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• The photolysis was highly induced by Fe(III) with citric, tartaric or malic acid. • The SMT couldn't influence the complexation between Fe(III) and three carboxylate. • The species of ·OH played a significant role in the photocatalytic degradation of SMT. • An interaction among ROS, Fe(III)-carboxylate complexes and SMT was first proposed. • Four degradation pathways were presented based on identified products by UPLC-QTOF/MS. 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 (1O 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, SO 2 extrusion, Smiles-type rearrangement and S-N bond cleavage. The system also had an application potential for removing SMT from practical water. [ABSTRACT FROM AUTHOR]

• Cr(VI) could greatly promote the oxidation and photolysis of TC at different pHs. • Under UV and sunlight irradiation, the contributions of Cr(VI) are 30.3% and 34.0%. • 1O 2 and O 2 − played significant roles in Cr(VI)-induced photolysis of TC. • The electron-transfer interaction among 1O 2 , Cr(VI)/Cr(III) and TC was proposed. • Five reaction pathways were presented based on identified products by UPLC-QTOF/MS. Tetracycline (TC) and chromate (Cr(VI)) are common organic or inorganic pollutants in the environment, and the interactions between them may mutually alter environmental behaviors and risks. However, the mutual effect between TC and Cr(VI) in aqueous solutions remains unclear. In this study, kinetic experiments, complexation and quenching experiments, electron spin resonance (ESR) analysis, density functional theory (DFT) calculation and identification of products, were performed to investigate the effects and underlying mechanism of Cr(VI) on oxidation and photolysis of TC. The results revealed that Cr(VI) could induce oxidation and photolysis of TC with or without light irradiation and the curve was well fitted by a pseudo first-order kinetic model. Moreover, the change of reaction conditions (such as initial concentration and pH) had great effect on oxidation or photolysis of TC. When Cr(VI) oxidized TC to form Cr(III) and TC radical, Cr(III) complexed with TC to accelerate the oxidation. In addition, oxidation still occurred under simulated irradiation. 1O 2 which promoted photolysis of TC increased upon irradiation at higher pH or with the increase of Cr(VI). The participation of Cr(VI) affected self-sensitization and product formation of TC. Therefore, an electron-transfer interaction for photolysis among 1O 2 arising from self-sensitization, Cr(VI)/Cr(III) and TC was first proposed. The transformation pathway of TC mainly included five reactions: hydrolysis, hydroxylation, deamination, dehydration and demethylation only for photolysis. This study identified new oxidation and photolysis of TC induced by Cr(VI), which will be helpful to further understand the fate of heavy metals and antibiotics in the natural aquatic environment. [ABSTRACT FROM AUTHOR]