Date

2022-12-27

Author

Davoudnezhad, Ramona

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The growing demand for environmental control for various chemical molecules has led to considerable interest in the research devoted to developing new materials for sensor devices. Since humidity is a prevalent component in our environment, measurements and control of humidity are essential for human comfort and a broad spectrum of industries and technologies. The constructive design of a good humidity sensor is a rather complicated topic due to its requirements, such as linear response, high sensitivity, fast response time, chemical and physical stability, wide operating humidity range, and low cost. Moreover, the sensor performance is strictly related to parameters like the chemical structure and the surface morphology of the developed sensor, which involve the adsorption/desorption process of water. In this thesis, titanosilicate ETS-10 and vanadosilicate AM-6 zeotype materials in powder and film forms were synthesized to observe the effect of -V-O-V- and -Ti-O-Ti- wires on the humidity sensing behavior. The choice of material preparation allowed one to investigate the effect of different parameters on humidity sensing. These can be summarized as the effect of film thickness, crystallographic orientation, type of seed crystals, different defect formations within the quantum wires, and lastly, vanadium doping in the ETS-10 structure. All samples were characterized by FE-SEM, XRD, Raman, and XPS analyses. For humidity sensing, a relative humidity experiment setup was designed with eleven saturated salt solutions with different relative humidity values. The determination of such humidity sensor parameters as sensor sensitivity and response time in constant humidity environments using saturated salt solutions was carried out via the impedance analyzer. The humidity sensors’ sensitivity to variations in relative humidity values was determined according to the impedance data measured at certain frequencies. In the first part of this study, titanosilicate ETS-10 and vanadosilicate AM-6 zeotypes powders were synthesized, and thin films were prepared by the spin coating method. The humidity sensing behavior of these two isostructural zeotypes shows high sensitivity at medium and high relative humidity levels. In the second part of this thesis, to better understand the effect of the quantum wires and their orientation on humidity sensing behavior, ETS-10 and AM-6 films were prepared by the secondary growth method. For this purpose, ETS-10 powder was used as the seed layer. The humidity sensing performance of these films revealed that AM-6 films prepared by vanadyl sulfate as a vanadium source performed better than all prepared films at the whole relative humidity range. In the last part of this thesis, to better understand the sensing mechanism, especially at low relative humidity levels, a structure with both vanadium and titanium atoms of differing coordinations in the quantum wire was investigated. This was accomplished by modifying titanosilicate ETS-10 by substituting vanadium into the structure. Sensors were prepared by spin coating methodology. Vanadium-doped samples with a V/Ti+V ratio of 0.2 showed better sensitivity at low relative humidity levels than other doped samples.

Subject Keywords

Zeotypes, Humidity Sensing, Films preparation methods, Titanosilicates, Vanadosilicates, Quantum wires

URI

https://hdl.handle.net/11511/101208

Collections

Graduate School of Natural and Applied Sciences, Thesis