Title : Studies on the effect of functional monomers and chelating ligands on the properties of Fe II ion imprinted polymers designed for iron speciation
Iron is one of the most essential, chemical elements in an aquatic environment due to its role of catalyzer in phytoplankton photosynthesis and its involvement in metabolic processes – nitrate reduction, nitrogen fixation and respiration. Total dissolved Fe concentrations in an aquatic environment include kinetically labile complexes of Fe(II) and Fe(III), organically bound Fe and colloidal Fe species. The selective determination of dissolved species of both Fe(II) and Fe(III) at environmentally relevant very low concentrations is an actual task in environmental analytical chemistry.
In this work, we report a study on the effect of template species – Fe(II) complexes with 4-(2-pyridylazo)resorcinol or 2,2’-bipyridine as well as the functional monomers: acidic (methacrylic acid) and neutral (hydroxyethyl methacrylate) on the extraction efficiency and applicability of Fe(II) ion-imprinted polymers (Fe(II)-IIPs) for iron speciation in surface waters. The polymers were synthesized by precipitation copolymerization of functional monomer, trimethylolpropane trimethacrylate (crosslinking agent) and 2,2’-azo-bis-isobutyronitrile (initiator) in the presence of template and characterized by elemental microanalysis, scanning electron microscopy and Brunauer–Emmett–Teller analyses. Extraction efficiency was examined by batch solid-phase extraction. The optimization experiments showed quantitative sorption of both Fe(II) and Fe(III) ions on the surface of Fe(II)-IIPs at pH 7, however selective sorption of only Fe(II) could be achieved in the presence of fluoride ions as a masking agent for Fe(III). The desorption behaviour of both Fe(II) and Fe(III) was also identical and loaded Fe species were eluted quantitatively with 4 M HNO3. The kinetic studies indicated that the adsorption of Fe(II) ions best fitted with the pseudo-second-order kinetic model. The equilibrium experimental data of adsorption processes with different synthesized sorbents were well fitted by Langmuir isotherms models. Under the optimum conditions pH 7 and equilibrium time of 30 min the highest extraction efficiency and selectivity toward Fe(II) was achieved for Fe(II)-IIP containing methacrylic acid and Fe(II)–4-(2-pyridylazo)resorcinol complex as a template. The analytical procedure for Fe speciation was developed and validated with this sorbent.