SORPTION OF COPPER (II) CATIONS FROM AQUEOUS SOLUTIONS BY THERMALLY REDUCED GRAPHENE OXIDE

Samples of multilayer graphene oxide in electrolytes based on H2SO4 have been synthesized by the electrochemical method. The results of differential scanning calorimetry and thermogravimetric analysis reveal an endothermic peak in the scanning interval up to 100 degrees C accompanied by the weight loss of about 7%, which may be caused by desorption and evaporation of a certain amount of retained water in the samples. Another endothermic peak appears at 252 degrees C on the DTA curve and the weight loss of 15% that can be explained by decomposition of labile hydroxyl, epoxy, and carboxyl oxygen-containing functional groups, including those between the layers of polygraphene planes. Thermal exfoliation of multilayer graphene oxide at 250 degrees C leads to removal of oxygen-containing functional groups, a significant increase in the particle size (K-v = 1490 cm(3) g(-1)) and formation of worm-like structures with a large number of V-shaped pores with a size of 1-10 mu m and thickness of polygraphene planes up to 0.01 mu m. A specific surface area of the heat-treated graphene oxide powder is 400-500 m(2) g(-1). The distribution range of thermally reduced multilayer graphene oxide particles in water is 0.3-1400 mu m, and the modal size is 211 mu m. Under ultrasonic action on an aqueous dispersion, the particle size of the dispersed phase reduces significantly to 0.2-400 mu m, with the modal size of 143 mu m, which allows a more uniform distribution of carbon material particles in the volume of water. FTIR spectroscopy of thermally reduced graphene oxide reveals the presence of sp2-hybridization C = C in the structure of graphene (its peak at 1627 cm(-1)), epoxy groups -COC- (band between 1106 cm(-1) and 1005 cm(-1)), and carboxyl groups -COOH- (the band at 1384 cm(-1)). The peak at 2300 cm(-1) corresponds to the peak of absorbed CO2 molecules. After exposure of thermally reduced graphene oxide in the solutions containing copper cations, the absorption bands are observed in the FTIR range of 690 - 1130 cm(-1), which can be considered as vibrations of groups formed on the surface as a result of interaction of copper cations with oxygen atoms in the composition of functional groups. The Cu2+ adsorption isotherms on a thermally reduced multilayer oxide graphene have the form typical for isotherms of H-2 class, and are characterized by a straight steeply ascending initial segment, which indicates a high affinity of the adsorbate to the adsorbent with formation of chemical compounds. A likely explanation is that there is an interaction of Cu2+ ions with carboxyl functional groups, which is confirmed by a slight decrease in the pH of the solution. The isotherm is approximated by a straight line, which allows us to use it to describe the adsorption process of the Langmuir model. The maximum sorption capacity of thermally reduced multilayer graphene oxide to Cu2+ was 25 mg g(-1), which is noticeably higher than the sorption capacity of activated carbon fibers.