A Core-Shell Nanoparticle

Abstract

The present invention relates to a core-shell nanoparticle comprising (a) an inorganic core comprising a nanoparticle comprising a metal, a metal oxide or combination thereof, and a silica component; (b) a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer; and (c) a crosslinker that conjugates the shell material to the inorganic core. There is also provided a method for producing the core-shell nanoparticle and uses thereof.

Claims

1. A core-shell nanoparticle comprising: a) an inorganic core comprising a nanoparticle comprising a metal, a metal oxide or combination thereof, and a silica component; b) a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer; and c) a crosslinker that conjugates the shell material to the inorganic core.

2. The core-shell nanoparticle of claim 1, wherein said metal or said metal oxide comprises a magnetic material, a ferromagnetic material or a superparamagnetic material.

3. The core-shell nanoparticle of claim 1, wherein said metal or said metal oxide comprises a metal selected from the group consisting of iron, cobalt, nickel, chromium, alloys of cerium, dysprosium, erbium, europium, gadolinium, holmium, lanthanum, lutetium, neodymium, praseodymium, promethium, samarium, scandium, terbium, thulium, ytterbium, yttrium, and mixtures thereof.

4. The core-shell nanoparticle of claim 1, wherein said metal oxide is selected from the group consisting of iron (III) oxide, iron (II) oxide, cobalt (III) oxide, cobalt (II) oxide, nickel (III) oxide, nickel (II) oxide, copper (II) oxide or copper (I) oxide, chromium (III) oxide, chromium (II) oxide, and mixtures thereof.

5. The core-shell nanoparticle of claim 1, wherein said silica component comprises a hydrocarbon group, an alkyl aryl group, an alkoxy silane group, or combinations thereof.

6. The core-shell nanoparticle of claim 1, wherein said copolymer is a block copolymer or a grafted copolymer.

7. The core-shell nanoparticle of claim 6, wherein said block copolymer comprises at least two blocks of polymers.

8. The core-shell nanoparticle of claim 1, wherein said pH-responsive polymer is selected from the group consisting of poly(4-vinylpyridine) (P4VP), poly(2-vinylpyridine) (P2VP), poly(methacrylic acid) (PMAA), poly(acrylic acid) (PAA), and poly(dimethylaminoethyl methacrylate) (PDMAEMA).

9. The core-shell nanoparticle of claim 1, wherein said hydrophobic polymer is selected from the group consisting of poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), polytetrafluoroethylene (PTFE), thermoplastic polyurethane (TPU), and polyvinylidene fluoride (PVDF).

10. The core-shell nanoparticle of claim 1, wherein said crosslinker is a bifunctional crosslinker.

11. The core-shell nanoparticle of claim 1, wherein said crosslinker comprises an alkyl group, an alkoxy group, a halogen group, a haloalkyl group, a silane group, or combinations thereof.

12. The core-shell nanoparticle of claim 1, wherein said core and said shell material are in a weight ratio of 10:90 to 90:10.

13. A method of preparing a core-shell nanoparticle comprising the step of: conjugating an inorganic core comprising a metal, a metal oxide or combination thereof, and a silica component, with a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer.

14. The method of claim 13, further comprising the step of: coating the surface of a nanoparticle comprising a metal, a metal oxide, or a combination thereof with a silica layer to form said inorganic core.

15. The method of claim 14, further comprising the step of: immersing said inorganic core in a solution of a crosslinker to form a crosslinked inorganic core.

16. The method of claim 15, further comprising the step of: immersing said crosslinked inorganic core in a solution of said copolymer to form said core-shell nanoparticle.

17. Use of a core-shell nanoparticle to remove oil and surfactant in an oil-in-water nanoemulsion, wherein said core-shell nanoparticle comprises: a) an inorganic core comprising a nanoparticle comprising a metal, a metal oxide, or combination thereof, and a silica component; b) a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer; and c) a crosslinker that conjugates the shell material to the inorganic core.

18. A method of removing oil and surfactant in an oil-in-water nanoemulsion comprising the steps of: a) mixing a core-shell nanoparticle in the oil-in-water nanoemulsion; b) adjusting the pH of the nanoemulsion to thereby trap the oil in the nanoemulsion on a surface of the core-shell nanoparticle; and c) applying an external magnetic field to separate the core-shell nanoparticle with entrapped oil from the water in the nanoemulsion, wherein said core-shell nanoparticles comprise i) an inorganic core comprising a nanoparticle comprising a metal, a metal oxide, or combination thereof, and a silica component; ii) a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer; and iii) a crosslinker that conjugates the shell material to the inorganic core.

19. A method of separating oil from an oil-absorbed core-shell nanoparticle comprising the steps of: a) immersing the oil-absorbed core-shell nanoparticle into a solution of acid; and b) washing the oil off a surface of the oil-absorbed core-shell nanoparticle with an aqueous solution at neutral pH, wherein said core-shell nanoparticles comprise i) an inorganic core comprising a nanoparticle comprising a metal, a metal oxide, or combination thereof, and a silica component; ii) a shell material comprising a copolymer having at least two polymers selected from a pH-responsive polymer and a hydrophobic polymer; and iii) a crosslinker that conjugates the shell material to the inorganic core.

20. The method of claim 19, further comprising the step of recycling said core-shell nanoparticle after said washing step (b).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0104] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0105] FIG. 1 shows a series of transmission electron microscopy (TEM) images of Fe.sub.3O.sub.4 (FIG. 1A), Fe.sub.3O.sub.4@SiO.sub.2 (FIG. 1B) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (FIG. 1C) (scale bar 20 nm).

[0106] FIG. 2 shows a series of FTIR spectra of Fe.sub.3O.sub.4(FIG. 2A), Fe.sub.3O.sub.4@SiO.sub.2 (FIG. 2B), PDMS-diBr (FIG. 2C), P4VP-PDMS-P4VP (FIG. 2D), and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (FIG. 2E).

[0107] FIG. 3 shows a series of .sup.1H NMR spectra of Br-PDMS-Br in CDCl.sub.3 (FIG. 3A) and P4VP-PDMS-P4VP in DMSO-d.sub.6/CDCl.sub.3 (2/1, v/v) (FIG. 3B). The chemical structures of both polymers are given at the top of the spectrum. Residual solvent peaks are labelled with stars.

[0108] FIG. 4 shows a series of TGA curves for Fe.sub.3O.sub.4@SiO.sub.2 (curve A), ITMS activated Fe.sub.3O.sub.4@SiO.sub.2 (curve B), Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (curve C), and P4VP-PDMS-P4VP triblock copolymer (curve D).

[0109] FIG. 5 shows a series of magnetic hysteresis loops for Fe.sub.3O.sub.4, (loop A), Fe.sub.3O.sub.4@SiO.sub.2 nanoparticle (loop B) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles (loop C).

[0110] FIG. 6 shows the diameter distribution of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles at pH 3 and 7, respectively.

[0111] FIG. 7 demonstrates a series of the modifications of the remote controlled oil-in-water nanoemulsion separation. FIG. 7A is a schematic diagram showing the overall process of absorbing and releasing oil from an oil-in-water nanoemulsion. FIG. 7B shows a series of the changes of the remote controlled oil-in-water nanoemulsion separation by the combination effect of pH-responsive and magnetic hybrid nanoparticles and the subsequent separation of hybrid nanoparticles from the obtained oil/nanoparticles mixtures (FIG. 7C).

[0112] FIG. 8 shows a series of UV-Vis spectra of oil-in-water nanoemulsions (line A) and after treatment with P4VP-PDMS-P4VP copolymers (line B), Fe.sub.3O.sub.4@SiO.sub.2 (line C) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (line D).

[0113] FIG. 9 shows a series of the diameter distribution of oil-in-water nanoemulsion (FIG. 9A) and after treatment with P4VP-PDMS-P4VP copolymers (FIG. 9B), Fe.sub.3O.sub.4@SiO.sub.2 (FIG. 9C) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (FIG. 9D). Insert images showing the corresponding samples used for dynamic light scattering (DLS) measurements. FIG. 9B and FIG. 9C have the same x-axis (diameter in nm) as FIG. 9A.

[0114] FIG. 10 shows the dipole value calculations of the optimized unit structure of P4VP-PDMS-P4VP triblock copolymer at pH=7 (FIG. 10A) and pH=3 (FIG. 10B). FIG. 10C shows the hydrogen bond between a H.sub.2O molecule and a pyridyl group in protonated P4VP-PDMS-P4VP at pH=3.

[0115] FIG. 11 shows a series of images where FIG. 11A shows the pristine oil-in-water nanoemulsion (bottle A) and after treatments with Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles for 1-3 cycles (bottles B to D). FIG. 11B shows the optical transmittance of the corresponding solutions (bottles A to D) at 500 nm (*P<0.001).

DETAILED DESCRIPTION OF DRAWINGS

[0116] Referring to FIG. 7, FIG. 7A shows a schematic diagram of the overall process of the remote controlled separation of oil-in-water nanoemulsion by the combination effect of pH-responsive and magnetic core-shell hybrid nanoparticles, and the subsequent separation of hybrid nanoparticles from the obtained oil/nanoparticles mixtures under a magnetic field. Oil-in-water nanoemulsion with the hybrid nanoparticles (101) were prepared and at high pH (of 7), the pH-responsive polymer blocks were in the deprotonated state and exhibited oleophilic properties, while the hydrophobic polymer block is more hydrophobic than the pH-responsive polymer blocks. Therefore, the oleophilic and hydrophobic surfaces of the hybrid nanoparticles had a high affinity to the oil in the oil-in-water nanoemulsion. Hence, the hybrid nanoparticles congregated together upon contact with the oil and the hybrid nanoparticles can trap the oil onto their surface due to the surface's superoleophilic nature (103). When an external magnetic field was applied, the oil trapped on the surface of hybrid nanoparticles can be easily separated from the water (105). The oil captured on the surface of the hybrid nanoparticles was then released (107) by placing the hybrid nanoparticles into acid water having a pH value (such as pH of 3) (109). When contacted with acidic water, most of the pH-responsive functional groups on the pH-responsive polymer blocks became protonated and the surface acquired hydrophilic property. Thus, the captured oil can be easily washed from the surface of the hybrid nanoparticles and can be separated from the hybrid nanoparticles by using an external magnetic field (111).

EXAMPLES

[0117] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

[0118] List of Abbreviations Used

[0119] Ar: argon

[0120] 4-VP: 4-vinyl pyridine

[0121] bs: broad signal (broad peak).sup.1H NMR

[0122] cat.: catalyst

[0123] CuBr: copper(I) bromide

[0124] DCM or CH.sub.2Cl.sub.2: dichloromethane or methylenechloride

[0125] DI: deionized water

[0126] FTIR: fourier transform infrared

[0127] H: hour(s)

[0128] HPLC: high pressure liquid chromatography

[0129] HBr: hydrobromic acid

[0130] IPTMS: 3-iodopropyl trimethoxysilane

[0131] L: litre(s)

[0132] LC-MS: Liquid chromatography-mass spectrometry

[0133] MgSO.sub.4: magnesium sulfate

[0134] m.p.: melting point

[0135] min: minute(s)

[0136] MS: mass spectrometry

[0137] NPs: nanoparticles

[0138] NMR: Nuclear Magnetic Resonance

[0139] PMDETA: N,N,N,N,N-pentamethyldiethylenetriamine

[0140] Rt: room temperature

[0141] NaHCO.sub.3: sodium bicarbonate

[0142] TEOS: tetraethyl orthosilicate

[0143] THF: tetrahydrofuran

[0144] NEt.sub.3: triethylamine

[0145] TLC: thin layer chromatography

Materials and Methods

[0146] Octadecene (>99%), Oleic Acid (>99.9%), IGEPAL CO-520, cyclohexane, toluene (anhydrous, 99.8%), copper(I) bromide (CuBr, 99%), tetrahydrofuran (THF, anhydrous, 99.9%), iron(III) acetylacetonate, cyclohexene (anhydrous, 95%), ethanol (>99.8%), ethylenediamine (>99%), isopropyl alcohol (>99.8%), ammonium hydroxide (28 wt %), tetraethyl orthosilicate (TEOS, 99.999% trace metals basis), magnesium sulfate (MgSO.sub.4, >97%), poly(dimethylsiloxane), bis(3-aminopropyl) terminated (M.sub.n=2500 g/mol), 2-bromoisobutyryl bromide (98%), N,N,N,N,N-pentamethyldiethylenetriamine (PMDETA, 99%), (3-iodopropyl) trimethoxysilane (IPTMS, >95%), 4-vinyl pyridine (4VP, >95%) were purchased from Sigma-Aldrich Corp. (St. Louis, Mo., U.S.A.) and were used as received. All other reagents were used as received, except where otherwise noted in the experimental text below. All anhydrous solvents were also purchased from Sigma-Aldrich Corp. (St. Louis, Mo., U.S.A.) and used without further purification.

[0147] Nuclear magnetic resonance (.sup.1H NMR) spectra were recorded on a Bruker AV-400 NMR spectrometer at room temperature. Chemical shifts were recorded in parts per million (ppm) in reference to the solvent peaks of CHCl.sub.3 ((7.3 ppm) and DMF ((8.03, 2.92 and 2.75 ppm). .sup.1H NMR data are reported in the following order: chemical shift, multiplicity (br=broad, s=singlet, d=doublet, t=triplet, q=quartet and m=multiplet), integration and assignment. Transmission electron microscopy (TEM) images were obtained on a high-resolution transmission electron microscope (JEOL 2100-JEOL Ltd., Tokyo, Japan). The samples were suspended in ethanol and supported onto 200 mesh copper grids before measurement, which were coated in advance with supportive Formvar films and carbon (Agar Scientific Ltd, Stansted, Essex, United Kingdom). Dynamic light scattering (DLS) were performed using a Brookhaven BI-200SM multi-angle goniometer equipped with a BI-APD detector (Brookhaven Instruments Corporation, Holtsville, N.Y., U.S.A). The light source was a 35 mW He-Ne laser emitting vertically polarized light of 632.8 nm wavelength. Fourier transform infrared (FTIR) spectra were performed using Perkin-Elmer Spectrum 2000 (PerkinElmer, Inc. Waltham, Mass., U.S.A). The data were collected in the range of 400 to 4000 cm.sup.1 with a resolution of 4 cm.sup.1 and a scan number of 64 at room temperature. Wide-angle x-ray diffraction (WXRD) patterns of powder samples were obtained using a D8 Advance X-ray diffractometer (Bruker, AXS Inc., Madison, Wis., U.S.A), using Ni-filtered Cu K of =1.5418 operated at 40 kV and 40 mA with a step size of 0.004 and step duration of 1 second. The magnetic properties of the as-synthesized nanoparticles were measured using a vibrating sample magnetometer (VSM, Lakeshore, Model 665 (Lake Shore Cryotronics, Ohio, U.S.A.). Thermogravimetric analysis (TGA) measurements were performed on a TA Q500 (TA Instruments, Delaware, U.S.A). All samples were equilibrated at 100 C. to remove any volatile solvent and moisture. The samples were then heated to 800 C. at 20 C./min under nitrogen at a flow rate of 60 mL/min.

Density Functional Theory (DFT)

[0148] Density functional theory calculations were performed to further understand the working mechanism of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles at different pH values. All the calculations were carried out with Gaussian 091 at m062x/6-31G(d) level. Utilizing the rule of miscibility which indicates that good miscibility is influenced by the polarity, we calculated the dipole of P4VP-PDMS-P4VP at pH=7 and pH=3, respectively with the converged structure, and further use the dipole value to estimate the polarity of P4VP-PDMS-P4VP copolymers and its interaction with oil and water molecules.

Example 1

[0149] An oil absorber based on pH-responsive block copolymer modified magnetic nanoparticles was constructed for effective separation of oil-in-water emulsion. The fabrication of core-shell Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP magnetic nanoparticle is schematically shown below in Scheme 1. The superparamagnetic Fe.sub.3O.sub.4 nanoparticles was designed as the core materials for providing the separation force, and surface modification with poly(4-vinylpyridine-b-dimethyl siloxane-b-4-vinylpyridine) (P4VP-PDMS-P4VP) block copolymer was performed to supply the switchable oil wettability properties. These hybrid nanoparticles showed excellent separation performance and could absorb octadecene up to 78.2 times of their own weight. It can be envisioned that this recyclable formulation should have great potential for practical applications in oily wastewater treatment.

[0150] According to Scheme 1, a silica layer was first coated on the surface of the Fe.sub.3O.sub.4 magnetic nanoparticles. Then, the formed Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles were immersed in an anhydrous toluene solution of IPTMS to functionalize the surface with iodopropyl groups via silanization, which acted as an intermediate anchoring layer for the block copolymer grafting. Finally, the triblock copolymers P4VP-PDMS-P4VP were coated on the Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles via quaternization between the iodopropyl groups and the pyridyl groups on the P4VP blocks, yielding a layer of the grafted block copolymer.

Example 2Preparation of Fe.SUB.3.O.SUB.4.@SiO.SUB.2.@P4VP-PDMS-P4VP Hybrid Nanoparticles (NPs) Synthesis of Magnetite Fe.SUB.3.O.SUB.4 .Nanoparticles

[0151] In a typical procedure, 2.5 mmol of iron (III) acetylacetonate (Fe(acac).sub.3) and 20 mmol of oleic acid (OA) are added into a 100 mL tri-neck round bottom flask (RBF) containing 12.8 mL of octadecene. First, the resulting mixture was heated to 160 C. for 30 minutes under argon purging. After that, the reactant was further heated to 320 C. at a rate of 5 C./minutes for another 60 minutes. The mixture was then cooled down to room temperature, and the final product was collected by centrifuging and washing by a standard hexane/isopropanol approach for 3 times.

[0152] The Fe.sub.3O.sub.4 magnetic nanoparticles were prepared via the solvothermal method. The TEM images of the morphology and size of the nanoparticles are shown in FIG. 1A. It can be observed that the prepared Fe.sub.3O.sub.4 nanoparticles take nearly uniform spherical shapes with a mean diameter of about 10 nm.

Synthesis and Surface Functionalization of Fe.sub.3O.sub.4@SiO.sub.2 Nanoparticles (NPs)

[0153] For the preparation of Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles, 100 mg of Fe.sub.3O.sub.4 particles dispersed in 5.0 mL were added into a conical flask containing 7.5 g of IPEGAL CO-520 and 12.5 mL of cyclohexane, and the mixtures were stirred vigorously at room temperature for 60 minutes. Then, ammonia solution (150 uL, 28 wt %) was added to form a brownish reverse microemulsion solution. After further stirring for 60 minutes, 250 uL of tetraethyl orthosilicate (TEOS) was added and the reaction was aged overnight. The final product was collected by centrifugation and washed with water/ethanol mixture for 3 times.

[0154] For the purpose of preventing aggregation and facile surface functionality, a silica coating on Fe.sub.3O.sub.4 nanoparticles was performed. Furthermore, the inert surface of silica layer can prevent Fe.sub.3O.sub.4 core from corrosion under any acid circumstances. After the reaction was completed, the size of the nanoparticles increased and the light silica layer can be observed clearly, as shown in FIG. 1B. Further, the successful silica coating onto Fe.sub.3O.sub.4 nanoparticles was confirmed by FT-IR technique where the characteristic absorption bonds at 1080 cm.sup.1 assigned to the SiOSi vibrations can be clearly seen in the spectrum of Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles (FIG. 2B) unlike the spectrum of Fe.sub.3O.sub.4 nanoparticles, as indicated in FIG. 2A.

[0155] The surface of Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles was further functionalized with iodoalkyl groups via silanization. Typically, 50 mg of Fe.sub.3O.sub.4@SiO.sub.2 particles dispersed in 15 mL of anhydrous toluene were mixed with 1.5 mL of (3-iodopropyl) trimethoxysilane (IPTMS) and stirred for 12 hours at room temperature. The silanized Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles were then washed with toluene and ethanol twice to remove the unreacted silanes, followed by drying with a flow of nitrogen. The surface functionalized Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles were dispersed in anhydrous THF for further preparation of multifunctional hybrid nanoparticles.

Preparation of P4VP-PDMS-P4VP Triblock Copolymer

[0156] The triblock copolymer P4VP-PDMS-P4VP was synthesized according to the procedure as shown in Scheme 2. The triblock copolymers were prepared by atomic transfer radical polymerization (ATRP). PDMS-diBr was used as macroinitiator to polymerize 4-VP by ATRP to produce the triblock copolymer P4VP-PDMS-P4VP.

[0157] Firstly, poly(dimethylsiloxane) (PDMS) was modified into ATRP macroinitiator PDMS-diBr by esterification of its amino end group with 2-bromoisobutyryl bromide in anhydrous CH.sub.2Cl.sub.2. A 5 times excess of 2-bromoisobutyryl bromide with respect to NH.sub.2 end groups was added and triethylamine was used to trap hydrobromic acid (HBr) generated during the reaction. The reactants were stirred at room temperature for 24 hours and the resultant solution was then washed three times using 100 mL of aqueous sodium bicarbonate solution. The organic layer was then isolated and dried with anhydrous MgSO.sub.4 over 4 hours and filtered, followed by vacuum drying at 40 C. overnight. The yield of the product (PDMS-diBr) is 94%.

##STR00001##

[0158] For the synthesis of P4VP-PDMS-P4VP triblock copolymer, 0.56 g of PDMS-diBr, 72.8 mg of PMDETA and 2.28 g of 4-VP were introduced into a 25 mL Schlenk tube, sealed with rubber plug. Next, the tube was purged and refilled with nitrogen three times using the vacuum-nitrogen-circling system. 57.6 mg of CuBr and 5.0 mL of degassed ethanol/THF solution (v/v: 1/1) were quickly added into the tube under a nitrogen atmosphere. Polymerization was allowed to proceed under continuous stirring at 75 C. for 24 hours. The reaction was stopped by diluting the reaction mixture with THF and exposing it to ambient atmosphere for 1 hour. Copper complex was removed by passing the reaction mixture through a short neutral aluminium oxide column. After concentrating the filtrates, the solutions were dialyzed against water for two days followed by freeze drying to obtain the titled compound.

[0159] The chemical structure of the titled copolymer P4VP-PDMS-P4VP was confirmed by .sup.1H NMR spectroscopy. As compared with the .sup.1H NMR spectrum of PDMS-diBr (FIG. 3A), the respective characteristic peaks for methylene and methine protons at 1.48 ppm and for pyridine ring protons at 6.49 and 8.25 ppm of P4VP blocks can be seen clearly (FIG. 3B), indicating that PDMS-diBr successfully initiated polymerization of 4-VP monomers.

[0160] In addition, FT-IR spectroscopy shown in FIG. 2D, provides further evidence for the successful formation of the triblock copolymer P4VP-PDMS-P4VP, where the absorption peaks at 1690, 1451 and 1415 cm.sup.1 were corresponding to the pyridine ring vibration, as compared to PDMS-diBr as indicated in FIG. 2C.

Preparation of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP Hybrid Nanoparticles (NPs)

[0161] Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4V hybrid nanoparticles were prepared by grafting or conjugating the P4VP-PDMS-P4VP triblock copolymers onto surface functionalized Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles via quaternization between the iodopropyl groups and the pyridyl groups on the P4VP blocks.

[0162] Typically, 50 mg of silanized Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles were incubated with 5.0 mg/mL P4VP-PDMS-P4VP polymer solution in anhydrous THF for 20 minutes, and then the collected particles were put in a vacuum oven at 120 C. for 12 hours to enable sufficient quaternization between the iodoalkyl groups and the pyridine groups of the block copolymers. The unconjugated P4VP-PDMS-P4VP polymers were removed by washing with copious amount of THF.

[0163] In the TEM image of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles as shown in FIG. 1C, the outer shell of the grafted block copolymers can be seen clearly, indicating that the grafting was successful. The formed Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were also examined by TGA and FT-IR techniques. The FT-IR spectrum as shown in FIG. 2E demonstrated that Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were synthesized accordingly. The characteristic absorption peaks belonging to the copolymer P4VP-PDMS-P4VP appeared clearly as compared with the inorganic Fe.sub.3O.sub.4@SiO.sub.2 (FIG. 2B), further demonstrating the successful conjugation of the copolymer P4VP-PDMS-P4VP onto the surface of the Fe.sub.3O.sub.4@SiO.sub.2 core.

[0164] As shown in FIG. 4, native Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles and ITMS activated Fe.sub.3O.sub.4@SiO.sub.2 nanoparticles have a tiny weight loss from the temperature of 100 C. to 800 C., while a step-wise degradation profile (clear stage) was found in the TGA curve of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles (curve C) by contrast. The weight loss at above 300 C. can be attributed to the cleaving of the P4VP-PDMS-P4VP copolymers. Based on the TGA analysis, the weight ratio between the inorganic Fe.sub.3O.sub.4@SiO.sub.2 core and P4VP-PDMS-P4VP layer was evaluated to be approximately at 62:38.

Example 3

[0165] Magnetic Properties of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP Hybrid Nanoparticles (NPs)

[0166] The magnetic properties of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were investigated using the vibrating sample magnetometer (VSM) technique at room temperature. FIG. 5 shows the magnetization curves/loops of pure Fe.sub.3O.sub.4 nanoparticle (loop A), Fe.sub.3O.sub.4@SiO.sub.2 nanoparticle (loop B) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles (loop C). It was found that Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were superparamagnetic since neither remanence nor coercivity was detected when the magnetic field was removed. The behavior of these hybrid nanoparticles no longer show the magnetic interactions, which means that there are reduced aggregations between them. The mean magnetization saturation (Ms) value of Fe.sub.3O.sub.4 is 78.0 emu/g, which is similar to previous reports. The Ms of the hybrid nanoparticles was normalized with the mass of Fe.sub.3O.sub.4 cores based on the weight ratios evaluated from the TGA thermogram. The normalized Ms of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles is 64.5 emu/g. Therefore, no obvious loss of Ms was observed between the hybrid nanoparticles and the bare Fe.sub.3O.sub.4 nanoparticles. This result indicates that the polymeric shell did not affect/influence the magnetic properties of Fe.sub.3O.sub.4 nanoparticles significantly.

PH-Responsiveness of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP Hybrid Nanoparticles (NPs)

[0167] The pH-responsiveness of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles was investigated by dynamic light scattering (DLS). From FIG. 6, it was found that the mean hydrodynamic radius of the nanoparticles increase from 43.83.6 nm to 75.25.3 nm when the neutral pH is reduced to a value of 3. This phenomenon could be attributed to the fact that P4VP segments in Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were protonated at lower pH and subsequently swelled due to the electrostatic repulsion between the charged P4VP segments.

Example 4

Preparation of Oil-in-Water Nanoemulsions and Separation Efficiency Assay

[0168] Oil-in-water nanoemulsions were prepared by adding octadecene (1.0 mL) stained with oil red O to the mixture of sodium dodecyl sulfate (0.1 mg) and deionized (DI) water (50 mL) under stirring for 1 day. Then, it was diluted 10 before mixing with Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles for separation efficiency assay.

Controlled Oil/Water Separation

[0169] Based on the pH and magnetic responsiveness, the prepared Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles can be employed to selectively collect oil droplets from surfactant-free oil/water emulsions and control the transport/movement of the oil phase under a magnetic field. A schematic diagram of the overall process of absorbing and releasing oil from an oil-in-water nanoemulsion is shown in FIG. 7A. In particular, FIG. 7B shows the process of the remote controlled separation of oil-in-water nanoemulsion by the combination effect of pH-responsive and magnetic hybrid nanoparticles, and the subsequent separation of hybrid nanoparticles from the obtained oil/nanoparticles mixtures under a magnetic field as indicated in FIG. 7C. Here, the hybrid nanoparticles of FIG. 7A is Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles, the pH-responsive polymer blocks in FIG. 7A is P4VP while the hydrophobic polymer block in FIG. 7A is PDMS. FIG. 7B shows a series of pictures depicting the process where the oil-in-water nanoemulsion was prepared using the oil red O and the color of the nanoemulsion is pink (131). The hybrid nanoparticles solution in light yellow (133) were prepared accordingly, and both nanoemulsion and hybrid nanoparticles were mixed together to achieve the mixture of nanoemulsion and hybrid nanoparticles in an orange-pink colour solution, as shown as 135. The pH level was adjusted to pH 7 (as described above), where the P4VP and PDMS segments become superoleophilic nature (their surfaces) and able to trap the oil onto their surfaces of the nanoparticles (137). By applying the external magnetic field, the oil trapped on the surface of nanoparticles can be easily separated from the water (139). FIG. 7C shows the subsequent separation of hybrid nanoparticles from the obtained oil/nanoparticles mixtures (151), where the pH level was adjusted to 3 (as described above). Due to the pyridyl groups (being the pH-responsive functional group of the pH-responsive polymer blocks) on the P4VP segments that became protonated, the surfaces of the nanoparticles acquired the hydrophilic property and thus, release the captured oil (153). By applying the external magnetic field, the hybrid nanoparticles were separated from the oil (155).

[0170] P4VP, which is a weak polybase has a pH-responsive property that can alter its wettability via protonation and deprotonation of the pyridyl groups if there is a change in the surrounding pH values. When the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles were mixed with the oil-in-water nanoemulsion with a pH of 7, the P4VP segments were in the deprotonated state and exhibited oleophilic properties. Meanwhile, the flexible PDMS segment is more hydrophobic than the P4VP segments. As a consequence, the oleophilic and hydrophobic surface of the hybrid nanoparticles had a high affinity to the oil in the oil-in-water nanoemulsion with a pH of 7. Upon contact with the oil, Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles can trap the oil onto their surface due to the surface's superoleophilic nature. When an external magnetic field was applied, the oil trapped on the surface of nanoparticles can be easily separated from the water. The oil captured on the surface of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles was then released by placing the nanoparticles into acid water having a pH value of 3. When contacting with acidic water, most of the pyridyl groups on the P4VP segments became protonated and the surface acquired hydrophilic property. Thus, the captured oil can be easily washed from the surface of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles. The efficiency of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles for controlled oil/water separation was tested using UV and DLS techniques.

[0171] FIG. 8 shows the UV-Vis spectra of oil-in-water nanoemulsions (line A) and after treatment with P4VP-PDMS-P4VP copolymers (line B), Fe.sub.3O.sub.4@SiO.sub.2 (line C) and Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles (line D), respectively. It can be observed that a transparent liquid was obtained after the system was treated with Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles, implying that there was no trace of oil in the water. The high separation efficiency was also confirmed by DLS measurements. Based on FIG. 9, it can be seen that there were no significant changes in the diameter of oil-in-water nanoemulsion (FIG. 9A) in orange-pink solution (161) after treatment with P4VP-PDMS-P4VP copolymers (FIG. 9B) and Fe.sub.3O.sub.4@SiO.sub.2 (FIG. 9C) of a light pink solution (181), indicating that the oil droplets are still remaining in the water. The slight reduction in the diameter of oil-in-water nanoemulsion after treatment with P4VP-PDMS-P4VP copolymers is due to the partial oil droplets that are being captured by the copolymers floating on the surface (171). In contrast, the oil droplets disappear in the clean water (191) after separation by the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP hybrid nanoparticles (FIG. 9D).

Example 5

[0172] Absorption Capacity of Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP Hybrid Nanoparticles (NPs)

[0173] The absorption capacity is defined as the weight of oil that can be absorbed by the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles per unit weight of nanoparticles. Based on the investigation, the maximum amount of oil that the functionalized sponge could absorb was measured to be 78.2 times the hybrid nanoparticles' weight (oil absorption ratio: 7820%). The high absorption capacity of the Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles could be due to the higher density of the block copolymer P4VP-PDMS-P4VP that is on the surface of Fe.sub.3O.sub.4@SiO.sub.2 core.

[0174] FIG. 10 shows the optimized structure of P4VP-PDMS-P4VP at pH 7 and pH 3 respectively, and the dipole value for each geometry. In neutral conditions, P4VP-PDMS-P4VP has a very small dipole of 4.05 Debye (FIG. 10A) that is expected to be a non-polar molecule and demonstrated a good miscibility in octadecene which is also non-polar. This is in line with the experimental phenomenon that hybrid Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles had a high affinity with oil at pH 7 as shown in FIG. 7. While in acidic conditions, the P4VP-PDMS-P4VP triblock copolymer was protonated and the DFT calculations predicted that the dipole would show a value of 192.16 Debye (FIG. 10B). In this regard, such a high dipole value would suggest that the protonated P4VP-PDMS-P4VP is polar and would result in good miscibility in polar solvents such as water (H.sub.2O). These calculations correspond with the experimental findings on the release of absorbed oils from Fe.sub.3O.sub.4@SiO.sub.2@P4VP-PDMS-P4VP nanoparticles at pH 3.

[0175] In summary, the different dipole values of P4VP-PDMS-P4VP and protonated P4VP-PDMS-P4VP are responsible for the different miscibility of the nanoparticles, where the polymer is non-polar and polar in neutral and acidic solvent environments respectively. Furthermore, there would be strong hydrogen bond between water molecules and pyridyl groups in protonated P4VP-PDMS-P4VP (H.sub.2OHN). The calculated bond length and bond energy is 1.68 and 1.00 eV respectively. The existence of this hydrogen bond facilitates the miscibility of protonated P4VP-PDMS-P4VP in H.sub.2O.

[0176] Moreover, the absorbed oil could be easily released from the hybrid nanoparticles by placing the oil-loaded hybrid nanoparticles into acidic water at pH 3. After washing with water at neutral pH and drying with nitrogen flow, the used hybrid nanoparticles that are being regenerated would have uperoleophilicity in neutral aqueous solution, making it reusable for selective removal of oil from water. As shown in FIG. 11A of the pink solution (201), no obvious changes can be found in the absorption capacity of the regenerated hybrid nanoparticles after three cycles of usage, indicating the excellent stability and reusability of the nanoparticles.

INDUSTRIAL APPLICABILITY

[0177] The core-shell nanoparticle as defined above may be used to absorb oil from an oil-in-water nanoemulsion. Hence, the core-shell nanoparticle may be used in wastewater treatment or in treatment of oil spill or in industries where oil generated during a processing stage is required to be separated from the aqueous medium that it is generated in.

[0178] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.