CN112156753A - Graphene aerogel and preparation method and application thereof - Google Patents

Graphene aerogel and preparation method and application thereof Download PDF

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Publication number
CN112156753A
CN112156753A CN202011009338.5A CN202011009338A CN112156753A CN 112156753 A CN112156753 A CN 112156753A CN 202011009338 A CN202011009338 A CN 202011009338A CN 112156753 A CN112156753 A CN 112156753A
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graphene
graphene aerogel
adsorption
aerogel
adsorption capacity
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戴彩丽
李琳
孙雯
赵明伟
吴一宁
孙永鹏
赵光
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China University of Petroleum East China
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/20—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising free carbon; comprising carbon obtained by carbonising processes
    • B01J20/205—Carbon nanostructures, e.g. nanotubes, nanohorns, nanocones, nanoballs
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28047—Gels
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C01B32/19—Preparation by exfoliation
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02B—HYDRAULIC ENGINEERING
    • E02B15/00—Cleaning or keeping clear the surface of open water; Apparatus therefor
    • E02B15/04—Devices for cleaning or keeping clear the surface of open water from oil or like floating materials by separating or removing these materials
    • E02B15/10—Devices for removing the material from the surface
    • E02B15/101—Means floating loosely on the water absorbing the oil
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/20—Controlling water pollution; Waste water treatment
    • Y02A20/204—Keeping clear the surface of open water from oil spills

Abstract

The invention relates to the field of environment functional materials, and discloses graphene aerogel and a preparation method and application thereof. The graphene aerogel contains C element, S element and N element, wherein the S element and the N element are respectively combined with the C element in a chemical bond mode, and the density of the graphene aerogel is 4-6.5mg/cm3. When the graphene aerogel is used as an adsorption material, the graphene aerogel has better adsorption performance, good hydrophobicity and oil-water selectivity, and can be used as a good adsorption material for offshore oil spill treatment.

Description

Graphene aerogel and preparation method and application thereof
Technical Field
The invention relates to the technical field of environment functional materials, in particular to graphene aerogel, a preparation method thereof and application of the graphene aerogel as an adsorption material.
Background
Along with the transfer of the gravity center of oil development from land to sea, oil pollution caused by oil spill accidents is frequent, which not only causes serious damage to the marine ecosystem, but also brings immeasurable economic loss. How to rapidly, effectively and thoroughly remove and collect the floating oil on the surface of the seawater without causing secondary pollution is a problem to be solved urgently at present.
After an oil spill accident occurs, according to the actual condition of petroleum pollution, a treatment mode combining multiple methods is often adopted, and an adsorption material is usually adopted for thorough treatment in the later stage. Among the adsorption materials, the natural adsorption material has the defects of low adsorption capacity, poor oil-water selectivity, difficult collection and poor cyclicity; the synthetic resin, the modified sponge and the like optimize the compressibility and the oil-water selectivity of the oil absorption material to a certain extent, but are still deficient in adsorption capacity.
The novel material graphene is the most potential oil-water separation material at present due to the fact that the novel material graphene has oleophylic and hydrophobic properties and high mechanical strength, and the graphene aerogel has the advantages of being high in porosity, large in specific surface area, oleophylic and hydrophobic properties and the like, has certain elasticity, and can rebound and keep an original pore structure when being extruded or stressed. The two-dimensional lamellar structure of the graphene and the high porosity and multiple adsorption active sites of the aerogel endow the graphene aerogel with extremely high adsorption efficiency, so that the graphene aerogel has strong adsorption capacity on various organic substances. However, in an actual preparation process, the adsorption capacity of the graphene aerogel is often lower than a theoretical value due to the stacking effect of the two-dimensional graphene sheets, so that the expected superior performance cannot be achieved, and therefore, researches on how to improve the adsorption capacity and the adsorption life of the graphene aerogel are being conducted on fire and heat.
CN102847510A discloses a graphene-based water purification material and a preparation method and application thereof, thiourea is added into a graphene oxide aqueous solution, graphene oxide is self-assembled into a graphene sponge by adopting a hydrothermal method, the structure of the graphene sponge is regulated and controlled by changing the size of the graphene oxide and the addition amount of the thiourea, the problem that the adsorption performance and the cycle performance are affected by the restacking of the graphene oxide during the reduction in the traditional adsorption process is solved, but the adsorption capacity of the graphene sponge to diesel oil is not more than 130 g/g.
CN106423100A discloses a polyacrylonitrile/graphene-based composite aerogel and a preparation method thereof, the method comprises mixing polyacrylonitrile and graphene oxide together to obtain a dispersion solution, then carrying out solvothermal reaction to obtain polyacrylonitrile/graphene gel, replacing the solvent with water to obtain hydrogel, and then carrying out freeze drying in liquid nitrogen to obtain the polyacrylonitrile/graphene-based composite aerogel. According to the method, the adsorption capacity and the adsorption cycle capacity of the graphene aerogel are improved by adding polyacrylonitrile, but the adsorption capacity is low, the adsorption capacity to tetrahydrofuran is not more than 45g/g, and the adsorption capacity to pump oil is less than 80 g/g.
CN110282620A discloses a graphene oxide aerogel and a preparation method and application thereof, wherein the method comprises the step of crosslinking and assembling graphene oxide lamella by taking graphene oxide as a substrate and ethylenediamine and lysine as a crosslinking agent and a reducing agent at the same time to obtain the aerogel with a three-dimensional network structure. The preparation method is simple, the prepared solution is placed in a reaction container for standing after being mixed, and the required temperature is not high (70-90 ℃). However, the reaction time in the temperature range is long (10-24h) by adopting the method, and the prepared graphene aerogel has the adsorption capacity of not more than 180g/g for diesel oil, less than 90g/g for tetrahydrofuran, less than 145g/g for pump oil, and the adsorption performance needs to be further improved.
Disclosure of Invention
The invention aims to provide a graphene aerogel with better adsorbability, and a preparation method and application thereof.
In order to achieve the above object, a first aspect of the present invention provides a graphene aerogel, which is characterized by containing C element, S element and N element, wherein the S element and the N element are each chemically bonded to the C element, and the density of the graphene aerogel is 4 to 6.5mg/cm3。
The second aspect of the invention provides a preparation method of graphene aerogel, which comprises the steps of uniformly mixing a graphene oxide dispersion solution, a reducing agent and a cross-linking agent, and then carrying out hydrothermal reaction to obtain graphene hydrogel; removing the solvent in the graphene hydrogel to obtain the graphene aerogel; wherein the cross-linking agent is cysteamine and/or L-cysteine.
The third aspect of the invention provides a graphene aerogel prepared by the method.
The invention provides a method for preparing graphene aerogel, which comprises the following steps of preparing graphene aerogel, and preparing graphene oxide aerogel.
Through the technical scheme, the invention has the following advantages:
(1) the graphene aerogel disclosed by the invention contains S element and N element at the same time, and the S element and the N element are respectively combined with the C element in a chemical bond form, so that the graphene aerogel has lower density (4-6.5 mg/cm)3) So that the adsorbent has good adsorption performance and oil-water selectivity when being used as an adsorption material. Under the optimal condition, the graphene aerogel has a double three-dimensional network structure with layered stacking and longitudinal crosslinking, the pores are rich, the pore diameter is smaller, when the graphene aerogel is used as an adsorption material, the adsorption capacity on trichloromethane can be up to 310g/g, the adsorption capacity on diesel oil can be up to 248g/g, the adsorption capacity on tetrahydrofuran can be up to 147g/g, the adsorption capacity on pump oil can be up to 213g/g, and the adsorption constants on gasoline and ethanol can be up to 78.7 multiplied by 10 respectively-3s-1And 76.6X 10-3s-1The composite material has good adsorption performance and oil-water selectivity, and has wide application prospect in the field of offshore oil spill treatment;
(2) according to the preparation method of the graphene aerogel, from the perspective of regulating the structure of the graphene aerogel, a mode of combining a reducing agent and a cross-linking agent (cysteamine and/or L-cysteine) is adopted, the prepared graphene aerogel contains S elements and N elements in a certain proportion, and the S elements and the N elements are respectively combined with the C elements in a chemical bond mode, so that the graphene aerogel has a double three-dimensional network structure with layered stacking and longitudinal cross-linking. The addition of the cross-linking agent (cysteamine and/or L-cysteine) is helpful for improving the reduction degree, can also increase the connection between adjacent graphene sheets, and effectively improves the adsorption capacity of the graphene aerogel. In addition, by adopting the method, the hydrothermal reaction time can be greatly shortened (0.5-2h), the adsorption performance of the graphene aerogel can be improved without additional additives, the preparation process is simple, the raw material cost is low, and the method is favorable for promoting industrial production and large-scale application.
Drawings
Fig. 1 is a field emission scanning electron microscope image of a graphene aerogel;
fig. 2 is an atomic force microscope image of a graphene aerogel;
fig. 3 is an X-ray photoelectron spectrum of a graphene aerogel;
fig. 4 is a fourier transform infrared spectrum of a graphene aerogel;
fig. 5 is a pore size distribution diagram of a graphene aerogel;
fig. 6 is a water contact angle diagram of a graphene aerogel;
fig. 7 is a physical photograph of a graphene aerogel;
fig. 8 shows the adsorption capacity of the graphene aerogel for different types of oils and organic solvents;
fig. 9 is a graph showing the change of the adsorption capacity of the graphene aerogel on different types of oils and organic solvents with the adsorption time.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
As described above, the first aspect of the present invention provides a graphene aerogel, wherein the graphene aerogel contains C element, S element, and N element, and the S element and the N element are each chemically bonded to the C element, and the density of the graphene aerogel is 4 to 6.5mg/cm3；
Preferably, the density of the graphene aerogel is 4-6mg/cm3Preferably 4.2 to 5mg/cm3More preferably 4.2 to 4.6mg/cm3. The lower the density of graphite alkene aerogel, means when forming the graphite alkene aerogel of equal volume, the quality is lower, and graphite alkene aerogel skeleton structure's quality is lower relatively promptly, and consequently, pore structure is abundanter, and adsorption capacity is bigger.
In the present invention, the density of the graphene aerogel is measured by a liquid discharge method, and a specific test method will be described below.
In some embodiments of the invention, the chemical composition of the graphene aerogel is characterized by X-ray photoelectron spectroscopy (XPS) as tested on an Escalab 250Xi model X-ray photoelectron spectrometer equipped with Thermo Avantage V5.926 software, available from Thermo Scientific, with an excitation source of monochromated Al K α X-rays, a resolution of 0.1-1eV, an energy of 1486.6eV, a power of 150W, a transmission energy for narrow scan of 30eV, and a base vacuum of 6.5 × 10 for analytical testing-10mbar. And qualitatively analyzing the element types of the graphene aerogel according to the photoelectron binding energy, and qualitatively analyzing the chemical valence and molecular structure of the elements according to the change of the inner-layer electron binding energy of the atoms, namely the chemical shift of a spectrum peak on a spectrogram. The electron binding energy was corrected with the C1s peak (284.0eV) of elemental carbon, data processed on Thermo Avantage software, and quantified in the analytical module using the sensitivity factor method.
Graphene aerogel in the present inventionCharacteristic peaks of S, C, N and O are correspondingly formed in an X-ray photoelectron spectrum of the gel, which indicates that the graphene aerogel contains S elements, C elements, N elements and O elements. The spectrum of C1S consisted of peaks for C-C (284.7eV), C-O (286.5eV), C-S (287eV), C ═ O (288eV), and O-C ═ O (289.1 eV); the N1s map shows that the N elements are represented by C-N (399.8eV) and C-NH2A state of (402eV) exists; the S2p spectrum was divided into two peaks, C-S-C (164.0eV) and C-SOx-C (168.6eV), which indicates that the graphene aerogel of the present invention contains the above functional groups.
In some embodiments of the present invention, the graphene aerogel of the present invention determines the total amount of C element by the area of the peak of the C1S spectrum in the X-ray photoelectron spectrum, determines the total amount of S element by the area of the peak of the S2p spectrum, and determines the total amount of N element by the area of the peak of the N1S spectrum. The molar ratio of the C element, the S element and the N element is (74.5-83.5): (0.5-5.5): (0.8-2);
in some embodiments of the present invention, the graphene aerogel of the present invention has a molar ratio of the functional group of C-C, C-O, C-S, C ═ O and O-C ═ O of (54-65), as determined by X-ray photoelectron spectroscopy: (20-23): (6-9): (5-8): (4-6); functional groups C-S-C and C-SO of the S element determined by X-ray photoelectron spectroscopyx-C in a molar ratio (70-85): (15-30); functional groups C-N and C-NH of the N element determined by X-ray photoelectron spectroscopy2In a molar ratio of (16-36): (64-84).
In some embodiments of the present invention, the functional groups of the graphene aerogel are characterized by fourier transform infrared spectroscopy (FTIR), which iS tested on a Nicolet iS5 type fourier transform infrared spectrometer from Thermo Scientific, with a spectral range of 400--1Resolution of 4cm-1. In a Fourier transform infrared spectrogram, the graphene aerogel disclosed by the invention is 760cm-1And 1204cm-1The absorption peaks corresponding to C-S and C-N vibrations, respectively, appear at 1048cm-1、1213cm-1、1726cm-1、3430cm-1The absorption peaks appear corresponding to the vibrations of C-O, C-O-C, C ═ O and O-H, respectively, in comparison with the prior artCompared with the graphene aerogel of C-O, C-O-C, C ═ O and O-H, the absorption peak intensity of the oxygen-containing functional groups is obviously weaker.
In some embodiments of the present invention, the graphene aerogel has a dual three-dimensional network structure of lamellar stacking and longitudinal cross-linking.
In some embodiments of the invention, the surface morphology and internal structure of the graphene aerogel is observed using a field emission scanning electron microscope (FE-SEM), which is a test on a Sigma300 type field emission scanning electron microscope, zeiss, germany, using an acceleration voltage of 20-30kV and a resolution of 1.6 nm. In a field emission scanning electron microscope image, the surface of the graphene aerogel disclosed by the invention is relatively flat, and the surface has wrinkles, namely a layered structure of graphene sheets. The internal structure shows that besides the layered stacking of the graphene sheets, more connections are formed between the graphene sheets in the longitudinal direction, the pores are more abundant, and the pore diameter is smaller, namely the double three-dimensional network structure of the layered stacking and the longitudinal crosslinking.
In some embodiments of the invention, the three-dimensional surface topography of the graphene aerogel is observed using an Atomic Force Microscope (AFM), which is tested on a Multimode 8 atomic force microscope equipped with NanoScope 9.1 software, Bruker, germany, in a scanasyst, performed on NanoScope Analysis1.8 software. In an atomic force microscope picture, parallel stripes, namely a layered structure, can be seen on the surface of the graphene aerogel disclosed by the invention, the layered surface is accompanied by columnar protrusions and has certain roughness, namely longitudinal cross-linking, the height of the columnar protrusions is 23.1-422.4nm, and the root mean square Roughness (RMS) of the layered surface is 150-275 nm.
In some embodiments of the invention, the graphene aerogel has pore sizes centered between 2 and 40nm, with a predominantly mesoporous structure.
In some embodiments of the invention, the graphene aerogel has a porosity of 90 to 99.5%, preferably 95 to 99.5%.
In some embodiments of the inventionIn an embodiment, the specific surface area of the graphene aerogel is 250-500m2(ii)/g, preferably 290-2/g。
In the invention, the porosity and the specific surface area are measured by a nitrogen adsorption method, and specifically, the specific surface area of a solid substance is measured by a gas adsorption BET method in GB/T19587-2004.
In some embodiments of the invention, the graphene aerogel has a surface contact angle to water of greater than 110 °, preferably greater than 120 °.
In the present invention, the measurement was carried out 5 times by using a contact angle tester available from Dataphysics, Germany, having a model number of OCA20, and the average of the 5 measurements was taken.
In some embodiments of the invention, the graphene aerogel has an adsorption capacity of 310g/g for oil products and organic solvents, wherein the oil products include diesel oil, gasoline, light crude oil, soybean oil, pump oil, and rapeseed oil; the organic solvent comprises n-hexane, ethanol, petroleum ether, chloroform, toluene, tetrahydrofuran, dichloromethane and methanol.
Preferably, the adsorption capacity of the graphene aerogel on diesel oil is more than 195g/g, the adsorption capacity on tetrahydrofuran is more than 101g/g, and the adsorption capacity on pump oil is more than 173 g/g.
In some embodiments of the invention, the graphene aerogel has an adsorption constant of 8.5 × 10 for diesel oil-3-12×10-3s-1Adsorption constant for tetrahydrofuran of 65X 10-3-75×10-3s-1Adsorption constant for pump oil of 0.25X 10-3-0.4×10-3s-1The adsorption constant for gasoline can be as high as 78.7 x 10-3s-1. In the present invention, the adsorption capacity and adsorption constant are related to the chemical properties and viscosity of the oil and the organic solvent, and generally, the adsorption capacity of the oil and the organic solvent with higher viscosity or higher density is higher than that of the oil and the organic solvent with lower viscosity and lower density.
In the present invention, the method for measuring the adsorption capacity and adsorption constant will be described below.
The second aspect of the invention provides a preparation method of graphene aerogel, wherein the method comprises the steps of uniformly mixing a graphene oxide dispersion solution, a reducing agent and a cross-linking agent, and then carrying out hydrothermal reaction to obtain graphene hydrogel; removing the solvent in the graphene hydrogel to obtain the graphene aerogel; wherein the cross-linking agent is cysteamine and/or L-cysteine, and preferably cysteamine.
In some embodiments of the present invention, the internal structure of the graphene sheet layer is controlled by combining a reducing agent and a cross-linking agent (cysteamine and/or L-cysteine), so that the graphene oxide is deprived of hydrophilic oxygen-containing groups and is restored to sp with strong hydrophobicity2The addition of the cysteamine and/or the L-cysteine not only contributes to improving the reduction degree of the graphene, but also can enhance the binding force between graphene sheets, promote the gelation of the graphene sheets, form covalent bond crosslinking, improve the internal structure of the graphene, and obviously improve the structural stability of the graphene aerogel.
In some embodiments of the invention, the reducing agent is ascorbic acid and/or ethylenediamine. In order to reduce graphene oxide well to allow it to self-assemble, thereby forming a graphene hydrogel with an intact shape, preferably, the reducing agent is ascorbic acid.
In some embodiments of the present invention, the mass ratio of the reducing agent to the graphene oxide is (0.2-2.5): 1. In order to improve the integrity and regularity of the graphene hydrogel formed by the mixed solution in the hydrothermal reaction process, the mass ratio of the reducing agent to the graphene oxide is preferably (0.5-2): 1.
In some embodiments of the invention, the mass ratio of the reducing agent to the crosslinking agent is (2-20): 1. In order to better adjust the internal structure of the graphene aerogel, increase the bonding points between graphene sheet layers and effectively improve the mechanical properties and the adsorption capacity, the mass ratio of the reducing agent to the crosslinking agent is preferably (4-16): 1.
In some embodiments of the invention, the temperature of the hydrothermal reaction is 90-100 ℃, preferably 92-98 ℃; the time is 0.5-2h, preferably 1-1.5 h. In the preparation process of the graphene aerogel, the reducing agent and the cross-linking agent (cysteamine and/or L-cysteine) are added at the same time, and the cross-linking agent (cysteamine and/or L-cysteine) contains active sulfydryl and amino and can also play a role in partial reduction in the reaction process, so that the preparation method of the graphene aerogel disclosed by the invention has shorter time for reducing graphene oxide in the hydrothermal reaction process. Meanwhile, as other doping materials are not added, the hydrothermal temperature of the invention can be reduced to 90 ℃, and the hydrothermal time can be shortened to 0.5 h.
In some embodiments of the invention, the graphene oxide dispersion has a concentration of 1-5 mg/mL. In order to form effective contact and overlap, complete self-assembly while avoiding serious self-assembly stacking, so as to obtain graphene aerogel with high specific surface area and high porosity, preferably, the concentration of the graphene oxide dispersion is 2-4 mg/mL.
In some embodiments of the present invention, the manner of preparing the graphene oxide dispersion liquid includes: graphene oxide prepared by the Hummers method or the modified Hummers method is dispersed in deionized water in the presence of ultrasonic waves to form a uniform graphene oxide dispersion. Techniques for preparing graphene oxide using the Hummers method or the modified Hummers method are well known to those skilled in the art and can be performed with reference to the prior art.
In some embodiments of the present invention, the solvent in the graphene hydrogel may be removed in various ways, as long as the solvent in the graphene hydrogel can be effectively removed to obtain the graphene aerogel, for example, a method of placing the graphene hydrogel in an ethanol aqueous solution for dialysis, and then drying the graphene hydrogel can be adopted. The drying method can be various, such as freeze drying, supercritical drying, etc. In order to avoid volume shrinkage and structural collapse caused by the surface tension of the solvent present inside the gel matrix, preferably, the drying is freeze-drying. The freeze drying can realize the dehydration process with the liquid sublimation in the graphite alkene aquogel, furthest remains the internal skeleton structure of graphite alkene aerogel.
In some embodiments of the invention, the drying is carried out at a temperature of-10 to-100 ℃ for a period of 15 to 30 hours. In order to realize the reduction of the graphene oxide in a short time, self-assemble the graphene aerogel to form a graphene aerogel with a complete structure and a good pore structure and avoid the stacking of graphene sheets, the drying temperature is preferably-60 to-80 ℃, and the drying time is preferably 24 to 36 hours.
In some embodiments of the present invention, the dialysis may be performed with an aqueous solution of ethanol, or may be performed with acetone, as long as impurities in the graphene hydrogel can be effectively replaced/removed. The ethanol aqueous solution dialysis can get rid of impurity on the one hand, and on the other hand ethanol can prevent effectively that the ice crystal from growing too big when the aquogel is frozen, prevents that graphite alkene from piling up seriously, improves the adsorption capacity of graphite alkene aerogel. The operation of such dialysis is well known to those skilled in the art and will not be described in detail herein.
In some embodiments of the invention, the concentration of the aqueous ethanol solution is5 to 25 volume%, preferably 10 to 20 volume%.
In some embodiments of the invention, the dialysis is performed for a period of 5 to 15 hours, preferably 8 to 12 hours.
In some embodiments of the invention, the incorporation of the cross-linking agent is confirmed by the C-S peak at 287eV, which is predominantly from graphene, and the C-O peak at 286.5eV, the C ═ O peak at 288eV, and the O-C ═ O peak at 289.1eV, which are from unreduced epoxy, hydroxyl, and carboxyl groups, in the X-ray photoelectron spectroscopy C1S spectrum of the graphene aerogel prepared using the method of the invention. Compared with the C1s spectrum of the graphene aerogel prepared without adding the crosslinking agent, the graphene aerogel prepared by the method of the present invention has a C1s spectrum with lower intensity of C-O, C ═ O and O-C ═ O peaks, which may be caused by the nucleophilic ring-opening reaction of the epoxy group and further reduction of graphene oxide due to the crosslinking agent. The N1s map shows that N elements in the graphene aerogel are C-N (399.8eV) and C-NH2The presence of the state (402eV) indicates that the crosslinker forms covalent bonds with the graphene oxide sheets. C-N and C-NH2The presence of the thiol in the cross-linking agent is also indicatedBoth the base and amine groups can react with the graphene oxide sheets. The S2p spectrum was divided into two peaks, with the C-S-C peak (164.0eV) coming from the covalent bond between the crosslinker and the graphene sheet, and the C-SOxthe-C peak may be related to the graphene oxide preparation process. The cross-linking agent plays two roles in the assembly of the aerogel, and the addition of the cross-linking agent reduces the oxygen content of the aerogel, which indicates that the cross-linking agent plays a certain role of a reducing agent. The formation of C-S-C and C-N, on the other hand, results from the interaction of the thiol and amino groups in the crosslinker with the epoxy groups and carbon-carbon double bonds in the graphene oxide sheets, confirming the bonding of adjacent graphene oxide sheets to the crosslinker.
In some embodiments of the present invention, the graphene aerogel prepared by the method of the present invention has a fourier transform infrared spectrogram at 760cm-1And 1204cm-1The shock absorption peaks appeared from C-S and C-N, respectively, indicating that the introduction of the crosslinking agent was successful. At 1048cm-1、1213cm-1、1726cm-1、3430cm-1The vibration absorption peaks at (A) are assigned to C-O, C-O-C, C ═ O and O-H, respectively. Compared with the graphene aerogel prepared without adding the cross-linking agent, the graphene aerogel prepared by the method disclosed by the invention has the advantages that the strength of oxygen-containing functional groups such as C-O, C-O-C, C ═ O and O-H is relatively weak, so that the cross-linking agent also plays a role of a reducing agent in the preparation process of the graphene aerogel.
In some embodiments of the present invention, the graphene aerogel prepared by the method of the present invention has a double three-dimensional network structure of lamellar stacking and longitudinal cross-linking, wherein the lamellar stacking is a three-dimensional network structure formed by self-assembly of graphene oxide by van der waals force and conjugated pi-pi bond after reduction and lamellar stacking aggregation; longitudinal crosslinking is covalent bond crosslinking formed between the crosslinking agent and the graphene sheet layer. Covalent bond crosslinking increases the number of connection points between the stacked graphene sheets in the longitudinal direction, thereby obtaining the double three-dimensional network structure of the layered stack and the longitudinal crosslinking.
In some embodiments of the present invention, in an atomic force microscope image, a parallel wave lamellar structure can be observed on the surface of the graphene aerogel prepared without adding the cross-linking agent, and the surface of the graphene aerogel prepared by the method of the present invention has a columnar protrusion besides the lamellar structure, indicating that the addition of the cross-linking agent increases the surface roughness of the graphene sheet.
In some embodiments of the present invention, in the field emission scanning electron microscope image, the graphene aerogel presents a flat surface with some wrinkles, i.e., a layered structure. The graphene aerogel prepared without adding the cross-linking agent has a horizontally layered ordered stacked structure inside. The graphene aerogel prepared by the method not only keeps the layered stacking structure of the graphene sheets, but also forms more longitudinal connections among the graphene sheets, thereby forming more abundant holes and having smaller aperture. Namely, the graphene aerogel prepared by the method forms a double three-dimensional network structure with layered stacking and longitudinal crosslinking, and is more favorable for adsorption of oil or organic solvent than the graphene aerogel with only a layered stacking structure.
The third aspect of the invention provides an application of the graphene aerogel as an adsorption material.
The graphene aerogel of the invention can be directly applied to the adsorption of oil products and organic solvents with different viscosities and chemical properties as an adsorption material, wherein the oil products include but are not limited to: diesel oil, gasoline, light crude oil, soybean oil, pump oil and rapeseed oil; the organic solvents include, but are not limited to: n-hexane, ethanol, petroleum ether, chloroform, toluene, tetrahydrofuran, dichloromethane, and methanol.
When the graphene aerogel disclosed by the invention is used as an adsorbing material and applied to oil products and organic solvents, the graphene aerogel shows remarkable adsorption performance, and the adsorption capacity is over 100 g/g. Wherein, the adsorption capacity to trichloromethane is up to 310g/g, the adsorption capacity to diesel oil is up to 248g/g, the adsorption capacity to tetrahydrofuran is up to 147g/g, the adsorption capacity to pump oil is up to 213g/g, and the adsorption constants to gasoline and ethanol are respectively up to 78.7 multiplied by 10-3s-1And 76.6X 10-3s-1Has higher adsorption rate, and compared with the prior art, the graphene aerogel disclosed by the invention has adsorption performanceThe method has great advantages.
The present invention will be described in detail by way of examples, but it should be understood that the scope of the present invention is not limited by the examples.
The following examples and comparative examples used the following starting materials:
natural flake graphite (99.9%, 325 mesh) used for preparing graphene oxide was purchased from alatin;
cysteamine (95 wt%) was purchased from Macklin;
potassium permanganate, hydrogen peroxide (30 wt%), concentrated sulfuric acid (98 wt%), sodium nitrate and ascorbic acid were purchased from pharmaceutical chemicals, Inc.
The method for preparing the graphene oxide by improving the Hummers method comprises the following specific steps: 3.0g of graphite and 1.5g of NaNO were mixed3Added to 75mL of H2SO4(98%) solution, stirred in ice bath for 30min, then 15g KMnO was slowly added4The reaction was continued for 30 min. After the reaction, the reaction mass was transferred to a 35 ℃ water bath and allowed to continue reacting for 30 min. Then 150mL of deionized water was slowly added to the reaction mixture and heated to 90 ℃ for 10 min. To the reaction mixture was added 200mL of deionized water and 10mL of hydrogen peroxide and stirred until the solution turned golden yellow. And washing the obtained solution with a 10% hydrochloric acid solution and deionized water, performing ultrasonic treatment and centrifugation, and finally performing freeze-drying for 72 hours to obtain the graphene oxide.
The test methods involved in the examples and comparative examples are as follows:
(1) x-ray photoelectron spectroscopy (XPS) test
The test was carried out using an Escalab 250Xi model X-ray photoelectron spectrometer equipped with Thermo Avantage V5.926 software, from Thermo Scientific, with monochromatic Al Ka X-rays as excitation source, resolution 0.1-1eV, energy 1486.6eV, power 150W, transmission energy for narrow scan 30eV, and base vacuum of 6.5X 10 for analytical test-10mbar, qualitatively analyzing element types of the graphene aerogel according to the photoelectron binding energy, and qualitatively analyzing the chemical valence and molecular structure of the elements according to the change of the inner-layer electron binding energy of atoms, namely the chemical shift of a spectrum peak on a spectrogram, wherein the electron binding energy is usedThe C1s peak (284.0eV) of elemental carbon was corrected, data processed on Thermo Avantage software, and quantified using the sensitivity factor method in the analytical module.
(2) Fourier transform Infrared Spectroscopy (FTIR) testing
The test iS carried out by adopting a Nicolet iS5 type Fourier transform infrared spectrometer of Thermo Scientific company, and the spectral range iS 400--1Resolution of 4cm-1。
(3) Field emission scanning electron microscope (FE-SEM) testing
The test was carried out using a field emission scanning electron microscope of the Sigma300 type from Zeiss, Germany, with an acceleration voltage of 20-30kV and a resolution of 1.6 nm.
(4) Atomic Force Microscope (AFM) testing
The test was carried out using a Multimode 8 atomic force microscope equipped with NanoScope 9.1 software, Bruker, germany, using a scanasyst, on which the data processing was carried out with NanoScope analysis1.8 software.
(5) Density test
Adopt the flowing back method to carry out density test to graphite alkene aerogel, concrete step is: weigh the quality of graphite alkene aerogel earlier, then soak it completely in the graduated flask that is equipped with absolute ethyl alcohol, observe the volume that the liquid level changes and be graphite alkene aerogel's volume promptly, then calculate graphite alkene aerogel's density according to following formula:
ρ＝m0/V0
where ρ is the density of the graphene aerogel, m0Is the mass of the graphene aerogel, V0Is the volume of the graphene aerogel.
(6) Specific surface area and porosity measurements
The nitrogen adsorption method is adopted, and specifically, the GB/T19587-2004 ' BET method for gas adsorption ' is referred to for measuring the specific surface area of the solid substance '.
(7) Water contact Angle test
The measurements were carried out 5 times in total using a contact angle tester, model OCA20, from Dataphysics, Germany, and the average of the 5 measurements was taken.
(8) Adsorption capacity test
Firstly, weighing the initial mass m of the graphene aerogel by using an electronic balanceiThen completely soaking the graphene aerogel below the liquid level of the organic solvent or oil product and staying for enough time until the graphene aerogel is saturated and adsorbed, then quickly taking out the saturated and adsorbed graphene aerogel, weighing and recording the mass m of the saturated and adsorbed graphene aerogelsAnd finally, calculating the adsorption capacity of the graphene aerogel on a corresponding oil product or organic solvent according to the following formula:
Figure BDA0002697052500000141
in the formula: m issRepresents the mass of the graphene aerogel subjected to saturated adsorption, and the unit is g; m isiRepresenting the initial mass of the graphene aerogel, and the unit is g; qmThe unit of the adsorption capacity of the graphene aerogel is g/g when the graphene aerogel is saturated by adsorption.
(9) Adsorption constant test
The adsorption process before saturation was simulated using the following equation:
Figure BDA0002697052500000151
in the formula: qmThe unit of the adsorption capacity of the graphene aerogel is g/g when the graphene aerogel is saturated by adsorption; qtThe adsorption capacity of the graphene aerogel under different adsorption time t is expressed in the unit of g/g; k represents the adsorption constant in s-1(ii) a t represents time in units of s.
T is taken as x axis, 1/(Q)m-Qt) And establishing a coordinate system for the y axis to draw an image, wherein the slope of the image is the adsorption constant K.
Example 1
(1) Dispersing graphene oxide prepared by an improved Hummers method in deionized water, and performing ultrasonic treatment to form a uniform graphene oxide dispersion liquid with the concentration of 4 mg/mL;
(2) adding 4mg/mL of ascorbic acid and 0.25mg/mL of cysteamine into the graphene oxide dispersion liquid prepared in the step (1), uniformly stirring and mixing by magnetic force, placing in an oven with the temperature of 95 ℃ for hydrothermal reaction for 1h, and obtaining graphene hydrogel after the reaction is finished;
(3) and (3) putting the graphene hydrogel prepared in the step (2) into an ethanol water solution with the concentration of 10 vol% for dialysis for 12h, and then carrying out freeze drying at the temperature of-80 ℃ for 36h to obtain the graphene aerogel, wherein the label is S1.
S1 was subjected to field emission scanning electron microscopy and the results are shown in fig. 1(b) and (d). As can be seen from fig. 1(b), the surface of S1 is relatively flat, and the surface has some wrinkles, i.e. the layered structure of the graphene sheet; as can be seen from fig. 1(d), the internal structure of S1 shows that in addition to the layered stack of graphene sheets, more connections are formed between graphene sheets, i.e., in the longitudinal direction, the pores are more abundant, the pore size is smaller, and a dual three-dimensional network structure of layered stack and longitudinal cross-linking is formed.
S1 was subjected to atomic force microscopy and the results are shown in fig. 2 (b). As can be seen from FIG. 2(b), parallel stripes, i.e., layered structure, are observed on the S1 surface, the layered surface is accompanied by columnar protrusions with certain roughness, i.e., longitudinal cross-linking, the height of the columnar protrusions is 23.1-422.4nm, and the root mean square Roughness (RMS) of the layered surface is 150-275 nm.
S1 was subjected to X-ray photoelectron spectroscopy and the results are shown in FIG. 3. As can be seen from fig. 3, S1 contains C, S, N and O elements, C, S, N and the molar ratio of O elements is 75.42: 0.74: 1.33: 22.51, respectively; the molar ratio of the functional groups C-C, C-O, C-S, C ═ O and O-C ═ O in the element C is 60.2: 21.6: 7.6: 6: 4.6; functional groups C-S-C and C-SO in S elementx-C molar ratio 76.15: 23.85; functional groups C-N and C-NH in N element2In a molar ratio of 30.66: 69.34.
the results of the fourier transform infrared spectroscopy test of S1 are shown in fig. 4. As can be seen from FIG. 4, S1 is at 760cm-1And 1204cm-1Shows absorption peaks corresponding to the functional groups C-S and C-N, respectively, at 1048cm-1、1213cm-1、1726cm-1、3430cm-1The absorption peak appears and corresponds to the functional group C-O, C-O-C, C ═ respectivelyO and O-H.
From the content of each functional group in the C1S map of fig. 3S1, it is understood that the oxygen group in S1 is significantly reduced, which is consistent with the results of fig. 4.
S1 was subjected to specific surface area and pore size distribution tests, and the results are shown in fig. 5. As can be seen from FIG. 5, the pore diameter of S1 was concentrated at 2 to 40nm, and it was mainly a mesoporous structure, with a porosity of 99.29% and a specific surface area of 397.87m2The adsorption average pore diameter is 5.9 nm.
S1 was subjected to the water contact angle test, and the results are shown in fig. 6 (b). As can be seen from fig. 6, when a water droplet was placed on the surface of S1, the water contact angle was measured to be 140 °.
S1 was placed on the green bristled, and the results are shown in FIG. 7. As can be seen from FIG. 7, S1 was able to be undeformed on the green grass villi, further confirming its ultra low density (4.2 mg/cm)3)。
S1 was subjected to adsorption performance test, and the results are shown in fig. 8 and 9. As can be seen from FIG. 8, S1 shows significant adsorption performance on diesel oil, gasoline, light crude oil, soybean oil, pump oil, rapeseed oil, n-hexane, ethanol, petroleum ether, chloroform, toluene, tetrahydrofuran, dichloromethane, methanol and other oil products and organic solvents, and the adsorption capacity is above 145g/g, wherein S1 has an adsorption capacity of 310g/g for chloroform, 248g/g for diesel oil, 147g/g for tetrahydrofuran and 213g/g for pump oil.
As can be seen from fig. 9, the adsorption capacity of S1 for oil and organic solvent increased rapidly in the first 3-5 seconds and then slowly increased to reach equilibrium within 10 seconds. This can be explained by the adsorption rate being proportional to the number of free adsorption sites at the start of adsorption. As the adsorption capacity increases, the effective adsorption sites in the graphene aerogel decrease, resulting in a decrease in the adsorption rate and the final adsorption equilibrium. Among the adsorption constants of S1 for oil and organic solvent, the adsorption constant of S1 for diesel oil is 12 x 10-3s-1(ii) a Adsorption constant for tetrahydrofuran was 73.2X 10-3s-1(ii) a Adsorption constant for pump oil of 0.4X 10-3s-1Wherein the adsorption constants of S1 on gasoline and ethanol are respectively as high as 78.7 multiplied by 10-3s-1And 76.6X 10-3s-1Indicating that S1 has a faster adsorption rate.
Example 2
(1) Dispersing graphene oxide prepared by an improved Hummers method in deionized water, and performing ultrasonic treatment to form a uniform graphene oxide dispersion liquid with the concentration of 4 mg/mL;
(2) adding 4mg/mL of ascorbic acid and 1mg/mL of cysteamine into the graphene oxide dispersion liquid prepared in the step (1), magnetically stirring and uniformly mixing, placing in an oven with the temperature of 95 ℃ for hydrothermal reaction for 1h, and obtaining graphene hydrogel after the reaction is finished;
(3) and (3) putting the graphene hydrogel prepared in the step (2) into an ethanol water solution with the concentration of 10 vol% for dialysis for 12h, and then carrying out freeze drying at the temperature of-80 ℃ for 36h to obtain the graphene aerogel, wherein the label is S2.
The adsorption performance of S2 is tested to obtain S2, the adsorption capacity of the S2 to diesel oil is 245g/g, and the adsorption constant is 11.9 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 144g/g, and the adsorption constant was 73.2X 10-3s-1(ii) a The adsorption capacity to pump oil was 211g/g, and the adsorption constant was 0.39X 10-3s-1。
Example 3
(1) Dispersing graphene oxide prepared by an improved Hummers method in deionized water, and performing ultrasonic treatment to form a uniform graphene oxide dispersion liquid with the concentration of 4 mg/mL;
(2) adding 4mg/mL of ascorbic acid and 0.5mg/mL of cysteamine into the graphene oxide dispersion liquid prepared in the step (1), uniformly stirring and mixing by magnetic force, placing in an oven with the temperature of 95 ℃ for hydrothermal reaction for 1h, and obtaining graphene hydrogel after the reaction is finished;
(3) and (3) putting the graphene hydrogel prepared in the step (2) into an ethanol water solution with the concentration of 10 vol% for dialysis for 12h, and then carrying out freeze drying at the temperature of-80 ℃ for 36h to obtain the graphene aerogel, wherein the label is S3.
The adsorption performance test of S3 shows that the adsorption capacity of S3 to diesel oil is 246g/g, and the adsorption constant is 11.8 multiplied by 10-3s-1(ii) a Method for preparing tetrahydrofuranThe adsorption capacity is 144g/g, and the adsorption constant is 73.4 multiplied by 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 210g/g, and the adsorption constant is 0.39 multiplied by 10-3s-1。
Example 4
(1) Dispersing graphene oxide prepared by an improved Hummers method in deionized water, and performing ultrasonic treatment to form a uniform graphene oxide dispersion liquid with the concentration of 2 mg/mL;
(2) adding 1mg/mL of ascorbic acid and 0.25mg/mL of cysteamine into the graphene oxide dispersion liquid prepared in the step (1), magnetically stirring and uniformly mixing, placing in an oven with the temperature of 98 ℃ for hydrothermal reaction for 1.5h, and obtaining graphene hydrogel after the reaction is finished;
(3) and (3) putting the graphene hydrogel prepared in the step (2) into an ethanol water solution with the concentration of 20 vol% for dialysis for 12h, and then carrying out freeze drying at the temperature of-80 ℃ for 36h to obtain the graphene aerogel, wherein the label is S4.
The adsorption performance of S4 is tested to obtain S4, the adsorption capacity of the S4 to diesel oil is 245g/g, and the adsorption constant is 11.6 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 144g/g, and the adsorption constant was 73.2X 10-3s-1(ii) a The adsorption capacity to pump oil was 211g/g, and the adsorption constant was 0.39X 10-3s-1。
Example 5
(1) Dispersing graphene oxide prepared by an improved Hummers method in deionized water, and performing ultrasonic treatment to form a uniform graphene oxide dispersion liquid with the concentration of 4 mg/mL;
(2) adding 4mg/mL of ascorbic acid and 0.75mg/mL of cysteamine into the graphene oxide dispersion liquid prepared in the step (1), magnetically stirring and uniformly mixing, placing in a drying oven with the temperature of 92 ℃ for hydrothermal reaction for 1.5h, and obtaining graphene hydrogel after the reaction is finished;
(3) and (3) putting the graphene hydrogel prepared in the step (2) into an ethanol water solution with the concentration of 10 vol% for dialysis for 12h, and then carrying out freeze drying at the temperature of-80 ℃ for 36h to obtain the graphene aerogel, wherein the label is S5.
The adsorption performance of S5 is tested to obtain that the adsorption capacity of S5 to diesel oil is 243g/g, adsorption constant 11.2X 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 145g/g, and the adsorption constant was 72.9X 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 208g/g, and the adsorption constant is 0.36 multiplied by 10-3s-1。
Example 6
Following the procedure of example 1, except that in the preparation of the graphene aerogel, the ascorbic acid was replaced by the same mass of ethylenediamine, the prepared graphene aerogel, labeled S6.
The adsorption performance of S6 is tested to obtain S6 with diesel oil adsorption capacity of 232g/g and adsorption constant of 10.2X 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 126g/g, and the adsorption constant was 69.4X 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 197g/g, and the adsorption constant is 0.31 multiplied by 10-3s-1。
Example 7
Following the method of example 1, except that during the preparation of the graphene aerogel, cysteamine was replaced by the same mass of L-cysteine, the prepared graphene aerogel, labeled S7.
The adsorption performance of S7 is tested to obtain S7 with the diesel oil adsorption capacity of 236g/g and the adsorption constant of 10.7 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 132g/g, and the adsorption constant was 71.3X 10-3s-1(ii) a The adsorption capacity to pump oil was 199g/g, and the adsorption constant was 0.32X 10-3s-1。
Example 8
The procedure of example 1 was followed except that the concentration of graphene oxide was 5mg/mL and the amount of ascorbic acid added was 2 mg/mL.
The result was the graphene aerogel prepared in this example 8, labeled as S8.
The adsorption performance of S8 is tested to obtain S8 with the diesel oil adsorption capacity of 222g/g and the adsorption constant of 9.9 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 121g/g, and the adsorption constant was 68.8X 10-3s-1(ii) a Has an adsorption capacity for pump oil of190g/g, adsorption constant 0.3X 10-3s-1。
Example 9
The procedure of example 1 was followed except that ascorbic acid was added in an amount of 3mg/mL and cysteamine was added in an amount of 1.25 mg/mL.
The result was the graphene aerogel prepared in this example 9, labeled as S9.
The adsorption performance of S9 is tested to obtain S9 with the diesel oil adsorption capacity of 203g/g and the adsorption constant of 9.5 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 103g/g, and the adsorption constant was 67.9X 10-3s-1(ii) a The adsorption capacity to pump oil is 165g/g, and the adsorption constant is 0.28X 10-3s-1。
Example 10
The procedure of example 1 was followed except that the hydrothermal reaction temperature was 90 ℃.
The result is the graphene aerogel prepared in this example 10, labeled as S10.
The adsorption performance of S10 is tested to obtain S10 with the diesel oil adsorption capacity of 199g/g and the adsorption constant of 9.3 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 107g/g, and the adsorption constant was 67.6X 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 172g/g, and the adsorption constant is 0.28 multiplied by 10-3s-1。
Example 11
The procedure of example 1 was followed except that the hydrothermal reaction was carried out for 2 hours.
The result was the graphene aerogel prepared in this example 11, labeled as S11.
The adsorption performance of S11 is tested to obtain S11 with the diesel oil adsorption capacity of 198g/g and the adsorption constant of 9.3 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 106g/g, and the adsorption constant was 67.5X 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 179g/g, and the adsorption constant is 0.29X 10-3s-1。
Example 12
The procedure of example 1 was followed except that freeze-drying was replaced with supercritical drying.
The result is the graphene aerogel prepared in this example 12, labeled as S12.
The adsorption performance of S12 is tested to obtain S12 with the diesel oil adsorption capacity of 242g/g and the adsorption constant of 11.1 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 143g/g, and the adsorption constant was 72.6X 10-3s-1(ii) a The adsorption capacity to pump oil was 209g/g, and the adsorption constant was 0.34X 10-3s-1。
Example 13
The procedure of example 1 was followed except that the graphene hydrogel was not dialyzed against an aqueous ethanol solution before freeze-drying.
The result was the graphene aerogel prepared in this example 13, labeled as S13.
The adsorption performance of S13 is tested to obtain S13 with the diesel oil adsorption capacity of 195g/g and the adsorption constant of 8.9 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 101g/g, and the adsorption constant was 65.3X 10-3s-1(ii) a The adsorption capacity of the adsorbent to pump oil is 173g/g, and the adsorption constant is 0.26X 10-3s-1。
Comparative example 1
Following the method of example 1, except that cysteamine was not added during the preparation of the graphene aerogel, the prepared graphene aerogel, labeled D1.
D1 was subjected to a field emission scanning electron microscope test, and the results are shown in FIGS. 1(a) and (c). As can be seen by comparing fig. 1(a) and (c) with fig. 1(b) and (D), D1 exhibits a horizontally layered ordered stack structure. The S1 not only maintains the layered stacking structure of the D1, but also forms more longitudinal connections among the graphene nano sheets, so that more abundant holes are formed, and the pore size is smaller, namely, the layered stacking and longitudinal cross-linked dual three-dimensional network structure formed by the S1 is more beneficial to the adsorption of oil products or organic solvents than the D1.
D1 was subjected to atomic force microscopy and the results are shown in figure 2 (a). As can be seen by comparing fig. 2(a) and (b), a parallel wave-like layered structure is present on the surface of D1, and columnar protrusions appear on the surface of S1 layered structure, indicating that the addition of cysteamine increases the surface roughness of the graphene sheet layer.
D1 was subjected to X-ray photoelectron spectroscopy and the results are shown in FIGS. 3(a) and (c). As can be seen from fig. 3(a), D1 contains no S element. As can be seen by comparing fig. 3(b) and (C), the intensity of the C-O, C ═ O and O-C ═ O peaks in S1 was relatively weak compared to the C1S spectrum of D1, due to the nucleophilic ring-opening reaction of the epoxy group and the further reduction of graphene oxide by cysteamine.
The result of subjecting D1 to fourier transform infrared spectroscopy is shown in fig. 4. As can be seen from fig. 4, compared with D1, the strength of the oxygen-containing functional groups C-O, C-O-C, C ═ O and O-H in S1 is relatively weak, indicating that cysteamine also acts as a reducing agent in the preparation process of graphene aerogel.
D1 was subjected to a water contact angle test, and the results are shown in FIG. 6 (a). As can be seen by comparing fig. 6(a) and (b), the increase in hydrophobicity of S1 compared to the water contact angle (100 °) of D1 is due to the enhancement of the degree of reduction and the simultaneous effect of the micro/nano-roughness structure on the surface of the graphene aerogel, which is consistent with the results of FTIR, XPS and AFM of S1 and D1 with respect to surface chemistry and surface roughness. The density of S1 was 4.2mg/cm3Significantly lower density than D1 (6.7 mg/cm)3) This is consistent with SEM results for the S1 and D1 internal structures. It can be seen that under the action of cysteamine, S1 forms more longitudinal links between graphene nanoplatelets.
The adsorption performance of D1 was tested to obtain D1 having an adsorption capacity of 90g/g for n-hexane and 174g/g for diesel oil, as shown in FIG. 8 (a). In addition, the adsorption capacity of D1 for tetrahydrofuran is 82g/g, and the adsorption capacity for pump oil is 142 g/g; the adsorption constant for diesel oil is 6.5X 10-3s-1(ii) a Adsorption constant for tetrahydrofuran of 55.2X 10-3s-1(ii) a Adsorption constant for pump oil of 0.15X 10-3s-1. As can be seen from fig. 8(a), S1 has higher adsorption capacity than D1, demonstrating that the addition of cysteamine effectively modulates the internal pore structure of aerogel, improving adsorption performance.
Comparative example 2
Graphene aerogel, labelled D2, prepared according to CN110282620A example 1.
The adsorption performance of D2 is tested to obtain D2, the adsorption capacity of the D2 to diesel oil is 179g/g, and the adsorption constant is 6.9 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 88g/g, and the adsorption constant was 56.1X 10-3s-1(ii) a The adsorption capacity to pump oil was 145g/g, and the adsorption constant was 0.18X 10-3s-1。
Comparative example 3
Following the method of example 1, except that during the preparation of the graphene aerogel, cysteamine was replaced by the same mass of lysine, the prepared graphene aerogel, labeled D3.
The adsorption performance of D3 is tested to obtain D3 with the diesel oil adsorption capacity of 184g/g and the adsorption constant of 7.6 multiplied by 10-3s-1(ii) a The adsorption capacity for tetrahydrofuran was 92g/g, and the adsorption constant was 57.3X 10-3s-1(ii) a The adsorption capacity to pump oil was 156g/g, and the adsorption constant was 0.21X 10-3s-1。
As can be seen from the results of examples and D2 and D3, the adsorption performance of the graphene aerogel prepared using ascorbic acid as a reducing agent is better than that of the graphene aerogel prepared using ethylenediamine as a reducing agent; the adsorption performance of the graphene aerogel prepared by adopting cysteamine as a cross-linking agent is superior to that of the graphene aerogel prepared by adopting lysine as a cross-linking agent; the graphene aerogel prepared by using ascorbic acid as a reducing agent and cysteamine as a cross-linking agent has the best adsorption performance.
Graphene aerogels S1-S13 and D1-D3 were subjected to density, porosity, specific surface area and water contact angle tests, and the results are shown in table 1.
TABLE 1
Figure BDA0002697052500000241
The results of the examples, the comparative examples and the table 1 show that the graphene aerogel disclosed by the invention is more abundant in pores, smaller in pore size, lower in density, better in adsorption performance, and good in hydrophobicity and oil-water selectivity, and can be used as an excellent adsorption material for offshore oil spill treatment.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (10)

1. The graphene aerogel is characterized by containing C element, S element and N element, wherein the S element and the N element are respectively combined with the C element in a chemical bond mode, and the density of the graphene aerogel is 4-6.5mg/cm3。
2. The graphene aerogel according to claim 1, wherein the density of the graphene aerogel is 4-6mg/cm3Preferably 4.2 to 5mg/cm3More preferably 4.2 to 4.6mg/cm3；
Preferably, the graphene aerogel has a porosity of 90-99.5%, preferably 95-99.5%; the specific surface area is 250-500m2(ii)/g, preferably 290-2/g；
More preferably, the graphene aerogel has a surface contact angle to water of greater than 110 °, preferably greater than 120 °.
3. The graphene aerogel according to claim 1 or 2, wherein the graphene aerogel has an adsorption capacity of 195g/g or more for diesel oil, 101g/g or more for tetrahydrofuran, and 173g/g or more for pump oil;
preferably, the adsorption constant of the graphene aerogel on diesel oil is 8.5 × 10-3-12×10-3s-1Adsorption constant for tetrahydrofuran of 65X 10-3-75×10-3s-1Adsorption constant for pump oil of 0.25X 10-3-0.4×10-3s-1。
4. The graphene aerogel according to any one of claims 1 to 3, wherein the graphene aerogel has a double three-dimensional network structure of lamellar stacking and longitudinal cross-linking;
preferably, in an atomic force microscope picture of the graphene aerogel, the layered surface of the graphene aerogel has columnar protrusions, and the height of the columnar protrusions is 23.1-422.4 nm; the root mean square roughness of the layered surface of the graphene aerogel is 150-275 nm.
5. The graphene aerogel according to any one of claims 1 to 4, wherein the molar ratio of the C element to the S element to the N element is (74.5 to 83.5): (0.5-5.5): (0.8-2);
wherein, in the graphene aerogel, the molar ratio of the functional group C-C, C-O, C-S, C ═ O and O-C ═ O of the C element determined by X-ray photoelectron spectroscopy is (54-65): (20-23): (6-9): (5-8): (4-6); functional groups C-S-C and C-SO of the S element determined by X-ray photoelectron spectroscopyx-C in a molar ratio (70-85): (15-30); functional groups C-N and C-NH of the N element determined by X-ray photoelectron spectroscopy2In a molar ratio of (16-36): (64-84).
6. The preparation method of the graphene aerogel is characterized by comprising the steps of uniformly mixing a graphene oxide dispersion solution with a reducing agent and a cross-linking agent, and carrying out hydrothermal reaction to obtain a graphene hydrogel; removing the solvent in the graphene hydrogel to obtain the graphene aerogel;
wherein the cross-linking agent is cysteamine and/or L-cysteine.
7. The preparation method according to claim 6, wherein the crosslinking agent is cysteamine; the reducing agent is ascorbic acid and/or ethylenediamine, preferably ascorbic acid;
preferably, the mass ratio of the reducing agent to the graphene oxide is (0.2-2.5) to 1, preferably (0.5-2) to 1;
the mass ratio of the reducing agent to the crosslinking agent is (2-20) to 1, preferably (4-16) to 1;
more preferably, the concentration of the graphene oxide dispersion liquid is 1-5mg/mL, preferably 2-4 mg/mL;
further preferably, the temperature of the hydrothermal reaction is 90-100 ℃, preferably 92-98 ℃; the time is 0.5-2h, preferably 1-1.5 h.
8. The preparation method according to claim 6 or 7, wherein the removing of the solvent in the graphene hydrogel comprises: putting the graphene hydrogel into an ethanol water solution for dialysis, and then drying;
preferably, the drying is freeze-drying or supercritical drying, preferably freeze-drying;
more preferably, the temperature of the freeze-drying is from-10 to-100 ℃, preferably from-60 to-80 ℃; the time is 15-48h, preferably 24-36 h;
further preferably, the concentration of the ethanol aqueous solution is5 to 25 vol%, preferably 10 to 20 vol%; the dialysis time is 5-15h, preferably 8-12 h.
9. The graphene aerogel prepared by the method of any one of claims 6 to 8, wherein the density of the graphene aerogel is 4 to 6.5mg/cm3Preferably 4 to 6mg/cm3More preferably 4.2 to 5mg/cm3More preferably 4.2 to 4.6mg/cm3；
Preferably, the graphene aerogel has a porosity of 90-99.5%, preferably 95-99.5%; the specific surface area is 250-500m2(ii)/g, preferably 290-2/g；
More preferably, the graphene aerogel has a surface contact angle to water of greater than 110 °, preferably greater than 120 °;
more preferably, the adsorption capacity of the graphene aerogel on diesel oil is more than 195g/g, the adsorption capacity on tetrahydrofuran is more than 101g/g, and the adsorption capacity on pump oil is more than 173 g/g;
the adsorption constant of the graphene aerogel to diesel oil is 8.5 multiplied by 10-3-12×10-3s-1Adsorption constant for tetrahydrofuran of 65X 10-3-75×10-3s-1Adsorption constant for pump oil of 0.25X 10-3-0.4×10-3s-1。
10. Use of the graphene aerogel according to any of claims 1-5 and 9 as an adsorption material.
CN202011009338.5A 2020-09-23 2020-09-23 Graphene aerogel and preparation method and application thereof Pending CN112156753A (en)

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