Sorption properties of porous spray-dried microspheres functionalized by phosphonic acid groups

We have shown that mesoporous silica microspheres with phosphonic groups Si(CH2)(2)P(O)(OH)(2) in their pore surface layer have interesting properties for the sorption of neodymium(III) and dysprosium(III) from aqueous solutions, as well as for the adsorption of n-hexane, water, and triethylamine molecules from the gas phase. Such systems form the complexes LnL(3) and LnL(2) in the surface layer in case of Lanthanide sorption. We found that at low equilibrium concentrations of metal ions in the solution the composition of the formed complexes is mainly LnL(3), quickly reaching their saturation limit in the surface layer. Therefore, the further increase of sorption with the growing equilibrium concentration is observed due to the formation of complexes LnL(2). However, the ratio between these two types of complexes for neodymium(III) and dysprosium(III) are different probably because of the differences in Lanthanide radius. The mesoporous microspheric sorbents used are easily regenerated by hydrochloric acid, without substantial changes in their structure and in the composition of their surface layer. During sorption from the gas phase (in the absence of water molecules on the surface) phosphonic group could form hydrogen bonds among themselves or with silanol groups, which prevents their interaction with the electron-donor molecules (e.g. triethylamine). (C) 2011 Elsevier Inc. All rights reserved.