Physicochemical and sorption properties of multi-walled carbon nanotubes decorated with silver nanoparticles

Abstract

Abstract Multi-walled carbon nanotubes (CNTs) modified with silver nanoparticles were tested as adsorbents of l -phenylalanine amino acid. CNTs were impregnated with an aqueous solution of silver nitrate(V) in the amount necessary to obtain the Ag loading of 1, 3 and 5 wt.%. The materials were characterised by X-ray diffraction, transmission electron microscopy and low-temperature nitrogen adsorption. TEM and XRD data clearly revealed the presence of spherical Ag nanoparticles of the mean size ∼20 nm on the carbon nanotubes surface. The modification with silver was evidenced to strongly affect the textural properties of the support. l -Phenylalanine was adsorbed on the surface of the materials obtained from buffer solutions of pH 5.6 at 20 °C. The sorption capacities of the silver-modified multi-walled carbon nanotubes towards amino acid increased with increasing percentage content of silver. The process of l -phenylalanine adsorption onto the materials studied can be described by a Langmuir type isotherm. Thermogravimetric measurements of the samples after l -phenylalanine adsorption proved that for temperatures from the range ∼160–250 °C, the condensation of l -phenylalanine molecules takes place on the nanotubes surface leading to formation of peptides that desorb into the gas phase at ∼270 °C.