Effects of Ni doping on the structural, photoelectric, and antibacterial properties of ZnCo₂O₄ thin films

This study addresses improving the electrical properties and demonstrating the antibacterial capability of spinel ZnCo₂O₄ films. We used sol–gel and spin-coating techniques to prepare samples and analyzed their crystal structures, microstructures, as well as their photoelectric and antibacterial properties, in relation to Ni doping. Single-phase spinel oxide is maintained in all of the Zn(Co_1-xNi_x)₂O₄ films. The replacement of cobalt by nickel causes a decrease in the average grain size and surface roughness. Both the grain size and the surface roughness affect the optical properties of the film translucence. The transmittances of all films at a wavelength of 600 nm is ~31.3–48.6%. The characteristic absorption peak of the photon-excited electron is about 400 nm. A higher doping content ratio (Ni_x = 0.15–0.30) causes the absorption characteristic peak to gradually disappear. The direct energy gap of all spinel oxides ranges from 2.45 to 2.57 eV. All films are p-type semiconductors, and nickel can replace cobalt to increase the carrier concentration, resulting in a decrease in the resistivity of Zn(Co_1-xNi_x)₂O₄ from 312.5 Ω-cm (Ni_x = 0) to 15.8 Ω-cm (Ni_x = 0.30). The antibacterial rate for Escherichia coli and Staphylococcus aureus associated of the material can reach more than 99.9%, and no photocatalysis is necessary. Therefore, Ni-doped ZnCo₂O₄ possesses excellent properties for potential applications.