One-step preparation of size-defined aggregates of TiO 2 nanocrystals with tuning of their phase and composition

Abstract

One-step route based on the thermal decomposition of the double salt (NH 4) 2TiO(SO 4) 2 (ammonium titanyl sulfate, ATS) is presented to prepare size-defined aggregates of Ti-based nanoparticles with structural hierarchy. The component of Ti-based networks is tunable from anatase/rutile TiO 2, nitrogen-doped TiO 2, TiN x O 1− x , to TiN depending on the atmospheres and reaction temperatures. The as-prepared Ti-based powders were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS), and BET surface area techniques. It is found that TiO 2 in the predominant rutile phase could be achieved by the thermal decomposition of ATS in flowing Ar gas. Furthermore, the nitrogen-doped TiO 2, TiN x O 1− x solid solution and TiN were prepared by the thermal decomposition of ATS in flowing NH 3 gas by varying the temperatures. The network of anatase TiO 2 with a specific surface area up to 64 m 2 g −1 contains large mesopores with a mean diameter of ca. 15 nm, and the large pore size allows more accessible surface and interface available for the photocatalytic degradation of large-molecule dyes. The photocatalytic activity of the prepared TiO 2 and nitrogen-doped TiO 2 under UV–vis light irradiation is compared to Degussa P-25 using the photocatalytic degradation of methylene blue (MB) as a model reaction. The anatase TiO 2 nanoparticles derived from one-step route show the highly efficient photocatalytic activity for the degradation of MB in comparison with Degussa P-25. The presence of large-sized rutile in the TiO 2 powder decreases the specific surface area and thus the powder exhibits a lower photocatalytic activity.