Turning trash into tools: agricultural waste-derived biochars and composites for microplastic removal from wastewater

Abstract

Microplastics (MPs) have become ubiquitous pollutants in the aquatic ecosystem and pose a serious threat to environmental safety. The rising concerns about MP contamination have driven research into sustainable materials capable of removing MPs efficiently. Agricultural residues with the merits of low cost and high abundance can be transformed into renewable adsorbents, as burning them in open fields causes air pollution and soil degradation. Transforming agricultural wastes into biochars offers eco-friendly yet highly effective adsorbents owing to their high specific surface area, large pore volume, and chemically active functional moieties. This review offers a comprehensive evaluation of waste-derived biochars, focusing on biomass conversion routes and advanced surface modifications, including the fabrication of metal, magnetic, layered double hydroxide, mineral, and nanosize-based biochar composites, for efficient MP adsorption. Additionally, it examines the mechanisms underlying MP removal, evaluates the efficiency of biochars and composites, and integrates in-depth bibliometric and literature analyses to reveal key research trends, scientific impact, and existing knowledge gaps. This review reinforces global sustainability trends and circular economy principles by highlighting waste valorization and solutions for cleaner water and outlining future research directions and challenges to optimize the biochar efficiency and enhance its real-world performance in environmental remediation.