Lignin-driven valorization of lignocellulosic biomass to functional biochar for advanced wastewater remediation: A...

The escalating global challenges of waste accumulation and water pollution demand sustainable solutions aligned with the United Nations Sustainable Development Goals (SDGs). This review emphasizes biochar as the central functional material derived from lignocellulosic biomass and its macromolecular precursors cellulose, hemicellulose, and lignin. Unlike traditional remediation methods that fail to remove low-concentration contaminants and risk secondary pollution, biochar uniquely integrates the inherent structural and chemical features of its precursors to deliver multifunctionality. Cellulose contributes hydroxyl-rich frameworks for hydrogen bonding, hemicellulose introduces carboxyl/acetyl groups for ion exchange, and lignin provides aromaticity and redox-active moieties for catalytic transformation. Through thermochemical conversions (pyrolysis, hydrothermal carbonization) and precursor-specific modifications (e.g., nanocellulose templating, lignin-mediated nanoparticle stabilization), these features are translated into biochar's high porosity, tailored surface chemistry, and catalytic activity. Such engineered biochar nanohybrids consistently achieve >90 % removal of heavy metals (Pb²⁺, Cd²⁺), dyes (methylene blue), pharmaceuticals, and microplastics. Emerging applications including 3D-printed cellulose scaffolds, lignin-biochar composites, and hemicellulose-functionalized hydrogels showcase biochar's scalability in industrial effluent treatment. Nonetheless, challenges persist, such as the recalcitrance of lignin to large-scale utilization, instability of hemicellulose-derived structures, and regulatory barriers. By explicitly connecting precursor functionality to final biochar performance, this review provides a coherent blueprint for engineering next-generation biochar composites that synergize adsorption, catalysis, and hybridization, ultimately advancing both environmental sustainability and industrial scalability.