Pivotal Contribute of EPR‐Characterized Persistent Free Radicals in the Methylene Blue Removal by a Bamboo‐Based Biochar‐Packed Column Flow System

Abstract

Water remediation with biomass derivatives has attracted attention for its sustainable impact on the earth. Chemical procedures for new adsorbent and active biomaterials must be implemented to remove organic pollutants more efficiently.Herein, we obtained a sustainable, environmentally, and low‐cost biochar from bamboo Dendrocalamus giganteus (BBC, B400) by thermal treatment at 400 °C without physical and chemical pre‐ and post‐treatments. By electron paramagnetic resonance (EPR), we determined the quantification and ageing of persistent free radicals (PFRs) present in BBC over time. The removal efficiency (R%) of B400 against methylene blue (MB) solutions without and with different concentrations of H2O2 was demonstrated using a novel B400‐packed column‐flow system. MB removal efficiency via physical adsorption and chemical degradation strongly depended on the concentration of carbon‐centred PFRs and their stability over time. Collectively, a reduced concentration of PFRs and their full passivation by proper treatments led to a remarkable loss of MB removal efficiency, thus evidencing that a PFR‐mediated radical degradation mechanism was predominant in the MB removal process. Kinetics studies established that MB removal was best described by a pseudo‐second‐order kinetic model, thus suggesting that chemical mechanisms such as electron transfer reactions and PFRs‐mediated degradation were the main contributors to MB removal.