Surface Mineralization of Cellulose by Metal Chloride - an Original Pathway for the Synthesis of Hierarchical Urchin and Needle Carpetlike TiO2Superstructures

Reductive mineralization of cellulose with vanadium, iron and tungsten chlorides and access to MxOy metal oxides and MxOy/C metal oxide/carbon composites

M_xO_y and M_xO_y/C composites (M=V, Fe and W) were obtained by mineralization of cellulose with several metal chlorides. Cellulose was used both as a templating agent and as an oxygen and a carbon source. Soluble chloride molecules (VOCl₃ and WCl₆) and a poorly soluble ionic chloride compound (FeCl₃) were chosen as metal oxide precursors. In a first time, primary metal oxide/cellulose composites were obtained via a thermal treatment by reacting urea impregnated filter paper with the corresponding metal chlorides in an autoclave at 150°C after 3days. After either pyrolysis or calcination steps of these intermediate materials, interesting metal oxides with various morphologies were obtained (V₂O_5, V₂O₃, Fe₃O₄, WO_3, H_0.23WO₃), composites (V₂O₃/C) as well as carbides (hexagonal W₂C and WC, Fe₃C) This result highlight the reductive role that can play cellulose during the pyrolysis step that allows to tune the composition of M_xO_y/C composites. The materials were characterized by FTIR, Raman, TGA, XRD and SEM. This study highlights that cellulose can be used for a convenient preparation of a variety of highly demanded M_xO_y and M_xO_y/C composites with original shapes and morphologies.

Synthesis of Titania@Carbon Nanocomposite from Urea-Impregnated Cellulose for Efficient Lithium and Sodium Batteries

Nanostructured TiO2 and TiO2@C nanocomposites were prepared directly from urea-impregnated cellulose by a simple reaction/diffusion process and evaluated as negative electrode materials for Li and Na batteries. By direct treatment with TiCl4 under anhydrous conditions, the urea impregnation of cellulose impacts both the TiO2 morphology and the carbon left by cellulose after pyrolysis. Hierarchical TiO2 structures with a flower-like morphology grown from-and-at the surface of the cellulose fibers are obtained without any directing agent. The resulting TiO2/cellulose composite is then transformed either into pure TiO2 flowers by calcination in air at 600 °C, or into TiO2@C nanocomposites by pyrolysis under Ar at 600 °C. Electrochemical studies demonstrate that both samples can (de)insert lithium and sodium ions and are promising electrode materials.

Conversion of Nanocellulose Aerogel into TiO2 and TiO2@C Nano-thorns by Direct Anhydrous Mineralization with TiCl4. Evaluation of Electrochemical Properties in Li Batteries

Nanostructured TiO2 and TiO2@C nanocomposites were prepared by an original process combining biotemplating and mineralization of aerogels of nanofibrillated cellulose (NFC). A direct one step treatment of NFC with TiCl4 in strictly anhydrous conditions allows TiO2 formation at the outermost part of the nanofibrils while preserving their shape and size. Such TiO2@cellulose composites can be transformed into TiO2 nanotubes (TiO2-NT) by calcination in air at 600 and 900 °C, or into TiO2@C nanocomposites by pyrolysis in argon at 600 and 900 °C. Detailed characterization of these materials is reported here, along with an assessment of their performance as negative electrode materials for Li-ion batteries.