Colossal dielectric constant and excellent dye-depollution properties of Mo doped CuO/ZnO/NiO (p-n-p) tertiary-heterojunctions

Mo doped CuO/ZnO/NiO (p-n-p) tertiary-composite exhibited a remarkable dielectric constant, high adsorption capacity and rapid photocatalytic activity for the removal of Congo red pollutant. This study involved the synthesis of two composites consisting of pure and Mo doped CuO/ZnO/NiO through the coprecipitation method. The X-ray diffraction analysis confirmed the formation of monoclinic CuO, hexagonal ZnO, and cubic NiO structures. The incorporation of Mo ions reduced the band gap energy of NiO, ZnO, and CuO components to 3.4 eV, 2.6 eV, and 1.56 eV, respectively. The Mo doped CuO/ZnO/NiO tertiary-composite displayed a BET surface area of 1.8679 m²/g, pore size of 0.053158 cm³/g, and pore volume of 11.384 nm. The SEM micrographs of the Mo doped CuO/ZnO/NiO composite revealed the formation of rod-shaped and spherical particles. The EDX mapping of Mo doped CuO/ZnO/NiO sample verified the homogeneous distribution of Cu, Zn, Ni and Mo elements within the sample. The X-ray photoelectron spectroscopy (XPS) analysis showed that the Mo dopant has mixed oxidation states of + 4 and + 6. The dielectric constant of pure and Mo doped CuO/ZnO/NiO tertiary-composites was 12,200 and 29,073 at 42 Hz, respectively. The Mo doped CuO/ZnO/NiO composite exhibited an adsorption capacity of 90% and a rapid photocatalytic activity of 99% for 20 mg/L Congo red pollutant in 30, and 20 min, respectively.