A review on polysiloxane-immobilized ligand systems: Synthesis, characterization and applications

The immobilized silica gel ligand systems made by modification of silica surfaces have been briefly summarized. Short background was described based on the synthesis methods and their applications. In this review more attention towards the functionalized polysiloxane xerogels and their postmodification has been given. Polysiloxane-immobilized ligand systems bearing organofunctionalized ligand groups of general formula P–(CH2)3–X (where P represents a three-dimensional silica like network-matrix and X is an organofunctional group) were prepared through the sol–gel process by hydrolytic polycondensation of Si(OR)4 and the appropriate silane coupling agent (RO)3Si(CH2)3X (where R is an alkyl group, e.g CH3 or C2H5). There are many other immobilized ligand systems, which were prepared by treatment of post-polysiloxane precursors with an appropriate organofunctional ligand. Variety of functionalized materials ranging from simple up to macrocyclic immobilized ligand systems were prepared and well characterized. These materials have the advantage over the functionalized silica, as they can be prepared using different molar ratios of Si(OR)4 and (RO)3Si(CH2)3X silane agents, and therefore their metal uptake capacities can be altered. A mixture of two different ligand groups can also be achieved on the same matrix. Analytical and environmental applications of these materials have been reported including extraction, separation and preconcentration of metal ions. A variety of physical chemistry techniques that were employed to characterize the surface and the bulk of the immobilized systems were reported. These included high-resolution solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR).