Evaluation of adsorption performance of CuO and ZnO nanoparticles synthesized by green method for treatment of Cr(VI)-polluted waters

This study focused on the removal of hexavalent chromium (Cr(VI)) from water using copper oxide (CuO) and zinc oxide (ZnO) nanoparticles synthesized via a simple biosynthesis method using turmeric (Curcuma longa) root extract as a bioreducing agent. The nanoparticles were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), and Brunauer-Emmett-Teller (BET) analysis. Adsorption studies were conducted to evaluate the Cr(VI) removal efficiency under varying pH, temperature, contact time, and initial concentration. Kinetic models indicated that CuO followed pseudo-first-order (PFO) kinetics, whereas ZnO followed pseudo-second-order (PSO) kinetics, showing different adsorption mechanisms. Isotherm studies demonstrated that the Freundlich model provided the best fit, suggesting multilayer adsorption for both nanoparticles, with maximum adsorption capacities of 166.4 mg/g for CuO and 48.5 mg/g for ZnO. Thermodynamic analysis revealed that adsorption was spontaneous and exothermic. Tests with real water samples (drinking water, tap water, and wastewater) confirmed the effectiveness of the nanoparticles. Recycling studies demonstrated good reusability, with CuO retaining 75 % efficiency and ZnO 65 % after four cycles. These findings highlight the potential of CuO and ZnO nanoparticles as sustainable adsorbents for Cr(VI) remediation during water treatment.