Microwave-assisted rapid synthesis of anatase TiO2 nanocrystals with exposed {001} facets

Anatase TiO2 nanocrystals with tunable percentage of reactive {0 0 1} facets were rapidly synthesized by a microwave-assisted hydrothermal treatment of the mixed solution of tetrabutyl titanate (20g), HF solution (3 ml) and additional water (0-21 g) at 200 degrees C for 30 min. The resulted sample is denoted as Wx, where x represents the volumes of additional water. The photocatalysts were characterized by Xray diffraction, transmission electron microscopy, nitrogen adsorption-desorption isotherms and X-ray photoelectron spectroscopy. The photocatalytic activity of the photocatalyst was evaluated by degradation of brilliant red X3B (X3B), an anionic dye, and by a photoluminescence technique using coumarin as a probe molecule. With increasing the amount of additional water from 0 to 21 ml, the shapes of TiO2 nanocrystals evolve from nanosheets to truncated octahedral bipyramids, resulting in a steady decrease in the percentage of exposed {0 0 1} facets (from 71% to 23%). The photocatalytic activity of the resulted surface fluorinated TiO2 nanocrystals increases first and then decrease with increase in the amount of water, and W3 sample with exposed 60% of {0 0 1} facets shows the highest photocatalytic activity. However, for the surface clean TiO2 samples by washing with NaOH solution, W9 with 51% of {0 0 1} facets shows the highest photocatalytic activity. Our experimental results reflect that both crystal planes and surface chemistry play very important roles on the photocatalytic activity of anatase TiO2 nanocrystals. (C) 2012 Elsevier B.V. All rights reserved.