Sorption of Hg2+, Nd3+, Dy3+, and Uo2+2 ions at polysiloxane xerogels functionalized with phosphonic acid derivatives

The sorption properties of silicas with mono- and bifunctional surface layers containing the complexing fragment ≡Si(CH2)3NHP(S)(OC2H5)2 were studied. It was found that xerogels synthesized by the solgel method (like mesoporous silicas obtained by the template method) can extract mercury(II) ions from acidified solutions (SSC up to 450 mg/g). In a nonporous xerogel with a bifunctional surface layer (≡P=S/-SH), thiol groups proved to be primary sorption sites for Hg2+ ions; part of the ligand groups were inaccessible to metal ions. Xerogels containing the phosphonic acid residues ≡Si(CH2)2P(O)(OH)2 sorbed uranyl and lanthanide ions from their nitrate solutions. The resulting surface complexes contained two (for the UO 2 2+ ion) or three innersphere ligand groups (for the Nd3+ and Dy3+ ions). The maximum SSCs were 340 mg/g for the uranyl ion and 120 mg/g for the lanthanide ions.