A method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent.

Abstract

This invention provides a method for preparing aluminum-doped zinc oxide (AZO) powder with the assistance of a complexing agent, belonging to the field of metal oxide materials. The method first dissolves zinc salt in ethylene glycol methyl ether, then adds a complexing agent and a dopant. After the solution is mixed evenly, it is dried, the dried gel is ignited, and finally the dried gel is calcined in a muffle furnace to obtain AZO powder. This invention can alter the lattice structure and crystal defects of the material, affecting its electronic structure and band gap, resulting in a smaller band gap and thus better electrical and optical properties. It can also, to some extent, improve the problems of uneven mixing and particle agglomeration of raw materials. The AZO powder prepared by this invention has a c-axis preferred orientation, uniform particle dispersion, a small band gap, and a photocatalytic efficiency of up to 94%. Furthermore, the process is simple, low-cost, and easily achieves molecular-level doping.

Description

Technical Field

[0001] This invention relates to the field of metal oxide materials technology, and to a method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent. Background Technology

[0002] Nanoscale semiconductors have attracted great interest due to their size-dependent electrical and optical properties. ZnO nanomaterials are multifunctional materials with a wide range of technological applications and excellent physical / chemical stability.

[0003] On the one hand, ZnO exhibits higher photocatalytic efficiency under ultraviolet light but weaker photocatalytic activity under visible light. On the other hand, its inherent properties, such as a wide direct bandgap energy (3.37 eV) and a large binding energy (60 meV), enable ZnO materials to be applied in many fields such as electronics, optics, and piezoelectricity. Its excellent optical and electrical properties have attracted widespread attention, especially ZnO nanoparticles doped with metal elements. While some elements improve the photoelectric properties of ZnO, others may have the opposite effect. In existing technologies, Al doping is one of the effective methods to improve the optical and electrical properties of ZnO. Al doping makes ZnO an N-type semiconductor. In the ZnO crystal structure, the substitution of Zn atoms by Al leads to an increase in free electrons, thereby reducing resistivity. Appropriate Al atom doping can also improve the crystallinity of ZnO and the ability to adjust the bandgap.

[0004] In recent years, various morphologies of AZO, such as thin films, wires, rods, disks, and particles, have been extensively studied. Many physical and chemical techniques have been used to synthesize various AZO nanoparticles, including co-precipitation, hydrothermal, solvothermal, and sol-gel methods. However, previous studies on AZO powder preparation have encountered problems such as uneven mixing of raw materials. Furthermore, high-temperature annealing leads to significant particle growth, agglomeration, and a reduction in the active surface sites, resulting in poor crystallinity and sintering activity of the prepared nanoparticles. Conversely, relatively low calcination temperatures result in less than ideal particle dispersibility and crystallinity. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent. The experiment utilizes a sol-combustion-calcination method assisted by a complexing agent. In the initial stage, the metal salt is dissolved, and the complexing agent is added in the liquid phase to control the hydrolysis rate and ion complexation of the metal salt, ensuring uniform mixing of the raw materials at the molecular level. During subsequent ignition, the complexing agent acts as a combustion aid, decomposing to generate a reducing atmosphere, which facilitates the thermal decomposition and oxidation of the powder, accelerates the reaction process, and prevents nanoparticle agglomeration. Firstly, this method effectively controls the crystal structure and particle size of the powder, thereby reducing the density of lattice defects and improving crystal stability and optical properties. Secondly, this method can also control the composition and morphology of the material, influencing its electronic structure and band gap, resulting in a smaller band gap and thus better electrical properties. Finally, this method can also control the surface chemical properties of the material, thereby improving its surface reactivity and biocompatibility.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent includes the following steps:

[0008] Step (1) Preparation of AZO sol

[0009] Zinc salt was dissolved in a solvent and stirred vigorously until completely dissolved. A complexing agent was slowly added dropwise, and stirring was continued until the mixed solution became clear and transparent. A dopant was added and stirring was continued. The mixed solution was transferred to an oil bath and heated at a suitable temperature to prepare AZO sol.

[0010] Step (2) Preparation of initial AZO powder

[0011] The prepared AZO sol was dried at an appropriate temperature to obtain a dry gel. The dry gel was placed in a N2 atmosphere and then ignited to convert it into initial AZO powder. During the ignition process, the combustion temperature and time need to be properly controlled to ensure that high-quality AZO powder is obtained.

[0012] Step (3) Preparation of (002) oriented photocatalytic AZO powder

[0013] The powder is placed in a muffle furnace for calcination at a heating rate of 3-10 °C / min, a calcination temperature of 300-700 °C, and a holding time of 1-3 h. After calcination, the powder is cooled and then ground and sieved to obtain (002) oriented photocatalytic AZO powder.

[0014] Further, in step (1), the zinc salt includes zinc nitrate, zinc chloride, and zinc acetate; the solvent includes water, methanol, isopropanol, ethanol, and ethylene glycol methyl ether; and the dopant includes aluminum chloride and aluminum nitrate.

[0015] Further, in step (1), the concentration of AZO sol is 0.5–1.25 mol / L; Al 3+ The doping ratio of Zn is 1% to 5%. 2+ The molar ratio of the complexing agent is 1:1 to 1:2. That is, the zinc salt is dissolved in the solvent to prepare a precursor solution with a concentration of 0.5 to 1.25 mol / L. The amount of dopant added is 1% to 5% of the zinc salt content. The amount of each component is limited by the above ratio.

[0016] Furthermore, in step (1), the complexing agent includes ethanolamine, citric acid, tetramethylammonium hydroxide, acetylacetone, salicylic acid, and glucose.

[0017] Two or more complexing agents can also be used in combination during the reaction to enhance the complexing ability of metal ions through synergistic or additive effects, thereby improving the preparation efficiency and stability of the material.

[0018] Furthermore, in step (2), the drying method of the sol includes rotary evaporation in a vacuum rotary evaporator, constant temperature drying in an oven, or heating and evaporation with an electric heating mantle, with a drying temperature of 50-150℃.

[0019] Furthermore, in step (2), the combustion temperature is 200-300℃ and the time is 15-40min.

[0020] Furthermore, in step (3), the atmosphere of the muffle furnace is air, nitrogen, or vacuum.

[0021] The present invention also relates to the (002) oriented photocatalytic AZO powder obtained by the above method, characterized in that: the prepared AZO powder is preferentially grown in the c-axis direction, the particle distribution is uniform without agglomeration, the particle size is fine, and the band gap is small.

[0022] Furthermore, another objective of this invention is to prepare a photocatalytic AZO powder with a preferred c-axis orientation, fine particle size, and small band gap, and a preferred orientation of the (002) crystal plane.

[0023] In this invention, determining the complexing agent and annealing temperature is crucial. During the research and development process:

[0024] (1) Uniformity of Zinc Oxide and Aluminum Mixing: Ensuring uniform dispersion of zinc oxide and aluminum during mixing is crucial. Inhomogeneous mixing can lead to incomplete reactions or the production of undesirable products. To overcome this problem, high-energy mixing techniques such as ultrasonic treatment and stirring magnets can improve the uniformity of mixing. These techniques utilize high-energy physical or acoustic effects to promote particle dispersion and mixing.

[0025] (2) Gel formation and drying: In the sol-gel combustion process, the formation of a homogeneous gel is crucial. Gel formation depends on the selection of precursor materials and appropriate reaction conditions. Gel formation is promoted by controlling the reaction temperature, pH value, and adding a gelling agent. The drying process also requires careful handling to avoid gel breakage or uneven shrinkage.

[0026] (3) Control of the combustion process: During the combustion process, it is necessary to ensure an appropriate reaction temperature and atmosphere supply to promote product formation. Temperatures that are too high or too low may lead to a decrease in product quality. To control the combustion process, this invention uses appropriate combustion devices and monitoring technologies to measure temperature and atmosphere, thereby adjusting the reaction conditions.

[0027] The solution of the present invention has the following advantages:

[0028] The raw materials used in this invention are low-cost, non-toxic, and chemically stable. By using Al as a dopant to occupy Zn atomic positions, an increase in free electrons is achieved, forming an n-type semiconductor and reducing resistivity. Compared to other preparation methods, this method can achieve molecular-level uniformity in a very short time, altering the lattice structure and crystal defects in the material (as shown in Table 1 and...). Figure 1 As shown), increase its band gap (such as Figure 3 and Figure 4 As shown), improve the material aggregation problem (e.g. Figure 2 As shown), improve its optical performance (such as Figure 5 and Figure 6 (As shown).

[0029] The AZO nanoparticles obtained by this invention have high purity, fine grains, good crystallinity, and excellent optical properties, and have high photocatalytic efficiency, making them important for applications in the field of inorganic functional semiconductor photocatalytic materials. Attached Figure Description

[0030] Figure 1 These are the XRD spectra of AZO powders prepared at 500°C using different complexing agents in the embodiments of the present invention;

[0031] Figure 2 These are SEM images of AZO powders prepared with different complexing agents in the embodiments of the present invention;

[0032] Figure 3 These are UV-Vis spectra of AZO powders prepared with different complexing agents in the embodiments of the present invention;

[0033] Figure 4 These are the absorbance and band gap spectra of AZO powders prepared with different complexing agents in the embodiments of the present invention;

[0034] Figure 5These are PL spectra of AZO powders prepared with different complexing agents in the embodiments of the present invention;

[0035] Figure 6 These are the photodegradation effects of AZO powders prepared at 500°C using different complexing agents in the embodiments of the present invention;

[0036] Figure 7 These are the XRD spectra of AZO powder prepared at different temperatures in the embodiments of the present invention;

[0037] Figure 8 The XRD patterns of AZO powders prepared at precursor concentrations of 0.5 M, 0.75 M, 1 M, 1.25 M, and 1.5 M are shown.

[0038] Figure 9 These are the XRD patterns of AZO powders with different Al doping amounts. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased. Example 1

[0040] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0041] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 2.25 mL of ethanolamine dropwise (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. The mixed solution becomes clear and transparent. Then stir it at 60 °C for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 60 °C for 1 h to obtain AZO sol.

[0042] Step (2) The obtained sol is dried at 90°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 15 minutes. After cooling to room temperature, the gel is removed and ground to obtain the initial AZO powder.

[0043] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min, a calcination temperature of 500℃, and a holding time of 1h. The atmosphere in the muffle furnace is air. Finally, cool the powder in the furnace, grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 2

[0044] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0045] Step (1) Weigh 10.98g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 1 mol / L solution. Then add 9.61g of citric acid (i.e., the molar ratio of zinc salt to complexing agent is 1:1). Continue stirring at room temperature for 0.5 h, then stir at 70 ℃ for 1 h. Finally, add 0.281g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h to obtain AZO sol.

[0046] Step (2) The obtained sol is dried at 90°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 15 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0047] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min, a calcination temperature of 500℃, and a holding time of 1 h. The atmosphere in the muffle furnace is air. Finally, cool the powder in the furnace, grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 3

[0048] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0049] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 3.36 mL of tetramethylammonium hydroxide (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5) dropwise. Continue stirring at room temperature for 10 min, then stir at 70 ℃ for 2 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 3 h. Seal and store the resulting solution and age it at room temperature for 24 h to obtain AZO sol.

[0050] Step (2) The sol is dried at 90°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 200°C for 15 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0051] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min, a calcination temperature of 500℃, and a holding time of 1h. The atmosphere in the muffle furnace is air. Finally, cool the powder in the furnace, grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 4

[0052] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0053] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 3.85 mL of acetylacetone dropwise (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.093 g of aluminum nitrate nonahydrate (i.e., the doping amount is 1% of the zinc salt) and continue stirring at 70 ℃ for 1 h. Seal and store the resulting solution and age it at room temperature for 24 h to obtain AZO sol.

[0054] Step (2) Dry the sol at 90°C to remove water and solvent until a dry gel is formed. Then transfer the resulting dry gel into a crucible and place it in a tube furnace. Purge with a certain amount of nitrogen to remove oxygen and water vapor. After rinsing, start heating at 300°C for 15 minutes. Cool to room temperature, remove and grind to obtain the initial AZO powder.

[0055] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min, a calcination temperature of 500℃, and a holding time of 3h. The atmosphere in the muffle furnace is air. Finally, cool the powder in the furnace, grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 5

[0056] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0057] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 3.85 mL of acetylacetone dropwise (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h. Seal and store the resulting solution and age it at room temperature for 24 h to obtain AZO sol.

[0058] Step (2) The sol is dried at 90°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 15 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0059] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min, a calcination temperature of 400℃, and a holding time of 1 h. The atmosphere in the muffle furnace is air. Finally, cool the powder with the furnace and grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 6

[0060] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0061] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 3.85 mL of acetylacetone dropwise (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h. Seal and store the resulting solution and age it at room temperature for 24 h to obtain AZO sol.

[0062] Step (2) The sol is dried at 90°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 15 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0063] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min. The calcination temperature is 300℃ and the holding time is 1 h. The atmosphere of the muffle furnace is air. Finally, cool the powder with the furnace and grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 7

[0064] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0065] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 7.204 g of citric acid (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h to obtain AZO sol.

[0066] Step (2) Dry the sol at 150°C to remove water and solvent until a dry gel is formed. Then transfer the resulting dry gel into a crucible and place it in a tube furnace. Purge with a certain amount of nitrogen to remove oxygen and water vapor. After rinsing, start heating at 300°C for 15 minutes. Cool to room temperature, remove and grind to obtain the initial AZO powder.

[0067] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 3℃ / min, a calcination temperature of 500℃, and a holding time of 1 h. The atmosphere in the muffle furnace is air. Finally, cool the powder in the furnace, grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 8

[0068] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0069] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 7.204 g of citric acid (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h to obtain AZO sol.

[0070] Step (2) The sol is dried at 150°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 15 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0071] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min. The calcination temperature is 500℃ and the holding time is 1 h. The atmosphere of the muffle furnace is air. Finally, cool the powder with the furnace and grind and sieve it to obtain (002) oriented photocatalytic AZO powder. Example 9

[0072] The method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent in this embodiment includes the following steps:

[0073] Step (1) Weigh 5.49 g of zinc acetate dihydrate crystals and add them to 50 mL of ethylene glycol methyl ether. Stir vigorously at room temperature until dissolved to prepare a 0.5 mol / L solution. Then add 7.204 g of citric acid (i.e., the molar ratio of zinc salt to complexing agent is 1:1.5). Continue stirring at room temperature for 0.5 h. Then stir at 70 ℃ for 1 h. Finally, add 0.281 g of aluminum nitrate nonahydrate (i.e., the doping amount is 5% of the zinc salt) and continue stirring at 70 ℃ for 1 h to obtain AZO sol.

[0074] Step (2) The sol is dried at 150°C to remove water and solvent until a dry gel is formed. The resulting dry gel is then transferred to a crucible and placed in a tube furnace. A certain amount of nitrogen is introduced for rinsing to remove oxygen and water vapor. After rinsing, heating is started at 300°C for 40 minutes. After cooling to room temperature, the powder is removed and ground to obtain the initial AZO powder.

[0075] Step (3) Place the initial AZO powder into a crucible and calcine it in a muffle furnace at a heating rate of 7℃ / min. The calcination temperature is 500℃ and the holding time is 1 h. The atmosphere of the muffle furnace is air. Finally, cool the powder with the furnace and grind and sieve it to obtain (002) oriented photocatalytic AZO powder.

[0076] The performance of the above AZO powder was tested:

[0077] Table 1. Structural parameters of AZO powder prepared with different complexing agents; Figure 1 These are the XRD spectra of AZO powders prepared at 500°C using different complexing agents in Examples 1-4;

[0078] ;

[0079] The experimental results show that 11 characteristic peaks of the four AZO powders appear at diffraction angles of 2θ = 31.7°, 34.4°, 36.2°, 47.5°, 56.5°, 62.8°, 66.3°, 67.9°, 69.0°, 72.5°, and 76.9°, corresponding to the (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202) planes, respectively. Comparison with the pure ZnO standard PDF card reveals that the prepared AZO powders all exhibit a hexagonal wurtzite structure. This indicates that the crystal phase of the AZO powders obtained after adding different stabilizing agents remains unchanged; the difference lies in the significant change in the relative intensity of the crystal plane orientations. Samples prepared with MEA, TMAH, and Hacac as complexing agents exhibited higher diffraction peak intensities and good preferred orientation. In contrast, samples prepared with CA as a complexing agent showed relatively weaker diffraction peak intensities, indicating a weakened preferred orientation of the film. Furthermore, no characteristic peaks of impurities such as zinc, aluminum, alumina, and zinc hydroxide were observed in any of the four samples, suggesting that the doped Al element did not exist as a separate phase. Instead, smaller Al atoms (0.0535 nm) entered the ZnO lattice, interstitials, or surface, replacing larger Zn atoms (0.074 nm), forming a pure AZO phase. The table shows that the 002 full width at half maximum (FWHM) of AZO powders prepared with different complexing agents exhibited certain differences. On the other hand, AZO powder prepared using Hacac as a complexing agent exhibits the largest grain size, while AZO powder prepared using CA as a complexing agent exhibits the smallest grain size. This is because AZO powder prepared using CA as a complexing agent is composed of randomly arranged atoms or molecules, resulting in poor crystal quality. The micro-strain generated can inhibit grain growth, thus reducing the grain size.

[0080] Figure 2 These are SEM images of AZO powders prepared with different complexing agents in Examples 1-4;

[0081] The above experimental results show that the surface morphology and grain size of AZO powder vary with the properties of the stabilizer. For AZO powder prepared with ethanolamine (… Figure 2 a) Its surface consists of non-uniform spherical nanoparticles, and XRD results show that these nanoparticles are mostly polycrystalline. However, some particles exhibit sintering and agglomeration, resulting in significant powder adhesion. In contrast, AZO powder crystals prepared using citric acid as a complexing agent exhibit a skeletal porous structure. Due to the residual hydroxyl groups, they complex with the surface of the particles, hindering the formation of new crystal nuclei and resulting in a lower crystal count. Figure 2c shows the surface morphology of AZO powder prepared using TMAH as a complexing agent. The morphology of these particles is completely different from that of AZO samples synthesized in the presence of MEA and CA. The AZO powder grains obtained using single Haacac as a complexing agent are irregular spherical, and these spherical particles are significantly different from those obtained using TMAH as a complexing agent. Figure 2 The particles in a have a smaller surface area.

[0082] Figure 3 These are the UV-Vis spectra of AZO powders prepared with different complexing agents in Examples 1-4; Figure 4 These are the absorbance and band gap spectra of AZO powders prepared with different complexing agents in Examples 1-4;

[0083] It can be seen that the light absorption band of AZO powder is concentrated in 300-400 nm, and exhibits a strong absorption band at 355 nm. AZO powder prepared with CA, TMAH, and Hacac complexing agents shows a sharp increase in absorbance below 380 nm, while AZO powder prepared with MEA as a complexing agent does not exhibit the above phenomenon. This is because lattice defects in the crystal structure affect the incident angle and refractive index of light, thereby affecting the absorption and reflection of light, and thus affecting the optical properties of the material.

[0084] Figure 5 These are PL spectra of AZO powders prepared with different complexing agents in Examples 1-4;

[0085] To further understand the recombination of photogenerated electrons and holes and intrinsic defects in AZO powder, fluorescence tests were performed on the AZO powder. Figure 5 To excite the photoluminescence spectrum of AZO nanoparticles at a wavelength of 320 nm, and considering that all samples exhibited an overtone peak exceeding the instrument's measurement range before 340 nm, the emission wavelength was set to 340 nm–500 nm. It can be seen that the samples exhibited strong emission peaks within the 340–500 nm wavelength range. All samples showed similar emission spectra, with slight variations in individual peak positions. Three main emission peaks were observed at λ = 380 nm, 400 nm, and 470 nm. Although AZO has many emission peaks, the intrinsic emission peak at 380 nm is the strongest, corresponding to near-band edge emission of AZO, which is due to the recombination of electron-hole pairs in zinc oxide. The ultraviolet emission peak at 400 nm is also an intrinsic emission peak of AZO, caused by the recombination of free excitons in the conduction band. The blue peak at 460 nm is a defect emission peak, which may be a result of non-uniform interface defects.

[0086] Figure 6 These are the photodegradation effects of AZO powders prepared at 500°C using different complexing agents in Examples 1-4;

[0087] It can be seen that methylene blue solutions (MB) with different AZO powders degraded rapidly, indicating that the AZO powders destroyed the chromophores of MB. The photocatalytic performance of AZO powders synthesized with acetylacetone or tetramethylammonium hydroxide as complexing agents was excellent at any calcination temperature (the degradation efficiency could exceed the self-degradation efficiency of MB solutions). The catalytic efficiency of acetylacetone could reach 90%, while the catalytic efficiency of AZO powders prepared with ethanolamine or citric acid as complexing agents for MB solutions was not very good.

[0088] Figure 7 These are the XRD spectra of AZO powders prepared at different temperatures in Examples 4-6.

[0089] The results show that as the calcination temperature increases, the sol decomposition time is shorter and complete, the grain size increases and the orientation is enhanced, the intensity of the characteristic diffraction peaks gradually increases, the half-peak width narrows, the grain boundary defects decrease, and the degree of crystallization of the crystals increases.

[0090] Figure 8 The XRD patterns of AZO powders prepared with precursor concentrations of 0.5 M, 0.75 M, 1 M, 1.25 M, and 1.5 M are shown. All prepared samples exhibit diffraction peaks near a diffraction angle of 2θ = 34.4°. Comparing with the JCPDS standard spectrum of pure ZnO crystals, the diffraction peaks near 2θ = 34.4° are the (002) crystal plane diffraction peaks of ZnO crystals. This indicates that all samples produced ZnO crystals with a preferred c-axis orientation perpendicular to the substrate. The figure shows that the orientation degree of the (002) crystal plane of the powder differs under different conditions. With the increase of precursor concentration, the probability of collisions between grains increases, resulting in an initial increase followed by a decrease in sample crystallinity. Therefore, the intensity of the diffraction peaks at (100), (002), and (101) first increases and then decreases. The powder sample with a precursor concentration of 0.5 M exhibited very low peak intensity, indicating that the low concentration significantly reduced the probability of collisions between grains, thus decreasing crystallinity. Furthermore, the low colloidal viscosity resulted in weak adhesion to the substrate, leading to agglomeration of ZnO particles during heat treatment due to the evaporation of the organic solvent. When the precursor concentration exceeded the critical concentration (1.25 M), the film was prone to cracking, causing lattice distortion and ultimately destroying the crystal structure.

[0091] Figure 9 These are the XRD patterns of AZO powders with different Al doping amounts. The patterns show peaks at (100), (002), and (101), indicating that the prepared samples have all formed wurtzite-structured ZnO crystals. Furthermore, no obvious alumina diffraction peaks are observed in the patterns, suggesting that Al... 3+The doping was incorporated into the ZnO structure. When the doping concentration was 1%, the powder preferentially grew along the (002) direction, with a narrow half-width at half-maximum (FWHM) and improved crystallinity. When the doping concentration exceeded 1%, the (002) preferred orientation of the sample began to weaken with increasing doping concentration, while the (100) and (101) crystal planes began to grow, and the intensity of the powder's diffraction peaks decreased significantly. This is because in the unit cell with excessive aluminum ion doping, only a portion of Al3+ is present. + Zn in the lattice 2+ The distribution of ions in the grain boundaries causes lattice distortion, which leads to impurity accumulation, damages the crystal structure, and also affects the preferential growth of the powder (002).

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing aluminum-doped zinc oxide powder with the assistance of a complexing agent, characterized in that: Includes the following steps: Step (1) Preparation of AZO sol Zinc salt was dissolved in a solvent and stirred vigorously until completely dissolved. A complexing agent was slowly added dropwise, and stirring continued until the mixture became clear and transparent. A dopant was added and stirring continued. The mixture was then transferred to an oil bath and heated at a suitable temperature to prepare AZO sol. The concentration of the AZO sol was 0.5–1.25 mol / L. The dopant was aluminum nitrate nonahydrate. 3+ The doping ratio of Zn is 1%; 2+ The molar ratio of the complexing agent is 1:1 to 1:2; the complexing agent is tetramethylammonium hydroxide or acetylacetone; Step (2) Preparation of initial AZO powder The prepared AZO sol was dried at an appropriate temperature of 50–150°C to obtain a dry gel. The dry gel was placed in a N2 atmosphere and then ignited to convert it into initial AZO powder at a temperature of 200–300°C for 15–40 minutes. Step (3) Preparation of (002) oriented photocatalytic AZO powder The powder is placed in a muffle furnace for calcination at a heating rate of 3-10 ℃ / min, a calcination temperature of 300-700 ℃, and a holding time of 1-3 h. After holding, the powder is cooled and then ground and sieved to obtain (002) oriented photocatalytic AZO powder.

2. The method according to claim 1, characterized in that: In step (1), the zinc salts include zinc nitrate, zinc chloride, and zinc acetate; the solvents include water, methanol, isopropanol, ethanol, and ethylene glycol methyl ether.

3. The method according to claim 1, characterized in that: In step (2), the drying methods of the sol include rotary evaporation in a vacuum rotary evaporator, constant temperature drying in an oven, or heating and evaporation using an electric heating mantle.

4. The method according to claim 1, characterized in that: In step (3), the atmosphere in the muffle furnace is air.

5. The aluminum-doped zinc oxide powder obtained by the method according to any one of claims 1 to 4, characterized in that: The prepared AZO powder preferentially grows along the c-axis, with uniform particle distribution and no agglomeration.

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