Patent Description:
Gold (III) oxide of the molecular formula Au<NUM>O<NUM> is an inorganic compound having redbrown color, insoluble in water. It has a rhombic crystallographic structure, the density of <NUM>/cm<NUM> at <NUM> and the melting point of <NUM>. Such a structure and the presence of oxygen in the crystallographic lattice affect the unique catalytic properties of Au<NUM>O<NUM>. In addition, the energy gap value of <NUM> eV causes that this material has the semiconductor properties, which is known, for example, from the publication by <NPL>.

As described in the publication by<NPL>, from the thermodynamic point of view, the spontaneous oxidation process of gold and the synthesis of gold (III) oxide as the product under the normal conditions (T = <NUM>, p = <NUM> atm) is practically impossible. In addition, gold (III) oxide is known to be an unstable compound - this compound is only stable at the temperature of <NUM>. In order to produce gold (III) oxide on a macrometric scale, the process must be carried out in strictly thermodynamically controlled conditions, relaying on the oxidation of gold at high temperature in an oxygen atmosphere and with the use of appropriate techniques.

Currently, gold (III) oxide is produced, for example, in the process of metal (Au) surface treatment with an oxygen-containing plasma, as described in the publication by <NPL>. The authors of the above-mentioned publication produced gold (III) oxide by subjecting a thin gold foil to an oxygen plasma. For this purpose, they used Plasma Electronics P300 and a gas in the pressure range from <NUM> to <NUM> mbar.

In turn, <NPL>, described a method for obtaining gold oxide in the form of Au<NUM>O<NUM> by sputtering reactive oxygen in a UHV (Ultra High Vacuum) compatible chamber. The authors of the work showed that the obtained oxide decomposes under the influence of thermal treatment.

In another work by <NPL>), Au<NUM>O<NUM> was obtained by exposing the gold surface to highly reactive ozone. In this procedure, Au films were oxidized under UHV conditions by exposing them to UV radiation and ozone. The Au films were characterized by X-ray photoelectron spectroscopy. It was observed that as the result of the carried out oxidation process, the gold surface becomes heterogeneous, and as the result of chemisorption, some of the oxygen exists in the free form. The rest of the adsorbed oxygen formed the layer of gold oxide with the stoichiometry similar to Au<NUM>O<NUM>, having few millimeters on average. Both the oxide and the chemisorbed oxygen were slowly removed when heated to <NUM>.

In turn, in the work by <NPL> , thin layers of gold (III) oxide were obtained by the pulsed laser deposition method in an O<NUM> atmosphere. The background gas pressure was varied in the range from <NUM> to <NUM> Pa, and the distance from a target to a substrate was kept at the constant level of <NUM>. It was noticed that the resulting gold oxide Au<NUM>O<NUM> was unstable and decomposed slowly at room temperature under the influence of surrounding atmosphere.

From the publication by <NPL>, is also known a method for producing nanoparticles containing gold (III) oxide by reactive magnetron sputtering in the presence of reactive gas.

From the patent application <CIT> is known a method for producing metal oxide nanoparticles, which comprises the following steps: mixing a doubly hydrophilic block copolymer with a metal precursor in a solvent, then adding a base to obtain a suspension, adding a reducing agent dropwise to the suspension and mixing to form hydrated metal oxide nanoparticles, and in the final step, heating the metal oxide nanoparticles at a temperature of <NUM>-<NUM>. The copolymer comprises a polymer selected from the group: poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA), poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA), poly(ethylene glycol)-b-poly(ethyleneimine) (PEG-b-PEI), poly(ethylene glycol)-b-poly(aspartic acid) (PEG-b-PAsp), poly(dimethylaminoethyl methacrylate)-b-poly(dihydropropyl methacrylate) (PDMAEMA-b-PHMA), poly(acrylic acid)-b-polyacrylamide (PAA-b-PAM), poly(acrylic acid)-b-poly(hydroxyethyl acrylate) (PAA-b-PHEA) or a mixture thereof. Preferably, the metal precursor is selected from, among others, hydrated ruthenium chloride (RuCl<NUM>·H<NUM>O), nickel chloride hexahydrate (NiCl<NUM>·<NUM><NUM>O), ferric chloride hexahydrate (FeCl<NUM>·<NUM><NUM>O), tin chloride (SnCl<NUM>), palladium chloride (PdCl<NUM>), platinum chloride (PtCl<NUM>), gold chloride (AuCl<NUM>), gold chloride hydrate (HAuCl<NUM>·<NUM>(H<NUM>O)) or a mixture thereof. The base is selected from the group consisting of sodium hydroxide (NaOH), potassium hydroxide (KOH), magnesium hydroxide (Mg(OH)<NUM>), calcium hydroxide (Ca(OH)<NUM>) or a mixture thereof. Hydrazine, ascorbic acid, sodium ascorbate, sodium borohydride or a mixture thereof are used as the reducing agent.

As is apparent from the prior art, the known methods for producing gold (III) oxide typically require expensive and complex devices, multiple reagents, and strictly controlled conditions necessary to be maintained during the process.

The aim of the present invention is to develop a method for producing nanometric gold (III) oxide, which, in contrast to the known solutions, does not require the use of complex and expensive devices, is simple and cheap, and is also efficient.

The gist of the method for producing nanometric gold (III) oxide particles in the form of colloidal solution, relaying on mixing a precursor solution containing Au (III) ions in the form of HAuCl<NUM> solution with a reducing agent in the form of ascorbic acid, and optionally adding particle stabilizers and auxiliary substances, is characterized in that <NUM>-<NUM> of an aqueous solution of L-ascorbic acid or D-ascorbic acid or L,D-ascorbic acid having a concentration of <NUM>· <NUM>-<NUM> - <NUM>·<NUM>-<NUM> mol/dm<NUM> is added to <NUM>-<NUM> of HAuCl<NUM> solution having a concentration of <NUM>·<NUM>-<NUM> - <NUM><NUM>-<NUM> mol/dm<NUM> and a temperature in the range of <NUM>-<NUM>, and is stirred at <NUM>-<NUM> rpm for <NUM>-<NUM> minutes, and a temperature is maintained at <NUM>-<NUM>. Then the resulting colloidal solution is cooled down to room temperature.

Preferably, a steric particle stabilizer in the form of polyvinyl alcohol or polyvinyl pyrrolidone is added in an amount of up to <NUM> per <NUM> to the cooled colloidal solution, and then is stirred until the stabilizer is completely dissolved.

Preferably, a chlorate salt in the form of NaClO<NUM> or KClO<NUM> is added in an amount of up to <NUM> per <NUM> of solution to the colloidal solution containing the steric particle stabilizer, which is intended to remove the residues of reducing agent from the surface of nanoparticles.

Preferably, the resulting colloidal solution, after its cooling, is left for at least <NUM> hours in a darkroom in order to protect it from sunlight. Thanks to this, the solution retains its properties longer.

Ascorbic acid is used as a reducing agent of Au (III) ions, but also as a stabilizer of clusters of transiently formed gold Au (<NUM>), and then as a stabilizer of the resulting nanometric gold oxide Au<NUM>O<NUM>, and also as a source of ionized oxygen obtained as the result of oxidation of the dissociated form of ascorbic acid with oxygen dissolved in water. The mechanism of obtaining Au<NUM>O<NUM>, according to the invention, consists of several steps described in detail below. As the result of mixing Au (III) ions in the form of a complex, e.g. [AuCl<NUM>]- with ascorbic acid in an acidic-neutral environment, the following reactions take place:.

In parallel to the steps I and II, the reactions related to the dissociation of ascorbic acid and its oxidation with oxygen dissolved in a solvent and additionally catalyzed by metal ions from the group of transition metals (including gold ions) take place:
<CHM>.

Then, the dissociated form of ascorbic acid undergoes oxidation with oxygen dissolved in water, and the reaction products are free radicals, what is known and described in the literature: <NPL>, and <NPL>.

The ionic oxygen radical (O<NUM>. -) is unstable and in an acidic environment it forms the radical HO<NUM>, according to the following reaction known from Bielski's publication "<NPL>.

The obtained gold in zero oxidation state (in step II) forms clusters which, due to their small size (below <NUM>, i.e. the critical size characteristic of nanoparticles), are metastable and undergo oxidation under the conditions of the carried out synthesis as the result of the reactions with the coexisting radicals <NUM>O<NUM>. -, <MAT> according to the reactions below:.

2Au + 2HO<NUM>. → Au<NUM>O<NUM> + H<NUM>O.

<NUM>Au + <NUM>O<NUM>. - + <NUM>H+ → Au<NUM>O<NUM> + H<NUM>O.

The method according to the invention allows to achieve nanometric gold (III) oxide particles with high yield, about <NUM>%. The advantage of the proposed solution is the lack of necessity to use complex and expensive devices, which makes the method simple, cheap, and the synthesis time short. It is possible to carry out the synthesis at room temperature. The produced gold oxide nanoparticles are stable under the normal conditions (T = <NUM>°) for about <NUM> week, and this time can be further extended by storing the material in a package that protects against light, such as dark glass, and optionally by lowering the temperature, e.g. by storing in a refrigerator.

The method for producing nanometric gold (III) oxide particles according to the invention is explained below in the practical embodiments and in the drawing, in which <FIG> shows a high-resolution image of a single Au<NUM>O<NUM> crystal, obtained by the HRSTEM technique (High Resolution Scanning Transmission Electron Microscopy) along with its FFT analysis (Fast Fourier Transform), and <FIG> shows spectrum characteristic of spherical gold oxide particles, obtained in the spectrophotometric studies.

<NUM> of the aqueous solution of L-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM> ·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature. After <NUM> hours, the steric particle stabilizer in the form of polyvinyl alcohol powder was added in the amount of <NUM> per <NUM> of the solution to the solution. The solution was stirred on a magnetic stirrer until the stabilizer was completely dissolved. Then, <NUM> of NaClO<NUM> was added and the whole was stirred again for about <NUM> minutes, then was left for <NUM> hours in a darkroom to protect it from sunlight. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense pink color was obtained.

Then, the sizes of Au<NUM>O<NUM> particles suspended in the solution were determined using the High Resolution Scanning Transmission Electron Microscopy HRSTEM and their average diameter was determined to be <NUM>-<NUM>. In addition, the FFT analysis (Fast Fourier Transform) of the image of the microstructure of areas <NUM> and <NUM> marked in <FIG> was performed, enabling the measurement of the distance {<NUM> for (<NUM>-<NUM>-<NUM>) and <NUM> for (<NUM>-<NUM><NUM>), <NUM> for (-<NUM> -<NUM><NUM>) and <NUM> for (-<NUM><NUM><NUM>)} and the angles between the crystallographic planes (~<NUM> and ~<NUM> degrees, respectively) of the resulting product, confirming its rhombic crystallographic structure, characteristic of gold (III) oxide. In addition, in the spectrophotometric studies (UV-Vis spectrophotometer, Shimadzu), the absorption spectrum was recorded (<FIG>) with the maximum of peak located at <NUM>, typical of metallic particles.

The resulting colloidal solution of Au<NUM>O<NUM> can be used immediately after production. At the temperature of <NUM> it is stable for <NUM> days.

<NUM> of the aqueous solution of D-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature, and then was left for <NUM> hours in a darkroom, in order to protect it from sunlight. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense red color and the average particle diameter of <NUM>-<NUM>, confirmed by the studies using the High Resolution Scanning Transmission Electron Microscopy HRSTEM along with its FFT analysis, was obtained. In addition, in the spectrophotometric studies, the absorption spectrum was recorded with the maximum of peak located at <NUM>, typical of metallic particles.

<NUM> of the aqueous solution of L-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature. After <NUM> hours, the steric particle stabilizer in the form of polyvinyl alcohol powder was added in the amount of <NUM> per <NUM> of the solution. The solution was stirred on a magnetic stirrer until the stabilizer was completely dissolved and was left for <NUM> hours in a darkroom. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense pink color and the average particle diameter of <NUM>-<NUM>, confirmed by the studies using the High Resolution Scanning Transmission Electron Microscopy HRSTEM along with its FFT analysis, was obtained. In addition, in the spectrophotometric studies, the absorption spectrum was recorded with the maximum of peak located at <NUM>, typical of metallic particles.

<NUM> of the aqueous solution of D-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. Immediately after mixing the reagents, the solution turned pink-red. The solution was stirred for another <NUM> minutes at <NUM> rpm and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature, and then was left for <NUM> hours in a darkroom, in order to protect it from sunlight. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense red color and the average particle diameter of <NUM>-<NUM>, confirmed by the studies using the High Resolution Scanning Transmission Electron Microscopy HRSTEM along with its FFT analysis, was obtained. In addition, in the spectrophotometric studies, the absorption spectrum was recorded with the maximum of peak located at <NUM>, typical of metallic particles.

<NUM> of the aqueous solution of L,D-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature, and then was left for <NUM> hours in a darkroom, in order to protect it from sunlight. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense red color and the average particle diameter of <NUM>-<NUM>, confirmed by the studies using the High Resolution Scanning Transmission Electron Microscopy HRSTEM along with its FFT analysis, was obtained. In addition, in the spectrophotometric studies, the absorption spectrum was recorded with the maximum of peak located at <NUM>, typical of metallic particles.

<NUM> of the aqueous solution of L-ascorbic acid having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM> was added to <NUM> of HAuCl<NUM> solution having the concentration of <NUM>·<NUM>-<NUM> mol/dm<NUM> and the temperature of <NUM>. The whole was stirred on a magnetic stirrer at <NUM> rpm for <NUM> minutes and the temperature was maintained at <NUM>. The obtained colloidal solution was left to slowly cool down to room temperature. After <NUM> hours, the steric particle stabilizer in the form of polyvinylpyrrolidone powder was added in the amount of <NUM> per <NUM> of the solution. The solution was stirred on a magnetic stirrer until the stabilizer was completely dissolved. Then <NUM> of KClO<NUM> was added and the whole was stirred again for about <NUM> minutes, then was left for <NUM> hours in a darkroom. As the result of the carried out synthesis, the stable colloidal solution of gold (III) oxide having intense pink color and the average particle diameter of <NUM>-<NUM>, confirmed by the studies using the High Resolution Scanning Transmission Electron Microscopy HRSTEM along with its FFT analysis, was obtained. In addition, in the spectrophotometric studies, the absorption spectrum was recorded with the maximum of peak located at <NUM>, typical of metallic particles.

Claim 1:
A method for producing nanometric gold (III) oxide particles in the form of colloidal solution, relaying on mixing a precursor solution containing Au (III) ions in the form of HAuCl<NUM> solution with a reducing agent in the form of ascorbic acid and optionally adding particle stabilizers and auxiliary substances, characterized in that <NUM>-<NUM> of an aqueous solution of L-ascorbic acid or D-ascorbic acid or L,D-ascorbic acid having a concentration of - <NUM>·<NUM>-<NUM> mol/dm<NUM> is added to <NUM>-<NUM> of HAuCl<NUM> solution having a concentration of <NUM>·<NUM>-<NUM> - <NUM>·<NUM>-<NUM> mol/dm<NUM> and a temperature in the range of <NUM>-<NUM>, and is stirred at <NUM>-<NUM> rpm for <NUM>-<NUM> minutes, and a temperature is maintained at <NUM>-<NUM>, after which the resulting colloidal solution is cooled down to room temperature.