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Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles

1
Hubei Provincial Key Laboratory of Green Materials for Light Industry, Hubei University of Technology, Wuhan 430068, China
2
Institute for Catalysis (ICAT), Hokkaido University, N21 W10, Sapporo 001-0021, Japan
3
Laboratory of Physical Chemistry, CNRS UMR 8000, Université Paris-Saclay, 91400 Orsay, France
*
Authors to whom correspondence should be addressed.
Nanomaterials 2019, 9(10), 1447; https://doi.org/10.3390/nano9101447
Received: 9 September 2019 / Revised: 4 October 2019 / Accepted: 4 October 2019 / Published: 11 October 2019
(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)
Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modified samples. Photocatalytic activities of bare and modified OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed different influence on the activity depending on the semiconductor support, i.e., gold-modified TNW and platinum-modified OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modified samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical effect on the overall photocatalytic performance. TRMC analysis confirmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the efficiency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity).
Keywords: noble metal; faceted titania; octahedral particle; titanate nanowire; plasmonic photocatalysis; photocatalyst morphology; morphology-governed activity; gold; silver; platinum noble metal; faceted titania; octahedral particle; titanate nanowire; plasmonic photocatalysis; photocatalyst morphology; morphology-governed activity; gold; silver; platinum
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MDPI and ACS Style

Wei, Z.; Endo-Kimura, M.; Wang, K.; Colbeau-Justin, C.; Kowalska, E. Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles. Nanomaterials 2019, 9, 1447.

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