Design Of Functional Mesoporous Materials And Their Humidity Sensing Properties

Mesoporous materials have attracted considerable attention because of their regular porestructure, high specific surface area and pore volume, uniform and adjustable pore size. Inthe application of humidity sensor, the water molecules in the atmosphere were adsorbedby the mesoporous materials and then the electricity properties of the mesoporous mater ialchanged, and the change of the humidity could be detected. The preparation and humiditysensing application of mesoporous materials have been receiving wide attention from manyresearchers. In this thesis, several mesoporous compounds were used as the humiditysensing materials. The surface modification by bulk material improved the humidity activesite on the surface of the materails, and enhanced the humidity sensing properties of thematerails. The synthesis and tune of nano-mesoporous materials are the bases of theirproperties researching and application, which are important for understanding the physicaland chemical problems between the strctures and the properties. In humidity sensing field,exploring the intrinsic link between the in-phase component, morphology, structure andhumidity sensing properties of the materials also has important theoretical significance andapplication value.This thesis mainly based on traditional mesoporous SBA-16, MCM-48, MCM-41andsemiconductor metal oxide In₂O₃. Various structure and morphology of mesoporous materials were prepared using different methods. In₂O₃nanobelts and nanofibers werefabricated by an electrospinning method. The structural and morphological characteristicsof the resultant products were investigated by X-ray diffraction （XRD）, scanning electronmicroscopy （SEM）, transmission electron microscopy （TEM）, Brunauer-Emmett-Teller（BET） and infra-red spectrum （IR）. The results showed that the synthesized materialsobtain good crystallization, good mesoporous structures and uniform size. Humiditysensors based on these materials exhibited high sensitivities and fast response.LiCl was used as a dopant to the mesoporous SBA-16with a three-dimensional character.The optimized humidity sensors exhibited excellent humidity sensitive properties. Theimpedance changed four orders of magnitude in the whole humidity range. The largesthumidity hysteresis was about2%RH and the response and recovery times were10s and25s, respectively. The three-dimensional mesoporous structure could supply more transportchannels for water molecules, which enhanced the activity of sensitive materials, anddissolved the problems of easy to drain, prone to failure, and can not be used in fullhumidity range.Similarly, LiCl was also used as a dopant to the mesoporous MCM-48and MCM-41.The composite materials maintained the characteristics of mesoporous structure. Goodhumidity-sensitive properties of the composite materials were obtained by an appropriateproportion of LiCl loading. Compared with pure MCM-48,3wt%LiCl/MCM-48-basedcomposite materials showed higher sensitivity （impedance change from an order ofmagnitude to the three orders of magnitude）, shorter response time （154s to20s） and lesshumidity hysteresis （9%RH to4%RH）.The mesoporous In₂O₃material was synthesized through the nanocasting method andIn₂O₃nanofibers and nanobelts were obtained by electrospinning method. Mesoporousstructured In₂O₃zeolite showed highly ordered pore structure. The humidity sensor basedon the of mesoporous In₂O₃showed a complex impedance change up to four orders ofmagnitude in the entire humidity range, and the maximum humidity hysteresis is about3%RH. The humidity sensor showed fast response and recovery properties （10s and15s,respectively）. The humidity hysteresises of In₂O₃nanofibers and nanobelts were9%RH and2%RH, respectively. They both have a fast response speed of recovery. The responseand recovery times of In₂O₃nanofiber and nanobelts were35s and10s, and10s and5s,respectively.In clusion, this thesis contains a lot of basic researches on synthesis and humidityproperties research of mesoporous materials. These works are meanful for exploring theirpotential application in the chemical-sensing field.