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A novel ZnO incorporated MoO 3 nanostructured thin film system exhibiting high sensitivity and selectivity to ethanol has been developed. The MoO 3 :ZnO nanostructures exhibit enhanced ethanol sensing performance in non-humid and humid (75% r.H. at 21 C) atmospheres compared to the pure MoO 3 layer; with increase in ZnO concentrations, the sensitivity and stability increased, and the response/ recovery time decreased. The response (G ethanol /G air ) of the 25% MoO 3 :ZnO sensor at an operating temperature of 300 C against 500 ppm ethanol is up to 171 under non-humid and 117 under humid (75% r.H.) conditions. By comparing the response of the 25% ZnO added MoO 3 sensor toward various gases (H 2 , CO, C 3 H 6 , CH 4 and C 2 H 5 OH), distinctive selectivity to ethanol is observed. The ethanol sensitivity action over MoO 3 nanostructures can be ascribed to the catalytic oxidation of ethanol to acetaldehyde, and the enhancement of gas sensing response of the MoO 3 :ZnO system can be attributed to more active centers that are obtained from the enhanced oxygen vacancy defects induced by ZnO. The presence of a humid atmosphere has a dramatic influence on the sensor performance towards ethanol; the sensitivity diminishes drastically due to the partial site precluding nature of the adsorbed hydroxyl groups to the analyte. The ZnO incorporated MoO 3 nanostructure based sensing layers in the present work show significantly superior ethanol sensing performance to the works previously reported for various metal oxide systems.

MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

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We have investigated basic mechanisms of concrete corrosion by studying wollastonite in aqueous environments. This well-defined crystalline mineral is well-suited as a model system of calcium–silicate phases, the main constituent of this important building material. A detailed peak-shape analysis of X-ray diffraction (XRD) signals recorded for wollastonite powders exposed to water allowed monitoring of dramatic changes in particle shape as a result of the so-called metal–proton exchange reaction (MPER). Since these experiments were carried out for well-defined particles with known orientation, state-of-the art calculations using density functional theory (DFT) could be employed to more precisely study this behavior, which previously has not attracted much attention. The free energies of the different crystalline surfaces of wollastonite are strongly affected when brought into contact with water, thus providing a strong driving force for changes in particle shape. A more detailed analysis of the corresponding Wulff constructions reveals, however, that a quantitative description of these phenomena also requires a detailed analysis of the kinetics. Implications for concrete corrosion will be discussed, and strategies for its prevention will be outlined.