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.