An In-Depth Review of Chemically Modified Agricultural Waste Materials for Dye Adsorption

Dye pollution from industrial effluents poses significant environmental and health challenges due to the toxicity and persistence of synthetic dyes. Agricultural waste materials offer a sustainable and cost-effective alternative for dye removal through adsorption, owing to their natural abundance and rich composition of cellulose, lignin, and functional groups. However, raw agricultural wastes often exhibit limited adsorption capacity, necessitating chemical modification techniques such as acid and alkali treatment, impregnation with functional agents, and carbonization to enhance surface area, porosity, and active sites. This review critically examines the types of agricultural wastes used as adsorbents, their chemical modification methods, adsorption mechanisms, and models governing performance. It further discusses operational parameters influencing adsorption efficacy, comparative adsorption capacities, and environmental sustainability considerations. Despite promising laboratory-scale results, challenges remain in scaling up, regeneration, and multi-dye system selectivity. Future research directions emphasize the development of eco-friendly modification techniques, comprehensive life cycle assessments, and the integration of these materials into circular economy frameworks for sustainable wastewater treatment.