Boron-Doped Diamond for Hydroxyl Radical and Sulfate Radical Anion Electrogeneration, Transformation, and Voltage-Free Sustainable Oxidation.

Boron-doped diamond-based electrochemical advanced oxidation processes (BDD-EAOPs) have attracted much attention. However, few systematic studies concerning the radical mechanism in BDD-EAOPs have been published. In situ electron paramagnetic resonance spectrometry is used to confirm that SO4 •- is directly electrogenerated from SO4 2- . Then, excess SO4 •- dimerizes to form S2 O8 2- and accumulates in the BDD-EAOP system. But no S2 O8 2- accumulates at pH = 10 owing to the rapid transformation of SO4 •- and S2 O8 2- . Above the overpotential of water oxidation, • OH is electrogenerated and cooperated with SO4 •- . In the power-off phase, the accumulated S2 O8 2- can be reactivated to SO4 •- via specific degradation intermediates to achieve sustainable degradation. Di-n-butyl phthalate (DnBP), a typical endocrine disruptor, is selected as a model contaminant. Surprisingly, 99.8% of DnBP (initial concentration of 1 mg L-1 ) is removed, using an intermittent power supply strategy with a periodic 10 min power-on phase at a duty ratio of 1:2, reducing the electrical energy consumption (1.8 kWh m-3 ) by more than 30% compared with continuous power supply consumption. These radical electrogeneration transformation mechanisms reveal an important new strategy for sustainable oxidation, especially for in situ water restoration, and are expected to provide a theoretical basis for BDD applications.