Recent advances in lignin-based carbon materials for pollutant removal and oil–water separation: a review

Abstract

The rapid escalation of water pollution from industrial effluents, oil spills, and emerging contaminants has created an urgent need for sustainable, high-performance remediation materials. Although surface water covers nearly 71% of the Earth's surface, only about 2.5% constitutes freshwater, and less than 1.2% is readily accessible for human use. Moreover, over 113 billion m³ of untreated wastewater is discharged annually into natural water bodies, further exacerbating global water scarcity and pollution. Lignin accounts for 15–30% of lignocellulosic biomass and contributes more than 60% of its carbon content. It has emerged as a promising precursor for advanced carbon materials. Globally, over 100 million tonnes of lignin are generated annually by the pulp and paper industry, yet 98% is still underutilised or combusted for low-value energy recovery. This review critically summarises recent advances in the conversion of lignin into porous, heteroatom-doped carbon materials via thermochemical routes, including pyrolysis, hydrothermal carbonisation, and chemical activation. Lignin-derived carbons exhibit exceptionally higher surface areas (1700–2285 m² g⁻¹), tunable pore structures, and rich surface functionalities, enabling efficient removal of heavy metals, dyes, pharmaceuticals, and oils. Furthermore, the adsorption capacities exceed 300 mg g⁻¹ for organic pollutants, while lignin-based foams, aerogels, and sponges demonstrate oil absorption efficiencies greater than 20–40 g g⁻¹ with excellent recyclability. Key adsorption mechanisms, including electrostatic attraction, π–π interactions, surface complexation, and pore filling, are systematically discussed. Furthermore, current challenges related to scalability, regeneration, and process economics are highlighted. Overall, lignin-derived carbon materials offer a low-cost, sustainable, and scalable solution for advanced wastewater treatment and oil−water separation, aligning closely with the principles of the circular bioeconomy and UN Sustainable Development Goals (SDGs 6, 12, and 13).