Design of flexible PANI-coated CuO-TiO₂-SiO₂ heterostructure nanofibers with high ammonia sensing response values

We report a room-temperature ammonia sensor with extra high response values and ideal flexibility, including polyaniline (PANI)-coated titanium dioxide-silicon dioxide (TiO₂-SiO₂) or copper oxide-titanium dioxide-silicon dioxide (CuO-TiO₂-SiO₂) composite nanofibers. Such flexible inorganic TiO₂-SiO₂ and CuO-TiO₂-SiO₂ composite nanofibers were prepared by electrospinning, followed by calcination. Then, in situ polymerization of aniline monomers was carried out with inorganic TiO₂-SiO₂ and CuO-TiO₂-SiO₂ composite nanofibers as templates. Gas sensing tests at room temperature indicated that the obtained CuO-TiO₂-SiO₂/PANI composite nanofibers had much higher response values to ammonia gas (ca. 45.67-100 ppm) than most of those reported before as well as the prepared TiO₂-SiO₂/PANI composite nanofibers here. These excellent sensing properties may be due to the P-N, P-P heterojunctions and a structure similar to field-effect transistors formed on the interfaces between PANI, TiO₂, and CuO, which is p-type, n-type, and p-type semiconductor, respectively. In addition, the prepared free-standing CuO-TiO₂-SiO₂/PANI composite nanofiber membrane was easy to handle and possessed ideal flexibility, which is promising for potential applications in wearable sensors in the future.