Review of different CdS/TiO2 and WO3/ g-C3N4 composite based photocatalyst for hydrogen production

The production of hydrogen from water is one of the best sustainable energy resources to fulfill the increasing energy deficiency of the world. As most of the available energy resources are harmful in one way or another as nuclear waste is dangerous for human life and burning fossil fuels caused the production of carbon, nitrogen, and Sulphur oxides which increases global warming as well as air pollution. The earth is almost 70% consist of water so that there is need to use this water in efficient way to produce hydrogen as it is more sustainable energy resource and environment friendly. This is an emerging field for researchers and they trying to find the best photocatalyst for hydrogen production. The motivation of this study is to provide improved mechanism for hydrogen production because the developing countries like Pakistan faced serious energy crisis and available energy resources in these countries are the fossil fuels mostly which are not environmentally friendly creating chaos of global warming. The background of this study shows that researcher used doped, composite, and many other different techniques to enhance its efficiency. For the last decade, researchers mainly focused on the doped photocatalyst. In recent decade researcher shifted to composite based photocatalysts. The hypothetical question arises in this study weather these composite useful to improve efficiency of hydrogen production by using photocatalyst method? This review paper especially focuses on different composite photocatalysts for hydrogen production. The composites of Cadmium Sulfite/Titanium dioxide (CdS/TiO2) and Tungsten trioxide/graphite Carbon nitride (WO3/ g-C3N4) have been the main area of interest in this review due to their immense use in research to produce hydrogen. This study will also help to understand the mechanism of the production of hydrogen through water splitting and organic compounds. The study also elaborates on the zigzag (Z) and step (S) schemes used for the photocatalytic activity of composites. Present work showed that composite photocatalyst are better and increased efficiency of hydrogen production because active sites of surface increased. This review will be helpful for new apprentices in this field to understand the basic mechanism, helpful for industrialists and experts to decide which composite photocatalyst is best according to their interests.