Single-Atom Cocatalyst-Loaded Semiconductors for Photo-Fenton-Like Wastewater Treatment

Solar-driven photo-Fenton reaction offers a sustainable solution to wastewater treatment by using photogenerated hydroxyl radicals (^•OH) to oxidize organic/inorganic contaminants (dyes, pigments, antibiotics, drugs, phenol derivatives, etc.) to nontoxic chemicals. The oxidation potential of ^•OH (E⁰ = 1.9-2.7 V vs. NHE) is high enough to completely oxidize most of the organic contaminants to CO₂. For an effective photo-Fenton process, the choice of an appropriate photocatalyst system with a suitable bandgap and band positions is crucial. Further, the loading of a cocatalyst can substantially improve the charge transfer dynamics, thus reducing the electron-hole recombination and providing active sites for substrate adsorption for the photocatalytic process. Recently, atomic site cocatalysts have been integrated into semiconductors to attain an improved atom economy, high surface-active sites, and hence an improved photo-Fenton activity. In this review, we have described the recent progress and utilization of single-atom cocatalyst (SAC)-loaded photocatalysts for photo-Fenton reactions, their structural features, synthetic strategies, and applications to water treatment. The advantages of photo-Fenton reactions with SAC-loaded photocatalysts over the conventional water treatment processes, which often face difficulty in treating low pollutant concentrations, have been described in detail.