Synthesis, characterization and analytical applications of a new and novel 'organic―inorganic' composite material as a cation exchanger and Cd(Ⅱ) ion-selective membrane electrode: polyaniline Sn(Ⅳ) tungstoarsenate

摘要

Composite materials formed by the combination of inorganic ion exchangers of multivalent metal acid salts and organic conducting polymers (polyaniline, polypyrrole, polythiophene, etc.), providing a new class of 'organic-inorganic' hybrid ion exchangers with better mechanical and granulometric properties, good ion-exchange capacity, higher stability, reproducibility and selectivity for heavy metals. Such a type of ion exchanger 'polyaniline Sn(Ⅳ) tungstoarsenate' was developed by mixing polyaniline into inorganic precipitate of Sn(Ⅳ) tungstoarsenate. This material was characterized using atomic absorption spectrometry, elemental analysis, Fourier transform infrared spectroscopy, simultaneous thermogravimetry-differential thermogravimetry, X-ray and scanning electron microscopy studies. Ion-exchange capacity, pH-titrations, elution and distribution behavior were also carried out to characterize the material. On the basis of distribution studies, the material was found to be highly selective for Cd(Ⅱ) and its selectivity was tested by achieving some important binary separations like Cd(Ⅱ)―Zn(Ⅱ), Cd(Ⅱ)―Pb(Ⅱ), Cd(Ⅱ)―Hg(Ⅱ), Cd(Ⅱ)―Cu(Ⅱ), etc., on its column. Using this composite cation exchanger as electroactive material, a new heterogeneous precipitate based selective ion-sensitive membrane electrode was developed for the determination of Cd(Ⅱ) ions in solutions. The membrane electrode is mechanically stable, with a quick response time, and can be operated within a wide pH range. The selectivity coefficients for different cations determined by mixed solution method were found to be less than unity. The electrode was also found to be satisfactory in electrometric titrations.