Sustainable reduction of Cr (VI) by green synthesized chitosan coated copper (II) nanoparticles in batch reactor system: Isotherm, thermodynamics and kinetic study

This study explores the use of green-synthesized chitosan-coated Cu2O nanoparticle (Ch-CuNs) for the sustainable removal of hexavalent chromium (Cr (VI)). Scanning electron microscope (SEM) analysis confirmed the formation of spherical nanoparticles, while energy dispersive X-ray analyzer (EDX) and elemental analysis verified the presence of Cr (VI) on the nanoparticle surface, indicating successful adsorption. Fourier Transform Infrared (FTIR) spectroscopy analysis identified functional groups on the nanoparticles that actively participated in Cr (VI) adsorption. The specific surface area of Ch-CuNs was increased due coating of chitosan on nanoparticle surface. Freundlich isotherm model best fitted (R2 = 0.99) and described multilayer adsorption of Cr (VI) onto Ch-CuNs. Pseudo-second-order model was best fitted for the adsorption process and this suggests that Cr (VI) adsorption was chemisorption. The thermodynamic parameters, with a positive enthalpy change (ΔH° = 885.97 J mol−1) and entropy change (ΔS° = 60.09 J K−1 mol−1), indicate that the adsorption process is endothermic and favourable. The results show that Ch-CuNs exhibit high Cr (VI) adsorption capacity (91.96 mg/g). In series reactor system, complete removal of Cr (VI) was achieved. This study highlights the potential of chitosan coated green-synthesized Ch-CuNs as effective and sustainable agents for removing Cr (VI) from contaminated water. © 2025 Elsevier B.V.