The Activity of Nanomaterials in Photocatalysis ^†

Several environmental issues need to be addressed, including air pollution and human exposure to the low concentrations of volatile organic compounds that have been detected indoors. Replacing fossil fuels with, for example, green and renewable hydrogen to reduce carbon dioxide emissions and air pollution is another recent challenge. Photocatalysis is an attractive technology with the potential to do both: abate air pollutants and synthesize hydrogen. In order to increase the potential of the environmental applications of photocatalysis, the synthesis of catalytic materials with significantly higher activity is a priority. The semiconductor oxide TiO₂ in the form of an immobilized nano-powder and in the form of thin films is the most studied and most promising photocatalyst. The photocatalytic activity of TiO₂ is associated with its defects, where both types of charge carriers—electrons and holes—can reach the surface in nanosized materials to form effective interactions [1]. Favorable defect distribution can be determined by the presence of specific facets, although obtaining high-purity anatase crystals with controlled crystallographic facet purity remains a challenge [2]. It has also been found that oxygen vacancies are critical for the adsorption of oxygen on the particle surface and the capture of photogenerated electrons. However, the engineering of oxygen vacancies has not yet been developed for practical applications of photocatalytic air purification or hydrogen generation [3,4]. At present, there is still a gap in the efficient use of photocatalytic nanomaterials between laboratory-scale research and practical applications. The development of materials science in the field of nanomaterials, along with developments in the field of photocatalytic systems engineering, should provide solutions for increasing the efficiency of photocatalysis.