Influence of Heat Treatment Temperature of Graphene Oxide on the Transport of Charge in Nanocomposites with Pressure Sensitive Paints
Authors: Brito de Souza Camila , Dias Impere Ana Gabrielle , Barbosa Hilario Rodrigo , Gama Adriana Medeiros , Gonçalves Emerson Sarmento 
Published: February 2020

The vast majority of polymeric materials are insulators, which limits their application in some areas, such as electronics and sensors, and research is being carried out to increase the conductivity through the insertion of nanocharges, mainly of origin such as graphene and carbon nanotubes. Thus, the change in the electrochemical properties generated in pressure sensitive paints (PSP) was analyzed by adding thermally reduced graphene oxide at two temperatures. Graphite oxide (GrO) was produced by the Hummers method, which was thermally reduced in a Splemby furnace, at temperatures of 400 ºC (752ºF) and 1000 ºC (1832ºF), at a speed of 10 ˚C / min, with a step of 15 minutes. The reduced graphene oxide (rGO) was ultrasonically mixed with the paint UniFIB® UF: 400-470 at a concentration of 4 mg/ml and then dripped 4 times on aeronautical steel and aluminum 2024 electrodes, and dried at room temperature. Crystallographic structures were determined using X-ray diffractometer Panalytical XPertPRO, with a rotating anode X-ray generator working at 5˚≤2θ≤90˚, with Cu monochromatic radiation (0,154 nm) and Fourier Transform Infrared Spectroscopy(FT-IR) using a Perkin Elmer Spectrum Onespectrometer, with transmission by KBr pads technique. Electrochemical Impedance Spectroscopy (EIS) characterization was performed through Autolab PGSTAT 302 potentiostat-galvanostat, using three electrode cell - at work of composite electrode, at auxiliary of Pt mesh; reference of Ag/AgCl. The diffractograms, Figure 1, are similar to those in the literature [1], indicating that rGO was obtained. This can be confirmed by comparing the FTIR spectra of the produced material and commercial rGO, Figure 2, and it was possible to verify the transformation obtained after the heat treatment, when comparing the spectrum of the GrO and rGO, noting the difference in the intensity of the oxygen groups. In addition, it can be seen that the thermal process of 1000 ˚C was more efficient in the removal of oxygen than the 400 ˚C, as indicated by the bands of approximately 1740 cm-1 (- C = O) and 1200 cm-1 (-COC-), whereas in the treatment of 1000 ˚C there was a reduction of both, while in the 400 ˚C the band of 1740 cm-1 was reduced and there was an increase in 1200 cm-1, which shows that the treatment of 400 ˚C was sufficient to transform the less stable (mainly hydroxylic) species of GrO into metastable oxygenated species (carbonyls and alkoxy). For the electrodes produced, it was possible to notice that rGO probably facilitates the locomotion of the electrons in the existing bonds in the paint, and each substrate used has a tendency to donate or receive electrons, which varies according to the type of bond involved. This trend seems to be verified in Nyquist Plot. Table 2 was obtained from them, and made it possible to analyze the electrochemical properties of the double layer formed on the surface of each electrode. The double layer formed on the rGO@Paint composite electrode using rGO annealed at 400 ° C has lower ohmic resistance when tested on both metals. In the case of the one prepared with rGO annealed at 1000 ˚C, the ohmic resistance value doubles in the case of steel and quintuple in the case of Aluminum. This fact demonstrates that rGO with higher degree of oxygen groups generates a greater migration of charge between the obtained electrodes and the electrolyte. The paint insulating character is significantly mitigated after the addition of nanometer powder, but the rGO reduction process can not be performed in order to completely expel the oxygen groups from the paint, since these are probably responsible for the migration of charge between the components of the composite electrode and between this and the electrolyte, as suggested by Duan [2], when analyzing the effect of oxygenated groups on the sensitivity of studied sensor, it was noted the greater the amount of oxygenated groups, the more intense the charge transfer.
References
[1]Seung, H. H. Thermal reduction of graphene oxide. In Physics and Applications of Graphene Experiments; Mikhailov, S., Ed.; InTech:New York, 2011; 5 ,73 −90.
[2]Duan, L; Bo, Z., Chen, X. et al Ab initio characterization and experimental validation on the roles of oxygen-containing groups in graphene based formaldehyde sensors.Analyst, 2018, 143, 106.
Acknowledgement
The authors thank Ana Cristina Avelar of aerodynamic division of IAE, the CAPES/ITA and Postgraduate Support Program (PROAP)/ITA.

Figure 1