Homogeneous photocatalytic degradation of sulfamethazine induced by Fe (III)-carboxylate complexes: Kinetics, mechanism and products

Sulfamethazine (SMT), taken as model compound, have been exposed to a photocatalytic system driven by ultraviolet light (UV) irradiation with Fe(III) and three carboxylic acids (citric, tartaric and malic acid). The kinetic experiments, quenching experiments, electron paramagnetic resonance (EPR), species model theoretical calculation, density functional theory (DFT) and intermediates analyses, were conducted to analyze the formation of reactive oxygen species (ROS) and underlying mechanism of Fe(III)-carboxylate complexes on photocatalytic degradation of SMT. The results indicated the complexes easily induced the degradation under UV irradiation. Enough hydroxyl radicals (OH) were produced and the singlet oxygen (O-1(2)) originated from the self-sensitized oxidation. An interaction among ROS, Fe(III)-carboxylate complexes and SMT was firstly proposed. The active sites and groups were characterized through Frontier electron densities (FEDs), Fourier Transform-Infrared (FTIR) and Two-dimensional correlation FTIR spectroscopy (2D-FTIR-CoS) analyses. The transformation pathway mainly included four reactions: hydroxylation, SO2 extrusion, Smiles-type rearrangement and S-N bond cleavage. The system also had an application potential for removing SMT from practical water.