Effect of partial exfoliation in carbon dioxide adsorption-desorption properties of carbon nanotubes

Abstract

In this study, we have experimentally studied the effect of partial exfoliation in low-pressure (<100 kPa) carbon dioxide adsorption and desorption behavior of multiwalled carbon nanotubes (MWNTs). MWNTs were partially exfoliated by controlled oxidation followed by hydrogen assisted low temperature exfoliation method. The adsorption capacity of partially exfoliated MWNTs (PEMWNTs) is 3.4 times that of MWNTs. Adsorption-desorption isotherms of MWNTs are unique, which shows trapping behavior. The desorption behavior in association with isothermal adsorbate retention of MWNTs and PEMWNTs suggests possible CO2 trapping inside the tubes and at interstitials. It is found that the CO2 adsorbed PEMWNTs system has higher molecular orbital energy than CO2 adsorbed MWNTs system. Areal adsorption capacity analysis suggests the significant influence of surface functional groups on adsorption capacity. Adsorption isosteres of both adsorbents follow the Arrhenius relation stating the temperature dependent adsorption rate. The isosteric heats and change in entropy of adsorption have been determined at multiple adsorbed amounts from the corresponding adsorption isosteres.