Imre Miklós Szilágyi

Cu-doped resorcinol-formaldehyde (RF) polymer and carbon aerogels.

Introduction of transition metal salt(s) onto the surface of porous carbons may increase the selectivity and/or efficiency of these adsorbents in catalysis or separation. Carbon aerogels with low pressure drop are particularly suited for these applications. Moreover the sol-gel process used in the synthesis of the resorcinol-formaldehyde polymer gel (RF) precursors offers an extra opportunity for introducing metal ions. Salts of different metals modify both the macroscopic texture and the porosity, depending on the synthesis protocol. In this paper we show, by means of low temperature nitrogen adsorption measurements and SEM, as well as small- and wide-angle X-ray scattering (SAXS and WAXS), how the addition of copper acetate at three different stages influences not only the specific surface area but also the resulting overall structure over a wide range of length scales. Posttreatment in either the polymer or the carbon aerogel stage provides a means of adjusting the copper content. While the Cu-containing carbon aerogels differ mainly in their micropore volume but not in the width of the distribution, their pore size window in the mesopore range can be tuned between 50 and 400 A by the protocol of Cu addition. The synthesis protocol also determines the chemical form of the copper.

Effect of the morphology and phases of WO3 nanocrystals on their photocatalytic efficiency

Understanding of the effect of the morphology and crystal phase on photocatalytic efficiency and their precise control are still a great challenge in photocatalysis. In this paper, we use WO3 as an example to study how to control the morphology through understanding the effect of solution pH, EtOH and polymeric surface modulator on the morphology, crystalline phase, band gap and the photocatalytic efficiency of WO3 nanostructures. The photocatalytic efficiency of nano WO3 is a compromise of the band gap, crystal phase, morphology, and the oxidation state. Cuboid-shaped m-WO3 with Eg = 2.7 eV and nanoneedle h-WO3 with Eg = 3.1 eV give high photocatalytic efficiency, while nanowire h-WO3 with Eg = 2.9 eV gives the lowest photocatalytic efficiency. Detailed control of the morphology and crystal phase of nanoscale WO3 were also presented in this paper. pH 1.05 was found to be a transition point for the crystalline phase, crystal size and band gap. pH values lower than 1.05 preferred monoclinic, whereas pH values higher than 1.05 favoured hexagonal WO3 formation. At pH 1.05, the crystal shape changed from cuboid to a fine nanoneedle shape, which was followed by a sudden size decline and an exponential increase in the aspect ratio. At the transition pH, the band gap reached a peak.

Gas sensing properties of very thin TiO2 films prepared by atomic layer deposition (ALD)

Very thin titanium dioxide (TiO2) films of less than 10 nm were deposited by atomic layer deposition (ALD) in order to study their gas sensing properties. Applying the quartz crystal microbalance (QCM) method, prototype structures with the TiO2 ALD deposited thin films were tested for sensitivity to NO2. Although being very thin, the films were sensitive at room temperature and could register low concentrations as 50-100 ppm. The sorption is fully reversible and the films seem to be capable to detect for long term. These initial results for very thin ALD deposited TiO2 films give a promising approach for producing gas sensors working at room temperature on a fast, simple and cost-effective technology.

Photocatalytic WO3/TiO2 nanowires: WO3 polymorphs influencing the atomic layer deposition of TiO2

50–70 nm hexagonal (h-) and 70–90 nm monoclinic (m-) WO3 nanoparticles (NPs) were prepared by controlled annealing of (NH4)xWO3 in air at 470 and 600 °C, respectively. In addition, 5–10 nm thick and several micrometer long h-WO3 nanowires (NWs) were obtained by microwave hydrothermal synthesis at 160 °C with Na2WO4, HCl and (NH4)2SO4 as starting materials. TiO2 was deposited on h-WO3 NWs by atomic layer deposition (ALD) at 300 °C using Ti(iOPr)4 and H2O as precursors. The as-prepared materials were studied by TG/DTA-MS, XRD, Raman, SEM-EDX, TEM, ellipsometry, UV-Vis, and their photocatalytic activity was also tested by the photodecomposition of aqueous methyl orange. Our study is the first evidence of diverse ALD nucleation on various WO3 polymorphs, since on h-WO3 NWs TiO2 nucleated only as particles, whereas on m-WO3 conformal TiO2 film was formed, explained by the different surface OH coverage of h- and m-WO3. The h-WO3 NWs had significantly higher photocatalytic activity compared to h-WO3 NPs, and similar performance as m-WO3 NPs. By adding TiO2 to h-WO3 NWs by ALD method, the photocatalytic performance increased by 65%, showing clearly the uniqueness of ALD to obtain superior oxide composite photocatalysts.

Review on one-dimensional nanostructures prepared by electrospinning and atomic layer deposition

This paper reviews the various lD nanostructures, which were prepared by electrospinning and atomic layer deposition (ALD). On the one hand, electrospinning served to make sacrificial polymer templates for the ALD growth; and thus various single or multilayer inorganic nanotubes were obtained. On the other hand, polymer, polymer/inorganic or inorganic nanowire templates were produced by electrospinning. By a consecutive ALD reaction various core/shell nanowires were synthesized.

Controlling the Composition of Nanosize Hexagonal WO3 for Gas Sensing

Hexagonal (h-) WO3 was prepared through heating hexagonal ammonium tungsten bronze (HATB), (NH4)0.07(NH3)0.04(H2O)0.09WO2.95. By adjusting the heating temperature and atmosphere of HATB, we could control the oxidation state of tungsten atoms and the residual NH3/NH4 + content in h-WO3. The as-produced h-WO3 nanoparticles with different composition were tested as gas sensors and the effect of composition on gas sensing properties was studied. Our results showed that oxidized h-WO3 had the best sensitivity to H2S.

Nanostructured hexagonal tungsten oxides for ammonia sensing

Among the family of wide band-gap semiconducting metal oxides, tungsten trioxide is the most promising oxide for gas sensing. A metastable open-structured hexagonal phase of WO3 was successfully synthesized using acid precipitation method. The oxide was characterized using SEM, TEM and XRD. The sensing property to reducing ammonia gas was measured. The sensitivity is much higher than that of monoclinic tungsten oxides. The oxide polymorph exhibits a p-n type transition when the temperature goes from 100 °C to 300 °C.

Synthesis and Examination of Hexagonal Tungsten Oxide Nanocrystals for Electrochromic and Sensing Applications

Tungsten oxides are among the most used materials in hazardous gas detection. In this work, a soft chemical nanocrystalline processing route was demonstrated for the preparation of hexagonal tungsten oxides. The structure of parent phases was studied by scanning and transmission electron microscopy and by X-ray diffraction.

Quantification of low drug concentration in model formulations with multivariate analysis using surface enhanced Raman chemical imaging.

This paper reports the application of surface enhanced Raman chemical imaging (SER-CI) as a potentially non-destructive quantitative analytical method for the investigation of model pharmaceutical formulations containing the active pharmaceutical ingredient (API) in low concentrations (0.5-2%). The application of chemometric techniques for processing the spectra enables the determination of API distribution in products of different concentrations. In addition, the applied multivariate curve resolution can be proper method to identify unexpected contaminants in illicit drugs. The drastic Raman signal enhancement in the presence of silver nanoparticles provides significantly improved calibration accuracy and, at the same time, radically decreased image acquisition time compared to conventional Raman chemical imaging.

Photocatalytic hollow TiO 2 and ZnO nanospheres prepared by atomic layer deposition

Carbon nanospheres (CNSs) were prepared by hydrothermal synthesis, and coated with TiO2 and ZnO nanofilms by atomic layer deposition. Subsequently, through burning out the carbon core templates hollow metal oxide nanospheres were obtained. The substrates, the carbon-metal oxide composites and the hollow nanospheres were characterized with TG/DTA-MS, FTIR, Raman, XRD, SEM-EDX, TEM-SAED and their photocatalytic activity was also investigated. The results indicate that CNSs are not beneficial for photocatalysis, but the crystalline hollow metal oxide nanospheres have considerable photocatalytic activity.