Adsorption of naphthenic acids to the nitrogen-coordinated transition-metal embedded graphene: A DFT study

Abstract

The adsorption properties of two types of naphthenic acids (NAs), benzoic acid and cyclohexane carboxylic acid on four-nitrogen coordinated transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) embedded graphene (TMN₄-G) were investigated in detail by means of density functional theory method. The calculation results indicate that NAs prefer the perpendicular adsorption configuration by bonding interactions between their carbonyl oxygen atom and TMN₄ active site, and could be chemisorbed on FeN₄-G, MnN₄-G, and ZnN₄-G. The FeN₄-G gives the strongest adsorption to the NAs, indicating it is the best adsorbent among them. Electron density maps further confirm that NAs are chemically adsorbed on the FeN₄-G surface, accompanied by electron transfer in the adsorption systems. The calculations indicate that benzoic acid has relatively stronger adsorption energy than that of cyclohexane carboxylic acid for the perpendicular adsorption on TMN₄-G surface.