Theoretical investigation on the healing mechanism of divacancy defect in CNT growth by C2H2 and C2H4

Abstract

Experimental studies have shown that chemical vapor decomposition method by using C₂H₂/C₂H₄ as carbon source could dramatically decrease the defects in prepared CNT. However, the inherent mechanism with regards to reduction of defects is quite unclear. In the present paper, density functional theory is used to study the healing process of CNT with divacancy defect by C₂H₂/C₂H₄ molecule. The healing processes undergo three evolution steps: (i) the chemisorption of the first C₂H₂/C₂H₄ molecule on defective CNT; (ii) the insertion of C atoms from C₂H₂/C₂H₄ molecule into defective CNT; (iii) the removal of the H atoms on CNT, forming perfect CNT. The estimated adsorption energy barrier of C₂H₂/C₂H₄ molecules on defective CNT is within the range from 1.10 to 1.63 eV, and the eventual formation of CNT is strongly exothermic (4.40/4.54 eV in (8, 0) CNT). In light of the unique conditions of CNT synthesis, i.e., high temperature in a closed container, such healing processes could most likely take place. Therefore, we propose that during CNT synthesis procedures, both C₂H₂ and C₂H₄ could act as a carbon source and the defect healer.

The healing of B- or N-vacancy defective BNNTs by using CO molecule: a DFT study

“…[30][31][32] Earlier studies 18,33 have indicated that BNNTs with N-vacancies show a greater chemical stability than those with B-vacancies. Like CNTs [34][35][36] and BNNS, [37][38][39] single vacancy defects in BNNTs can be effectively healed by small molecules, such as NO and N 2 O. 40 Since the energy released during NO or NO 2 chemisorption completely offsets the subsequent barrier, a perfect BNNT can be easily achieved by using NO or NO 2 and defective BNNT as reactants.…”

Healing double vacancy defects on graphene: reconstruction by C2adsorption

“…The same authors also studied the mechanism of healing in carbon nanotubes by ethylene and acetylene, although the details on the preferred orientation of carbon sources on DV were not mentioned. 36…”

“…The same authors also studied the mechanism of healing in carbon nanotubes by ethylene and acetylene, although the details on the preferred orientation of carbon sources on DV were not mentioned. 36 Using vdW-DFT calculations, Zhang et al found that the potential energy decreases when acetylene moves from the edge to the center of DV, suggesting that the center of DV is energetically more favourable for acetylene adsorption. Moreover, they reported that acetylene fills DV in graphene with no energy barrier, which is in compliance with previous studies.…”

Graphene Synthesis Using a CVD Reactor and a Discontinuous Feed of Gas Precursor at Atmospheric Pressure

“…For graphene synthesis by CVD the use of both saturated and unsaturated hydrocarbons is essential [5,8,37,38]. Saturated hydrocarbons are stable and less reactive than unsaturated hydrocarbons.…”