Design And Preparation Of Electrospinning Nanofiber Membrane / Quartz Crystal Microbalance Ammonia Sensor

With the improvement of living level and environmental awareness, higher requirements have been put forward in real-time monitoring of trace ammonia. Electrospinning is a relatively simple technique for fabricating one-dimensional nanofibrous membranes with ultra-thin fiber diameter,high specific surface area(SSA), high porosity, three-dimensional(3D) structure, etc. Sensitive groups will increase within the unit area which facilitates the gas adsorption, making the nanofibrous membrane a promising high-performance sensing material in the field of gas sensing.The thesis combines the electrospinning and QCM(Quartz Crystal Microbalance, QCM)technology to fabricate ammonia sensors with high sensitivity, fast response, good reversibility and easy operation. Based on the structure design and regulation of nanofibers, the thesis managed to fabricate three electrospun sensing membranes, namely poly(styrene-block-maleic acid)(PS-b-PMA) nanofibers, nanoporous carboxyl graphene(G-COOH)/Polystyrene(PS)nanofibers and cellulose acetate(CA)/Polyethylenimine(PEI)/Poly(acrylic acid)(PAA) composite nanofibers. They are integrated on QCMs to in situ detect ammonia. The sensing performance were investigated. Additionally, adsorption mechanism and the relationship between SSA and sensing performance were studied. The details are presented as follows:Firstly, one-step process of PS-b-PMA nanofibers/QCM combined system was developed as a novel ammonia detection. It can retain the original high SSA of electrospun nanofibers, and simplify fabrication process of nanofibrous sensing materials. The PS-b-PMA coated QCM sensor had rapid response, excellent reversibility and high sensitivity(low detection limit at 1.5 ppm) at room temperature. Based on the fabrication and structure regulation of electrospun sensing materials, sensing membranes with different SSAs were fabricated to investigate the relationship between SSA and sensing performance. The results showed that sensitivity increased linearly with SSA.Secondly, nanoporous G-COOH/PS composite nanofibers integrated on QCM were developed based on one-step fabrication of porous PS nanofibers developed by our research group.The as-prepared G-COOH/PS nanofibers, agglomerated with ultrathin nanowires, possess a high SSA of 24.64 m2/g. The unique structure will provide a large surface active region, and thus improve the sensor performance. The developed ammonia sensor exhibited low detection limit(1ppm), fast response and a good reversibility.Thirdly, CA/PEI/PAA composite nanofibrous membranes were integrated on QCM to realize ammonia detection. Based on the combination of electrospinning and the electrostatic layer-by-layer(LBL) adsorption, positively charged charged PEI and negatively charged G-COOH were alternatively assembled on the surface of negatively charged CA nanofibers. The CA/PEI/PAA-based sensor had both the high SSA of the electrospun membranes and optimal exposure of sensing material to the analytes, thus will improve the sensing performance. The developed ammonia sensor exhibited low detection limit(1 ppm), quick response and a good reversibility. Moreover, sensing membranes with different PAA mass were fabricated to investigate the relationship between carboxyl amount and ammonia adsorption mass. The results showed that adsorption process of nanofiber/QCM sensing system may exists more molecular layer adsorption when the carboxyl amount reaches a certain degree.Based on the structure design and regulation of electrospun nanofibers, this thesis fabricated three kinds of electrospun nanofibers/QCM ammonia detecting systems with fast response, high sensitivity and good reversibility. Additionally, further study of adsorption mechanism and the relationship between SSA and sensing performance lay a certain theoretical foundation for the fabrication of high-performance electrospun nanofibers/QCM ammonia detecting system.