| As one of the common volatile organic compounds(VOCs), formaldehyde could cause human health problem and is identified as the major gas to raise sick building syndrome(SBS). SBS mainly comes from chemical, biological pollutants and insufficient ventilation, contributing to occurrence of disease. Wood, carpeting and plastic products in our daily life release formaldehyde. We have strict limits on its concentration to this harmful gas. 0.08 ppm is the concentration limit of World Health Organization(WHO). American National Institute for Occupational Safety and Health(NIOSH) has set a maximum long-term exposure limit of 0.016 ppm. In this paper, the author fabricated formaldehyde sensor to detect concentration of ambient gas. Hope render to the best of our own for atmospheric environment we live in.In the second chapter, Zn@Sn O2 3D flower-like nanostructure was prepared by solvothermal method. The effects of Zn doping on formaldehyde sensing performance were also investigated. The results showed that Zn-doping with construction of unique nano-structure can improve their HCHO sensing performance, maybe because introduction of zinc leads to increased oxygen vacancy and broad surface area of nanosheets enhance gas sensitive catalytic activity. When the operating temperature is 160 °C, sensor based on Zn@Sn O2 exhibited response of 15.2 to 100 ppm formaldehyde. The response – recovery time is both 2 s, super than pure Sn O2. The detection concentration ranged from 1to 2000 ppm. The sensitivity displayed an excellent linearity and selectivity toward formaldehyde. Furthermore, the as-prepared 3D flower-like nanostructure possessed regular morphology, with horizontal diameter of 7 0.5 μm and vertical diameter of 80 5 nm.In the third chapter, Sn O2 and Cu@Sn O2 3D sphere-like nanomaterials with followed heater devices were prepared by one-step solvothermal process, and sensitivity to formaldehyde were also discussed. The response – recovery time of Cu@Sn O2 sensor is both 2 s. When the formaldehyde concentration increased, the response increased rapidly. And then the response gradually tended to saturation when the formaldehyde concentrations reached 1000 ppm. The Cu@Sn O2 sensor’s response to 200 ppm formaldehyde decreases with the humidity increasing from 11 to 95% RH(adsorption process). When the humidity decreases from 95 to 11% RH(des-orption progress), the sensor’s response increases. The maximum hysteresis value is less than 1% RH, which shows good reliability of the sensing material. The size of each sphere ranges from 1.3 0.2 μm horizontally and 15 ± 2 nm vertically in SEM images Cu@Sn O2. Diameter and thickness of the sphere nanostructure are about 2 0.3 μm and 15 2 nm in SEM images Sn O2. Smaller size of doped material maybe one of the reasons for improving response. Cu@Sn O2 sensor’s response to 200 ppm formaldehyde is 81.48, much higher than response to same concentrations of SO2, C6H6, C2H6 O, NH3, C8H10, C3H6 O,C2H2(1.961-25.926). Sn O2 sensor’s response to 200 ppm formaldehyde is 56.52, lower than response to former, ranging from 0.99 to 14.53.The doping sensor exhibited better selectivity.In the fourth chapter, Sn O2 and La@Sn O2 composited microspheres were fabricated by solvothermal method and displayed well-aligned morphologies with diameter among 2.5 0.3 μm. The sensor based on La@Sn O2 showed good gas sensing performance, whose response – recovery time is far more quickly than Sn O2 sensor to 1000 ppm formaldehyde. For the former sensor, response to SO2, NH3?H2O, C8H10, C6H6, C2H6 O, C3H6 O is far lower than formaldehyde at 230 °C. It can be concluded that La@Sn O2 sensor is more suitable to detect low concentration formaldehyde with superior sensitivity and selectivity. |
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