Tuning the Microstructural and Magnetic Properties of ZnO Nanopowders through the Simultaneous Doping of Mn and Ni for Biomedical Applications

Undoped and Mn＋Ni doped ZnO nanopowders were synthesized using a simple soft chemical route by varying the Ni doping level （1, 3, 5 and 7 at.%） and keeping the Mn doping level （10 at.%） constant, X-ray diffraction studies reveal that the incorporated Ni^2＋ ions form a secondary phase of cubic NiO beyond the Ni doping level of 3 at.%, which is also confirmed by Fourier transform infrared spectroscopy. The band gap of the nanopowders increases （from 3.32 to 3.44 eV） up to 3 at.% of Ni doping and decreases with further doping. ZnO：Mn：Ni nanopowders with 3 at.% of Ni concentration exhibit good antibacterial efficiency. The variation in the size of the nanoparticles, as observed from the TEM images and hydroxyl radicals as evidenced from the photoluminescence results, clearly substantiate the discussion on the antibacterial efficiency of the synthesized nanopowders. Magnetic properties of the synthesized nanopowders were studied using a vibrating sample magnetometer, and the results showed that the doping of Mn and Ni largely influences the magnetic properties of ZnO nanopowders.