Erp study of graphite oxide thermal reduction: the evolution of paramagnetism and conductivity

The evolution of paramagnetic centers (PMC) and conductivity of graphite oxide (GO) during its thermal reduction has been studied by electron paramagnetic resonance (EPR) at $150$ and $165^\circ$ C. The GO samples for the study were prepared by systematically varying the $\mathrm{KMnO}_4$/Graphite weight ratios in the oxidation reaction. It has been shown that the PMC concentration increase in GO correlates with the intense evolution of gaseous products originating from the former oxygen-containing species of GO. The PMC concentration decrease has been described by the kinetic equation of the first order with an effective $k_e$ and an activation energy value of $33$ kcal/mol. The values of $k_e$ decreased with increasing the quantities of $\mathrm{KMnO}_4$ used in graphite oxidation reaction. The changes in GO conductivity were followed by measuring the microwave power absorption in the EPR-spectrometer resonator. The conductivity changes correlated with the decay of the radicals and occurred after the decomposition of the oxygen-containing groups was complete.