Abstract
DFT-D3 calculations were carried out to investigate interaction of H2S and CH4 between numerous functionalized CNTs (f-CNTs), including hydroxyl, carboxyl, and cyclodextrin groups as potential candidates for selective adsorption and elimination of toxic pollutants. It was found that pristine CNTs as well as nanotube surface of functionalized CNTs cannot stably adsorb the H2S molecule (adsorption energy of −0.17 eV). However, H2S adsorption was significantly enhanced with different magnitudes upon the functionalization of CNT. For f-CNTs, H2S adsorption was accompanied by releasing energies in the range between −0.34 to −0.54 eV where the upper limit of this range belongs to the cyclodextrin-functionalized CNT (CD-CNT) as the consequence of the existence of both dispersion and electrostatic interactions between the adsorbate and substrate. Findings also demonstrated a significantly weaker interaction between CH4 and CD-CNT in comparison to the H2S molecule with adsorption energy of −0.14 eV. Electronic properties of the selected substrates revealed no significant changes in the inherent electronic properties of the CNTs after functionalizing and adsorbing the gas molecules. Moreover, DFTB-MD simulation demonstrated high adsorption capacity as well as CD-CNT ability for H2S molecules against the CH4 one under ambient condition.
Highlights
Since one of the most important ongoing threats facing the human community is the growing concern of environmental pollution, which affects the lives of millions of people all around the world and requires immediate strategies to alleviate their hazardous effects on the civilization
Considering the fact that the H2S molecule has two active sites that might potentially interact with the π-extended surface of the carbon nanotubes (CNTs), one can conclude that the only possible orientation of the H2S would be the case that hydrogen atoms of the molecule approach the surface of the CNT
According to the optimized structure of the most stable complex as shown in Fig. 1d, the H2S molecule oriented above the surface of CNT in a way that its hydrogen atoms approach to the neighboring carbon atoms of the CNT with the average distance of about 2.7 Å, which is within the range of bonding distances in www.nature.com/scientificreports non-covalent interactions[63]
Summary
Since one of the most important ongoing threats facing the human community is the growing concern of environmental pollution, which affects the lives of millions of people all around the world and requires immediate strategies to alleviate their hazardous effects on the civilization. According to the experimental studies, the CNTs tend to form bundle or arrays because of the existence of strong van der Waals (vdW) interactions between their surfaces[24] This process will provide additional surface areas for physical adsorption of the guest molecules, as well as adsorption capabilities of the CNTs. The chemical modification of CNTs can be taken into consideration for enhancing their chemical properties through direct attachment of functional groups to the terminal edges of the graphitic surface, chemical doping of impurities or the use of nanotube-bound carboxylic acids[25,26,27]. The following sections present further information regarding computational procedure and the obtained results
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