Insights into the sulfite activation by cobalt(II) sulfide for acetaminophen removal: A synergistic catalysis and DFT calculations

Abstract

This paper offers novel insights into the recently reported cobalt(II) sulfide (CoS) activated sulfite (S(IV)) process. After adding 0.5 g/L CoS and 0.4 mM S(IV) at pH 9.0, 83.1% of acetaminophen (ACP) was removed in 10 min. However, this effect was subject to the inhibition of coexisting chloride or humic acid. Dissolved O2 played an important role in the reaction. The interactive impacts between S(IV) concentration and initial pH were found the most significant. The CoS/S(IV) system involved synchronous homogeneous and heterogeneous catalysis, which demonstrated sizable ACP degradation. The generated sulfate radical (SO4•−) and hydroxyl radical (HO•) were primarily responsible for ACP degradation. DFT-based first-principle calculations show the electrons transferred from sulfite to the CoS surface in heterogeneous activation. The pathway of ACP degradation was determined to primarily comprise addition and substitution reactions based on the detected intermediates. Besides, the CoS/S(IV) system demonstrated good reusability and was successful in degrading the other five organics: bisphenol A, metoprolol, estriol, atenolol, and imipramine. The ACP removal performance under real water background was also acceptable. As a result, the CoS/S(IV) system is expected to be a reliable approach for water treatment.