Exploring electron-transfer pathways in co-pyrolyzed waste-derived carbocatalyst for enhanced peroxydisulfate activation

Heterogeneous catalyst-activated peroxydisulfate (PDS) process has great potential in environmental remediation, but its complex preparation process, high cost, low efficiency, and unclear mechanism hinder its practical application. To overcome these limitations, we introduced an innovative metal-free biochar catalyst (SCSS-NC) derived from waste biomass through co-pyrolysis of shrimp shell and sludge with nitrogen doping. This catalyst improved its performance, achieving 78.45 % degradation of tetracycline, outperforming sludge carbon/PDS systems (46.89 %) and shell carbon/PDS systems (22 %) under the dosage of PDS (0.5 mM) and catalysts (0.5 g/L) within 60 min. This improvement stems from its increased surface area, porosity, and electron transport capabilities. Quenching experiments, delayed contaminant addition experiments, and EPR results demonstrated that the SCSS-NC/PDS system relies on electron transfer, in which activated PDS binds to the catalyst surface, forming a highly reactive composite [SCSS-NC/PDS]* to degrade pollutants. The open-circuit potential and linear scanning voltammetry results confirm the existence of an electron transfer pathway, while the situ Raman spectroscopy results validate the presence of the composite [SCSS-NC/PDS]*. The DFT theoretical calculations provide further confirmation of the conductivity, low energy barrier, and ability to expedite electron transfer exhibited by SCSS-NC. The catalyst performance and characterization before, after, and post-recovery from the reaction pinpoint key active sites: pore adsorption, sp2 graphitic carbon, and graphitic nitrogen doping sites. The SCSS-NC/PDS system demonstrates robust anti-interference capability, suggesting its potential for practical organic wastewater treatment. This study provides novel insights into economical carbocatalyst and their mechanisms for environmental applications.