Characterization of magnetic nanocomposites based on cellulosic membranes

This thesis is dedicated to understanding the mechanism of the in situ synthesis of magnetic nanocomposites based on cellulosic substrates and characterizing the products of this synthesis. The preparation of uniform membranes containing large quantities of magnetite particles (Fe$ sb2$O$ sb3$) of defined site was our specific objective. For that purpose, cellulosic substrates of two different kinds: one of bacterial origin bacterial cellulose--BC), the other (Lyocell) derived from dissolving-grade wood-pulp through a dissolution/coagulation process (film-casting) were used as never-dried gel membranes. BC has also been used in the form of a suspension of open fibrillar pellets which were dried to a parchment after the in situ treatment. Characterization of the resulting magnetic materials was performed using transmission electron microscopy (TEM) in imaging and diffraction mode, X-ray diffraction (XRD), vibrating sample magnetometry (VSM) and Mossbauer spectroscopy. In BC membranes, needle-like lepidocrocite ($ gamma$-FeOOH) formed along the cellulose fibrils, using the crystalline surface as a nucleation site. Spherical magnetite particles subsequently formed around the needles. The less swollen Lyocell substrates produced needle-like feroxyhite ($ delta$-FeOOH) concentrated at the membrane surface while spherical magnetite particles formed within the membrane after several cycles of treatment. The treated BC and Lyocell membranes were both superparamagnetic at room temperature. The BC suspensions had no space constraint hence the treatment conditions were more critical for controlling the morphology of synthesized ferrites. These conditions could be defined to yield homogeneous membranes containing magnetite particles uniform in size, too large however to behave superparamagnetically at room temperature