Li Huixia

Development of ammonia sensors by using conductive polymer/hydroxyapatite composite materials.

In order to improve the gas sensing properties, hydroxyapatite (HAp)-based composites were prepared by mixing with different contents of conductive polymers: polypyrrole (PPy) and polyaniline (PAni). The compositions, microstructures and phase constitutions of polymer/HAp composites were characterized, and the sensing properties were studied using a chemical gas sensing (CGS-8) system. The results showed that, compared to pure HAp, the sensitivities of the composites to ammonia were improved significantly. 5%PPy/HAp and 20%PAni/HAp composites exhibited the best sensitivities to ammonia, and the sensitivities at 500ppm were 86.72% and 86.18%, respectively. Besides, the sensitivity of 5%PPy/HAp at 1000ppm was up to 90.7%. Compared to pure PPy and PAni, the response and the recovery time of 5%PPy/HAp and 20%PAni/HAp at 200ppm were shortened several times, and they were 24s/245s and 15s/54s, respectively. In addition, the composites showed a very high selectivity to ammonia. The mechanism for the enhancement of the sensitivity to ammonia was also discussed. The polymer/HAp composites are very promising in applications of ammonia sensors.

Room temperature gas sensing properties of tubular hydroxyapatite

Tubular hydroxyapatite (HAp) was prepared by a combined method of cation exchange membrane-assisted and electrochemical deposition. For comparison, rod-like HAp was also fabricated by the hydrothermal method. The products were characterized by scanning electron microscope (SEM), X-ray diffraction analysis (XRD) and Brunauer–Emmett–Teller (BET) analysis. The gas sensing properties toward ammonia were studied particularly. The selectivity to various volatile organic compounds was also investigated, then, the response and the recovery time were determined. Results showed that the hollow mesoporous and nanocrystalline nature are the key factors that increases the sensing properties of HAp. Tubular HAp based sensors exhibit 1.35–1.65 times of response value to ammonia than the rod-like based one. At the concentration of ammonia of 2000 ppm, the response value of HAp tubes was up to 84.58%, and the response time was as short as 10 s. Even at a low concentration of 50 ppm, the response was still detectable. Furthermore, tubular HAp shows great stability and reproducibility for gas sensing. Results also indicated that tubular HAp has obvious response to various gases, but has the highest response to ammonia. The growth mechanisms of tubular HAp and the gas sensing mechanisms were proposed.