Anion induced gelation in polyvinyl alcohol: a probe for metal ion speciation studies

Salt solutions of certain anions viz., sulphate, phosphate and citrate are reported herein to form hydrogels in PVA solutions for the first time. Hydrogels in sulphate medium have very high viscoelastic property and higher porosity than the phosphate or citrate hydrogels as can be seen from the SEM images. An attempt to find a chemical application of these gels in the field of elemental speciation reveals that smaller cations have lesser tendency to get adsorbed on the hydrogel surface. Fe(II), Fe(III), Mn(II) have either very less or no adsorption possibility. Mn(VII) undergoes species transformation to Mn(II) in the hydrogel and shows similar behavior as Mn(II) itself. Cr(III) has a certain adsorption in the sulphate hydrogel owing to some specific interactions. Cr(VI) remains in its anionic form and hence is not adsorbed. Fe(II) and Fe(III) however can be adsorbed upon suitable complexation in the hydrogel. Phosphate hydrogel serves as the better adsorber in these two cases. All the adsorptions follow Freundlich isotherm very nicely. The hydrogels are thus eligible probes for species dependent metal adsorption studies.