ABSTRACT
Consideration of the properties of mesoporous silica, the technology of its synthesis, and prospects for its use in humidity sensors is the main objective of this chapter. It is shown that silica is an attractive material for humidity-sensing applications because of its high surface area, stability over a fairly wide range of pH (excluding alkaline), relative inertness in many environments, transparency in the UV-visible spectrum, and its morphological control. Moreover, the silane chemistry gives possibility to covalently attach molecular probes to the pore walls. Resistive, impedance, cantilever, SAW, and QCM humidity sensors can be developed based on mesoporous silica. Typically, humidity sensors are being developed based on ordered mesoporous silica of the SBA-15 type. However, ordered mesoporous silica of other types such as SBA-16, KIT-6, MCM-41, and HMS can also be used. At that, it was shown that silica-based humidity sensors, regardless of their type, demonstrate good reversibility, reproducibility, and stability of the parameters. Studies also established that the factors affecting the humidity-sensing response of porous silica include accessibility of inner mesopores, processing condition, calcination temperature, film thickness, working voltage, working frequency, and electrode configuration.
