The sulfur-doped graphene oxide/graphite oxide composite material was synthesized in an original way, and a detailed study of its structural arrangement was carried out using XRD and Raman spectroscopy. Negative differential resistive properties of the obtained material were observed on the current-voltage curve at room temperature as a result of limited proton hopping through water molecules adsorbed on the hydrophilic surface of graphene oxide layers in the presence of a sulfur-enriched graphite oxide component with high electron conductivity, which promotes spatial charge separation and increases the efficiency of H+ transport. The obtained result offers a new way for the one-pot synthesis of new graphene-based composite materials with a wide range of possible applications.

The sulfur content present in graphene oxide prepared by Hummers' method has only been addressed by few papers so far. By modified Hammers method we synthesized thermally stable in ambient environment multilayer sulphur-doped graphene oxide. The samples were heat treated in an electrical furnace setup at different ambient temperatures and their crystallite size and linear coefficient of thermal expansion were extracted from Raman band intensity peak ratio as a function of temperature. We found unusually large (in comparison with graphene oxide) contraction on heating of multilayer two weight percent sulphur-doped graphene oxide with carbon to oxygen ratio of 2.3 in a narrow temperature range (308-318 K) with the lowest value of the linear thermal expansion coefficient of -18 ppm 1/K. Based upon an examination of the synthesized sulphur-doped graphene diffractograms, it is suggested that negative thermal expansion stems from the phonon backscattering by the sulphur impurity sites and the edges of the layers. The obtained experimental results have potential practical applications for fabrication of solar cells, sensors, lubricators, thermal actuators and also wavelike (second sound) thermal transport structures.

The paper presents an analysis of SEM, EDX, Raman scattering, and FTIR of Gadolinium-doped multi-walled carbon nanotubes obtained by hydrothermal method. The morphological characteristics of the materials were studied and their compositions were analyzed. Hydrothermal doping of MWCNs with Gd causes the formation of 3D network architecture and sharply increases the content of oxygen surface functionality. An unidentified intense broad peak for Gd-doped material at 2940 cm-1 was observed. The defect state of Gd-doped MWCNTs was studied by Raman spectroscopy.