Recent advances in metal-modified biochar fabrication: From conventional methods to integrated co-pyrolysis for environmental applications

Abstract

Biochar has emerged as a promising sustainable material for environmental pollution control. However, the limitations of pristine biochar have prompted numerous studies focusing on modifying its physicochemical properties. Incorporating transition metals to produce metal-modified biochar (MBC) has gained increasing attention because of its tunable surface chemistry, enhanced adsorption capacity, and catalytic functionality. Various fabrication strategies, including impregnation-pyrolysis, co-precipitation, hydrothermal carbonization, and co-pyrolysis, have been widely explored to tailor the physicochemical properties of MBC. However, previous reviews have largely focused on individual preparation methods or specific applications, providing limited integration of synthesis routes, material structures, and functional performance. In this review, a unified method-structure-function framework is established to how fabrication strategies influence the structural characteristics and functional performance of MBC. The four major preparation methods are comparatively analyzed to highlight their distinct influences on metal dispersion, pore development, surface functionality, and catalytic activity. Particular emphasis is placed on co-pyrolysis as an integrated route that enables in situ metal anchoring and enhanced carbon-metal coupling, thereby improving structural uniformity and functional efficiency. Furthermore, this review systematically analyzes the key factors governing adsorption and catalytic mechanisms, including metal-carbon interactions, redox processes, and electron transfer pathways. The implications of these structure-function relationships are evaluated in the context of environmental applications such as pollutant adsorption, catalytic degradation, and soil remediation. Finally, remaining challenges and future perspectives are discussed to guide the rational design and scalable development of high-performance MBC materials.