Layer-by-layer self-assembly of polyaniline nanofibers/TiO2 nanotubes heterojunction thin film for ammonia detection at room temperature.

In this paper, for the first time, polyaniline nanofibers/TiO2 nanotubes (PANI/TiO2) heterojunction thin film has been prepared on Pt interdigital electrodes by layer-by-layer self-assembly method and applied in room temperature NH3 detection. It is found that the optimal self-assembly layer number is three (PANI/TiO2-3) compared to one layer (PANI/TiO2-1) and five layers (PANI/TiO2-5). The PANI/TiO2-3 thin film sensor possesses superior response characteristics compared with our other PANI based sensors, including higher response value (336%@5 ppm NH3), acceptable response/recovery time (110 s/1 086 s@5 ppm NH3), low detection limit (0.5 ppm), and remarkable selectivity. The enhanced gas sensing performances could be ascribed to the tremendous variation of the carrier concentration caused by the p-n junctions as well as the increased specific surface area and pore volume. This work not only offers a superb strategy to fabricate heterojunction thin film but also accelerates the development of room-temperature operable NH3 sensors.