Significant photocatalytic activity enhancement of titania inverse opals by anionic impurities removal in dye molecule degradation

Min Wu, Anmin Zheng, Feng Deng, Bao Lian Su

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The photocatalytic behavior in dye molecule degradation of highly ordered three dimensional macroporous titania inverse opals prepared by the polystyrene spheres templating method has been investigated. The sulfate impurity stemming from K2S2O8 used as initiator for the styrene polymerization and remaining in the final materials in a form of sulfate anions was found to strongly inhibit the photocatalytic process of titania inverse opals. The mechanism of the negative effect of sulfate anionic impurity has been studied by the theoretical calculations and the comparison of samples subject to a wash process or not, the artificial addition of sulfate anions to the reaction medium and cycle experiments of samples without the washing process. Raman spectroscopy confirmed that in TiO2 inverse opal structures, sulfate ions are present in divalent forms. However, in aqueous photocatalytic medium, monovalent hydrosulfate anions can also be present. Theoretical calculations on the interaction of sulfate (mono and divalent) anions and Rhodamine B (RhB) with TiO2 inverse opal indicated that the adsorption binding energy of divalent sulfate anions on the titania surface (168kcal/mol) is over four times as that of the Rhodamine B (36kcal/mol) in the photocatalytic system and that of hydrosulfate anions is around 53-57kcal/mol, still much higher than that of Rhodamine B. The strong adsorption of the anionic sulfate impurity on the surface of titania inverse opals would block the active sites and thus strongly affect the photocatalytic performance. A model of the negative action of sulfate anions has been proposed. This work leads to a new physic-chemical insight on the behavior of sulfate anions in the photocatalytic degradation of RhB and revealed that a single washing process to remove the impurity suggested significant promotion effect of the photocatalytic reaction without any surface modulations. This washing process dramatically suppressed the adsorption effect induced by the sulfate impurity and simplified the procedures, improving the photocatalytic performance.

langue originaleAnglais
Pages (de - à)219-228
Nombre de pages10
journalApplied Catalysis B: Environmental
Les DOIs
Etat de la publicationPublié - 17 juil. 2013

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