Fluorination of ZnWO4 photocatalyst and influence on the degradation mechanism for 4-chlorophenol.

The fluorine doped ZnWO4 photocatalyst was synthesized by hydrothermal synthesis and annealing treatment. The existing states of fluorine in the crystal were elucidated, and the effects of fluorine on the crystal structure, photocatalytic activity, and degradative intermediates were investigated. The doping concentration of fluorine in the interstitial lattice of ZnWO4 crystal can be controlled bythe annealing conditions. The photocatalytic activity can be enhanced about 50% after the doped ZnWO4 was annealed at 450 degrees C for 1 h due to perfect crystal structure. The enhancement of photocatalytic activity after fluorine doping could be attributed to the higher separation efficiency of electron-hole pairs, which results in a large number of holes participated in the photocatalytic process. The fluorine doping does not change the degradation pathway of 4-chlorophenol (4-CP) in our system. 4-CP was mainly transformed into hydroxylated aromatic intermediates such as benzoquinone (BQ), hydroquinone (HQ), and 4-chlorocatechol (4-CC). The photodegradation of 4-CP in powdered F-doped ZnWO4 system proceeded via direct holes oxidation reactions.