Composite Photocatalysts Containing BiVO4 for Degradation of Cationic Dyes

Kanlaya Pingmuang,Sukon Phanichphant,Wiyong Kangwansupamonkon,Andrew Nattestad,Gordon G Wallace,Jun Chen

doi:10.1038/s41598-017-09514-5

Abstract

The creation of composite structures is a commonly employed approach towards enhanced photocatalytic performance, with one of the key rationales for doing this being to separate photoexcited charges, affording them longer lifetimes in which to react with adsorbed species. Here we examine three composite photocatalysts using either WO3, TiO2 or CeO2 with BiVO4 for the degradation of model dyes Methylene Blue and Rhodamine B. Each of these materials (WO3, TiO2 or CeO2) has a different band edge energy offset with respect to BiVO4, allowing for a systematic comparison of these different arrangements. It is seen that while these offsets can afford beneficial charge transfer (CT) processes, they can also result in the deactivation of certain reactions. We also observed the importance of localized dye concentrations, resulting from a strong affinity between it and the surface, in attaining high overall photocatalytic performance, a factor not often acknowledged. It is hoped in the future that these observations will assist in the judicious selection of semiconductors for use as composite photocatalysts.

Highlights

Bismuth vanadate (BiVO4) has attracted much attention as a highly responsive, visible-light driven, photocatalyst due to its comparatively narrow band gap (EG) energy of 2.4 eV
As the above band edge potentials are obtained from different sources, and measured under different conditions, optical band gap and Mott-Shotkey measurements are conducted in order to confirm the predicted offsets
A number of mechanisms for photocatalytic degradation of dyes by semiconductors are summarised in Fig. 2, including (1) direct photolysis of dyes (2) dye photosensitization and (3) photocatalytic degradation of dyes attack by radical generated by photoexcitation of semiconductor (SC)[22,23,24,25]

Summary

Introduction

Bismuth vanadate (BiVO4) has attracted much attention as a highly responsive, visible-light driven, photocatalyst due to its comparatively narrow band gap (EG) energy of 2.4 eV, (as compared to TiO2, which remains a benchmark, with an EG of 3.0–3.2 eV). The results show that the semiconductor composite photocatalysts were more active than individual catalysts for all photocatalytic degradation of organic pollutants - notwithstanding the fact that it is less likely that composites providing lower photocatalytic performances would be published While most of these reports on composite catalysts acknowledge the role of band edge offsets, detailed investigations of reaction mechanisms are often not undertaken, nor has the nature of these energy offsets been thoroughly scrutinized[8, 10, 13, 18, 20]. CeO2/BiVO4, TiO2/BiVO4 and WO3/BiVO4 provide these different valence band (VB) and conduction band (CB) edge offsets, with the CB and VB potential edges of BiVO4 being more positive than those of CeO2, in between those of TiO2, and more negative than those of WO3; as shown in Fig. 1 6, 7, 20–22 Direct photolysis is very slow, impractical as a means to www.nature.com/scientificreports/

Methods

Results

Conclusion