Innovative experimental and theoretical strategies for sustainable heavy metal ion removal using chitosan@TiO2 composites functionalized with nanostructured metal oxides

This study presents sustainable approaches for the removal of toxic heavy metal ions from contaminated water using novel composite adsorbents based on Chitosan@TiO2@ZnO (CTZ), Chitosan@TiO2@CuO (CTC), and Chitosan@TiO2@rGO (CTG). The incorporation of metal oxides (ZnO, CuO, and rGO) into the Chitosan@TiO2 matrix aimed to enhance the adsorption efficiency, stability, and recyclability of the materials. To that purpose, an exhaustive investigation was performed to evaluate their physicochemical, morphological, electrical, and wettability properties, with an emphasis on their potential as next-generation catalyst materials. FESEM demonstrated that the CTG compounds display a well-defined porosity network with an average pore size of 1.78 µm, enabling improved surface contacts. CTG showed good electrical conductivity (17.6 S/m) and a surface roughness of 6.2 µm. The total dipole moment (TDM), HOMO-LUMO orbitals, band gaps, and the Fukui index f–j charge distribution (Mulliken and Hirshfeld) were studied using density functional theory (DFT).The adsorption capacity, kinetics, and isotherms for removing heavy metal ions—such as chromium (Cr3+), iron (Fe2+), cobalt (Co2+), nickel (Ni2+), copper (Cu2+), zinc (Zn2+), arsenic (As3+), and cadmium (Cd2+)—from aqueous solutions were evaluated. Results demonstrated that CTZ, CTC, and CTG are excellent candidates for environmental remediation due to their substantial adsorption capacities and rapid removal rates. The enhanced performance is attributed to high surface area, abundant functional groups, and strong interactions between the Chitosan matrix and the doped nanostructures. Notably, the rGO hybridization with Chitosan@TiO2 led to the largest improvement in electrical and reactivity properties, with a high TDM (23.4362 Debye) and low band gap (0.2329 eV), suggesting the CTG composite holds significant potential for environmental sensing, catalysis, and energy storage applications. Additionally, experimental recyclability tests revealed that the composite adsorbents retained over 85 % of their initial adsorption efficiency after five adsorption–desorption cycles, confirming their practical reusability in environmental remediation applications. While ZnO and CuO hybrids showed moderate improvements, rGO demonstrated superior utility. This study advances green wastewater treatment technologies and promotes the development of low-cost, high-performance adsorbents for sustainable environmental management.