The effect of simultaneous 3d transition bimetal doping (Ni/Mn, Co/Mn, Ni/Co) on the structural, optical and photocatalytic properties of ZnO based materials

This paper reports the synthesis of 3d transition bimetal simultaneously incorporated in ZnO with different dopant concentration via coprecipitation method. These materials (Zn_1-x(M₁M₂)_xO; M₁M₂= Mn/Ni, Ni/Co and Mn/Co in 1:1 i.e., x = 0.04 and 0.07;) were characterized by XRD, FE-SEM, EDS, UV–visible and fluorescence spectroscopies. The XRD results confirmed that low concentration of bimetal doped ZnO exhibits no extra diffraction peak (single phase) while high concentration co-doped ZnO had few extra peaks, which corresponded to NiO, Co₂O₃ and Mn₂O₃. Bimetal doped ZnO confirmed the hexagonal wurtzite phase with an average crystallite size of 22–29 nm. All the synthesized materials showed no extra element except the dopants, confirmed by EDX analysis. The morphology of pure and bimetal doped ZnO was found to be spherical. When compared to pure ZnO, the bimetal doped ZnO showed enhanced solar light response due to red shift in band gap energies [UV to visible (3.16 eV to 2.4 eV)]. PL emission peaks confirmed the presence of various intrinsic defects within the band gap of ZnO and its doped form. Bimetal doping leads to lowering of recombination rate of photo generated electron (e^-) and holes (h⁺) in ZnO. The synthesized materials were ultimately applied for the photodegradation of methylene blue (MB) dye and the degradation efficiency was found to be above ∼90 %. Moreover, the quenching experiment (radical trapping) confirmed the role of dopants in the activation of radicals or active species in the visible region of light spectrum and effectiveness in MB degradation. The reusability study revealed that photocatalysts are durable, stable, and economical.