Adsorption of l-Phenylalanine on Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes (SWNTs) became soluble in water and formed a stable solution when\nl-phenylalanine (Phe) was adsorbed. The adsorption selectivity of Phe zwitterions for larger diameter SWNTs\nwas confirmed by analysis of Fourier transform infrared spectra and by differential thermogravimetric analysis.\nEnhanced adsorption of Phe on the oxidized single-walled carbon nanotubes (OSWNT) was observed in\ncomparison with that of the purified single-walled carbon nanotubes (PSWNT). The Phe zwitterions are thought\nto adsorb on the surface of OSWNT by joint interaction of the π−π stacking, hydrogen bond, and part of the\ncovalent bond. The π−π stacking is the dominant interaction in the sidewall of OSWNT without defects.\nThe hydrogen bond and covalent bond formed with oxygen-containing groups becomes dominant on the end\nof OSWNT. For the PSWNT system, π−π stacking is an important factor to realize the adsorption of Phe\nzwitterions on the sidewall of PSWNT. The intermolecular hydrogen bond between Phe zwitterions is also\nformed when Phe zwitterions are adsorbed on the PSWNT.