Preparation And Gas-sensing Properties Of Mesoporous Crystalline Sn_XTi_1-xO₂

SnO₂ is a MO₂ type metal oxide semiconductor material, used for sensing material of gas sensor. Tradition gas sensor usually based on single material, however in practical application these sensors have poor gas-sensing of rather high working temperature, low sensitivity and worse stability. Further study found that, with SnO₂ as the main component of gas sensor material, synthesis two or more metal oxide, forming a composite material, or doped with precious metals, rare earth that can reduce the activation energy measured gas chemisorption, effectively improve the sensitivity and shortening response time.In this paper, coral-like SnO₂ mesoporous material and Sn_XTi_1-xO₂ solid solution material were prepared by hydrothermal method using SnCl4?5H2O&Ti（OC4H9）4 as raw material and sucrose as the template, the CuO was doped into SnO₂ material. SnO₂, Sn_XTi_1-xO₂ and CuO-SnO₂ materials were characterized by XRD, XPS, SEM, TEM, BET, etc. We also have investigated the gas sensing properties of Sn_XTi_1-xO₂ system and SnO₂/CuO-SnO₂ system under VOCs, H2, H2 S, etc. The main results are as follows:1:Sn_XTi_1-xO₂ system: The as-prepared Sn_XTi_1-xO₂ materials both have tetragonal rutile structure, and the morphology of the crystals is similar to the shape of corals. The Ti4+ of the composite materials replaced the Sn4+ through isomorphous way, formed a solid solution, so there is no TiO2 characteristic peak in the XRD pattern, so we analysis sample by XPS, resulting shows Ti element in the composite powder. The diameter of the particles is about 5.5⁸.9nm, with very small grain size. The specific surface area of coral-like Sn_XTi_1-xO₂ range from 60.59⁶4.38 m2/g, the pore size was ca.14nm²0nm, the pore volume is from 0.265 to 0.325 cm3/g, all the Sn_XTi_1-xO₂ composite materials have very large specific surface area and nanocrystal forming coral-like agglomeration with mesopporous structure. The composite Sn_XTi_1-xO₂ of Ti content is 9.1% sensor shows excellent gas sensing properties in the lower working temperature（160℃）, the response time and recovery time are both about 15 s, when the operating temperature is 160℃, the ethanol gas concentration is 600 ppm, the sensors have the sensitivity of 1842. Compared with the pure SnO₂, Sn_XTi_1-xO₂ has a wide detection range of H2（5-2000ppm）, when the operating temperature is 200℃, the H2 gas concentration is 100 ppm, the sensitivity up to S=19.6, thus having a great practical value.2. SnO₂/CuO-SnO₂ system: The as-prepared SnO₂ and CuO-SnO₂ materials both have tetragonal rutile structure. Using Scherrer formula to calculate the crystal size of doped-SnO₂ is about 9.6nm. The surface morphology of SnO₂ material was similar to kind of marine organism called coral, and the coral-like SnO₂ had cross-linked structure in deep zones, the samples of SnO₂-CuO-0.2, SnO₂-CuO-0.5, SnO₂-CuO-1.0, SnO₂-CuO-2.0 were mesopous material, and the specific surface area were 72.97 m2/g, 58.77 m2/g, 49.72 m2/g, 54.95 m2/g. Though the systematic testing, the sensors target to ethanol, formaldehyde and H2 S gas, having excellent sensitivity to H2 S, but having low sensitivity to ethanol and formaldehyde, which show high selectivity. When the operating temperature is 100℃, the H2 S concentration is 10 ppm, the sensitivity of SnO₂-CuO-0.5 is 4173. In this experimental, when the doping amount is 0.5%, the sensor is not only working at low temperature but also exhibited high sensitivity, when the content of CuO increased to 2%, the sensor’s sensitivity was reduced, thus, doping can improve the gas sensing properties of materials, but need carefully consider the problem of doping amount.