Morphology-promoted synergistic effects on the sensing properties of polyaniline ultrathin layers on reduced graphene oxide sheets for ammonia and formaldehyde detection

The control in morphology and microstructure is an efficient approach to regulate the gas sensing properties of the sensor. In this work, polyaniline (PANi) layer in nanoscale film morphology was coated on the surface of reduced graphene oxide (rGO) sheets through the in situ polymerization method. The microstructure and properties of the composite sheets were characterized by scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectrometry, Raman spectrometry and thermal gravimetric analysis. It is found that there are strong effects of morphology-dependent structures of PANi layers on the sensing behaviors for ammonia detection, and more importantly, the utilization of the composite sheets as a new type of sensing material for highly sensitive detection of formaldehyde. Moreover, the best sensing properties can be achieved for the composite sheets with the thickness of PANi layer of 1.3 nm, benefiting from the strongest interaction between graphene sheet and PANi chains among all the composite sheets. Furthermore, a wide linear response range from 12 to 1500 ppm, 10 s response time for 100 ppm, 3.0 x 10(-4)/ppm sensitivity and 10 ppm detection limit can be achieved for ammonia, while 8 to 250 ppm, 35 s, 1.1 x 10(-3)/ppm and 4 ppm for formaldehyde. With the advantages in simplicity in material preparation and device operation as well as significant synergistic effects, PANi in nanoscale film morphology covered on the rGO sheets with large surface area can provide an efficient approach for fabricating sensitive and cheap chemiresistive sensor as an early warning system in some particular situations where either ammonia or formaldehyde is used widely or produced largely.