CN109916973B - Ball-milled graphene-MOFs composite material, and preparation and application thereof - Google Patents
Ball-milled graphene-MOFs composite material, and preparation and application thereof Download PDFInfo
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Abstract
The invention belongs to the field of nano material technology and electrochemical sensors, and particularly relates to a ball-milled graphene-Metal Organic Framework (MOFs) composite material, a preparation method thereof and application thereof in an electrochemical sensor. The graphene is a large graphene nanosheet prepared by ball milling and stripping, and the metal organic framework is uniformly dispersed on the surface of the graphene nanosheet. The preparation method comprises the following steps: (1) preparing a graphene nanosheet (2) by wet ball milling and stripping, fully adsorbing metal ions on the surface of the graphene nanosheet (3), and growing a metal organic framework in situ on the surface of the graphene by combining an organic ligand. Finally, the ball-milled graphene-metal organic framework compound with good stability and conductivity, large specific surface area and high porosity is obtained. The ball-milled graphene-metal organic framework composite prepared by the method is excellent in electrochemical performance and can be used for preparing a high-sensitivity electrochemical sensing platform.
Description
Technical Field
The invention belongs to the field of nano material technology and electrochemical sensors, and particularly relates to a ball-milled graphene-Metal Organic Framework (MOFs) composite material, a preparation method thereof and application thereof in the field of electrochemical sensing.
Background
In recent years, Metal-organic frameworks (MOFs for short) have been widely used in the field of electrochemical sensing due to their advantages such as large porosity and specific surface area, adjustable pore size, and variable functional groups. However, the practical application and future development of MOFs are limited due to their own instability and poor conductivity. In order to solve the problem, it has become a popular direction for research to construct a composite material of the MOFs and other materials to improve the stability, adsorption performance and conductivity of the MOFs. To date, various materials have been reported to be used for the composite MOFs to improve their electrochemical properties, such as metal particles/nanorods, quantum dots, high molecular conductive polymers, carbon nanotubes, porous carbon, and the like.
With the development of graphene research, the graphene-based MOFs compound draws wide attention of people, and the synthetic composite material can make up the respective defects of the materials, realize advantage complementation and effectively improve the sensing performance. However, most of the existing graphene-based MOFs compounds adopt graphene oxide or reduced graphene oxide as substrate-supported MOFs, and such graphene is prepared by using a chemical oxidation-reduction method, which has many inherent disadvantages, such as the use of a large amount of toxic chemical reagents, a complicated preparation process and risks in the operation process.
Disclosure of Invention
Aiming at the defects or improvement requirements in the prior art, the invention provides a ball-milled graphene-metal organic framework composite material, a preparation method thereof and application thereof in the field of electrochemical sensing.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method for preparing a graphene-MOFs composite, comprising the steps of:
(1) stripping graphite powder by adopting a wet ball milling method, wherein the shearing force is dominant in the ball milling stripping process to obtain a mixed system containing graphene nanosheets;
(2) removing non-peeled graphite flakes in the mixed system containing the graphene nanosheets obtained in the step (1) by adopting a gradient centrifugal separation method to obtain graphene nanosheet solids;
(3) mixing metal salt dispersed in an organic solvent with the graphene nanosheets obtained in the step (2), and stirring to enable metal ions in the metal salt to be adsorbed on the graphene nanosheets to obtain metal ion-loaded graphene nanosheets;
(4) and (4) mixing the metal ion loaded graphene nanosheets obtained in the step (3) with an organic ligand, and promoting in-situ synthesis of MOFs on the surface of the graphene nanosheets under the auxiliary action of an alkali source, so as to finally obtain the graphene-MOFs composite material.
Preferably, a surfactant is also adopted in the wet ball milling process for improving the stripping efficiency of graphite in the ball milling process; the surfactant is an anionic surfactant, a cationic surfactant or a nonionic surfactant.
Preferably, the surfactant is cetyltrimethylammonium bromide.
Preferably, the mass ratio of the graphite powder and the surfactant in the step (1) is 3:1 to 1: 3.
Preferably, in the step (1), the graphite powder is dispersed in an ethanol aqueous solution for wet ball milling, the ball milling rotation speed is controlled to ensure that the shearing force is dominant in the ball milling process, and the ball milling time is not less than 12 hours.
Preferably, the gradient centrifugation separation method in step (2) is specifically: firstly, primarily separating and taking out graphite powder precipitate which is not completely stripped through centrifugation at 500-2000 rpm for 5-45 minutes, and then further obtaining graphene nanosheet solid through centrifugation at 8000-12000 rpm for 5-45 minutes.
Preferably, the metal salt in step (3) is Cu (NO)3)2·3H2O、Ni(NO3)2·6H2O、Zn(NO3)2·6H2O、Co(NO3)2·6H2One or more of O; the organic solvent is N, N-dimethylformamide, methanol or an aqueous solution of methanol.
Preferably, the mass ratio of the metal salt to the graphene nanoplatelets in the step (3) is 10:1-20:1, and the stirring time is 0.1 to 2 hours.
Preferably, the organic ligand in the step (4) is one or more of 1, 4-terephthalic acid, 1, 3, 5-trimesic acid and 2-methylimidazole.
Preferably, the alkali source is a mixed solution of triethylamine/N, N-dimethylformamide, wherein the volume concentration of triethylamine in the mixed solution is 1%, and 1 to 10 ml of alkali source is added per gram of organic ligand.
According to another aspect of the invention, the ball-milled graphene/MOFs modified electrochemical sensor comprises an electrode and an active ingredient positioned on the surface of the electrode, wherein the active ingredient is the graphene-MOFs composite material prepared by the preparation method.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) according to the invention, ball-milled graphene is used as a substrate, metal ions are directly adsorbed, and then metal ion sites are adsorbed on a graphene nanosheet to grow the MOFs in situ, the existence of the graphene can effectively reduce the agglomeration of the MOFs, the dispersibility of the MOFs is improved, the MOFs with uniform size and distribution are obtained, and thus, the property uniformity, the stability and the recycling performance of the composite material are greatly improved.
(2) The graphene is prepared by adopting a wet ball milling method, which is different from graphene synthesized by an oxidation-reduction method, so that the use of harmful reagents in synthesis is avoided, the method is safer, simpler and more convenient, and the mass production of the graphene can be realized with potential.
(3) The synthesis reaction of the ball-milled graphene/MOFs composite material is carried out at room temperature (20-30 ℃), the reaction period is short, the cost is greatly reduced, and the large-scale production is facilitated.
(4) The ball-milled graphene/MOFs compound prepared by the invention has good electrochemical reaction activity, and the high-sensitivity electrochemical sensor is prepared based on the compound, can detect trace Xanthine (XA), Hypoxanthine (HXA), bisphenol A (BPA) and parachlorophenol (CP), does not need excessive sample pretreatment, separation and purification, and is more suitable for actual sample analysis. The detection limits for XA, HXA, BPA and CP were 0.0011, 0.0073, 0.0012 and 0.0019 milligrams per liter, respectively, based on the triple signal-to-noise ratio.
(5) The ball-milled graphene/MOFs modified electrochemical sensor provided by the invention is simple in preparation method, low in cost, good in practical prospect as online monitoring and strong in practicability.
Drawings
FIG. 1 is a scanning electron micrograph of exfoliated ball-milled graphene according to the method of example 1;
FIG. 2 is a scanning electron micrograph of ball-milled graphene/Cu-BTC prepared according to the method of example 1;
FIG. 3 is a transmission electron micrograph of ball-milled graphene/Cu-BTC prepared according to the method of example 1;
FIG. 4 is a simulated Cu-BTC (d) XRD pattern for ball-milled graphene prepared by the method of example 1 (a), ball-milled graphene prepared by comparative example 1 (b), Cu-BTC prepared by comparative example 2 (c), and Cu-BTC prepared by example 1;
FIG. 5 is a thermogravimetric analysis plot of ball-milled graphene/Cu-BTC prepared by the method of example 1, wherein (a) is the ball-milled exfoliated graphene of comparative example 1, (b) is the ball-milled graphene/Cu-BTC of example 1, and (c) is the Cu-BTC of comparative example 2;
fig. 6 is a nitrogen sorption and desorption curve of the ball-milled graphene/Cu-BTC and the ball-milled graphene prepared by the method of example 1, wherein curve a is the ball-milled graphene/Cu-BTC of example 1, and curve b is the ball-milled graphene of comparative example 1;
FIG. 7 is a graph of heterogeneous electron transfer rate constants of a bare glassy carbon electrode calculated using NADH as a probe and of ball-milled graphene/Cu-BTC prepared by the method of example 1, wherein (a) is the bare glassy carbon electrode, (b) is the ball-milled exfoliated graphene nanosheet modified electrode of comparative example 1, (c) is the Cu-BTC modified electrode of comparative example 2, and (d) is the ball-milled graphene/Cu-BTC modified electrode of example 1;
FIG. 8 is a differential pulse plot obtained with XA and HXA (a), BPA (b), and CP (c) substances as probes, where plot a is the ball-milled graphene/Cu-BTC modified electrode of example 1, plot b is the ball-milled exfoliated graphene nanoplatelet modified electrode of comparative example 1, plot c is the Cu-BTC modified electrode of comparative example 2, and plot d is a bare glassy carbon electrode;
FIG. 9 is a graph comparing the response signals of the ball-milled graphene/Cu-BTC modified electrode of example 1 with differential pulse voltammetry for XA (a), HXA (b), BPA (c), and CP (d).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a preparation method of a ball-milled graphene-MOFs composite material, which comprises the following steps:
(1) stripping graphite powder by adopting a wet ball milling method, wherein the shearing force is dominant in the ball milling stripping process to obtain a mixed system containing graphene nanosheets;
(2) removing the graphite which is not peeled in the mixed system containing the graphene nanosheets obtained in the step (1) by adopting a gradient centrifugal separation method to obtain graphene nanosheet solids;
(3) mixing metal salt dispersed in an organic solvent with the graphene nanosheets obtained in the step (2), and stirring to enable metal ions in the metal salt to be adsorbed on the graphene nanosheets to obtain metal ion-loaded graphene nanosheets;
(4) and (4) mixing the metal ion loaded graphene nanosheets obtained in the step (3) with an organic ligand, and promoting the in-situ synthesis of MOFs on the surfaces of the graphene nanosheets under the auxiliary action of an alkali source, so as to finally obtain the graphene-MOFs composite material.
Theoretically, the finer the particle size of the graphite powder is, the more beneficial the graphite powder is to wet ball milling and stripping to obtain the graphene nanosheet. Taking the stripping efficiency and cost into consideration, the graphite powder with medium granularity, such as 1200 meshes, is generally used.
In some embodiments, a surfactant is further used in the wet ball milling process to improve the stripping efficiency of graphite in the ball milling process; the surfactant is an anionic surfactant, a cationic surfactant or a nonionic surfactant, and is preferably cetyl trimethyl ammonium bromide.
In some embodiments, the graphite powder and the surfactant are present in a mass ratio of 3:1 to 1: 3.
In some embodiments, the graphite powder is dispersed in the ethanol aqueous solution for wet ball milling in step (1), the ball milling speed is controlled to ensure that the shearing force is dominant in the ball milling process, the ball milling time is not less than 12 hours, and the ball milling speed is not less than 300 r/min.
In some embodiments, the gradient centrifugation method in step (2) is specifically: the gradient centrifugal separation method in the step (2) comprises the following specific steps: firstly, primarily separating and taking out graphite powder precipitate which is not completely stripped through centrifugation at 500-2000 rpm for 5-45 minutes, and then further centrifuging at 8000-12000 rpm for 5-45 minutes to obtain the graphene nanosheet solid. And further cleaning the solid to remove residual surfactant, and drying in an oven to obtain the final ball-milled graphene nanosheet.
In some embodiments, the metal salt in step (3) is Cu (NO)3)2·3H2O、Ni(NO3)2·6H2O、Zn(NO3)2·6H2O、Co(NO3)2·6H2One or more of O; the organic solvent is N, N-dimethylformamide, methanol or an aqueous solution of methanol.
In some embodiments, the mass ratio of the metal salt to the graphene nanoplatelets of step (3) is 10:1-20:1, the stirring time is from 0.1 to 2 hours, preferably from 0.2 to 0.4 hour. According to the preparation method, when the graphene-MOFs composite material is prepared, after the graphene nanosheets are prepared, firstly, an organic solution of metal salt and graphene are mixed and stirred for a period of time, so that metal ions are fully adsorbed and compounded on the surfaces of the graphene nanosheets, the adsorption compounding time has a large influence on the performance of the finally prepared graphene-MOFs composite material, and in experiments, proper stirring time is preferably controlled within 0.1-2 hours, and the preferable stirring compounding time is 0.2-0.4 hour.
In some embodiments, the organic ligand of step (4) is one or more of 1, 4-terephthalic acid, 1, 3, 5-trimesic acid, and 2-methylimidazole.
In some embodiments, the base source is a mixed solution of triethylamine/N, N-dimethylformamide, wherein the volume concentration of triethylamine in the mixed solution is 1%, and 1 to 10 ml of base source is added per gram of organic ligand.
In some embodiments, step (4) is specifically: and (3) mixing the composite system of the graphene nanosheets and the metal salt obtained in the step (3) with an organic ligand, slowly dropwise adding an alkali source into the system, promoting the in-situ synthesis of MOFs on the surface of the graphene nanosheets under the auxiliary action of the alkali source, and controlling the in-situ synthesis time to be not shorter than 5 minutes after the dropwise adding is completed, so as to finally obtain the graphene-MOFs composite material. The longer the in-situ synthesis reaction time in the step is, the larger the MOFs particles in the obtained composite material are, and the suitable reaction time is 5-90 minutes.
The invention also provides a ball-milled graphene/MOFs modified electrochemical sensor which comprises an electrode and an active ingredient positioned on the surface of the electrode, wherein the active ingredient is the graphene-MOFs composite material prepared by the preparation method. The electrochemical sensor is obtained by the following method: dispersing the prepared graphene-MOFs composite material solid in an organic solvent to obtain ball-milled graphene/MOFs suspension; and coating the suspension on the surface of an electrode of an electrochemical sensor, and volatilizing an organic solvent to obtain the ball-milled graphene/MOFs modified electrochemical sensor. Wherein the organic solvent can be N, N-dimethylformamide, water, ethanol or N-methylpyrrolidone.
Different from the chemical oxidation-reduction method for preparing graphene, the physical stripping method is a method for preparing graphene which is efficient, simple, convenient, mild and effective. Ball-milling exfoliation is a physical exfoliation method. The ball milling method simultaneously considers the high efficiency of production and the good quality of the obtained graphene, and is an ideal method for preparing the graphene. Meanwhile, compared with graphene oxide or reduced graphene oxide, the ball-milled exfoliated graphene is proved to have more excellent electrochemical sensing activity. The use of toxic reagents and dangerous operation processes in the synthesis process can be avoided by in-situ compounding of the ball-milled graphene and the MOFs, and the method for preparing the graphene-based MOFs is simpler, more convenient and safer. The compounded material has the advantages of graphene and MOFs, and can be effectively applied to construction of electrochemical sensing platforms.
In the synthesis method of the ball-milled graphene-metal organic framework composite material, the graphene is a large graphene nanosheet prepared by ball-milling stripping, and the metal organic framework is uniformly dispersed on the surface of the graphene nanosheet. The preparation method comprises the following steps: (1) preparing graphene nanosheets by wet ball milling and stripping; (2) fully adsorbing metal ions on the surface of the graphene nanosheet; (3) and (3) growing a metal organic framework on the surface of the graphene in situ by combining an organic ligand. Finally, the ball-milled graphene-metal organic framework compound with good stability and conductivity, large specific surface area and high porosity is obtained.
According to the method, metal salt and the graphene nanosheet obtained by stripping through a ball milling method are mixed for a period of time, so that metal ions in the metal salt are fully adsorbed on the surface of the graphene nanosheet, and then an organic ligand and an alkali source are added, so that a metal organic framework is synthesized in situ at the adsorption sites on the surface of the graphene nanosheet. The in-situ synthesis method can effectively reduce the agglomeration of MOFs by means of the existence of graphene, improve the dispersibility of the MOFs, and obtain the MOFs with uniform size and distribution, thereby greatly improving the property uniformity, stability and recycling performance of the composite material.
According to the invention, the synthesis idea and the synthesis process are adjusted, so that the room-temperature synthesis of the ball-milled graphene-metal organic framework composite material is realized, and the synthesis process is simple.
The ball-milled graphene-metal organic framework composite prepared by the method is excellent in electrochemical performance and can be used for preparing a high-sensitivity electrochemical sensing platform.
The electrode used in the electrochemical sensor of the present invention is a conventional electrode, such as a commonly used glassy carbon electrode.
In some embodiments, a glassy carbon electrode includes a glassy carbon electrode head, an electrode sheath, and a copper rod-shaped wire; the glassy carbon electrode tip is hermetically encapsulated in the electrode jacket and is positioned in the center of the cylindrical electrode jacket, one end of the surface of the glassy carbon electrode tip and one end of the electrode jacket are positioned on the same plane, the other end of the surface of the glassy carbon electrode tip is connected with the copper rod-shaped lead, and the copper rod-shaped lead extends to the outer end of the electrode jacket.
The ball-milled graphene/MOFs modified electrochemical sensor, and the preparation and application thereof provided by the invention have the following technical advantages:
(1) the preparation method is safe and simple
The graphene is obtained by physically stripping graphite powder in an ethanol/water mixed solution by a wet ball milling method, and toxic reagents and complex and dangerous experimental operations are not involved. Meanwhile, MOFs grows in situ on the surface of the obtained graphene at room temperature, and the compound with the MOFs uniformly loaded on the ball-milled graphene is obtained.
(2) High sensitivity
Due to the good conductivity and electrochemical reaction activity of the obtained ball-milled graphene/MOFs, the high-sensitivity electrochemical sensor is prepared. The detection limits for XA, HXA, BPA and CP were 0.0011, 0.0073, 0.0012 and 0.0019 milligrams per liter, respectively, based on the triple signal-to-noise ratio.
(3) The analysis speed is high
The liquid chromatography method needs about half an hour for detecting a sample, the sensor can be used for simultaneously and directly detecting the sample, the analysis time of the whole sample is about 2 minutes, and the requirement of on-site rapid monitoring is met.
(4) High practicability
The sensor can detect simultaneously during detection, does not need excessive sample pretreatment and separation and purification, is more suitable for detection of actual samples, and has the advantages of simple preparation method, low cost, good practical prospect as online monitoring and strong practicability.
Therefore, compared with the traditional detection methods such as a chromatography-mass spectrometry method and the like, the electrochemical sensor developed by the method has the advantages of high sensitivity, rapidness, environmental friendliness, simplicity in operation, high accuracy and strong practicability.
The following are examples:
example 1
A preparation method of a ball-milled graphene/Cu-BTC composite material comprises the following steps:
dispersing 300 mg of 1200-mesh graphite powder and 300 mg of hexadecyl trimethyl ammonium bromide powder in 30 ml of aqueous solution containing 15% ethanol, controlling the ball milling rotation speed to be 300 revolutions per minute to ensure that the shearing force is dominant in the ball milling process, and performing ball milling reaction for 12 hours, and then obtaining the graphene nanosheet mixed solution through ball milling stripping.
The mixed solution was centrifuged at 2000 rpm for 20 minutes to remove the incompletely exfoliated graphite powder precipitate. The resulting solution was centrifuged at 9000 rpm for 20 minutes to give a solid, the solid was repeatedly washed with ethanol and ultrapure water to remove residual cetyltrimethylammonium bromide, and finally air-dried at 60 ℃.
0.7 g of Cu (NO)3)2·3H2O is uniformly dispersed in 50 ml of DMF solution, then 50 mg of ball-milled graphene powder is added, and after stirring for 0.5 hour, 0.42 g of H is directly added3BTC. Then, 1 ml of a mixed solution of triethylamine/DMF in which the concentration of triethylamine in the mixed solution was 1% (v/v) was dropped into the above mixed solution, and after stirring was continued for 0.5 hour, the resulting complex was collected by centrifugation, and the resulting solid was repeatedly washed 3 times with ethanol and ultrapure water, and finally air-dried at 30 ℃ for 24 hours. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a ball milled graphene/Cu-BTC suspension.
A preparation method of an electrochemical sensor modified by ball-milled graphene/Cu-BTC composite material comprises the following steps:
and polishing the glassy carbon electrode by using 0.05 micron aluminum oxide powder until the surface of the glassy carbon electrode presents a smooth mirror surface, and then ultrasonically cleaning the glassy carbon electrode by using ethanol and water. And dropwise coating the obtained dispersion liquid of the ball-milled graphene/Cu-BTC compound on the surface of a clean electrode, and volatilizing a dry solvent under an infrared lamp to obtain the ball-milled graphene/Cu-BTC modified electrochemical sensing membrane. Glassy carbon electrodes were purchased from warhan guosri co-technologies ltd. The glassy carbon electrode tip has a diameter of 3 mm and a length of 4 mm. The jacket material is polytetrafluoroethylene. The diameter of the copper rod-shaped lead is 1 mm, one section of the copper rod-shaped lead is connected with the glassy carbon, and the other end of the copper rod-shaped lead extends out of the bottom of the electrode jacket.
Comparative example 1
A preparation method of ball-milled graphene comprises the following steps:
dispersing 300 mg of 1200-mesh graphite powder and 300 mg of hexadecyl trimethyl ammonium bromide powder in 30 ml of aqueous solution containing 15% ethanol, controlling the ball milling rotation speed to be 300 revolutions per minute to ensure that the shearing force is dominant in the ball milling process, and performing ball milling reaction for 12 hours, and then obtaining the graphene nanosheet mixed solution through ball milling stripping. The mixed solution was centrifuged at 2000 rpm for 20 minutes to remove the incompletely exfoliated graphite powder precipitate. The resulting solution was centrifuged at 9000 rpm for 20 minutes to give a solid, the solid was repeatedly washed with ethanol and ultrapure water to remove residual cetyltrimethylammonium bromide, and finally air-dried at 60 ℃. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a ball-milled graphene suspension.
Comparative example 2
A preparation method of Cu-BTC comprises the following steps:
0.7 g of Cu (NO)3)2·3H2O is uniformly dispersed in 50 ml of DMF solution, and after stirring for 0.5 hour, 0.42 g of H is directly added3BTC. Then, 1 ml of 1% (v/v) triethylamine/DMF was slowly dropped into the above mixed solution, and after stirring was continued for 0.5 hour, the resulting complex was collected by centrifugation, and the resulting solid was repeatedly washed 3 times with ethanol and ultrapure water, and finally air-dried at 30 ℃ for 24 hours. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a Cu-BTC suspension.
Fig. 1 is a scanning electron microscope image of ball-milled graphene peeled by the method in example 1, and it can be seen from the scanning electron microscope image that the obtained ball-milled graphene is a graphene nanosheet with a planar size reaching a micron level, and the micron-level large size of the ball-milled graphene is favorable for serving as a metal-organic framework for in-situ growth on the surface of a load substrate.
FIG. 2 is a scanning electron micrograph of ball-milled graphene/Cu-BTC prepared by the method of example 1, from which it can be seen that Cu-BTC nanoparticles having a diameter of about 30 nm are uniformly distributed on the graphene.
Fig. 3 is a transmission electron microscope image of ball-milled graphene/Cu-BTC prepared by the method of example 1, from which it can be seen that graphene has a lamellar structure on which Cu-BTC nanoparticles are uniformly supported.
Fig. 4 is XRD patterns of ball-milled graphene/Cu-BTC (a) prepared by the method of example 1, ball-milled graphene (b) prepared in comparative example 1, Cu-BTC (c) prepared in comparative example 2, and simulated Cu-BTC (d), from which it can be seen that the ball-milled graphene/Cu-BTC composite was successfully synthesized.
Fig. 5 is a thermogravimetric analysis plot of ball-milled graphene/Cu-BTC prepared by the method of example 1, wherein (a) is the ball-milled exfoliated graphene of comparative example 1, (b) is the ball-milled graphene/Cu-BTC of example 1, and (c) is the Cu-BTC of comparative example 2, the calculated weight fractions of the resultant Cu-BTC and ball-milled graphene nanoplatelets being about 63.11% and 36.98%, respectively.
Fig. 6 is a nitrogen adsorption and desorption curve of the ball-milled graphene/Cu-BTC and the ball-milled graphene prepared by the method of example 1, wherein a curve a is the ball-milled graphene/Cu-BTC of example 1, and a curve b is the ball-milled graphene of comparative example 1, and it can be seen from the figure that the adsorption capacity is greatly improved by the introduction of Cu-BTC.
FIG. 7 shows that the electron transfer rate constants of the heterogeneous phase calculated by rotating the disc electrode with nicotinamide adenine dinucleotide as a probe are (a) a bare glassy carbon electrode, (b) a ball-milled exfoliated graphene nanosheet modified electrode of comparative example 1, (c) a Cu-BTC modified electrode of comparative example 2, and (d) a ball-milled graphene/Cu-BTC modified electrode of example 1, and the structure shows that the ball-milled graphene/Cu-BTC has the optimal electrocatalytic capacity.
FIG. 8 is a differential pulse curve obtained by probing XA and HXA (a), BPA (b), and CP (c) substances, wherein curve a is the ball-milled graphene/Cu-BTC modified electrode of example 1, curve b is the ball-milled exfoliated graphene nanosheet modified electrode of comparative example 1, curve c is the Cu-BTC modified electrode of comparative example 2, curve d is a bare glassy carbon electrode, and the structure shows that the ball-milled graphene/Cu-BTC has optimal electrochemical reaction capability.
FIG. 9 is a graph comparing the response signals of the ball-milled graphene/Cu-BTC modified electrode of example 1 with differential pulse voltammetry for XA (a), HXA (b), BPA (c), and CP (d).
A common three-electrode system is adopted, an electrochemical sensor probe modified by ball-milled graphene/Cu-BTC is used as a working electrode, a saturated calomel electrode is used as a reference electrode, a platinum column electrode is used as a counter electrode, and an electrochemical workstation and a computer are connected to collect and record experimental data.
The electrochemical sensor prepared by the preparation method is used for detecting XA, HXA, BPA and CP.
The practical application is as follows: differential pulse voltammetry was used to detect the response signals of XA, HXA, BPA and CP with sufficient agitation. The medium was 10.0 ml of 0.1 mol per liter of phosphate buffer solution at pH 7.0. Enrichment was carried out for 2 minutes under stirring, and the peak current intensity of differential pulse voltammetry was measured as a response signal. When the concentration of one substance is kept unchanged in the detection of XA and HXA, the concentration of the substance to be detected is changed, and the result shows that no interference is generated between XA and HXA, and the constructed sensor can be used for simultaneously detecting XA and HXA.
The ball-milled graphene/Cu-BTC of example 1 was fabricated into electrochemical sensors, tested for different concentrations of contaminants, and a linear fit was made to the test results with detection limits of 0.0011, 0.0073, 0.0012, and 0.0019 milligrams per liter for XA, HXA, BPA, and CP, respectively, based on a triple signal-to-noise ratio. The developed electrochemical probe is used for detecting actual samples including urine, plasma, shopping tickets and industrial wastewater. Triplicate determinations were made for each sample, with Relative Standard Deviations (RSD) of less than 5%, indicating the reproducibility of the sensor. In order to verify the accuracy of the method, a relatively mature high performance liquid chromatography measurement is used for comparison, the relative error between the high performance liquid chromatography measurement result and the sensor measurement result is less than 9 percent, and the deviation is generally within an acceptable range, which indicates that the sensor has high accuracy.
The electrochemical sensor is composed of a glassy carbon electrode and ball-milled graphene/MOFs modified on the surface of the glassy carbon electrode, and can be used for direct, rapid, high-sensitivity and accurate detection of XA, HXA, BPA and CP. Compared with the method for preparing the graphene/MOFs compound, the method disclosed by the invention has the advantages of high sensitivity, simplicity in operation and environmental friendliness, and the synthesized compound has excellent electrochemical sensing performance, can be used for constructing a high-sensitivity electrochemical sensing platform, and has a prospect of realizing real-time online environment monitoring.
Example 2
A preparation method of a ball-milled graphene/Co-BTC composite material comprises the following steps:
dispersing 300 mg of 1200-mesh graphite powder and 300 mg of hexadecyl trimethyl ammonium bromide powder in 30 ml of aqueous solution containing 15% ethanol, controlling the ball milling rotation speed to be 300 revolutions per minute to ensure that the shearing force is dominant in the ball milling process, and performing ball milling reaction for 12 hours, and then obtaining the graphene nanosheet mixed solution through ball milling stripping.
The mixed solution was centrifuged at 2000 rpm for 20 minutes to remove the incompletely exfoliated graphite powder precipitate. The resulting solution was centrifuged at 9000 rpm for 20 minutes to give a solid, the solid was repeatedly washed with ethanol and ultrapure water to remove residual cetyltrimethylammonium bromide, and finally air-dried at 60 ℃.
0.85 g of Co (NO)3)2·6H2O is uniformly dispersed in 50 ml of DMF solution, then 50 mg of ball-milled graphene powder is added, and after stirring for 0.5 hour, 0.42 g of H is directly added3BTC. Then, 1 ml of 1% (v/v) triethylamine/DMF was slowly dropped into the above mixed solution, and after stirring was continued for 1.5 hours, the resulting complex was collected by centrifugation, and the resulting solid was repeatedly washed 3 times with ethanol and ultrapure water, and finally air-dried at 30 ℃ for 24 hours. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a ball milled graphene/Co-BTC suspension.
The ball-milled graphene/Co-BTC prepared in the example 2 is prepared into an electrochemical sensor, and the sensor has high accuracy through testing and can be used for direct and rapid detection of XA, HXA, BPA and CP.
Example 3
A preparation method of a ball-milled graphene/Cu-BTC composite material comprises the following steps:
dispersing 300 mg of 1200-mesh graphite powder and 300 mg of hexadecyl trimethyl ammonium bromide powder in 30 ml of aqueous solution containing 15% ethanol, controlling the ball milling rotation speed to be 300 revolutions per minute to ensure that the shearing force is dominant in the ball milling process, and performing ball milling reaction for 12 hours, and then obtaining the graphene nanosheet mixed solution through ball milling stripping.
The mixed solution was centrifuged at 2000 rpm for 20 minutes to remove the incompletely exfoliated graphite powder precipitate. The resulting solution was centrifuged at 9000 rpm for 20 minutes to give a solid, the solid was repeatedly washed with ethanol and ultrapure water to remove residual cetyltrimethylammonium bromide, and finally air-dried at 60 ℃.
0.7 g of Cu (NO)3)2·3H2O is uniformly dispersed in 50 ml of DMF solution, then 50 mg of ball-milled graphene powder is added, and after stirring for 0.5 hour, 0.42 g of H is directly added3BTC. Then, 1 ml of a mixed solution of triethylamine/DMF in which the concentration of triethylamine in the mixed solution was 1% (v/v) was dropped into the above mixed solution, and after stirring was continued for 1 hour, the resulting complex was collected by centrifugation, and the resulting solid was repeatedly washed with ethanol and ultrapure water 3 times, and finally air-dried at 30 ℃ for 24 hours. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a ball milled graphene/Cu-BTC suspension.
The ball-milled graphene/Cu-BTC prepared in the example 3 is prepared into an electrochemical sensor, and the sensor has high accuracy through testing, and can be used for direct, rapid and high-sensitivity detection of XA, HXA, BPA and CP.
Example 4
A preparation method of a ball-milled graphene/Cu-BTC composite material comprises the following steps:
dispersing 300 mg of 1200-mesh graphite powder and 300 mg of hexadecyl trimethyl ammonium bromide powder in 30 ml of aqueous solution containing 15% ethanol, controlling the ball milling rotation speed to be 300 revolutions per minute to ensure that the shearing force is dominant in the ball milling process, and performing ball milling reaction for 12 hours, and then obtaining the graphene nanosheet mixed solution through ball milling stripping.
The mixed solution was centrifuged at 2000 rpm for 20 minutes to remove the incompletely exfoliated graphite powder precipitate. The resulting solution was centrifuged at 9000 rpm for 20 minutes to give a solid, the solid was repeatedly washed with ethanol and ultrapure water to remove residual cetyltrimethylammonium bromide, and finally air-dried at 60 ℃.
0.7 g of Cu (NO)3)2·3H2O is uniformly dispersed in 50 ml of DMF solution, then 50 mg of ball-milled graphene powder is added, and the mixture is stirred for 0.5 hourThereafter, 0.42 g of H were added directly3BTC. Then, 1 ml of a mixed solution of triethylamine/DMF in which the concentration of triethylamine in the mixed solution was 1% (v/v) was dropped into the above mixed solution, and after stirring was continued for 1.5 hours, the resulting complex was collected by centrifugation, and the resulting solid was repeatedly washed 3 times with ethanol and ultrapure water, and finally air-dried at 30 ℃ for 24 hours. The dried product was then dispersed in N, N-dimethylformamide at a concentration of 2.0 mg per ml to give a ball milled graphene/Cu-BTC suspension.
The ball-milled graphene/Cu-BTC prepared in the example 4 is prepared into an electrochemical sensor, and the sensor has high accuracy through testing and can be used for direct and rapid detection of XA, HXA, BPA and CP.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An in-situ preparation method of a graphene-metal organic framework composite material is characterized by comprising the following steps:
(1) stripping graphite powder by adopting a wet ball milling method, wherein the shearing force is dominant in the ball milling stripping process, and finally obtaining a mixed system containing graphene nanosheets;
(2) removing non-completely stripped graphite flakes in the mixed system containing the graphene nanosheets obtained in the step (1) by adopting a gradient centrifugal separation method to obtain graphene nanosheet solids;
(3) mixing metal salt dispersed in an organic solvent with the graphene nanosheets obtained in the step (2), and stirring to enable metal ions in the metal salt to be adsorbed on the graphene nanosheets to obtain metal ion-loaded graphene nanosheets;
(4) mixing the metal ion loaded graphene nanosheets obtained in the step (3) with an organic ligand, and promoting in-situ synthesis of a metal-organic framework on the surfaces of the graphene nanosheets under the auxiliary action of an alkali source to finally obtain a graphene-metal-organic framework composite material;
according to the method, a graphene nanosheet obtained by ball milling of graphene is used as a substrate, metal ions in metal salt are directly adsorbed, and then a site for adsorbing the metal ions on the graphene nanosheet is combined with a ligand to grow a metal organic framework in situ.
2. The preparation method of claim 1, wherein a surfactant is further used in the wet ball milling process to improve the stripping efficiency of graphite in the ball milling process; the surfactant is an anionic surfactant, a cationic surfactant or a nonionic surfactant.
3. The preparation method according to claim 2, wherein the mass ratio of the graphite powder to the surfactant in the step (1) is 3:1 to 1: 3.
4. The preparation method of claim 1, wherein the graphite powder is dispersed in the ethanol aqueous solution in the step (1) for wet ball milling, the rotation speed of the ball milling is controlled to ensure that the shearing force is dominant in the ball milling process, and the ball milling time is not less than 12 hours.
5. The method according to claim 1, wherein the gradient centrifugation method of step (2) is specifically: firstly, primarily separating and removing graphite powder precipitate which is not completely stripped by centrifuging at 500-2000 rpm for 5-45 minutes, and then further obtaining graphene nanosheet solid by centrifuging at 8000-12000 rpm for 5-45 minutes.
6. The method according to claim 1, wherein the metal salt in the step (3) is Cu (NO)3)2·3H2O、Ni(NO3)2·6H2O、Zn(NO3)2·6H2O、Co(NO3)2·6H2One or more of O; the organic solvent is N, N-dimethylformamide, methanol or aqueous solution of methanol。
7. The preparation method according to claim 1, wherein the mass ratio of the metal salt to the graphene nanoplatelets in step (3) is 10:1-20:1, and the stirring time is 0.1 to 2 hours.
8. The method according to claim 1, wherein the organic ligand in the step (4) is one or more of 1, 4-terephthalic acid, 1, 3, 5-trimesic acid and 2-methylimidazole.
9. The method according to claim 1, wherein the base source is a mixed solution of triethylamine/N, N-dimethylformamide, wherein the volume concentration of triethylamine in the mixed solution is 1%, and 1 to 10 ml of the base source is added per gram of the organic ligand.
10. An electrochemical sensor modified by ball-milled graphene-metal organic framework, which is characterized by comprising an electrode and an active ingredient positioned on the surface of the electrode, wherein the active ingredient is the graphene-metal organic framework composite material prepared by the preparation method of any one of claims 1 to 9.
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