| Abstract [eng] |
Graphene is used in the development of innovative electrode materials for supercapacitors, biosensors or fuel cells due to its unique physicochemical properties. However, in order for the application of graphene to become widespread some problems need to be solved. The main one being related to the difficulties during its large-scale production. Since any damage to the graphene sheet structure may cause changes to the vast majority of its properties. These properties include not only electrical and thermal conductivity, but also the mechanical, physical and chemical behaviors. Therefore, the aim of this work was to thermally reduce graphite oxide (GO) samples in presence of additives, to evaluate the structural changes and defect properties of the obtained products and to perform a study of the thermal decomposition reaction kinetics of GO. The influence of malonic acid and P2O5 additives, temperature and different initial GO samples on the structural properties of thermally treated products was analysed. Changes in the structure that occurred during the reduction were determined by X-ray diffraction, Fourier transform infrared and Raman scattering spectroscopies. The morphology of the obtained products was evaluated using scanning and transmission electron microscopy methods. The electrical properties of the samples were investigated by plotting the dependencies of the electrical conductivity against the bulk density on a logarithmic scale. The obtained data showed that during thermal reduction, graphene sheets tend to deform, bend, and their surface wrinkles. In addition to that, thermally reduced samples were determined to have a polycrystalline graphite structure. Mainly partial reduction of GO samples was achieved since hydroxy, carboxy, carbonyl, quinone and phenolic functional groups remained on the surface of the products. Electrical conductivity measurements showed that sample that was reduced at 800 ℃ with a malonic acid additive of 10 % by mass exhibited the highest value. In the second part of this work, the analysis of GO thermal decomposition reaction kinetic parameters was performed. Thermal stability of pure GO and a mixture containing GO with 10 % by mass of malonic acid was evaluated by thermogravimetric analysis. Using the results of differential scanning calorimetry measurements and three kinetic models: Borchardt-Daniels, Ozawa, and Kissinger, activation energy values for the thermal decomposition reaction of GO were calculated. The addition of malonic acid and P2O5 mixture was found to increase the reactivity of GO. While the calculated enthalpy values for the decomposition showed that the additives reduced the amount of heat that was released. The degree of thermal decomposition reaction for GO and GO mixture with additives was also determined to be 0.7. The obtained kinetic parameters for pure GO are very similar to the data reported in the literature. |
