Comparative studies of “3d” transition metals (Co, Mn, Ni) doped ZnO nanoparticles for visible light degradation of methylene blue

The development of efficient visible-light photocatalysts is highly desired for a clean and sustainable environment. Herein, we report the fabrication and functionalization of zinc oxide (ZnO) nanostructures for the degradation of organic pollutants, one of the key components of environmental pollution. Pure and “3d” transition metal ions doped ZnO (Zn_1−xM_xO, where M = Mn, Ni, Co with varying doping concentration x = 1 % and 7 %) were synthesized by co-precipitation method and their structural, electronic, morphological, and optical properties were investigated in detail. The powder X-ray diffraction (XRD) pattern of pure and Zn_1−xM_xO nanostructures confirmed the hexagonal wurtzite phase (p63mc) with an average crystallite size of around 22–27 nm. The energy dispersive x-ray (EDX) analysis confirmed the presence of metal dopants in ZnO. The morphology of synthesized nanostructures was found to be spherical. The band gap of ZnO was considerably narrowed from 3.15 to 1.8 eV through doping, indicating extension towards visible light absorption. Photoluminescence (PL) emission spectra of doped ZnO revealed a low recombination rate of electrons (e^-) and holes (h⁺) and various possible defect states within the bandgap. Furthermore, electron spin resonance showed the presence of Mn²⁺ centers. Optimized metal-doped zinc oxide revealed higher photocatalytic activity, during degradation of methylene blue model dye under visible light.