Hydrogen producing water treatment through solar photocatalysis†

Hydrogen is being intensively investigated as a new energy carrier that stores and transports energy obtained from renewable energy resources (e.g., solar and wind power) to the point of use. In particular, efficient methods that can convert solar energy into hydrogen are being actively sought. One of the ideal methods is solar hydrogen production from water splitting that can be driven by photocatalysis or photoelectrochemical reaction. Photocatalytic hydrogen production through water splitting has been demonstrated but the number of successful cases of overall water splitting are limited. Many studies of photocatalytic hydrogen production are based on sacrificial systems and have been carried out in the presence of an excess of electron donors (e.g., alcohols, organic acids). On the other hand, the photocatalytic oxidation of organic compounds has been intensively studied and found to be successful in achieving the mineralization of various organic pollutants in water and air. In particular, TiO2-based photocatalysts have demonstrated excellent performances for this purpose. The general stoichiometry of the photocatalytic degradation of organic compounds can be represented by the following equation.