Adsorption and decomposition of formamide over zigzag (n,0) silicon-carbide nanotubes (n=5-7): Investigation of curvature effects

The adsorption and decomposition of formamide (FM) on the surface of zigzag silicon carbide nanotubes (SiCNTs) are investigated using density functional theory (DFT) calculations. The structures of monomers and complexes are optimized and characterized by frequency calculations at the M06-2X/6-31G** computational level. The calculated adsorption energies (E-ads) for the formation of FM/SiCNT complexes are all exothermic. The energy barriers for the dehydrogenation, decarbonylation, and dehydration processes are found to be in the range of 0.1-53 kcal/mol. Our results indicate that dehydrogenation and decarbonylation pathways are possible routes to get gaseous HNCO, H-2, NH3 and CO molecules. In contrast, the reaction of HCONH --> CONH + H needs a large activation energy which makes the FM dehydration an unfavorable reaction compared to dehydrogenation and decarbonylation pathways. The DFT calculations reveal that both the adsorption energies and reaction energy-barriers display a curvature effect and small-diameter SiCNTs with large curvature would be beneficial for capture and decomposition of FM. (C) 2015 Elsevier B.V. All rights reserved.