Tungsten Trioxide (WO3) is an important N-type semiconductor material, which has excellent photoelectric properties and has a wide application prospect in solar cells, photoelectric devices, photocatalysis, sensor materials and other fields. At present, there are many commonly used methods to prepare Tungsten Trioxide, among which hydrothermal synthesis is a common one.
1.The origin of hydrothermal synthesis method
When it comes to hydrothermal synthesis, we have to mention hydrothermal method, which was studied by geologists in the mid-19th century by simulating mineralization in nature. After 1900, scientists established the theory of hydrothermal synthesis, and then began to turn to the research of dingal materials. At present, more than 100 kinds of crystals have been prepared by hydrothermal method. Hydrothermal method, also known as hydrothermal method, belongs to the category of liquid-phase chemical method, which refers to the chemical reaction in a sealed pressure vessel with water as solvent under the conditions of high temperature and high pressure. Hydrothermal reaction can be divided into hydrothermal oxidation, hydrothermal reduction, hydrothermal precipitation, hydrothermal synthesis, hydrothermal hydrolysis, hydrothermal crystallization and so on. Hydrothermal synthesis is a common method to prepare Tungsten Trioxide.
2.The principle of hydrothermal synthesis
Hydrothermal synthesis refers to the synthesis method by chemical reaction of substances in aqueous solution at 100-1000°C and 1Mpa-1GPa. Under subcritical and supercritical hydrothermal conditions, hydrothermal reaction can replace some high-temperature solid-state reactions because the reaction is at the molecular level and the reaction activity is improved. Because the homogeneous and heterogeneous nucleation mechanism of hydrothermal reaction is different from the diffusion mechanism of solid reaction, it can create advantages that other methods cannot have.
3.How to make Tungsten Trioxide
Generally, sodium tungstate is used as raw material, hydrochloric acid is added into sodium tungstate solution for acidification, and hydrothermal reaction is carried out at 130-200°C for 1-5 days, finally Tungsten Trioxide with uniform particle size distribution can be obtained.
4.Advantages and disadvantages of hydrothermal synthesis method
Advantages:
(1)It can reduce the step of converting metal or its precursor into oxide by calcination in general liquid phase synthesis;
(2)It can effectively control the particle size, particle size distribution and morphology of powder;
(3)It can greatly reduce or even avoid the formation of hard agglomeration;
(4)The prepared Tungsten Trioxide powder has the characteristics of complete grain development, small grain size, uniform distribution and good dispersibility.
Disadvantages:
(1)Poor safety performance;
(2)It is carried out in a closed container, and the growth process cannot be observed, which is not intuitive;
(3)High equipment requirements (high temperature and high pressure resistant steel and corrosion resistant lining), high technical difficulty (strict temperature and pressure control) and high cost.
