  Titanic acid nanotubes (with a chemical formula H2Ti2O4(OH)2, abbreviated as
TANTs) were synthesized by the hydrothermal method using commercial TiO2
nanoparticle powder (P25, Degussa, Germany) including anatase and rutile phase
as a starting material. Conversion from nanoparticles to nanotubes was achieved
by treating the nanoparticle powder with 10 M NaOH aqueous solution. Absorption
and photoluminescence (PL) data indicate that the nanotubes obtained under slow
and suitable drying and heating conditions had very strong and stable visible
absorption with three peaks at 515, 575, and 675 nm and photoluminescence at
room temperature in air.
