Effect of fuel to oxidant molar ratio on the photocatalytic activity of ZnO nanopowders

Abstract

In this study, the effects of fuel to oxidant (F/O) molar ratio on the characteristics and photocatalytic activity of ZnO nano-powders were investigated. A simple and inexpensive combustion process was utilized to synthesize the nano-powders. A range of analytical techniques including X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy (DRS) and Photoluminescence spectroscopy (PL) were employed to characterize the nano-powders. XRD patterns showed that the synthesized powders have hexagonal wurtzite structure and high crystallinity without any secondary phase. The calculated crystallite size was in the range of 35–29nm which decreased by increasing the F/O ratio. UV–vis diffuse reflectance spectroscopy showed a gradual shift of optical absorption spectra in the visible region of light when F/O ratio was increased. PL spectroscopy confirmed that the prepared photocatalysts had better charge separation capability as compared to the commercial ZnO. The photocatalytic activity of different samples was investigated by degradation of methyl orange (MO) dye under UV and visible light irradiation. The results demonstrated that F/O ratio had a significant influence on photocatalytic degradation of methyl orange compared to the commercially available ZnO and TiO2 powders. Moreover, the photocatalysis of ZnO (F/O=1.7) powder with particle size (31nm) showed excellent performance for photodegradation of MO, which suggests a balance among the recombination rate, surface hydroxyl groups and specific surface area.