Abstract
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).
Highlights
Solid-state gas sensors have recently played an important role in environmental monitoring and chemical process control
The flame-made pure Zinc oxide (ZnO) and 1-5mol%Pd/ZnO nanoparticles used as ethanol gas sensors were successfully produced by flame spray pyrolysis
Pd peaks were not found all of samples, and the corresponding Al2O3, Au, and ZnO peaks were seen from the flame made ZnO nanoparticles printed on Al2O3 substrate interdigitated with Au electrodes after sensing test at 400°C as an ethanol sensor
Summary
Solid-state gas sensors have recently played an important role in environmental monitoring and chemical process control. An ethanol sensor based on ZnO nanorods prepared by hydrothermal method [25] showed high sensitivity to ethanol concentrations ranging from 10 to 2000 ppm at 330°C, with good responses and recovery times. The gas sensing results showed that the sensor signal for detection of 400 ppm ethanol vapor was about 20 at an operating temperature of 250oC [47] In this case, catalysts such as Pd, Pt, Rh, Ru or Ag are often added to improve selectivity and sensitivity [43,44,45,46, 75, 76]. With the Pd loading, the ZnO-La2O3-Pd-based sensor element showed excellent ethanol vapor sensing properties at a lower operating temperature in air with respect to sensitivity and response rate. It is interesting to apply FSP for production of Pd/ZnO nanoparticles [65, 70, 71] as used in gas sensors for ethanol vapor
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