Comparison of response towards NO 2 and H 2S of PPy and PPy/TiO 2 as SAW sensitive films

Abstract

We have compared the performance of polypyrrole (PPy) and PPy/TiO 2 as surface acoustic wave sensitive films for NO 2 detection at room temperature. Our sensors, based on a dual-delay-line pattern, were fabricated on ST-X quartz substrates by the combination of polymerization and self-assembly method. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopic (FT-IR) techniques were used to characterize the PPy and PPy/TiO 2 films. The dynamical frequency shift of sensors was measured as a function of NO 2 concentration. When exposed to NO 2, sensors with PPy and PPy/TiO 2 films shows a negative frequency shift tendency and a positive one, respectively. The latter has a faster response speed and a higher sensitivity. A negative frequency shift of 30 Hz was measured for a PPy film with 15 ppm NO 2, while nearly the same amount of positive frequency shift was obtained for a PPy/TiO 2 film with only 10 ppm NO 2. The selectivity of both films to NO 2 and H 2S were also assessed. Negative frequency shifts of about 90 and 50 Hz were observed for a sensor with a PPy film to 100 ppm NO 2 and 100 ppm H 2S, respectively. In contrast, positive frequency shifts of 110 and 5 Hz for a PPy/TiO 2 film were measured to NO 2 and H 2S, respectively. Therefore, the use of a PPy/TiO 2 sensitive film can improve the sensor selectivity of NO 2 from H 2S.