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The kinetics of the sorption and the subsequent desorption of 4He by thestarting graphite oxide (GtO) and the thermally reduced graphene oxide samples(TRGO, Treduction = 200, 300, 500, 700 and 900 C) have been investigated in thetemperature interval 1.5 - 20 K. The effect of the annealing temperature on thestructural characteristics of the samples was examined by the X-ray diffraction(XRD) technique. On lowering the temperature from 20 K to 11-12 K, the time of4He sorption increased for all the samples, which is typically observed underthe condition of thermally activated diffusion. Below 5 K the characteristictimes of 4He sorption by the GtO and TRGO-200 samples were only weaklydependent on temperature, suggesting the dominance of the tunnel mechanism. Inthe same region (T<5 K) the characteristic times of the TRGOs reduced at highertemperatures (300, 500, 700 and 900 C) were growing with lowering temperature,presumably due to the defects generated in the carbon planes on removing theoxygen functional groups (oFGs). The estimates of the activation energy (Ea) of4He diffusion show that in the TRGO-200 sample the Ea value is 2.9 times loweras compared to the parent GtO, which is accounted for by GtO exfoliation due toevaporation of the water intercalated in the interlayer space of carbon. Thenonmonotonic dependences Ea vs T for the GtO samples treated above 200 C aredetermined by a competition between two processes - the recovery of thegraphite carbon structure, which increases the activation energy, and thegeneration of defects, which decreases the activation energy by openingadditional surface areas and ways for sorption. The dependence of theactivation energy on treatment temperature correlates well with the contents ofthe crystalline phase in GtO varying with a rise of the annealing temperature.

The effect of the thermal reduction on the kinetics of low temperature 4He sorption and the structural characteristics of graphene oxide