Modified biochar for remediation of potentially toxic elements in soils: a systematic review of modification approaches, novel mechanisms and field-scale applications

Modified biochar based remediation has emerged as a promising strategy for addressing potentially toxic elements (PTE) in soils, owing to its diverse physicochemical properties and environmental compatibility. Most prior reviews focus on pristine biochar for wastewater treatment, overlooking the enhanced potential of modified biochars in soil based PTE remediation. This review establishes a clear linkage between the pristine biochar modification methods to surface chemistry changes and novel immobilization mechanisms, while also evaluating field applicability and long-term risks. A bibliometric analysis of 1170 publications from 2010 to 2024 was conducted to map international collaborations, thematic evolution, and knowledge hotspots. Results showed that research themes clustered around bioremediation processes, metal adsorption/immobilization mechanisms, and biochar based pollution control. The analysis revealed a shift from foundational studies to application-driven research, with a surge in interest toward modified biochars and complex contaminant interactions after 2021. Biochar production parameters and post-synthesis modifications critically shape its functional properties, which in turn govern key immobilization mechanisms. However, field efficacy of modified biochar is influenced by environmental factors. Additionally, aging processes and potential metal remobilization pose long-term sustainability concerns. Modified biochars offer a context-dependent but promising tool for sustainable soil remediation, contingent on addressing their environmental trade-offs and implementation challenges.