Adsorption and degradation of sulfadiazine over nanoscale zero-valent iron encapsulated in three-dimensional graphene network through oxygen-driven heterogeneous Fenton-like reactions

[Display omitted] •3D-GN@nZVI activates DO to trigger the Fenton-like reaction.•Micro-electrolysis formed between nZVI and graphene enhances electron transfer.•nZVI acts as the adsorption site and electron donator.•The adsorption and oxidation mechanisms are originally proposed.•New insights advance the DO-driven Fenton-like process. Fe-based heterogeneous Fenton-like catalysts has shown tremendous potential for wastewater treatment, but the investigation of adsorption, reduction and oxidation mechanism remains challenging. In this study, nanoscale zero-valent iron encapsulated in three-dimensional graphene network (3D-GN@nZVI) was synthesized and characterized as a heterogeneous Fenton-like catalyst via the activation of dissolved oxygen (DO) for adsorption and degradation of sulfadiazine (SDZ). 3D-GN@nZVI had the synergistic effect of catalytic reactivity for sulfadiazine removal, which was evaluated in view of the effects of operational factors. The role of adsorption, reduction and oxidation was determined; in 3D-GN@nZVI/DO system, sulfadiazine was removed mainly by the attack of hydroxyl radicals (OH). The possible degradation pathway of sulfadiazine was inferred by identifying reactive oxidizing species and degradation intermediates. According to the X-ray photoelectron spectroscopy (XPS) analysis, Fourier Transform infrared spectroscopy (FTIR) analysis and density functional theory (DFT) calculations, the distribution and transfer of electrons on the surface of 3D-GN@nZVI were illustrated, and the adsorption and oxidation mechanisms of sulfadiazine through DO-driven and micro-electrolysis-enhanced heterogeneous Fenton-like reaction were proposed. The comprehensive mechanism was elucidated to provide new insights to advance the DO-driven Fenton-like process and to inspire the development of nZVI and relevant composites.