| Surface-enhanced Raman scattering(SERS)is one of the most important technology in the field of trace detection.SERS substrates based on gold(Au),silver(Ag),copper(Cu)and other noble metals with rough surface can produce a strong electromagnetic enhancement effect,so that molecules adsorbed on the surface of the substrate produce a strong Raman scattering signal.At present,SERS substrate also has the disadvantages of weak chemical stability,poor uniformity,low SERS characteristics,and non-recyclability.Since the discovery of Graphene-enhanced Raman scattering(GERS)by Xie et al.in 2009,graphene with the high chemical stability and chemically enhancement property combined with noble metal nanoparticles of electromagnetic enhancement property have made the SERS substrate of graphene/noble metal composite become a hotspot.TiO2 with excellent photoelectric properties can produce photogenerated electron-hole pairs(e--h+)under the irradiation of ultraviolet light,so that the molecules around can be redoxed.The photocatalytic properties of TiO2 can be applied to SERS substrate with the function of self-cleaning,in order to extend the life of the substrate.At the same time,the high electron mobility of graphene can play a role in suppressing the recombination of photo-generated electron-hole pair and thus improve the photo-catalytic efficiency in the composite structure.Based on the optical properties of the above three materials,the composite structure of noble metal nanomaterials,photo-catalytic semiconductors and graphene were made to study their preparation technology,homogeneity,SERS characteristics and photocatalytic performance.The specific research contents include:(1)The preparation method and optical properties of Ag/G composite SERS substrate were studied.The Ag nanoparticles were prepared by chemical reduction method which was simple,environment friendly and low cost.The adhesion of Ag nanoparticles on the target substrate was improved by the coupling agent of 3-aminopropyltrimethoxysilane(APTMS)method.Annealing process was used to suppress the Raman background noise caused by the residual organic matter on the surface of Ag nanoparticles.The effects of annealing temperature on the morphology of Ag nanoparticles on Ag,Ag-G and G-Ag substrates were studied combined with Ostwald maturation theory.The SERS activity of the substrate was further improved by increasing the APTMS volume fraction,extending the deposition time of Ag sol to increase the diameter of Ag nanoparticles and decreased the inter-particle size.The experimental results showed that the R6 G Raman spectra on the three substrates are less than 22% which means high uniformity.Annealing at 450 °C can effectively remove the background noise of the substrates.The substrates prepared with APTMS volume fraction of 10% and Ag sol deposition time of 48 hours have a high SERS effective with enhancement factor of 107.(2)The preparation,characterization,Raman properties and photocatalytic properties of TiO2,TiO2-G and G-TiO2 photocatalytic substrates were studied.For TiO2-G substrate,the aggregation effect of TiO2 nanoparticles on graphene was studied through Raman mapping and Atomic Force Microscope(AFM)analysis,and the TiO2 intensity affected by which on the composite substrate was also studied.The experimental results of aggregation effect were verified by simulation in which the simulation molel is built by reconstruction of AFM data.Through the comparison of different TiO2/G structures,Raman spectra of TiO2 and graphnen,the band shift and intensity of G and 2D band were analyzed.Through photocatalysis experiments,the photocatalytic properties of three kinds of substrates were studied,in which CVD graphene with high electron mobility was improved to enhance the photocatalytic effect of TiO2.The results showed that the photo-catalytic rate of G-TiO2 substrate is the largest,TiO2-G takes second place,TiO2 is the smallest.Our research provided the theoretical and experimental basis for the study of Raman enhancement properties and photo-catalytic properties of Ag/TiO2/G SERS substrate.(3)The preparation and characterization of Ag-TiO2-G,Ag-G-TiO2 and G-Ag-TiO2 photocatalytic SERS substrates were studied.Through Raman mapping analysis,the relationship between composite structure and Raman spectra of each substrate,TiO2 intensity were investigated by Raman mapping.R6 G Raman mapping analysis was used to study the difference between the SERS performance and the composite structure of three kinds of Ag/TiO2/G substrates and the experimental results were verified by simulation.The photo-catalytic properties of three kinds of Ag/TiO2/G substrates were studied by testing the Raman spectra of R6 G on each substrate at set intervals after UV lighting,and the photo-catalytic process was analyzed theoretically.The results showed that the SERS activity of the three structures ranked as : G-Ag-TiO2 > Ag-G-TiO2 > Ag-TiO2-G,and the R6 G enhancement factor is up to 106;the photo-catalytic effective in the first 30 min ranked as : Ag-G-TiO2 > Ag-TiO2-G > G-Ag-TiO2,and with the longer photo-catalytic time,it ranked as : Ag-TiO2-G > G-Ag-TiO2> Ag-G-TiO2.The Raman signal of R6 G on the substrate almost completely disappeared when the irradiation time was 50 min. |
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