Porphyrin-Embedded Organosilica Photocatalysts for Efficient Hydrogen Peroxide Production

The photosynthesis of hydrogen peroxide (H₂O₂) from O₂ and H₂O using solar energy offers a sustainable alternative to conventional processes. However, the H₂O₂ yield is lowered because the H₂O₂ is decomposed by the photocatalysts that are typically used. In this study, porphyrin-containing organosilica photocatalysts were developed for efficient H₂O₂ production. The as-synthesized photocatalysts successfully convert O₂ and H₂O into H₂O₂ upon irradiation with visible light. Organosilica with the optimal number of porphyrin sites exhibit H₂O₂ production rate of 108 µmol·L^-1·h^-1, which is 1.8-times higher than that of the precursor porphyrin ligand. Decomposition of H₂O₂ by the photocatalysts was negligible. Photoluminescence measurements revealed that the incorporation of an optimal number of porphyrin sites into the organosilica significantly enhanced the photocatalytic activity for H₂O₂ production because of the suppression of aggregation-induced quenching. The mechanistic study revealed that H₂O₂ production over the porphyrin-containing organosilica photocatalysts occurred predominantly via a direct two-electron oxygen reduction reaction pathway involving singlet oxygen and photogenerated electrons. These findings open new avenues for efficient photocatalytic production of H₂O₂ and have significant implications for the design of advanced silica-based photocatalytic materials.