| Carbon nanotubes（CNTs）have attracted widespread attentions of scientists due to their unique structures and excellent properties,especially CNTs with functional group modifications are used in various fields.In particular,carbon nanotubes modified with oxygen functional groups have become a research hotspot because their oxygen-containing functional groups are very easy to interact with various substances in the external environment（nanoparticles,catalysts,biomolecules,polymers,etc.）.The functionalized modified CNTs can alters the interfacial hydrophobicity and enhance the dispersibility and solubility of CNTs in organic solutions.Generally,the oxygen functional groups on the surface of CNTs seldom migrate or change under ambient conditions.The spontaneous dynamic migration of oxygen functional groups at the graphene oxide（GO）interface inspires us to investigate the dynamic behavior of oxygen functional groups on the CNTs surface in depth.We combined theoretical calculations and experimental observations to show that,with water being adsorbed,the GO is converted to a spontaneously dynamic covalent material under ambient conditions and presents structural for response to biomolecule adsorption,where the epoxy and hydroxyl groups are mediated by water molecules to spontaneously break/reform their C-O bonds to achieve dynamic oxygen migration.Compare with the structure of GO,CNTs have inherent curvature and chirality.These two particular parameters suggest that the oxygen functional groups on the carbon nanotube can achieve spontaneous dynamic migration without water adsorbed.In this paper,single-walled carbon nanotubes（SWCNTs）with a pair of hydroxyl and epoxy modification were selected and combined with density functional theory（DFT）calculations and ab initio molecular dynamics（AIMD）simulations to find that the oxygen functional groups exhibit spontaneous dynamic migration behavior on the interior surface of SWCNTs with different curvature:epoxy or hydroxyl groups migrate through C-O bond breaking/reforming reactions or proton transfer between neighboring hydroxyl and epoxy groups.On the interior surface of SWCNTs,the migration energy barrier is significantly lower than that of the GO surface,which has been lower or comparable to the thermal fluctuations,indicating that the oxygen-containing functional groups can spontaneously and dynamically migrate along the interior surface under ambient conditions;on the exterior surface of SWCNTs,the migration energy barrier is relatively high,making it difficult to achieve spontaneous dynamic migration.We also found that an intermediate state in the migration process（C-O dangling bond）,this conformation is lower in energy than the double bond of epoxy.This C-O dangling bond assists the proton transfer reaction,thus ensuring the dynamic migration of the oxygen functional group.In addition,combining static structural calculations and AIMD,it is further demonstrated that the interior surface oxygen functional groups of SWCNTs can migrate dynamically spontaneously under ambient conditions.Chirality is an important parameter to characterize the structure and properties of carbon nanotubes,so this paper also investigates the effect of chirality on the dynamic migration behavior of oxygen functional groups in CNTs.Only the chirality was changed with the same diameter.It was found that the migration energy barrier of oxygen functional groups on the exterior surface of CNTs has a significant effect with the change of chirality.CNTs with larger chiral angles,the energy barriers overcome by the oxygen functional groups along the chiral direction are lower or equivalent to the thermal perturbation level,allowing spontaneous dynamic migration at room temperature.The change of chirality not only leads to different charge distribution in carbon nanotubes,but also band gaps.CNTs with large chiral angles have smaller band gaps,which makes electron hopping easier.Besides,we found that the chemical hardness of CNTs with large chirality decreased and the carbon nanotubes were more reactive,promoting the migration of oxygen functional groups further.Migration of oxygen-containing functional groups along the surface of carbon nanotubes enables them to exhibit structural adaptability.In particularly,for the metal clusters used in catalyzing the chemical reactions within the CNTs,the structural adaptivity will improve the reaction rates and facilitate the reaction conditions.Therefore,our work provides an important theoretical insight at the molecular level,which is of great importance for the design of dynamic materials such as CNTs-based nanoreactors with high reactivity and sensitivity. |
