Gas-sensitivity Studies Of Organic Composite Film Sensor With Rapid Response At Room Temperature

Gas-sensitive materials and sensors have been widely used in the designs of electronic nose and tongue of bionic systems, and have many potential applications in food industry, environmental monitoring, and counter terror, inspection of drugs and toxic gases, and prognoses of some diseases. To study an organic film sensor with high sensitivity, rapid response and good reproducibility, and attempt to explore some rules to conduct the design and development of new materials by the research of relationship among materials, technologies and properties of devices, it would be very important for investigations in-depth and accelerating applications in these fields.The progresses of organic gas-sensitive materials were reviewed in this paper, and the affecting factors and improving approaches to gas-sensitivity were also analyzed. Being aimed at the sensitivity, response rate, reproducibility and reversibility at room temperature, how to improve these properties were discussed from sensitive materials and film-forming technologies.The gas-sensitivities of weak interaction systems between phthalocyanine film and absorbed gases were studied in this paper, good results on recovery at room temperature were obtained. The gas-sensitivities of zinc phthalocyanine (ZnPc) and its fluorinated derivative (zinchexadecafluorophthalocyanine-ZnF16Pc) films to a series of reducing gases at room temperature are investigated. The results indicate that the gas-sensitivities and the response rates of ZnPc film to ammonia, trimethylamine and methylamine can be improved significantly via fluorination, the gas-sensitivity values to some vapors were increased 2-3 orders, and the fluorination film has a good selectivity and stability, and it can be completely recovered by high-purity N2 at room temperature. The results of examination on the gas-sensitivities of zinc tetraphenylporphyrin evaporation film and zinc-meso-tetra (2,3,4,5,6-pentafluorophenyl)-porphyrin film to a series of organic volatiles under similar conditions show that the sensitivity of zinc porphyrin film to ammonia can also be improved greatly via fluorination, the response speed was enhanced over 30 folds.In order to enhance the sensitivities and response rates of organic films greatly, the gas-sensitivities of conductive polymers and their composite films were studied. Basing on the conductivity of polymer strongly depending on the doping and undoping, several organic films with high sensitivity and rapid response were obtained via in-situ polymerization approach and self-dopingmethod. The values of gas-sensitivity and response rate are much higher than that of poly(aniline) film obtained via conventional spin-coating (polyaniline was dissolved in N-methylpyrrolidone). The gas-sensitivity value was increased 3-4 orders. To improve the film-forming further, the film-forming technology was improved greatly by adding a small amount of poly (sodium-p-styrenesulfonate) under holding high sensitivity.Polythiophene composite film on the interdigital electrodes of carbon was formed with an in-situ polymerization approach at room temperature by adding a small amount of boron trifluoride etherate, which purpose is decreasing the oxidation potential utilizing interaction between molecules. The results indicated that this film showed a good sensitivity to ammonia, and had also a good selectivity to analogy gases and a fast response while exhibiting a good reproducibility. The gas-sensitivity value can reach to 3 orders within 250s.To increase the heat stability of organic films, and expect to obtain new kind composite materials with synergetic or complementary behaviors, and be used in electronic or nanoelectronic devices. Considering P-zeolite being one of type materials with regular channels, which has outstanding surface feature, and is widely used in carrier of catalyze. At the same time, it is also good candidates for template of nano-materials preparation, some organic-inorganic hybrid materials were investigated. The results indicated that, in spite of the heat stability of organic films increasing at certain extent, the gas-sensitivities of some composite systems were decreased. However, the gas-sensitivity was enhanced obviously via adjusting the ratio of Si/Al in zeolite, organic-inorganic hybrid materials with synergetic or complementary behaviors was obtained.Some conductive polymers with nano-structure were obtained via several simple methods, such as: template method, non-template approach and nano-fiber seeding method. Their gas-sensitivities were also examined, and preliminary discussions on dependences among materials, technology, structure and their properties to obtain some valuable information. Comparing to that of conventional polyaniline film via organic solution spin-coating, the value of gas-sensitivity and response rate of the film with nano-wire structure obtained by non-template approach were increased dramatically. Its gas-sensitivity value was increased 3-4 orders.