| Quartz crystal microbalance (QCM) is a mass sensitive device being widely usedto monitor the solid/liquid interface processes. It has been successfully demonstrated theapplications of the QCM in electrochemistry, solution chemistry and biosensors.Generally, two film electrodes are deposited on the surface of the quartz crystal sensorto induce the oscillation of the QCM. The active sensing region is restricted near thecenter region where the electrodes are attached. The frequency stability and lifetime of aQCM depend greatly on the chemical stability of the film electrodes. If the electrode iseroded in a strong corrosive condition, the lifetime of the QCM is much shortened. Inthis thesis，an electrodeless quartz crystal microbalance (EL-QCM) in gaseous phase isdesigned and applied in monitoring the adsorption process of iodine onzeolitic-imidazolate framework-8(ZIF-8) film. Details are listed below.1. Responses of EL-QCM in gaseous phase measured in an impedance analysismethodTo eliminate the electrode corrosion on the frequency stability of a QCM, anEL-QCM sensor is designed. In the EL-QCM, the electrodes are separated by an airlayer of several millimeters. The high frequency excitation voltage is applied on theQCM by the conductance of the air layer. To understand the response of the EL-QCM ingaseous phase, the equivalent circuit parameters were derived according to a modifiedmodel and measured by an impedance analysis method. The influence of the gap size,area, position, and shape of the electrodes on the resonant and equivalent circuitparameters of the EL-QCM was investigated. Compared with a conventional QCM, theintensity of the resonant peak in the EL-QCM reduces markedly, but the effectivequality factor decreases only slightly even with at the gap of1cm. The motionalinductance, motional capacitance and motional resistance of the EL-QCM are (1+C0/C12)2,(1+C0/C12)2and (1+C0/C12)2times of those of the bare PQC itself, respectively. Where，C0is the static capacitance of the QCM, C12the air capacitance between theelectrode and QCM. The by-bass effect from the stray capacitance reduces the effectivequality factor of the EL-QCM. In the applications of EL-QCM, the electrodes gapshould be short as possible. In general, the concentric configuration of the electrodesand quartz disc is preferable. But the electrodes can be mounted beside the center of thequartz disc or outside of the detection cell if needed. The mass change on the electrodesurface does not vary the resonant frequency of the EL-QCM, eliminating the influenceof electrode corrosion in the case of a conventional QCM sensor. The quartz disc in theEL-QCM can be treated by chromosulfuric acid. The EL-QCM offers the advantageslike optical transparency, longer lifetime, better experimental reproducibility, reducednumber of preparation steps and lower costs.2. Monitoring adsorption of iodine vapor on zeolitic-imidazolate frame work-8filmMetal-organic frameworks (MOFs), a particular class of ordered porous solids, holdpromise to solve many key challenging societal needs (e.g., hydrogen storage, carbondioxide capture, renewable catalysts, controlled drug delivery). ZIF-8, as a prototypicalMOFs, is formed by combining a Zn2+source and2-methylimidazole in a suitablesolvent and crystallizes in a sodalite-type structure. It was reported that ZIF-8is anexcellent sorbent for molecular I2because of its suitable pore aperture size, largespecific surface area, and high chemical and thermal stability. In this work, a speciallydesigned EL-QCM was applied to monitor the adsorption process of iodine vapor onZIF-8film. To eliminate the electrode corrosion by iodine, the excitation electrodeswere mounted outside of the adsorption cell. And the combination of EL-QCM with anabsorbance measurement was demonstrated. The series combination of two EL-QCMsensors was designed to monitor the transfer process of iodine between two ZIF-8films. |
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