Optimal pH condition for hydrogen production using δ-FeOOH under UV irradiation

δ-FeOOH was synthesized to produce hydrogen and its properties were investigated. Although δ-FeOOH has a band gap energy that absorbs sufficient visible light, it cannot produce hydrogen in the visible-light region. However, δ-FeOOH can successfully produce hydrogen under UV. These results indicate that the hydrogen production reaction with δ-FeOOH under UV irradiation is related to the photo-Fenton reaction. The hydrogen production ability was investigated by controlling the pH of the solution, which is an important factor in the photo-Fenton reaction. As the pH of the solution decreased, the amount of hydrogen produced increased. The crystal structures of δ-FeOOH before and after hydrogen production were compared, and it was confirmed that the two crystal structures were identical. This result represents that the photo-Fenton reaction is a circular reaction, and δ-FeOOH can produce hydrogen semi-permanently under UV.