Comparison of Four Tourmalines for PS Activation to Degrade Sulfamethazine: Efficiency, Kinetics and Mechanisms

Abstract

Four types of tourmalines (TMs, S1, S2, S3 and S4) for activating persulfate (PS) to degrade sulfamethazine (SMT) were compared to find the most efficient catalyst. The four TMs were mesoporous materials with abundant functional groups, but were different in terms of size, composition, specific surface area, contact angle, and zero potential point. The removal of SMT in S1, S2, S3 and S4 systems with PS at the optimum reaction conditions ([SMT]0 = 5 mg/L, [PS]0 = 4 mM, [TM]0 = 5 g/L, pH0 = 5, and T = 25 °C) were 99.0%, 25.5%, 26.0%, and 51.0%, respectively, which might be related to the metal content of TM. Although the degradation of SMT in the S1/PS/SMT system was not dominated by SO4•− and •OH, the radicals contributed to the SMT removal in the S2, S3, and S4 systems. 1O2 and holes both contributed to the degradation of SMT in the four systems. The metal at the X position might be related to the generation of 1O2 and holes, while Fe of TM was mainly related to the generation of free radicals, such as SO4•−. Electrochemical impedance spectroscopy tests confirmed that the separation of electrons and holes on the TM surface could be promoted by adding PS and SMT. S1 presented a higher electron-transfer rate than the other three TMs. The PS activation by TM with a high metal content at the X position provided an efficient and low-consumption treatment for antibiotic refractory wastewater.