Biochar co-modification by magnetization and mineral impregnation: a step towards improved agri-environmental applications

Abstract Biochar has emerged as an environmentally sustainable material for addressing agri-environmental issues owing to its porous structure, versatile surface chemistry, and stability. While pristine biochars have demonstrated effectiveness in various applications, ranging from agricultural soil enhancement to contaminant immobilization, their performance is often constrained by insufficient reactivity and limited selectivity. This review begins by outlining the biochar production process, emphasizing how key factors influence its physicochemical properties and overall performance. A major barrier to practical deployment is the difficulty of recovering fine biochar particles from treated media, often requiring energy-intensive methods, which limits the scalability for agri-environmental applications. To overcome these constraints, the review explores various biochar modification methods, focusing on magnetization and mineral impregnation techniques. As such, magnetic biochars (MBCs) not only retain the adsorptive benefits of carbonaceous materials but also enable facile recovery via external magnetic fields, addressing a major obstacle in post-treatment separation. In addition, the mineral doping of MBCs further enhances surface functionality and reactivity, improving removal efficiencies for a wide spectrum of pollutants. This review critically explores the synthesis routes, structural characteristics, and functional performance of magnetized and mineral-enriched biochars, with an emphasis on their applications in environmental remediation and soil enrichment. Mechanistic insights into adsorption pathways including pore-filling, electrostatic binding, and surface complexation are detailed, along with emerging approaches involving light-assisted degradation pathways. By synthesizing laboratory findings and field-scale observations, this review identifies current improvements and limitations, and outlines key directions for future research toward the practical and scalable use of engineered biochars for more sustainable agri-environmental applications. Graphical Abstract