Synthesis And Low Temperature Gas Sensing Properties Of P-N And N-N Hetrojunction Nanocomposites

Since human beings have entered the era of rapid development of modern industry, the consumption of non-renewable fossil fuel is increasing. However, the poisonous and harmful gas treatment technologies still fall behind. Attendantly, the problems of air pollution are more and more serious. Toxic and harmful gases, especially NOx, are very harmful to human beings, which can produce photochemical smog, acid rain, and even cause human poisoning directly.This article has successfully fabricated WO3 nanoparticles through short-time hydrothermal method and then coating with p-type polythiophene (PTP) by in situ oxidative polymerization. Finally we have synthetized p-n hetrojunctions formed by PTP-WO3 hybrids. We foud that the electron transfer from the S element to W built a new chemical bond (S?+-W5+), which had improved the thermal stability of PTP and been demonstrated by SEM?BET?FTIR?XPS?TG analysis. The PTP-WO3 hybrid was applied to detect NO2 at room temperature, and the sensor response obtained with 40 wt% PTP-WO3 reaches 48.2, which is 3.5 times higher than that obtained with pure PTP. The response rate for the hybrid was calculated to be 4.7 ppm-1 with the extrapolated detection limit of about 450 ppb. The improvement of gas-sensing properties may be attributed to the highly sensitive modulation of a conductive PTP layer for the NO2 exposure due to the shrinkage of p-n depletion region in the PTP-WO3 hybrid.For detecting the gas sening of ppb level NO2 at low temperature, we had synthesized single dispersed SnO2 and ZnO-SnO2 hollow spheres using SiO2 template fabricated by improved Stober method. The sensing measurements reveal that the composites not only exhibit higher response to ppb level NO2 at 100? but also better selectivity compared with pure SnO2. The response of 11.7 at% ZnO-SnO2 composite can reach 81, which is four times higher than SnO2 at the same measure condition. The morphology and structure of the materials were characterized by SEM? BET?FTIR?XPS, etc. We think that the enhancement of NO2 sensing performance can be attributable to the formation of n-n heterojunction.Besides, we also tried to use a new flexible sensing device substrate called PET film during our research. The PET film is flexible and cheaper than we used before.