Search

The photocatalytic activity of TiO2 polymorphs has been frequently debated in literature. Numerous studies reported that rutile TiO2 exhibits low photocatalytic activity, and it is generally accepted that rutile has lower photoactivity than the anatase phase. Herein, we studied the photocatalytic activity of phase-pure rutile TiO2 nanoparticles prepared via microwave-assisted hydrothermal method (MW-R NPs). The syntheses were performed with relatively short reaction time (1−3h) at 180 °C using a microwave digestion system. The samples were characterized in detail and then tested in the photodegradation of methyl orange (MO). We demonstrate that the photodegradation of MO with MW-R NPs is highly efficient in the presence of H2O2. By employing 4.4 mM H2O2, ~90% of total decolorization was achieved after 2 min of UV-A irradiation. At the same experimental conditions, MO degradation with Degussa P25 TiO2 was only ~7%. The superior photoactivity of MW-R NPs was related to the effective photogeneration of O2•− radicals as revealed by EPR investigation. These rutile nanoparticles are excellent photocatalysts in the presence of H2O2, signifying that this oxygen source react easily with the photogenerated holes on the MW-R NPs, and thus the interfacial charge transfer lead to the formation of a large amount of O2•− radicals.

Hierarchically assembled flower-like rutile TiO2 (FLH-R-TiO2) nanostructures were successfully synthesized from TiCl4 at room temperature without the use of surfactants or templates. An initial sol–gel synthesis at room temperature allowed long-term hydrolysis and condensation of the precursors. The resulting FLH-R-TiO2 possessed relatively high crystallinity (85 wt%) and consisted of rod-shaped subunits assembling into cauliflower-like nanostructures. Hydrothermal evolution of FLH-R-TiO2 at different temperatures (150, 200 and 250 °C) was followed by means of X-ray diffraction, transmission and scanning electron microscopy. These FLH-R-TiO2 nanostructures were tested as photocatalysts under simulated daylight (full-spectrum lighting) in the degradation of methyl orange and in the inactivation of a multiresistant bacterium, Klebsiella pneumoniae. The effects of hydrothermal treatment on the structure, photocatalytic behavior and antibacterial activity of FLH-R-TiO2 are discussed.

Nanostructured indium tin oxide (ITO) powders and thin films differing in morphology and porosity were prepared by a sol–gel method. In3+ and Sn4+ were hydrolyzed in aqueous medium through the use of ethanolamine (EA) or sodium acetate (AC). X-ray diffraction measurements demonstrated that both EA and AC furnished indium tin hydroxide, which became nanocrystalline after aging for one day. The indium tin hydroxide samples calcined at 550 °C afforded ITO with a cubic crystal structure, but the morphology differed significantly, depending on the agent used for hydrolysis. Electron microscopy revealed the formation of round monodisperse nanoparticles when AC was used, whereas the application of EA led to rod-like ITO nanoparticles. Both types of nanoparticles were suitable for the preparation of transparent and conductive ITO thin films. The influence of the morphology and porosity on the optical properties is discussed.

Titanate nanotubes were synthesized from TiO{sub 2} in alkaline medium by a conventional hydrothermal method (150 Degree-Sign C, 4.7 bar). To obtain hydrogen titanates, the as-prepared sodium titanates were treated with either HCl or H{sub 3}PO{sub 4} aqueous solutions. A simple synthesis procedure was devised for stable titanate nanotube sols without using any additives. These highly stable ethanolic sols can readily be used to prepare transparent titanate nanotube thin films of high quality. The resulting samples were studied by X-ray diffraction, N{sub 2}-sorption measurements, Raman spectroscopy, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy and spectroscopic ellipsometry. The comparative results of using two kinds of acids shed light on the superior thermal stability of the H{sub 3}PO{sub 4}-treated titanate nanotubes (P-TNTs). X-ray photoelectron spectroscopy revealed that P-TNTs contains P in the near-surface region and the thermal stability was enhanced even at a low ({approx}0.5 at%) concentration of P. After calcination at 500 Degree-Sign C, the specific surface areas of the HCl- and H{sub 3}PO{sub 4}-treated samples were 153 and 244 m{sup 2} g{sup -1}, respectively. The effects of H{sub 3}PO{sub 4} treatment on the structure, morphology and porosity of titanate nanotubes are discussed. - Graphical Abstract: TEM picture (left) showsmore » P-TNTs with diameters about 5-6 nm. Inset shows a stable titanate nanotube sol illuminated by a 532 nm laser beam. Due to the presence of the nanoparticles the way of the light is visible in the sol. Cross sectional SEM picture (right) as well as ellipsometry revealed the formation of optical quality P-TNT films with thicknesses below 50 nm. Highlights: Black-Right-Pointing-Pointer H{sub 3}PO{sub 4} treatment led to TNTs with high surface area even after calcination at 500 Degree-Sign C. Black-Right-Pointing-Pointer H{sub 3}PO{sub 4}-treated TNTs preserved their nanotube morphology up to 500 Degree-Sign C. Black-Right-Pointing-Pointer Stable TNT sols can be prepared by the peptization of TNT gels. Black-Right-Pointing-Pointer High-transparency TNT thin films of high quality were fabricated.« less

Indium tin hydroxide (ITH) xerogel powders and thin films with different polyvinylpyrrolidone (PVP) contents (0–22%, w/w) were prepared by a classical sol–gel method. To obtain nanocrystalline indium tin oxide (ITO), the ITH xerogels were calcined at 550 °C. The effect of the initial polymer content on the structure of the ITO powders was studied by means of N 2 -sorption measurements, small-angle X-ray scattering (SAXS), transmission and scanning electron microscopy. The N 2 -sorption measurements revealed that the ITO powders obtained contained micropores and both their porosity and specific surface area decreased with increasing PVP content of the ITH xerogels. The SAXS measurements confirmed the enhanced sintering of the particles in the presence of PVP. The calculated mass fractal dimensions of the ITO powders increased significantly, indicating a significant compaction in structure. The pre-sintered structure could be achieved at relatively low temperature, which induced a significant decreasing (three orders of magnitude) in the electrical resistance of the ITO films.

A series of ordered mesoporous phosphate-modified SnO2 samples (mP-SnO2) with varying P content were synthesized in a template-assisted sol–gel process, with the use of hexadecylpyridinium chloride as structure-directing agent. In order to enhance the thermal stability, sol–gel derived SnO2 × nH2O was treated with H3PO4 at room temperature. The bulk and surface compositions of mP-SnO2 were studied by means of inductively coupled plasma atomic emission spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. Elemental analysis revealed that the mesostructured hybrid network adsorbed a significant amount of phosphate during the H3PO4 treatment. The measured atomic ratio P:Sn of the powder samples varied between 0.08 and 0.45. After calcination at 600 °C, both the unmodified mesoporous SnO2 (mSnO2) and mP-SnO2 with low P content (P:Sn

Gold nanoparticles (Au NPs) were prepared by the reduction of HAuCl4 acid incorporated into the polar core of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) copolymer micelles dissolved in toluene. The formation of Au NPs was controlled using three reducing agents with different strengths: hydrazine (HA), triethylsilane (TES), and potassium triethylborohydride (PTB). The formation of Au NPs was followed by transmission electron microscopy, UV–Vis spectroscopy, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). It was found that the strength of the reducing agent determined both the size and the rate of formation of the Au NPs. The average diameters of the Au NPs prepared by reduction with HA, TES, and PTB were 1.7, 2.6, and 8 nm, respectively. The reduction of Au(III) was rapid with HA and PTB. TES proved to be a mild reducing agent for the synthesis of Au NPs. DLS measurements demonstrated swelling of the PS-b-P2VP micelles due to the incorporation of HAuCl4 and the reducing agents. The original micellar structure rearranged during the reduction with PTB. ITC measurements revealed that some chemical reactions besides Au NPs formation also occurred in the course of the reduction process. The enthalpy of formation of Au NPs in PS-b-P2VP micelles reduced by HA was determined.

Vanadium oxide thin films were prepared by sol–gel method, then subjected to Nd:YAG laser (CW, 1064 nm) radiation. The characteristics of the films were changed by varying the intensity of the laser radiation. The nanocrystalline films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD revealed that above 102 W/cm2 the original xerogel structure disappears and above 129 W/cm2 the films become totally polycrystalline with an orthorhombic structure. From TEM observations, we can see that due to laser radiation, the originally fibrillar-like particles disappear and irregular shaped, layer structured V2O5 particles are created. From XPS spectra we can conclude that due to laser radiation the O/V ratio increased with higher intensities.

This study aims to analyze the elemental composition, and temporal- and spatial distributions of vanadium atoms and ions in the laser-induced vanadium oxide plasma under high vacuum using optical emission spectroscopy. Neutral atoms and singly charged V ions were detected under high vacuum in the emission spectra. The mean translational velocity of neutral V atoms in their first 25 mm propagation was estimated to be 15.7 km/s using the temporal- and spatial dynamics investigation of neutral V species in the plasma.

A series of PF-co-doped titanium dioxide (PF-TiO2) samples with various PF contents were synthesized hydrothermally at 250 degrees C and systematically investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. For the PF-codoping of TiO2, hexafluorophosphoric acid (HPF6) was used. Increasing HPF6 concentration did not decrease the crystallinity of the synthesized samples, but the dopant concentration strongly influenced the size and morphology of the PF-TiO2 nanoparticles. The undoped TiO2 consisted of polymorphic and polydisperse nanoparticles, whereas smaller, predominantly spherical particles were observed for the PF-TiO2 samples. Diffuse reflectance UV-vis spectroscopy revealed that PF-TiO2 exhibited a slightly higher band gap energy than that of undoped TiO2. Despite this blue-shift in absorption edge, the photocatalytic activity of PF-TiO2 was higher than that of undoped TiO2 even under visible light irradiation. The effects of the dopant concentration on the structure and photocatalytic activity are discussed in detail. (C) 2014 Elsevier Ltd. All rights reserved.

A novel method was developed for the synthesis of titanate nanosheets with high surface area. A solid-state mixture of NaOH and TiO 2 was reacted at 600 °C for several minutes. The aqueous dispersion of the resulting melt was aged at room temperature for periods up to 14 days. After hydrochloric acid treatment and washing procedures, the reaction product was characterized by X-ray diffraction, Raman spectroscopy, N 2 -sorption and small-angle X-ray scattering measurements. The titanate compound not subjected to the aging process was amorphous and possessed a microporous framework, while the aged samples displayed nanosheet morphology and high specific surface area (396–509 m 2 g −1 ). It was revealed that the very short heat treatment is of crucial importance for the titania-titanate phase transformation, while the aging process is needed for the morphological evolution of the titanate samples. The effects of the aging time on the structure and the morphology are discussed.

In this work, we present X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis of laser treated vanadium oxide sols. The films were also observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to reveal how the original xerogel structure changes into irregular shaped, layer structured V 2 O 5 due to the laser radiation. XRD revealed that above 102 W/cm 2 the original xerogel structure disappears and above 129 W/cm 2 the films become totally polycrystalline with an orthorhombic structure. XPS spectra showed O/V ratio increment by using higher laser intensities.