Deriving bridged polysilsesquioxane xerogels with ≡Si(CH2)3NHP(O)(OC2H5)2 functional groups

Abstract

The reaction of hydrolytic polycondensation of (C2H5O)3SiC2H4Si(OC2H5)3 [or (C2H5O)3SiC6H4Si(OC2H5)3] and (C2H5O)3Si(CH2)3NHP(O)(OC2H5)2 was used to obtain xerogels containing a phosphine oxide complexing group (0.9–1.4 mmol/g). The presence of this functional group, as well as organic bridges, polysiloxane bonds, noncondensed silanol, and ethoxysilyl groups in the synthesized bridged polysilsesquioxane xerogels, was established using IR spectroscopy and solid-state 1H MAS NMR spectroscopy. The AFM data indicate that the structure of xerogels is similar to that of other materials of this class (conglomerates of aggregates with the size of 35–40 nm); however, all the obtained samples are practically nonporous. They extract ions of neodymium(III) and dysprosium(III) from aqueous solutions (sorption equilibrium is established in 72 h for neodymium and in 24 h for dysprosium). However, some ligand groups remain inaccessible to lanthanide ions. The whole set of the obtained results indicates that the geometrical sizes of a functional group produce a considerable effect on formation of xerogel porous structure and in the case of using bridged alkoxysilanes as structure-forming agents.