Method for manufacture of pure, carbon free nanoparticles

Abstract

The invention provides a process for the production of nanoparticles as well as a device that is disposed for the production of the nanoparticles. The process is especially characterized in that the nanoparticles are pure, especially free from organic carbon compounds, preferably carbon-free, and are obtained continuously. The nanoparticles which are obtainable by the process of the invention are characterized in that they are present without an organic ligand in suspension and are especially preferred stable as a suspension against agglomeration, wherein the medium having the particles suspended therein is free from organic carbon compounds, especially carbon-free.

Claims

1. Process for the production of nanoparticles of gold and/or a metal of the platinum group, comprising: providing first particles of gold and/or of the platinum metal suspended in an aqueous medium, adding an inorganic oxidizing agent to the aqueous medium, wherein the inorganic oxidizing agent has a redox potential in the aqueous medium higher than that of an oxidized form of the first particles of gold and higher than that of an oxidized form of the first particles of the platinum metal, and irradiating the medium having the first particles suspended therein with a pulsed laser irradiation, whereby a suspension of the nanoparticles in the medium is generated, and wherein the aqueous medium is free from organic carbon compounds other than CO.sub.2.

2. Process according to claim 1, wherein the first particles have a size of at maximum 200 nm.

3. Process according to claim 1, wherein the providing the first particles comprises removal or oxidation of organic compounds from an admixture of the organic compounds and the first particles.

4. Process according to claim 1, wherein the providing comprises generation of a flow of the aqueous medium to which the inorganic oxidizing agent is added and having the first particles suspended therein, and wherein the irradiating comprises directing pulsed laser irradiation is directed onto at least a section of the flow.

5. Process according to claim 4, wherein the flow of the medium having the first particles suspended therein is a free liquid flow.

6. Process for the production of nanoparticles of gold and/or a metal of the platinum group, comprising: providing first particles of gold and/or of the platinum metal suspended in an aqueous medium, adding an inorganic oxidizing agent to the aqueous medium, wherein the inorganic oxidizing agent has a redox potential in the aqueous medium higher than that of an oxidized form of gold and/or higher than that of an oxidized form of the metal of the platinum group, and irradiating the medium having the first particles suspended therein with a pulsed laser irradiation, whereby a suspension of the nanoparticles in the medium is generated, wherein the providing comprises generation of a flow of the aqueous medium to which the inorganic oxidizing agent is added and having the first particles suspended therein, and wherein the irradiating comprises directing pulsed laser irradiation is directed onto at least a section of the flow, and wherein the diameter of the section of the flow is at maximum as large as the focus of the pulsed laser irradiation directed onto this section.

7. Process according to claim 1, wherein the first particles suspended in the aqueous medium are provided by production by application of a first pulsed laser irradiation onto a metal containing body containing gold and/or a metal of the platinum group arranged in an aqueous medium, or by wire erosion of a metal containing body in the form of a wire of gold and/or of a metal of the platinum group in the aqueous medium, wherein the aqueous medium is free from organic carbon compounds.

8. Process according to claim 1, wherein the pulsed laser irradiation has a wavelength of 330 to 1500 nm at a repetition rate of at least 10 Hz.

9. Process according to claim 1, wherein the medium in which the first particles are suspended consists of water with an inorganic oxidizing agent contained therein and the oxidizing agent is selected from the group consisting of H.sub.2O.sub.2, dissolved ozone, a derivative of oxygenhydrogen compounds, a nitrogen oxide, antimonic acid, arsenious acid, arsenic acid, boric acid, chlorous acid, bromous acid, chloric acid, chromic acid, cyanic acid, dichromic acid, disulphuric acid, hypochlorous acid, hypobromous acid, hypoiodous acid, iodous acid, iodic acid, isocyanic acid, carbonic acid, metasilicilic acid, molybdic acid, orthodisilicilic acid, orthosilicilic acid, perbromic acid, perchloric acid, periodic acid (orthoperiodic acid), peroxodisulphuric acid, peroxonitric acid, nitric acid, nitrous acid, sulphuric acid, sulphurous acid, telluric acid, thiosulphuric acid, tungstic acid and its salts, hypofluorous acid, hypofluorite, oxyacid of chlorine, hypochlorite, chlorite, chlorate, perchlorate, oxyacid of bromine, hypobromite, bromous acid, bromite, bromic acid, bromate, perbromic acid, perbromate, oxyacids of iodine, hypoiodite, iodite, iodic acid, iodate, orthoperiodic acid, periodate, meta-periodic acid and admixtures of these, wherein the inorganic oxidizing agent comprises a gas dissolved in the aqueous medium, wherein the inorganic oxidizing agent has a redox potential in the aqueous medium that is higher than that of the oxidized form of gold and/or the oxidized form of the metal of the platinum group by at least an amount of an overpotential of the gas compared to the nanoparticles.

10. Process according to claim 1, wherein the nanoparticles suspended in the medium are subsequently contacted with a substance which is selected from organic ligands, an inorganic carrier and an optically active solid.

11. Process according to claim 1, wherein the pulsed laser irradiation has a fluence of the least 0.8 J/cm.sup.2.

12. Process according to claim 1, wherein the nanoparticles are clusters.

13. Process according to claim 1, wherein the aqueous medium carbon-free.

14. Process according to claim 1, wherein the aqueous medium consists of water and the inorganic oxidizing agent with or without CO.sub.2.

15. Process according to claim 10, further comprising removing the inorganic oxidizing agent prior to the nanoparticles suspended in the medium being contacted with the substance.

16. Process for the production of nanoparticles of a metal of the platinum group, comprising: providing first particles of the metal of the platinum group suspended in an aqueous medium, adding an inorganic oxidizing agent to the aqueous medium, wherein the inorganic oxidizing agent has a redox potential in the aqueous medium higher than that of an oxidized form of the metal of the platinum group, and irradiating the medium having the first particles suspended therein with a pulsed laser irradiation, whereby a suspension of the nanoparticles in the medium is generated, and wherein the aqueous medium is free from organic carbon compounds other than CO.sub.2.

17. Process according to claim 16, wherein the first particles have a size of at maximum 200 nm.

18. Process according to claim 16, wherein the providing the first particles comprises removal or oxidation of organic compounds from an admixture of the organic compounds and the first particles.

19. Process according to claim 18, wherein the diameter of the section of the flow is at maximum as large as the focus of the pulsed laser irradiation directed onto this section.

20. Process according to claim 16, wherein the providing comprises generation of a flow of the aqueous medium to which the inorganic oxidizing agent is added and having the first particles suspended therein, and wherein the irradiating comprises directing pulsed laser irradiation is directed onto at least a section of the flow.

21. Process according to claim 20, wherein the flow of the medium having the first particles suspended therein is a free liquid flow.

22. Process according to claim 16, wherein the first particles suspended in the aqueous medium are provided by production by application of a first pulsed laser irradiation onto a metal containing body containing a metal of the platinum group, or by wire erosion of a metal containing body in the form of a wire of a metal of the platinum group, wherein the aqueous medium is free from organic carbon compounds.

23. Process according to claim 22, wherein the metal containing body is a pure metal or a metal alloy of at least two metals of the platinum group.

24. Process according to claim 16, wherein the pulsed laser irradiation has a wavelength of 330 to 1500 nm at a repetition rate of at least 10 Hz.

25. Process according to claim 16, wherein the pulsed laser irradiation has a fluence of the least 0.8 J/cm.sup.2.

26. Process according to claim 25, wherein the medium in which the first particles are suspended consists of water with an inorganic oxidizing agent contained therein and the oxidizing agent is selected from the group consisting of H.sub.2O.sub.2, dissolved ozone, a derivative of oxygenhydrogen compounds, a nitrogen oxide, antimonic acid, arsenious acid, arsenic acid, boric acid, chlorous acid, bromous acid, chloric acid, chromic acid, cyanic acid, dichromic acid, disulphuric acid, hypochlorous acid, hypobromous acid, hypoiodous acid, iodous acid, iodic acid, isocyanic acid, carbonic acid, metasilicilic acid, molybdic acid, orthodisilicilic acid, orthosilicilic acid, perbromic acid, perchloric acid, periodic acid (orthoperiodic acid), peroxodisulphuric acid, peroxonitric acid, nitric acid, nitrous acid, sulphuric acid, sulphurous acid, telluric acid, thiosulphuric acid, tungstic acid and its salts, hypofluorous acid, hypofluorite, oxyacid of chlorine, hypochlorite, chlorite, chlorate, perchlorate, oxyacid of bromine, hypobromite, bromous acid, bromite, bromic acid, bromate, perbromic acid, perbromate, oxyacids of iodine, hypoiodite, iodite, iodic acid, iodate, orthoperiodic acid, periodate, meta-periodic acid and admixtures of these, wherein the inorganic oxidizing agent comprises a gas dissolved in the aqueous medium, wherein the inorganic oxidizing agent has a redox potential in the aqueous medium that is higher than the oxidized form of the metal of the platinum group by at least an amount of an overpotential of the gas compared to the nanoparticles.

27. Process according to claim 16, wherein the nanoparticles suspended in the medium are subsequently, optionally following removal of the inorganic oxidizing agent, contacted with a substance which is selected from organic ligands, an inorganic carrier and an optically active solid.

28. Process according to claim 16, wherein the nanoparticles are clusters.

29. Process according to claim 16, wherein the aqueous medium carbon-free.

30. Process according to claim 1, wherein the aqueous medium consists of water and the inorganic oxidizing agent with or without CO.sub.2.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention is now described in greater detail by the way of examples and with reference to the figures which show in

(2) FIG. 1 schematically the arrangement of a device according to the invention,

(3) FIG. 2 a photospectrum of nanoparticles produced according to the invention in water with H.sub.2O.sub.2,

(4) FIG. 3a the TEM-photo of nanoparticles according to the invention,

(5) FIG. 3b the size distribution of nanoparticles produced according to the invention measured by way of TEM,

(6) FIG. 3c a graphic representation of the sphericity of nanoparticles according to the invention,

(7) FIG. 3d a graphic representation of the sum distribution of sizes of nanoparticles according to the invention,

(8) FIG. 3e a graphic representation of sizes of nanoparticles according to the invention, measured by means of a disk centrifuge,

(9) FIG. 4 in a) the relative abundance of sizes of nanoparticles produced according to the invention and their electron microscopic representation, and in b) the relative abundance of sizes of first particles and their electron microscopic representation,

(10) FIG. 5 a scanning electron microscopic photo of a carrier,

(11) FIG. 6 a scanning electron microscopic photo of a carrier with nanoparticles according to the invention arranged thereon,

(12) FIG. 7 a scanning electron microscopic photo of a carrier with nanoparticles according to the invention arranged thereon,

(13) FIG. 8 the result of an EDX-analysis of nanoparticles according to the invention on a carrier, and

(14) FIG. 9 the calculated molar concentration of oxidizing agents and the calculated number of surface atoms of nanoparticles of gold at a concentration of 20 mg/L.

EXAMPLE 1: PRODUCTION OF NANOPARTICLES OF GOLD

(15) As the metal containing body, 99.99% gold arranged in highly purified water having a content of 10 wt.-% H.sub.2O.sub.2 was irradiated with laser pulses of 10 ns at a wavelength of 1064 nm having a maximum energy of 80 mJ per pulse, beam diameter 6 mm at a distance of approximately 100 mm from the lens (focus 100 mm) and the metal body at a pulse repetition rate of 100 Hz. The layer height of the medium between the metal body and the laser was approximately 1 cm, the pH value of the water ca. 3 to 5.

(16) It could be observed that at the metal body a red coloring spread within the liquid, as is known for gold nanoparticles. A plasmon resonance (increased extinction) at 520 nm showed. These first particles agglomerated to hydrodynamic diameters of ca. 50 nm, measured by means of dynamic laser light scattering and measurements in a disk centrifuge.

(17) The medium with the first nanoparticles produced in this way under the influence of gravity or by means of a pump exited through a nozzle which was arranged within a larger glass body as a protective container. The nozzle was directed vertically to the ground and the medium having the first particles suspended therein generated a free falling flow of ca. 1.2 mm diameter. A second laser, having the same beam properties as the previously utilized laser but a frequency-doubled wavelength of 532 nm was focused on the flow of the medium such that the focused laser completely covered the flow of the medium in one section. The speed of the flow was ca. 0.6 m/s and the volumemetric exchange rate of the irradiated section was 100 Hz. The nanoparticles obtained showed a size of smaller than approximately 5 nm, a median quantity size distribution of approximately 2.5 nm and generally showed no resonance frequency in the green range, especially none at 520 nm as is shown in the spectrum of FIG. 2. The red colouring and extinction at 520 nm of the first particles completely disappeared when the medium repeatedly passed through the second laser beam, e.g. up to 60 times. In a preferred embodiment the nanoparticles that were generated by irradiating the flow of the medium having the first particles suspended therein were irradiated at least once again in a free flow of medium by the second pulsed laser irradiation, for example by recirculation of the nanoparticles suspended in the medium through the nozzle, again with sectionwise irradiation of the flow by the second pulsed laser irradiation. As generally preferred, the repetition rate of the laser was adapted to the speed of the flow such that each volume element of the flow is subjected to a pulse of the laser irradiation exactly one time.

(18) The nanoparticles obtained were stable as a suspension without further additive to the medium which contained inorganic oxidizing agent, e.g. for at least 4 d, preferably for at least 5 to 30 d. The stability could also be seen in that no plasmon resonance occurred, which is a sign for an agglomeration of non-plasmon resonant nanoparticles.

(19) The device utilized for this process is schematically shown in FIG. 1. Therein, a container 1 contains the metal body 2 of gold in a holding device and is surrounded by medium 3. A first laser 4 generates the first laser irradiation 5, which is directed through an optically transparent window 6 of the container 1 onto the metal body 2. Preferably, container 1 is a chamber flowed through by medium 3, the chamber having an inlet and an outlet. Subsequent to the irradiation with first laser irradiation 5, the medium 3 is transported, optionally continuously, from container 1 to a reservoir. Optionally, a spectrometer 20 is arranged in the duct between the container 1 and the reservoir 7 and/or in the duct between the reservoir 7 and the nozzle 8, which spectrometer 20 is devised for measuring the extinction. By way of this arrangement, the spectrometer 20 is arranged in a duct which is arranged upstream to the nozzle 8 and is therefore disposed to measure the medium fed to the nozzle 8. Preferably, a spectrometer 20 is arranged to control the dosing device for addition of the inorganic oxidizing agent. The medium 3 having the first particles contained therein is fed from the reservoir 7 to a nozzle 8, which is directed vertically to the ground and generates a free medium flow 9. For avoiding the formation of aerosols, the nozzle 8 is arranged within a housing 10 in which the medium flow 9 freely falls, optionally driven by a pump. A section of the flow of the medium 9 is irradiated by the second laser irradiation 12 generated by a second laser 11, the second laser irradiation 12 e.g. passing through a window or whole 13 of the housing 10 that is transparent for the second laser irradiation 12. As indicated schematically the window 13 can have or consist of an optical element, especially a collimating lens. The housing 10 has an outlet 14 out of which the medium exits that now contains the nanoparticles therein, for example into a collecting vessel 15. Optionally, at the outlet 14 there is arranged a further spectrometer 21, which can especially be connected with a control device of the second laser 11 or with a control device of the pump that drives the medium flow 9. The collecting vessel 15 can be connected to the nozzle 8 by means of a return duct in order to allow for a repeated irradiation of the medium now having the nanoparticles contained therein and/or first particles with second laser irradiation 12. A carrier 18 can be arranged in the collecting vessel 15, wherein the carrier 18 especially covers the cross-section of the flow of the collecting vessel 18. Such a carrier is e. g. arranged in the collecting vessel 15 in order to arrange nanoparticles on the carrier 18. The carrier 18 can e.g. be titanium dioxide or aluminium oxide as a powder or moulding, onto which nanoparticles sorb. In the return duct 16, which can have a pump, optionally a filter 19 is arranged that retains particles having a size above a preset size, e.g. retaining particles having a size above 10 nm. A dosing device for inorganic oxidizing agent is shown by way of a reservoir 17 for the oxidizing agent which is connected by means of a duct to the duct that leads to the nozzle 8. In this way the dosing device, which preferably is controlled in dependence on the spectrometer 21 arranged at the outlet 14, can be devised to introduce inorganic oxidizing agent into the medium containing first particles.

(20) FIG. 2 shows a spectrum of nanoparticles of gold produced according to the invention in water containing H.sub.2O.sub.2 in comparison to nanoparticles of gold in pure water, and therefore without inorganic oxidizing agent, which were otherwise produced by the same process. The absence of the plasmon resonance at 420 nm of nanoparticles according to the invention shows that the nanoparticles produced according to the invention in the medium having a content of an inorganic oxidizing agent are smaller than 5 nm, especially smaller than 3.5 nm in diameter and did not aggregate to one another to larger plasmon resonant aggregates. The particles according to the invention also subsequent to storage for e.g. 20 d show the same optical properties and therefore prove the stability of the nanoparticles which are suspended in the medium. As a reason for this stability there is presently assumed an electrostatic stabilization of the nanoparticles. Therefore the suspension of nanoparticles which is obtainable by the process according to the invention can also be termed an electrostatically stabilized colloid.

(21) FIG. 3a shows the particle sizes of nanoparticles of gold produced according to the invention in a TEM-photo which are deposited on a grid and measured in a transmission electron microscope (TEM). These data show that the nanoparticles produced according to the invention have a mean particle size of ca. 3 nm and a size range of ca. 1-5 nm.

(22) FIG. 3b shows the size distribution of nanoparticles according to the invention which were determined from TEM-photos. In the size distribution, a primary and a secondary Gaussian distribution were determined. The particle size that lies in the intersection of the Gaussian distributions is shown as the border on the representation of the sphericity in FIG. 3c. For a sphericity of below 0.8 (sector II) no spherical form is assumed.

(23) From FIGS. 3b and 3c it results that the spherical form particles in sector I are nanoparticles according to the invention having a particle size of smaller than 5 nm, wherein their main portion has a size of smaller than 3 nm.

(24) From the data of FIGS. 3b and 3c one can conclude that larger particles possibly are first particles or were formed as artifacts during the preparation of the particles on the TEM-grid, e.g. caused by removal of the inorganic oxidizing agent.

(25) FIG. 3d shows the sum distribution of single and cumulated Gaussian distributions. It can be seen from this that preferably 92% of all particles generated by the process are present in the medium with a diameter of smaller than 3 nm.

(26) The data of the measurement of the sizes of nanoparticles by means of a disk centrifuge are shown in FIG. 3e. These data confirm that nanoparticles produced according to the invention essentially have a size of smaller than 5 nm with a mean size of smaller than 3 to smaller than 4 nm.

(27) FIG. 4a shows the size distribution of these nanoparticles produced according to the invention and an inset electron microscope picture of these nanoparticles. FIG. 4b shows the size distribution of the first particles generated by means of laser irradiation to the gold body arranged in water having 10% wt.-% H.sub.2O.sub.2. The electron microscopical picture inset in FIG. 4b shows these first particles. In the alternative, the water in this step can be without additive. The first particles show a diameter of ca. 7.5 to maximally 50 nm, especially of ca. 10 to 35 nm having a mean particle size of 20, e.g. for at least 90% of first particles.

(28) These results show that the nanoparticles produced according to the invention have a size of essentially below 5 nm, preferably of 1 to 3 nm, e.g. having a mean size of 2.5 nm, generally preferred with a mono-modal size distribution.

EXAMPLE 2: PRODUCTION OF A COMPOUND OF NANOPARTICLES WITH ORGANIC LIGANDS

(29) Nanoparticles of gold produced according to Example 1 in a medium having a content of H.sub.2O.sub.2 where first transferred to a non-oxidizing medium. Subsequently, the suspension of the nanoparticles was contacted with an organic ligand as an example for a substance, for example with an oligonucleotide, a protein, preferably a binding molecule, especially an antibody, or with a polysaccharide. Optionally, the substance contained a thiol group.

(30) It has shown that the nanoparticles obtainable according to the invention have a sufficient reactivity for forming a bond with the organic molecule added as the substance. The organic molecules therefore were labelled by the nanoparticles. The compounds obtained of the substance with nanoparticles produced according to the invention where fluorescent and not plasmon resonant, as is generally preferred.

EXAMPLE 3: COATING OF AN INORGANIC CARRIER WITH NANOPARTICLES

(31) As an example for an inorganic carrier, zinc oxide or an electrode having a metal surface was used. The nanoparticles were deposited on the carrier by contacting with the medium containing the nanoparticles. Therein it showed that no external or additional electrical field was necessary for arranging the nanoparticles on the carrier. The nanoparticles could alternatively be deposited on the surface of the carrier by electrophoretic deposition and formed an adsorbing layer on the carrier that preferably had superficial charges. The zinc oxide that was coated by the nanoparticles of gold was characterized by a homogenous arrangement or layer, respectively, of sorbed nanoparticles. FIG. 5 shows the zinc oxide particles used as a carrier in a scanning electron microscope (REM) picture, FIGS. 6 and 7 show the zinc oxide particles following contacting with the suspended nanoparticles. Here it becomes clear that these nanoparticles sorb onto the surface of the carrier.

(32) FIG. 8 shows an EDX-analysis of nanoparticles of gold according to the invention, which are arranged on a ZnO-carrier. Oxygen was determined by means of the K-line (O K), zinc by means of the K-line (ZnK) and gold by means of the L-line (AuL) of the spectrum.

(33) From the EDX-analysis it becomes clear that the nanoparticles of gold which are non-plasmon resonant and which preferably are clusters, are sorbed on the carrier and form a non-plasmon resonant coating.

(34) FIG. 9 shows the calculated molar concentrations of oxidizing agents ozone, H.sub.2O.sub.2 (according to the invention) and oxygen, each at standard pressure under standard conditions in water (not according to the invention), as well as those for a gold nanoparticle size of 2 nm at a concentration of 20 mg/L calculated molar concentration of nanoparticles. It shows that for H.sub.2O.sub.2 a concentration of 1 wt.-% already gives a molar relation higher by a factor of 1000 to the molar concentration of nanoparticles than the saturation with oxygen.

(35) On the example of gold nanoparticles the number of surface atoms of nanoparticles is given for the given particle sizes. This makes it clear that with increasing size of the nanoparticles the number of surface atoms of each nanoparticle increases, but not in a linear way.

EXAMPLE 4: PRODUCTION OF AN OPTICAL ELEMENT

(36) As an example for an optical element a glass was contacted with the nanoparticles suspended in the medium. The medium could have the content of inorganic oxidizing agent, alternatively, the inorganic oxidizing agent could be removed from the medium.

(37) The nanoparticles obtainable according to the invention could be deposited on the glass by mere contacting with the suspension.

(38) The optical element produced this way under irradiation, especially at a wavelength range of 350 to 1064 nm showed a limitable non-transparency which shows the suitability of the nanoparticles obtainable according to the invention for use as optical limiters against radiation of this wavelength.

EXAMPLE 5: PRODUCTION OF NANOPARTICLES OF GOLD

(39) In accordance with Example 1, first particles were irradiated with pulsed laser irradiation, wherein the first particles were not generated by irradiation of the metal body with first laser irradiation, but were synthesized by colloid chemistry and were present in aqueous medium. These first particles had PVA for stabilization.

(40) For removal of the organic carbon compound PVA prior to irradiation with pulsed laser irradiation the medium, in which the first particles were contained was washed at least 3-fold with ultra pure water and resuspended in ultra pure water, admixed with H.sub.2O.sub.2 in additional quantity stochiometrically sufficient for complete oxidation of organic carbon compounds and/or were irradiated additionally with a pulsed laser prior to adding H.sub.2O.sub.2.

(41) The irradiation of the first particles was preferably performed in a free liquid flow, in the alternative in a container under stirring.