A comprehensive review of cadmium removal by adsorptive mechanism from wastewater using carbon-based nanotubes

Cadmium (Cd) contamination of aquatic ecosystems poses significant environmental and public health risks. Conventional wastewater treatment methods including ion exchange, coagulation, membrane filtration, chemical precipitation, and biological degradation exhibited operational limitations in Cd removal efficiency and cost-effectiveness. Consequently, adsorption-based technologies utilizing nanomaterials have gained prominence as advanced alternatives. Engineered nanomaterials, particularly metallic/metalloid oxides and carbon-based structures, offer superior Cd adsorption capabilities due to their exceptional surface area-to-volume ratios, tunable surface chemistry, and multifunctional reactivity. Among these, carbon nanotubes (CNTs), especially multi-walled variants (MWCNTs), present a cost-effective, scalable, and sustainable solution for heavy metals (HMs) remediation. This review critically evaluates the adsorption mechanisms of Cd onto MWCNTs, Synthesis and functionalization strategies to enhance adsorption capacities, and comparative efficacy of CNTs against emerging metallic oxide nanomaterials. Recent advances in nanomaterial design, including surface modification and composite synthesis, are highlighted for their role in optimizing Cd removal kinetics and selectivity. Future research directions emphasize assessing long-term ecotoxicological risks of nanomaterial deployment and developing encapsulation protocols to mitigate environmental release while advancing next-generation adsorbents.