Engineered doped and codoped polyaniline gas sensors synthesized in N,N,dimethylformamide media

Conducting Polyaniline films (Pani) on Corning glass substrates, produced using either an in-situ doping process or a co-doping process, were prepared by the oxidative polymerization of aniline in N,N,dimethylformamide. Bicyclic aliphatic camphorsulfonic acid (CSA), aromatic toluenesulfonic acid (TSA) and carboxylic trifluoroacetic acid (TFA) were employed as doping agents, and CSA mixed with TSA and CSA mixed with TFA were employed as the co-doping materials. The topography of the Pani films was analyzed by atomic-force microscopy (AFM), and their doping and oxidizing states were characterized by Fourier-transform infrared (FT-IR) spectroscopy and optical (UV-Vis) spectroscopy. Flower-like clusters, microfibers, and nanofibers were obtained by doping with CSA, TSA, and the mix of both (CSATSA), respectively. The flower-like morphology limits the conductivity of the film while the microfiber morphology leads to a highly conductive film. The conductivity of the films increases with the doping level, coil-like conformation of the chain and the protonation of the imine in quinoid units. The codoped process reduces the roughness of the CSA-doped films by 50%, but the conductivity depends on the acid type used for this process (TSA or TFA). The optical gas sensor response of the films is related to both the morphology and the degree of protonation. In this study, Pani with a microfiber morphology obtained from TSA-doping is the most sensitive to ammonia gas sensing, and Pani with flower-like morphology is the least sensitive.