Enhancing the photocatalytic activity of BiOX (X = Cl, Br, and I), (BiO)2CO3 and Bi2O3 by modifying their surfaces with polar organic anions, 4-substituted thiophenolates

Abstract

When its surface is modified by using polar organic anions, 4-substituted thiophenolate anions 4-Z-C₆H₄S⁻ (Z = NO₂, COOH, H, CH₃, and NH₂), the Bi-based semiconductor BiO(HCOO) was found to exhibit a greatly enhanced photocatalytic activity. To establish the generality of this phenomenon, we examined the photocatalytic activities of other Bi-based semiconductors, BiOX (X = Cl, Br, and I), (BiO)₂CO₃ and Bi₂O₃, by modifying their surfaces with 4-carboxythiophenolate anions (4CBTs). As observed for BiO(HCOO), it is found that the surface modification with the 4CBT anions enhances the photocatalytic activities of BiOX (X = Cl, Br, and I), (BiO)₂CO₃ and Bi₂O₃, and this enhancement originates from a synergetic effect between the polarity of the polar organic anions and the internal electric field of those Bi-based semiconductors. Several factors affecting the photocatalytic activity were probed in some detail, which includes the nature of the facets and the sample sizes modified by using 4CBT anions in BiOCl and (BiO)₂CO₃, the structures of Bi₂O₃ phases as well as the electron-withdrawing or electron-donating ability of the 4-substituent Z of 4-Z-C₆H₄S⁻ in BiOX (X = Cl, Br, and I).