Effects of mixed sacrificial reagents on hydrogen evolution over typical photocatalysts

Sacrificial reagents (SRs) are widely used in photocatalytic H₂-evolution systems, and the physical/chemical properties of SRs may be changed after mixing. In our study, triethanolamine, methanol, and lactic acid were selected as three kinds of typical organic SRs, which were of alkaline amine, neutral alcohol, and acidic carboxylic acids, respectively. Graphic carbon nitride (g-C₃N₄) and titanium dioxide (TiO₂), which are of metal-free polymerized-organic and metal-oxide inorganic semiconductors, respectively, were selected as two kinds of typical photocatalysts. By measuring and comparing the photocatalytic H₂-evolution performance of g-C₃N₄ and TiO₂ in single-sacrificial-reagent systems, corresponding binary-sacrificial-reagent systems, and trinary-sacrificial-reagent (TSR) systems, the effects of mixed-sacrificial-reagents (MSRs) on H₂ evolution over these two typical photocatalysts were investigated. It was found that the photocatalytic H₂-evolution rates could be enhanced by mixing appropriate SRs to corresponding photocatalysts, for instance, TiO₂ showed the best photocatalytic performance in 20% TSR system. However, g-C₃N₄ showed the best photocatalytic performance in 20% triethanolamine compared with MSR systems. The effects of MSRs on H₂ evolution over typical photocatalysts could be explained by the adsorptivity between SRs and photocatalysts. Functional groups of SRs that are concerned with the adsorption between SRs and photocatalysts might change in the MSR systems. The weakening of adsorption between SRs and photocatalysts led to the decreased photocatalytic H₂ evolution rates over photocatalysts. We provide useful guidance to the design of MSR systems in order to promote the photocatalytic H₂ evolution.