Porous silica and polysilsesquioxane with covalently linked phosphonates and phosphonic acids

Abstract

In this paper we report on synthesis and characterisation of the first phosphonate and phosphonic acid-modified porous silicas and polysilsesquioxanes. The organosilicon phosphonates [(EtO)3Si(CH2)3PO(OEt)2] 1 and [(EtO)3Si(CH2)2PO(OEt)2] 2 have been used to introduce phosphonate and phosphonic acid functionalities to silica and a polysilsesquioxane. Compounds 1 and 2 have been fully characterised (1H, 29Si, 31P and 13C NMR and elemental analysis). Xerogels [from tetraethylorthosilicate (TEOS) or 1,4-bis(triethoxysilyl)benzene (BTESB), and 1 or 2] bearing functionality of the type [On/2(EtO)3 − nSi(CH2)mPO(OEt)2] and, after treatment with concentrated HCl, functionality of the type [On/2(EtO)3 − nSi(CH2)mPO(OH)2], (n can be 0–2, m = 2 or 3) were synthesised and characterised using solid state 29Si, 31P and 13C NMR spectroscopy, elemental analyses and porosimetry measurements. High surface area mesoporous phosphonic acid-modified silicas with a narrow pore size distribution are described.