Experimental and Theoretical Studies on the Enhanced Photocatalytic Activity of ZnWO4 Nanorods by Fluorine Doping

We present a combined study of the photocatalysis of the F interstitially doped ZnWO4 (F-i-ZnWO4) nanocrystals by means of experiment and DFT band structure calculations, including an analysis of the chemical bonding. The F-i-ZnWO4 nanorods were prepared via a two-step hydrothermal process by adjusting the pH of the reaction solution. The results showed that the F-i-ZnWO4 samples exhibited stronger absorption in the UV-visible range with a red shift in the band-gap transition. The photocatalytic activity of the F-i-ZnWO4 samples was highly enhanced for the photocatalytic decomposition of RhB under ultraviolet light irradiation. The morphology and crystallinity of F-i-ZnWO4 have a significant influence on the photocatalytic activity; the F-i-ZnWO4 nanorod showed much higher photocatalytic activity than the nanoparticle one. The DFT calculations show that the mixing of F 2p and O 2p states in the top of the valence band induces the valence band to extend to higher energy, which accounts for the slight red shift of the optical absorption edge observed in the experiment. In addition, the interstitial F impurity creates a new half-filled state in the band gap, which can supply a hole carrier to improve the photocurrent density for the F-doped ZnWO4 under UV radiation, thus enhancing the photocatalytic activity of ZnWO4. The excellent agreement between the measured spectra and calculated electronic structure can provide a solid basis for understanding the enhanced photocatalytic activity of F-i-ZnWO4 nanocrystals.