Manufacturing 3D nano-porous architecture for boron-doped diamond film to efficient abatement of organic pollutant: Synergistic effect of hydroxyl radical and sulfate radical

Abstract

Electrochemical advanced oxidation process (EAOP) has caught increasing attention in purification of organic wastewater. However, its degradation performance is chiefly relevant to electrode micro-structure and radical species. Herein, the three-dimensional (3D) nano-porous boron-doped diamond (BDD) film with controllable nano-pore size is tailored for enhancing the production of hydroxyl radical (•OH) and activating sulfate to sulfate radical (SO4•-) in EAOP. The nano-porous BDD film favors interconnected porous structure, channel-like pores with size ranged from 10 nm to 1 μm, highly improved electron-transfer rate and large oxygen evolution potential (>2.0 V). It is effective for elimination of p-nitrophenol (PNP) with pseudo first-order kinetics rate of 1.14 × 10-2 min−1 and remove rate of 92.43 % after 180 min. The indirect oxidation is the dominant mechanism of PNP degradation. Benefited from enhanced active surface area and fast mass diffusion based on 3D interconnected porous channel, the generation of •OH increases from 1.41 mM to 2.20 mM after 180 min, which not only eliminates polymer intermediate, but also signally stimulates the degradation efficiency. Additionally, SO4•- is produced by activation of sulfate on the nano-porous BDD film, resulting in the 79.58 % of remove rate of chemical oxygen demand in Na2SO4 which is higher than that in NaNO3 (55.20 %). Oxidation of PNP with radical quenchers is conducted and PNP remove rate slightly decreases with addition of ethanol compared to that in presence of tert-butanol, indicating both •OH and SO4•- contribute to the oxidation of PNP but •OH is more important. Based on intermediate characterization, it’s found that detachment of nitro, abstraction of hydrogen atom, cleavage of aromatic ring and decarboxylation reactions rapidly occur and effectively accelerate the mineralization of organic pollutant. This study enriches the EAOP application of nano-grade porous BDD film and broadens the aspect of designing porous electrode in the environment fields.