Improving the Photo-Oxidative Performance of Bi₂MoO₆ by Harnessing the Synergy between Spatial Charge Separation and Rational Co-Catalyst Deposition

Abstract

It has been reported that photogenerated electrons and holes can be directed toward specific crystal facets of a semiconductor particle, which is believed to arise from the differences in their surface electronic structures, suggesting that different facets can act as either photoreduction or photo-oxidation sites. This study examines the propensity for this effect to occur in faceted, plate-like bismuth molybdate (BiMoO), which is a useful photocatalyst for water oxidation. Photoexcited electrons and holes are shown to be spatially separated toward the {100} and {001}/{010} facets of BiMoO, respectively, by facet-dependent photodeposition of noble metals (Pt, Au, and Ag) and metal oxides (PbO, MnO , and CoO). Theoretical calculations revealed that differences in energy levels between the conduction bands and valence bands of the {100} and {001}/{010} facets can contribute to electrons and holes being drawn to different surfaces of the plate-like BiMoO. Utilizing this knowledge, the photo-oxidative capability of BiMoO was improved by adding an efficient water oxidation co-catalyst, CoO , to the system, whereby the extent of enhancement was shown to be governed by the co-catalyst location. A greater oxygen evolution occurred when CoO was selectively deposited on the hole-rich {001}/{010} facets of BiMoO compared to when CoO was randomly located across all of the facets. The elevated performance exhibited for the selectively loaded CoO/BiMoO was ascribed to the greater opportunity for hole trapping by the co-catalyst being accentuated over other potentially detrimental effects, such as the co-catalyst acting as a recombination medium and/or covering reactive sites. The results indicate that harnessing the synergy between the spatial charge separation and the co-catalyst location on the appropriate facets of plate-like BiMoO can promote its photocatalytic activity.

Modulation of Bi2MoO6‐Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

“…As shown in Figure a, the rGO/Bi 2 MoO 6 demonstrated significantly enhanced O 2 evolution of 18 µmol L −1 under 3 h simulated solar light irradiation with AgNO 3 as an electron scavenger, which was 1.8 times as high as pure BMO hierarchical microspheres (10 µmol L −1 ) . Using photochemical labeling, Wu et al demonstrated that, the electrons and holes were readily to be drawn to (100) and (001)/(010) facets, respectively, which were favorable for the dominant deposition of noble metals and metal oxides as shown in Figure b,c . Thus, they selectively deposited CoO x onto the hole‐rich facets of Bi 2 MoO 6 to trap the photogenerated h + and then achieved a high oxygen evolution rate of ca.…”

“…Copyright 2016, Elsevier B.V. SEM images of the spatial distribution of b) Pt and c) MnO x on the surface of Bi 2 MoO 6 . Reproduced with permission . Copyright 2018, American Chemical Society.…”

Cocatalysts on Semiconductor Photocatalyst: A Mini Review

“…This strategy is especially effective in photocatalyst with distinctive reductive and oxidative sites [16]. When the reductive and oxidative sites of a photocatalyst are identified (currently, the dominant method is through crystal-facet engineering of oxide semiconductor photocatalysts such as BiVO4, Bi2MoO6, and TiO2), the reduction cocatalyst and oxidative cocatalyst can be selectively deposited on the respective sites via photodeposition method [17,18]. Beside the promotion of reduction and oxidation reactions, cocatalyst can sometimes contribute to generate additional charges in the overall photocatalyst hybrid when it is responsive to irradiation.…”

Efficient Degradation of Phenol and 4‐Nitrophenol by Surface Oxygen Vacancies and Plasmonic Silver Co‐Modified Bi2MoO6 Photocatalysts

“…[9] Recently,s ome studies clearly revealed that Bi 2 MoO 6 might be ap romising candidate as an excellent photocatalyst owing to as eries of advantages, such as high chemicald urability,n ontoxicity,n aturally abundant, and an appropriate bandgap (2.5-2.8 eV). [12][13][14][15][16] Nevertheless, pure Bi 2 MoO 6 suffers from low visible-light utilization efficiency,t he relativelyr apid recombination of photoexcited electron-hole pairs,a nd slow carrier transport, which limit its practical application. [12][13][14][15][16] Nevertheless, pure Bi 2 MoO 6 suffers from low visible-light utilization efficiency,t he relativelyr apid recombination of photoexcited electron-hole pairs,a nd slow carrier transport, which limit its practical application.…”

“…[10,11] This mate-rial has generally been used in many fields includingL i-ion batteries, water splitting, hydrogen energy,a nd organic pollutant degradation. [12][13][14][15][16] Nevertheless, pure Bi 2 MoO 6 suffers from low visible-light utilization efficiency,t he relativelyr apid recombination of photoexcited electron-hole pairs,a nd slow carrier transport, which limit its practical application. [17,18] Therefore, to furtherextend the visible-light response region and improve the photocatalytic activity of Bi 2 MoO 6 -based materials is highly challenging though appealing.…”