Preparation of Silver Phosphate Photocatalyst

Silver phosphate (Ag₃PO₄) is one of the ideal candidate materials in the field of photocatalysis due to its low toxicity, wide photoresponse range, and good photocatalytic performance, and has attracted wide attention from people from all walks of life. So far, researchers have prepared Ag₃PO₄ through various methods, which will provide technical support for the development and utilization of Ag₃PO₄, and other Ag-based or PO₄-based photocatalysts can also learn from its preparation methods.

Preparation Methods

1. Solid phase grinding method

The solid phase grinding method uses grinding technology to realize the preparation of photocatalytic materials through ion exchange between reactants at room temperature. Using solid AgNO₃ and Na₂HPO₄ or Na₃PO₄ as raw materials, irregular Ag₃PO₄ particles are prepared by grinding at room temperature with a size of about 0.5~2.0 µm. Usually, the morphology of materials prepared by this method is uncontrollable.

2. Aqueous precipitation method

Aqueous phase precipitation is usually a method of precipitation from solution by the formation of insoluble metal salts or metal hydrated oxides in the aqueous phase by a metal salt solution and precipitant. However, the product prepared by the aqueous precipitation method depends on the system environment and nucleation rate; the reaction speed is fast, and the crystal growth process cannot be controlled, so the morphology of the precipitated product cannot be controlled.

By adding some auxiliaries to form different reaction precursors, the nucleation rate and growth rate of the crystal can be controlled, and some Ag₃PO₄ products with controllable morphology can be obtained. For example, adding NH₃·H₂O to AgNO₃ solution to form silver ammonia solution ([Ag(NH₃)₂]NO₃) solution, and then adding Na₂HPO₄ solution to the system to form hierarchical cubic Ag₃PO₄ microcrystals.

3. Organic phase precipitation method

Due to the different existing states of reactants in the organic phase and aqueous phase, materials with special morphology can be prepared by the organic phase precipitation method. Tetrahedral Ag₃PO₄ crystals exposed to highly active {111} faces were prepared by using AgNO₃ ethanol solution and H₃PO₄ ethanol solution.

4. Organic/aqueous precipitation method

Taking advantage of the special existing state of the reactants in the organic/water mixed phase and controlling the reaction kinetics, some precipitated products exposing specific crystal planes and morphologies can also be prepared. Dendritic, tetragonal, nanorod, and triangular Ag₃PO₄ products were obtained after adding H₃PO₄ to the static and ultrasonic dimethylformamide/water mixed solution (DMF/H₂O (1:1)) at different time. It was found that the reaction conditions, reaction time, and the ratio of mixed solvents had a great influence on the morphology and properties of the products.

5. Liquid-solid oxidation and ion exchange method

Using Ag, H₂O₂, and NaH₂PO₄ as raw materials, Ag₃PO₄ products can also be prepared by liquid-solid oxidation and ion exchange, which is a new idea for the preparation of Ag₃PO₄. Two-dimensional dendritic Ag₃PO₄ products were prepared by Ag nanowires, polyvinylpyrrolidone (PVP), NaH₂PO₄, and H₂O₂.

6. Hydrothermal method

The hydrothermal method refers to a chemical reaction carried out in a specially designed sealed pressure vessel, using an aqueous solution as the reaction system, under high temperature and pressure conditions, to dissolve and recrystallize commonly insoluble or insoluble substances. It is an effective method for preparing inorganic materials. The material prepared by this method has high purity, good grain development, and few structural defects. A highly active Ag₃PO₄ product with exposed {110} crystal planes was prepared by hydrothermal reaction using AgNO₃ and H₃PO₄ as raw materials and urea hydrolysis to adjust the pH value of the system.

References

1. Yi, Z.; et al. An orthophosphate semiconductor with photooxidation properties under visible-light irradiation. Nature materials 9.7 (2010): 559-564.
2. Kumar, S.; et al. Template-free and eco-friendly synthesis of hierarchical Ag₃PO₄ microcrystals with sharp corners and edges for enhanced photocatalytic activity under visible light. Materials Letters 123 (2014): 172-175.
3. Martin, D. J.; et al. Facet engineered Ag₃PO₄ for efficient water photooxidation. Energy & Environmental Science 6.11 (2013): 3380-3386.
4. Dong, P.; et al. Shape-controllable synthesis and morphology-dependent photocatalytic properties of Ag₃PO₄ crystals. Journal of Materials Chemistry A 1.15 (2013): 4651-4656.
5. Bi, Y.; et al. Two-dimensional dendritic Ag₃PO₄ nanostructures and their photocatalytic properties. Physical Chemistry Chemical Physics 14.42 (2012): 14486-14488.
6. Wang, .; et al. Facile synthesis of novel Ag 3 PO 4 tetrapods and the {110} facets-dominated photocatalytic activity. CrystEngComm 15.1 (2013): 39-42.