| In recent years, humidity testing has become an important issue in the socialdevelopment, such as its wide and essential application in industrial process control,environment monitoring, and food quality preservation. As the device for detectingthe humidity, humidity sensor has attracted enormous attention. The humidity sensoris consisted with an electrode, sensing film and test circuit. The sensing film is animportant part of the sensor, which determines the value of the sensor. Typically, thesensing film must possess large surface area, effective active sites, and physical andchemical stability.In this thesis, porous materials and NaTaO3are chosen as the sensing film. Firstly,we chose porous NaA zeolite and NH2-MIL-125(Ti) as sensing film because of theirregular channels and larger surface areas. NaA is a typical zeolite which is built up byfour and six ring. It possesses a cage at the center of the unit cell and result a3Dstructure. The maximum diameter of the cage is11.4. In this configuration, theentire strcture is neutral due to charge-balancing cations of Na+. Therefore, it has goodphysical and chemical stability, and can still maintain the structural in harshconditions. The NH2-MIL-125(Ti) is built up by cyclic octamers of corner-oredge-sharing titanium octahedral connected to12otheroctamers through the2-amino-benzene-1,4-dicarbox-ylate linkers. In the NH2-MIL-125(Ti), the NH2groupsare free without coordination, resulting in a porous three dimensional (3D) structureof a quasi-cubic tetragonal and showing good mechanical properties, as well aspermanent porosity. The3D structure provides two types of cages corresponding tothe octahedral and tetrahedral, and their free apertures are in the range5–7.Moreover, the framework possesses high density of hydrophilic active sites, whichmakes the water molecules to be absorbed on the MOF surface and then get into thecages easily. Furthermore, the NH2-MIL-125(Ti) remains crystalline even afterexposing in the100%RH environment. In order to improve the humidity sensitivecharacteristics, doping treatment is carried out. NaTaO3is a typical peroskite oxide,which has active sites. The humidity sensitive properties of NaTaO3are also studied inour thesis. The main researches are listed as follows:(1) The NaA was synthesized by a simple hydrothermal method, and humidity sensor based on NaA was fabricated. The device shows good impedance-RH (relativehumidity) linearity when the RH increases from11%to95%RH.LiCl/NaA with different LiCl content was prepared, and humidity sensor basedon LiCl/NaA was investigated. After adding LiCl, the humidity sensitivecharacteristics of the sensor are much improved in the RH range of11%-95%RH.(2) The porous metal organic framework NH2-MIL-125(Ti) was synthesized alsoby solvothermal method. The humidity sensor based on NH2-MIL-125(Ti) wasfabricated. When the RH increases form11%RH to95%RH, the impedancedecreases about two orders of magnitude.FeCl3-NH2-MIL-125(Ti) with different FeCl3content was successfully preparedby a simple way. The sensor based on FeCl3-NH2-MIL-125(Ti) was investigated in thewhole RH range. Compared with NH2-MIL-125(Ti), FeCl3-NH2-MIL-125(Ti) wasmore effective for the humidity sensing. The optimal mixing ratio was8wt%FeCl3-NH2-MIL-125(Ti), the impedance of which decreases almost three orders ofmagnitude in the whole RH.(3) In the last part, we synthesize the nanosize NaTaO3for humidity test. Ahumidity sensor based on nanosize NaTaO3was fabricated. The device shows goodimpedance-RH linearity and narrow hysteresis. The impedance decreases three ordersof magnitude when the RH decreases from33%to95%RH.In conclusion, the porous materials and NaTaO3can be used as sensitive film forthe humidity sensor. The doping method can improve the humidity sensitivecharacteristic. Our thesis provides a new field for the development of humiditysensitive film. |
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