Fabrication Of Mesoporous Oxide Semiconductor And The Study Of Chemical Sensing Properties

In recent years, the rapid development of industrialization, various types of gasare frequently used. Volatile organic gases （VOCs, such as C2H5OH, CH₃COCH₃,HCHO）, flammable or explosive gases （such as H₂, CH₄, CO）; toxic and harmfulemissions （such NO_x、NH₃、H₂S、SO₂、Cl₂） not only pollute the environment, but alsohave seriously harm to human health. Requirements detection of these gascomponents are also increasing. Water vapor as a special kind of gas, play a vital rolein numerous fields, such as environmental monitoring, food processing industries,medicine, meteorology and research labs. All nature processes are closely related towater vapor （humidity）. Therefore, the development of high sensitivity, fast response,low detection limit, high selectivity, portable gas and humidity sensors are urgentissue to be solved.Mesoporous materials with tubular, worm-like and spherical pore structure, havehigh surface area, large pore volume, uniform pore diameter, easy surfacefunctionalization and strong adsorption capacity, rendering the unique materials usefulin wide spectrum of fields. They are widely used in catalysts, adsorbents,optoelectronic devices, and other important areas.Mesoporous metal oxides are also considered promising candidates in thedevelopment of chemical sensors. In this paper, several mesoporous metal oxideshave been successfully synthesized by hard template method to detect several typical gas （CH₃COCH₃, H₂, NO₂） and humidity （H₂O）, and the sensing mechanism is furtherto be discussed.The ordered mesoporous SnO₂have been successfully synthesized viananocasting method using the hexagonal mesoporous SBA-15as template. A study ontheir gas sensing properties for CH₃COCH₃reveals that the sensor utilizingmesoporous SnO₂displays swift response and recovery rate, and much highersensitivity to CH₃COCH₃compared to those based on nanoparticle SnO₂viaprecipitation technique. It is supposed that the outstanding gas sensing properties ofmesoprous SnO₂sensor synthesized by hard template is arisen from the large surfacearea and high porosity, which lead to highly effective surface reaction between thetarget gas molecules and the surface active sites in mesoporous SnO₂sensor.The ordered mesoporous SnO₂and Pd/SnO₂have been successfully synthesizedvia nanocasting method using the hexagonal mesoporous SBA-15as template. Astudy on their gas sensingproperties for H₂reveals that the sensor utilizing Pd/SnO₂via direct synthesis method displays swift response and recovery rate and much highersensitivity to H₂compared to those based on mesoporous SnO₂and Pd/SnO₂viaimpregnation technique. It is supposed that the outstanding gas sensing properties ofPd/SnO₂sensor synthesized by direct synthesis method is arisen from the largesurface area, high activity and well dispersion for Pd additive, as well as high porosity,which lead to highly effective surface reaction between the target gas molecules andthe surface active sites in Pd/SnO₂.The utilization of mesoporous KIT-6silica as a hard template has turned out to bea versatile tool for the synthesis of mesoporous Fe-doped In2O₃in the nanocastingprocess. It exhibits high specific surface area, oredered periodically arrangedmesopores structure with well crystalline walls and high thermal stability. The productis a promising material for application as gas sensor, since its excellent physical andchemical properties. The Gas sensing measurements reveal significantly increasedsensitivity response to NO₂gas in comparison with the mesoporous pure In2O₃. It issupposed that the outstanding gas sensing properties of the mesoporous Fe-dopedIn2O₃sensor is attributed to higher specific surface area and the pore volume. Besides, Fe species loaded on the sensor is effective to adsorb NO₂gas on the surface, which isalso beneficial to the sensitive response of the sensor.Mesoporous LaFeO₃was successfully synthesized via the nanocasting methodby using SBA-15as a replica matrix. A ceramic humidity sensor based on themesoporous LaFeO₃was fabricated and evaluated. Humidity sensing measurementsreveal that impedance greatly changes by more than five orders magnitude when therelative humidity varies from11%to98%at10Hz, and it also displays high response,fast response time, low hysteresis and long-time stability in the entire humidity region.The sensing mechanism of humidity sensors was interpreted by the compleximpedance spectra （Nyquist plot）. Furthermore, the sensor based on the mesoporousLaFeO₃displays the higher response compared with that of bulk LaFeO₃prepared bythe sol–gel method. It can be concluded that thus-obtained mesoporous LaFeO₃is anexcellent material for application as humidity sensor because of their high surfacearea and pore volume with mesoporous structure.In the paper, we have fabricated of mesoporous oxide semiconductor and studiedof chemical sensing properties. The results show that the mesoporous oxidesemiconductor sensing materials display more excellent gas and humidity sensingperformence than that of nanoparticles sensing materials. It provides a new strategy tobuild excellent chemical sensors.