| Surface enhanced Raman scattering?SERS?is a high-sensitivity analysis technique.SERS has been widely used in scientific fields such as food safety and biochemistry.The main mechanisms are the electromagnetic field enhancement effect based on local surface plasmon resonance and the chemical enhancement effect based on charge transfer.Therefore,precious metals were used as effective SERS substrates.A huge and strong local electromagnetic field is generated on the surface of metal's nanoparticles and the gaps of them,which greatly improves the target molecule information and the characteristic Raman signal of it.However,the disadvantages of high cost,non-uniformity,and poor biocompatibility limit their wide application.In the past ten years,the research focusing on SERS substrates has gradually turned to low-cost semiconductor materials.Nowadays,there have been many reports on the study of semiconductor materials as SERS substrates,but their enhancement factors are low.In order to take advantage of the high enhancement factor of precious metals and low cost of semiconductors,the hybrid materials of precious metals and semiconductors as SERS substrates have become an inevitable choice for surface enhanced Raman scattering.Cu2O is one of the rare p-type semiconductors.It has non-toxicity,low cost as well as abundant raw materials,and spherical Cu2O particles have a large surface area.It is of great significance to carry out SERS characteristics and application based on hybrid Cu2O spherical nanoparticles?NPs?and noble metal.The main contents of this thesis are as follows:?1?With copper sulfate and sodium hydroxide as precursors,ethylene glycol and PVP as dispersants and stabilizers,and glucose as reducing agent.Cu2O nanospheres with uniform particle size were obtained in the liquid phase system?water:ethylene glycol=1:1?by a simple chemical precipitation method.The Cu2O nanospheres?NSs?were characterized by various techniques.From SEM and TEM images.It was found that the Cu2O NSs showed a uniform spherical structure with rough surface.XRD proved that the prepared sample was a face-centered cubic structure Cu2O.The EDS revealed that the sample is composed of Cu and O elements.The XPS spectrum shows that the Cu2O XPS spectrum contains Cu2p and O1s peaks.The binding energy of the Cu2p peak corresponds to the standard Cu+peak,and the O1s peak corresponds to Cu2O.Finally,the influences of reaction time,sodium hydroxide quality,glucose quality,and the addition of ethylene glycol solvent on the particle size of Cu2O NSs were investigated.?2?Among of the obtained Cu2O NSs with different diameters,three types of NSs with average diameters of 200,400,and 800 nm were selected as SERS substrates,and the SERS spectra of rhodamine B molecules on the Cu2O NSs with different sizes were studied using rhodamine B as a probe molecule.The results showed that for 200 nm NSs substrate rhodamine B molecule with a concentration of 1.0×10-3 M had the smallest fluorescence background intensity count in the SERS spectrum;for 400 nm NSs one the fluorescence background intensity was slightly larger;whereas for 800 nm NSs one the fluorescence background intensity count is the largest.In order to further compare the SERS performance of NSs with different diameters,the peak at 611 cm-1is selected to calculate the limit of detection?LOD?and LOD?200 nm?is 6.15×10-8 M;LOD?400 nm?=1.18×10-7 M;LOD?800 nm?=1.43×10-6 M.?3?The hrbrid Cu2O/Au and Cu2O/Ag NSs were prepared using NSs of 200 nm in diameter as the basic material.The SERS spectra of rhodamine 6G?R6G?molecules as probe molecule were studied on three structures?Cu2O NSs,the hybrid Cu2O/Au and Cu2O/Ag NSs?.The relationship between the SERS signal intensity at 611 cm-1and the concentration of the R6G molecule was chosen to establish a calibration curve.It was found that the LOD of Cu2O NSs is 1.01×10-7 M;the LOD of the hybrid Cu2O/Au NSs is 8.07×10-12 M;the LOD of the hybrid Cu2O/Ag one is 1.13×10-13 M.In addition,the enhancement factor?EF?was calculated.The EF of Cu2O NSs is 3.87×103;the EF of Cu2O/Au NSs is 1.25×108;the EF of Cu2O/Ag NSs is 2.74×109.In addition,three characteristic peaks 1367,1509,and 1650 cm-1 of R6G molecules were selected to evaluate the reproducibility of SERS signal of R6G molecules on Cu2O/Ag NSs substrate.It revealed that the relative standard deviations are 14.23%,14.07%,and15.15%,respectively.These results indicate that Cu2O/Ag NSs composite is excellent SERS substrate and has great application prospects.?4?According to the Herzberg-Teller selection rule on the chemical strengthening mechanism,the influence of precious metal coupling with Cu2O NSs is studied.By analyzing R6G molecular SERS spectra of Cu2O,Cu2O/Au and Cu2O/Ag nanomaterials,the symmetric mode enhancement and incomplete symmetric mode enhancement results,the charge transfer degrees of the above three substrates were calculated as 0.607,0.574 and 0.639,respectively.In order to explain the CT mechanism,we established Cu2O-R6G,Au-Cu2O-R6G,and Ag-Cu2O-R6G models,and connected the charge transfer effect in the SERS model with the corresponding energy level transition.?5?The electric fields around the Cu2O,Cu2O/Au and Cu2O/Ag NSs were simulated by discrete coupling approximation methods,and it indicated that the electric field distributions around the Cu2O,Cu2O/Au and Cu2O/Ag NSs depend greatly on the excitation wavelength.However,comparing them under similar excitation,it revealed that the electric field distribution of the Cu2O/Ag NSs is the strongest,that of the Cu2O/Au structure is the second,and that of the Cu2O NSs is the weakest.The simulation results further illustrate that the surface plasmon resonance between Au and Ag NPs greatly enhances the electric field,and the localized surface plasmon resonance caused by the coupling of Ag and Au NPs with Cu2O NSs also enhances the electric field. |
PDF Full Text Request