Tunneling Electron-Mediated Electrochemical Activation of Peroxydisulfate for the Removal of Refractory Pollutants

Abstract

In the SO 4 •− radical-based advanced oxidation processes (AOPs), activation of peroxydisulfate (PS) is an effective method for the removal of refractory organic pollutants. Within this context, we report a novel electrochemical activation of PS (E-PS) by solvated electrons generated via the electron tunneling effect. The results demonstrated that the sulfamethoxazole (SMX) could be completely degraded (∼100% degradation efficiency) within 30 min (k = 0.0957 min −1 ) at the pH-neutral conditions when n + Si/Al 2 O 3 was employed as the cathode. Further investigations based on electron paramagnetic resonance (EPR) and scavenger tests indicated that both SO 4•− and • OH were responsible for SMX degradation. Electrochemiluminescence (ECL) and current−voltage (I−V) characterization fitted by the tunneling models revealed the dominance of the direct electron tunneling effect at negative potential on the metal oxide semiconductor (MOS)-structured n + Si/Al 2 O 3 cathode. The tunneling electrons were accepted by the lowest unoccupied orbital energy level (LUMO) of the water molecule to produce solvated electrons (e solv − ) for subsequent PS activation and SMX removal. This study represents a paradigm shift to advance the electrochemical advanced oxidation process by creating an electron tunneling effect.