Molecular dynamics simulation of phenolic compound adsorption on amine-functionalized carbon nanotubes

Abstract

The interactions between green tea phenolic compounds, including (−)-epigallocatechin gallate (EGCG) and (−)-epigallocatechin (EGC), and various amine groups functionalized on carbon nanotube (CNT) were studied by all-atom molecular dynamics (MD) simulations. The amine functional groups: ethylenediamine (EDA), triethylenetetramine (TETA), and melamine (MA) were considered in this study. Simulated results showed that amine molecular structure grafted on CNT surface affected diffusion and adsorption of EGCG and EGC. The EDA-functionalized CNT (EDA/CNT) provided a strong adsorption affinity to EGCG and EGC with their bicyclic segments located within the EDA layer. It is because the functionalized-EDA structure was well-defined and given empty site for adsorption. TETA showed dense packing with self-aggregation, resulting the difficulty in adsorption of EGCG and EGC. MA with aromatic amine structure oriented perpendicularly to the CNT axis, prevented the conjugating phenolic molecules to adsorb onto surface. In addition, the results obtained from radial density profiles and radial distribution functions suggested that the smaller EGC molecule adsorbed on the EDA/CNT greater than the larger EGCG molecule. The results obtained not only provide fundamental understanding on the adsorption process, but also complement experimental studies, and perhaps could design new sorbent materials for separation.