The Role of Common Alcoholic Sacrificial Agents in Photocatalysis: Is It Always Trivial?

Abstract

Photocatalytic hydrogen production is proposed as a sustainable energy source. Simultaneous reduction and oxidation of water is a complex multistep reaction with high overpotential. Photocatalytic processes involving semiconductors transfer electrons from the conduction band to the valence band. Sacrificial substrates that react with the photochemically formed holes in the conduction band are often used to study the mechanism of H2 production, as they scavenge the holes and hinder the charge carrier recombination. The desired sacrificial agent is one forming a radical that is a fairly strong reducing agent, and that its oxidized form is not a good electron acceptor that might suppress the hydrogen evolution reaction (HER). In an acidic medium, methanol was found better to fulfill both these requirements than ethanol and 2-propanol in the TiO2 -(M0 -NPs) (M = Au or Pt) system, while in an alkaline medium, the alcohols exhibit a reverse order of activity. Moreover, we report that CH2(OH)2 is by far the most efficient sacrificial agent in a non-trivial mechanism in acidic media. Our study provides general guidelines for choosing an appropriate sacrificial substrate and helps to explain the variance in the performance of alcohol scavengers-based photocatalytic systems.