Component-specific biochar from biomass fractions regulates radical/non-radical pathway selectivity for organic degradation

Abstract

The complex and disordered structure of biochar hinders further exploration and comprehension of its catalytic mechanism and degradation pathway. Herein, the prepared deep eutectic solvents (DESs) were employed to achieve fine fractionation of biomass, and the corresponding biochar catalysts—lignin-derived biochar (HLBC), residue-derived biochar (HRBC), and pristine biochar (HBC) from walnut shells—were manufactured based on a biomass fractionation-guided strategy to explore their catalytic performance. The experimental results showed that the efficiency and pathway of biochar/PDS for tetracycline hydrochloride (TCH) degradation were determined by the biochar microstructure, which stemmed from the components of biomass. Specifically, the graphitic-like basal planes of HLBC, assembled with surface vacancy-type defects, were likely to inspire catalytic behavior completely mediated by the electron transfer process (ETP). By combining the correlations between PDS consumption and k_obs in the quenching and delayed addition experiments at different pH levels, we modified the contribution of different pathways to the catalytic degradation of TCH by the three biochar catalysts. In this context, ETP absolutely dominated the degradation pathway in the HLBC/PDS system, while the radical-mediated pathway had a competitive advantage in HBC performance. Electrochemical tests demonstrated that the potential of biochar-PDS* was the decisive factor for ETP initiation and determined its catalytic efficiency and selectivity. Our work reinforces the underlying insight of two principle degradation pathways dependent on the structure of biomass components, offering a new avenue for guiding the optimization of functional biochar and the adjustment of catalytic pathways.