CN107478635A - A kind of MOF noble metals composite S ERS substrates and preparation method thereof - Google Patents

Abstract

The invention relates to the field of MOF-noble metal nanocomposite materials, in particular to a MOF-noble metal composite SERS substrate and a preparation method thereof. In the alcohol solution, the CTAB-modified positively charged noble metal nanoparticles were supported on the surface of the MOF material through electrostatic interaction to form a MOF-noble metal nanocomposite SERS substrate. Compared with the in-situ growth method, the present invention loads noble metal nanoparticles on the surface of MOF through electrostatic interaction, while maintaining the high porosity, specific surface area and excellent adsorption capacity of MOF materials, it can achieve the metal nanoparticles on the surface of MOF. The shape, size and density can be precisely controlled to prepare a large number of Raman active sites, which can further effectively improve the SERS performance of the composite substrate. The MOF-AuNPs composite SERS substrate prepared by the present invention has dual functions of adsorption enrichment and Raman enhancement, without surface modification, and can realize direct and highly sensitive detection of molecules such as fluoranthene.

Description

A kind of MOF-noble metal composite SERS substrate and its preparation method

technical field

The invention relates to the field of MOF-noble metal nanocomposite materials, in particular to a MOF-noble metal composite SERS substrate and a preparation method thereof.

Background technique

Surface-enhanced Raman scattering technology is an ultrasensitive and non-destructive molecular detection technology, which is widely used in chemical sensing, biomedicine, environmental pollutant detection and other fields. Nowadays, it is still an important challenge to prepare SERS substrates with high sensitivity, good reproducibility and high stability to realize rapid, direct and highly sensitive detection of environmental organic pollutants. Polycyclic aromatic hydrocarbons, a product of petroleum combustion, have poor adsorption to the surface of traditional noble metal SERS substrates, and it is difficult to reach the local surface plasmon resonance region, and the SERS effect is weak. At present, surface modification-the method of introducing sulfhydryl groups is mostly used to capture and adsorb molecules, and the experimental process is complicated.

As a new type of organic-inorganic hybrid porous material, MOF material has regular pore structure, large specific surface area, high porosity and adjustable surface chemical properties compared with traditional porous materials. , Selective adsorption and drug transport and other fields have great potential application value. Especially in the field of surface-enhanced Raman scattering, MOF porous materials are combined with noble metal nanomaterials, taking advantage of the characteristics of MOF materials such as large specific surface area and high porosity, and effectively combining the excellent adsorption and enrichment ability of MOF with localized surface plasmons of noble metal nanoparticles The resonant nature can significantly improve the sensitivity and reproducibility of SERS detection. Li Gongke (Analyst. 2015, 140, 8165-8171) reported a kind of Au@MIL-100(Fe) core-shell nanocomposite structure, MOF material is used as the shell, which can enrich the detection molecules on the surface of the gold nano-core. The detection limit of malachite green molecule is as low as 8×10 ^-9 mol/L. However, such methods are difficult to prepare a large number of active sites between particles. Li Yuanfang used the method of in situ reduction in MIL-101(Fe) (Anal.Chem.2015, 87, 12177-12182) and MIL-101(Cr) (RSC Adv. 2016, 6, 79805-79810) MOF materials AgNPs/MOF composite SERS substrate with excellent performance was successfully prepared by loading silver nanoparticles on the surface. However, the in-situ reduction method cannot precisely control the size, morphology, and attachment density of metal nanoparticles, and metal nanoparticles/MOF composites prepared by in-situ growth methods, metal precursors and other impurities are likely to remain in the MOF pores. In the channel, the porosity and specific surface area of MOF materials are significantly reduced, which greatly reduces the adsorption capacity of MOF materials for detection molecules and the sensitivity and signal reproducibility of SERS detection.

The MOF-noble metal composite SERS substrate prepared in the present invention is loaded with gold nanoparticles (AuNPs) modified by CTAB (cetyltrimethylammonium bromide) on the surface of MIL-101 (Cr) through electrostatic interaction. The large specific surface area and high porosity realize the effective adsorption and enrichment of the molecules to be tested. By precisely adjusting the morphology, size and loading density of gold nanoparticles, a large number of Raman active sites between the particle gaps are prepared, and the SERS performance of the composite substrate is further adjusted to achieve a great enhancement of the Raman detection signal.

Contents of the invention

The invention prepares a MOF-AuNPs composite SERS detection substrate with gold nanoparticles loaded on the surface of a metal organic framework material, and realizes the effective combination of MOF and metal nanoparticles through electrostatic interaction. The composite particles combine the large specific surface area and high porosity of MOF materials, which can effectively adsorb and enrich the analyte molecules and the excellent surface plasmon properties of gold nanoparticles, which significantly improves the sensitivity of the composite SERS substrate for the detection of organic pollutants and solves the problem At present, due to the weak binding ability between polycyclic aromatic hydrocarbons and traditional precious metal materials, and the poor detection signal, the rapid, direct and highly sensitive SERS detection of polycyclic aromatic hydrocarbons has been successfully realized.

The present invention is achieved through the following technical solutions: a MOF-noble metal nanocomposite SERS substrate, in an alcohol solution, through electrostatic interaction, CTAB-modified positively charged noble metal nanoparticles are loaded on the surface of the MOF material to form a MOF-noble metal Nanocomposite SERS substrates.

The surface of MOF particles contains a large number of unsaturated metal sites. In alcohol solution, these unsaturated metal sites are easily occupied by electron-donating groups, which makes MOF negatively charged. The CTAB-coated noble metal nanoparticles are positively charged in solution, and can generate electrostatic attraction with the negatively charged MOF, thereby binding the two together through electrostatic interaction. Finally, a MOF-noble metal nanocomposite SERS substrate loaded with noble metal nanoparticles is formed.

As a further improvement of the MOF-noble metal nanocomposite SERS substrate technical solution of the present invention, the noble metal nanoparticles are gold nanoparticles, silver nanoparticles or gold-silver core-shell nanostructures.

As a further improvement of the MOF-noble metal nanocomposite SERS substrate technical solution of the present invention, the MOF material is MIL-101(Fe), MIL-101(Cr) or MIL-100(Fe).

The present invention further provides a method for preparing a MOF-noble metal nanocomposite SERS substrate, comprising the following steps:

(1) Preparation of AuNPs: quickly add sodium borohydride solution at 2-4 °C to the mixed solution of tetrachloroauric acid and CTAB, stir vigorously for 1 min, and stand at room temperature for 1 h to obtain gold seeds;

Add CTAB, tetrachloroauric acid, and ascorbic acid to ultrapure water in turn to prepare a growth solution for use; dilute the gold seeds and add them to the growth solution and stir for 1 min, and let stand at room temperature for 6 h to obtain AuNPs; centrifuge the product, Washed twice with ultrapure water and dispersed in methanol to form AuNPs dispersion;

(2) Preparation of MOF-AuNPs composite particles: The MOF material and AuNPs dispersion were quickly mixed, stirred for 1 min, and left at room temperature for 1 h to obtain a MOF-AuNPs composite SERS substrate loaded with gold nanoparticles on the surface.

The preparation method of the invention is simple, efficient, high in repetition rate and mild in reaction conditions. It provides a feasible solution for the design and preparation of new nanocomposite SERS substrates.

In specific operations, when the volume of the gold seed dispersion in the growth solution is larger (that is to say, the concentration is higher and the amount added is more), the particle size of the obtained AuNPs is smaller, and the shape tends to be spherical; on the contrary, when the growth solution The smaller the volume of the gold seed dispersion, the larger the particle size of the obtained AuNPs, and the shape tends to be polyhedral particles. In the AuNPs dispersion, the ratio of AuNPs to MOF materials determines the density of gold nanoparticles loaded on the surface of the MOF-AuNPs composite SERS substrate. The higher the ratio, the greater the loading density; the lower the ratio, the smaller the loading density. The above-mentioned precise adjustment mechanism of the size, shape and loading density of gold nanoparticles provided by the present invention is also applicable to the preparation of other MOF-noble metal nanocomposite SERS substrates.

As a further improvement of the technical solution of the preparation method of the present invention, the MOF material is MIL-101(Fe), MIL-101(Cr) or MIL-100(Fe).

Further, the present invention provides any one of the above-mentioned MOF-noble metal nanocomposite SERS substrates and the preparation method of any one of the above-mentioned MOF-noble metal nanocomposite SERS substrates. applications in organic compounds.

Specifically, the polycyclic aromatic hydrocarbons are fluoranthene, naphthalene, phenanthrene, and the like.

Compared with the prior art, the MOF-AuNPs composite SERS substrate prepared by electrostatic interaction has the following advantages and beneficial effects:

(1) Compared with the in-situ growth method, the present invention loads noble metal nanoparticles on the surface of MOF through electrostatic interaction, which can realize the precise and controllable shape, size and density of metal nanoparticles on the surface of MOF, and prepare a large number of Raman active sites, thereby further effectively improving the SERS performance of the composite substrate.

(2) For the MOF-metal nanoparticle composite SERS substrate prepared by the in-situ growth method, impurities such as metal precursors tend to remain in the MOF channels, resulting in a significant decrease in the porosity and specific surface area of the MOF material, which greatly reduces the ability of the MOF material to detect molecules. The adsorption capacity and the sensitivity and signal reproducibility of SERS detection. However, for the MOF-AuNPs composite SERS substrate prepared in the present invention, two kinds of particles are first synthesized separately, and then the two are combined through electrostatic interaction, which does not affect the adsorption performance of the MOF material on the detection molecules.

(3) It effectively solves the problems of poor adsorption between PAHs and traditional noble metal substrates and low SERS response. Polycyclic aromatic hydrocarbons have weak binding ability to noble metal nanoparticles, and SERS detection is difficult, so surface modification such as introducing sulfhydryl groups is often used. The MOF-AuNPs composite SERS substrate prepared by the present invention has dual functions of adsorption enrichment and Raman enhancement, without surface modification, and can realize direct and highly sensitive detection of molecules such as fluoranthene.

Description of drawings

Figure 1 is the SEM image of the MOF-AuNPs composite SERS substrate loaded with gold nanoparticles of different particle sizes (average diameter). (a) 48 nm (Example 7), (b) 54 nm (Example 6), (c) 66 nm (Example 5), (d) 84 nm (Example 4), the scale bar is 100nm.

Figure 2 is the SEM images of MOF-AuNPs (66 nm) composite SERS substrates with different loading densities. The volume ratio of MIL-101 dispersion to AuNPs dispersion is (a) 1:1 (Example 5), (b) 1:2 (Example 8), (c) 1:3 (Example 9), scale Both are 400nm.

Figure 3 is the Raman signal diagram of different concentrations of R6G on MOF-AuNPs (66nm, MIL-101 (Cr) methanol dispersion: AuNPs dispersion volume ratio 1:2) composite SERS substrate. Numbers 1 to 6 in the figure correspond to different concentrations of R6G.

Figure 4 is the Raman signal diagram of MOF-AuNPs (66 nm, MIL-101 (Cr) methanol dispersion: AuNPs dispersion volume ratio 1:2) composite SERS substrate with different concentrations of fluoranthene. Numbers 1 to 6 in the figure correspond to different concentrations of fluoranthene.

detailed description

The following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

In order to illustrate the MOF-noble metal nanocomposite SERS substrate described in the present invention more clearly, the present invention will describe the preparation method of the MOF-AuNPs composite SERS substrate in detail below. Compared with other preparation methods, the SERS substrate prepared by using the raw material ratio, concentration and process conditions of this preparation method is more sensitive to the detection of polycyclic aromatic hydrocarbons.

The preparation method of described MOF-AuNPs composite SERS substrate, comprises the steps:

① Preparation of MIL-101: Add 5mmol of chromium nitrate nonahydrate, hydrofluoric acid, terephthalic acid and 24mL of deionized water into the reaction kettle, keep the temperature at 220°C for 12h, then gradually cool down to 150°C within 1h, Slowly drop to room temperature within 12h. The product was centrifuged to obtain MIL-101(Cr) powder. Disperse 1 mg of MIL-101(Cr) powder in 10 mL of methanol to obtain a MIL-101(Cr) methanol dispersion with a concentration of 0.1 mg/mL.

(1) Preparation of AuNPs: Rapidly add sodium borohydride (0.01M, 0.6mL) solution at 2-4°C to tetrachloroauric acid (0.01M, 0.25mL) and CTAB (0.1M, 7.5mL) by seed growth method ) in the mixed solution, vigorously stirred for 1 min, and stood at room temperature for 1 h to obtain gold seeds.

Add CTAB (0.1M, 6.4mL), tetrachloroauric acid (0.01M, 6.8mL), and ascorbic acid (0.1M, 3.8mL) to 32mL ultrapure water in sequence to prepare a growth solution. After diluting the gold seeds 10 times, take 15 μL~40 μL and add them to the growth solution, stir for 1 min, and let stand at room temperature for 6 h to obtain AuNPs nanoparticles with an average particle size of 48 nm~84 nm. The product was centrifuged, washed twice with ultrapure water, and then dispersed in 8 mL of methanol to obtain the AuNPs dispersion.

(2) Preparation of MOF-AuNPs composite particles: MIL-101(Cr) methanol dispersion and AuNPs dispersion with different particle sizes were quickly mixed according to the volume ratio of 1:3~1:1, vigorously stirred for 1 min, and left to stand at room temperature for 1 h. The MOF-AuNPs composite SERS substrates with different particle sizes and densities loaded on the surface were obtained.

In the above preparation method, the stirring rate of the "vigorous stirring" used is 800r/min, and the stirring rate of the "stirring" is 350r/min.

Preferably, the MIL-101(Cr) powder obtained after centrifugation of the product in step (1) is washed with 60°C ethanol and N,N-dimethylformamide (DMF) solution. Then soak the above product in ethanol and reflux for 6 hours to fully remove unreacted residues in the pores. Vacuum drying at 150°C for 12 hours fully removes residual water molecules on the unsaturated metal sites on the surface of the MOF material.

Specifically, in step (2), 15 μL to 40 μL of the gold seeds were diluted 10 times and added to the growth solution to obtain AuNPs with a particle size of 48 nm to 84 nm. Among them, the preferred amount of gold seeds added is 20 μL, and when the added amount is 20 μL, the particle size of AuNPs is 66 nm.

Further, in step (3), the methanol dispersion of MIL-101(Cr) and the dispersion of AuNPs with different particle sizes are rapidly mixed according to the volume ratio of 1:3 to 1:1, and the preferred volume ratio is 1:2.

The MOF-AuNPs composite SERS substrate of the present invention will be described in detail below in conjunction with the accompanying drawings

Example 1:

The preparation of gold seed, its step is:

Quickly add sodium borohydride (0.01M, 0.6mL) solution at 2-4°C to a mixed solution of tetrachloroauric acid (0.01M, 0.25mL) and CTAB (0.1M, 7.5mL), stir vigorously for 1min, and After standing for 1 h, gold seeds (8.35 mL) were obtained.

Example 2:

The preparation of gold seed growth solution, its step is:

Add CTAB (0.1M, 6.4mL), tetrachloroauric acid (0.01M, 6.8mL), and ascorbic acid (0.1M, 3.8mL) to 32mL ultrapure water in sequence to prepare a gold seed growth solution (49 mL).

Example 3:

Preparation of MIL-101(Cr):

Add 5mmol of chromium nitrate nonahydrate, hydrofluoric acid, terephthalic acid and 24mL of deionized water into a 100mL reaction kettle. room temperature. The product was centrifuged and washed with 60°C ethanol and DMF solution. The above product was then soaked in ethanol, refluxed for 6 hours, and vacuum-dried at 150° C. for 12 hours to obtain MIL-101 (Cr) powder. Disperse 1 mg of MIL-101(Cr) powder in 10 mL of methanol to obtain a MIL-101(Cr) methanol dispersion with a concentration of 0.1 mg/mL.

Example 4:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

After diluting the gold seeds obtained in Example 1 by 10 times, 15 μL was added to the growth solution prepared in Example 2, stirred for 1 min, and left standing at room temperature for 6 h. AuNPs with an average particle size of about 84 nm were obtained. The product was centrifuged, washed twice with ultrapure water, and dispersed in 8 mL of methanol solution.

The MIL-101 (Cr) dispersion obtained in Example 3 and the AuNPs dispersion with an average particle diameter of 84 nm were quickly mixed at a volume ratio of 1:1, vigorously stirred for 1 min, and left to stand at room temperature for 1 h to obtain MOF-AuNPs Composite SERS substrate dispersion. As shown in Figure 1d.

Example 5:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

After diluting the gold seeds obtained in Example 1 by 10 times, 20 μL was added to the growth solution prepared in Example 2, stirred for 1 min, and left at room temperature for 6 h to obtain AuNPs with an average particle size of about 66 nm. The product was centrifuged, washed with ultrapure water and dispersed in 8 mL of methanol solution.

The MIL-101 (Cr) dispersion obtained in Example 3 and the AuNPs dispersion with an average particle diameter of 66 nm were quickly mixed at a volume ratio of 1:1, vigorously stirred for 1 min, and left to stand at room temperature for 1 h to obtain MOF-AuNPs Composite SERS substrate dispersion. As shown in Figures 1c and 2a.

Embodiment 6:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

After diluting the gold seeds obtained in Example 1 by 10 times, 30 μL was added to the growth solution prepared in Example 2, stirred for 1 min, and left at room temperature for 6 h to obtain AuNPs with an average particle size of about 54 nm. The product was centrifuged, washed with ultrapure water and dispersed in 8 mL of methanol solution.

The MIL-101 (Cr) dispersion obtained in Example 3 and the AuNPs dispersion with an average particle diameter of 54 nm were quickly mixed at a volume ratio of 1:1, vigorously stirred for 1 min, and left to stand at room temperature for 1 h to obtain MOF-AuNPs Composite SERS substrate dispersion. As shown in Figure 1b.

Embodiment 7:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

After diluting the gold seeds obtained in Example 1 by 10 times, 40 μL was added to the growth solution prepared in Example 2, stirred for 1 min, and allowed to stand at room temperature for 6 h. AuNPs with an average particle size of about 48 nm were obtained. The product was centrifuged, washed with ultrapure water and dispersed in 8 mL of methanol solution.

The MIL-101 (Cr) dispersion obtained in Example 3 and the AuNPs dispersion with an average particle diameter of 48 nm were quickly mixed at a volume ratio of 1:1, vigorously stirred for 1 min, and left to stand at room temperature for 1 h to obtain MOF-AuNPs Composite SERS substrate dispersion. As shown in Figure 1 a.

Embodiment 8:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

The MIL-101(Cr) dispersion obtained in Example 3 and the AuNPs dispersion with a particle size of 66 nm obtained in Example 5 were quickly mixed at a volume ratio of 1:2, vigorously stirred for 1 min, and left to stand at room temperature After 1h, the MOF-AuNPs composite SERS substrate dispersion was obtained. As shown in Figure 2b.

Embodiment 9:

A method for preparing a MOF-AuNPs composite SERS substrate, the steps of which are:

The MIL-101(Cr) dispersion obtained in Example 3 and the AuNPs dispersion with a particle size of 66 nm obtained in Example 5 were quickly mixed at a volume ratio of 1:3, vigorously stirred for 1 min, and left to stand at room temperature for 1 h , to obtain MOF-AuNPs composite SERS substrate dispersion. As shown in Figure 2c.

Example 10:

A MOF-AuNPs composite SERS substrate for detecting the bioprobe molecule rhodamine 6G, the detection step is: take 0.5mL of different concentrations of R6G solution to be detected in a 1mL centrifuge tube, and then add 0.5mL of the MOF-AuNPs obtained in Example 8 Composite SERS base dispersion, invert up and down to make it evenly mixed. After standing still for 40 min, centrifuge at 4000 rpm, and take out 0.8 mL of the upper layer liquid. The remaining solid-liquid part was ultrasonicated for 3 seconds, so that the MOF-AuNPs composite particles adsorbed with R6G molecules were redispersed. Pipette 15 μL of the dispersion onto the silicon wafer. Raman detection was performed after the methanol evaporated. The wavelength of the Raman detection laser is 532nm, the power is 3mW, and the integration time is 10s. As shown in Figure 3. Of course, the MOF-noble metal nanocomposite SERS substrate obtained by other preparation methods (with different raw material ratios, concentrations and process conditions) can also be used to detect the bioprobe molecule rhodamine 6G by the above detection method.

Example 11:

A MOF-AuNPs composite SERS substrate detects polycyclic aromatic hydrocarbons-fluoranthene molecules, and the detection steps are:

Take 0.5mL of different concentrations of fluoranthene to be tested in a 1mL centrifuge tube, then add 0.5mL of the MOF-AuNPs composite SERS substrate dispersion obtained in Example 8, invert up and down to mix evenly. After standing still for 40min, centrifuge at 4000rpm, and take out 0.8mL upper layer liquid. The remaining solid-liquid part was ultrasonicated for 3 seconds, so that the MOF-Au composite particles adsorbed with fluoranthene molecules were redispersed. Pipette 15 μL of the dispersion onto the silicon wafer. Raman detection was performed after the methanol evaporated. The wavelength of the Raman detection laser is 532nm, the power is 3mW, and the integration time is 10s. As shown in Figure 4. Of course, MOF-noble metal nanocomposite SERS substrates obtained by other preparation methods (with different raw material ratios, concentrations, and process conditions) can also be used to detect polycyclic aromatic hydrocarbons-fluoranthene molecules through the above-mentioned detection method.

Claims (7)

1. A MOF-noble metal nanocomposite SERS substrate, characterized in that, in an alcoholic solution, the positively charged noble metal nanoparticles modified by CTAB are supported on the surface of the MOF material by electrostatic interaction to form a MOF-noble metal nanocomposite SERS substrate . 2 . A MOF-noble metal nanocomposite SERS substrate according to claim 1 , wherein the noble metal nanoparticles are gold nanoparticles, silver nanoparticles or gold-silver core-shell nanostructures. 3. A kind of MOF-noble metal nanocomposite SERS substrate according to claim 1, it is characterized in that, described MOF material is MIL-101 (Fe), MIL-101 (Cr) or MIL-100 (Fe). 4. A method for preparing a MOF-noble metal nanocomposite SERS substrate, characterized in that, comprising the following steps: (1) Preparation of AuNPs: quickly add sodium borohydride solution at 2-4 °C to the mixed solution of tetrachloroauric acid and CTAB, stir vigorously for 1 min, and stand at room temperature for 1 h to obtain gold seeds; Add CTAB, tetrachloroauric acid, and ascorbic acid to ultrapure water in turn to prepare a growth solution for use; dilute the gold seeds and add them to the growth solution and stir for 1 min, and let stand at room temperature for 6 h to obtain AuNPs; centrifuge the product, After washing with ultrapure water, disperse in methanol to form AuNPs dispersion; (2) Preparation of MOF-AuNPs composite particles: The MOF material and AuNPs dispersion were quickly mixed, stirred for 1 min, and left at room temperature for 1 h to obtain a MOF-AuNPs composite SERS substrate loaded with gold nanoparticles on the surface. 5. the preparation method of a kind of MOF-noble metal nanocomposite SERS substrate according to claim 4, is characterized in that, described MOF material is MIL-101 (Fe), MIL-101 (Cr) or MIL-100 ( Fe). 6. A method for preparing a MOF-noble metal nanocomposite SERS substrate according to any one of claims 1 to 3 and a kind of MOF-noble metal nanocomposite SERS substrate according to any one of claims 4 to 5. The application of the MOF-noble metal nanocomposite SERS substrate in the detection of polycyclic aromatic hydrocarbons. 7. The application according to claim 6, characterized in that, the polycyclic aromatic hydrocarbon organic matter is fluoranthene or naphthalene, phenanthrene.