Enhanced Photocatalytic Performance of ZnO Nanorods Coupled by Two-Dimensional alpha -MoO sub(3) Nanoflakes under UV and Visible Light Irradiation

• Published in: Chemistry : a European journal Vol. 22; no. 36; pp. 12777 - 12784
• Main Authors: Hang, Da-Ren, Sharma, Krishna Hari, Chen, Chun-Hu, Islam, Sk Emdadul
• Format: Journal Article
• Language: English
• Published: 01.08.2016
• Subjects: Catalytic activity; Molybdenum oxides; Nanorods; Nanostructure; Performance enhancement; Photocatalysis; Two dimensional; Zinc oxide
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201602141

We exploit the utilization of two-dimensional (2D) molybdenum oxide nanoflakes as a co-catalyst for ZnO nanorods (NRs) to enhance their photocatalytic performance. The 2D nanoflakes of orthorhombic alpha -MoO sub(3) were synthesized through a sonication-aided exfoliation technique. The 2D MoO sub(3) nanoflakes can be further converted to substoichiometric quasi-metallic MoO sub(3-x) by using UV irradiation. Subsequently, 1D-2D MoO sub(3)/ZnO NR and MoO sub(3-x)/ZnO NR composite photocatalysts have been successfully synthesized. The photocatalytic performances of the novel nanosystems in the decomposition of methylene blue are studied by using UV- and visible-illumination setup. The incorporated 2D nanoflakes show a positive influence on the photocatalytic activity of the ZnO. The obtained rate constant values follow the order of pristine ZnO NR<MoO sub(3)/ZnO NR<MoO sub(3-x)/ZnO NR composites. The enhancement of the photocatalytic efficiency can be ascribed to a fast charge carrier separation and transport within the heterojunctions of the MoO sub(3)/ZnO NRs. In particular, the best photocatalytic performance of the MoO sub(3-x)/ZnO NR composite can be additionally attributed to a quasi-metallic conductivity and substoichiometry-induced mid-gap states, which extend the light absorption range. A tentative photocatalytic degradation mechanism was proposed. The strategy presented in this work not only demonstrates that coupling with nanoscale molybdenum oxide nanoflakes is a promising approach to significantly enhance the photocatalytic activity of ZnO but also hints at new type of composite catalyst with extended applications in energy conversion and environmental purification. 2D nanoflakes: Nanometer-thick molybdenum oxide flakes were employed as a co-catalyst for ZnO nanorods to enhance their photocatalytic performance (see figure; CB=conductive band, VB=valence band, MB=methylene blue). The recombination of photogenerated electrons and holes is suppressed by the double charge-transfer mechanism.