CN111289487A - Graphene-based surface-enhanced Raman scattering substrate and preparation method and application thereof - Google Patents
Graphene-based surface-enhanced Raman scattering substrate and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a preparation method of a graphene-based surface enhanced Raman scattering substrate, which comprises the following steps: preparing a composite film layer of graphene and silver nanoparticles by taking a graphene sheet layer with oxidized edges as a raw material, wherein an oxygen-containing functional group is modified in the edge region of the graphene sheet layer, and the silver nanoparticles are enriched in the edge region of the graphene sheet layer through the complexing action of the oxygen-containing functional group; applying external force to the composite film layer of the graphene and the silver nanoparticles to break the composite film layer to obtain a section serving as the graphene-based surface enhanced Raman scattering substrate, wherein the edge area of the graphene sheet layer and the silver nanoparticles are stacked on the section layer by layer, and a plasmon structure is formed among the silver nanoparticles. The invention also provides the graphene-based surface enhanced Raman scattering substrate prepared by the preparation method. The invention also provides application of the graphene-based surface enhanced Raman scattering substrate. The invention can prepare the graphene-based surface enhanced Raman scattering substrate with high performance and long-term stability at low cost.
Description
Technical Field
The invention relates to the technical field of detection, and particularly relates to a graphene-based surface-enhanced Raman scattering substrate, and a preparation method and application thereof.
Background
The Surface-enhanced Raman spectroscopy (SERS) can improve the intensity of a common Raman signal by more than ten orders of magnitude, can realize single-molecule level detection and provide fingerprint information of a molecular structure, and is a high-sensitivity spectroscopic detection technology. Therefore, the SERS technology is the rapid nondestructive testing means with the application potential at present and has wide application prospect in the fields of environmental pollution, food safety, disease diagnosis and the like. However, practical application of SERS techniques still faces many challenges. Common Raman enhancement substrates are mainly a rough gold nano-film, a silver nano-film, gold nano-particles, silver nano-particles and the like, and the principle is that plasmons are constructed in a noble metal nano-structure to enhance a localized electric field, so that Raman signals are improved, and the Raman enhancement substrate is a physical enhancement mechanism. However, on one hand, these noble metal substrates are expensive, which greatly increases the cost of detection; on the other hand, the nano-sized noble metal particles are easily oxidized and lose their activity, and are very disadvantageous in long-term storage of the substrate. Therefore, it is important to develop a raman-enhanced substrate that is inexpensive, excellent in performance, and stable.
The graphene is formed by sp from the thickness of 1-10 atomic layers2The two-dimensional carbon nanomaterial formed by carbon atoms has a large specific surface and excellent molecular adsorption capacity, and a large number of graphene sheets can be assembled to form a self-supporting macroscopic film layer with a layer-by-layer stacking structure by using the dispersion liquid, so that the two-dimensional carbon nanomaterial has the potential advantage of serving as a SERS substrate. In the aspect of SERS performance, in 2009 LingXi et al, in Nano Lett.2010,10,553-561, it is reported that a graphene sheet layer mechanically peeled off can quench molecular fluorescence, and the graphene sheet layer has a remarkable Raman enhancement effect on phthalocyanine (Pc), rhodamine 6G (R6G), protoporphyrin IX (PPP) and Crystal Violet (CV), and the molecular detection limit reaches 10-8mol/L, and it is explicitly suggested that photoinduced electron transfer between molecules (i.e. Pc, R6G, PPP, CV) and graphene sheets is the main mechanism of raman enhancement, i.e. a chemical enhancement mechanism different from the noble metal plasmon mechanism. The 2011 document ACS Nano 2011,5,2,952 and 958 also finds a remarkable Raman enhancement effect in Reducing Graphene Oxide (RGO), and the detection limit of R6G reaches 10-8mol/L, and the introduction of highly electronegative oxygen-containing functional groups, can introduce strong local electric fields on the adsorbed molecules, leading to significant raman enhancement, a chemical enhancement mechanism distinct from electron transfer. In conclusion, the method is superior toThe graphene has great potential as a Raman enhancement substrate due to large specific surface area and chemical enhancement mechanism and relatively low cost and chemical stability. However, the detection limit of graphene is poor compared to noble metals, and the advantage in practical application is not obvious.
In view of the above, a raman enhancement substrate based on a graphene and noble metal nanoparticle composite system is developed, in which a raman signal of a probe molecule is increased by graphene and noble metal nanoparticles distributed on the surface of the graphene. A large number of researches show that the composite substrate can simultaneously utilize the physical enhancement effect of the noble metal nano particles and the chemical enhancement effect of the graphene sheet layer, and has obvious advantages in performance. For example, patent documents CN 107445145 a and CN 104259475B respectively report composite substrates of reduced graphene oxide and silver nanoparticles prepared by different methods, and obtain better effects. However, in order to achieve uniformity of spatial distribution of substrate detection performance, silver nanoparticles in the existing composite structure are uniformly distributed on graphene material sheets, and the usage amount of the silver nanoparticles is still large. In addition, the silver nanoparticles distributed on the surface of the graphene sheet layer still have the problem of oxidative inactivation during long-term storage in air. Therefore, for the application of the noble metal nanoparticle-graphene composite substrate, further reducing the usage amount of the noble metal particles and simultaneously improving the stability of the noble metal particles are key technical problems which must be solved at present.
Disclosure of Invention
In order to solve the problems of poor stability and the like of a Raman enhancement substrate of a graphene and noble metal nanoparticle composite system in the prior art, the invention provides a graphene-based surface enhancement Raman scattering substrate and a preparation method and application thereof.
The invention provides a preparation method of a graphene-based surface enhanced Raman scattering substrate, which comprises the following steps: s1, preparing a composite film layer of graphene and silver nanoparticles by taking the graphene sheet layer with oxidized edges as a raw material, wherein the edge area of the graphene sheet layer is modified with an oxygen-containing functional group, and the silver nanoparticles are enriched in the edge area of the graphene sheet layer through complexation with the oxygen-containing functional group; and S2, applying external force to the composite film layer of the graphene and the silver nanoparticles to break the composite film layer to obtain a section serving as the graphene-based surface enhanced Raman scattering substrate, wherein the edge region of the graphene sheet layer and the silver nanoparticles are stacked on the section layer by layer, and a plasmon structure is formed among the silver nanoparticles.
It is understood that, in the plasmonic structure of the graphene-based surface enhanced raman scattering substrate, the spacing between the silver nanoparticles is smaller than the diameter of the silver nanoparticles and larger than 1 nm. In this range, the smaller the distance between the silver nanoparticles is, the more remarkable the plasmon resonance effect by the plasmon is, and the more remarkable the raman enhancing effect is.
Preferably, the edge-oxidized graphene sheets are provided by an electrochemically prepared aqueous edge-oxidized graphene solution. Specifically, graphite foil is used as a working electrode, foil is used as a counter electrode, terephthalic acid and NaOH are dissolved in water to be used as electrolytes, and an electrochemical stripping process is carried out by applying positive voltage to obtain graphene aqueous solution with oxidized edges. In a preferred embodiment, the concentration of the graphene aqueous solution is 0.5g/L-1.5 g/L.
Preferably, in step S1, a colloidal dispersion of silver nanoparticles is provided, and the graphene aqueous solution with oxidized edges and the colloidal dispersion of silver nanoparticles are mixed and then directly filtered, so as to prepare the composite film layer of graphene and silver nanoparticles by an ex-situ generation method. Preferably, the HAuCl is reduced by sodium citrate4Obtaining gold seeds, adding AgNO into gold seeds, sodium citrate and ascorbic acid3Obtaining the silver nanoparticle colloid dispersion liquid in the water solution. In a preferred embodiment, the concentration of the silver nanoparticle colloidal dispersion is 0.05g/L to 0.06 g/L. In a preferred embodiment, the mass ratio of the solid contents of the graphene aqueous solution and the silver nanoparticle colloidal dispersion is between 2:1 and 5: 1. In a preferred embodiment, the edge oxidized graphene aqueous solution and the silver nanoparticle colloidal dispersion are mixed and poured into a vacuum filter to be filtered and filtered into a membrane. In a preferred embodiment, the edge-oxidized graphene aqueous solution and the silver nanoparticle colloidal dispersion are mixed and poured into a vacuum filterFiltering the obtained product on an alumina filter membrane or a polyether sulfone filter membrane to form a membrane.
Preferably, in the step S1, the silver nanoparticles are generated at the edge region of the graphene sheet layer to form a composite sheet layer of graphene and silver nanoparticles, and then the composite sheet layer is assembled, so that the composite film layer of graphene and silver nanoparticles is prepared by in-situ generation. In a preferred embodiment, the graphene glucose aqueous solution is obtained by adding glucose to the edge-oxidized graphene aqueous solution, and the Ag (NH) is obtained by adding ammonia to the silver nitrate aqueous solution3)2OH solution, mixing graphene glucose aqueous solution and Ag (NH)3)2The OH solutions were mixed to form a composite sheet of graphene and silver nanoparticles. In a preferred embodiment, the edge oxidized graphene aqueous solution and silver nitrate particles are mixed, and then sodium citrate is added to form a composite sheet of graphene and silver nanoparticles. In a preferred embodiment, the edge-oxidized graphene aqueous solution is mixed with silver nitrate and polyvinylpyrrolidone, and then reduced by ultraviolet radiation or sodium borohydride to form a composite sheet of graphene and silver nanoparticles. Preferably, the assembly method for assembling the composite sheet layer of graphene and silver nanoparticles into the composite film layer of graphene and silver nanoparticles is one of suction filtration, spray coating, spin coating, blade coating and the like. In a preferred embodiment, the composite sheet layer of graphene and silver nanoparticles is assembled into a composite film layer of graphene and silver nanoparticles on a teflon plate, a teflon film, a polycarbonate filter film or a polyester film.
Preferably, in the composite film layer of graphene and silver nanoparticles, the graphene sheet layer is modified with oxygen-containing functional groups, and the oxygen-containing functional groups are mainly distributed in the edge region of the graphene sheet layer. In a preferred embodiment, at least 50% of the oxygen-containing functional groups are distributed at the edge regions of the graphene sheets. In a more preferred embodiment, at least 80% of the oxygen-containing functional groups are distributed at the edge regions of the graphene sheets. In a more preferred embodiment, at least 90% of the oxygen-containing functional groups are distributed at the edge regions of the graphene sheets.
Preferably, in the composite film layer of graphene and silver nanoparticles, the particle size (i.e., average diameter) of the silver nanoparticles is between 1nm and 100 nm. In a preferred embodiment of excitation with raman laser light of 532nm wavelength, the silver nanoparticles have a particle size between 60nm and 80nm for best SERS effect. It should be understood that the diameter of the silver nanoparticles is related to the wavelength of the raman laser used for excitation, the wavelength of the raman laser is 325nm, 532nm and 633nm, and the longer the wavelength is, the larger the diameter of the silver nanoparticles is required, and the difference between the SERS performance under the excitation of the raman laser with different wavelengths is not large as long as the diameter of the silver nanoparticles is matched.
Preferably, the thickness of the composite film layer of graphene and silver nanoparticles is between 1 μm and 50 μm. It will be appreciated that the greater thickness of the graphene-based surface enhanced raman scattering substrate thus formed facilitates subsequent testing operations, but results in increased silver usage. In a preferred embodiment, the thickness of the composite film layer of graphene and silver nanoparticles is between 10 μm and 30 μm.
Preferably, in the step S2, after the liquid nitrogen freezing treatment, an external force is applied to the composite film layer of graphene and silver nanoparticles to cause brittle fracture of the composite film layer, so as to obtain a regular cross section as the graphene-based surface-enhanced raman scattering substrate.
Preferably, the external force is one of longitudinal shear or transverse tension. It is to be understood that this step of applying an external force is performed shortly before testing by raman laser excitation profile to obtain a freshly prepared graphene-based surface enhanced raman scattering substrate, avoiding premature exposure of the silver nanoparticles between graphene sheets to oxidation.
The invention also provides the graphene-based surface enhanced Raman scattering substrate obtained by the preparation method, wherein in the graphene-based surface enhanced Raman scattering substrate, the edge area of the graphene sheet layer and the silver nanoparticles are stacked layer by layer on the section, and a plasmon structure is formed among the silver nanoparticles.
Preferably, in the graphene-based surface enhanced raman scattering substrate, the silver nanoparticles are densely distributed on the edge region of the graphene sheet layer.
The invention also provides application of the graphene-based surface enhanced Raman scattering substrate.
Preferably, the graphene-based surface enhanced raman scattering substrate has a significant raman enhancement effect on phthalocyanine (Pc), rhodamine 6G (R6G), protoporphyrin ix (ppp) and Crystal Violet (CV). Preferably, the graphene-based surface enhanced raman scattering substrate is soaked in an R6G aqueous solution or a crystal violet aqueous solution and then taken out for detection. In a preferred embodiment, the concentration of the aqueous solution of R6G or the aqueous solution of crystal violet is 10-8mol/L-10-7mol/L. Preferably, the graphene-based surface enhanced raman scattering substrate is used for the detection of thiram. In a preferred embodiment, the concentration of thiram in the ethanol solution is 24 μ g/kg.
According to the method, the graphene sheet layer with oxidized edges is used for enriching the silver nanoparticles, namely, the anchoring effect of oxygen-containing functional groups is used for controlling the preferential distribution of the silver nanoparticles in the edge area of the graphene sheet layer, so that a plasmon structure enriched with the silver nanoparticles is formed on the section of the composite film layer of the graphene and the silver nanoparticles, and the chemical enhancement effect of the graphene material and the physical enhancement mechanism of the nano silver material are fully utilized to obtain the excellent Raman enhancement effect. Compared with the traditional Raman enhancement structure which utilizes the silver nanoparticles uniformly distributed on the surface of the graphene to construct the plasmon structure, the method only needs to enrich the silver nanoparticles in the edge area of the graphene sheet layer, so that the use amount of the nano silver can be greatly reduced, and the cost can be reduced. Meanwhile, the silver nanoparticles among the graphene layers are isolated from the air, so that the oxidation process of the silver nanoparticles in the air is delayed or even prevented, the Raman enhancement performance of the silver nanoparticles cannot be obviously attenuated after long-term storage, and compared with the traditional method of utilizing the silver nanoparticles distributed on the surface of graphene, the graphene-based surface-enhanced Raman scattering substrate formed by the cross section has a more stable Raman enhancement effect. In summary, the present invention provides a graphene-based surface enhanced raman scattering substrate with high performance and long-term stability at low cost.
Drawings
Fig. 1 is a cross-sectional scanning electron microscope picture of a graphene-based surface enhanced raman scattering substrate obtained in example 1 according to the present invention;
fig. 2 illustrates the detection principle of a graphene-based surface enhanced raman scattering substrate according to the present invention;
fig. 3 is a raman enhancement spectrum of the graphene-based surface enhanced raman scattering substrate of example 1 and comparative example 1 for R6G;
fig. 4 is the decay of the raman enhancement effect of the graphene-based surface enhanced raman scattering substrate and the bare silver nanoparticles of example 1 and comparative example 2, respectively, on R6G with the time of sample placement;
fig. 5 is a scanning electron microscope image of a cross section of the graphene-based surface enhanced raman scattering substrate obtained in example 2 of the present invention;
fig. 6 is a raman-enhanced spectrum of the graphene-based surface-enhanced raman scattering substrate of example 2 against crystal violet;
fig. 7 is a cross-sectional scanning electron microscope image of the graphene-based surface enhanced raman scattering substrate obtained in example 3 according to the present invention;
fig. 8 is a raman-enhanced spectrum of the graphene-based surface-enhanced raman scattering substrate of example 3 for thiram;
fig. 9 is a scanning electron microscope image of a cross section of the graphene-based surface enhanced raman scattering substrate obtained in example 4 of the present invention;
fig. 10 is a cross-sectional scanning electron microscope image of the graphene-based surface enhanced raman scattering substrate obtained in example 5 according to the present invention.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
Example 1
Using graphite foil as the working electrode and foil as the counter electrode, 0.83g of terephthalic acid and 0.80g of NaOH were dissolved in 100ml of deionized water as the electrolyte. The electrochemical stripping process was carried out for 5h by applying a positive voltage of 10V. Thereafter, the exfoliated product was subjected to bath sonication for 1 h. Finally, large particles were removed by centrifugation at 3000rpm, and washing was repeated for 10 minutes each by centrifugation at 15000rpm to obtain an aqueous edge-oxidized graphene solution having a concentration of 0.5 g/L.
50mL (0.01 wt.%) of HAuCl4Heating to boiling, then 0.5mL (1 wt.%) sodium citrate solution was added and the solution was boiled for 20 minutes to complete the reduction of gold (Au) seeds. Next, 40mL of deionized water was taken and added with 2mL of Au seed solution, 2mL (1 wt.%) of sodium citrate and 2mL (0.02mol/L) of ascorbic acid in that order. Then, 1.6mL (0.01mol/L) of AgNO was added dropwise at a rate of 4mL/h3Obtaining silver nano-particle colloid dispersion liquid with the concentration of 0.05g/L by water solution, wherein the grain diameter of the silver nano-particles is in the range of 60nm-70 nm.
Mixing 10mL of edge oxidized graphene aqueous solution and 20mL of silver nanoparticle colloid dispersion liquid, wherein the solid content of the graphene aqueous solution and the silver nanoparticle colloid dispersion liquid is 5:1 (mass ratio), fully and uniformly stirring, pouring onto an alumina filter membrane of a vacuum filter, carrying out vacuum filtration for 5 hours, and drying in a 60 ℃ oven to obtain an edge oxidized graphene-nano silver composite membrane layer, namely the edge oxidized graphene and silver nanoparticle composite membrane layer.
And (3) performing liquid nitrogen freezing treatment on the edge graphene oxide-nano silver composite film layer, and then shearing the film layer to break the film layer to obtain the section serving as the graphene-based surface enhanced Raman scattering substrate. The scanning electron micrograph of the cross section is shown in fig. 1, so that the cross section structure is characterized by the edge region of the graphene sheet layer and the layer-by-layer stacking of the silver nanoparticles, and the silver nanoparticles are uniformly dispersed in the cross section region.
The section is set at 10-7And taking out the test after 30 minutes in a mol/L R6G aqueous solution. As shown in fig. 2, during the test, an excitation light source (532nm) directly irradiates the cross section of the edge graphene oxide-silver nanoparticle composite film layer, a raman signal of the molecule to be tested absorbed by the cross section is detected, and a raman spectrum is shown in fig. 3, and a significant signal peak of R6G can be seen.
Comparative example 1
In order to prove the particularity of the edge graphene oxide in the structural section structure, the graphene oxide-nano silver composite film layer prepared in the comparative example 1 is used for comparison.
Mixing 10mL of a commercially available graphene oxide aqueous solution (with the concentration of 0.5g/L) with 20mL of the silver nanoparticle colloidal dispersion prepared in example 1 (with the particle size of 60nm-70nm of 0.05 g/L), sufficiently and uniformly stirring, pouring the mixture onto an alumina filter membrane of a vacuum filter, performing reduced pressure filtration, and drying in an oven at 60 ℃ to obtain a graphene oxide-nano silver composite membrane layer, namely a traditional graphene and silver nanoparticle composite membrane layer.
And (3) performing liquid nitrogen freezing treatment on the graphene oxide-nano silver composite film layer, and then applying a shearing external force to break the graphene oxide-nano silver composite film layer to obtain a cross section.
The obtained cross section was used as a surface enhanced Raman scattering substrate and placed at 10-7And taking out the test after 30 minutes in a mol/L R6G aqueous solution. The raman spectrum of the graphene oxide-nano silver composite film excited by 532nm laser is shown in fig. 3, and a signal peak of R6G can be seen, but the enhancement effect is greatly reduced compared with the cross section of the edge graphene oxide-nano silver composite film. The result shows that under the condition of the same mass ratio, the edge graphene oxide has more obvious effects on the aspects of enriching silver nanoparticles at the edge and enhancing the plasmon coupling effect; due to the oxygen-containing functional groups uniformly distributed on the sheet layer, the silver nanoparticles are uniformly distributed, and cannot be enriched at the edge of the sheet layer, so that the cross-section plasmon coupling effect is relatively weak, and the Raman enhanced scattering effect on molecules is not obvious.
Comparative example 2
To demonstrate the protective effect of the cross-sectional structure of the edge graphene oxide structure on the nano-silver particles, this comparative example 2 prepared a sample of bare nano-silver particles for comparison.
1mL of the silver nanoparticle colloidal dispersion (0.05g/L, particle size in the range of 60nm-70 nm) prepared in example 1 was added dropwise onto a clean silicon wafer substrate, and dried in an oven at 60 ℃ to obtain a bare silver nanoparticle sample.
The newly prepared bare nano silver sample and the edge graphene oxide-silver nanoparticle composite film layer newly prepared in example 1 were taken and placed in an air environment at 25 ℃. A portion of each of the above samples was taken as a substrate every other day and placed at 10-7After being taken out from the water solution of R6G at mol/L for 30 minutes, the solution is respectively irradiated by an excitation light source (532nm)Shooting the cross sections of the bare nano-silver sample and the composite film layer sample, detecting and recording the Raman characteristic peak (612 cm) of the R6G molecules adsorbed by the samples-1) Intensity, resulting in the decay of the raman signal with time of standing as shown in fig. 4. It can be seen that, compared with the bare nano silver particles, the edge graphene oxide-nano silver cross-section structure prepared in embodiment 1 of the present invention has a significant protection effect on the nano silver particles, and effectively inhibits raman enhancement attenuation caused by long-time placement of the nano silver particles in an environment.
Example 2
20mL of an electrochemically prepared edge oxidized graphene aqueous solution (concentration 1.5g/L) and 0.8g of glucose was added thereto with stirring to give a solution A.
Slowly add 0.6mol/L ammonia to aqueous silver nitrate solution (12mL, 0.06mol/L) until AgOH/Ag2The O precipitate disappears to obtain clear Ag (NH)3)2OH solution, namely B solution.
And mixing and stirring the solution A and the solution B for 15 minutes, standing for 2 hours to obtain a composite sheet layer of edge oxidized graphene and silver nanoparticles, enriching the silver nanoparticles in the edge area of the graphene sheet layer, centrifuging the composite sheet layer, and repeatedly washing with water to remove impurities. Preparing a graphene-nano silver composite film on a Teflon plate by adopting a blade coating method, coating a certain thickness by blade coating, and drying in an oven at 60 ℃.
The membrane layer is frozen by liquid nitrogen, a stretching external force is applied to the surface of the membrane layer to obtain a section of the membrane layer, a section scanning electron microscope is shown in figure 5, silver nanoparticles synthesized in situ on the surface of the edge graphene oxide can be seen, the particle size of the silver nanoparticles is within the range of 10nm-20nm, the structure of the composite membrane layer also presents a layer-by-layer stacking characteristic, and the silver nanoparticles are uniformly dispersed in the section area.
The obtained cross section was used as a surface enhanced Raman scattering substrate and placed at 10-8Taking out the crystal violet solution of mol/L for 30 minutes and testing. When the sample was excited by a 325nm laser, a Raman spectrum was shown in FIG. 6, and a significant signal peak of crystal violet was observed.
Example 3
30mL of electrochemically prepared edge-oxidized graphene aqueous solution (concentration 4g/L) was prepared, and 5mg of silver nitrate (AgNO) was added3) And (3) granules. And then heating and stirring the mixture to 95 ℃, adding 0.8mL of 1 wt.% sodium citrate solution, and reacting for 30 minutes to obtain graphene-nano silver slurry (with the nano silver particle size being within the range of 40-50 nm).
And (3) spin-coating a graphene-nano silver composite film on the polytetrafluoroethylene film at 4000rpm by using a spin-coating method, and obtaining a layer-by-layer stacked film with a certain thickness through multiple spin-coating. And finally, taking down the film, freezing the film layer by liquid nitrogen, applying a stretching external force to the film layer surface to obtain the section of the film layer, wherein the section of the film layer presents the characteristics of a layer-by-layer stacking structure as can be seen from a scanning electron microscope image (figure 7) of the section, and the silver nanoparticles are uniformly dispersed in the section area.
And (3) performing surface-enhanced Raman scattering test, namely taking the section as a surface-enhanced Raman scattering substrate, and sucking residual thiram ethanol solution (with the concentration of 24 mu g/kg) on the fruits and vegetables by using the section. The raman spectrum of the molecule absorbed by the 532nm laser excitation section is shown in fig. 8, and a significant signal peak of thiram can be seen.
Example 4
40mL of electrochemically prepared edge oxidized graphene aqueous solution (1g/L) was prepared, and 10mg of silver nitrate (AgNO) was added3) And a certain amount of polyvinylpyrrolidone (PVP), fully and uniformly stirring, reducing by a 200W ultraviolet lamp for preparing nano silver, and irradiating for 30 minutes to obtain a dark brown solution (the particle size of the nano silver is within the range of 20-40 nm). Pouring the solution onto a polycarbonate filter membrane of a vacuum filter, filtering the solution under reduced pressure for 5 hours, and drying the solution in an oven at 60 ℃.
The graphene-nano silver composite film layer is subjected to liquid nitrogen freezing treatment, then a shearing external force is applied to fracture the graphene-nano silver composite film layer, so that an edge area of a graphene sheet layer and a section of silver nano particles stacked layer by layer are formed, a section scanning mirror image (figure 9) shows obvious layer-by-layer stacked structural characteristics, and the silver nano particles are uniformly dispersed in the section area. The obtained cross section was used as a surface enhanced Raman scattering substrate and placed at 10-7And (3) taking out the solution of R6G in mol/L for 30 minutes, testing, and exciting the molecules absorbed by the section by using a 325nm laser to obtain a Raman spectrum.
Example 5
Mixing electrochemically prepared graphene aqueous solution with oxidized edges (concentration of 0.5g/L) and nano-silver colloid dispersion (0.06mg/mL, particle size of 70nm-80 nm) prepared by reduction of sodium citrate according to mass ratio of 2:1, and stirring thoroughly and uniformly. And (3) filtering the mixed solution through a polyether sulfone filter membrane under the pressure of 0.25Mpa, and immediately putting the membrane into a 60-DEG C oven for drying after the filtration is finished.
The film layer is frozen by liquid nitrogen and a tensile external force is applied to the surface of the film layer to obtain a cross section, a cross section scanning mirror image (figure 10) shows obvious layer-by-layer stacking structural characteristics, and silver nanoparticles are uniformly dispersed in the cross section area. The obtained cross section was used as a surface enhanced Raman scattering substrate and placed at 10-7And taking out the test after 30 minutes in a mol/L R6G aqueous solution. The Raman spectrum is obtained by exciting the molecules absorbed by the section with 532nm laser.
Example 7
40mL of electrochemically prepared edge oxidized graphene aqueous solution (2g/L) was prepared, and 20mg of silver nitrate (AgNO) was added3) And a quantity of polyvinylpyrrolidone (PVP) 3mL sodium borohydride (NaBH)4) The solution (1g/L) is stirred rapidly and intensely, and the size of the nano silver obtained by reduction is between 1 and 40 nm. And spraying the graphene-nano silver composite film on a polyester film (PET) by using a continuous centrifugal spraying instrument.
Performing liquid nitrogen freezing treatment on the graphene-nano silver composite film layer, applying an external force facing to stretching to break the graphene-nano silver composite film layer, taking the obtained section as a surface enhanced Raman scattering substrate, and placing the substrate at 10 DEG C-7And taking out the test after 30 minutes in a mol/L R6G aqueous solution. Raman spectra were obtained by exciting the absorbed molecules in the cross section with a 325nm laser.
Example 8
15mL of electrochemically prepared edge-oxidized graphene aqueous solution (4g/L) was prepared, and 15mg of silver nitrate (AgNO) was added3) And a quantity of polyvinylpyrrolidone (PVP) added 4mL of sodium borohydride (NaBH)4) And (3) stirring the solution (0.5g/L) rapidly and violently, and reducing to obtain the nano silver with the size of 10-50 nm. Preparing a graphene-nano silver composite film on a Teflon plate by adopting a blade coating method, coating a certain thickness by using a blade, drying in an oven at 60 ℃, and finally introducingFreezing the film layer by liquid nitrogen and applying a shearing external force to the normal direction of the film layer to obtain the section of the film layer.
The obtained cross section is used as a surface enhanced Raman scattering substrate and is placed at 10-7And taking out the test after 30 minutes in a mol/L R6G aqueous solution. Raman spectra were obtained by exciting the absorbed molecules in the cross section with a 325nm laser.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.
Claims (9)
1. A preparation method of a graphene-based surface enhanced Raman scattering substrate is characterized by comprising the following steps:
s1, preparing a composite film layer of graphene and silver nanoparticles by taking the graphene sheet layer with oxidized edges as a raw material, wherein the edge area of the graphene sheet layer is modified with an oxygen-containing functional group, and the silver nanoparticles are enriched in the edge area of the graphene sheet layer through complexation with the oxygen-containing functional group;
and S2, applying external force to the composite film layer of the graphene and the silver nanoparticles to break the composite film layer to obtain a section serving as the graphene-based surface enhanced Raman scattering substrate, wherein the edge region of the graphene sheet layer and the silver nanoparticles are stacked on the section layer by layer, and a plasmon structure is formed among the silver nanoparticles.
2. The method of claim 1, wherein the edge-oxidized graphene sheets are provided by an electrochemically prepared aqueous edge-oxidized graphene solution.
3. The preparation method of claim 2, wherein in the step S1, a colloidal dispersion of silver nanoparticles is provided, and the graphene aqueous solution with oxidized edges and the colloidal dispersion of silver nanoparticles are mixed and directly filtered, so as to prepare the composite film layer of graphene and silver nanoparticles by ex-situ generation.
4. The method of claim 1, wherein in the step S1, the silver nanoparticles are generated at the edge region of the graphene sheet layer to form a composite sheet layer of graphene and silver nanoparticles, and then the composite sheet layer is assembled, thereby preparing the composite film layer of graphene and silver nanoparticles by in-situ generation.
5. The method according to claim 1, wherein in step S2, an external force is applied to the composite film layer of graphene and silver nanoparticles after the liquid nitrogen freezing treatment to cause brittle fracture of the composite film layer, thereby obtaining a regular cross section as the graphene-based surface-enhanced raman scattering substrate.
6. The method of claim 5, wherein the external force is one of longitudinal shear or transverse tension.
7. The graphene-based surface-enhanced Raman scattering substrate obtained by the preparation method according to any one of claims 1 to 6, wherein in the graphene-based surface-enhanced Raman scattering substrate, edge regions of graphene sheets and silver nanoparticles are stacked layer by layer at the section, and plasmon structures are formed among the silver nanoparticles.
8. Use of the graphene-based surface-enhanced raman scattering substrate of claim 7.
9. The use according to claim 8, wherein the graphene-based surface enhanced Raman scattering substrate has significant Raman enhancing effects on phthalocyanine, rhodamine 6G, protoporphyrin IX and crystal violet.
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| CN113433109A (en) * | 2021-06-22 | 2021-09-24 | 西安邮电大学 | Preparation method of silver fractal and graphene combined plasmon composite structure substrate |
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