Method for producing nanosized zinc(II) aluminate powders

Abstract

FIELD: nanomaterials.SUBSTANCE: invention relates to a method for producing nanosized zinc(II) aluminate powder, which can be used as a matrix for luminescent compositions, a photocatalyst, a component of ceramic composites, a protective coating against corrosion and UV radiation, as well as in gas sensors and optoelectronic devices. The method involves preparing a reaction aqueous solution from a mixture of zinc(II) and aluminum(III) nitrate salts taken in a molar ratio of 1:2. The mixture is mixed with a strongly basic gel anion exchanger AB-17-8 in hydroxyl form at a temperature of 60 °C for 1 hour. Then the mixture is passed through a sieve with a hole diameter of 0.16 mm to separate the anion exchanger, after which the precipitate is separated from the solution by filtration under vacuum, dried at a temperature of 80 °C for 2 hours and fired at a temperature of 600 °C within 1 hour.EFFECT: simplification by eliminating additional stages of cleaning and washing the sediment and reducing the temperature of high-temperature processing, as well as improving the quality of the target product by obtaining a single-phase nanosized product with a narrow particle size distribution.1 cl, 4 dwg, 2 ex

Description

[0001] The invention relates to a method for producing nanoscale zinc(II) aluminate powder, which can be used as a matrix for luminescent compounds and as a photocatalyst. Furthermore, zinc(II) aluminate is applicable as a component of ceramic composites, protective coatings against corrosion and UV radiation, as well as in gas sensors and optoelectronic devices.

[0002] Zinc aluminate (ZnAl2O4) is a complex oxide with a spinel structure, possessing high thermal and chemical stability, a wide band gap (3.8 eV), and the ability to undergo cationic substitution, which allows for the control of its optical and electrical properties. To improve its functional characteristics, the material can be doped with transition metal ions (Mn 2+ , Cr 3+ ) or rare earth elements (Eu 3+ , Tb 3+), partially replacing zinc or aluminum in the crystal lattice. Zinc aluminate nanoparticles are typically produced using solid-phase synthesis (followed by high-energy milling), hydroxide coprecipitation methods, sol-gel processes, hydrothermal synthesis, and self-propagating high-temperature synthesis (SHS).

[0003] A known method for producing zinc aluminate [US No. 1325016 A1, IPC C01F 7 / 04, published 23.07.1987], according to which zinc-containing waste (for example, dust sublimes with a zinc content of 70-75 wt.%) are leached with sulfuric acid, then the undissolved carbon residue is filtered off. Waste aluminum laminated foil is added to the resulting solution at a weight ratio of aluminum to zinc of 1: (1.2-5.0). The mixture is stirred at a temperature of 60-90 °C, which leads to the dissolution of aluminum and the precipitation of copper. A mixture of zinc and aluminum hydroxides is coprecipitated from the resulting solution using a 20% ammonia solution (or by adding sulfuric acid to a solution of sodium zincate and aluminate obtained using NaOH). The precipitate is washed, dried, and calcined at 1200-1300°C. The resulting product meets technical requirements for acid-soluble content (0.81-1.23%).

[0004] The disadvantages of this method include the high calcination temperature (1200-1300°C) and the associated high energy consumption; the need for careful control of the aluminum-zinc ratio and temperature; long contact time of the phases, as well as multi-stage washing of the final product from anions and cations.

[0005] A known method for producing ZnAl2O4 is based on a self-propagating high-temperature process using a mixture of urea and glycine as a fuel [Mirbagheri SA, Masoudpanah SM, Alamolhoda S. Structural and optical properties of ZnAl2O4 powders synthesized by solution combustion method: Effects of mixture of fuels / / Optik. - 2020. - Vol. 204. - Pp. 164-170], according to which zinc aluminum nitrates (oxidizers) are dissolved in distilled water, a mixture of fuels - glycine and urea in various ratios (φ = 0.5; 1; 2) - is added. The resulting solution is evaporated at 80 ° C, then the combustion reaction is carried out by heating to 250 ° C. To increase crystallinity, the combustion products are additionally calcined at 700 ° C. According to X-ray phase analysis, a practically single-phase ZnAl2O4 is formed with an average crystallite size of about 17 nm.

[0006] The disadvantages of this method include the need to use a mixture of two organic fuels, requiring precise ratio selection, and the multi-stage process (evaporation, combustion, and calcination at 700°C). If the fuel mixture composition deviates from the optimal composition, impurities, primarily residual ZnO, remain in the products. Excessive fuel content (φ = 2) leads to a decrease in combustion temperature, deterioration of crystallinity, the formation of amorphous or poorly crystallized products, and possible residual carbon. Furthermore, the method requires complex instrumentation to capture exhaust gases and monitor the combustion process.

[0007] A method for producing ZnAl2O4 by the sol-gel method is also known [Ávalos-Marrón E. et al. Facile sol-gel synthesis of ZnAl2O4 spinel nanoceramics for photocatalytic applications: H2 production and MB dye degradation / / Journal of Sol-Gel Science and Technology. - 2025. - Vol. 113. - No. 1. - Pp. 109-122]. The synthesis is carried out as follows: aqueous-alcoholic solutions of zinc nitrate and aluminum nitrate are mixed, citric acid and ethylene glycol are added, then the solution is heated to 110 ° C until a transparent gel is formed. The resulting gel is placed in a muffle furnace, preheated to 400 ° C, for 15 minutes to allow spontaneous combustion. The resulting dark porous foam is crushed and calcined at temperatures of 500-900°C for 2 hours. According to X-ray diffraction data, the cubic phase of ZnAl2O4 forms already at 500°C. The crystallite size ranges from 10-22 nm, depending on the calcination temperature.

[0008] The disadvantages of this method include the use of organic additives (citric acid, ethylene glycol), which must be carefully dosed; the need for two-stage heat treatment (spontaneous combustion at 400°C followed by calcination to 900°C); and a relatively low specific surface area for high-temperature samples.

[0009] A method for producing ZnAl2O4 by mechanochemical synthesis is also known [Fabian M. et al. A simple and straightforward mechanochemical synthesis of the far-from-equilibrium zinc aluminate, ZnAl2O4, and its response to thermal treatment / / RSC Advances. - 2015. - Vol. 5. - Pp. 54321-54328]. The synthesis is carried out as follows: a stoichiometric mixture of ZnO and γ-Al2O4 powders is placed in a high-energy planetary mill, tungsten carbide balls are added (ball:powder ratio = 40:1) and grinding is carried out at 600 rpm for 2 hours at room temperature in an air atmosphere. The resulting product is nanocrystalline ZnAl2O4 with an average crystallite size of about 10 nm.

[0010] Disadvantages of this method include the use of high-energy grinding, which requires specialized, expensive equipment; possible contamination of the product by the material of the balls and grinding chamber (tungsten carbide); and the need for subsequent high-temperature processing.

[0011] A method for producing ZnAl2O4 nanopowder using the ion-exchange synthesis method is also known, in which a pre-synthesized cation-exchange material is used as a matrix [Shergin A. V. et al. Ion-exchange synthesis of zinc aluminate / / Bulletin of NRNU MEPhI. - 2023. - Vol. 11. - No. 1. - Pp. 80-86]. According to the method, equimolar amounts of aqueous solutions of Zn(NO3)2 and Al(NO3)3 are mixed with a pre-synthesized cation-exchange material, left for 30 minutes to saturate the cation exchanger, then washed repeatedly in a Buchner funnel, dried in air for 24 hours and calcined in a muffle furnace at a temperature of 600 to 1000°C for 1 hour. According to XRD data, the onset of formation of the crystalline phase of ZnAl2O4 occurs at 600°C, but a single-phase structure without impurities of ZnO and Al2O3 is achieved only at 1000°C; the average crystallite size (ACS) is 26 nm, and the particle size is up to 100 nm.

[0012] The disadvantages of this method are the high temperature of formation of pure spinel (1000°C), the need for preliminary synthesis of a cation exchange matrix, which increases labor intensity, long drying (24 hours) before calcination, agglomeration of particles up to 1 μm with an increase in heat treatment time to 4 hours.

[0013] The closest technical solution to the proposed method is the production of zinc aluminate nanopowder using the co-precipitation method [Vinitha N., Rachana R., Mini Krishna K. Low-temperature Co-precipitation Synthesis of ZnAl2O4 Nanophosphors Probing its Luminescent, Antibacterial and Anticancer Potentials / / Journal of Fluorescence. - 2025. - V. 35. - P. 3873-3881]. According to the method, aqueous solutions of zinc nitrate and aluminum nitrate are mixed in a molar ratio of Zn:Al = 1:2, then a 25% ammonia solution is added dropwise with constant stirring until pH = 8 is achieved. The mixture is kept at room temperature for 24 hours for complete precipitation, after which it is filtered and dried in a drying oven at 80 °C for 12 hours. The resulting fine powder is calcined at temperatures of 300, 450, 600 or 750 °C for 2 hours. According to X-ray phase analysis, calcination at 750 °C is necessary to form the pure ZnAl2O4 phase.

[0014] The disadvantages of this method include: long contact time of the phases, the need for lengthy washing and purification of the resulting precipitate from anions and cations of the precipitant (ammonia and nitrate ions), the multi-stage and lengthy process: precipitation (24 hours), filtration, drying (12 hours), calcination.

[0015] The need for this invention stems from the shortcomings of traditional zinc aluminate (ZnAl2O4) synthesis methods, which require specialized equipment and high-temperature annealing to complete the crystallization of the spinel structure, leading to uncontrolled particle growth and a decrease in specific surface area. During anion-exchange synthesis from a mixture of various metal salts in the presence of an anion exchanger, highly active precursors are formed, so the formation of complex oxides occurs at a lower temperature. Furthermore, anion-exchange precipitation allows for the production of precursors with a composition close to stoichiometric, which facilitates the formation of a single-phase material. A significant advantage of this method is the absence of ion contamination of the final product, ensuring high chemical properties of the resulting product without the use of additional washing steps.Simplicity, speed, and the absence of complex reaction equipment make the proposed method convenient and easily reproducible under standard laboratory conditions. The use of anion exchange also ensures the production of a pure and homogeneous product with reproducible physicochemical properties.

[0016] The objective of the invention is to develop a simple, energy-efficient and easily scalable method for the anion-exchange synthesis of nanodispersed zinc aluminate (ZnAl2O4) with improved characteristics of the target product.

[0017] The technical result of the invention consists in simplifying the method by eliminating additional stages of cleaning and washing the sediment and reducing the temperature of high-temperature processing, as well as improving the quality of the target product by obtaining a single-phase nanosized product with a narrow particle size distribution.

[0018] The technical result of the invention is achieved in that in the method for producing nanosized zinc(II) aluminate powder, which includes preparing a reaction solution, obtaining a precipitate in the form of a powder, separating it, drying and firing, according to the invention, the reaction solution is prepared by dissolving a mixture of zinc(II) and aluminum(III) nitrate salts taken in a stoichiometric molar ratio (1:2), obtaining a precipitate in the form of a powder is carried out by mixing the resulting reaction solution with a strongly basic gel anion exchanger AB-17-8 in hydroxyl form at a temperature of 60°C for 1 hour, the separation of the product is carried out by passing the mixture through a sieve with a hole diameter of 0.16 mm, to separate the precipitate, filtration is carried out under vacuum, firing is carried out at a temperature of 600°C for 1 hour.

[0019] A comparative analysis of the claimed invention and the prototype shows that the distinctive features of the invention:

[0020] • a strongly basic gel anion exchanger AB-17-8 in hydroxyl form is used as a precipitant instead of adding an ammonia solution;

[0021] • the precipitate is obtained by stirring the reaction solution with anion exchanger at a temperature of 60°C for 1 hour, rather than keeping it at room temperature for 24 hours;

[0022] • after separating the precipitate from the anion exchanger, there is no long-term washing stage to remove precipitant ions (ammonium) and solution anions (nitrate ions), since the anion exchanger does not introduce contaminants and absorbs solution anions;

[0023] • The firing is carried out at 600°C for 1 hour, while the prototype requires calcination at 750°C for 2 hours to obtain a single-phase product.

[0024] In the claimed invention, the anion exchanger AB-17-8 is used as a precipitating agent - a strongly basic anion exchanger with a polystyrene matrix containing residues of quaternary ammonium bases - N + (СН3)3.

[0025] Thanks to these distinctive features, it was possible to obtain zinc(II) aluminate with a stoichiometric composition. Furthermore, the proposed method leads to the formation of a nanosized product.

[0026] Anion exchange resin AV-17-8 is prepared in the hydroxyl form. The initial AV-17-8 in the chloride form is poured into a 1 M NaOH solution (s:l = 1:3), then into a 2 M NaOH solution three times, holding each portion for 1 hour. The anion exchange resin is then rinsed with distilled water until a negative reaction to chloride ion is achieved, dried at a temperature of approximately 60°C, and before use, the anion exchange resin sample is soaked in distilled water for 5 minutes to allow swelling.

[0027] Prepare a reaction aqueous solution from a mixture of zinc(II) and aluminum(III) nitrate salts in a molar ratio of 1:2. Add a sample of anion exchange resin AB-17-8 to the resulting mixture, calculated using the formula:

[0028] ,

[0029] where n(Zn 2+ ), n(Al 3+) is the amount of substance (mol) of zinc(II) and aluminum(III); COE is the static exchange capacity, mmol-eq⋅g -1 .

[0030] The precipitation process is carried out with stirring on a shaker at a speed of 120 min -1 The anion exchange resin is heated at 60°C for 1 hour, after which the mixture is separated by passing it through a sieve with a mesh diameter of 0.16 mm. The precipitate is separated by vacuum filtration. The resulting precipitates are dried at 80°C in a drying oven for 2 hours and calcined at 600°C for 1 hour.

[0031] The invention is illustrated by drawings. Fig. 1 shows a flow chart for producing nanosized zinc aluminate powder. Fig. 2 shows an X-ray diffraction pattern of the obtained products fired at 600°C. Fig. 3 shows an X-ray diffraction pattern of the obtained products fired at 700°C. Fig. 4 shows a transmission electron microscopy micrograph of ZnAl2O4.

[0032] The method is confirmed by specific examples.

[0033] Example 1. Obtaining zinc aluminate nanoparticles from nitrate solutions of zinc(II) and aluminum(III) using anion exchange resin AB-17-8 in the OH form as a precipitating reagent, at a calcination temperature of 600°C for 1 hour.

[0034] Weighed portions of salts (0.595 g Zn(NO3)2⋅6H2O and 1.500 g Al(NO3)3⋅9H2O) were dissolved in 50 ml distilled water. To the resulting solution, 18.0 g of water-swollen anion exchange resin AB-17-8 (SOE 1.63 mmol-eq⋅g) were added. -1 ) while stirring on a shaker at a speed of 120 min -1and a temperature of 60°C for 1 hour. To separate the phases, the mixture was passed through a sieve with a mesh diameter of 0.16 mm (separation of the anion exchanger). To separate the precipitate from the solution, filtration was carried out under vacuum (separation of the precursors). The precursors were dried at 80°C in a drying oven for 2 hours and annealed at a temperature of 600°C for 1 hour (Fig. 1). The product yield is 96% (the metal content in the anion exchanger phase is ~4%). X-ray phase analysis (Fig. 2), supplemented by refinement of the phase composition and cell parameters of the obtained product by the Rietveld method using Topas 3 software, showed that it is a cubic phase of ZnAl2O4. The cell parameter was 8.0922±0.0018 Å. The phase RCS size, determined by full-profile analysis of the diffraction pattern, was 14.43 ± 0.15 nm, the calculated value of the specific surface area was 90.8 m 2 / G.

[0035] Example 2. Obtaining zinc aluminate nanoparticles from nitrate solutions of zinc(II) and aluminum(III) using anion exchange resin AB-17-8 in the OH form as a precipitating reagent, at a calcination temperature of 700°C for 1 hour.

[0036] Weighed portions of salts (0.595 g Zn(NO3)2⋅6H2O and 1.500 g Al(NO3)3⋅9H2O) were dissolved in 50 ml distilled water. 18.0 g of water-swollen anion exchange resin AB-17-8 (SOE 1.63 mmol-eq⋅g) were added to the resulting solution. -1 ) while stirring on a shaker at a speed of 120 min -1and a temperature of 60°C for 1 hour. To separate the phases, the mixture was passed through a sieve with a mesh diameter of 0.16 mm (separation of the anion exchanger). To separate the precipitate from the solution, filtration was carried out under vacuum (separation of the precursors). The precursors were dried at 80°C in a drying oven for 2 hours and annealed at a temperature of 700°C for 1 hour (Fig. 1). The yield of the product is 96% (the metal content in the anion exchanger phase is ~4%). X-ray phase analysis (Fig. 3), supplemented by refinement of the phase composition and cell parameters of the obtained product by the Rietveld method using Topas 3 software, showed that it is a cubic phase of ZnAl2O4. The cell parameter was 8.0889±0.0009 Å. The size of the coherent scattering region of the phase, determined by full-profile analysis of the diffraction pattern, was 34.1±0.5 nm. Micrographs of ZnAl2O4 sample (Fig.4) indicate that the particles of the obtained material are uniform in morphology and size, and contain nanometer-range particles with a size of 21±5 nm, the calculated value of the specific surface area was 61.6 m. 2 / G.

[0037] Thus, the claimed method for producing nanosized zinc(II) aluminate powder is simple and easy to use, requiring no aggressive media, high pressures, or additional purification or precipitate washing steps. This method improves the properties of zinc aluminate powders by producing a single-phase, finely dispersed nanosized product.

Claims

A method for producing nanosized zinc(II) aluminate powder, comprising preparing a reaction aqueous solution from a mixture of zinc(II) and aluminum(III) nitrate salts taken in a molar ratio of 1:2, obtaining a precipitate in the form of a powder, separating it, drying and firing, characterized in that the precipitate in the form of a powder is obtained by mixing the resulting reaction solution with a strongly basic gel anion exchanger AB-17-8 in hydroxyl form at a temperature of 60°C for 1 hour, then the mixture is passed through a sieve with a hole diameter of 0.16 mm to separate the anion exchanger, after which the precipitate is separated from the solution by vacuum filtration, dried at a temperature of 80°C for 2 hours and fired at a temperature of 600°C for 1 hour.

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