Titanium dioxide/amine hybrid nanotubes. Optical properties and behavior as lithium–ion electrode

Titanium dioxide based tubular nanocomposites containing long-chain amines were prepared by hydrothermal reaction of anatase with neutral surfactants, dodecylamine and octadecylamine, under strong alkaline conditions. Morphologically pure phases are obtained after reaction times of about 50 h at 130 °C. Dodecylamine derivates are structural and thermally more fragile than those with octadecylamine. Under more drastic reaction conditions, 72 h at 150 °C, amine is segregated leading to almost pure inorganic nanotubes or fibers for octadecyl and dodecyl derivatives respectively. The products characterized by electron microscopy, X-ray diffraction, FT-IR and elemental analysis are constituted by the hydrogen titanat H2Ti3O7. Diffuse reflectance spectra reveal the products present typical size-dependent optical properties. The photoluminescence spectra are qualitatively similar to that of anatase dominated by the presence of traps located in the band gap. The electrochemical lithium intercalation and lithium diffusion coefficients of the products were studied by intermittent galvanostatic method and galvanostatic pulse relaxation technique respectively. Products were tested in a lithium cell using the nanocomposites as the active material of the positive electrode. The hybrid dodecylamine derivative shows a first cycle irreversible capacity of 219 mAh/g, and a capacity of 113 mAh/g after the 7th cycle which results improved in comparison with those reported for H2Ti3O7 electrodes, thus pointing to a protective effect of the amine.