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

• Multi-walled carbon nanotubes modified with silver nanoparticles.
• AgNO3 strongly determine structural, textural and as well as thermal properties.
• Adsorption of l-phenylalanine increased with increasing concentration of amino acid solution.
• Amino acid adsorbs onto materials following a Langmuir type isotherm.

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.