Fabrication of Porous Phenolic Resins with High Photocatalytic H₂O₂ Generation via High Internal Phase Emulsion Method

Resorcinol-formaldehyde (RF) resin can photocatalytically generate hydrogen peroxide (H₂O₂) from pure water and oxygen systems. However, RF resin is typically synthesized as smooth solid microspheres with a relatively small specific surface area. Additionally, the commonly used approach of combining it with other catalysts to enhance its catalytic performance is cumbersome and increases the cost. Herein, hierarchical porous RF-based resins with good photocatalytic properties were synthesized by high internal phase emulsion (HIPE) template method using resorcinol (R), thiourea (T), melamine (M) and formaldehyde (F) as monomers at 140 ℃. The specific surface area of the RTMF and RTF resin reached 172.5 m²/g and 182.4 m²/g, respectively, when the volume fraction of the internal phase was 80%. The effects of thiourea/melamine ratio, reaction temperature and the light source on the photocatalytic activity of the resins were investigated. When n_M:n_T was 0∶2 and n_T+M∶n_F∶n_R was 2∶8∶1, the synthesized RTF resin exhibited remarkable photocatalytic performance with a high H₂O₂ yield of 751 μmol/(g·h) under the irradiation of 300 W Xe lamp and 295 μmol/(g·h) under visible light illumination, which was 3.6 times and 3.1 times those of RF resin, respectively, and also exceeded those of RTF-h resin prepared by high-temperature hydrothermal method. As the reaction temperature increased to 180 ℃, the photocatalytic H₂O₂ generation rate of RTF-180 increased to 640 μmol/(g·h) under visible light illumination. The systematical experiments revealed that the quinone content in resins played an important role in photocatalytic production of H₂O₂. In addition, the mechanism studies proved that RTF resin could photocatalyze H₂O₂ generation through both single-electron and two-electron reduction pathways. This study introduces a simple, economical and feasible approach for the straightforward and efficient synthesis of photocatalysts with enhanced catalytic performance, and the as-prepared modified RF resins show potential application in the field of photocatalytic H₂O₂ production.