Enhanced p-cresol photodegradation over BiOBr/Bi2O3 in the presence of rhodamine B

Bismuth oxide is a visible-light activated photocatalyst that is adversely affected by a high rate of electron-hole recombination. To mitigate this, BiOBr/Bi2O3 composites were synthesized where BiOBr formed submicron thick platelets at the surface of the Bi2O3 particles. XRD measurements show the preferential formation of a (110)-facetted BiOBr overlayer which can be attributed to the commensurate structure of this plane with the (120) plane of Bi2O3. The photodegradation of p-cresol and RhB was studied as representative of an organic pollutant and a dye, respectively. The composite with 85% BiOBr/Bi2O3 exhibited the highest photoactivity for both molecules. Its higher activity compared to that of either Bi2O3 or BiOBr alone, or a mechanical mixture with the same composition, supports the hypothesis that the formation of an hetero-epitactic interface between BiOBr and Bi2O3 is instrumental in reducing electron-hole pair recombination. Interestingly, in mixtures of p-cresol and RhB, the rate of p-cresol photodegradation was enhanced but that for RhB was decreased compared to the pure solutions. This is not caused by competitive adsorption of the molecules but rather by excitation transfer from RhB to the co-adsorbed p-cresol. Therefore, the RhB degradation by deethylation, which is a surface reaction, is suppressed and only the reaction channel through attack of the OH$ radical at the aromatic chromophore remains open.