Synthesis of M@TiO2 (M = Au, Pd, Pt) Core-Shell Nanoconnposites with Tunable Photoreactivity

The core-shell nanocomposites of M@TiO2 (M = Au, Pd, Pt) have been synthesized successfully via a facile hydrothermal treatment of TiF4 precursor and noble metal colloid particles. Their properties were determined by a collection of joint techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction spectra (XRD), ultraviolet/visible diffuse reflectance spectra (DRS), photoluminescence spectra (PL), and electron spin resonance spectra (ESR). Photocatalytic degradation of Rhodamine B (RhB) in the liquid phase served as a probe reaction to evaluate the activity of the as-prepared M@TiO2 (M = Au, Pd, Pt) core-shell nanocomposites under the irradiation of both visible light and ultraviolet (UV) light. The results reveal that these core shell nanocomposites possess tunable photoreactivity. It is interesting to find that the incorporation of noble metal core into the shell of TiO2 only contributes to enhancement of visible light photocatalytic activity of TiO2. The noble metal cores are believed to play an essential role in affecting the photoreactivity because they are able to trap electrons, improve the electron hole pairs life, and enhance the visible light absorption intensity that are all beneficial for enhancement of the visible light photocatalytic activity of TiO2. However, the incorporation of noble metal core significantly lowers the UV light absorption intensity, thus leading to the obervation that, under UV light irradiation, the bare TiO2 still exhibits higher activity than M@TiO2 core-shell nanocomposites. The possible radical species involved in the degradation of RhB were analyzed by means of the PL and ESR techniques. Recycled activity tests demonstrate that the incorporation of metal core into the shell of TiO2 will inhibit the photocorrison behavior and provide much better photocatalytic stability of M@TiO2 (M = Au, Pd, Pt) nano composites than the bare TiO2. It is hoped that our work could render guided information for steering toward the design and application of TiO2-coated core-shell nanomaterials with tunable photocatalytic activity.