Nanocomposite Adsorbents for Heavy Metal and Dye Removal: Performance, Mechanisms, and Regeneration Challenges

ABSTRACT Rapid industrialization and urban expansion have intensified the discharge of toxic heavy metals and persistent synthetic dyes into aquatic systems, posing severe ecological and human health risks. Conventional remediation technologies, while effective at high contaminant concentrations, often suffer from sludge generation, limited selectivity, and high operational costs. This review critically examines recent advances in nanocomposite adsorbents as next‐generation materials for sustainable wastewater treatment. Emphasis is placed on carbon‐based nanomaterials (graphene derivatives, carbon nanotubes, nano‐activated carbon), metal–organic frameworks (MOFs), polymer‐based nanocomposites, layered double hydroxides, molecularly imprinted polymers (MIPs), and zeolite‐based hybrids. They exhibit desirable physicochemical properties including ultrahigh specific surface areas (> 500 m 2 g −1 ), finely tuned pore structures, and tailored functional groups (–NH2, –SH, –COOH), that lead to exceptionally high adsorption capacities (generally > 500–1000 mg g ‐1 ) for Pb2 + , Cd2 + , Cr(VI), As(V), and dyes (methylene blue, Congo red). The adsorption mechanisms encompassing electrostatic attraction, surface complexation, ion exchange, π–π interactions, redox reactions, and size‐selective confinement are well interpreted by Langmuir/Freundlich isotherms and pseudo‐second‐order kinetic models. Efficient regeneration techniques involving chemical elution, thermal treatment, magnetic separation, and electro‐assisted desorption allow 5–15 reuse cycles with > 85%–99% capacity retention. Notwithstanding, these nanoadsorbents face nanoparticle release, energy‐intensive synthesis, environmental impacts of lifecycle, and lack of stringent regulations. Future directions should focus on green nanomaterial synthesis, multifunctional nanocomposites, holistic regeneration systems, and pilot‐scale applications for cost‐effective and environmentally friendly nanomaterial‐enabled water purification.