RESUMO
In this work, an innovative route to synthesize an anatase TiO2@C composite is presented. The synthesis was conducted using a soft chemistry microwave-assisted method using titanium(IV) butoxide as a titanium precursor. The residual (un)converted titanium precursor remaining after TiO2 synthesis was used as a carbon precursor and thermally treated under H2 to obtain nanoparticles of the TiO2@C composite. A superior reversible specific capacity was obtained with TiO2@C (120 mA h g-1 at a C/20 rate, 3rd cycle) compared to that with pristine TiO2 (66.5 mA h g-1 at a C/20 rate, 3rd cycle), in agreement with the importance of carbon coating addition to TiO2 nanoparticles as negative electrode materials for sodium-ion batteries.
RESUMO
In order to prepare self-standing and flexible slow neutron reflectors made of graphite fluoride (GF) with high contents of (C2F)n structural phase, graphite foils of different thicknesses were used as starting materials for gas (F2)/solid fluorination. The maximal interlayer distance of GF was obtained with this phase thanks to the stacking sequence FCCF/FCCF; this is mandatory for the efficient reflection of slow neutrons. 71 and 77% of the (C2F)n phase were achieved for graphite foils with thicknesses of 1.0 and 0.1 mm, respectively. The interlayer distances were 8.6 Å as expected. The fluorination conditions (static mode, a long duration of 24 h, annealing in pure F2 gas for 24 h, and temperatures in the 390-460 °C range) were adapted to large pieces of graphite foils (7 × 7 cm2) in order to both avoid exfoliation and achieve a homogeneous dispersion of fluorine atoms. This process was also efficient for thinner (0.01 mm thick) graphitized graphene oxide foil. 56% of the (C2F)n phase and an interlayer of 8.6 Å were achieved for this foil when fluorination was performed at 430 °C. Whatever the nature and the thickness of the foil, their flexibilities are maintained.
