The Preparation Of Compound Materials And Its Sueface-enhanced Raman Scattering Properties

Surface-enhanced Raman spectroscopy?SERS?has attracted considerable attention in chemical and biochemical analysis because it reveals unique vibrational fingerprint of analytes,high sensitivity,and has a very low detection limits even down to single molecule level.The widespread accepted mechanism for SERS is the electromagnetic enhancement and chemical enhancement.Electromagnetic enhancement,the dominated contribution to SERS,due to the localized surface plasmon resonance?LSPR?inspired by the noble metal nanoparticles under light radiation which is know as a kind of local phenomenon.It means to obtain a high SERS signal,an interaction between the analytes and the plasmonic nanoparticles to make a close distance less than 3-5 nm is required.In fundamental studies,a number of molecules that strongly chemisorb to the surface of metal nanoparticles were put to use to analyze the SERS performance of the substrate.However,many molecules show very weak affinity or even no affinity towards the metal nanoparticles.This issue hinders the practical application of SERS in vast fields like environmental monitoring,food security and the like.In addition,chemical enhancement?CE?,another significant contribution to SERS,has not been taken general attention due to its relatively weak enhancement and complex research methods.To solve problems,three schemes are proposed:?1?In order to solve the defects of MOF/metal particle composites for SERS at present,this experiment pioneered the electrostatic interaction to combine two kinds of nanoparticles to assemble MIL-101/Au composite nanoparticles.The SERS properties were optimized by adjusting the size and distribution density of the gold nanoparticles on the MIL-101 surface.It is proved by experiments that the composite nanoparticles not only enhance the performance of electromagnetic field,but also have the ability to adsorb and enrich the molecules to be tested,so that the molecules that are difficult to detect on the traditional SERS substrate can be bound to the surface of metal nanoparticles,and achieve micro detection.?2?To obtain a metal-MOF composites with outstanding SERS property and adsorption character,polydopamine-Ag?PA?film was firstly synthesized.The silver cations were reduced and formed the silver nanoparticles on the polydopamine?PDA?film surface by the reducing groups in PDA.Then the well-studied MOFs ZIF-8?Zn?m Im?₂,mIm=2-methylimidazolate?was synthesized and covered the PA surface by the strong adhesiveness of PDA.Surprisingly,we have found that the ZIF-8 preferentially grow on some positions where the density of Ag nanoparticles are large.The large density of Ag nanoparticles means the distances between Ag nanoparticles were shortened which is beneficial to SERS performance known as“hot-spots”.The probe molecules located in the“hot-spots”possess more outstanding SERS signal.However,it is hard to control the analytes to locate in the“hot-spots”.In this work,the MOFs has labeled the“hot-spots”location,combine its adsorption feature,the MOFs not only capture and enrich the analytes,but also guide the probe molecules to the“hot-spots”.The prepared PA-MOF?PAM?SERS substrate was used to detect some non-adsorbing molecules like fluoranthene,and VOCs like toluene.The excellent detection result endow us the confidence that the PAM has great application prospect in micro chemical detection.?3?A solar cell film consisting of CdTe/CdS p-n junction and Au nanoparticles were combined to construct SERS-active substrate.Fig.1 schematically illustrates the SCAu composite structures,wherein the top layer is Au nanoparticles and CdTe/CdS p-n junction and a Ni foil act as interlayer and bottom layer,respectively.The CdTe/CdS solar cell was selected because of its absorbance wavelength is 400-800 nm which including the general Raman laser wavelength?532,633,785 nm?.When the laser irradiating the SERS substrate,tremendous electron-hole pairs generated,the electrons move to the n-type region and holes move to the p-type region in the effect of built-in electric field formed by p-n junction.The Au nanoparticles were deposited on the surface of n-type semiconductor.The surface potential of CdS further injects the free electrons into Au nanoparticles.The potential of Au nanoparticles will be decreased and the density of free electrons in Au nanoparticles will be increased and promotes the SERS intensity under the laser irradiation.In addition,the potential of the Au nanoparticles can be adjusted by the intensity of the laser.In this work,different intensity of laser will be adopted to compare the SERS performance of the SCAu.The SERS performance of the SCAu substrate was tested by detecting various molecules including 4-Aminothiophenol?4-ATP?,Fluoranthene and 3,3',4,4'-Tetrachlorobiphenyl?PCB-77?.