Photocatalysis is the process of purifying some environmental pollutants using the absorption of ultraviolet and visible waves by metal oxide (semiconductor) particles. Today, the use of metal oxide nanoparticles is very developed due to their unique properties at the nano scale. Titanium oxide nanoparticles, zinc oxide nanoparticles and recently copper oxide nanoparticles are known as nanoparticles with photocatalytic properties. Also, in more recent researches, the combination of graphene with said nanoparticles has been used to increase the photocatalytic properties.

Photocatalytic process

The mechanism of pollutant degradation with the help of photocatalytic materials is one of the attractive fields for many researchers, and so far a lot of research has been done in the field of photocatalytic process and photocatalyst nanoparticles. Although the photocatalytic process for the destruction of pollutants differs from one type to another, the general function of producing hydroxyl radicals to destroy pollutants is the same in all of them.

When a photon with an energy equal to or greater than the energy gap hits the surface of the photocatalyst material (metal oxide), valence band electrons are excited and pass through the energy gap or energy gap to the conduction band, and it is called inhomogeneous photocatalytic process. to be
The forbidden gap energy of the photocatalyst is the energy difference between the high-valence band and the empty conduction band and is usually expressed in electron volts. After light absorption by the photocatalyst, the electrons go from the ground state to the excited state, and as a result, holes are created due to the lack of electrons in the valence band. Holes have very high oxidizing ability and electrons have strong reducing properties. Electron-holes produced as a result of the photocatalytic process, after contact with water and oxygen in the air, create oxygen and hydroxide free radicals, which have high oxidizing properties and can convert pollutants and harmful bacteria into harmless substances such as water. and decompose carbon dioxide. The general scheme of the photocatalytic process is shown in the figure below.

Photocatalytic process

Simple and mixed metal oxide nanostructures, including zinc oxide, nickel oxide, lead oxide, copper oxide, manganese oxide, spinels (AB ₂ O ₄ ) and peroxides (ABO ₃ ) due to their nanoscale dimensions, have special and unique properties. have a person These characteristics are completely different from the bulk structure and are just opposite to the molecular structure and are used in various fields such as magnetic electronics, optoelectronics, environmental catalysts, medicine, etc. Due to the wide range of nanostructures and their various applications, different methods are used to produce them. The choice of method depends on the type of material and its application.

The preparation of nano-mineral materials using soft chemical methods has advantages over traditional methods, including the possibility of more control of the stoichiometry of metals, low formation and crystallization temperatures, production of more homogeneous and pure materials, and the formation of a suitable coating. And uniformly about the layers, the production of dense materials at temperatures hundreds of degrees lower than the temperature required for dense powders and the possibility of forming two or three component materials. So it seems that soft chemical methods are a good alternative to old methods. Among the most important soft chemical methods for preparing metal oxide nanostructures, micelles (inverse microemulsions), hydrothermal, sol-gel, pyrolysis, etc. methods were mentioned. In soft chemical methods or solution-based methods, as their name implies, at least one of the steps in reaching the final mineral substance takes place in solution. In these methods, the step that is carried out in the solution has a profound effect on lowering the formation temperature, increasing the degree of purity and homogeneity of the final composition, and as a result, it enables the production of mineral material with excellent quality and better applications. Each of these methods has its own advantages and disadvantages. Because according to the method chosen to make the material, the characteristics of the final product will be different. Another point is that some methods are limited to making a certain category of materials. In general, the selection of each of the above methods is based on the fulfillment of several conditions and according to the following:

1: Desired particle size, particle size distribution, compound morphology, stoichiometric purity, product efficiency

2: Particle production facilities means the degree of complexity of the desired facilities, working conditions (temperature, pressure, toxicity, etc.) and price