LAUSR

Developing an efficient photocatalyst for concurrent hydrogen production and environmental remediation by using solar energy is a challenge. Defect engineering although it offers a strategical promise to enhance the photocatalytic performance, the limitations come from the ambiguity surrounding its role. In the current work, a comprehensive study on defects in promoting the charge transfer, band edge modulation and surface reaction were carried out. The excess electrons springing from defects act like donor states and causes band bending at the junction interface. Characterization techniques such as XPS, UPS, ESR, and PL were employed to investigate defects functionality and its ultimate effect on photocatalytic performance was studied by simultaneous H2 production and methylene blue (MB) degradation. The role of graphene on optoelectronics and defect formation in the composite catalysts were explored. In addition, efforts have been made to unveil the reaction pathway for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) where excess defect density greatly hampered the quantum yield of the process. Results suggest that maintaining optimal defect concentration aborts the undesired thermodynamically favoured back reactions. The conduction band (CB) and valence band (VB) values of the catalysts suggest that the photocatalytic mechanism was dominated by the electron pathway. Graphene acted as an effective electron sink when its concentration was around 2.5-3%. The superior activity of TiO2-ZnS-rGO was attributed to the low bandgap, rapid separation of photo-excited charge carriers and favourable conduction band position for photocatalytic reactions. This work may assist to explore the fundamental role of defects in driving the photocatalytic reactions and improve the selectivity in heterogeneous photocatalysis.