With the growth of population, vast industrialization and deforestation, the stored natural energy resources have been sharply consumed and toxic elements have been emitted in environment. As a result, the environmental pollution level is increasing causing a negative impact on human as well as animal life. In addition, increasing usage of fossil fuels can lead to a energy crisis in near future. light harvesting photocatalytic reaction in gas phase could be a necessary strategy for the organic pollutants degradation and the reduction of CO₂ to produce usable fuels.
TiO₂ has been known as an excellent photocatalyst, photovoltaic and others among several semiconductors because of its unique band position and surface structure. However, the large band gap of TiO₂ (Eg=3.2 eV) restricted the use of TiO₂ as a photocatalyst in natural sunlight which mostly consists of visible light. So junction of TiO₂ and other narrow band gap semiconductor would be the promising strategy in order to make visible light photocatalyst.
Here, highly efficient photocatalysts M/FeWO₄/TiO₂, and M/Sb0.9Sn0.1O2/TiO₂ (M=Au, Ag, Pt) were prepared. By the formation of heterojunction, the photocatalyst showed dramatic enhancement of photocatalytic activities in decomposing of model organic compounds under the visible light irradiation in gas and liquid medium phase whereas the single semiconductors showed either zero or negligible photocatalytic activities. The increasement of photocatalytic activities are due to the effective charge transfer between the narrow band gap semiconductor (NBS) and TiO₂. The detailed study has been performed to confirm the pathway of hole transfer, detect the reaction intermediate and propse the reaction mechanism.
Recently, photocatalytic CO₂ reduction become a global issue as a method to solve problems related to energy shortage and carbon emission. This artificial photosynthetic reaction shows a huge potential to generate alternative fuels by harvesting the sunlight. To achieve high photocatalytic CO₂ conversion efficiency, Ruthenium (RuOx), well known to Sabatier reaction catalysts from CO₂ to CH₄, loaded CuCr₂O₄, well known to photothermal materials, was prepared. Due to phototermal effect of CuCr₂O₄ and charge transfer from CuCr₂O₄ to Ruthenium, RuOx/CuCr₂O₄ system showed the highest efficiency among gas phase catalysts published so far.