Sustainable impact of tartaric acid as electron shuttle on hierarchical iron-incorporated biochar

Metal-biochar composite is considered as a promising alternative for future carbocatalysis in environmental decontamination. Nevertheless, unavoidable metal leaching impedes its scaling-up application and remains an environmental concern in the present scientific progress. Herein, a hierarchical Fe biochar (Fe/CBC) derived from cellulose was fabricated via a hydrothermal carbonization coupled with microwave irradiation and NH₃ activation. Several exterior organic electron shuttles (i.e., ascorbic acid, oxalic acid, tartaric acid, and hydroquinone) were accommodated onto Fe/CBC to introduce more electroactive functionalities (i.e., C–O and C = O). In particular, comprehensive material characterization was performed to elaborate the physicochemical properties of tartaric acid-treated biochar catalyst (Fe/CBC-TA). Synergies of inherent hierarchical structure, well-developed carbon π-electron network, and accommodated electron shuttle could mitigate the Fe leaching from 2.44 to 0.578 mg L⁻¹ in the peroxymonosulfate (PMS) activation system for catalytic degradation of bisphenol A. Based on the results of scavenging experiments and electron paramagnetic resonance (EPR) analysis, the catalytic mechanisms transformed from a one-phase pathway (mainly ^•OH) for the Fe/CBC system to a two-phase pathway (first phase: ¹O₂; second phase: ^•OH) for the Fe/CBC-TA system. The increased activation energy and improved catalyst recyclability of the Fe/CBC-TA in the redox reaction further pinpointed its environmental sustainability. Overall, this work offers new strategies to fabricate efficient metal-biochar catalyst and insights into its sustainable electrocatalysis.