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

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 similar to 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 degrees 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 similar to 160-250 degrees 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 similar to 270 degrees C. (C) 2014 Elsevier B.V. All rights reserved.