Phenolic-rich biomass-derived biochar as a low-cost alternative to activated carbon for cadmium stabilization in paddy soils

• Camphor leaf-derived sorbents outperformed corncob sorbents in Cd sequestration • Leaf-derived biochar matched activated carbon in aqueous and soil Cd stabilization • Surface basicity emerged as the key factor influencing Cd adsorption efficiency • Soil incubation confirmed the same Cd retention trends observed in aqueous sorption • Porewater matrix improved Cd immobilization model accuracy over DI water matrix Developing low-cost and sustainable materials for mitigating cadmium (Cd) contamination in paddy soils is critical for protecting food safety and supporting agricultural resilience. This study presents a systematic side-by-side comparison of activated carbon (AC), biochar (BC), and hydrochar (HC) produced from two contrasting agricultural residues—phenolic-rich camphor leaves and lignocellulosic corncobs—to evaluate their capacity for Cd stabilization in aqueous systems and flooded paddy soils. Across both matrices, camphor leaf–derived BC performed comparably to AC and consistently outperformed HC and corncob-derived sorbents, demonstrating its potential as a cost-effective and locally accessible alternative for sustainable soil remediation. Integrated material characterization, adsorption kinetics, equilibrium modeling, and statistical analysis revealed that surface basicity, rather than surface area, surface acidity, or charge, was the dominant factor controlling Cd retention, consistent with specific interactions between Cd²⁺ and π-electron–rich aromatic domains. Soil microcosm experiments under anaerobic conditions further confirmed that BC and AC substantially reduced porewater Cd concentrations with minimal perturbation of soil pH. Sorption modeling based on soil porewater, rather than deionized water, markedly improved prediction accuracy, underscoring the influence of dissolved organic matter in flooded soil systems. Collectively, these results highlight phenolic-rich biomass–derived BC as a promising sorbent for stabilizing Cd in contaminated paddy soils, particularly in resource-limited regions where commercial AC access is constrained.