Influence of Nanostructuring Sensors Based on Graphene Oxide and PEDOT:PSS for Methanol Detection

Graphene oxide (GO) composites with conducting polymer poly (3,4-ethylenedioxythiophene)-poly (styrenensulfonate) (PEDOT:PSS) were applied as methanol vapor sensors. The active layer was prepared with neat polymer and its composites for different mixing ratios with GO. An optimal ratio was found with 3% (v/v) PEDOT:PSS in GO dispersion and submitted to an additional sonication treatment to change the nanostructure. Devices with treated active layers showed higher responses when applied to methanol vapor sensors. The improved responses are related to differences found on the composite surface. 2-D materials improve the organization of polymer chains, changing PEDOT availability, number of functional groups, and defects in GO. Theoretical analysis by density functional theory (DFT) simulations indicated that the average adsorption energy of methanol molecules is elevated, around -0.8 eV, and a simple mechanism was proposed to explain the response (variation of the layer electrical resistivity in the presence of methanol). The adsorption of vapor molecules on the active layer passivates the doping effect of PSS and GO on PEDOT, decreasing the number of empty states and consequently the conductivity along PEDOT chains. It was also observed that the passivation effect is much accentuated in composites than only in PEDOT:PSS, demonstrating the advantage of using GO composites for methanol vapor detection. Therefore, understanding the dependence of surface, vapor adsorption, and response signal, can improve the development of sensors to be used for gas detection in confined spaces.