Degradation of atrazine by persulfate activation with copper sulfide (CuS): Kinetics study, degradation pathways and mechanism

In this study, copper sulfide (CuS) was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. A new method called one-eight-lives was proposed to investigate the kinetic parameters (i.e., atrazine concentration, CuS dosage, PS dosage). The t1/8 was calculated to analyze ATZ decay and degradation rate of ATZ, which could be expressed by the kinetic rate equation: −d[ATZ]/dt = (2.985 × 10−4 mmol L−1 min−1) [ATZ]0.023[PS]0.76318[CuS]0.80801. Besides, effects of the initial solution pH and the coexisting inorganic anions (i.e., nitrate ions (NO32−), chloride ions (Cl−), bicarbonate (HCO3−) and phosphate (HPO42−)) on ATZ degradation were also evaluated during the experiments. Also, the intermediate products were identified by ultrahigh performance liquid chromatograph-mass spectrometry (UPLC-MS). Based on the detected intermediates, possible reaction pathways were proposed. The stability and reusability of the CuS was investigated after three consecutive experiments. Characteristics of the fresh and used CuS were analyzed via SEM, EDS, XRD and XPS techniques. Furthermore, the different systems were set up to investigate the performance of CuS under the same experimental conditions. In addition, the radical scavengers (e.g., methanol, tert-butyl alcohol and phenol) experiences and PS decomposition study revealed that PS activation process occurred on the surface of CuS, and sulfate and hydroxyl radicals were the dominant active species for the ATZ degradation. The generation of sulfate and hydroxyl radicals was further confirmed by electron spin resonance (ESR). Besides, the generation of HO during the reaction process in CuS/PS system was quantified indirectly by HPLC. Finally, the possible reaction mechanism of CuS/PS system was proposed according to the comprehensive analysis. The findings of this study provided useful information for the application of CuS in recalcitrant organic contaminants degradation.