Synthesis of Anatase TiO2 Nanocrystals with Exposed {001} Facets

Abstract

This paper reports a facile synthesis of anatase TiO₂ nanocrystals with exposed, chemically active {001} facets. The nanocrystals were prepared by digesting electrospun nanofibers consisting of amorphous TiO₂ and poly(vinyl pyrrolidone) with an aqueous acetic acid solution (pH = 1.6), followed by hydrothermal treatment at 150 °C for 20 h. The as-obtained nanocrystals exhibited a truncated tetragonal bipyramidal shape with 9.6% of the surface being enclosed by {001} facets. The use of electrospinning is critical to the success of this synthesis as it allows for the generation of very small particles of amorphous TiO₂ to facilitate hydrothermal crystallization, an Ostwald ripening process. The morphology of the nanocrystals had a strong dependence on the pH value of the solution used for hydrothermal treatment. Low pH values tended to eliminate the {001} facets by forming sharp corners while high pH values favored the formation of a rodlike morphology through an oriented attachment mechanism. When acetic acid was replaced by inorganic acids, the TiO₂ nanocrystals further aggregated into larger structures with various morphologies.