Activation of peroxymonosulfate by magnesium−modified biochar for the degradation of imidacloprid: Effectiveness and mechanisms

The increasing environmental contamination by imidacloprid (IMI), a widely used neonicotinoid pesticides, has raised significant concern. While peroxymonosulfate (PMS) oxidation has shown great promise for removing such toxic organic compounds due to its high efficiency, the potential secondary pollution caused by toxic metal leaching from transition metal–based catalysts remains a critical challenge. To address this issue, we developed an environmentally friendly magnesium–modified biochar (WHMBC600) using water hyacinth as a carbon source and MgCl₂ as a modifier. The synthesized WHMBC600 exhibited excellent physicochemical properties, including substantial pore volume, high specific surface area, and abundant surface hydroxyl groups (Metal–OH), which collectively functioned as active sites for PMS activation. The WHMBC600/PMS system achieved 91.7 % removal of IMI within 60 min, demonstrating remarkable degradation efficiency. Comprehensive characterization, including DFT calculations, in situ Raman spectroscopy, and other analytical techniques revealed that magnesium modification significantly enhanced the electron transfer capacity and PMS adsorption capability of the WHMBC600 catalyst. These finding confirm that the metal–OH groups serve as the key active site for activating PMS to produce reactive oxygen species (ROS). Electron paramagnetic resonance (EPR) analysis combined with quenching experiments identified ·OH_, ¹O₂, and O₂^•– as the predominant ROS responsible for IMI degradation, with intermediate products clearly determined. This study not only provides an effective strategy for water hyacinth waste utilization but also establishes Mg–modified biochar as a sustainable, environmentally friendly, and efficient catalyst for water and wastewater treatment.