Advances in biochar modification for environmental remediation with emphasis on iron functionalization
Yue Zhang, Hao Chen, Shahidul Islam
Abstract
Biochar, a porous carbonaceous material produced from biomass pyrolysis under limited oxygen, has emerged as a promising material for environmental remediation due to its stability, adsorption capacity, and potential for carbon sequestration. Though raw or unmodified biochar often exhibits limited surface functionality, low surface area, and poor affinity for specific contaminants, its effectiveness in practical applications is restricted. Various modification techniques have been developed to address these limitations, including physical activation, chemical functionalization, and surface doping with metals. Among these, iron-modified biochar (Fe-BC) has attracted considerable attention due to the unique redox properties of iron and its strong binding affinity for anions and organic pollutants. Fe-BC is typically synthesized through impregnation, co-pyrolysis with iron salts, or post-pyrolysis treatment. These modifications enhance the surface area and porosity and introduce reactive sites that significantly improve the sorption of phosphate, arsenic, heavy metals, and dyes from wastewater, as well as facilitate catalytic reactions such as Fenton-like oxidation. Recent studies have demonstrated the multifunctionality of Fe-BC in wastewater treatment and soil remediation, as well as in agriculture as a slow-release nutrient carrier. Moreover, novel synthesis approaches using green chemistry principles and low-cost iron precursors have made Fe-BC more sustainable and scalable. Despite its potential, challenges remain regarding the long-term stability of leaching iron, regeneration, and environmental risks. This review provides a comprehensive analysis of current modification strategies for biochar with a focused evaluation of Fe-BC, including synthesis methods, physicochemical properties, contaminant removal mechanisms, and practical applications. Future perspectives are discussed to guide research toward optimizing Fe-BC for the circular economy and sustainable environmental technologies.