Effect of Fluorination on Photocatalytic Degradation of Rhodamine B over In(OH)ySz: Promotion or Suppression?

Fluorinated In(OH)(y)S-z solid solutions were synthesized via a hydrothermal method. The photocatalytic degradation of rhodamine B (RhB) over the fluorinated In(OH)(y)S-z solid solutions revealed that the process of the de-ethylation of RhB was enhanced, while in the meantime, the rate of the mineralization of RhB was suppressed when In(OH)(y)S-z was fluorinated. To elucidate the opposite effects of fluorination on the two processes of photocatalytic degradation of RhB (de-ethylation and mineralization) over In(OH)(y)S-z, the adsorption of RhB over In(OH)(y)S-z with and without fluorination, the active species involved in the de-ethylation and the mineralization of RhB, were investigated, and the electronic structure of fluorinated In(OH)(y)S-z was studied. The results indicated that the major active species involved in the de-ethylation and the mineralization of RhB are different, that is, the hole direct oxidation leads to the de-ethylation of RhB, while the major active species responsible for the mineralization of RhB is the O-2(is approximately equal to) radical. The fluorination on In(OH)(y)S-z solid solutions on one hand can enhance the adsorption of RhB on the catalyst surface, leading to a higher rate in the de-ethylation of RhB. On the other hand, fluorination lowers the conduction band of In(OH)(y)S-z, which leads to a lower capability of the photogenerated electrons in the reduction of O-2 to give O-2(is approximately equal to) radicals. Our results clearly show that the fluorine modifications can have ambilateral effects on the photocatalytic performance of semiconductor photocatalysts depending on the specific photocatalytic reactions.