Highly efficient removal of organic pollutants via a green catalytic oxidation system based on sodium metaborate and peroxymonosulfate

The development of highly efficient and green catalytic oxidation process based on peroxymonosulfate (PMS) activation has been identified to be a significant yet challenging objective in the environmental catalysis field. A simple, environmentally benign and highly effective catalytic oxidation system was innovatively constructed by coupling NaBO₂ and PMS for the removal of Acid Red 1. The catalytic mechanism in the NaBO₂/PMS system was elucidated by electron paramagnetic resonance (EPR) combined with several radical capture reagents (ascorbic acid, methanol, tert-butyl alcohol, ethanol and _l-histidine). The experimental results indicated that singlet oxygen (¹O₂) severed as the predominant reactive oxygen species (ROS) rather than the HO or during the catalytic oxidation process, at variance with the reported radical pathway in the Co²⁺/PMS system. Inspiringly, p-benzoquinone (p-BQ) as a trapping agent in most advanced oxidation process could be turned into the positive one in the NaBO₂/PMS system, achieving a nearly 3-times enhancement in terms of the rate constant for AR1 removal. More interestingly, sodium chloride (NaCl) presented the same enhancement effect as p-benzoquinone due to generation of hypochlorous acid (HOCl) and more ¹O₂, which was completely different from the reported. This study develops a highly efficient green oxidation process and opens up a new insight in the remediation of contaminated water.