Iron/nitrogen/sulfur co-doped cyanobacteria derived carbon composites for enhanced hydroxychloroquine degradation via primary nonradical pathway in peroxymonosulfate-based fenton-like system

Abstract

A green and efficient Fe/N/S co-doped carbon catalysts (ITC-X-800) was successfully prepared from Fe/N-rich salvaged cyanobacteria and thiourea for catalyzing peroxymonosulfate (PMS) to degradate hydroxychloroquine (HCQ). Characterization tests confirmed that defect degree, electron transfer capability, and the content of main functional groups like π-π*, Fe-N_X, graphitic N and thiophene S etc. in ITC-X-800 was firstly increased and then decreased with the increasing doping S, indicating the critical role of S for regulating functional sites containing Fe/N on the carbon nanosheets. Optimized ITC-2-800 with appropriate S showed suitable HCQ adsorption ability, lowest resistance and more PMS activation sites. Almost 100% of HCQ could be removed via ITC-2-800/PMS system in 60 min within 0.5 mM PMS and 0.1 g/L ITC-2-800, whose HCQ degradation kinetic constant was 2.5 times that of Fe/N doped carbon catalyst. Based on the basic strong electron transfer ability and HCQ adsorption affinity of π-π*, the high PMS adsorption and catalyzing capacity of Fe-N_X, and the extra enhanced carbon skeleton activation of thiophene S, the synergistic effect of these groups in ITC-2-800 was proved to play a more important role in enhanced PMS activation and HCQ degradation. Ascribed to the synergistic effect of Fe/N/S, non-radical pathway based on ¹O₂ and high-valent iron-oxo species played a dominant role in HCQ degradation. Furthermore, ITC-2-800 showed high universality, stability, reusability and potential practicability during comprehensive test. This study provided deeper insights for the resourceful treatment of algae mud and the synergistic mechanism of heteroatoms in carbon-based catalysts for PMS activation.