Fabrication of ternary metal oxide (ZnO:NiO:CuO) nanocomposite heterojunctions for enhanced photocatalytic and antibacterial applications

In this article, ZnO:NiO:CuO nanocomposites (NCPs) were synthesized using a hydrothermal method, with different Zn : Ni : Cu molar ratios (1 : 1 : 1, 2 : 1 : 1, 1 : 2 : 1, and 1 : 1 : 1). The PXRD confirmed the formation of a NCP consisting of ZnO (hexagonal), NiO (cubic), and CuO (monoclinic) structures. The crystallite sizes of NCPs were calculated using Debye Scherrer and Williamson-Hall methods. The calculated crystalline sizes (Scherrer method) of the NCPs were determined to be 21, 27, 23, and 20 nm for the molar ratios 1 : 1 : 1, 2 : 1 : 1, 1 : 2 : 1, and 1 : 1 : 2, respectively. FTIR spectra confirmed the successful formation of heterojunction NCPs via the presence of metal-oxygen bonds. The UV-vis spectroscopy was used to calculate the bandgap of synthesized samples and was found in the range of 2.99-2.17 eV. SEM images showed the mixed morphology of NCPs i.e., irregular spherical and rod-like structures. The dielectric properties, including AC conductivity, dielectric constant, impedance, and dielectric loss parameters were measured using an LCR meter. The DC electrical measurements revealed that NCPs have a high electrical conductivity. All the NCPs were evaluated for the photocatalytic degradation of Methylene blue (MB), methyl orange (MO), and a mixture of both of these dyes. The NCPs with a molar ratio 1 : 1 : 2 (Zn : Ni : Cu) displayed outstanding photocatalytic activity under sunlight, achieving the degradation efficiency of 98% for methylene blue (MB), 92% for methyl orange (MO) and more than 87% in the case of a mixture of dyes within just 90 minutes of illumination. The antibacterial activity results showed the more noxious nature of NCPs against Gram-negative bacteria with a maximum zone of inhibition revealed by the NCPs of molar ratio 1 : 2 : 1 (Zn : Ni : Cu). On the basis of these observations, it can be anticipated that the NCPs can be successfully employed for the purification of contaminated water by the degradation of hazardous organic compounds and in antibacterial ointments.