A Comprehensive Evaluation of Adsorption Techniques for Dye Elimination in Wastewater: From Conventional Adsorbents to Nanotechnology

The continuous discharge of hazardous synthetic dyes into aquatic environments as a result of rapid industrialization poses a serious threat to both environmental and human health. This review aims to provide a comprehensive and up to date evaluation of adsorption techniques for dye removal from wastewater, with a focus on both conventional and emerging adsorbent materials. The review examines and compares natural materials, such as clays, zeolites, charcoal, and agricultural wastes, as well as engineered and nano scale materials, including carbon nanotubes, graphene, metal organic frameworks, and nanocomposites, for wastewater decolorization. This study presents a critical analysis of published studies from 2018 to 2025, focusing on the performance of various adsorbents under key operational parameters such as pH, temperature, contact time, and adsorbent dosage. The dominant adsorption mechanisms, including electrostatic attraction, ion exchange, and surface complexation, are systematically discussed. Special attention is given to the role of nanotechnology and green synthesis strategies in improving adsorption efficiency and material reusability. The review indicates that nano engineered and hybrid adsorbents generally exhibit superior adsorption performance and represent promising candidates for scalable and environmentally sustainable wastewater treatment applications. Future research should prioritize the development of cost-effective regeneration methods, evaluation using real industrial effluents, and pilot scale studies to facilitate the transition from laboratory research to industrial implementation.