*5.3.1 Photocatalysis*

IO based photocatalysts are used for removal of volatile organic compounds, degradation of organic pollutants, hydrogen evolution and so on [76]. The photocatalytic activities of a single photocatalyst is usually limited due to their high recombination rate of photo-generated charge carriers and also their low utilization of visible light energy. In this respect, the fabrication of semiconductor nanocomposite based photocatalysts by imposing various novel strategies (such as doping impurity element into the metal oxide semiconductor or coupling with other semiconductor oxides, metals, and carbon) have been investigated as a feasible and promising strategy to overcome the shortcomings. Some IO based photocatalysts that are already studied by several researchers are displayed in **Table 1**.
