Synergistic activation of sulfate by TiO2 nanotube arrays-based electrodes for berberine degradation: Insight into pH-dependant ORR-strengthened reactive radicals co-generation mechanism

An anodic oxidation-cathodic ORR coupling system originated from TiO2 nanotube array (TNAs)-based electrodes was established. We first thoroughly investigated the effects of cell voltage, electrolyte type and pH on anodic reactive radicals co-generation and cathodic ORR pathway in the divided cells. Based on the results of anodic and cathodic half-reactions, the strengthening effect of the pH-dependant ORR process on the synergistic sulfate activation and reactive radicals co-generation mechanism were systematically elucidated in the undivided cells, by means of berberine degradation/mineralization degree and kinetics, electron spin resonance, radical quenching and energy consumption estimation. The real service lifetime of blue TNAs anode was evaluated, and the possible degradation pathways of berberine was also proposed. This pH-dependent ORR-strengthened synergistic sulfate activation system provide a multi-radical joint-attack mechanism for the pre-treatment or pointsource-treatment of sulfate-containing refractory organics wastewater.