The need to reduce CO2 and other greenhouse gases emissions in the atmosphere is currently a main global objective among policy makers as well as scientists to minimize global warming adverse effects. Traditionally, aqueous amine compounds were used to absorb CO2, mainly in thermal power plants. Recently, solid adsorbents have become popular as opposed to their liquid solvent counterparts whose regeneration requirements demand high energies. Among the solid adsorbents, carbon based adsorbents exhibit better stability towards moisture and corrosive fuel gases like sulphur dioxide and hydrogen sulphide. The recent nanotechnology evolution has presented carbon nanotubes and carbon nanohorns (CNHs) as potential materials for gas adsorption applications. Vertically aligned carbon nanotubes (CNTs) exhibit a promising adsorption behavior at high pressures, while as carbon nanohorns exhibit superior gas adsorption properties in the low pressure regime due to their inherent microporosity. However due to the absence of microporous adsorption sites, very low adsorption capacity is observed for vertically aligned carbon nanotubes at near ambient conditions. Impregnation with amine compounds is a commonly adopted approach to overcome this shortcoming. Nonetheless, CO2 often adsorbs irreversibly (chemisorption) onto this amine impregnated vertically aligned carbon nanotubes and the energy penalty for the sorbent regeneration seldom justifies this approach.
In a recently published research paper in the journal, PCCP, researchers led by Professor Jörg J. Schneider at Technische Universitaet Darmstadt in Germany proposed an in-depth study on the feasibility of an all carbon composite of carbon nanotubes and vertically aligned carbon nanotubes. Their main objective was to obtain a reasonable adsorption capacity over the wide range of pressures for the vertically aligned carbon nanotubes and carbon nanohorns. “CNTs and CNHs are lightweight and are high surface area materials, the process for their fabrication can be scaled up, so even the technological use of these potentially interesting materials is not out of reach” as Schneider proposed.
The authors observed that the surface area of the carbon nanohorns and vertically aligned carbon nanotubes increased significantly after the high temperature CO2 treatment. It was also seen that addition of opened vertically aligned carbon nanotubes to opened carbon nanohorns significantly improved the high pressure adsorption characteristics of the opened carbon nanohorns, thereby extending their superior adsorption characteristics from the micro into the mesoporous regime. To be precise, the team noted that at a pressure of 30 bar, addition of 50% by weight of opened the vertically aligned carbon nanotubes to opened carbon nanohorns resulted in an increase in the carbon dioxide adsorption capacity of 24%.
Professor Jörg J. Schneider’s research team successfully presented a practical investigation of the suitability of an all carbon composite composed of opened carbon nanohorns and opened vertically aligned carbon nanotubes for carbon dioxide adsorption. In their study CO2 gas was used to open vertically aligned carbon nanotubes and carbon nanohorns which were then oxidized at high temperatures. Therefore, the study has shown that combining tip opened carbon nanotubes with tip opened carbon nanohorns increases the CO2 adsorption capacity of the material by 24% compared to opened carbon nanohorns alone.
Divya Puthusseri, Deepu J. Babu, Sherif Okeil, Jörg J. Schneider. Gas adsorption capacity in an all carbon nanomaterial composed of carbon nanohorns and vertically aligned carbon nanotubes. Phys. Chem. Chem. Phys., 2017, 19, 26265—26271.
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