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

Photoluminescent and gas-sensing properties of ZnO nanowires prepared by an ionic liquid assisted vapor transfer approach

In this work, the ionic liquid assisted technique was used to control the growth characteristic of ZnO nanowires (NWs). The major change after adding ionic liquid into the growth system was the change in NW growth orientation, which was shifted from polar c- to non-polar a-orientation. Room temperature photoluminescence demonstrates a big reduction of the green luminescence which implies an annihilation of deep level emission. We propose two possible mechanisms responsible for the reduction of the green emission: The first mechanism is the passivation of ZnO NWs surface by fractions of ionic liquid employed for the growth, which further reduces the green emission. The second mechanism is the reduction of the defect density by changing the growth orientation. By using a semi-empirical Austin Model 1 method, the formation energy of oxygen vacancies in c- and a-oriented ZnO NWs has been simulated and compared. Accordingly, the gas-sensor constructed from ionic liquid assisted ZnO nanowires does not response when exposed to CO. This inert sensitivity is caused by the suppressed adsorption of CO molecules due to the presence of the passivation layer. The study presented here provides a new insight of how the recombination appears at the surface of ZnO NWs

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