A DFT-D study on the interaction between lactic acid and single-wall carbon nanotubes

Abstract

Density functional theory (DFT) was used to investigate the adsorption of lactic acid molecules on the surface of (4,4), (5,5), (6,6) and (7,7) single-walled carbon nanotubes (SWCNTs). A hybrid DFT method with the inclusion of dispersion correction was employed and the results compared to those obtained from the non-corrected DFT method. The energies and optimum distances for two different configurations were obtained after relaxation of the entire system. The calculations showed that the adsorption of lactic acid onto the outer wall of carbon nanotubes was thermodynamically favored. The adsorption of lactic acid outside the SWCNT with (4,4) chirality and via a vertical orientation to the tube axis above the center of a hexagon surface and through its hydroxyl group was the most stable state of physisorption with an adsorption energy of −13.39 kcal mol⁻¹. Total density of states (TDOS) and projected density of states (PDOS) analysis in the vicinity of the Fermi level region suggested the electronic states to be contributed from SWCNTs rather than lactic acid. The DFT calculations also showed that non-covalent functionalization of SWCNTs with lactic acid could give rise to new impurity states in the DOS of pristine SWCNTs and suggested possible carrier doping of carbon nanotubes via selective adsorption of molecules. The global reactivity descriptors in the gas phase and solvent were calculated.