Synthesis of gallium oxide nanoparticles in supercritical water

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry. Gallium oxide Ga2O3 nanoparticles are obtained by mixing 0.1 M aqueous solution of Ga(NO3)3·8H2O with supercritical water. The reaction is carried out at temperature of 365-384°C and at pressure of 220-240 atm. The ratio of the volume of the gallium salt solution to the volume of supercritical water is preferably equal to 2:10.

EFFECT: synthesis of metal oxide nanoparticles and ecologically clean, wasteless technology.

2 cl, 1 ex, 2 dwg

 

The invention relates to the field of nano - and microparticles of metal oxides in supercritical water and can be used in obtaining materials and compounds of high purity and with unique properties.

For the synthesis of nanostructured materials, which are nanoparticles, nanofilms and nanowires proposed many methods that can be divided into two principal groups. First, obtain nanostructures of materials normal size, i.e. bulk materials. Second, obtaining nanostructures from molecular level.

Clean the oxides of various metals are widely used in practice. Many oxides, primarily Al2O3, W2O5, Cr2O3, Fe2O3and others, are used as catalysts for other hardening metals and to obtain ferrites.

The main methods of synthesis or a pure metal oxides are thermal decomposition of salts of (dry method) at high temperatures, and precipitation of hydroxides from solutions (wet method) with their subsequent calcination.

The main disadvantages of the known methods for the synthesis of metal oxides as follows:

1. Nitrates of alkali metals, used as starting substances during combustion pass into nitrites and oxides do not form.

2. Use what Libanius some salts are very difficult to obtain, for example, the oxides of strontium or barium, as their carbonates begin to decompose only at 1200-1300°C.

3. By annealing the salts are difficult to obtain pure metal oxides.

4. Salts formed of non-volatile acids (phosphates, borates, wolframite and others), when heated, do not decompose, with the exception of ammonium salts and mercury, and therefore cannot serve as source materials for the production of oxides of the respective metals.

5. By calcination of ammonium salts released ammonia-reducing agent, which can lead to contamination of the obtained product of the lower oxides of elements.

6. Since most of hydroxides (for the method of obtaining the metal oxides of hydroxides), deposited from solution, it is difficult to obtain in pure, free from impurities condition, it is difficult to get individual oxides in pure form as well.

7. Dehydration of hydroxides when annealing is not always going to end, and often the resulting oxides contain a small amount of hydroxide.

8. The purity and properties of metal oxides obtained by these methods are highly dependent on the mode and temperature of annealing.

Supercritical fluids are an attractive environment for the synthesis, modification and formation of nanoparticles of inorganic materials, in particular metal oxides (TiO2, Cr2O3, LiFePO4) Reverchon E., Adami R. Nanomaterials and supercritical fluids // J. of Supercritical Fluids. 2006. V.37. P.1; Jung J., Perrut M. Particle design using supercritical fluids: Literature and patent survey // J. of Supercritical Fluids. 2001. V.20. P.179; Zhang Y., Erkey C. Preparation of supported metallic nanoparticles using supercritical fluids: A review // J. of Supercritical Fluids. 2006. V.38. P.252; Aymonier C., Loppiner-Serani, A., H. Reveron, Y. Garrabos, F. Cansell Review of supercritical fluids in inorganic materials science // J. of Supercritical Fluids. 2006. V.38. P.242]. Such nanostructures and materials exhibit unusual properties that are different from those for bulk materials.

A known method for the synthesis of particles of metal oxides [T.Adschiri, Y.Hakuta, K.Arai, Hydrothermal synthesis of metal oxide fine particles at supercritical conditions, Ind. Eng. Chem. Res. 39 (2000) 4901; T.Adschiri, Y.Hakuta, K.Sue, K.Arai, Hydrothermal synthesis of metal oxide nanoparticles at supercritical conditions, J. Nanopart. Res. 3 (2001) 227; A.Cabanas, J.Darr, E.Lester, M.Poliakoff, Continuous hydrothermal synthesis of inorganic materials in a near-critical water flow reactor; the one-step synthesis of nano-particulate Ce1-xZrxO2(x=0-1) solid solutions, J. Mater. Chem. 11 (2001) 561], in which the hydrothermal synthesis of nano - and microparticles of metal oxides in supercritical water - ck-N2O.

A few basic single and multistage chemical reactions of precursor metal salts may be implemented in the synthesis of particles in SK-N2A: hydrolysis and dehydration, thermolysis, restore (as a rule, in the presence of hydrogen and oxidation. In the area of critical parameters of water increases its dissociation and, therefore, the concentration of H+and HE-/sup> . As a result, hydrothermal synthesis in SK-N2Of nanoparticles of oxides of metals from their salts are carried out in the two-stage reactions of hydrolysis and dehydration:

Hydrolysis: MeBn+nOH-→Me(OH)n+nB-

Dehydration: Me(OH)n→MeOn/2+n/2H2O

Hydrothermal method is simple in implementation and scaling is carried out in reactors, autoclaves or tubular flow reactors, allows you to control the properties and particle size.

There is a method of hydrothermal synthesis of particles of metal oxides, we adopted for the prototype [S.Kawasaki, Y.Xiuyi, K.Sue, Y.Hakuta, A.Suzuki, K.Arai. Continuous supercritical hydrothermal synthesis of controlled size and highly crystalline anatase TiO2nanoparticles. J. Supercritical Fluids 50(2009) 276-282], which carry out continuous synthesis of nanoparticles of titanium dioxide - TiO2in supercritical water in the presence of KOH.

To the main disadvantage of the prototype should include the application of the law for changing the solubility of the precursor materials. As a result of application of KOH in the reaction formed potassium sulfate K2SO4the removal of the reaction products require additional rinsing.

The invention solves the problem of efficient synthesis of compounds of metal oxides.

Method for obtaining nanoparticles of oxide, gallium Ga2O3who are shmesani the m 0.1M aqueous salt solution Ga(NO 3)3·8H2O with supercritical water in a volume ratio of 2:10 at the reaction temperature 365-384°C and the pressure 220-240 ATM.

The amount of gallium salt solution to the volume of supercritical water is, preferably, 2:10.

The technical result - the synthesis of compounds metal oxide-based nanoparticles, creating an environmentally friendly waste-free technology.

The original mother liquor for the synthesis of Ga2O3prepare by dissolving in water equimolar amount of salt Ga(NO3)3·8H2O. Hydrothermal synthesis of oxide is carried out in continuous mode in a flow type reactor, Figure 1.

The mother liquor from the tank 2 syringe pump 4 serves in a tubular reactor 5 by volume 7.2 cm3placed in the furnace with a fluidized bed of sand 7, the flow 1 through the mixer 6, which is mixed with the SK-N2Oh, the thread 2 is supplied Porshnev pump 3 from the container 1 in a continuous mode. Transformation is carried out at temperatures and pressures close to the critical parameters of the mixture containing more than 95% water, temperature 365-384°C, pressure 220-240 ATM. The products of the interaction of salts with SK-N2About out of the reactor to the heat exchanger 8 through the valve back pressure 9 the holding tank 10.

The products of hydrothermal synthesis, depending on the size and properties of the formed crystals, the ACCS are neoshadows mixture of particles in the water. The selection of the formed particles of oxides of metals from the solution for analysis of solid phase is carried out by centrifugation of the solution or by evaporation, followed by drying of the solid phase.

The structure, phase and elemental composition of the samples obtained compounds analyzed by the methods of scanning electron microscopy (HRTEM), x-ray phase analysis (XRD). In some cases, the formed water products analyzed using the method of UV spectroscopy.

Hydrothermal synthesis of Ga2O3carried out in continuous mode in the reactor flow type with the aforementioned method.

The invention is illustrated by the following example and illustrations.

Example 1. Synthesis of gallium oxide Ga2O3

For the synthesis of Ga2O3prepare 0.1M salt solution Ga(NO3)3·8H2About in the water. The reaction temperature 365-384°C, a pressure of 235 MPa. Volumetric flow rate of water - flow 2 is 10 ml/min, the flow rate of the reagent stream is 1-2 ml/min In the hydrothermal reaction products are formed in the form of a homogeneous solution of dark color, after evaporation which produces a solid phase. According to the results of HRTEM analyses of the synthesized compound is a crystal with a high dispersion: 2-5 nm. Figa, b. In separate blocks present pseudomorphic crystals (dimensions pseudomorphic is kristallov - to 100 nm).

The results of XRD analysis show that the main phase of the synthesized compounds is a compound Ga2O3together with a small amount of an unidentified crystalline phase.

The example and illustrations demonstrate that the proposed method and conditions of hydrothermal synthesis allow to synthesize gallium oxide nanoparticles of the desired size and properties.

As can be seen from the text and examples, the invention solves the problem of synthesis of metal oxide-based nanoparticles, creating an environmentally friendly waste-free technology.

1. Method for producing nanoparticles of oxide, gallium Ga2O3, characterized in that the obtaining nanoparticles of gallium oxide is performed by mixing 0.1 m aqueous solution of salt of gallium Ga(NO3)3·8H2About with supercritical water at the reaction temperature 365-384°C and the pressure 220-240 ATM.

2. The method according to claim 1, characterized in that the ratio of salt solution of gallium Ga(NO3)3·8H2About to supercritical water is preferably 2:10.



 

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