**3.1 Semiconductor photocatalyst material**

Recently, charge recombination is delayed using either use of co-catalyst (platinum) on the surface of semiconductor photocatalyst which boosts the overall efficiency of hydrogen. Sacrificial agents such as methanol, EDTA, sulfides, sulfates and benzyl alcohol are also act as an oxygen scavenger in the process by enhancing the total yield of hydrogen production. After first report on TiO2 for hydrogen production by Gratzel *et al.* the hydrogen generation field is considered as of immense importance [18]. Many researchers have published in the photocatalytic hydrogen generation field by changing catalysts, co-catalysts, combination of two catalysts (composites, coupled system). Till date, nano metal oxides, sulfides, niobates, tantalates and vanadates which contained the metal of d0 or d10 electronic configurations such as In, Ga, Sb, Bi and Ag. Further, binary and ternary nano sulfides (CdS, ZnS, SnS2, ZnI2S4, CdI2S4 and Sb2S3) nitrides oxynitrides, carbon based, and organic semiconductor materials has been reported as alternative photocatalysts for H2 generation. Nanomaterial based semiconductor photocatalyst systems (TiO2, SnO2, WO3, ZnO, Si2O7, ZrO2, SrTiO3, LaCrO3, BaTiO3) have many advantages as compared to their bulk counterparts and hence preferred in photocatalytic hydrogen generation [18–20]. These advantages are, high surface area, higher optical absorption, shorter charge migration length, higher solubility, tunable electronic structure, plasmonic resonance assisted charge injection and separation. All these plus points can be utilized to scale up photocatalytic hydrogen production using nanostructured semiconductor photocatalyst system. Following are the two photocatalytic hydrogen production setups are discussed with schematic representation using water and hydrogen sulfide as a source of hydrogen.
