Synthesis of cobalt oxide nanoparticles

The cobalt oxide nanoparticles were synthesised using the coprecipitation method. The Qualitek-4 software and Taguchi method were used to optimise the synthesis of cobalt oxide nanoparticles with the highest antibacterial activity. To do so, 9 experiments were designed and the effect of 0.2, 0.4 and 0.6 M levels of Co(NO₃)₂.6H₂O and the levels of 1, 2 and 3 M of KOH at the stirring times of 30, 60, and 90 min were evaluated on the antibacterial activity of the synthesized nanoparticles (Table 1).

Taguchi design of experiments and antibacterial effect of manufactured cobalt oxide nanoparticles on gram-positive and gram-negative bacteria

A volume of 100 ml of KOH solution at concentrations of 1, 2 and 3 M and cobalt nitrates with the concentrations of 0.2, 0.4, and 0.6 M were prepared in separate containers. Then, according to the nine tests suggested by the Taguchi method, the solutions of KOH at different concentrations were added drop-by-drop to the containers containing cobalt nitrate solution while continuously stirring, which were mixed and combined at 30, 60 and 90 min, respectively. Initially, pink sediment was formed, which was easily oxidised in contact with the air, and dark sediment was obtained. The dark sediment was separated by centrifugation and washed out with deionised water several times. It was then dried in an oven at 100°C for 24 h. The cobalt hydroxide powder was calcined in air at 400°C furnace for four hours to obtain the cobalt oxide nanoparticles.