Sensing Characteristics of Flame-Spray-Made Pt/ZnO Thick Films as H2 Gas Sensor

Hydrogen sensing of thick films of nanoparticles of pristine, 0.2, 1.0 and 2.0 atomic percentage of Pt concentration doped ZnO were investigated. ZnO nanoparticles doped with 0.2–2.0 at.% Pt were successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate as precursors dissolved in xylene. The particle properties were analyzed by XRD, BET, SEM and TEM. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spheroidal and hexagonal particles were found to be ranging from 5 to 20 nm while ZnO nanorods were seen to be 5–20 nm wide and 20–40 nm long. ZnO nanoparticles paste composed of ethyl cellulose and terpineol as binder and solvent respectively was coated on Al2O3 substrate interdigitated with gold electrodes to form thin films by spin coating technique. The thin film morphology was analyzed by SEM technique. The gas sensing properties toward hydrogen (H2) was found that the 0.2 at.% Pt/ZnO sensing film showed an optimum H2 sensitivity of ∼164 at hydrogen concentration in air of 1 volume% at 300 °C and a low hydrogen detection limit of 50 ppm at 300 °C operating temperature

H2 Sensing Response of Flame-Spray-Made Ru/SnO2 Thick Films Fabricated from Spin-Coated Nanoparticles

High specific surface area (SSABET: 141.6 m2/g) SnO2 nanoparticles doped with 0.2–3 wt% Ru were successfully produced in a single step by flame spray pyrolysis (FSP). The phase and crystallite size were analyzed by XRD. The specific surface area (SSABET) of the nanoparticles was measured by nitrogen adsorption (BET analysis). As the Ru concentration increased, the SSABET was found to linearly decrease, while the average BET-equivalent particle diameter (dBET) increased. FSP yielded small Ru particles attached to the surface of the supporting SnO2 nanoparticles, indicating a high SSABET. The morphology and accurate size of the primary particles were further investigated by TEM. The crystallite sizes of the spherical, hexagonal, and rectangular SnO2 particles were in the range of 3–10 nm. SnO2 nanorods were found to range from 3–5 nm in width and 5–20 nm in length. Sensing films were prepared by the spin coating technique. The gas sensing of H2 (500–10,000 ppm) was studied at the operating temperatures ranging from 200–350 °C in presence of dry air. After the sensing tests, the morphology and the cross-section of sensing film were analyzed by SEM and EDS analyses. The 0.2%Ru-dispersed on SnO2 sensing film showed the highest sensitivity and a very fast response time (6 s) compared to a pure SnO2 sensing film, with a highest H2 concentration of 1 vol% at 350 °C and a low H2 detection limit of 500 ppm at 200 °C

The Monitoring of H2S and SO2 Noxious Gases from Industrial Environment with Sensors Based on Flame-Spray-Made SNO2 Nanoparticles

The noxious gas sensors were developed successfully using flame-spray-made SnO2 nanoparticles as the sensing materials. The functionalized nanoparticle properties were further analyzed by XRD, BET and TEM analyses. The SnO2 nanoparticles (SSABET: 141.6 m2/g) were investigated revealing non-agglomerated spheroidal, hexagonal, rectangle (3 - 10 nm), and rod-like (3 - 5 nm in width and 5 - 20 nm in length) morphologies. The sensing films were prepared by spin coating onto the Al2O3 substrates interdigitated with Au electrodes. The sensing films were significantly developed in order to detect with H2S (0.5 - 10 ppm) and SO2 (20 - 500 ppm) at the operating temperature ranging from 200 - 350°C. After sensing test, the cross-section of sensing film was analyzed by SEM analyses. It was found that SnO2 sensing film showed higher sensitive to H2S gas with very fast response at lower concentrations (3 s, to 10 ppm). The cross sensitivities of the sensor towards different concentrations of H2S, CO, H2, and C2H2 were measured at 300°C. The sensor evidently shows much less response to CO, H2, and C2H2 than to H2S indicating higher selectivity for H2S of the SnO2 sensor at the lower concentration (10 ppm). In addition, the SnO2 sensor was the most suitable candidate for the efficient detection of H2S noxious gas

Synthesis of Thermally Spherical CuO Nanoparticles

Copper oxide (CuO) nanoparticles were successfully synthesized by a thermal method. The CuO nanoparticles were further characterized by thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and high resolution transmission electron microscopy (HRTEM), respectively. The specific surface area (SSABET) of CuO nanoparticles was determined by nitrogen adsorption. The SSABET was found to be 99.67 m2/g (dBET of 9.5 nm). The average diameter of the spherical CuO nanoparticles was approximately 6–9 nm

A MEMS-based Benzene Gas Sensor with a Self-heating WO3 Sensing Layer

In the study, a MEMS-based benzene gas sensor is presented, consisting of a quartz substrate, a thin-film WO3 sensing layer, an integrated Pt micro-heater, and Pt interdigitated electrodes (IDEs). When benzene is present in the atmosphere, oxidation occurs on the heated WO3 sensing layer. This causes a change in the electrical conductivity of the WO3 film, and hence changes the resistance between the IDEs. The benzene concentration is then computed from the change in the measured resistance. A specific orientation of the WO3 layer is obtained by optimizing the sputtering process parameters. It is found that the sensitivity of the gas sensor is optimized at a working temperature of 300 °C. At the optimal working temperature, the experimental results show that the sensor has a high degree of sensitivity (1.0 KΩ ppm−1), a low detection limit (0.2 ppm) and a rapid response time (35 s)

Flame-Made Pt-Loaded TiO 2

The hydrogen gas sensors were developed successfully using flame-made platinum-loaded titanium dioxide (Pt-loaded TiO2) nanoparticles as the sensing materials. Pt-loaded TiO2 thin films were prepared by spin-coating technique onto Al2O3 substrates interdigitated with Au electrodes. Structural and gas-sensing characteristics were examined by using scanning electron microscopy (SEM) and showed surface morphology of the deposited film. X-ray diffraction (XRD) patterns can be confirmed to be the anatase and rutile phases of TiO2. High-resolution transmission electron microscopy (HRTEM) showed that Pt nanoparticles deposited on larger TiO2 nanoparticles. TiO2 films loaded with Pt nanoparticles were used as conductometric sensors for the detection of H2. The gas sensing of H2 was studied at the operating temperatures of 300, 350, and 400°C in dry air. It was found that 2.00 mol% Pt-loaded TiO2 sensing films showed higher response towards H2 gas than the unloaded film. In addition, the responses of Pt-loaded TiO2 films at all operating temperatures were higher than that of unloaded TiO2 film. The response increased and the response time decreased with increasing of H2 concentrations

Flame-Spray-Made Undoped Zinc Oxide Films for Gas Sensing Applications

Using zinc naphthenate dissolved in xylene as a precursor undoped ZnO nanopowders were synthesized by the flame spray pyrolysis technique. The average diameter and length of ZnO spherical and hexagonal particles were in the range of 5 to 20 nm, while ZnO nanorods were found to be 5–20 nm wide and 20–40 nm long, under 5/5 (precursor/oxygen) flame conditions. The gas sensitivity of the undoped ZnO nanopowders towards 50 ppm of NO2, C2H5OH and SO2 were found to be 33, 7 and 3, respectively. The sensors showed a great selectivity towards NO2 at high working temperature (at 300 °C), while small resistance variations were observed for C2H5OH and SO2, respectively

Synthesis of ZnO nanoparticles by flame spray pyrolysis and characterisation protocol

There is uncertainty concerning the potential toxicity of zinc oxide (ZnO) nanoparticles, which may be attributed in part to a lack of understanding with regard to the physiochemical properties of the nanoparticles used in toxicological investigations. This paper reports the synthesis of a ZnO nanopowder by flame spray pyrolysis and demonstrates that the typically employed characterisation techniques such as specific surface area measurement and X-ray diffraction provide insufficient information on the sample, especially if it is intended for use in toxicity studies. Instead, a more elaborate characterisation protocol is proposed that includes particle morphology as well as detailed compositional analysis of the nanoparticle surface. Detailed transmission electron microscopy analysis illustrated the polydispersity within the sample: particles were elongated in the c-crystallographic direction, with average Ferret length ∼23 nm and Ferret width ∼14 nm. Dynamic light scattering (0.1 w/v% in deionised water, pH 7.4) revealed the particles were agglomerated with a modal secondary particle size of ∼1.5 μm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated the presence of carbonate and hydroxide impurities on the surface of the ZnO nanoparticles and an increase of such impurities was observed as the sample was aged, which might influence the nanoparticle dissolution and/or cellular uptake behaviour. These data will be utilised, in order to facilitate the interpretation and understanding of results from toxicological investigations using in vitro cell lines

Effects of Palladium Loading on the Response of Thick Film Flame-made ZnO Gas Sensor for Detection of Ethanol Vapor

ZnO nanoparticles doped with 0-5 mol% Pd were successfully produced in asingle step by flame spray pyrolysis (FSP) using zinc naphthenate and palladium (II)acetylacetonate dissolved in toluene-acetonitrile (80:20 vol%) as precursors. The effect ofPd loading on the ethanol gas sensing performance of the ZnO nanoparticles and thecrystalline sizes were investigated. The particle properties were analyzed by XRD, BET,AFM, SEM (EDS line scan mode), TEM, STEM, EDS, and CO-pulse chemisorptionmeasurements. A trend of an increase in specific surface area of samples and a decrease inthe dBET with increasing Pd concentrations was noted. ZnO nanoparticles were observed asparticles presenting clear spheroidal, hexagonal and rod-like morphologies. The sizes ofZnO spheroidal and hexagonal particle crystallites were in the 10-20 nm range. ZnOnanorods were in the range of 10-20 nm in width and 20-50 nm in length. The size of Pdnanoparticles increased and Pd-dispersion% decreased with increasing Pd concentrations.The sensing films were produced by mixing the particles into an organic paste composedof terpineol and ethyl cellulose as a vehicle binder. The paste was doctor-bladed ontoAl2O3 substrates interdigitated with Au electrodes. The film morphology was analyzed bySEM and EDS analyses. The gas sensing of ethanol (25-250 ppm) was studied in dry air at400°C. The oxidation of ethanol on the sensing surface of the semiconductor wasconfirmed by MS. A well-dispersed of 1 mol%Pd/ZnO films showed the highest sensitivityand the fastest response time (within seconds)