Study On The Organic Sensing Films Of Quartz Crystal Microbalance Based Formaldehyde Gas Sensors

As one of the most prospective devices, piezoelectric bulk wave acoustic sensors have many advantages, such as high sensitivity, low cost, large response spectra, simple operation, real-time output, etc. Due to high mass effect sensitivity, the mass effect based quartz crystal microbalances (QCMs) are especially suitable for the detection of macromoleculars, which can be widely applied in the fields of clinic chemistry, pharmaceutics analysis, environmental detection and so on. During the development of QCM sensors, seeking fitful chemical thin films and the relevant modification techniques has become a great research interest. How to modify the sensing films effectively, simply, conveniently and quickly is the first problem to be solved in the construction of QCM sensors.In this thesis, different kinds of organic thin films were modified on to the crystal surface individually for the purpose of detecting formaldehyde gas, which has aroused much attention in recent years. The properties of the organic sensing films on the QCM surface were studied and the results were used as evidences for the selection of suitable sensitive membrane of macromolecular.In order to choose suitable organic sensing films for formaldehyde gas detection, the theory of molecular simulation was applied to study molecular reactions on the surface of the film. Simulation was performed at the molecular level to study the adsorption and nucleophilic addition reactions of the formaldehyde on the sensing films. The adsorptior model of formaldehyde molecular on the surface of the organic sensing film was built up Experimental results were well fitted to the simulated results, which confirmed the propose dynamics model.Base on diverse films discussed, formaldehyde absorbent film materials were developed with aqueous solution, including the mixtures of amide, hydrazine, organic amine, and acylic acid acyl unite ammonia. The sensing material was coated on the silver electrodes of the QCM. Then the characteristics of the QCM gas sensors to formaldehyde were tested. Experimental results showed that the QCM sensor with the polyacrylamide sensing film has good response to formaldehyde in the concentration range of 3~12 ppm.