CO2 metallothermic conversion to valuable nanocarbons by mixed Mg/Ca reductant

Abstract

The present study concerns conversion of greenhouse CO2 gas to nanocarbons by employing a simple metallothermic method and a mixture of Mg and Ca reducing agents. The conversion reaction was carried out in a tube furnace under constant CO2/Ar gas flow at three different temperatures of 675 °C, 775 °C and 875 °C. Increase in material crystallinity with the increase of reduction temperature was observed by using XRD analysis and Raman spectroscopy. The changes in the material morphology were investigated with the help of SEM and TEM techniques. The tubular and spherical nanostructures covered with smaller particulates characteristic for synthesis at 675 °C gradually disappeared being replaced by nanostructures with irregular shape and surface at higher temperatures, while the sponge-like structures were a common morphological feature of all materials. A set of electrochemical tests were applied to estimate specific capacitance of the prepared nanocarbons. The calculated capacitance for the material prepared at 675 °C was ∼ 430 F/g at scan rate 0.1 V/s compared to the value of ∼ 130 F/g for the material synthesized at 875 °C. The higher value can possibly be explained by the specific morphology which combined a branched network of nanotubes, nanospheres and sponge-like nanostructures.