Development of nanostructured polyaniline–titanium dioxide gas sensors for ammonia recognition

The performance at room temperature of nanostructured polyaniline (PANi)–titanium dioxide (TiO₂) ammonia gas sensors was investigated. The PANi–TiO₂ thin-film sensors were fabricated with a spin-coating method on glass substrates. PANi–TiO₂ (0–50%) sensor films were characterized for their structural, morphological, optical, and various gas-sensing properties. The structural analysis showed the formation of nanocrystalline TiO₂, whereas PANi exhibited an amorphous nature. Morphological analysis of the PANi–TiO₂ nanocomposites film revealed a uniform distribution of TiO₂ nanoparticles in the PANi matrix. The absorption peaks in the Fourier transform infrared spectra and ultraviolet–visible spectra of the PANi–TiO₂ composite film were found to shift to higher wave numbers compared to those observed in pure PANi. The observed shifts were attributed to the interaction between the TiO₂ particles and the PANi molecular chains. The gas-sensing properties showed that the sensors exhibited selectivity to ammonia (NH₃) at room temperature. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

CFD simulation of Taylor–Couette flow in scraped surface heat exchanger

The flow between two concentric cylinders which is termed as Taylor–Couette flow has been studied in scraped surface heat exchanger with and without blades. Shear rate in annular flow with and without blades was measured by Dumont et al. (2000a) using electrochemical method and determined the onset of Taylor vortices at specific Taylor number in both cases for Newtonian flow. CFD simulations have been carried out to determine the transition zone from laminar Couette flow to Taylor vortex flow using the same geometry for which Dumont et al. (2000a) had carried out the experiments. The Reynolds stress model (RSM) and k–? model are used for Taylor vortex flow (Ta > 300) to characterize the flow pattern in annular flow and SSHE respectively. The aim of the present work is to analyze the effect of rotating scraper on the existing flow patterns in simple annular flow using CFD simulations.     

Synthesis and characterization of Ru doped CuO thin films for supercapacitor based on Bronsted acidic ionic liquid

The synthesis of nanostructured ruthenium (Ru) doped copper oxide (CuO) thin films by colloidal solution method and ionic liquid are presented. The prepared colloidal solution was spin coated on the stainless steel substrates. The coated films were used to measure the specific capacitance in the task specific Bronsted acidic that is in 3-carboxymethyl-1-methylimidazolium bisulfate [CMIM] [HSO₄] ionic liquid (IL). Further, the films were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Fourier transform Raman spectroscopy (FT-Raman) and cyclic voltammetry (CV). The Ru doped CuO films exhibit higher specific capacitance, C_sp (C_sp = ratio of average current in CV and a product of scan rate and mass deposited on the film) with the larger potential window as compared to undoped CuO film. The highest C_sp of 406 F g⁻¹ was observed for 15 volume percent of Ru doping concentration. This is the first successful step towards development of ecofriendly CuO based supercapacitors in task specific IL synthesized by green technology.     

Synthesis and characterization of spray deposited PdO-NiO-SDC composite anode material for potential application in IT-SOFC

The synthesis of mixed conducting PdO-NiO-SDC composite films has been reported for the first time by a simple and cost effective spray pyrolysis technique. The films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. The structure, morphology and electrical properties of the films were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and impedance spectroscopy (IS). The substrate and annealing temperatures were optimized for obtaining nano-crystalline, porous, adherent and composite films with PdO, NiO and SDC phases. Films showed good microstructure with sufficient porosity and good connectivity of the deposited material. Crystallite size of the deposited material was found to be in the range of 7-9 nm. The deposited film showed high oxygen ion conductivity, 3.94 × 10⁻¹ S cm⁻¹ at 350 °C. Due to their nano-crystalline, porous and composite nature the spray deposited PdO-NiO-SDC films may have high three phase boundary area and hence can be considered as an anode for intermediate temperature solid oxide fuel cells.     

Synthesis of nanocrystalline nickel-zinc ferrite (Ni0.8Zn0.2Fe2O4) thin films by chemical bath deposition method

The nickel-zinc ferrite (Ni_0.8Zn_0.2Fe₂O₄) thin films have been successfully deposited on stainless steel substrates using a chemical bath deposition method from alkaline bath. The films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), static water contact angle and cyclic voltammetry measurements. The X-ray diffraction pattern shows that deposited Ni_0.8Zn_0.2Fe₂O₄ thin films were oriented along (3 1 1) plane. The FTIR spectra showed strong absorption peaks around 600 cm⁻¹ which are typical for cubic spinel crystal structure. SEM study revealed compact flakes like morphology having thickness ∼1.8 μm after air annealing. The annealed films were super hydrophilic in nature having a static water contact angle (θ) of 5°.The electrochemical supercapacitor study of Ni_0.8Zn_0.2Fe₂O₄ thin films has been carried out in 6 M KOH electrolyte.The values of interfacial and specific capacitances obtained were 0.0285 F cm⁻² and 19 F g⁻¹, respectively.     

Aqueous chemical route deposition of nanocrystalline ZnO thin films as acetone sensor: Effect of molarity

Nanocrystalline ZnO thin films were deposited onto glass substrate using a simple and inexpensive aqueous chemical method at low temperature (90 °C). The concentration of precursor solution was varied in order to study its effect on structural, morphological, and gas response properties. Field-emission scanning electron microscopy (FESEM) images indicate the growth of ZnO with hexagonal shaped nanostructure. Further these films were used to explore gas response properties towards acetone, propanol and ethanol vapors. The sensor response was found to be decreased with increase in precursor concentration. The highest sensor response of 92% was observed towards acetone for the film deposited at 0.05 M at an operating temperature of 350 °C. The higher vapor response towards acetone is attributed to size and surface morphology of the film deposited at 0.05 M.     

ZnO nanocrystalline thin films: a correlation of microstructural,optoelectronic properties

The compositional, structural, microstructural, dc electrical conductivity and optical properties of undoped zinc oxide films prepared by the sol–gel process using a spin-coating technique were investigated. The ZnO films were obtained by 5 cycle spin-coated and dried zinc oxide films followed by annealing in air at 600 °C. The films deposited on the platinum coated silicon substrate were crystallized in a hexagonal wurtzite form. The energy-dispersive X-ray (EDX) spectrometry shows Zn and O elements in the products with an approximate molar ratio. TEM image of ZnO thin film shows that a grain of about 60–80 nm in size is really an aggregate of many small crystallites of around 10–20 nm. Electron diffraction pattern shows that the ZnO films exhibited hexagonal structure. The SEM micrograph showed that the films consist in nanocrystalline grains randomly distributed with voids in different regions. The dc conductivity found in the range of 10⁻⁵–10⁻⁶ (Ω cm)⁻¹. The optical study showed that the spectra for all samples give the transparency in the visible range.     

Electrochemical processing of high-T c Bi(Pb)-Sr-Ca-CuO thin films

Superconducting thin films of Bi(Pb)-Sr-Ca-CuO system were prepared by depositing the film onto silver substrate by d.c. electrodeposition technique with dimethyl sulphoxide bath in order to examine the effect of Pb addition to the BSCCO system. The films were deposited at the potential of -0.8 V vs saturated calomel electrode (SCE) onto the silver substrate. The different preparative parameters such as deposition potential, deposition time were studied and optimized. These films were then oxidized electro-chemically at room temperature in an alkaline (1 N KOH) solution, and also at 600°C temperature in an oxygen atmosphere. The films showed the superconducting behaviour, with T_c values ranging between 85 K and 96 K, respectively.     

Effect of precursor concentration on the properties of ITO thin films

Tin-doped indium oxide (ITO) thin films have been prepared by the spray pyrolysis method using indium chloride as a precursor and stannic chloride as a dopant. The effect of a precursor concentration on the structural, morphological, electrical and optical properties of films has been studied. The concentration of InCl₃ in the spraying solution is varied from 6.25 to 37.5 mM keeping doping percentage of tin fixed at its optimized value of 5 wt.%. Bare glass is used as a substrate and oxygen as the carrier and reaction gas. X-ray diffraction (XRD) patterns show that films are polycrystalline and their crystallinities are dependent on the precursor concentration. A surface morphology has been observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The typical ITO film has minimum resistivity value of 2.71 × 10⁻³ Ω cm, whose carrier concentration and mobility were 7.45 × 10¹⁹ cm⁻³ and 31 cm²/(V s), respectively. In addition, the best ITO film has optical transmittance of 94.4% and figure of merit 1.20 × 10⁻³ Ω⁻¹.     

Preparation of transparent and conducting boron-doped ZnO electrode for its application in dye-sensitized solar cells

A simple and economic chemical spray pyrolysis method is used to prepare transparent and conducting boron-doped zinc oxide (B_nZnO) electrode having potential applications in dye-sensitized solar cells (DSSCs). The B_nZnO electrodes were critically characterized for their structural, morphological and electrical properties. The B_nZnO electrode with 2 at% boron doping showed average grain size of 20(±1) nm, surface roughness of 9 nm, ?95% transparency and resistivity of 4.5×10⁻³ Ω cm⁻¹. Furthermore, doping concentration of boron could also be easily controlled for achieving desired properties. Using this electrode as a substrate in DSSCs, the solar-to-electrical conversion efficiency with N3 dye as a sensitizer was noted to be 1.53%. This work suggests that the B_nZnO electrodes could be used as promising alternative to presently used indium- or fluorine-doped tin oxide as substrates.