Process for the formation of metal oxide nanoparticles coating of a solid substrate

Abstract

The present invention provides a process for the formation of a coating comprising peroxynanoparticles of metals selected from the group consisting of: Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb and Bi on a solid substrate, comprising providing a basic solution containing at least a first metal selected from said group and hydrogen peroxide, and contacting said solution with a solid substrate having oxygen-containing chemically reactive groups on its surface.

Claims

1. A process for forming a coating comprising metal oxide or mixed metal oxide nanoparticles of one or more metals selected from the group consisting of tin, antimony, germanium and tellurium on a solid substrate, comprising: providing a basic metal-containing solution containing at least one metal selected from said group and hydrogen peroxide, and contacting said basic metal-containing solution with a solid substrate having oxygen-containing chemically reactive groups on its surface, wherein said solid substrate having oxygen-containing chemically reactive groups on its surface is contacted with said basic metal-containing solution and hydrogen peroxide solution under conditions allowing formation of peroxynanoparticle coating on the solid substrate upon addition of an antisolvent capable of inducing a precipitation of the peroxynanoparticle coating, wherein peroxynanoparticles present in the peroxynanoparticle coating have a diameter of less than 10 nm, with no agglomeration occurring in the basic metal-containing solution, as is evident by scanning electron microscopy or transmission electron microscopy; and heat treating the peroxynanoparticle coating to obtain a metal oxide or mixed metal oxide nanoparticle coating layer of less than 20 nm; wherein the heat treating comprises calcining the peroxynanoparticle coating on the solid substrate at a temperature of 300-1000 C.

2. The process according to claim 1, wherein at least one metal is present in the metal-containing solution in its highest oxidation state prior to addition of hydrogen peroxide to a metal-containing solution.

3. The process according to claim 1, wherein the basic metal-containing solution comprises tin in its highest oxidation state (+4).

4. The process according to claim 3, wherein the basic metal-containing solution further comprises antimony.

5. The process according to claim 1, wherein a base present in the basic metal-containing solution is a nitrogen-containing base.

6. The process according to claim 1, wherein the antisolvent is alcohol, acetonitrile, ethylacetate, ethers and mixtures thereof.

7. The process according to claim 1, wherein the oxygen-containing chemically reactive group present on the surface of the solid substrate is selected from the group consisting of OH, OOH, O, M-O wherein M indicates the solid substrate, carbonate and oxygenated SP2 carbon.

8. The process according to claim 1, wherein the step of contacting the basic metal-containing solution with the solid substrate is performed by dip coating, spread coating, spray coating or spin coating.

9. The process according to claim 1, wherein the solid substrate is selected from the group consisting of clays, sol-gel materials, and lithium niobate and calcite.

10. The process according to claim 1, wherein the concentration of hydrogen peroxide in the basic metal-containing solution is between 1% and 50% weight percent.

11. The process according to claim 1, wherein a pH of the basic metal-containing solution is higher than 9.

12. The process according to claim 1, further comprising removing the solid substrate by means of a heat treatment or dissolution step to obtain a structure consisting of sheets made of peroxynanoparticles or metal oxide nanoparticles that are essentially devoid of substrate material.

Description

(1) In the figures:

(2) FIGS. 1a and 1b are SEM and TEM micrographs of ATO coated sepiolite, respectively.

(3) FIGS. 1c and 1d are SEM and TEM micrographs of ATO coated sol gel silica powder, respectively.

(4) FIGS. 1e and 1f are SEM and TEM micrographs of ATO coated calcite, respectively.

(5) FIGS. 2a and 2b are SEM and TEM micrographs of ATO coated kaolin, respectively.

(6) FIG. 2c is a TEM micrograph of ATO coated lithium niobate.

(7) FIG. 2d depicts the electron diffraction pattern of ATO coated single crystal lithium niobate.

(8) FIG. 3a is an SEM micrograph of uncoated muscovite.

(9) FIG. 3b is an SEM micrograph of muscovite coated by using a hydroperoxostannate and hydroperoxoantimonate precursor.

(10) FIG. 3c is a TEM micrograph of ATO coated muscovite.

(11) FIG. 3d is an SEM micrograph of ATO coated muscovite, prepared under identical condition as of FIG. 3b but without hydrogen peroxide.

(12) FIGS. 4(1) and 4(2) illustrate XRD studies of calcined (at 800 C.) and room temperature prepared ATO-coated muscovite, respectively.

(13) FIG. 5(a) illustrates XPS studies of 800 C. treated ATO coated muscovite. The two peaks at 539.06 and 540.46 eV correspond to antimony (III) and antimony (V) oxides.

(14) FIG. 5(b) presents a .sup.119Sn NMR spectra of (a) hydroxostannate, (b) peroxystannate, and (c) peroxystannate and antimonate solutions in 15% H.sub.2O.sub.2.

(15) FIG. 6a is a STEM (scanning transmission electron microscopy) micrograph of graphene oxide.

(16) FIG. 6b is a TEM micrograph of graphene oxide coated by peroxytin nanoparticles (before heat treatment).

(17) FIG. 6c is an SEM of tin oxide nanoparticle sheets prepared by subjecting the material of FIG. 6b to heat treatment at 800 C. in air.

(18) FIG. 6d is a TEM of tin oxide nanoparticle sheets prepared by subjecting the material of FIG. 6b to heat treatment at 800 C. in air.

(19) FIG. 7a is a TEM micrograph of graphene coated by peroxytin nanoparticles prepared by subjecting the materials of FIG. 6b to heat treatment at 800 C. in argon atmosphere.

(20) FIG. 7b is an SEM micrograph of tin oxide nanoparticle sheets prepared by subjecting the material of FIG. 6b to heat treatment at 800 C. in argon atmosphere.

(21) FIG. 8a is an SEM micrograph of antimony oxide coated mica.

(22) FIG. 8b illustrates XRD study of 800 C. calcined antimony oxide coated muscovite (asterisks denote Sb.sub.2O.sub.4 diffraction peaks).

(23) FIG. 9 is Muscovite coated by germanium oxide (after heat treatment at 500 C.)

(24) FIG. 10 is an SEM micrograph of tellurium oxide coated muscovite (after heat treatment at 400 C.).

EXAMPLES

(25) Materials

(26) Tin (IV) chloride, antimony (V) chloride, Germanium chloride, telluric acid, tetramethyl ammonium hydroxide (25% aq. solution), hydrogen peroxide (30%) and calcite were purchased from Sigma-Aldrich (Rehovot, Israel).

(27) Ammonium hydroxide and ethanol (abs.) were purchased from Biolab (Jerusalem, Israel).

(28) LiNbO.sub.3 was donated by Professor M. Rott from the Hebrew University.

(29) Sepiolite was purchased from Sigma-Aldrich and kaolin was donated by Mobichem Ltd, Israel.

(30) Sol-gel silica nanoparticles were prepared by a procedure described in reference Abarkan I.; Doussineau, T.; Smaihi, Polyhedron, 2006, 25, 1763-1770.

(31) Muscovite mica (Mica-M) was purchased from Merck (Darmstadt, Germany) and was cleaned before use by reflux in 2.6M nitric acid and annealing at 600 C. for 2 hours. Other clay minerals were treated by the same procedure.

(32) Graphene oxide was prepared in Preparation 5, hereinbelow.

(33) Measurements

(34) HR TEM imaging was performed at 200 kV using the FEI Technai F20 G2 (Eindhoven, Holland) High Resolution Transmission Electron Microscope (HR TEM). A drop of the suspension of the sample in ethanol was deposited onto 400 mesh copper grids covered with thin amorphous carbon films.

(35) SEM imaging was performed using the FEI Sirion High Resolution Scanning Electron Microscope (HR SEM, Eindhoven, Holland). Accelerating voltage was set at 5-15 kV, working distance 5 mm, using Ultra-High resolution mode with Through-the-Lens Detector. The dried samples were either placed directly onto carbon conductive film, or immersed in ethanol, placed in an ultrasonic bath for 10 min, and the suspension was then dropped on a glass surface and dried out. Samples were coated by Au/Pd for conductivity.

(36) The scanning transmission electron microscopy imaging was performed on Extra-High Resolution XHR SEM Magellan 400L, FEI company. The images were acquired on grids, (used for transmission electron microscopy) by using scanning-transmission (STEM) detector to obtain the TEM image. The acceleration voltages were 20-25 kV.

(37) .sup.119Sn NMR spectra were collected on a Bruker Avance-500 (11.7T) spectrometer at resonance frequency 186.4 MHz. The measurements were performed using a single pulse sequence with rf pulse duration of 10 s and recycling time 30 s.

(38) XPS measurements were performed on a Kratos Axis Ultra X-ray photoelectron spectrometer (Manchester, UK). High resolution spectra were acquired with monochromated Mg K (1253.6 eV) X-ray source with 0 takeoff angle. The pressure in the test chamber was maintained at 1.7 10.sup.9 Torr during the acquisition process. Data analysis was performed with Vision processing data reduction software (Kratos Analytical Ltd.) and CasaXPS (Casa Software Ltd.).

(39) X-ray powder diffraction measurements were performed on a D8 Advance diffractometer (Bruker AXS, Karlsruhe, Germany) with a goniometer radius 217.5 mm, Gbel Mirror parallel-beam optics, 2 Sollers slits and 0.2 mm receiving slit. The powder samples were carefully filled into low background quartz sample holders. The specimen weight amounted to approximately 0.5 g. XRD patterns from 5 to 60 2 were recorded at room temperature using CuK radiation (k=1.5418 ) under the following measurement conditions: Tube voltage of 40 kV, tube current of 40 mA, step scan mode with a step size 0.02 2 and counting time of 1 s/step. XRD patterns were processed using Diffrac Plus software.

(40) Resistivity of ATO coated mica samples. Triply coated mica powder was placed in a home-made hand press device, pressed by 2 10.sup.6 Pa and then the conductivity was measured.

Preparation 1

Preparation of Hydroxostannate Solution

(41) 10 mL of SnCl.sub.4 (0.086 mol) was dissolved in 5 mL of water and neutralized with ammonia until pH 7. The precipitate was washed several times with water and dissolved by mixing with 31 mL of 25% tetramethylammonium hydroxide (0.086 mol) under moderate heating (i.e., 30 C.) for about 30 minutes. After full dissolution, water was added to give a tin concentration of 1.4 M.

Preparation 2

Preparation of Hydroxoantimonate Solution

(42) 10 mL of SbCl.sub.3 (0.078 mol) was dissolved in 5 mL of water and neutralized with ammonia until pH 7. The precipitate was washed several times with water and dissolved by mixing with 28.5 mL of 25% tetramethylammonium hydroxide (0.078 mol) under moderate heating (i.e., 60 C.) for about 4 hours. After full dissolution, water was added to give an antimony concentration of 1.4 M.

Preparation 3

Preparation of Hydroxogermanate Solution

(43) 10 ml of GeCl.sub.4 (0.088 mol) was dissolved in 5 ml of water and neutralized with ammonia until pH 7. The precipitate was washed 5 times with water and dissolved in 31.6 ml of 25% tetramethylammonium hydroxide (0.088 mol) under moderate heating (i.e., 40 C.). After full dissolution, water was added to achieve 1.0M germanium concentration.

Preparation 4

Preparation of Hydroperoxotellurate Solution

(44) 0.6 g of telluric acid (H.sub.6TeO.sub.6, 0.00261 mol) was dissolved in 5 ml of deionized water, then 1 ml of 25% aqueous tetramethylammonium hydroxide solution (0.00279 mol) and 6 ml of 30% hydrogen peroxide solution were added.

Preparation 5

(45) Graphene oxide was prepared by a modified Hummers method (See for ex. Zhang et al, J Phys Chem C, 113, 2009, 10842). 1 g of exfoliated carbon was added to a solution of 6.66 g of potassium peroxodisulfate and 6.66 g of phosphorus pentoxide in 32 ml sulfuric acid (98%). The mixture stirred at 80 C. during 4.5 h. After cooling, it was diluted with deionized water, filtered, washed on the filter with water. The clean material was dried for 2 h at 120 C. Preoxidized material was redispersed in H.sub.2SO.sub.4 (98%), then 5 g of potassium permanganate was added slowly to the mixture upon stirring and ice bath cooling. The temperature was adjusted to 35 C. and the mixture was stirred for 2 h, then 180 ml of deionized water was slowly added, and the dispersion left to stir for an additional 2 h. At last, 300 ml of deionized water and 8 ml of hydrogen peroxide (30%) were sequentially added, and a bright brown-yellow colored solution was produced. The oxidized graphene was filtered, washed with distilled water and with alcohol, dried in vacuum at 80 C. for 4 h.

Example 1

Preparation of ATO Coated Solid Substrates

(46) A precursor solution was first prepared as follows. 1.9 mL of the hydroxostannate solution of Preparation 1 and 5 mL of the hydroxoantimonate solution of Preparation 2 were mixed together with 15 mL 30% hydrogen peroxide solution and 8 mL water. An excess of hydroxoantimonate is used due to its partial solubility in ethanol.

(47) For the coating of the solid substrates, 600 mg of substrate was dispersed in 15 mL of the precursor solution by sonication. Following 10 minutes of stirring, precipitation of particles onto the substrate surface was accomplished by the addition of 120 mL of ethanol. The coated substrate was washed with ethanol, dried and calcined at 800 C. for 3 hours.

(48) Six different solid substrates were coated by the procedure described above: sepiolite (magnesium silicate 1-D clay), muscovite (potassium mica), kaolin (2-D aluminosilicate), sol-gel silica powder, lithium niobate (LiNbO.sub.3) and calcite.

(49) The SEM and TEM micrographs of coated and heat treated sepiolite, sol gel silica powder and calcite are depicted in FIGS. 1a and 1b, 1c and 1d, and 1e and 1f, respectively. The SEM and TEM micrographs of kaolin are presented in FIGS. 2a and 2b, respectively. The TEM micrograph of lithium niobate is presented in FIG. 2c, while FIG. 2d depicts the electron diffraction pattern of ATO coated single crystal lithium niobate. SEM micrographs of uncoated muscovite and ATO coated muscovite are depicted in FIGS. 3a and 3b, respectively. TEM micrograph of coated muscovite is presented in FIG. 3c.

(50) The SEM micrographs of the coated and heat treated substrates (FIGS. 1a, 1c, 1e, 2a and 3b) show that the ATO is exclusively attached to the substrate and is not agglomerated elsewhere.

(51) The TEM micrographs of the coated substrates (FIGS. 1b, 1d, 1f, 2b, 2c, and 3c), taken at the edge of the particles, show approximately 5 nm crystalline ATO particles almost uniform in size, for all exemplified coated substrates.

(52) The active oxygen content of tin oxide coated muscovite before heat treatment to obtain the micrograph exhibited in FIG. 3b was determined by permanaganatometry to be 1.5%.

(53) The single crystal diffraction dots of the lithium niobate and the multicrystalline diffraction rings of the ATO nanocrystals are apparent in FIG. 2d, illustrating the electron diffraction pattern of ATO coated single crystal lithium niobate. These crystalline rings are apparent in all other heat treated coated samples, though they are not shown here.

(54) It may be appreciated that in the case of the two acid-sensitive substrates, namely, lithium niobate and calcite, the coating took place exclusively on the minerals and the size of the crystallite was again around 5 nm, despite the lack of external silica tetrahedera or surface silanols in these minerals.

(55) XRD studies of calcined (at 800 C.) and room temperature prepared ATO-coated muscovite are depicted in FIGS. 4(1) and 4(2), respectively. The room temperature coated mica shows some broad shallow peaks at 2=50-55 and at 25-35 degrees corresponding to amorphous tin oxide. Heat treatment resulted in formation of a tin-oxide phase as observed by the crystalline x-ray diffraction. The crystalline size by Scherrer equation is 9 nm, which is somewhat larger compared to the uniform 5 nm size obtained in the TEM studies.

(56) XPS studies of the 800 C. treated ATO coated muscovite are illustrated in FIG. 5(a). The XPS studies reveal the Sn 3d 3/2 binding energy levels of Sn(IV) at 495.73 and Sn 3d 5/2 at 487.32 eV. The antimony 3d 3/2 peak can be deconvoluted to two peaks at 539.06 and 540.46 corresponding to Sb(III) and Sb(V) oxides, respectively. Deconvolution of the 3d 5/2 peak reveals two peaks at 529.72 and 531.12 matching the 3d 3/2 signals, in addition to an overlapping broad oxygen 1S signal. The ratio between the Sb 3d 3/2 and the 3d 5/2 signals was as expected 2:3. The molar Sn:Sb ratio by the XPS studies was 12:88. The ratio between the Sb(V) and Sb(III) by the XPS studies was 11:1.

(57) The conductivity of the coated muscovite was measured to be 15 cm.

Example 2Comparative

Preparation of a Coated Solid Substrate from a Hydroxostannate and Hydroxoantimonate Solution (No Peroxide Added)

(58) For the purpose of comparison, a muscovite substrate was ATO-coated by using a hydroxostannate and hydroxoantimonate precursor.

(59) A precursor solution was first prepared by mixing 1.9 mL of the hydroxostannate solution of Preparation 1 and 5 mL of the hydroxoantimonate solution of Preparation 2.

(60) 600 mg of muscovite was dispersed in 15 mL of the precursor solution by sonication. Following 10 minutes of stirring, 120 mL of ethanol were added, however, no precipitation was observed.

(61) A mild and gradual acidification of the solution by the addition of 0.1M HCl down to pH 7 yielded only agglomerated material that did not coat the mica surface (FIG. 3d).

Example 3

Preparation of Antimony Oxide Coated Solid Substrates

(62) 0.2 g of Muscovite clay was dispersed by sonication in the precursor solution, containing 2 ml of tetramethylammonium hydroxoantimonate (see preparation 2) and 5 ml of hydrogen peroxide (60%). After additional 10 min of stirring, precipitation of particles on the clay surface was accomplished by the addition of 35 ml of ethanol. Coated clay was washed with ethanol, dried, and calcined at 500 C. for 6 h. The mineral was identified as Sb.sub.2O.sub.4 cervantite by powder x-ray diffraction. Crystallite size was estimated to be 5 nm by the x-ray diffraction (FIG. 8a provides the SEM micrograph and FIG. 8b illustrates the XRD diffractogram).

Example 4

Preparation of Germanium Oxide Coated Solid Substrates

(63) 0.2 g of muscovite clay was dispersed by sonication in the precursor solution, containing 3 ml of tetramethylammonium hydroxogermanate (see preparation 3) and 30 ml of hydrogen peroxide (30%). After additional 10 min of stirring, precipitation of particles onto the clay surface was accomplished by addition of 160 ml of mixture ethanol:diethyl ether (4:1). Coated clay was washed with ethanol, dried, and calcined at 500 C. for 6 h. A uniform coating of the mica was obtained as depicted in the micrograph of FIG. 9. The presence of germanium on the surface of the particles was confirmed by EDAX measurements showing 1.0 atom percent of Ge.

Example 5

Preparation of Tellurium Oxide Coated Solid Substrates

(64) 0.6 g of muscovite clay was dispersed in the precursor solution (Preparation 4) by sonication, and after an additional 10 min of stirring precipitation of peroxytellurate particles on clay surface was accomplished by addition 80 ml of mixture ethanol-diethyl ether (1:1). Resulting product was separated by centrifuge, washed 5 times by ethanol, dried in vacuum and calcined at 500 C. for 1 h. A non uniform coating of the mica was obtained as depicted in the micrograph of FIG. 10. The presence of tellurium on the surface of the particles was confirmed by EDAX measurements.

Example 6

Preparation of Tin Peroxide and Tin Oxide Coated Graphene Oxide

(65) 50 mg of graphene oxide was redispersed by sonication in the precursor, consisting of 1 ml of 1.4 tetramethylammonium hydroxostannate solution (preparation 1) and 30 ml hydrogen peroxide (30%). 300 ml of mixture ethanol-diethyl ether (1:1) was added to the dispersion under vigorous stirring to achieve a coating of tin peroxyparticles on graphene surfaces. Then, coated material was filtered by means of centrifuge, washed with mixture of ethanol-diethyl ether (1:1) and dried in vacuum. Typical uniformly coated graphene oxide is shown in the STEM micrograph of FIG. 6b. Mean particle size was 5 nm.

(66) Graphene oxide coated by tin peroxystannate was heated in an Ar atmosphere at 800 C. for 4.5 h to produce graphene coated by tin oxide. TEM and SEM micrographs (FIGS. 7a and 7b) show approximately 10 nm particles coating the thermally distorted graphene sheets.

(67) Graphene oxide coated by tin peroxystannate was heated in air at 800 C. for 4.5 h to produce tin oxide sheets. FIG. 6c and FIG. 6d show the resulting sheets. It can be observed that the sheet is comprised of two layers of nanoparticles (that were formed by stacking of the two layers that covered the two sides of the graphene oxide). The average thickness of the sheets was approximately 35 nm.