Surface Modification of Aminopropylated Silica Gel with Tetraphosphorylated bis-Methoxycarbonylmethoxycalix[4]Arenes for Effective Europium(Iii) Sorption

bis-Methoxycarbonylmethoxy derivatives capable of reacting with the surface of aminopropylated silica gel with the formation of chemically and thermally stable amide bonds were obtained by regioselective distal dialkylation of hydroxyl groups of phosphorylated tetrahydroxycalix[4]arenes in high yields. It was found that phosphine oxide and phosphonate P=O groups localized on the upper rim cooperatively bind Eu 3+ cations and effectively sorb them from nitric acid solutions.