PVA modified ZnO nanowire based microsensors platform for relative humidity and soil moisture measurement

the present work, we have investigated Polyvinyl Alcohol (PVA) modified Zinc Oxide nanowires (ZnONW) heterostructure based microsensors platform to measure the relative humidity and gravimetricsoil moisture contents for agriculture applications. For this the hydrothermal growth of ZnO NW is carried out on Inter Digitated Electrodes (IDEs) patterned on Si/SiO2 substrates. Further, ZnO NW surfaceis functionalized by drop casting PVA solution. The surface characterization of the PVA coated ZnO NWs-film is carried out by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ScanningElectron Microscopy (SEM) and Current-Voltage (IV) measurements. These measurements revealed the successful formation of PVA-ZnO NW heterostructure. The microsensors are exposed to different levels of relative humidity (% RH) ranging from 40 to 90% and various moisture contents of bentonite and redsoils. It is observed that the microsensors resistance decreases with increase in humidity (% RH) and gravimetric soil moisture contents (red and bentonite), respectively. The sensor exhibited a sensitivityof 4.6 K Omega / 0.1% change in RH. Further, sensitivities of 7.5 and 12.2 Omega/ 0.1% change in gravimetric water content when exposed to bentonite and red soil samples respectively were achieved. The low cost, goodre producibility, repeatability and good stability with time indicated that PVA modified ZnO NW hetero structure microsensors platform is potentially useful for measurement of humidity and soil moisture contents in agriculture applications. (C) 2017 Elsevier B.V. All rights reserved

Liquid phase oxidation of alkanes using Cu/Co-perchlorophthalocyanine immobilized MCM-41 under mild reaction conditions

Amino-functionalized MCM-41 (NH<SUB>2</SUB>-MCM-41) was used to immobilize Cu/Co-Cl<SUB>16</SUB>Pc complex, i.e. Cu/Co-AM(PS) for liquid phase oxidation of alkanes under mild reaction conditions. Higher rates of reaction and better catalytic activity values were obtained for Cu/Co-AM(PS) as compared to Cu/Co-Cl<SUB>16</SUB>Pc grafted on (i) amino-functionalized SiO<SUB>2</SUB> [Cu/Co-ASiO<SUB>2</SUB>] and (ii) non-functionalized MCM-41 [Cu/Co-M(I)] catalysts along with neat metal complex under identical conditions. The catalysts were evaluated by comparing two different oxidants: (i) TBHP and (ii) O<SUB>2</SUB>/aldehyde. The rate of conversion and percent selectivity differ for the above two oxidants due to differences in stability of radical species and in their homolytic/heterolytic pathways. The homolytic dissociation of oxygen favors a higher rate of conversion in the case of TBHP, whereas the heterolytic mechanism favors a higher selectivity for cyclohexanone in the case of O<SUB>2</SUB>/aldehyde. The catalysts were characterized by XRD, MAS NMR, N<SUB>2</SUB>-adsorption, microanalysis, UV-vis, FTIR and cyclic voltammetry. The UV-vis spectra reveal a blue shift for the metal phthalocyanine-immobilized samples, indicating unimolecular dispersion of metal complex within the channels of MCM-41. Cyclic voltammetry results suggest some coordinative interaction of the amino group of NH<SUB>2</SUB>-MCM-41 with the metal on grafting with the complex

Zinc oxide hierarchical nanostructures as potential NO2 sensors

A superficial thermal evaporation method has been employed for the fabrication of hierarchical zinc oxide (ZnO) nanostructured films, composed of nanorods (NR's) and bunch of nanowires (BNW's), on glass substrate and the diverse atmospheric annealing effect on their structural, morphological, compositional, and gas sensing properties has been systematically studied and reported. Structural investigation corroborates the formation of crystalline hexagonal wurtzite ZnO. The arrays of vertically aligned nanorods and bunch of nanowires of ZnO were observed on the substrate surface. As-prepared ZnO NR's and BNW's are utilized as a sensing material for detection of toxic nitrogen dioxide (NO2). The ZnO sensors exhibit high response to NO2 along with rapid response and recovery time values @200 degrees C. In addition, ZnO sensors respond to a very small exposure of NO2 gas i.e. 1 ppm. Furthermore, the developed sensors attain excellent stability and reproducibility in response. Finally, the interaction of NO2 gas molecules with hierarchical nanostructured ZnO sensors has successfully been studied and discussed by employing an electrochemical impedance spectroscopy measurement

Enhanced ammonia sensing characteristics of tungsten oxide decorated polyaniline hybrid nanocomposites

Polyaniline (PAni)-tungsten oxide (WO3) hybrid nanocomposites sensor have been lucratively synthesized by in-situ chemical oxidative polymerization method by entrapping tungsten oxide nanoparticles (10-50%) in the polyaniline matrix on precleaned glass substrate. The structural, morphological and surface composition elucidation of PAni-WO3 hybrid nanocomposites were explored by X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The existence of WO3 in PAni matrix and interaction between them was confirmed using XRD and Raman spectroscopy. The incorporation of WO3 nanoparticles into the PAni matrix introduces porosity which enhanced gas sensing properties. The TEM image of PAni-WO3 hybrid nanocomposite film exploded the average diameter of WO3 nanoparticles ranging from 40 to 50 nm. Chemical composition of PAni-WO3 hybrid nanocomposites was characterized by using X-ray photoelectron spectroscopy (XPS). In order to investigate the gas sensing parameter of PAni-WO3 hybrid nano composite, hybrid nanocomposite film was exposed to different oxidizing gases (Cl-2, NO2) and reducing gases (NH3, H2S, CH3OH, C2H5OH) in range 5-100 ppm concentration of gas. It was observed that the sensors of PAni-WO3 hybrid nanocomposites showed better sensitivity, selectivity, stability and reproducibility compared to pure PAni and pure WO3. PAni-WO3 (50%) hybrid nanocomposite sensor operating at room temperature reveals maximum response of 158% towards 100 ppm of NH3 gas and also capable to respond very little concentration of 5 ppm NH3 gas with reasonable response of 24%. The gas sensing mechanism of the nanocomposites in presence of air and with target NH3 gas atmosphere was discussed in detail with the help of energy band diagram. The interaction of NH3 and NO2 gas with PAni-WO3 hybrid nanocomposite sensor was investigated by employing an impedance spectroscopy also

Thermally evaporated copper oxide films: A view of annealing effect on physical and gas sensing properties

The present paper reports a facile approach to prepare copper oxide (CuO) films directly onto a glass substrate by thermal evaporation method and their chemiresistive properties towards hazardous nitrogen dioxide (NO2). The influence of annealing temperature on structural, morphological, and gas sensing properties of the CuO films has been thoroughly investigated and reported. Structural and morphological analyses has confirmed the formation of polycrystalline monoclinic CuO with uniformly distributed nanoparticles over the substrate surface. Gas sensing measurements on CuO films reveal the high response, excellent selectivity, fast response recovery time signatures, good repeatability, and stability towards lower concentration of NO2 gas @150 C-circle. A maximum response of 48% towards 100 ppm NO2 has been achieved. Gas sensing results demonstrate an influence of morphology on the NO2 sensing performance of CuO films. In addition, the interactions between CuO sensor film and NO2 gas molecules are studied through an impendence spectroscopy analysi