Combined DFT and experimental study of CuO and Ni–CuO nanoparticles: structural characterization, photocatalytic degradation, and antimicrobial activities

In this study, pure and nickel-doped copper oxide (CuO and Ni-CuO) nanoparticles were synthesized <i>via</i> a sol-gel route and comprehensively characterized to investigate their structural, electronic, photocatalytic, and antimicrobial properties. X-ray diffraction (XRD) confirmed the formation of monoclinic CuO with successful Ni incorporation, evidenced by peak broadening and lattice strain. Field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX) analyses revealed quasi-spherical morphologies and homogeneous Ni doping, while FTIR spectra confirmed Cu-O bonding with subtle changes induced by Ni substitution. Photocatalytic degradation of methylene violet (MV) dye under UV irradiation demonstrated enhanced efficiency for Ni-CuO (88.62% at 20 ppm) compared to pure CuO (84.92%), with kinetics following a pseudo-first-order model. Additionally, Ni-CuO exhibited improved antimicrobial activity against Gram-positive and Gram-negative bacteria as well as <i>Candida albicans</i>, achieving up to 99.72% inhibition at 250 μg mL^-1. To support the antimicrobial findings, molecular docking studies were performed using Cu₄O₄ and Ni-doped Cu₃NiO₄ nanoclusters against microbial target proteins. The Ni-doped nanocluster displayed stronger binding affinities with key proteins from <i>E. coli</i>, <i>S. typhi</i>, and <i>Candida albicans</i>, forming stabilizing interactions such as hydrogen bonds, metal-acceptor contacts, and π-sulfur bonds. These interactions were especially pronounced in the <i>Candida</i> model, aligning well with experimental inhibition data. Density Functional Theory (DFT) calculations on Cu₄O₄ and Ni-doped Cu₃NiO₄ nanoclusters revealed modifications in bond lengths, HOMO-LUMO gaps, and charge distribution upon doping, which correlated well with experimental observations. Notably, partial density of states (PDOS) and charge analyses indicated increased electronic delocalization and orbital hybridization in Ni-CuO, supporting its superior photocatalytic and antimicrobial performance. This integrative study provides atomistic insight into the structure-property relationships of doped CuO nanostructures, underscoring their potential for multifunctional environmental and biomedical applications.