Namdev S. Harale

Ultrasensitive Gold Nanostar–Polyaniline Composite for Ammonia Gas Sensing

Gold in the form of bulk metal mostly does not react with gases or liquids at room temperature. On the other hand, nanoparticles of gold are very reactive and useful as catalysts. The reactivity of nanoparticles depends on the size and the morphology of the nanoparticles. Gold nanostars containing copper have rough surfaces and large numbers of active sites due to tips, sides, corners, and large surface area-to-volume ratios due to their branched morphology. Here the sensitivity of the gold nanostar-polyaniline composite (average size of nanostars ∼170 nm) toward ammonia gas has been investigated. For 100 ppm ammonia, the sensitivity of the composite increased to 52% from a mere 7% value for pure polyaniline. The gold nanostar-polyaniline composite even showed a response time as short as 15 s at room temperature. The gold nanostars act as a catalyst in the nanocomposite. The stability and sensitivity at different concentrations and the selectivity for ammonia gas were also investigated.

Chemically synthesized PbS Nano particulate thin films for a rapid NO2 gas sensor

Abstract Rapid NO2 gas sensor has been developed based on PbS nanoparticulate thin films synthesized by Successive Ionic Layer Adsorption and Reaction (SILAR) method at different precursor concentrations. The structural and morphological properties were investigated by means of X-ray diffraction and field emission scanning electron microscope. NO2 gas sensing properties of PbS thin films deposited at different concentrations were tested. PbS film with 0.25 M precursor concentration showed the highest sensitivity. In order to optimize the operating temperature, the sensitivity of the sensor to 50 ppm NO2 gas was measured at different operating temperatures, from 50 to 200 °C. The gas sensitivity increased with an increase in operating temperature and achieved the maximum value at 150 °C, followed by a decrease in sensitivity with further increase of the operating temperature. The sensitivity was about 35 % for 50 ppm NO2 at 150 °C with rapid response time of 6 s. T90 and T10 recovery time was 97 s at this gas concentration.

CdO and CdO-ZnO composite nanowires: Synthesis, characterization and ethanol gas response

A pure and ZnO added CdO thin films are prepared by chemical bath deposition to study their ethanol sensing properties. The depositions were carried out in a highly alkaline condition where in cadmium acetate was used as a source of cadmium while zinc acetate was added as the source of Zn inclusion. These films were subsequently annealed at 723K and studied for its morphological, optical and gas sensing response to understand the effect of ZnO addition. The optical response for the composite film interestingly depicted the existence of separate absorption signature for CdO and ZnO in visible region at around 550 nm and 360nm respectively, thereby confirming the formation of composite structure. The smooth surfaced CdO nano-wires apparently got transformed in to beaded nano wires with the addition of ZnO. The overall diameter of the CdO wires decreased from around 60 nm to approximately 40 nm for CdO-ZnO composite films. This has remarkably enhanced the ethanol gas sensing response from 39% to 61% for the CdO-ZnO composite thin film.

Facile green synthesis of In2O3 bricks and its NO2 gas sensing properties

Recently, metal oxide semiconductor based gas sensors have been used to monitor and maintain amount of toxic gases in environment. Use of In2O3 nano/microstructures have been increased as a heterogeneous catalyst for gas sensing due to its high response, good selectivity, short response and recovery time. In the present work, synthesis of In2O3 bricks was carried by a hydrothermal method using biomolecule as green product. The effect of precursor concentrations of In2O3 thin film was studied in this particular work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Photoluminescence (PL), scanning electron microscope (SEM), Field emission scanning electron microscope (FE-SEM) and Brunauer–Emmett–Teller (BET) analyses were used for structural, optical, morphological and surface analysis characterizations. The In2O3 thin film displays high sensitivity and selectivity due to its active sites present on sensing layer. The results assures that optimized In2O3 thin films exhibit a high response with very low response and recovery time about 600 for NO2 gas.

Synthesis and characterization of chemically deposited ZnO nanorods for NO 2 gas sensing applications

Zinc oxide (ZnO) nanorod arrays were deposited on to the soda-lime glass substrates by wet chemical route using zinc acetate as precursor. The structural and surface morphological properties of the ZnO nanorod arrays (ZNAs) were investigated by X-ray diffraction (XRD), and scanning electron microscopy (SEM) respectively. The XRD pattern revealed wurtzite crystal structures of ZNAs, preferentially orienting in the (002) direction. Depending on the length of nanorod, the intensity of the (002) plane was found to be varied. SEM micrographs show the vertical alignment of ZNAs perpendicular to the substrate and increase in rod length with increase in deposition time. The Gas sensing device was prepared by using ZNAs and tested for NO2 gas at different temperatures, concentrations and size of nanorods. Response increased with gas concentration as well as temperature. It was revealed that ZNAs gas sensor operating at 150 0C temperature could detect NO2 at low concentration (100ppm) with very high sensitivity (90 %).