Insights into the nonradical degradation mechanisms of antibiotics in persulfate activation by tourmaline

Abstract A natural mineral tourmaline (TM) was used to activate persulfate (PS) for sulfamethazine (SMT) removal. No adsorption of SMT by TM was observed and the SMT removal by PS alone was only 10%. The TM/PS system presented a 97.8% SMT removal in 150 min with a reaction rate constant (k) of 0.026 min-1 at [SMT]0 = 5 mg/L, [PS]0 = 4 mM, [TM]0 = 5 g/L, T = 25 °C, and pH = 5. High removal efficiency was achieved in a wide pH range (2-10) with the highest k (0.0423 min-1) obtained at initial pH 2 and similar ks (0.0252 min-1, 0.0261 min-1 and 0.0225 min-1) obtained at pH 5, 7 and 10. SMT removal could still reach over 80% at the fifth reuse of TM. The radical quenching experiments verified that 1O2 and holes rather than ⋅OH and SO4⋅- were the main reactive species for SMT degradation. Electron paramagnetic resonance spectroscopy was used to confirm the generation of 1O2. Electrochemical measurements indicated that the charge transfer rate and the electron-hole separation efficiency on the surface of TM were effectively improved in the presence of PS. The activation of PS by TM as a cheap and effective catalyst presented a promising method for contaminant removal, which could avoid the water matrix interference.