Design And Construction Of Complex Structure SERS Substrates For Application On The Environmental Detection And Catalytic Monitoring

In recent years, it benefited from the rapid development of nanomaterials science and nanotechnology, the combination of sensitive element based on sensitive nanomaterials and sensor technology formed nano sensor, which opens up new areas for the production of the new sensor as well as provides a number of new ideas and new methods. Among numerous new type sensors, optical nanosensor, which based on surface enhanced Raman spectroscopy (SERS) technology, is a new active frontier for researchers. As to the SERS development, design and construction of all kinds of SERS substrates for the different requirements are the most important research title. In general, the universality problems such as the stability, controllability and repeatability of the SERS substrates are the basic conditions for the qualitative and quantitative analysis, the research methodology is necessary condition, and and application requirements is goal oriented. Based on this, with the emergence of various nanostructures building methods, as well as the urgent requirements of reliable, controllable SERS active substrates, design and construction of complex structure SERS substrate with reat electromagnetic enhancement by means of synergistic combination of chemical research have become an important research direction in the field of SERS. Here, complex structures SERS substrates refers to one or more units, through physical or chemical method, used to form composites with significantly improved performance, which can better satisfy various application requirements. In addition, in the field of application, with the development of SERS technology, people expect the practical application of SERS can be extended to other aspects, such as for environmental detection, and as catalysts combined with in situ real-time monitoring of the catalytic reaction.Herein, in this thesis, many complex structure SERS substrates have been designed and constructed, and their applications in environmental detection and catalysis research work were carried out by the following several parts:1) Au nanoparticles (NPs) grafted on dendritic α-Fe2O3(NPGDF) is designed as highly uniform SERS substrate with a feature of optical visualization by optical microscope (OM) system and used for in situ detection of pesticide residues that are annually used in agriculture. With this strategy, the dendritic a-Fe2O3has been synthesized by hydrothermal method and significantly functionalized by an inductively coupled plasma (ICP) apparatus and then Au NPs were grafted on it densely and uniformly. In addition, the profile of NPGDF can be observed by OM platform of Raman spectrometer clearly, and the profile of SERS mapping with NPGDF as substrate almost exactly coincides with OM image, electron microscope (EM) image and elemental mapping of NPGDF, which indicates the remarked uniformity of the NPGDF as SERS substrate, thus it can ensure the laser beam focus on the efficient sites of the substrate under OM platform. Moreover, NPGDF can be dispersed in the liquor and the NPGDF microparticles can be adsorbed on target surface. Therefore, it can be used for in situ detection of pesticide residues on tea leaves, fruits and so on with high sensitivity and reproducibility.2) Au nanorods coated Fe3O4(Fe3O4@NRs) microspheres were designed as functional SERS substrate with a feature of magnetic property and used for detection of pesticide residues that are annually used in agriculture by near-infrared (NIR) excitation. With this strategy, the Fe3O4microspheres were synthesized by hydrothermal method and surface functionalized with polyethylenimine (PEI), and then coated with Au nanorods densely. The Raman spectra were carried out by NIR excitation and4-ATP was chosen as the probe molecule. The results showed a good SERS activity of the Fe3O4@NRs microspheres. Moreover, this substrate could be used for pesticide analysis by portable Raman spectrometer with NIR excitation. Especially, the microspheres could be transferred from pesticides contaminated fruits peel to specially cleaned glass slide with the aid of the external magnetic field, by which the strong fluorescence of the apple components can be avoided while performing the pesticide analysis of fruits peel.3) Investigating the kinetics of catalytic reactions with SERS on a single particle remains a significant challenge. The aim of this part of the study was to develop an efficient platform for researching the process of plasmon-driven surface catalyzed reaction of4-nitrothiophenol (4-NTP) dimerizing into4,4’-dimercaptoazobenzene (DMAB). We firstly synthesized monodisperse and hierarchical peony-like silver microflowers assembled by nanostructures with tailored surface topographies in the absence of any other surfactants. The single particle of the constructed hierarchical silver microflowers with highly roughened surface led to the coupling of high catalytic activity with a strong SERS effect, which own to an excellent bifunctional platform for in situ monitoring of surface catalytic reactions. The kinetics of the reaction of4-NTP dimerizing into DMAB was investigated and comparative studied by using SERS technique on single particle of different morphologies. The results indicate that fully developed nanostructure of hierarchical silver micro flower has both larger SERS enhancement and apparent reaction rate constant k, which may be useful for monitoring and understanding the mechanism of plasmon-driven surface catalyzed reactions.4) Microenvironment catalytic reactors of Au NPs multi-assembled on the inner wall of capillary were designed and constructed. This part discussed the impacts of the number of assembly processes on the SERS effect and the catalytic activity. The assembled nanostructures on the inner wall of capillary were used for in situ monitoring of catalyzed reduction of4-NTP to4-ATP, and the reaction kinetics were also studied. The research results show that, from the perspective of the SERS enhancement effect, the triple-assembled nanostructure exhibits the most significant enhancement effect, twice-assembled comes second, followed by fourth-assembled and first-assembled nanostructures. From the point of view of homogeneity and stability, twice-assembled nanostructure perform best, triple-assembled is next, fourth-assembled comes third, and first-assembled nanostructure is relatively poor. Therefore, to consider in comprehensive performance for SERS, twice-and triple-assembled nanostructures are advisable. From the results of different assembled nanostructure for in situ monitoring of catalytic reaction, with the increase of number of assembly, catalytic rate become significantly faster, which reveals that the catalytic activity and SERS performance show different trends of variation.And it is also suggested that microenvironment catalytic reactors of Au NPs multi-assembled on the inner wall of capillary for in situ monitoring of catalytic reaction kinetics have certain advantages.