Tungsten Trioxide Photocatalyst

Photocatalysts are chemical substances which do not change itself under the irradiation of light and can be used as a catalyst. 

Photocatalytic principle: After the photocatalyst is irradiated by light, the valence band electron on the semiconductor surface absorbs the light and is excited to the conduction band. 

Therefore, the conduction band has a negative charge (e-) and is reductive. At the same time, the valence band generates a hole (h +) with a positive charge and owns oxidability because the excited electrons are removed. In this way, an oxidation-reduction system is formed. Photogenerated holes (h+) and photogenerated electrons (e-) interact with dissolved O2 and H2O to produce highly chemically active hydroxyl radicals (- OH) and H2O2.

The 21st century is the age of environment protection. Photocatalytic technology, as a highly effective, safe and environmentally-friendly cleaning technology, can be applied to the environmental purification, self-cleaning material, advanced energy, cancer treatment, anti-microbial and other frontiers. Because it can directly use the sunlight to mineralize organic pollutants completely at room temperature.

Tungsten trioxide is a kind of common photocatalytic material. The experiment shows that the photocatalytic performance of single tungsten trioxide is not good, but its photocatalytic performance can be improved by a lot of ways, such as semiconductor compound, metal doping and metal ion doping. Compared with other common photocatalysts such as TiO2 and ZnO, tungsten trioxide has a smaller band gap and wider range of light absorption. Therefore, it can effectively utilize visible light which accounts for nearly half of solar radiation energy. Its volume effect, surface effect, quantum size effect and macroscopic quantum tunneling effect are significant.

Common semiconductor compound photocatalysts include WO3/α-Fe2O3、WO3/CeO2、WO3/Y2O3、WO3/TiO2、WO3/CdS/W and so on.

The common metal doping is to add noble metals, such as Pt. The metal ions such as Y3+, La3+, Eu33+ and Tb3+ are added. Meanwhile, it has a lot of external forms, such as powder and paint.

Photocatalysis has been discovered for more than 40 years. Researchers have found a wider range of applications based on the in-depth study of tungsten trioxide. Tungsten trioxide photocatalyst can be used in inorganic and organic syntheses, water splitting, oxygen evolution, photocatalytic reduction of metal ions (such as heavy metal chromium, mercury, lead, etc.), photocatalytic degradation of organic pollutants (such as formaldehyde), self-cleaning (such as used in automotive rear-view mirror), anti-microbial and so on.

In recent years, photocatalysis has attracted great attention from the government, scientific community, enterprises and other fields. A large number of funds and research forces have been invested to carry out the study of the basic theory, application technology development and engineering, which makes photocatalysis one of the hottest research fields at home and abroad. The data show that the number of photocatalytic material production enterprises in China increased from 47 to 89 in 2012-2016, and the output of photocatalytic materials increased from 2676.2 tons to 4015.0 tons. However, the output of photocatalytic materials in China is still unable to meet the growing demand, so we need to import some products from abroad every year.

Some professionals predict that photocatalytic technology is one of the important means to solve environmental pollution. With the increasing efforts to improve environment, the growth rate of China's market demand for photocatalytic materials will remain between 11.0% and 14.3% in the future. The demand for photocatalytic materials in China is expected to exceed 9000 tons in 2022.

At the same time, the demand for tungsten trioxide will increase as well. According to data, China's demand for tungsten trioxide increased from 88,000 tons to 94,400 tons in 2015-2017. It is estimated that China's demand for tungsten trioxide will increase to 149,000 tons by 2022.

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