Sequential surface functionalization of multiwalled carbon nanotubes for enhanced cadmium ion sequestration from aqueous environments

Heavy metal contamination in aqueous environments poses severe ecological and human health risks necessitating the development of highly efficient remediation technologies. This study aims to synthesize and evaluate novel surface modified carbon nanotube derivatives as advanced adsorbents for the highly effective removal of Cd 2+ ions from water. Pristine multi walled carbon nanotubes were chemically oxidized and sequentially functionalized via divergent pathways to graft 3-mercaptopropyl trimethoxysilane and poly acrylic acid yielding two distinct functionalized nanocomposites. The synthesized materials were comprehensively characterized to confirm structural integrity and functionalization success. Systematic batch adsorption experiments were conducted to evaluate the effects of initial concentration and temperature on adsorption performance optimize colloidal dispersion. Characterization confirmed the successful covalent attachment of thiol silane groups and polymer chains onto the oxidized carbon framework providing dense active sites. The functionalized nanotubes demonstrated significantly enhanced colloidal stability and superior affinity for Cd 2+ compared to bare oxidized variants. Isotherm modeling revealed that the adsorption data perfectly fit the Langmuir model. The maximum adsorption capacities achieved were remarkable reaching approximately 304.3 mg/g and 288.7 mg/g for the silane and polymer modified carbon nanotubes respectively. Thermodynamic analyses demonstrated that the metal sequestration is an exothermic process with the functionalized adsorbents maintaining robust structural integrity and binding performance even under elevated thermal conditions. In conclusion surface engineered carbon nanotubes featuring targeted chemical moieties serve as highly efficient thermally resilient chelating agents for targeted heavy metal remediation.