Biomimetic matrix-mediated syntheses of mesoscopic iron-containing aggregates

Biomimetic approach has been employed in studies on fabrication of iron-containing mesoscopic aggregates in polymer-containing media. The work has been divided into two parts. Part one concerns the hydrolysis of various iron(III) compounds in the solutions of watersoluble polymers both natural and synthetic that are carrying various functional groups. The process of the hydrolysis and the properties of obtained composite materials have been studied by means of viscometry, FTIR. electrophoresis, UV-vis-spectroscopy. transmission electron microscopy and electron diffraction. X-ray powder diffraction. Mossbauer spectroscopy and magnetic susceptibility measurements. The data showed that the polymers present can exert a significant influence on the stability and organisation of the iron(III) hydrolytic products formed. Small (2-4 nm) nanoscale electron dense structures of ferrihydrite observed in the presence of PVA and PAA demonstrate an additional degree of aggregation and ordering in acidic polysaccharide - containing media that reflects the significant structural differences of the latter - the presence of comparatively rigid polysaccharide backbone and formation of an entangled polymer network entrapping the iron aggregates, due to the overlapping and cross-linking of the rodlike molecules. In the solutions containing two phases - organic and aqueous, high molecular weight acidic polysaccharide interfacial films have been observed to host a mesoscopic iron(III)-containing semi-crystalline structures of geometry and morphology different from that of the bulk precipitate formed during the slow hydrolysis of iron(III) compounds. Part two of the current work is dealing with the studies of biomimetic mineralisation of particularly designed synthetic symplex polysaccharide matrices. The ability of polyanion polycation pairs to undergo self-assembly in the solutions has been employed in the syntheses of ordered insoluble materials formed through combined effect of Coulombic and hydrophobic interactions, and hydrogen bonds. The process of polysaccharide symplex formation, its subsequent mineralisation with iron(III)-containing compounds and the properties of materials obtained have been studied by means of viscometry, surface tension measurements, ljC solid state nuclear magnetic resonance spectroscopy, transmission electron microscopy, electron diffraction and energy dispersive X-ray analysis, thermogravimetry, Mossbauer spectroscopy and magnetic susceptibility measurements. The formation of biomimetic composite materials containing mesoscopic rod-like aggregates of iron(III)-oxo hydroxy compounds with a geometry clearly defined by that of the polymer matricestemplates has been observed. Following the manufacturing of the iron(III)-containing nanoscale aggregates within polymer matrices, attempts to produce zero-valent Fe particles incorporated in the polymer matrix by various methods of reduction have been carried out. The gradual reduction of the symplex composite iron(III)-containing materials with sodium borohydride in non-aqueous media has produced solid powders of composite material containing nanoscale “soft” iron particles. The properties of the materials have been studied by means of Mossbauer spectroscopy and magnetic susceptibility measurements