Photocatalytic properties of ZnO powders synthesized by conventional and microwave-assisted solution combustion method

Zinc oxide (ZnO) powders have been prepared by solution combustion synthesis method using conventional and microwave ignition routes. The effects of starting solution acidity on the combustion behavior, phase evolution, microstructure, optical properties and photocatalytic performance were investigated by thermal analysis, X-ray diffractometry, electron microscopy and diffuse reflectance spectrometry techniques. The chelated species in dried gels were predicted by theoretical calculations and confirmed by Fourier transform infrared spectroscopy. The combustion reaction rate increased with the increase of pH values. Single phase and well-crystalline ZnO powders were achieved by both of ignition methods regardless of pH values. The hexagonal particles (200–80?nm) formed by microwave ignition were larger than the spherical particles (60–40?nm) in conventional heating. Conventionally combusted ZnO powders exhibited higher photocatalytic activity under ultraviolet irradiation, due to their narrower band gap and smaller particle size.

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C/C0 vs. irradiation time for photodegradation of MB dye under ultraviolet light irradiation by the as-combusted ZnO powders (filled symbols present conventional combusted powders and open symbols are for the microwave combusted powders)