Regulating Chlorine Activation Pathways via Triphase Photothermal Catalysis for Enhanced Removal of Emerging Contaminants and Control of Disinfection Byproducts

Diphase photocatalysis/chlorine processes with nanophotocatalysts can simultaneously degrade emerging contaminants (ECs) and disinfect water. However, they suffer from poor recyclability, disinfection byproduct (DBP) formation, and inefficient interfacial mass transfer. Therefore, we develop a gas-liquid-solid triphase photothermal catalysis (PTC)/chlorine system featuring a metal-free catalyst that regulates chlorine activation for superior EC removal and DBP control. This system achieves a high carbamazepine degradation rate constant of 0.38 min^-1, which is 5.51 and 1.63 times that achieved by solar/chlorine and diphase systems. Moreover, PTC/chlorine can effectively degrade various ECs, including those lacking electron-donating groups, thus reducing their toxicity. This is attributed to the reduction of oxygen by photogenerated electrons to produce superoxide radicals, which regulate chlorine activation pathways to produce sufficient hydroxyl radicals for EC degradation while suppressing the generation of chlorine radicals, a major contributor to DBP formation. The PTC/chlorine system significantly suppresses DBP formation and DBP-associated toxicity by reducing chlorine exposure, promoting organic mineralization, and controlling pollutant degradation pathways. It is also highly practicable, as it remains largely unaffected by water matrices and possesses excellent reusability. The proposed triphase PTC/chlorine system thus represents an advanced, environmentally friendly, and sustainable chlorination process.