Nanostructured NiO-polyaniline fibers composite smart material as a room temperature ammonia sensor

The NiO-PAni nanofibrous composite thin film were synthesized efficiently using a hybrid Dip-coating SILAR technique in which PAni films were activated by coating on a NiO precoated glass substrate. The analysis of structure was done using FTIR, which made evident of IR absorption bands specific to PAni as well as the appearance of new bands that are indicative of NiO particles. Surface morphology study carried out by employing SEM, demonstrated the nanofibrous PAni morphology with 50 to 60 nm width of fibers for 4 cycle NiO + PAni composite which decreased to 30 to 40 nm for 12 cycle NiO + PAni. As the cycles of NiO increased uneven morphology resulted in decrease in length of PAni nanofibers from around 500 nm to 100 nm. EDS gave elemental analysis in accordance with expected proportion. XRD study shown cubic crystalline phase for synthesized NiO with 10 to 30 nm crystallite size. TEM analysis indicated formation of NiO + PAni composite with 10 nm sized NiO particles embedded in PAni nanofibers. At a low operating temperature of 25 +/- 5 degrees C, the NiO-PAni thin film gas sensor presented the best selectivity for NH3 among the several other gases including C2H5OH, formaldehyde, LPG and H2S. Gas sensing studies were done with a custom fabricated gas sensor. All synthesized NiO-PAni thin films exhibited improved NH3 sensing capabilities; the optimized NiO + PAni composite thin film showed the maximum sensitivity of 125.61% and 912.12% at 40 ppm and 1500 ppm, respectively.