Biopolymer Networks for the Solid-State Production of Porous Magnetic Beads and Wires


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Aqueous solutions of sodium carboxymethyl cellulose are used for the morphosynthesis of spherical and wire-shaped biopolymer networks, in which Fe3+ cations serve as a crosslinking and hardening agent. Their morphology remains intact upon drying, resulting in monolithic beads (1 mm) and wires (ca. 80 μm), which are exploited as reaction vessels to pre-encapsulate poly(ethylene glycol) 400 (PEG 400) and cobalt cations. A solid-state reaction in an inert atmosphere at 600 °C affords porous carbonaceous xerogels, macroscopically shaped as beads or wires and decorated with nanocrystalline magnetic iron oxide, metallic iron, or iron–cobalt alloy particles, thus imparting magnetic properties to the products. As such the reduction of Fe3+ species to α-Fe nanoparticles can be achieved without H2 treatment, since poly(ethylene glycol) serves as a reducing agent and the encapsulated Co2+ aids in the subsequent growth of the metallic iron particles. Particularly interesting are the magnetic properties of the carbon–α-Fe composite, in which the size of the magnetic particles, estimated near the boundaries of the single magnetic domain, gives rise to increased coercivity compared with that of bulk iron.