Influence of Fluorine on Structure, Morphology, Optical and Photocatalytic Properties of ZnWO4 Nanostructures
Nguyen Manh Hung, Le Thi Mai Oanh, Danh Bich Do, Ngoc Diep Lai, Nguyen Thi Thao, Du Thi Xuan Thao, Nguyen Van Minh
We report on the synthesis of Fluorine (F) doped -ZnWO4 photocatalysts and the influence of F-doping on their structure, morphology, optical and photocatalytic properties. A two-step process was used to produce F-doped ZnWO4 photocatalysts. The quality of synthesized materials was characterized using different analytical methods, such as X-ray diffraction analysis, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectra (FTIR), as well as photoluminescence (PL) measurement. It was found that the photocatalyst morphology and band gap energy strongly depend on the F-doping concentration. The band gap energy of the photocatalysts decreased when increasing F-doping concentration, and reached a lowest value at a concentration of 4 mol%, and then increased thereafter. At 4 mol% of F-doping, nanowires were formed with approximately 1 μm in length and 50 nm in diameter. On the contrary, others F-doped ZnWO4 samples were obtained in the shape of nanorods or a mixture of nanorods and granular particles. Moreover, it was demonstrated that F-doped ZnWO4 enhanced photocatalytic activity by a factor of three, as compared to that of un-doped ZnWO4. This enhancement can be explained by the nanowire shape of synthesized F-doped ZnWO4, its narrow band gap energy and the small recombination rate of photogenerated electron-hole pairs, which was indirectly proved by PL spectra.