Adsorption of Various Monoterpenoids on the Surface of Graphene and Nitrogen-Doped Graphene: A DFT Based Study

Monoterpenoids are widely distributed in nature and have been recognized to possess various pharmacological properties such as antifungal, antibacterial, antioxidant, anticancer, antispasmodic, etc. We analyzed the adsorptive interaction of certain monoterpenoids (such as carvacrol, carvone, g-terpinene, limonene and menthol) with pristine graphene and nitrogen-doped graphene using DFT calculations. In addition, the adsorption properties are compared with two of the commercially available polymeric resins namely Amberlite XAD-4 and XAD-7. Full geometry optimization have been carried out in water medium at B3LYP and M06-2X levels. We observed that the level of the calculations does not affect the trend of the results and addition of dispersion interaction is important for getting meaningful energies. The basis set superposition errors (BSSE) are estimated by using counterpoise-correction method at M06-2X level. BSSE estimation lowers the interaction energies values but the overall trend is not affected with this estimation. The adsorption energy (Delta E-ads) is higher for parallel orientation of terpeniods to graphene and nitrogen-doped graphene surface compared to perpendicular orientation. In addition, Delta E-ads values for carvacrol is highest and for menthol is lowest. Monoterpenoids absorbs more efficiently on the surface of nitrogen-doped graphene compared to graphene. This study offers an effective way to design promising adsorbent for selective separation of the terpenoids.