Vaporized metal species generated in the plasma are subjected to rapid thermal quenching as they move into the cooler argon-filled region (18-25 C.), leading to supersaturation of metal vapor. Supersaturation is a critical driver of nucleation, favoring the formation of numerous small nuclei rather than allowing extended growth into larger particles or bulk material. Nanoparticle formation in our system is governed primarily by homogeneous nucleation in a supersaturated vapor phase, followed by condensation-driven growth. Agglomeration occurs to a limited extent, while heterogeneous nucleation plays a minimal role due to controlled purity and system design.

[0163] The rate at which vaporized metallic species cool is not actively controlled by a single parameter; rather, it is regulated indirectly through a number of important experimental conditions. Because of these parameters, we are able to exert control over the rate at which the heated vapor cools down and condenses into nanoparticles. With this current situation, it is extremely challenging to determine the precise quantitative relationship that exists between the rate of cooling and the average diameter of nanoparticles.

[0164] The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0165] Benefits, other advantages, and solutions to problems have been described above about specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.