ИСТИНА

Although expanded graphite is known for decades and found some applications it is still an interesting object for investigations. The developed surface area, variable density, electrical conductivity and gas permeability makes it a promising material for membranes, adsorbents, catalyst supports and capacitors. For different aims some micro-scale additives, for example, metal oxides, are necessary. Herein we report the technique for preparation of expanded graphite doped with transition metal oxides, its structural characteristics, properties and applications. First, expandable graphite was prepared through graphite flakes anodic oxidation in an electrolyte of metal nitrate aqueous solutions. Then, expandable graphite was heated up at different temperatures to give expanded graphite. Graphite morphology transformations occur during oxidation and exfoliation were studied using X-ray diffraction, Raman Spectroscopy, IR-spectroscopy, scanning electron microscopy and nitrogen adsorption. Thermal properties of both expandable and expanded graphite were investigated using DSC, TG and laser-flash analysis. The optimum conditions for preparation of expanded graphite contained the desired amount of metal oxides were determined: current density of 10 mA/cm2, specific charge of 700-1500 Q/g, and exfoliation temperature of 250-500 oC. The preferable electrolytes should contain metal salts with a metal in a stable oxidation state (Fe(III), Co(III), Ni(II)) and ω(NO3-) = 30-60 wt.%. The deep graphite oxidation and low-temperature exfoliation leads to formation of expanded graphite with the largest surface area up to 160-180 m2/g. In order to improve expanded graphite pore structure samples were subjected to steam-and-gas activation. The expanded graphite samples with the lowest bulk density, the most developed surface area and different metal oxide content were electrochemically tested to determine capacity.