Sulfur and nitrogen co-doped magnetic biochar coupled with hydroxylamine for high-efficiency of persulfate activation and mechanism study

Biochar has recently become a central issue in advanced oxidation processes (AOPs) based on peroxydisulfate (PDS) activation. However, the PDS activation by biochar must be improved. In this study, S, N co-doped magnetic biochar (IBC) was prepared by a simple impregnation-pyrolysis method using Eichhornia crassipes stems with inherent sulfur and nitrogen as the raw materials for biochar. The reductant hydroxylamine (HA) was employed to further enhance PDS activation by the IBC for organic pollutant degradation. Incorporating HA in PDS activation over IBC significantly improved its compatibility with complex water, catalytic degradation, stability performance, and mineralization rate of organic pollutants. The outstanding performance of the HA/PDS/IBC system for organic degradation was due to the increased free radicals SO4·-, O2·-, and non-radical 1O2 generated, as well as the electrons transferred between IBC, PDS, and organic pollutants, which were verified by electron paramagnetic resonance (EPR) detection and electrochemical characterizations. Furthermore, HA-enhanced Fe(III)/Fe(II) cycling, surface functional groups, and S and N doping contributed to the generation of reactive oxygen species (ROS). Moreover, the toxicity assessment indicated that the toxicity of the degradation intermediates decreased. Therefore, this research proposes a new insight into the enhanced degradation of pollutants by increasing PDS activation using biochar-based catalytic materials.