Transparent zeolite-like mesoporous TiO2 nanocrystalline thin films with high photocatalytic activity were synthesized via a surfactant-templated method. The films were characterized by TGA−DTA, XRD, nitrogen adsorption, SEM, TEM, UV/vis, and FT-IR spectroscopy.
The photocatalytic activity of the films was evaluated by photodecomposition of acetone in
air at ambient conditions. It was found that thermal treatment resulted in surfactant
elimination, framework solidification, as well as pore-wall crystallization of the mesoporous
TiO2. The resulting zeolite-like mesoporous TiO2 nanocrystalline films had large specific
surface areas (∼100 m2/g), high porosity (∼40%), extended band gap energy (∼3.3 eV), tri-directional communicating pore systems, and enhanced photocatalytic activity. The optimum
calcination temperature was found to be 500 °C, at which the film possessed a cubic ordered
mesoporous structure and exhibited the highest photocatalytic activity. A comparison with
a conventional TiO2 film (prepared from a sol−gel method) showed that the ordered
mesoporous TiO2 nanocrystalline film (calcined at 500 °C) had over 2 times the specific
photocatalytic activity as the conventional film. The high photocatalytic activity of zeolite-like mesoporous TiO2 thin films can be explained by the large specific surface area and the
three-dimensionally connected mesoporous architecture.
NaV6O15 and Na2V6O16·3H2O nanowires were selectively prepared from the reaction between V2O5
and NaHSO4·H2O/Na2SO4 under hydrothermal conditions. The synthesized products were characterized by XRD,
SEM, TEM, SAED, EDX, HRTEM, and XPS analytical techniques. SAED and HRTEM analyses confirm the single-crystalline nature of both NaV6O15 and Na2V6O16·3H2O nanowires. The nanowires of NaV6O15 are uniform and
straight, with around 80 nm in diameter and several tens of micrometers in length. Na2V6O16·3H2O nanowires
have an average diameter of 60 nm and length up to 10 μm. The key factors to control the phase composition and
morphology, such as the amount of sulfates and the selective absorption of SO4
2- in different crystal facets, are
discussed. The optimum hydrothermal temperatures for the nanowire growth are 180 °C for NaV6O15 and 180 to
140 °C for Na2V6O16·3H2O. A tentative formation mechanism is proposed.
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