Preparation Of Mesoporous Nickel-based Metal Oxides And Their Application In Gas Sensors

With economic development and increasing attention to methane gas explosion, industrial toxic gas leak, indoor air pollution and other environmental security issues, developing vavious gas-sensing materials with high sensitivity, high selectivity and high stability and advanced gas sensors is of importance for national security and life safety. Mesoporous materials have some advantages when applied in gas sensors because of its large surface area, uniform pore, adjustable aperture and many other advantages. Mesoporous materials as a class of potentially sensitive materials, has attracted many researchers’ attention. In this thesis, we have successfully prepared several mesoporous nickel-based metal oxide with different pore structure, pore size and pore wall thickness by hard template method and investigated the influence of structure parameters and chemical composition on their gas-sensing properties.1. In this paper, we synthesized a series of mesoporous silica KIT-6 with different pore sizes (5.7～9.4 nm) and specific surface area by controlling hydrothermal synthesis temperature and used them as hard template for preparing mesoporous nickel oxide with different pore wall thickness (5.1～9.4 nm), X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy demonstrate that all the mesoporous nickel oxide have ordered mesostructure, large specific surface area, high pore volume and adjustable (from single-modal to bi-modal) mesoporous structure. We have also investigated its response to formaldehyde gas, found that mesoporous nickel oxide’s sensitivity is higher than the bulk nickel oxide, its sensitivity is about 4～10 times more than the bulk of nickel oxide under the formaldehyde concentration in 380 ppm; Moreover, mesoporous nickel oxide with pore walls thinner, pore diameter higher is provided with higher sensitivity to formaldehyde gas, with dual-pore mesoporous nickel oxide and thin wall under the optimum working temperature 300℃, its sensitivity to formaldehyde is 20.5 under the formaldehyde concentration in 380 ppm, higher than the synthesis of mesoporous nickel oxide materials.2. The chemical composition of gas sensing material also has significant impact on its gas sensing properties. We use different proportions of ferric nitrate and nickel nitrate (Fe/Ni=0.01～0.35) mixed solution as precursor, KIT-6 molecular sieve via 40℃ hydrothermal synthesis as hard template, utilize nanocasting route synthesis a series of mesoporous composite materials. Wide-angle XRD only detected a diffraction peak of nickel oxide, indicated Fe ions into the crystal lattice of nickel oxide, iron oxide phase separation does not occur. EDS characterization results showed that the synthesized mesoporous Fe-doped oxide nickel composite material’s doping amount as same as actuality. Small angle XRD and TEM results show that ferric nitrate affects continuous growth of nickel oxide in the pores KIT-6, with the increasing of Fe doping amount, the mesoscopic ordering of preparation material has decreased, nitrogen adsorption-desorption tests show that the preparation of material maintains a large specific surface area, high pore volume and dual-mesoporous structure. We have also investigated its response to formaldehyde gas, found that mesoporous Fe-doped oxide nickel composite material’s sensitivity significantly increased. When the Fe/Ni=0.2, its response is highest (the response towards 90 ppm formaldehyde concentrations could be up to 554), mesoporous Fe-doped oxide nickel composite material’s sensitivity is 65 times more pure mesoporous nickel oxide.3. Further increases the proportion of iron nitrate in iron nitrate and nickel nitrate mixed solution (Fe/Ni=2) and the heating temperature, we synthesized a series of different pore wall thickness with spinel structure ordered mesporous nickel ferrite, which were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy. We have also investigated its response to to formaldehyde gas. The results demostrate mesporous nickel ferrite has high sensitivity to formaldehyde gas (under the formaldehyde concentration in 46 ppm is up to 60).