Study On Nano-sensitive Membrane Modified QCM Gas Sensor And Application In The Ammonia Gas Detection

As a kind of common irritant gas, ammonia gas can cause harm to human body health.The Ministry of Health stipulated it for chemical class of the occupational-disease-inductivefactors in the catalog of occupational-disease-inductive factors classification. Therefore, underthe normal temperature detection with low concentration ammonia gas is very necessary. Inthis paper, we applied the Quartz Crystal Microbalance gas sensor technology, modified nano-sensitive membrane in the quartz crystal surface, to achieve the purpose of ammonia gasdetection.We modified nanometer TiO2and ZnO nanorods sensitive membrane in the quartzcrystal surface respectively. Then we connected lead wire that is on both ends of the electrodeto the resonance circuit. Finally we connected this to the QCM gas sensor testing system. Byself-developed frequency testing software of QCM gas sensor based on LabVIEW platform,the output signal acquisition and processing work can be accomplished. The whole testsystem had a stable performance and a good frequency waveform figure.The two sensitive membrane’s detection of ammonia gas had sensitive and rapidresponse, good linear relationship, which can fully achieve the gas adsorption and desorptionprocess. By characterized the surface morphology of the sensitive membrane withfield-emission scanning electron microscope (FE-SEM, JSM-6700F), we found that two kindsof sensitive membrane had nano-structure and formed a stable physical film in the quartzcrystal surface.We produced sensitive membranes which are made of nanometer TiO2and a mixture ofNafion membrane reagent with10%,20%and50%respectively, and5%,2.5%,1%,0.3%ofTiO2ethanol solution of sensitive membranes. Through the experiment data prove that1%ofTiO2ethanol solution, which is the final choice of nanometer TiO2sensitive membrane, hasthe most sensitive effect to ammonia detection. The maximum frequency difference value ofnanometer TiO2sensitive membrane modified QCM gas sensor for10×10-6～50×10-6concentration range of ammonia is33.68Hz～108.32Hz. Fitting correlation coefficient is0.9994. At the same time, the SEM image shows that the experiment of the preparation ofstructural unit mainly for nanometer TiO2sensitive membrane, which dispersed evenly, withlarger specific surface area, can fully achieve the gas adsorption desorption process.ZnO nanorods sensitive membrane is made of the ZnO crystal layer growth in95℃water bath containing liquid growth after3h. The sensitive membrane response to ammoniais more sensitive than ZnO seed layer, the1.5h,2h growth of water sensitive membranes.Experiments in the process of testing the concentration of ammonia is5×10-6～50×10-6, themaximum frequency difference value is1.1Hz～10.9Hz, the correlation coefficient of0.9983. The SEM image shows that ZnO nanorods structure sensitive membrane, evenly on the electrode surface. The height of the ZnO nanorods is1μm. The unique physical structurecan fully achieve the ammonia adsorption desorption process.Finally, we took two kinds of sensitive membranes humidity for measurementrespectively. The experimental results show that two kinds of sensitive membranes are verysensitive to humidity response. The maximum difference frequency value of nanometer TiO2Sensitive membrane for humidity range54%RH to74%RH is960Hz. The maximumdifference frequency value for humidity range66%RH to86%RH is950Hz. The maximumdifference frequency value of ZnO nanorods sensitive membrane for humidity range54%RHto74%RH is960Hz.