Natural coal gangue activated persulfate for tetracycline hydrochloride degradation: Mechanisms, theoretical calculations, and comparative study

The development of catalysts with low-cost and high-efficiency for advanced oxidation process is the key issue to remove organic pollutants. In this work, natural coal gangue (CG) was used to activate potassium monopersulfate (PMS) for the removal of tetracycline hydrochloride (TC). For comparison, sodium persulfate (PS), potassium persulfate (PDS), and hydrogen peroxide (H2O2) were also activated by CG to remove TC. The active species in the TC degradation processes in PMS/CG, PS/CG, PDS/CG, and H2O2/CG systems were investigated by capture experiments and electron spin resonance (ESR) tests. DFT calculation indicated that PMS was more easily adsorbed by CG in comparison with PS, PDS, and H2O2. In addition, Fukui function was adopted to determine how electrophilic, nucleophilic and free-radical attacks occurred on sites of TC molecules in detail. Mechanism investigation showed that the surface-bonded and structural hydroxyl groups of natural CG were favorable for the adsorption of PMS molecules onto the CG surface and thus facilitated the generation of active species, which were crucial in the TC degradation process. This paper sheds new light for natural minerals or solid wastes to participate in advanced oxidation process (AOPs) for wastewater treatment.