Integrated experimental and theoretical study of CuO/ZnO nanocomposites for photocatalytic and supercapacitor applications

In this study, CuO, ZnO, and CuO/ZnO nanocomposites were synthesized via a sol-gel method and systematically investigated for photocatalytic and supercapacitor applications. XRD confirmed the formation of monoclinic CuO, hexagonal wurtzite ZnO, and a composite structure free of secondary phases, with average crystallite sizes of 26, 34, and 19 nm, respectively. FTIR and Raman analyses verified the presence of characteristic metal-oxide vibrations, while UV-DRS revealed band gaps of 2.30, 3.16, and 2.60 eV for CuO, ZnO, and CuO/ZnO. FESEM showed uniform dispersion of CuO over ZnO, and EDS confirmed elemental homogeneity. The CuO/ZnO nanocomposite achieved a Rhodamine-B degradation efficiency of 92.6 % within 180 min, following pseudofirst-order kinetics (k = 0.0168 min-1, t1/2 = 41.2 min), outperforming CuO (33.6 %) and ZnO (67.1 %). Electrochemical measurements demonstrated a specific capacitance of 98 F g-1 at 0.5 A g-1, with 84.1 % retention after 5000 cycles and low charge transfer resistance (17.6 Omega), confirming superior energy-storage capability. DFT calculations revealed bidentate adsorption of Rhodamine-B on the CuO/ZnO interface with optimal interaction energy (-8.67 eV), reduced band gap, and enhanced density of states near the Fermi level, explaining the observed experimental efficiency. Overall, the synergistic heterojunction interface in CuO/ZnO enhances charge separation, photocatalytic reactivity, and electrochemical performance, making it a promising multifunctional material for environmental and energy applications.