Abstract
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).
Highlights
Titanium(IV) oxide has been widely investigated for environmental and energy applications due to many advantages, such as good stability, strong redox ability, nontoxicity, low cost and high availability [1,2,3]
titanate nanowires (TNW) were mainly composed of K2Ti8O17, whereas anatase was the major phase in other samples of crystallite sizes in the range from 8 to 15 nm
TNW had wire-like morphology (1D), other samples consisted of fine NPs (0D), including Octahedral anatase particles (OAP) NPs with well-defined shape of octahedron
Summary
Titanium(IV) oxide (titania, TiO2) has been widely investigated for environmental and energy applications due to many advantages, such as good stability, strong redox ability, nontoxicity (except nanomaterial toxicity), low cost and high availability [1,2,3]. Different methods of titania synthesis have been reported, including hydrothermal reaction (HT), solvothermal, sol-gel, electrosynthesis, soft- and hard-templating, micelle and inverse micelle, direct oxidation, chemical and physical vapor deposition, sonochemical, microwave, gas-phase and green synthesis (“bio-reduction” using different biological extracts) [26,28,29,30,31]. “Hydrothermal Synthesis of Nanomaterials”, 2019 and Materials “Conventional and Microwave Hydrothermal Synthesis of Functional Materials”, 2019/2020), due to feasible preparation of required nanostructures by simple changing of process conditions [23]. In this study, the comparison between zero-dimensional (0D) and one-dimensional (1D) semiconductors, i.e., faceted anatase particles vs titanate nanowires, has been investigated
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