Utilization of photochemical circulation between NO3− and NO2− in water to degrade photoinert dimethyl phthalate: Influence of organic media and mechanism study.

• Cycling between NO 2 − and NO 3 − could degrade high-level DMP (>[NO x -]) at λ =300 nm. • Self regeneration of NO 2 − enabled Δ[NO 2 −:ΔOH] <<1 at λ =350 nm. • NO 3 − was more efficient for treating low-level DMP. • NO 2 − more efficient for catalyzing DMP decomposition at higher concentrations. • OH was the dominant ROS for DMP degradation. Photoconversion of NO 3 −/NO 2 − at wastewater relevant concentrations as an advanced oxidation approach to degrade dimethyl pthalate (DMP), a relatively photoinert endocrine disruptor, were examined. Three different wavelengths (350 nm, 300 nm, 254 nm) were involved. The influence of NO 3 − or NO 2 − was found to be wavelength-dependent. The 254 nm UV light could decompose DMP efficiently, but photolysis of DMP was slow at λ =300 nm and noneffective at λ =350 nm, which could be catalyzed by the presence of NO 3 − or NO 2 −. Both OH and O 2 − were detected, while OH was identified as the primary contributor to DMP decomposition. NO 2 − plays a dual role as both a source and sink of OH, depending on the relative abundance between NO 2 − and DMP. NO 3 − was more efficient than NO 2 − for treating low-level DMP. However, higher organic content could effectively inhibit the quenching role of NO 2 −, making NO 2 − more efficient for catalyzing DMP decomposition. For irradiation at λ =350 nm, NO 3 − was completely ineffective, while self regeneration of NO 2 − enabled Δ[NO 2 −:ΔOH] <<1. For irradiation at λ =300 nm, cycling between NO 2 − and NO 3 − occurred, and the transformation from NO 2 − to NO 3 − proceeded much faster. Complete decomposition of DMP at concentrations higher than those of NO 2 − or NO 3 − was observed, and mineralization was also achieved. Based on the identification of the intermediates, OH addition to the aromatic ring and hydrogen atom abstraction by OH were the dominant pathways, while nitration products were detected at low levels. [ABSTRACT FROM AUTHOR]