Modification of Wide Bandgap Semiconductors for Visible Light Driven Hydrogen Generation

Abstract

As fossil fuels are likely to be exhausted in the near future, Hydrogen, a new cheap, renewable and non-polluting energy, has been considered as next-generation energy carrier. Photocatalytic H2 generation, as practiced in the present dissertation, is the central process to achieve the goal of H2 production from renewable resources. Photocatalytic activities for H2 production, using some wide band gap semiconductors have been demonstrated successfully, but under UV light irradiation. Hence, to utilize the sunlight more efficiently, new visible light active photocatalysts need to be developed. While development of noble visible light active photocatalysts is in progress, chemical modifications of UV-active wide bang gap semiconductors to extend the photoactivity into visible region, have become a promising way. Several strategies, such as, (i) element doping, (ii) Forming Solid Solution, (iii) Interfacial Hetero-junction, (iv) Plasmonic modification, and (v) Surface Catalyst Decoration have been proposed. The above strategies have been adopted in the current project, to use chemically modified nanostructures of wide band gap semiconductors, such as ZnS, ZnO and TiO2, to demonstrate significant advancement in the photocatalytic water splitting. The first effort concerns about band engineering by doping; P,Cl- and N,F- codoping in ZnS (and CdS) reduces the band gap and could be used for visible light induced water splitting. Then ZnO was used to make a solid solution with CdO to narrow the band gap and tried to use in visible light induced H2 generation. ZnO and TiO2 was sensitized with CdS and morphology dependent H2 generation was demonstrated by ZnO(TiO2)/CdS heterostructure. An unsuccessful attempt was made to do plasmonic modification of TiO2 by ReO3, which shows SPR in visible region, but could not be used in water splitting due to instability in water. Lastly, CuS cocatalyst loaded ZnO has showed H2 evolution by visible light driven water splitting.