Preparation Of Metal @ TiO₂ Core @ Shell Nanoparticles And SERS Research

Metal@TiO₂ composite nanoparticles have tremendous potential application in the fields of catalysis. Surface-enhanced Raman spectroscopy(SERS) has also aroused great attention due to its high sensitivity, along with its rich structural information of the spectrum. By combing the above aspects, a novel composite would be obtained, possessing both the photocatalysis property and the SERS effects. On the one hand, a recyclable SERS substrate could be acquired by using the catalytic ability of TiO₂ under the ultraviolet irradiation; on the other hand, a high sensitive detection technique on the molecular level would be developed to study the reaction processes on the interfacial of the TiO₂ by utilizing high-sensitivity of SERS effect. The paper was focused on the following issues:(1) By the layer-by-layer technique, various layers of TALH (precursor of TiO₂) were coated on Au or Ag nanoparticles with different diameters immobilized on the substrate of silicon wafer or ITO. After annealing treatment, the Au@TiO₂ and Ag@TiO₂ core-shell nanoparticles were thus prepared with different core sizes and TiO₂ shell thicknenss. SEM, TEM, UV-vis and Raman spectroscopy were employed to characterize the surface morphology, size and crystal type of the TiO₂ at different coating stages.(2) Thiophenol (TP), mercaptobenzoic acid (MBA) and methylene blue(MB) were served as model probes to study the feasibility of SERS long-range enhancement. In addition, by combining the photocatalytic technique, the recyclable usage as SERS substrate was achieved. The reproducibility and stability were explored in SERS detection. The novel composite substrate provided the experimental basis for extending SERS to the high-sensitive quantitative and semi-quantitative analysis.(3) The photodegradation of pollutants such as methylene blue (MB), aniline (AN) molecules were utilized to characterize the catalytic activity and recyclable capacity of the Au@TiO₂ core-shell nanoparticles with different sizes and shell thickness. Besides, Au@TiO₂ core-shell nanoparticles were also assembled onto the inner wall of the quartz tube. The catalytic efficiency was also studied by the degradation rate of the waste water. The result showed that the composite nanoparticles exhibted a high catalytic ability and recyclable performance.(4)Developing a novel high-sensitive technique to in situ study the mechanism of the photocatalysis by combining the unique photocatalytic property of the TiO₂ shell with the considerable SERS effect of the noble metal core. The changes of the species among the photocatalytic process could be detected with the in-situ SERS technique to afford the absorption and degradation mechanism at the molecular level. The photocatalytic process of methylene blue (MB) was also investigated on Au@TiO₂ under UV illumination with in-situ SERS technique. The possible degradation mechanism was thus detailed discussed according to the changes of the spectral feature.