CN113880077B - High-strength high-elasticity graphene aerogel free of slag falling and preparation method thereof - Google Patents
High-strength high-elasticity graphene aerogel free of slag falling and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a high-strength high-elasticity graphene aerogel free of slag falling and a preparation method thereof. The method comprises the following steps: uniformly mixing a graphene oxide solution, a dimethyl siloxane oligomer and an alkaline catalyst, and carrying out prehydrolysis and pre-organization reaction to obtain a pre-lapped graphene oxide precursor; adding a foaming agent, a reducing agent and a dimethyl siloxane cross-linking agent into the pre-lapped graphene oxide precursor, uniformly stirring, and then carrying out high-temperature reaction to obtain modified graphene wet gel; and sequentially freezing, freeze-drying and thermally annealing the modified graphene wet gel to prepare the high-strength high-elasticity graphene aerogel without slag falling. The graphene aerogel disclosed by the invention has a structure formed by mutually penetrating a polydimethylsiloxane network and a graphene framework network structure, and the polydimethylsiloxane network plays a role in enhancing the lap joint of graphene sheet layers, particularly edges, so that the problems of easiness in slag falling and low strength of the graphene aerogel are effectively solved.
Description
Technical Field
The invention belongs to the technical field of graphene aerogel, relates to a preparation method of graphene aerogel, and particularly relates to high-strength high-elasticity graphene aerogel free of slag falling and a preparation method of the high-strength high-elasticity graphene aerogel.
Background
The high-elasticity graphene aerogel is a porous graphene three-dimensional macroscopic assembly with the pore diameter of tens to hundreds of microns, which is formed by taking graphene sheets with certain elasticity as intrinsic building elements and overlapping the graphene sheets in three dimensions through various physical or chemical actions. In addition to the excellent characteristics of the conventional graphene aerogel, such as ultrahigh porosity, large specific surface area, ultralow density, excellent electrical conductivity, ultralow thermal conductivity and the like, the elastic graphene aerogel has the mechanical characteristic of compression resilience, and the elastic material with the larger reversible deformation function has wide requirements in various engineering applications, such as heat insulation, adsorption, sensing and the like, and has attracted strong attention of researchers. However, due to insufficient lap joint between graphene sheet layers, especially insufficient lap joint of the graphene sheet layers at the edges, on one hand, the aerogel pore structure is easy to collapse when being used under large deformation, so that the overall mechanical strength of the elastic graphene aerogel material is low, and the elasticity of the material can be irreversibly damaged under large deformation acting force; on the other hand, the graphene aerogel can be easily broken and broken slag can be easily dropped out when the graphene aerogel is compressed, particularly when the graphene aerogel is compressed in a repeated use process, so that great safety risk is caused. The practical application process of the elastic graphene aerogel is greatly limited by the problems of easy slag falling and low strength of the elastic graphene aerogel.
In view of the above, in recent years, many researchers have been dedicated to improving the mechanical strength of graphene aerogel, chinese patent CN109734076B adopts a wet pressing method to compress a graphene wet gel obtained after foaming and reduction after freezing-thawing treatment to obtain a graphene wet gel with a density of 30-90 mg/cm 3 The large-area high-strength elastic graphene aerogel has the maximum compression strength of 0.045MPa under 50% deformation, and the essence of strength improvement is that the density of the material is improved through aftertreatment, so that the strength is improved. The Chinese patent application CN111847430A adopts the graphene oxide dispersed by alkali to prepare the graphene aerogel, and the alkali treatment mode is helpful for forming an ordered hole structure, so that the mechanical strength of the material is improved, and the maximum compression strength under 50% deformation can reach 0.007MPa. Chinese patent application CN108525649A uses polyethyleneimine as a cross-linking agent of a graphene oxide precursor, and uses sodium alginate as a reinforcing material, and sodium alginate is cross-linked under the action of calcium ions to form a graphene oxide aerogel with an interpenetrating network structure, so as to prepare a high-strength graphene aerogel material, however, the graphene aerogel material is not subjected to reduction reaction and high-temperature thermal annealing treatment, and the lap joint between graphene sheets is relatively weak. Chinese patent application CN111100291A reports a preparation method of polybenzoxazine reinforced three-dimensional graphene foam, wherein polybenzoxazine macromolecules are introduced into a three-dimensional graphene system, so that the polybenzoxazine reinforced three-dimensional graphene foam can play a role in crosslinking graphene sheets and can disperse and transfer stress, and further, the polybenzoxazine reinforced three-dimensional graphene foam can be used for preparing graphene foamThe construction of the high-strength three-dimensional graphene structure is realized, however, a benzoxazine monomer which is a raw material having great environmental pollution and great harm to the body is used in the preparation process, and a large amount of organic solvent is required to be used for cleaning in the following process, so that the preparation method is not environment-friendly.
In a word, the preparation technology of the high-elasticity graphene aerogel is greatly developed at present, but the strength of the prepared material still needs to be further improved, and more seriously, the problem of slag falling of the graphene aerogel is not reported to be solved, and the preparation of the high-strength high-elasticity graphene aerogel without slag falling by using a simple and easy method has a remarkable significance for promoting the engineering application of the high-strength high-elasticity graphene aerogel.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a high-strength high-elasticity graphene aerogel without slag falling and a preparation method thereof; according to the invention, pre-hydrolyzed dimethyl siloxane oligomer and graphene oxide sheets are introduced for pre-organization, so that the upper side, the lower side and the edge of a graphene oxide sheet layer are fully lapped, and then a double-network structure in which a graphene sheet layer network and a polydimethylsiloxane high-molecular network (polydimethylsiloxane network) are mutually penetrated is formed under the action of a dimethyl siloxane cross-linking agent, so that the graphene aerogel is endowed with extremely high elasticity and mechanical strength, and the aerogel can be kept without slag falling in multiple compression rebound cycles.
The invention provides a preparation method of a high-strength high-elasticity graphene aerogel without slag falling, which comprises the following steps:
(1) Uniformly mixing a graphene oxide solution, a dimethyl siloxane oligomer and an alkaline catalyst, and then carrying out prehydrolysis and pre-organization reaction to obtain a pre-lapped graphene oxide precursor;
(2) Adding a foaming agent, a reducing agent and a dimethyl siloxane cross-linking agent into the pre-lapped graphene oxide precursor, uniformly stirring, and then carrying out high-temperature reaction to obtain modified graphene wet gel;
(3) And sequentially freezing, freeze-drying and thermally annealing the modified graphene wet gel to prepare the high-strength high-elasticity graphene aerogel without slag falling.
Preferably, the dimethyl siloxane oligomer is one or more of PDMS Sylgard 184A glue, PDMS RTV 163A glue, PDMS RTV165A glue, PDMS RTV 655A glue; the dimethyl siloxane cross-linking agent is one or more of PDMS Sylgard184B glue, PDMS RTV 163B glue, PDMS RTV 165B glue and PDMS RTV 655B glue; and/or the mass ratio of the dimethyl siloxane oligomer to the dimethyl siloxane cross-linking agent is 1: (0.05-0.2).
Preferably, the basic catalyst is one or more of ammonia water, ammonium fluoride solution, sodium carbonate solution, sodium bicarbonate solution and sodium formate solution.
Preferably, the mass ratio of the graphene oxide contained in the graphene oxide solution to the dimethyl siloxane oligomer to the basic catalyst is 1: (0.1-1.5): (0.001-0.03).
Preferably, the time for the prehydrolysis and the pre-organization reaction is 1 to 12 hours.
Preferably, the high-temperature reaction is carried out at the temperature of 80-160 ℃ for 8-36 h.
Preferably, the number of graphene oxide layers contained in the graphene oxide solution is 1 to 6; and/or the concentration of the graphene oxide contained in the graphene oxide solution is 2-40 mg/mL.
Preferably, the foaming agent is one or more of alkyl glycoside, styrene maleic anhydride resin, alkylphenol ethoxylates and sodium dodecyl sulfate; the mass ratio of the graphene oxide solution to the foaming agent is 1: (0.001-0.05); the reducing agent is one or more of dithiothreitol, sodium ascorbate, hydroiodic acid, sodium sulfite and hydrazine hydrate; and/or the mass ratio of the graphene oxide contained in the graphene oxide solution to the reducing agent is 1: (1-10).
Preferably, the temperature of the thermal annealing is 200-400 ℃, and the time is 2-16 h.
In a second aspect, the invention provides the high-strength high-elasticity graphene aerogel without slag falling, which is prepared by the preparation method in the first aspect of the invention, wherein the high-strength high-elasticity graphene aerogel without slag falling has a double-network structure in which a graphene sheet layer network and a polydimethylsiloxane network are mutually penetrated, and the polydimethylsiloxane networks are lapped between the graphene sheet layers and at the edges.
Advantageous effects
Compared with the existing graphene aerogel prepared by other reported technologies, the high-strength high-elasticity graphene aerogel without slag falling, which is prepared by the invention, has a unique microstructure and special macroscopic physical properties brought by the microstructure:
(1) The density of the high-strength high-elasticity graphene aerogel without slag falling, prepared by the invention, is 4-30 mg/cm 3 The thermal conductivity is 0.015-0.021W/(m.K), the resilience rate under 99% strain compression can reach 100%, the ultra-light weight characteristic, the ultra-high heat insulation capability and the excellent resilience performance are shown, the density of the material is not obviously increased by introducing the polydimethylsiloxane network, and no adverse effect is brought to the thermal conductivity and the elasticity of the graphene aerogel.
(2) The high-strength high-elasticity graphene aerogel without slag falling, which is prepared by the invention, has the compression strength of up to 0.16MPa under 50% of compression deformation and the ultimate compression strength of over 63MPa under 99% of ultimate compression deformation, shows ultrahigh strength and greatly leads the strength of the elastic graphene aerogel reported in documents. Under the same density, the compression strength of the graphene aerogel without introducing a polydimethylsiloxane network structure is only 0.004MPa under 50% compression deformation, the polydimethylsiloxane network and a graphene framework network (graphene sheet layer network) penetrate through each other, and the structural characteristics of the polydimethylsiloxane network and the flexibility of polydimethylsiloxane are lapped between the graphene sheet layers and at the edges of the graphene sheet layers, so that the mechanical strength of the elastic graphene aerogel can be greatly improved.
(3) After the high-strength high-elasticity graphene aerogel without slag falling, which is prepared by the invention, is subjected to 1000 times of compression rebound cycle tests, no obvious slag falling phenomenon exists, and the shape is kept complete. Compared with the prior art, the phenomenon of slag falling of the graphene aerogel without enhancement of polydimethylsiloxane after 1000 compression rebound cycles is very obvious, and numerous cracks and fissures are generated in an aerogel block. The reason is that the carbon chain skeleton of the prehydrolyzed dimethyl siloxane oligomer is hydrophobic, the upper and lower layers in the center of the graphene oxide sheet layer are also hydrophobic, certain hydrophobic effects (supramolecular effect) exist on the upper and lower sides of the graphene oxide sheet layer, the side chain of the prehydrolyzed dimethyl siloxane oligomer contains hydrophilic hydroxyl groups, and the side chain of the prehydrolyzed dimethyl siloxane oligomer has the effects of hydrogen bonds and the like with surface functional groups such as hydroxyl, carboxyl, amino, epoxy and the like at the edge of the graphene oxide sheet layer, although the effects of the hydrophobic groups, the hydrogen bonds and the like are weak interactions, the cumulative effect of a plurality of weak interactions causes that the acting force is still very large; in addition, the hydrophobic carbon chain skeleton and the side chain hydroxyl group of the prehydrolyzed dimethyl siloxane oligomer and the hydrophobic central part of the graphene oxide sheet layer are provided with the upper layer, the lower layer, the edge hydroxyl group, the carboxyl group and other groups, due to the pre-organization effect, the hydrophobic and hydrogen bond effects between the two groups can generate the adjustment of the action space and the action direction so as to maximize the synergistic effect between the two groups, and the pre-organization effect ensures that the upper side and the lower side of the graphene oxide sheet layer are fully lapped and adhered with the prehydrolyzed dimethyl siloxane oligomer at the edge; in addition, after pre-organization, the hydroxyl group of the side group of the pre-hydrolyzed dimethyl siloxane oligomer and the hydroxyl group and the carboxyl group at the edge of the graphene oxide can also be condensed under the action of a catalyst, so that the adhesion between the pre-hydrolyzed dimethyl siloxane oligomer and the graphene oxide is further increased, and finally, the pore wall of the graphene aerogel prepared by the invention is obviously thickened, and the combination of the pore connection part is stronger, so that the graphene aerogel prepared by the invention can be ensured to have no obvious slag falling phenomenon after multiple compression rebound cycle tests, and the shape can still keep complete; in the compression process, the hole wall junction is a weak part, and the hole wall of the graphene aerogel prepared by the prior art is generally thin, and the combination of the hole junction is weak, so that the graphene aerogel is easy to crack at the position in multiple times of cyclic compression, and further the graphene is subjected to slag falling.
(4) The method effectively solves the problems that the elastic graphene aerogel is easy to remove slag and low in strength, greatly promotes the application process of the graphene aerogel in various engineering such as heat insulation, adsorption, sensing and the like, and has the advantages of simplicity, strong operability, relative greenness, environmental friendliness and the like.
Drawings
Fig. 1 is an outline view of a high-strength high-elasticity graphene aerogel block without slag falling, which is prepared in example 1 of the present invention. As can be seen from fig. 1, the high-strength and high-elasticity graphene aerogel block without dropping residue prepared in example 1 has an ultra-light weight, and can be supported on a flower.
Fig. 2 is a shape change diagram of the high-strength high-elasticity graphene aerogel block without slag falling, which is prepared in example 1 of the present invention, in a 1000 th extreme pressure limiting cycle test process.
Fig. 3 is a scanning electron microscope image (right side) of the high-strength high-elasticity graphene aerogel without slag falling, which is prepared in example 1 of the present invention, and a scanning electron microscope image (left side) of the polydimethylsiloxane-free reinforced elastic graphene aerogel, which is prepared in comparative example 1 of the present invention. As can be seen from fig. 3, the pore walls of the high-strength high-elasticity graphene aerogel without slag falling, prepared in example 1 of the present invention, are significantly thicker than those of the elastic graphene aerogel without polydimethylsiloxane reinforcement, prepared in comparative example 1.
Fig. 4 is a stress-strain curve of the high-strength high-elasticity graphene aerogel without slag falling, prepared in example 1 of the present invention, and the polydimethylsiloxane-free reinforced elastic graphene aerogel prepared in comparative example 1 of the present invention.
Fig. 5 is an element distribution diagram of the high-strength high-elasticity graphene aerogel without slag falling, which is prepared in example 1 of the present invention.
Fig. 6 is a photograph of a contact angle between a high-strength high-elasticity graphene aerogel block without falling slag and water, which is prepared in example 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention provides a preparation method of a high-strength high-elasticity graphene aerogel without slag falling, which comprises the following steps:
(1) Uniformly mixing a graphene oxide solution, a dimethyl siloxane oligomer and an alkaline catalyst, and then carrying out prehydrolysis and pre-organization reaction to obtain a pre-lapped graphene oxide precursor; in the invention, the graphene oxide solution is a graphene oxide aqueous solution; in the invention, after uniformly mixing a graphene oxide solution, a dimethyl siloxane oligomer and a basic catalyst, carrying out prehydrolysis on the dimethyl siloxane oligomer under the action of the basic catalyst to obtain the prehydrolyzed dimethyl siloxane oligomer, and carrying out pre-organization (namely pre-lap joint) on the edges of the prehydrolyzed dimethyl siloxane oligomer, the upper and lower sides of a graphene oxide sheet layer and the edge of graphene oxide to obtain a pre-lap joint graphene oxide precursor; in the invention, the pre-organization refers to a concept in supramolecular chemistry, and the pre-organization in the supramolecular chemistry enables the optimal matching of an action space and an action force direction to be realized through the autonomous regulation effect when a host and an object act, so that the maximum action force between the host and the object is realized; in the invention, the pre-organization is to uniformly mix the graphene oxide solution, the dimethyl siloxane oligomer and the basic catalyst and then react for a period of time, and the hydrophobic carbon chain skeleton and the side chain hydroxyl group of the pre-hydrolyzed dimethyl siloxane oligomer are found to be in contact with the upper and lower layers and the hydroxyl, carboxyl and other groups at the edges of the hydrophobic central part of the graphene oxide sheet layer, the hydrophobic effect and the hydrogen bond effect between the two groups are adjusted and matched according to the action space and the action force direction so as to maximize the combined action between the two groups, and the pre-organization effect ensures that the upper and lower sides of the graphene oxide sheet layer are fully lapped and adhered with the pre-hydrolyzed dimethyl siloxane oligomer at the edges; in the present invention, the prehydrolysis and the pre-organization reaction may be performed at room temperature (e.g., room temperature 10 to 35 ℃ C.), for example.
(2) Adding a foaming agent, a reducing agent and a dimethyl siloxane cross-linking agent into the pre-lapped graphene oxide precursor, uniformly stirring, and then carrying out high-temperature reaction to obtain modified graphene wet gel; in the invention, the modified graphene wet gel is a graphene wet gel penetrating through a polydimethylsiloxane network.
(3) Sequentially freezing, freeze-drying and thermally annealing (thermal annealing treatment) the modified graphene wet gel to prepare high-strength high-elasticity graphene aerogel without slag falling; the present invention is not particularly limited with respect to the conditions of the freezing and the freeze-drying; the freezing may be, for example: freezing for 6-48 h at-40 to-196 ℃; the conditions for the freeze-drying are, for example: the pressure intensity (absolute pressure intensity) of the freeze drying is 1-30 Pa, the temperature of the freeze drying is 10-35 ℃, and the time of the freeze drying is 24-96 h; the high-strength high-elasticity graphene aerogel without slag falling has a special structure formed by mutually penetrating polydimethylsiloxane networks in the whole graphene macroporous network structure, and the polydimethylsiloxane networks play a role in enhancing the lap joint of graphene sheet layers, particularly edges.
Chinese patent application CN108525649A discloses that polyethyleneimine is used as a cross-linking agent and a nitrogen source, a large number of amino groups on the surface of the polyethyleneimine can be covalently and non-covalently bonded with oxygen-containing functional groups of graphene oxide lamella to cross-link the graphene lamella, but the polyethyleneimine is a hydrophilic polymer, the hydrophilic skeleton and the hydrophobic central upper and lower layers of the graphene oxide lamella have no hydrophobic effect, and only the oxygen-containing functional groups of the graphene oxide lamella and the amino groups of the polyethyleneimine side chain are reacted; in addition, in chinese patent application CN108525649A, the connection between graphene oxides mainly depends on polyethyleneimine polymers, and fragmented lapups are formed (i.e., graphene oxides in a certain region are connected by one polyethyleneimine polymer, and graphene oxides in another region are connected by one polyethyleneimine polymer), and since covalent crosslinking is not possible between polyethyleneimine polymers, a polymer crosslinked network structure of polyethyleneimine cannot be formed to directly and completely lap-joint graphene oxides in all discrete regions, the connection between fragmented lapups of the present application depends on an interpenetrating network structure formed by indirect connection of pore wall of a alginic acid anion-calcium cation network structure, and this indirect connection manner makes the aerogel of the final graphene oxide generally thinner, the pore junctions combine weakly, and residues easily fall off during multiple compressions; in addition, the patent application does not carry out chemical reduction reaction and high-temperature thermal annealing treatment, and graphene oxide lamella layers can have strong pi-pi effect only after reduction treatment, so that complete overlapping can be realized. The invention is totally different from the Chinese patent application CN108525649A in that the pre-hydrolyzed dimethyl siloxane oligomer skeleton and side chains are simultaneously acted with the upper surface, the lower surface and the edge of the center of a graphene oxide sheet layer, and the invention discovers that the joint action of the pre-hydrolyzed dimethyl siloxane oligomer and the graphene oxide is stronger; compared with macromolecular polyethyleneimine, the prehydrolyzed dimethyl siloxane oligomer used in the invention has the advantages of small molecular weight, higher molecular motion speed and quicker and more effective action with graphene oxide; according to the invention, oxidized graphene is firstly connected by using a prehydrolyzed dimethyl siloxane oligomer to form a fragmented lapping body, a polydimethylsiloxane high-molecular network structure is formed under the action of a subsequent dimethyl siloxane cross-linking agent, all fragmented graphene areas are completely connected by the complete high-molecular network structure, and an interpenetrating network structure is directly formed with the reduced graphene network structure, so that the finally prepared graphene aerogel has generally thicker hole walls and stronger combination at the hole connection positions, and can still keep integrity without slag falling after multiple compression.
Although the chinese patent application CN106084276A discloses a method for synthesizing a graphene-polydimethylsiloxane functional sponge, the method adopts graphene powder as a filler, and the graphene powder is filled into PDMS high polymer to prepare a porous material functional sponge, and has the structural characteristics that the graphene is coated by PDMS high polymer molecules, and cannot play a functional role of graphene, and the powdered graphene cannot be uniformly dispersed in a PDMS prepolymer on a micro-nano scale. The invention is completely different from the technical field of porous material functional sponge prepared by taking graphene as a filler in CN106084276A, and belongs to the technical field of graphene aerogel mainly constructed by taking graphene as a main construction element. The high-strength high-elasticity graphene aerogel without slag falling has a double-network structure in which graphene sheet layers and Polydimethylsiloxane (PDMs) networks are mutually penetrated, and the polydimethylsiloxane networks are lapped among the graphene sheet layers and at the edges; in the invention, the graphene is not coated by the PDMS high molecular polymer. In the invention, the elasticity of the graphene aerogel depends on the macroporous structure on one hand and is also related to the elasticity of lap joints among graphene sheet layers and at the edges, and the elasticity and the strength of the graphene aerogel material can be improved by proper amount of PDMS (polydimethylsiloxane) due to the flexibility of the PDMS bridging the graphene sheet layers.
According to some preferred embodiments, the dimethylsiloxane oligomer is a commercial PDMS prepolymer, preferably one or more of PDMS Sylgard 184A gum, PDMS RTV 163A gum, PDMS RTV165A gum, PDMS RTV 655A gum, more preferably PDMS Sylgard 184A gum; PDMS Sylgard 184A glue, PDMS RTV 163A glue, PDMS RTV165A glue, PDMS RTV 655A glue, which are all available from the market directly; the dimethyl siloxane cross-linking agent is a cross-linking agent corresponding to a commercial PDMS prepolymer, preferably one or more of PDMS Sylgard184B glue, PDMS RTV 163B glue, PDMS RTV 165B glue and PDMS RTV 655B glue, and more preferably PDMS Sylgard184B glue; PDMS Sylgard184B glue, PDMS RTV 163B glue, PDMS RTV 165B glue, PDMS RTV 655B glue, which are all available from the market directly; and/or the mass ratio of the dimethyl siloxane oligomer to the dimethyl siloxane cross-linking agent is 1: (0.05 to 0.2) (e.g., 1: (0.08 to 0.15), more preferably 1.
According to some preferred embodiments, the basic catalyst is one or more of ammonia, ammonium fluoride solution, sodium carbonate solution, sodium bicarbonate solution, sodium formate solution, preferably ammonia; the concentration of the aqueous ammonia in the present invention is not particularly limited, and for example, the aqueous ammonia may be 10 to 28% (containing ammonia (NH) 3 ) 10-28 percent of concentrated ammonia water.
According to some preferred embodiments, the mass ratio of the graphene oxide, the dimethylsiloxane oligomer, and the basic catalyst contained in the graphene oxide solution is 1: (0.1-1.5): (0.001-0.03) (e.g. 1. In the present invention, it is preferable that the mass ratio of the graphene oxide contained in the graphene oxide solution, the dimethyl siloxane oligomer, and the basic catalyst is 1: (0.1-1.5): (0.001-0.03), if the amount of the dimethyl siloxane oligomer relative to the graphene oxide is too small, the dimethyl siloxane oligomer cannot play a good lapping role, and if the amount of the dimethyl siloxane oligomer relative to the graphene oxide is too large, the mechanical properties such as elasticity of the material are influenced.
According to some preferred embodiments, the time for the prehydrolysis and the pre-tissue reaction is 1 to 12h (e.g. 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5 or 12 h), preferably 1.5 to 4h, more preferably 2h. In the present invention, it is preferable that the time for the prehydrolysis and the pre-organization reaction is 1 to 12 hours, and if the time for the prehydrolysis and the pre-organization reaction is too short, the degree of hydrolysis of the dimethylsiloxane oligomer is insufficient, and the upper layer and the lower layer of the graphene oxide sheet are not completely overlapped with the edges of the graphene oxide sheet, so that the overlapping is insufficient, and the time for the prehydrolysis and the pre-organization reaction is too long, which affects the efficiency.
According to some more preferred embodiments, the mass ratio of the graphene oxide, the dimethylsiloxane oligomer, and the basic catalyst contained in the graphene oxide solution is 1: (0.1-1.5): (0.001-0.03), and the time of the prehydrolysis and the pre-organization reaction is 1-12 h; according to the invention, by controlling the mass ratio of the graphene oxide, the dimethyl siloxane oligomer and the alkaline catalyst contained in the graphene oxide solution and the time of the prehydrolysis and the pre-organization reaction, the weak interaction force can be accurately regulated and controlled, the action between the prehydrolyzed dimethyl siloxane oligomer and the graphene oxide can be strengthened to the greatest extent, and the upper layer, the lower layer and the edge of the central part of the prehydrolyzed dimethyl siloxane oligomer and the graphene oxide sheet layer can be more fully lapped.
According to some preferred embodiments, the high temperature reaction is at a temperature of 80 to 160 ℃ (e.g., 80 ℃, 90 ℃, 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ or 160 ℃) for 8 to 36 hours (e.g., 8, 10, 12, 18, 20, 24, 28, 30 or 36 hours); in the present invention, it is more preferable that the high temperature reaction (i.e., the sol-gel and crosslinking reaction is performed) is performed at a temperature of 120 ℃ and the high temperature reaction time is 24 hours.
According to some preferred embodiments, the number of graphene oxide layers contained in the graphene oxide solution is 1 to 6 (e.g., 1, 2, 3, 4, 5, or 6); in some preferred embodiments, the number of graphene oxide layers contained in the graphene oxide solution is 1, that is, a single layer of graphene oxide; and/or the concentration of graphene oxide contained in the graphene oxide solution is 2 to 40mg/mL (for example, 2, 5, 10, 15, 20, 25, 30, 35, or 40 mg/mL), more preferably 5 to 20mg/mL, and still more preferably 20mg/mL.
The foaming agent and the reducing agent are not particularly limited in kind and amount, and may be those commonly used in the art.
According to some preferred embodiments, the foaming agent is one or more of alkyl glycoside, styrene maleic anhydride resin, alkylphenol ethoxylates and sodium lauryl sulfate, and preferably, the foaming agent is alkyl glycoside; the mass ratio of the graphene oxide solution to the foaming agent is 1: (0.001 to 0.05) (e.g., 1; the reducing agent is one or more of dithiothreitol, sodium ascorbate, hydroiodic acid, sodium sulfite and hydrazine hydrate, and preferably dithiothreitol; and/or the mass ratio of the graphene oxide contained in the graphene oxide solution to the reducing agent is 1: (1-10) (e.g. 1.
According to some preferred embodiments, the thermal annealing is at a temperature of 200 to 400 ℃ (e.g., 200 ℃, 250 ℃, 300 ℃, 350 ℃ or 400 ℃) for 2 to 16 hours (e.g., 2, 4, 6, 8, 10, 12, 14 or 16 hours); in some preferred embodiments, the thermal annealing is performed at 300 ℃ for 8h.
In a second aspect, the invention provides a high-strength high-elasticity graphene aerogel without slag dropping, which is prepared by the preparation method in the first aspect of the invention, and the high-strength high-elasticity graphene aerogel without slag dropping has a double-network structure in which a graphene sheet layer network and a polydimethylsiloxane network penetrate each other, and the polydimethylsiloxane networks are lapped between the graphene sheet layers and at the edges.
The invention will be further described by way of example only, without the scope of protection of the invention being limited to these examples. The present invention is capable of other embodiments, and various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Example 1
(1) 50mL of single-layer graphene oxide solution with the concentration of 20mg/mL, 0.3g of dimethyl siloxane oligomer PDMS Sylgard 184A glue and 0.01g of concentrated ammonia water (the mass fraction of ammonia contained in the concentrated ammonia water is 28%) are uniformly mixed under magnetic stirring, and prehydrolysis and pre-organization reaction are carried out for 2 hours under room-temperature stirring to obtain the pre-lapped graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.03g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the pre-lapped graphene oxide precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at the high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator at the temperature of-40 ℃ overnight, then putting the modified graphene wet gel in a freeze dryer for freeze drying, controlling the pressure in the freeze dryer to be below 20Pa, controlling the temperature to be 25 ℃, and after freeze drying for 48 hours, putting the obtained graphene aerogel in a muffle furnace at the temperature of 300 ℃ for thermal annealing for 8 hours to finally obtain the high-strength high-elasticity graphene aerogel without slag falling.
Example 2
(1) 50mL of single-layer graphene oxide solution with the concentration of 20mg/mL, 0.1g of dimethyl siloxane oligomer PDMS Sylgard 184A glue and 0.001g of concentrated ammonia water (the mass fraction of ammonia contained in the concentrated ammonia water is 28%) are uniformly mixed under magnetic stirring, and prehydrolysis and pre-organization reaction are carried out for 12 hours under room-temperature stirring to obtain the pre-lapped graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.01g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the pre-lapped graphene oxide precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at a high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator at the temperature of-40 ℃ overnight, then putting the modified graphene wet gel in a freeze dryer for freeze drying, controlling the pressure in the freeze dryer to be below 20Pa, controlling the temperature to be 25 ℃, and after freeze drying for 48 hours, putting the obtained graphene aerogel in a muffle furnace at the temperature of 300 ℃ for thermal annealing for 8 hours to finally obtain the high-strength high-elasticity graphene aerogel without slag falling.
Example 3
(1) 50mL of a monolayer graphene oxide solution with the concentration of 20mg/mL, 1.5g of dimethyl siloxane oligomer PDMS Sylgard 184A glue and 0.03g of strong ammonia water (the mass fraction of ammonia contained in the strong ammonia water is 28%) are uniformly mixed under magnetic stirring, and prehydrolysis and pre-organization reaction are carried out for 1h under room-temperature stirring to obtain a pre-lapped graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.15g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the pre-lapped graphene oxide precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at the high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator with the temperature of-40 ℃ overnight, then freezing and drying in a freeze dryer, controlling the pressure in the freeze dryer to be below 20Pa and the temperature to be 25 ℃, after freezing and drying for 48 hours, putting the obtained graphene aerogel in a muffle furnace with the temperature of 300 ℃ for thermal annealing for 8 hours, and finally obtaining the high-strength high-elasticity graphene aerogel without slag dropping.
Example 4
Example 4 is essentially the same as example 1, except that:
the dimethylsiloxane oligomer in this example is PDMS RTV 163A gum, and the dimethylsiloxane crosslinker is PDMS RTV 163B gum.
Example 5
(1) 50mL of single-layer graphene oxide solution with the concentration of 20mg/mL, 0.05g of dimethyl siloxane oligomer PDMS Sylgard 184A glue and 0.01g of concentrated ammonia water (the mass fraction of ammonia contained in the concentrated ammonia water is 28%) are uniformly mixed under magnetic stirring, and prehydrolysis and pre-organization reaction are carried out for 2 hours under room-temperature stirring to obtain the pre-lapped graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.005g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the pre-lapped graphene oxide precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at a high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator with the temperature of-40 ℃ overnight, then freezing and drying in a freeze dryer, controlling the pressure in the freeze dryer to be below 20Pa and the temperature to be 25 ℃, freezing and drying for 48 hours, and then placing the obtained graphene aerogel in a muffle furnace with the temperature of 300 ℃ for thermal annealing for 8 hours to obtain the elastic graphene aerogel.
Example 6
(1) 50mL of single-layer graphene oxide solution with the concentration of 20mg/mL, 1.8g of dimethyl siloxane oligomer PDMS Sylgard 184A glue and 0.01g of concentrated ammonia water (the mass fraction of ammonia contained in the concentrated ammonia water is 28%) are uniformly mixed under magnetic stirring, and prehydrolysis and pre-organization reaction are carried out for 2 hours under room-temperature stirring to obtain the pre-lapped graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.18g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the pre-lapped graphene oxide precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at the high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator at the temperature of-40 ℃ overnight, then putting the modified graphene wet gel in a freeze dryer for freeze drying, controlling the pressure in the freeze dryer to be below 20Pa and the temperature to be 25 ℃, and after freeze drying for 48 hours, putting the obtained graphene aerogel in a muffle furnace at the temperature of 300 ℃ for thermal annealing treatment for 8 hours to obtain the elastic graphene aerogel.
Example 7
Example 7 is essentially the same as example 1, except that:
in step (1), the prehydrolysis and the pre-organization reactions were carried out for 0.5h.
Example 8
Example 8 is essentially the same as example 1, except that:
in step (1), the prehydrolysis and the pre-organization reaction were carried out for 15 hours.
Comparative example 1
(1) Adding 0.5g of foaming agent alkyl glycoside and 4g of reducing agent dithiothreitol into 50mL of single-layer graphene oxide solution with the concentration of 20mg/mL, uniformly stirring, and carrying out sol-gel reaction at the high temperature of 120 ℃ for 24 hours to obtain the graphene wet gel.
(2) And (2) freezing the graphene wet gel in a refrigerator with the temperature of-40 ℃ for one night, then freezing and drying in a freeze dryer, controlling the pressure in the freeze dryer to be below 20Pa and the temperature to be 25 ℃, freezing and drying for 48 hours, and then placing the obtained graphene aerogel in a muffle furnace with the temperature of 300 ℃ for thermal annealing for 8 hours to obtain the elastic graphene aerogel.
Comparative example 2
(1) And (3) uniformly mixing 50mL of a monolayer graphene oxide solution with the concentration of 20mg/mL and 0.3g of dimethyl siloxane oligomer PDMS Sylgard 184A glue under magnetic stirring to obtain a graphene oxide precursor.
(2) And adding 0.5g of foaming agent alkyl glycoside, 4g of reducing agent dithiothreitol and 0.03g of dimethyl siloxane cross-linking agent PDMS Sylgard184B glue into the oxidized graphene precursor, uniformly stirring, and carrying out sol-gel and cross-linking reaction at the high temperature of 120 ℃ for 24 hours to obtain the modified graphene wet gel.
(3) And (2) freezing the modified graphene wet gel in a refrigerator at the temperature of-40 ℃ overnight, then putting the modified graphene wet gel in a freeze dryer for freeze drying, controlling the pressure in the freeze dryer to be below 20Pa and the temperature to be 25 ℃, and after freeze drying for 48 hours, putting the obtained graphene aerogel in a muffle furnace at the temperature of 300 ℃ for thermal annealing treatment for 8 hours to obtain the modified graphene aerogel.
Comparative example 3
(1) Dissolving 24mg of graphite oxide in 3mL of distilled water, placing the solution in an ultrasonic machine, and carrying out ultrasonic treatment for 1 hour at the ultrasonic frequency of 100Hz to obtain a graphene oxide aqueous solution with the uniformly dispersed concentration of 8 mg/mL.
(2) 60mg of polyethyleneimine 90mgSA (sodium alginate) is dissolved in 3mL of deionized water, and the solution is mechanically stirred for 1 hour to obtain a PEI/SA mixed solution which is uniformly mixed.
(3) And (3) uniformly mixing the mixed solution obtained in the step (1) and the step (2), and reacting at 60 ℃ for 24 hours to obtain the composite graphene hydrogel.
(4) Soaking the composite hydrogel prepared in step (3) into 2% of CaCl 2 And (5) obtaining the hydrogel with the interpenetrating network structure by using the aqueous solution for 12h.
(5) And (3) carrying out auxiliary dialysis on the hydrogel obtained in the step (4) by using a 10% ethanol aqueous solution for 12h, and then carrying out freeze drying for 24h to obtain the graphene aerogel material.
(6) And (5) putting the graphene aerogel material obtained in the step (5) into a muffle furnace at the temperature of 300 ℃ for thermal annealing treatment for 8 hours to obtain the elastic graphene aerogel.
The graphene aerogels finally prepared in examples 1 to 7 and comparative examples 1 to 3 were subjected to performance tests, and the test results are shown in table 1. A scanning electron microscope image of the high-strength and high-elasticity graphene aerogel (abbreviated as reinforced graphene aerogel in the figure) without slag falling, which is prepared in the embodiment 1 of the invention, and a scanning electron microscope image of the polydimethylsiloxane-reinforced-free elastic graphene aerogel (abbreviated as non-reinforced graphene aerogel in the figure) prepared in the comparative example 1 are shown in fig. 3; as can be seen from fig. 3, the pore walls of the high-strength high-elasticity graphene aerogel without slag falling, which is prepared in example 1 of the present invention, are significantly thicker than the pore walls of the elastic graphene aerogel without polydimethylsiloxane reinforcement, which is prepared in comparative example 1; stress-strain curves of the high-strength high-elasticity graphene aerogel without slag falling (abbreviated as reinforced graphene aerogel in the figure) prepared in example 1 of the invention and the polydimethylsiloxane-reinforced-free elastic graphene aerogel without reinforced graphene aerogel prepared in comparative example 1 (abbreviated as non-reinforced graphene aerogel in the figure) are shown in fig. 4.
Table 1: the performance indexes of the graphene aerogels finally prepared in the embodiments 1 to 7 and the comparative examples 1 to 3 of the present invention.
In table 1, the method for testing the slag dropping rate after 1000 times of compression rebound cycle test is as follows: dividing the weight loss of the graphene aerogel after 1000 times of compression and rebound cycle tests by the original weight of the graphene aerogel before the compression test; wherein, each compression rebound refers to each compression to 50% compression set and then rebound.
The invention has not been described in detail and is in part known to those of skill in the art.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (7)
1. The preparation method of the high-strength high-elasticity graphene aerogel without slag falling is characterized by comprising the following steps:
(1) Uniformly mixing a graphene oxide solution, a dimethyl siloxane oligomer and an alkaline catalyst, and then carrying out prehydrolysis and pre-organization reaction for 1-12 h to obtain a pre-lapped graphene oxide precursor; the mass ratio of graphene oxide contained in the graphene oxide solution to the dimethyl siloxane oligomer to the basic catalyst is 1: (0.1-1.5): (0.001 to 0.03);
(2) Adding a foaming agent, a reducing agent and a dimethyl siloxane cross-linking agent into the pre-lapped graphene oxide precursor, uniformly stirring, and then carrying out high-temperature reaction to obtain modified graphene wet gel; the temperature of the high-temperature reaction is 80-160 ℃, and the time is 8-36 h;
(3) Sequentially freezing, freeze-drying and thermally annealing the modified graphene wet gel to prepare a high-strength high-elasticity graphene aerogel without slag falling; the high-strength high-elasticity graphene aerogel without falling slag has a double-network structure in which a graphene sheet layer network and a polydimethylsiloxane network are mutually penetrated, and the polydimethylsiloxane networks are lapped between the graphene sheet layers and at the edges.
2. The production method according to claim 1, characterized in that:
the dimethyl siloxane oligomer is one or more of PDMS Sylgard 184A glue, PDMS RTV 163A glue, PDMS RTV165A glue and PDMS RTV 655A glue;
the dimethyl siloxane cross-linking agent is one or more of PDMS Sylgard184B glue, PDMS RTV 163B glue, PDMS RTV 165B glue and PDMS RTV 655B glue; and/or
The mass ratio of the dimethyl siloxane oligomer to the dimethyl siloxane cross-linking agent is 1: (0.05-0.2).
3. The method of claim 1, wherein:
the alkaline catalyst is one or more of ammonia water, ammonium fluoride solution, sodium carbonate solution, sodium bicarbonate solution and sodium formate solution.
4. The production method according to any one of claims 1 to 3, characterized in that:
the number of layers of the graphene oxide contained in the graphene oxide solution is 1-6; and/or
The concentration of the graphene oxide contained in the graphene oxide solution is 2-40 mg/mL.
5. The production method according to any one of claims 1 to 3, characterized in that:
the foaming agent is one or more of alkyl glycoside, styrene maleic anhydride resin, alkylphenol polyoxyethylene and lauryl sodium sulfate;
the mass ratio of the graphene oxide solution to the foaming agent is 1: (0.001 to 0.05);
the reducing agent is one or more of dithiothreitol, sodium ascorbate, hydroiodic acid, sodium sulfite and hydrazine hydrate; and/or
The mass ratio of the graphene oxide contained in the graphene oxide solution to the reducing agent is 1: (1-10).
6. The production method according to any one of claims 1 to 3, characterized in that:
the temperature of the thermal annealing is 200-400 ℃, and the time is 2-16 h.
7. The high-strength high-elasticity graphene aerogel free of slag falling, prepared by the preparation method of any one of claims 1 to 6.
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