Engineering porous biochar for capacitive fluorine removal

[Display omitted] •Porous biochar was synthesized by the control of calcination temperature.•The defluorination process on CBE followed well with the pseudo-second-order model.•Biochar electrode showed better performance than activated carbon electrode.•Regeneration process was energy recyclable and environmental-friendly.•The defluorination process on CBE was studied systematically. Chronic accumulation of fluoride (F−) threats human health and eventually brings about skeletal fluorosis, dental fluorosis and joint deformation, which has aroused global attention. As an emerging technique, electrosorption presented great potential in wastewater purification. The key role in electrosorption is the exploitation of economical, environmentally-friendly and efficient electrode material. Nowadays, many existing investigations on the preparation of porous carbon material focused on the introduction of extra dopant and activation reagent. However, the information concerning the preparation of pure porous biochar and the inherent environmental significance is neglected. Here, a win–win strategy, named conversion waste biomass into porous biochar, has been applied in capacitive fluorine removal. The results indicated that the capacity of porous biochar electrode was 1.28 mg/g, which was improved by 48.8% in contrast to activated carbon electrode. Furthermore, competition experiments revealed concentration-dependence interference in the present of foreign ions. Electrosorption cycle experiment manifested excellent stability of the biochar electrodes. The electrode was regenerated without consuming any chemicals and could produce current for energy recovery. More importantly, continuous-flow experiment showed that the removal efficiency of F− was 91.98% at the synthetic wastewater. High specific capacitance, low internal resistance and appropriate pore distribution were responsible for the F− removal mechanism. Overall, this work would pioneer a facile method in the preparation of low-price electrode material and their potential applications in environmental remediation.