Resorcinol–Formaldehyde Based Polymeric Photocatalysts for Sustainable H 2 O 2 Production from H 2 O and O 2 : Advances, Mechanisms, and Future Directions

Phenolic resins, among the earliest synthetic polymers, are valued for their thermal, mechanical, and chemical stability. Recently, resorcinol–formaldehyde (RF) resins have attracted attention as visible-light-active photocatalysts for hydrogen peroxide (H 2 O 2 ) production. Their tunable cross-linked structure and donor–acceptor π-conjugated network facilitate efficient charge separation, oxygen adsorption, and selective two-electron oxygen reduction and water oxidation pathways. H 2 O 2 is a green oxidant widely used in chemical synthesis, disinfection, and environmental remediation, yet conventional anthraquinone-based production is energy-intensive and polluting. Sunlight-driven H 2 O 2 generation from water and oxygen offers a sustainable alternative, with RF-based photocatalysts showing strong potential due to their visible-light activity and efficient charge transport. This review highlights recent advances in RF photocatalysts, focusing on synthesis strategies, molecular design, heteroatom doping, π-stacking control, and hybridization with semiconductors, which enhance light absorption, catalytic selectivity, and oxygen activation, establishing RF resins as scalable materials for solar-driven H 2 O 2 generation and green oxidation chemistry.