ZnO powder combustion synthesis with (Fe, Co, Cu, Mg) mono-doping for enhancing photocatalytic activity in phenol degradation

The combustion synthesis was used to prepare ZnO powder from solution of glycine as fuel and zinc nitrate as precursor and oxidizer, as well as for doping ZnO with one of the elements Fe, Co, Cu, and Mg the concentration of which was from 0.1 to 10 wt.% using their nitrates, to enhance ZnO photocatalytic activity in the decomposition of phenol under ultraviolet and visible light irradiation. As-synthesized ZnO was strong contaminated with free and bound carbon (10 - 30 wt.%) but after air calcination (1 h, 650°C), the carbon content reduced to the level of 1 wt.%. The calcinated and doped ZnO powder consisted of individual highly dispersed (<1 µm) nano-sized and submicron ZnO particles with a crystallite size of about 30 nm and sintered porous agglomerates ranging in size from 0.2 to 100 µm. Of all dopants, only Mg improved the photocatalytic activity of ZnO powder in the decomposition of phenol under ultraviolet irradiation. The powder with 1 wt.% Mg showed the greatest increase in the activity reducing the time of almost complete decomposition of phenol by more than 2 times: from 3.75 - 5 h to 1.75 - 2.25 h. However, Mg-doped ZnO was not effective under action of visible light.