Efficient degradation of sulfachloropyridazine by sulfite activation with CuO-Al2O3 composites under neutral pH conditions: Radical and non-radical

In this work, CuO-Al2O3 composites were synthesized at higher temperatures to control the leaching of metal ions, which can activate sulfite (S(IV)) to degrade organic contaminants by generating reactive oxygen species (ROSs). The synthesized catalysts were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, Brunauer-Emmett-Teller, Raman spectroscopy, and Fourier transform infrared spectrophotometry. Sulfachloropyridazine (SCP) was almost completely removed (＞99%) at pH 6.8, and the leaching amount of Cu accounted for 0.027% of the total amount of Cu after the reaction. Notably, singlet oxygen (1O2) was found for the first time in the activated sulfite system, which removed organic pollutants together with sulfate (SO4•-) and hydroxyl (∙OH) radicals. And Al2O3 plays an important role in the catalyst, including anti-sintering, reducing the leaching of copper ions, and promoting the generation of oxygen vacancies. Based on the types of ROSs and X-ray photoelectron spectroscopy results, a possible ROSs generation mechanism was proposed. In addition, the stability of the catalyst and the effect of different factors on the degradation of SCP, including operating parameters and water quality, were further investigated. The intermediates were detected by using gas chromatography-mass spectrometry and a developmental toxicity assessment of the intermediates was defined based on the Toxicity Estimation Software Tool (TEST). Overall, this paper not only provides a new strategy for sulfite activation but also promotes more attention to non-radical processes in activated sulfite systems.