Adsorption of l-phenylalanine onto mesoporous silica

• SBA-3, SBA-15, SBA-16, KIT-6 materials were prepared by hydrothermal method.
• Ordered mesoporous silicas are promising as adsorbents of l-phenylalanine.
• Adsorption of l-phenylalanine was studied from solutions with different pH.
• Sorption capacities decrease in the following order: KIT-6 > SBA-15 > SBA-16 > SBA-3.
• Large pore size of KIT-6 and SBA-15 permit the amino acid to enter into the pores.

Mesoporous silica materials, such as SBA-3, SBA-15, SBA-16 and KIT-6 were synthesized using tetraethyl orthosilicate as the silica source and different surfactants as templates. The products were characterised by a number of techniques, including low-temperature nitrogen sorption, X-ray diffraction and transmission electron microscopy. Results of the studies confirmed the ordered mesoporous structures of all silica samples obtained. Adsorption of l-phenylalanine on various mesoporous adsorbents was studied from solutions with different pH (5.6–9.4). Maximum sorption capacity was observed at pH 5.6, which is close to the isoelectric point of l-phenylalanine (pI = 5.48). Above this pH value, the amount of adsorbed amino acid decreased. In the range of equilibrium concentration (pH 5.6), the adsorption capacities of ordered silica samples decreased in the following order: KIT-6 (420 μmol g−1) > SBA-15 (389 μmol g−1) > SBA-16 (357 μmol g−1) > SBA-3 (219 μmol g−1). The lowest sorption capacity towards l-phenylalanine was found for SBA-3 despite the fact that it showed the largest surface area, which can be explained assuming that part of the pores in SBA-3 can be inaccessible to l-phenylalanine molecules. Large pore size of KIT-6 and SBA-15 permitted the amino acid molecule to enter into the pores of these mesoporous molecular sieves.