Promoting effect of Far-UVC on the oxidation of diatrizoic acid in secondary effluent by heterogeneous MoS₂/peroxymonosulfate catalysis

The persistent presence and detection of pharmaceuticals and personal care products in wastewater pose a significant threat to environmental health and efficient wastewater treatment. Herein, a multiphase activation system of molybdenum disulfide (MoS₂) and peroxymonosulfate (PMS) driven by far ultraviolet at 222 nm (UV₂₂₂) was developed for their removal. This system achieved complete degradation of diatrizoic acid (DTA) within 20 min and significantly reduced total organic carbon in secondary effluent. The high photon energy of UV₂₂₂ could efficiently catalyze MoS₂ and activate PMS, thereby enhancing the kinetics. Additionally, the adsorption of PMS onto the active sites of MoS₂ promoted the formation of a multi-radical generation network. Characterization results indicated that the redox cycling of Mo(IV)/Mo(VI) continually drove the decomposition of PMS to generate SO₄·⁻, while the low production ratio of Mo(VI) facilitated multiple efficient cycles. Mass spectrometry analysis revealed twelve intermediates formed during the degradation of DTA through deiodination, hydroxylation, iodine substitution, and amide hydrolysis. The generation of SO₄·⁻ and ·OH constitutes the main mechanism for DTA degradation. Moreover, ECOSAR predictions revealed that deiodination played a critical role in reducing the ecological toxicity of DTA transformation products. This study presents an innovative UV₂₂₂-driven advanced oxidation process that overcomes the limitations of conventional photocatalysis and Fenton-like systems—such as narrow pH windows, excessive oxidant requirements, and ionic interference, offering a robust and efficient strategy for the removal of emerging contaminants from wastewater.