Preparation Of Semiconductor Oxide Nanoparticles In Microemutsion And Its Gas Sensing Performance

Industrial waste gas, coal gas and automobile exhaust are pollutting ourenvironment all the time. There are many flammable and combustible gases and toxicgases which are harmful to people even though they are at low concentration, whilewe ourselves only have a limited ability to distinguish and cognize gas. Oxidesemiconductor gas sensor can be widely used in the field of the measurement ofambient gas and the detection and alarm of explosive gases and toxic gas. Thehigh-performance gas sensor can not only safeguard the smooth progress of theproduction and learning activities, but also can detect the atmospheric environment,and guarantee the safety of people’s health and property from damage. So the researchof semiconductor type gas sensor which has short response and recovery time, highsensitivity, high selectivity and long-term stability is especially important.This article prepared NiO nanoparticles, WO₃-NiO composite oxides andCuO-SnO₂composite oxides with the novel microemulsion method usingcyclohexane as oil, polyethylene glycol octylphenyl ether （Triton X-l00） as surfactant,n-hexanol as cosurfactant. We also measured and analysed the gas-sensing propertiesof the above materials.NiO nanoparticles with different particle size were synthesized by a water-in-oilmicroemulsion. The particle size of NiO can be controlled from11.5to31.5nm byvarying the proportion of water and oil in the microemulsion, method of mixing, andcalcining temperature. Gas sensors based on as-synthesized NiO were fabricated andmeasured. They show much higher sensitivities to nitrogen dioxide, ethanol andhydrogen sulfide, compared to those based on the conventional bulk nickel oxide. Thesensitivities based on NiO prepared by microemulsion to all kinds of target gasesincreases with the decreasing of the particle size of materials. The NiO with particlesize of11.5nm exhibits high degree of selectivity, coupled with high sensitivity value,making it especially interesting for H₂S-monitoring applications. WO₃-NiO was prepared with microemulsion method. The synthesized samplewas characterized by inductively coupled plasma mass spectrometry （ICP MS）,powder X-ray diffraction （XRD）, scanning electron microscope （SEM） and nitrogenadsorption/desorption measurement. The content of WO₃is21.7%（weight ratio） fromICP MS result. The contrast sample which has the same WO₃concentration wassynthesized by grinding the mixture of WO₃and NiO. The sensing properties of twosamples for Cl2were investigated. As a result, the two samples both showed p-typesemiconducting properties and the sensitivity of the gas sensor based on WO₃-NiOsynthesized by microemulsion is much higher than the sensitivity of the sensingdevice based on WO₃-NiO synthesized with grinding method.Four CuO-SnO₂gas-sensing materials were synthesized by microemulsion,through altering calcining temperature and source of copper. Gas sensors based onas-synthesized CuO-SnO₂were fabricated and investigated. The gas sensor based onCuO-SnO₂which was calcined at600℃and prepared with Cu（NO）2has a goodgas-sensing performance for acetone. Its sensitivity to1000ppm acetone at150℃is48, and it show a high degree of selectivity for acetone.