Engineering biochar through surface oxygenation: a green approach for sustainable environmental applications

Hydrogen peroxide (H₂O₂) oxidation has emerged as a promising and sustainable strategy to enhance the surface chemistry and functional performance of biochar due to its environmentally friendly nature compared to other modification methods. This study systematically investigated the effect of controlled H₂O₂ oxidation (1–30%) on palm kernel shell (PKS) biochar (termed OxyAChar), evaluating its physicochemical characteristics, sorption behavior, water retention, and thermal stability. The results revealed that moderate oxidation (3% H₂O₂) produced OxyAChar-3 with the highest BET surface area (520.21 m²·g⁻¹ micropores, 360.48 m²·g⁻¹ mesopores), improved pore connectivity, and enriched oxygen-containing functional groups. These modifications significantly enhanced methylene blue sorption capacity and water retention ability biochar. The observed effects were attributed to persistent free radicals (PFRs) on the biochar surface, which catalyzed H₂O₂ decomposition into reactive •OH and •OOH radicals, promoting delignification and surface oxygenation. However, excessive oxidation (>3%) disrupted structural integrity of pores and reduced functional group density, thereby decreasing sorption and water retention efficiency of biochar. Comparative analysis with existing literature confirmed that optimal H₂O₂ concentrations are both feedstock- and pyrolysis-dependent. These insights highlight the potential of machine learning-assisted biochar design to predict ideal oxidation parameters, minimize experimental trial-and-error, and accelerate the development of high-performance, sustainable biochar materials. Overall, this study provides a mechanistic and practical framework for the rational design of surface-oxidized biochar for future applications in soil remediation, water conservation, and long-term carbon sequestration.