CN102895938B - Preparation method of graphene covered silica gel - Google Patents

Abstract

The invention discloses a preparation method of a graphene-wrapped silica gel material. In the method, graphene oxide is firstly adsorbed on the surface of amino silica gel through electrostatic adsorption, and then subjected to hydrothermal reduction treatment to obtain a graphene-wrapped silica gel material. The preparation method of the material is simple, safe and environmentally friendly, and has good reproducibility. The material obtained by this preparation method has a high graphene content, and the prepared graphene-wrapped silica gel material has a higher adsorption capacity than the literature value as a solid-phase extraction (SPE) filler, and it is used to enrich bovine serum albumin (BSA) enzymatic digestion of peptides in solution and a desalting step for matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOFMS) analysis with good results.

Description

A kind of preparation method of graphene wrapped silica gel

technical field

The invention relates to a preparation method of a graphene-wrapped silica gel material, which belongs to the sample pretreatment technology.

Background technique

Graphene is a two-dimensional substance with a hexagonal honeycomb structure composed of a single layer of carbon atoms. Since it was first experimentally prepared in 2004, it has attracted widespread attention from scientists all over the world. Graphene has a large theoretical specific surface area (2630 m ² /g), so it can provide abundant adsorption sites; graphene is a substance rich in π-electron systems, which can generate π-electrons with substances containing benzene rings. π interaction; graphene has excellent thermal and mechanical stability; graphene is cheap to produce. These advantages make graphene an ideal enrichment material in sample pretreatment.

Solid phase extraction (SPE) has the advantages of high enrichment multiple, high recovery rate, less consumption of organic solvents, and low cost. It is a commonly used sample pretreatment technique. The excellent characteristics of graphene determine that it is an excellent SPE adsorbent. However, when pure graphene is directly used as SPE filler, the following problems will also be encountered: graphene will undergo irreversible agglomeration, resulting in a decrease in effective adsorption sites, which in turn will cause a decrease in adsorption capacity and difficulty in desorption; In actual application, it will be lost, which will cause the blockage of SPE small column and the decrease of extraction efficiency.

In order to solve the above problems while ensuring the excellent adsorption properties of graphene, graphene-silica gel composites are an effective solution. At present, there are two main methods for preparing graphene-silica gel composite materials reported in the literature: the first method is the sol-gel method of hydrolyzing silylating reagents in the presence of graphene, which can generate a A layer of silica gel matrix material; the second method is based on electrostatic adsorption or dehydration condensation reaction between graphene oxide and modified silica gel (such as amino silica gel), immobilizing graphene oxide on the surface of silica gel, and finally reducing graphene oxide. . However, in the material prepared by the first method, a large number of adsorption sites of graphene will be occupied by silica gel, resulting in a decrease in the adsorption capacity; in the composite material prepared by the second method, graphene is wrapped on the surface of silica gel, which can effectively solve the problem. However, the method reported in the literature not only has a long preparation period, but also uses toxic substances such as hydrazine in the reduction process of graphene oxide, which is not conducive to human health and does not meet the development requirements of green chemistry. More importantly, due to the harsh dehydration conditions during the reaction, the bonded amount of graphene in the final prepared material is low.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing graphene-wrapped silica gel which is mild, green and has high graphene content.

The technical scheme that the present invention adopts for solving the above-mentioned technical problems is: a kind of preparation method of graphene-wrapped silica gel material, preparation graphene oxide dispersion liquid and amino silica gel dispersion liquid; The concentration is 3.5~35 mg/mL, the concentration of graphene oxide is 0.5~2.5 mg/mL, stir the mixed solution for a stirring time ≥1 h; put the mixed solution into the reactor for hydrothermal reduction treatment, the hydrothermal temperature ≥ 200°C, hydrothermal time ≥ 2 h; Flotate the reaction product with an organic solvent to remove the graphene not wrapped on the silica gel, and obtain pure graphene-wrapped silica gel.

The hydrothermal temperature in the hydrothermal reduction treatment is 200-230°C, and the hydrothermal time is 2-3 h.

The stirring time of the mixture is 1~2 h.

The organic solvent is N-methyl-2-pyrrolidone or N,N-dimethylformamide.

In the process of preparing graphene-wrapped silica gel materials, graphene oxide is adsorbed on the surface of amino silica gel through electrostatic interaction, and then subjected to hydrothermal reduction treatment to obtain graphene-wrapped silica gel materials. After the graphene oxide is reduced, it will be adsorbed on the surface of the graphene-wrapped silica gel through the π-π stacking effect, which ensures that the content of graphene in the material prepared by this method is relatively high. Then, using the different densities of graphene-wrapped silica gel and graphene, the reaction product is floated with an organic solvent to remove the graphene not wrapped on the silica gel to obtain a pure graphene-wrapped silica gel material.

The preparation method provided by the invention is simple, quick, mild, green and has good reproducibility, and the prepared graphene-wrapped silica gel material not only has high graphene content, but also has good adsorption performance. The graphene-coated silica gel material was used for the enrichment of estrogen compounds and pentachlorophenol and the desalting step of MALDI-TOF MS analysis, and good results were obtained.

Description of drawings

Fig. 1 is the photo of the amino silica gel in embodiment 1, graphene oxide wrapping silica gel and the graphene wrapping silica gel prepared by two different methods, among the figure A is amino silica gel, B is graphene oxide wrapping silica gel, C is prior art In D, only the graphene-wrapped silica gel obtained by reducing the method of graphene oxide-wrapped silica gel material, D is the graphene-wrapped silica gel prepared by the present invention.

Fig. 2 is the scanning electron micrograph of the amino silica gel in embodiment 1, graphene oxide wrapping silica gel and the graphene wrapping silica gel prepared by two different methods, among the figure A is amino silica gel, B is graphene oxide wrapping silica gel, C is present In the prior art, only the graphene-wrapped silica gel obtained by reducing graphene oxide-wrapped silica gel, D is the graphene-wrapped silica gel prepared by the present invention.

Figure 3 is a comparison of the effect of graphene-wrapped silica gel and other commercial SPE fillers in enriching pentachlorophenol. In the figure, A is amino silica gel, and C is obtained by reducing graphene oxide-wrapped silica gel material in the prior art. Graphene-wrapped silica gel, CNTs is carbon nanotube, GCB is graphitized carbon black, C18 is C18 bonded silica gel, and D is graphene-wrapped silica gel prepared by the present invention.

Figure 4 is the determination of the adsorption of pentachlorophenol on graphene-coated silica gel C and graphene-coated silica gel D.

Figure 5 is a comparison of graphene-wrapped silica gel and other commercial SPE fillers in the enrichment of estrogen compounds. In the figure, A is amino silica gel, D is graphene-wrapped silica gel prepared by the present invention, C18 is C18 bonded silica gel, CNTs is carbon nanotubes, and GCB is graphitized carbon black.

Figure 6 is the determination of the adsorption capacity of estriol on amino silica gel and graphene-coated silica gel.

Figure 7 is the MALDI-TOF MS image of the peptides in the graphene-coated silica gel enriched bovine serum albumin BSA hydrolyzate, from top to bottom are the effect diagrams after direct analysis and enrichment of 10 nM BSA hydrolyzate.

Figure 8 is the effect diagram of graphene-coated silica gel used in the MALDI-TOF MS desalting step. From top to bottom, it is the effect diagram of direct analysis of 200 nM BSA enzymatic hydrolysis product, effluent and desalination.

Detailed ways

The present invention will be further described below by way of examples.

Example 1

(1) Preparation of graphene-coated silica gel

First prepare amino silica gel dispersion liquid with a concentration of 7.0 g/mL and graphene oxide dispersion liquid with a concentration of 2.0 g/mL, and then mix the two. After mixing, the concentrations of amino silica gel and graphene oxide are 3.5 g/mL and 1.0 g, respectively. /mL, stir the mixture for 2 h, put the mixture into the reaction kettle, react at 230 °C for 3 h, use N,N-dimethylformamide to float the reaction product, and remove the graphite not wrapped on the silica gel ene to obtain graphene-wrapped silica gel D (as shown in Figure 2).

(2) Comparison of materials prepared by the present invention and materials prepared by prior art

In order to compare with the method of reducing graphene oxide-wrapped silica gel material in the prior art, free graphene oxide is removed before thermal reduction, only graphene oxide-wrapped silica gel is thermally reduced, and graphene-wrapped silica gel material C is prepared. (As shown in Figure 2), the specific steps are: Mix the amino silica gel dispersion with a concentration of 7.0 g/mL prepared above and the graphene oxide dispersion with a concentration of 2.0 g/mL. After mixing, the concentrations of amino silica gel and graphene oxide were 3.5 g/mL and 1.0 g/mL, respectively, and the mixture was stirred for 2 h, and the free graphene oxide was removed by flotation with N,N-dimethylformamide. Finally, the pure graphene oxide-wrapped silica gel was put into the reactor and reacted at 230 °C for 3 h. Obtain graphene-wrapped silica gel material C. The above-mentioned graphene-coated silica gel C and graphene-coated silica gel D were washed with ethanol and dried at 60 °C. As shown in Figure 1, since graphene oxide is brown, compared with amino silica gel A, the color of graphene oxide-wrapped silica gel B is brown, indicating the existence of graphene oxide; while graphene-wrapped silica gel C and graphene The colors of the coated silica gel D are gray and black, respectively, indicating the presence of graphene. As shown in Figure 2, the surface of amino silica gel is smooth, and after adsorbing graphene oxide by electrostatic action, the surface of amino silica gel becomes rough, indicating that graphene oxide is successfully wrapped on the surface of amino silica gel; after thermal reduction, graphene is successfully wrapped on the surface of amino silica gel. Silicone exterior. It can be preliminarily judged from the scanning electron microscope that the content of graphene in graphene-wrapped silica gel D is higher than that of graphene-wrapped silica gel C. After elemental analysis, it can be calculated that the content of graphene oxide in graphene oxide-wrapped silicon B is 2.6%, and the content of graphene in graphene-wrapped silica gel C and graphene-wrapped silica gel D is 3.3% and 8.3%, respectively. The results of photographs, scanning electron microscopy and elemental analysis are mutually supportive, indicating that this method can prepare graphene-wrapped silica gel materials with high graphene content.

Example 2

Preparation of graphene-coated silica gel

First prepare amino silica gel dispersion liquid with a concentration of 7.0 g/mL and graphene oxide dispersion liquid with a concentration of 1.0 g/mL, and then mix the two. The concentrations of amino silica gel and graphene oxide in the mixed liquid are 3.5 g/mL and 0.5 g/mL respectively. g/mL, stir the mixture for 2 h, put the mixture into a reaction kettle, react at 230 °C for 3 h, use N,N-dimethylformamide to float the reaction product, and remove the uncoated silica gel Graphene, get graphene-coated silica gel.

Example 3

Preparation of graphene-coated silica gel

First prepare amino silica gel dispersion liquid with concentration of 7.0 g/mL and graphene oxide dispersion liquid with concentration of 5.0 g/mL, and then mix them. After mixing, the concentrations of amino silica gel and graphene oxide were 3.5 g/mL and 2.5 g/mL, respectively, and the mixture was stirred for 1 h. Put the mixture into the reactor and react at 230 °C for 3 h. The reaction product is then floated with N,N-dimethylformamide to remove the graphene not wrapped on the silica gel to obtain the graphene-wrapped silica gel.

Example 4

Preparation of graphene-coated silica gel

First prepare amino silica gel dispersion with concentration of 70 g/mL and graphene oxide dispersion with 2.0 g/mL, and then mix them. After mixing, the concentrations of amino silica gel and graphene oxide were 35 g/mL and 1.0 g/mL, respectively, and the mixture was stirred for 1 h. Put the mixture into the reactor and react at 230 °C for 3 h. The reaction product is then floated with N,N-dimethylformamide to remove the graphene not wrapped on the silica gel to obtain the graphene-wrapped silica gel.

Example 5

Preparation of graphene-coated silica gel

First prepare amino silica gel dispersion with concentration of 7.0 g/mL and graphene oxide dispersion with 2.0 g/mL, and then mix them. After mixing, the concentrations of amino silica gel and graphene oxide were 3.5 g/mL and 1.0 g/mL, respectively, and the mixture was stirred for 2 h. Put the mixture into the reactor and react at 200 °C for 2 h. Then, the reaction product is floated with N-methyl-2-pyrrolidone to remove the graphene not wrapped on the silica gel to obtain the graphene-wrapped silica gel.

Example 6

Comparison of graphene-wrapped silica gel as SPE filler and other commercial SPE fillers in the enrichment of pentachlorophenol

The prepared graphene-coated silica gel was washed with ethanol and dried at 60 °C. 20 mg of graphene-coated silica gel filler was filled into an empty SPE column tube, and then the filler was activated and equilibrated with 3 mL of acetonitrile and 3 mL of water in sequence. Pass 5 mL of 50 ng/mL pentachlorophenol standard aqueous solution through the SPE packing, and desorb with 1 mL of desorption solution. The desorption solution of C18 bonded silica gel (C18) filler is 1 mL methanol, and the rest is 1 mL alkalized methanol. Add 1.5 mL1 M NaOH solution to 50 mL methanol to obtain alkalized methanol. All SPE steps rely on gravity to move the solution. Before high-performance liquid chromatography-ultraviolet (HPLC-UV) analysis, neutralize the base in the stripping solution with 30 μl of 1 M HCl. HPLC-UV conditions: the mobile phase is acetonitrile/20 mM phosphate buffer at pH 2.5 (v/v, 80/20), the flow rate is 1.0 mL/min, and the chromatographic column is HiSep C18 (250 mm × 4.6 mm i.d., 5 μm ), the column temperature was 40°C, and the UV detection wavelength was 300 nm. As shown in Figure 3, it can be seen that the extraction effect of the prepared material on pentachlorophenol is better than other commercialized materials.

Example 7

Determination of the adsorption capacity of pentachlorophenol by graphene-wrapped silica gel as SPE filler

Different volumes of 0.2 μg/mL pentachlorophenol solutions passed sequentially through the SPE column equipped with 20 mg graphene-wrapped silica gel filler, and the amount of the target substance adsorbed by the material was calculated by measuring the content of pentachlorophenol in the effluent. The data were fitted with the Langmuir model, and the adsorption capacities of the two graphene-coated silica gels for pentachlorophenol were 781.5 μg/g and 286.3 μg/g, respectively. Due to the improvement of the graphene bonding amount, the adsorption capacity of the graphene-wrapped silica gel D to pentachlorophenol is 2.7 times that of the graphene-wrapped silica gel C obtained by reducing the graphene oxide-wrapped silica gel material in the prior art. As shown in Figure 4.

Example 8

Comparison of graphene-encapsulated silica gel as SPE filler and other commercial SPE fillers in enriching estrogen compounds

The prepared graphene-coated silica gel was washed with ethanol, dried at 60 °C, and 20 mg of graphene-coated silica gel filler was filled into an empty SPE column tube, and then the filler was activated and equilibrated with 3 mL of acetonitrile and 3 mL of water in sequence. Pass 5 mL of 50 ng/mL standard aqueous solution of estrogen compounds through the SPE packing, desorb with 1 mL of acetonitrile, blow dry the desorbed solution with mild _N2 at 35 °C, and dissolve it with 0.1 mL of mobile phase, then perform HPLC- UV analysis. All SPE steps rely on gravity to move the solution. HPLC-UV conditions: the mobile phase is acetonitrile/water (v/v, 48/52), the flow rate is 1.0 mL/min, the chromatographic column is HiSep C18 (250 mm × 4.6 mm id, 5 μm), the column temperature is 40°C, The UV detection wavelength is 280 nm. It can be seen that the extraction effect of the prepared material on estrogen compounds is better than other commercialized materials. As shown in Figure 5.

Example 9

Determination of the adsorption capacity of estriol on graphene-coated silica gel and amino silica gel as SPE fillers

Different volumes of 0.2 μg/mL estriol solutions passed sequentially through the SPE cartridges equipped with 20 mg adsorbent, and the amount of the target substance adsorbed by the material was calculated by measuring the content of estriol in the effluent. The data were fitted with the Langmuir model, and the adsorption capacities of amino silica gel and graphene-coated silica gel for estriol were 25.1 μg/g and 104.1 μg/g, respectively. As shown in Figure 6.

Example 10

Graphene-coated silica gel used as SPE filler to enrich peptides in bovine serum albumin BSA hydrolyzate

The prepared graphene-coated silica gel was washed with ethanol, dried at 60 °C, and 20 mg of graphene-coated silica gel filler was filled into an empty SPE column tube, and then the filler was activated and desorbed with 1 mL of desorption solution and 2 mL of water in sequence. Equilibrium, the desorption solution is 0.1% trifluoroacetic acid aqueous solution/acetonitrile mixture (v/v, 20/80), pass 4 mL of 10 nmol/L bovine serum albumin BSA enzymatic hydrolysis solution through the SPE packing, and wash with 1 mL of water , and finally desorbed with 0.5 mL of desorption solution. All SPE steps rely on gravity to move the solution. Spin 20 μL of desorbed liquid to dryness in vacuum, and dissolve it with 2 μL matrix solution, which is α-cyano-4-hydroxycinnamic acid (CHCA) dissolved in 0.1% trifluoroacetic acid aqueous solution/acetonitrile (v/v, 50/ 50) In the mixed solution, make the concentration of CHCA 2 mg/mL. Then it was dropped on the MALDI target plate, and then MALDI analysis was carried out after drying at room temperature. Submitting the MALDI data to the short-range MASCOT server (Matrix Science, London, UK) for database searching retrieved 24 peptide signals. As shown in Figure 7.

Example 11

Graphene-coated silica gel as SPE packing for MALDI-TOF MS desalting step

The prepared graphene-coated silica gel was washed with ethanol, dried at 60 °C, and 20 mg of graphene-coated silica gel packing was filled into an empty SPE column tube, and then the packing was sequentially activated and desorbed with 1 mL of desorption solution and 2 mL of water. Equilibrium, the desorption solution is 0.1% trifluoroacetic acid aqueous solution/acetonitrile mixture (v/v, 20/80). Pass 0.5 mL of bovine serum albumin BSA hydrolyzate with a concentration of 200 nmol/L through the SPE filler. Wash with 2 mL of water, and finally desorb with 0.5 mL of desorption solution. All SPE steps rely on gravity to move the solution. Spin 20 μL of desorbed liquid to dryness in vacuum, and dissolve it with 2 μL matrix solution, which is α-cyano-4-hydroxycinnamic acid (CHCA) dissolved in 0.1% trifluoroacetic acid aqueous solution/acetonitrile (v/v, 50/ 50) In the mixed solution, make the concentration of CHCA 2 mg/mL. Then it was dropped on the MALDI target plate, and then MALDI analysis was carried out after drying at room temperature. Due to the presence of a large amount of salt in the sample solution, the ionization signal of the target will be suppressed during MALDI analysis. No peptide signal is observed in the effluent, and the number of peptide signals observed in the desorption solution is not only more than that in the sample solution. Moreover, the signal intensity has also increased, indicating that the material prepared by the present invention has a good application in the desalting step of MALDI-TOF MS analysis. As shown in Figure 8.

Claims (5)

1. a preparation method of graphene-wrapped silica gel material, is characterized in that: prepare graphene oxide dispersion liquid and amino silica gel dispersion liquid; Two dispersion liquids are mixed, and the concentration of amino silica gel in the mixed solution is 3.5～35 mg/mL, The concentration of graphene oxide is 0.5~2.5 mg/mL, and the mixed solution is stirred for ≥1 h; the mixed solution is put into the reaction kettle for hydrothermal reduction treatment, the hydrothermal temperature is ≥200°C, and the hydrothermal time is ≥2 h ; The reaction product is carried out by flotation with an organic solvent to remove the graphene not wrapped on the silica gel to obtain pure graphene-wrapped silica gel. 2. the preparation method of a kind of graphene-wrapped silica gel material according to claim 1, is characterized in that: the hydrothermal temperature in described hydrothermal reduction treatment is 200～230 ℃, and hydrothermal time is 2～3 h . 3. the preparation method of a kind of graphene-wrapped silica gel material according to claim 1 or 2, is characterized in that: the stirring time of described mixed solution is 1～2 h. 4. the preparation method of a kind of graphene-wrapped silica gel material according to claim 1 or 2, is characterized in that: described organic solvent is N-methyl-2-pyrrolidone or N,N-dimethylformamide . 5. The preparation method of a graphene-wrapped silica gel material according to claim 3, characterized in that: the organic solvent is N-methyl-2-pyrrolidone or N,N-dimethylformamide.