Synthesis of pure, Ni doped ZnO, Mn doped ZnO and Mn co-doped Ni/ZnO was carried out using AnalaR grade zinc acetate dihydrate [Zn (CH3COO)2·2H2O], nickel acetate dihydrate [Ni (CH3COO)2·2H2O], manganese acetate dihydrate [Mn (CH3COO)2·2H2O] and sodium hydroxide (NaOH) chemicals in as-received condition. In the synthesis process, a required amount of zinc acetate was completely dissolved in deionized water and a required amount of aqueous NaOH solution was added drop wise to the mixture. Later, the solution forms a white precipitate which was stirred at room temperature for 30 min and then kept at 80 °C for 5 h. Thereafter, the white precipitate was washed several times with double distilled water and ethanol. Finally, the precipitate was dried at 120 °C for an hour. The prepared powder was annealed at 400 °C in air for 2 h. Thus, the nanopowder of ZnO NPs was obtained and used for further studies.
For the synthesis of Zn0.80Ni0.20O (Ni/ZnO) nanoparticles, a calculated amount of nickel acetate in water was mixed with an aqueous zinc acetate solution. The required amount of aqueous NaOH solution was added drop by drop to the above homogenous mixture to get a white precipitate with pale green color. Later, a similar procedure adopted for the preparation of pure ZnO NPs was followed for the synthesis of Ni doped ZnO NPs. The same procedure adopted for the preparation of Ni doped ZnO was followed for Zn0.80Mn0.20O (Mn/ZnO) and Zn0.80Ni0.10Mn0.10O (Mn-Ni/ZnO) NPs. Mn doped ZnO and Mn co-doped Ni/ZnO NPs were obtained from a homogenous mixture to get a precipitate with a pale brown color and black color, respectively.