Mechanistic inference on the roles of oxygenic functional groups that activate peroxymonosulfates in graphene for advanced oxidation

Abstract

Developing carbon-based catalysts for advanced oxidation processes, owing to their abundant reserves, metal-free properties, superior biocompatibility as well as great resistance to acids and alkalis, presents an enticing prospect for environmental remediation. The thermally reduced graphene with diverse surface functional groups from vacuum-promoting thermal expansion of graphene oxide was fabricated by the progressive carbonization from 250 °C to 1000 °C (denoted as G250, G600, and G1000 according to temperature). Among them, G1000 possessed highest defective degrees, the largest specific surface area, and the most abundant, highly active oxygen-containing functional groups such as ketones and quinones. 0.10 g L⁻¹ of G1000 could almost completely eliminate bisphenol A (19 mg L⁻¹) within 15 min under the synergistic effect of adsorption and degradation. The structural evolution of graphene during the thermal-reduction process was systematically characterized and analyzed to understand the peroxymonosulfate-activated mechanism. The technological means included active species quenching experiments, electron paramagnetic resonance tests, and electrochemical analyses. This work presents some solid evidence to support the origin of active sites for catalytic degradation and provides new insights into the design of non-metallic catalysts in advanced oxidation processes.