Environmental photochemistry in hematite-oxalate system: Fe(III)-Oxalate complex photolysis and ROS generation

Oxalates, together with iron (hydr)oxides, play important roles in environmental decontamination by photochemical generation of reactive oxygen species (ROS). However, comprehending reaction mechanism about photolytic behaviors across solid-liquid interface is scarce. Here, the photochemical properties of hematite-oxalate system were investigated from complexation, photolysis, and ROS generation tests. Results implied adsorbed oxalate on hematite surface was detached via non-reductive dissolution by irradiating light. Then, the photolysis of Fe(III)-oxalate complexes on hematite surface or dissolved in solution was followed by photodissociation mechanism, in which per Fe(III)-oxalate complex led to two CO2− formation. Moreover, O2−/OOH and OH amounts induced by photodissociation mechanism were much higher than that by classic intramolecular ligand-to-metal charge transfer mechanism in Fe3+-Ox homogeneous system. The photo-degradation and mineralization of sulfadimidine (5 mg/L) reached 95 % and 59 % within 2 h using hematite-Ox system. These findings can help in implementing environmental remediation by utilizing iron (hydr)oxides and oxalate in natural environment.