One-Step Hydrothermal Synthesis of TiO2@MoO3 Core–Shell Nanomaterial: Microstructure, Growth Mechanism, and Improved Photochromic Property

Photochromic TiO 2 @MoO 3 core–shell (TM) nanopowder was synthesized by a one-step hydrothermal method and characterized with XRD, TEM, Raman, and a spectrophotometer. The nanopowder has a very small particle size of 5–10 nm in diameter, and a well-defined core–shell structure with the tight interface; that is, an anatase TiO 2 core is tightly surrounded with amorphous MoO 3, to form an ideal heterojunction structure. The growth mechanism was proposed with a surface-induced nucleation of amorphous MoO 3 from a well-mixed precursor, where the mutual inhibition between core and shell led to the confined core size. The photochromic performance of TiO 2 @MoO 3 was evaluated in solution as well as casted thin film on glass using a spectrophotometer, with a comparison to that of single MoO 3 . A significant enhancement in the photochromic properties was demonstrated for TM; that is, the change of the absorbance in water at 600 nm is about 30 times larger than that of α-MoO 3, and a 20% transmittance regulation at 500–800 nm was obtained for the TM-based thin film. Meanwhile, the samples in ethanol showed much stronger photochromic coloration efficiency than that in water by 66.6% enhancement in the absorption at 600 nm. Such a significant photochromic enhancement is considered to the formation of a relatively ideal heterojunction at the interface, leading to an efficient electron–hole separation. The size effect of TM provides a high specific surface area for cation insertion/extraction and diffusion and decreases the distance of electron transfer. Furthermore, a shift of excitation wavelengths from UV to visible was also observed due to the appearance of extra defect bands by Mo doping into TiO 2 in their interface, which was supported by XRD and Raman measurements. The enhanced photochromic performance of TiO 2 @MoO 3 is expected to be used for color displays and smart windows.