CN113816367A - Graphene oxide film and preparation method thereof - Google Patents
Graphene oxide film and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a preparation method of a graphene oxide film. The method combines the oxidation method optimization of graphite and the functional group liquid phase regulation and control process of the graphene oxide lamella to achieve the purpose of regulating the chemical structure between the graphene oxide lamella, thereby comprehensively improving the orientation degree of the graphene oxide film and the interaction of hydrogen bonds between the layers, and obviously improving the mechanical property of the graphene oxide film.
Description
Technical Field
The invention relates to the field of new materials and preparation thereof, and particularly relates to a preparation method of a high-strength graphene oxide film.
Background
Graphene is a polymer made of carbon atoms in sp2The two-dimensional atomic lattice formed by the hybridized form has outstanding electric and heat conduction capability and good mechanical properties. Having a limited sizeThe assembly formed by the graphene oxide is an important precursor of a graphene macroscopic material. After the chemical oxidation treatment of the crystalline flake graphite, the conjugated structure is damaged, and functional groups such as hydroxyl, epoxy, carboxyl and the like are generated at the defect position of the crystalline flake graphite, so that the crystalline flake graphite becomes graphene oxide. The existence of the oxygen-containing functional group not only can enable the graphene oxide to be stably dispersed in a polar solvent, but also is beneficial to large-scale preparation and processing of graphene materials, and meanwhile, a bonding effect can be formed between layers of the graphene oxide, so that the mechanical property of an assembly is improved. At present, a thin film assembled by graphene oxide lamellar layers has important application in the fields of selective permeation films, electrode materials, conductive/heat-conducting films and the like.
The graphene oxide film can be prepared by vacuum-assisted suction filtration, casting, blade coating and other methods. Ruoff et al used a vacuum assisted suction filtration method to obtain a graphene oxide film for the first time, the tensile strength of which was 121MPa, and the modulus of which was 44GPa at the highest (Nature, 448, (2007): DOI: 10.1038/Nature 06016). In order to improve the mechanical properties of the graphene oxide film, it is studied to introduce various additives into the graphene oxide film to improve the interlayer interaction, for example:
1) the hydrogen bonding type additive is disclosed in cited document 1. Polyvinyl alcohol (PVA) has rich hydroxyl functional groups on the molecular chain and can generate strong hydrogen bond action with graphene oxide sheet layers, so that the tensile strength of the GO/PVA composite film reaches 266 MPa;
2) citation 2 discloses an ion-bonding type additive. the-COOH functional group with electronegativity on the surface of the graphene oxide can be bonded with polyvalent metal cations, so that the ionic crosslinking effect, Ca, is introduced2+The Young modulus of the cross-linked graphene oxide film is about 68% higher than that of the unmodified graphene oxide film, and the maximum tensile strength of the cross-linked graphene oxide film can reach 1.5 times that of the unmodified graphene oxide film;
3) citation 3 discloses a covalent bond type additive. Boric acid, p-diaminophenol and other small molecules can be covalently bonded with oxygen-containing functional groups on the surface of graphene oxide to form a cross-linked network between sheets, and the breakage of the film needs to overcome the strong acting force, so that the tensile strength of the cross-linked graphene oxide film is improved by twice of that of unmodified graphene oxide.
Relevant studies including the above documents are effective in improving the tensile strength of the film, but it is difficult to improve the modulus thereof. This is because the graphene oxide sheets used in the above documents simultaneously form a wrinkled structure during the assembly of the films, and reduce the degree of orientation of the films, and generate defect sites such as voids, thereby weakening the tensile strength and modulus thereof.
Citation 4 discloses a solvent intercalation plasticizing technique for realizing post-stretching of a graphene oxide film so as to improve the orientation degree and mechanical properties of the graphene oxide film, but the method is complex in treatment process and high in cost. The prior art can not synchronously improve the orientation degree and the interlayer bonding effect of the graphene oxide film under low-cost conditions to obtain the graphene oxide film with high mechanical property.
Cited documents:
cited document 1: small, 2013, 9, DOI: 10.1002/smll.201300819
Cited document 2: ACS nano, 2008, 2, DOI: 10.1021/nn700349a
Cited document 3: ACS nano, 2019, 13, DOI: 10.1021/acsano.9b00158
Cited document 4: nature communications,2020,11, DOI 10.1038/s41467-020-16494-0
Disclosure of Invention
The interlayer effect and the mechanical property of the graphene oxide film are not only dominated by the bonding effect among the sheets, but also influenced by the stacking state and the wrinkle appearance of the sheets. In order to regulate and control the assembling process of graphene oxide sheets and improve the interlayer bonding effect of the assembled film, the invention overcomes the defects of the prior art and provides the graphene oxide film which can realize more regular sheet stacking and less folded structures, has strong interlayer hydrogen bond effect and can realize excellent mechanical property.
Another object of the present invention is to provide a method for preparing the high-strength graphene oxide thin film, wherein the graphene oxide lamellae have appropriate functionality by controlling the oxidation preparation and dispersion treatment processes of graphene oxideThe graphene oxide film obtained by assembling the energy clusters has high orientation degree and strong interlayer hydrogen bond interaction, in some specific embodiments, the highest tensile strength can reach 750MPa, and the maximum fracture toughness can reach 8MJ/m3。
The invention provides the following technical conception: by enabling the graphene oxide lamella layers to have proper types and numbers of functional groups, the graphene oxide lamella layers can have bonding property with enough strength, and meanwhile, the graphene oxide lamella layers can be well oriented in the assembling and film forming process, so that the formation and development of a wrinkle structure are reduced, and the graphene oxide film with excellent mechanical properties is obtained.
The specific implementation approach of the technical scheme is as follows:
[1] the present invention first provides a graphene oxide thin film, wherein the graphene oxide thin film is formed of graphene oxide having a lamellar structure and has an oxygen-containing functional group in the lamellar structure, wherein,
the atomic ratio of carbon atoms to oxygen atoms in the graphene oxide film is 1.8-3.4: 1;
the oxygen-containing functional group at least comprises an OH functional group, an epoxy group and a C ═ O functional group, wherein the content of the OH functional group is 30-80% and the content of the C ═ O functional group is 5.0% or less based on the total number of atoms of the oxygen-containing functional group.
[2] The film according to [1], wherein the atomic ratio of carbon atoms to oxygen atoms in the graphene oxide film is 2.6 to 3.2: 1.
[3] the film according to [1] or [2], wherein the content of the OH functional group is 37 to 75%.
[4] The film according to any one of [1] to [3], wherein a content of the C ═ O functional group is 4.0% or less.
[5] The thin film according to any one of [1] to [4], wherein the graphene oxide sheet has a lateral dimension of 0.8 to 20 μm; the thickness of the graphene oxide film is 0.01-50 mu m.
[6] Further, the present invention also provides a method for producing the thin film according to any one of the above [1] to [5], wherein the method comprises the steps of:
(1) a step of treating graphite with an oxidizing agent to form graphene oxide;
(2) a step of forming a dispersion liquid containing the graphene oxide, which includes adjusting a pH value of the dispersion liquid containing the graphene oxide;
(3) and a step of forming a graphene oxide film, in which the graphene oxide film is obtained by treating the dispersion liquid containing graphene oxide.
[7] The method according to [6], wherein the graphite is derived from flake graphite, expanded graphite or artificial graphite; the graphite has a size of 100-1000 mesh.
[8] The method according to [6] or [7], wherein the oxidation treatment is carried out in the presence of a strong acid solution containing a strong oxidizing agent.
[9] The method according to any one of [6] to [8], wherein the method of adjusting the pH of the dispersion comprises diluting or adding a basic substance comprising one or more of a water-soluble alkali metal, a hydroxide of an alkaline earth metal, or a weak acid salt thereof, aqueous ammonia, and the like.
[10] The method according to any one of [6] to [9], wherein the pH of the graphene oxide-containing dispersion after the pH adjustment is 2.5 to 11.
[11] The method according to any one of [6] to [10], wherein a condition for forming the graphene oxide thin film from the graphene oxide-containing dispersion liquid is any one of methods such as vacuum filtration, casting, spray coating, spin coating, and blade coating molding.
[12] The method according to any one of [6] to [11], further comprising a step of subjecting the dispersion liquid containing graphene oxide to ultrasonic treatment before the step of forming the graphene oxide thin film.
ADVANTAGEOUS EFFECTS OF INVENTION
Through the implementation of the technical scheme, the invention can obtain the following technical effects:
1) compared with the graphene oxide film reported by common documents, the graphene oxide film disclosed by the invention can not only increase the bonding force between graphene oxide layers by adjusting the composition of functional groups between graphene oxide layers, but also form good orientation during film formation, so that the problem that the orientation degree and the interlayer bonding force are difficult to coordinate, which is difficult to solve in the past, is balanced, and the obtained graphene oxide film is perfect in crystallization, highly oriented and has better mechanical properties;
2) the invention provides a selection principle of high-quality raw materials of the graphene oxide composite film taking graphene oxide as the raw material, and simultaneously provides a new thought, the orientation degree of the graphene oxide film is improved by using the high-quality raw materials, and the preparation of the graphene oxide composite film with better performance is favorably realized;
3) the preparation method of the high-strength graphene oxide film does not relate to a post-treatment process for the graphene oxide film, and is simple in process and low in cost.
Drawings
FIG. 1: a flow chart for preparing a high-strength graphene oxide film in a specific embodiment of the invention;
FIG. 2: the X-ray photoelectron spectroscopy (XPS) (a) and XPS C1s peak-to-peak fitting results (b, C, d) of the graphene oxide thin film obtained in the first, second and fourth embodiments of the present invention;
FIG. 3: scanning electron micrographs of sections of the graphene oxide thin films obtained in the first embodiment (a), the second embodiment (b), and the fourth embodiment (c) of the present invention;
FIG. 4: typical tensile curves of the graphene oxide thin films obtained in the first, second and fourth embodiments of the present invention.
Detailed Description
The present invention will be described in detail below. The technical features described below are explained based on typical embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:
in the present specification, the numerical range represented by "numerical value a to numerical value B" means a range including the end point numerical value A, B.
In the present specification, the numerical ranges indicated by "above" or "below" mean the numerical ranges including the numbers.
In the present specification, the meaning of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.
In the present specification, the term "more" means a numerical value of 2 or more.
As used herein, the term "optional" or "optional" is used to indicate that certain substances, components, performance steps, application conditions, and the like are used or not used.
As used herein, "room temperature" means an indoor ambient temperature of "25 ℃.
In the present specification, the term "OH functional group" is used to mean a hydroxyl group bonded to the non-carbonyl carbon (C), i.e., a hydroxyl group in the carboxyl group is excluded.
In the present specification, the unit names used are all international standard unit names, and the "%" used means weight or mass% content, if not specifically stated.
In the present specification, reference to "some particular/preferred embodiments," "other particular/preferred embodiments," "embodiments," and the like, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.
The invention provides a film prepared based on graphene oxide nanosheets, which is obtained by oriented lamination of graphene oxide sheets, wherein the graphene oxide sheets have various oxygen-containing functional groups.
Further, the technical scheme of the invention is mainly obtained based on the following insights:
a large number of oxygen-containing functional groups exist among graphene oxide sheets obtained by oxidizing graphite raw materials, the functional groups provide dispersibility and processability, and meanwhile, the interlayer hydrogen bond function can be established in the assembled graphene oxide film, so that the mechanical property of the film is improved. However, due to the existence of these oxygen-containing functional groups, taking the aqueous phase as an example, the graphene oxide has an interaction with water molecules under the condition of liquid-phase dispersion, which is shown as an increase in the viscosity of the dispersion, and this tendency is unfavorable for the process of assembling graphene oxide sheets in the liquid phase to form a thin film: during the process, the concentration of the dispersion liquid is increased, the distance between sheets is reduced, and the viscosity of the system is gradually increased, so that the graphene oxide is hindered when rotating and conformation adjusting are carried out in the assembling process, and finally, the formation of a wrinkle structure in the film is not expected. Based on the above knowledge, the present invention utilizes the optimization of the oxidation method and the dispersion treatment to adjust the type and number of oxygen-containing functional groups of the obtained graphene oxide sheets, reduce the content of C ═ O functional groups (particularly carboxyl groups), and increase the proportion of OH functional groups, thereby ensuring that the obtained sheets have a sufficiently strong bonding force therebetween, and also ensuring that the graphene oxide sheets are oriented during the film formation process and relieving the wrinkled structure of the film, and as a result, a graphene oxide film with enhanced mechanical properties and a regular structure can be obtained.
(graphite starting material)
The graphene oxide thin film of the present invention is obtained through steps such as oxidation treatment and film formation treatment of a graphite raw material.
The size of the graphite material in the present invention is not particularly limited in principle, and flake graphite, expanded graphite, or artificial graphite having a mesh size of 1000 mesh or less can be used, and flake graphite or expanded graphite having a mesh size of 100 to 300 mesh is preferably used.
In addition, with respect to the purity of the graphite starting material, the present inventors believe that the improvement in purity of the graphite starting material is beneficial to the overall performance of the final graphene oxide film, and in particular embodiments graphite having a purity of 95% or greater may be used, with graphite having a purity of 98% or greater being preferred.
The graphite material may be subjected to a pretreatment before the oxidation treatment described below to further improve the purity.
The pretreatment means is not particularly limited, and may include a washing step, a drying step, and the like in some specific embodiments of the present invention. With respect to the washing step, there is no particular limitation, and preferably, washing with deionized water is performed. For the drying step, for example, the washed graphite raw material may be dried to obtain a dried product.
(Oxidation of graphite)
At present, the most used oxidation methods for preparing graphene oxide mainly comprise a Brodie method, a Hofmann method, a Hummer method, a Staudenmai method and the like. In some specific embodiments, the step of oxidation treatment of graphite according to the present invention is carried out in the presence of a strong acid solution containing a strong oxidizing agent, and for such a strong acid, concentrated sulfuric acid, concentrated nitric acid and sodium nitrate, or a mixed system of concentrated nitric acid and concentrated sulfuric acid may be used. Further, the strong acid solution containing a strong oxidizing agent may contain a salt substance having a strong oxidizing property. The salt with strong oxidizing property can be one or more of chlorate, perchlorate, ferrate or permanganate.
In addition, the temperature and time of the oxidation treatment are not particularly limited, and may be adjusted according to the Hummer method or a modified Hofmann or Hummer method in the art.
In some exemplary processes of the invention, the oxidation treatment of the graphite employs one of the following steps:
an example of the implementation steps based on the foregoing modified Hummers method is as follows: adding sodium nitrate and high-purity crystalline flake graphite into 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, controlling the reaction temperature to be below 5 ℃, and then slowly adding potassium permanganate into the reaction solution. After the raw materials are added, the reaction liquid is heated to 35 ℃ for reaction for 3h, a certain amount of deionized water is slowly added into the reaction liquid, the reaction temperature is gradually increased to 80-95 ℃, the reaction temperature is kept for 15min, and the reaction liquid is added into 1000mL of deionized water to finish the reaction. In the reaction process, 1g of high-purity flake graphite corresponds to 30mL of concentrated sulfuric acid, 0.5g of sodium nitrate, 3g of potassium permanganate and 40mL of deionized water.
An example of another implementation of the aforementioned modified Hofmann process is as follows: mixing 68 wt% of concentrated nitric acid and 98 wt% of concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding high-purity flake graphite, and slowly adding potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 20-25 ℃ for 96 h; the reaction solution was poured into 1000mL of deionized water to terminate the reaction. In the reaction process, 1g of high-purity crystalline flake graphite corresponds to 10mL of 68 wt% concentrated nitric acid, 17.5mL of 98 wt% concentrated sulfuric acid, 11g of potassium chlorate and 140mL of deionized water.
Further, after the oxidation treatment is completed, optionally, the excess strong acid or strong oxidizing salt component can be removed by adopting the steps of suction filtration washing, centrifugation and the like to obtain a dispersion liquid of the graphene oxide, or the solid graphene oxide can be dried or freeze-dried.
(graphene oxide liquid phase control)
Graphene oxide is obtained by the aforementioned oxidation treatment, and various oxygen-containing functional groups are introduced on the surface of the graphene oxide sheet or between the graphene oxide sheet layers. For these oxygen-containing functional groups, carboxyl groups (COOH), hydroxyl groups (OH) derived from the linkage with the non-carbonyl carbon (C), epoxy groups, other carbonyl groups, and the like are generally included.
Further, the invention considers that the proportion of oxygen-containing functional groups in the graphene oxide can be regulated and controlled by regulating and controlling the liquid phase of the graphene oxide, so that the bonding force between graphene oxide lamella and the orientability in the film forming process are balanced or optimized.
In some specific embodiments, the graphene oxide is configured as a dispersion with a certain solid content, and the pH value of the dispersion is further adjusted. The solid content of the dispersion liquid containing graphene oxide in the present invention may be 0.5 to 30mg/mL, preferably 1 to 10mg/mL, and more preferably 2 to 4 mg/mL.
As the means for adjusting pH which can be employed in the present invention, a means for diluting or adding an alkaline substance can be employed.
For the dilution, deionized water or the like can be used without particular limitation.
The alkaline substance which can be added is not particularly limited as long as it can cause a change in the pH of the dispersion. Typically, these basic substances may include one or more of water-soluble alkali metal, alkaline earth metal hydroxides or their weak acid salts, ammonia water, and the like.
The pH of the dispersion liquid containing graphene oxide obtained by liquid phase adjustment may be 2.5 to 11, preferably 5 to 10, more preferably 7 to 10, and still more preferably 8 to 9 in the present invention.
For a typical liquid phase conditioning process, the following can be cited:
adjusting the solid content of the dispersion liquid containing the graphene oxide to be 0.5-5 mg/mL, and adjusting the volume of the graphene oxide dispersion liquid to be 7-1500 mL; preferably, the solution containing the alkaline substance is one of 0.2mol/L sodium hydroxide, 0.2mol/L potassium hydroxide, and 2 wt% ammonia water. In some specific embodiments, the pH of the dispersion liquid containing graphene oxide is adjusted to 2.9 to 10.2 by liquid phase adjustment. In some specific embodiments, the dispersion containing graphene oxide initially exhibits acidity, and the added alkaline solution can adjust the kind and content of functional groups in graphene oxide sheets, and thus can adjust the bonding force between sheets to a suitable range. More preferably, in the liquid phase adjustment, the pH of the dispersion liquid containing graphene oxide is finally adjusted to 8.2 to 8.6.
The invention considers that the function of adding alkaline substances into the prepared graphene oxide dispersion liquid to adjust the pH value is as follows: under the induction of an alkaline dispersion liquid environment, epoxy functional groups contained between graphene oxide lamella layers undergo nucleophilic substitution reaction, and one epoxy group can be converted into trans-diol, namely two hydroxyl groups, so that the total number of the functional groups is increased compared with the original lamella.
In addition, during and after the liquid phase adjustment or before the graphene oxide film formation described below, it is also preferable to peel off the multilayer graphene oxide that may be contained by means of ultrasonic dispersion or the like to improve the dispersibility of the solid phase. For the ultrasonic treatment conditions, the preferred ultrasonic frequency is 30-60 KHz, the ultrasonic power is 200-300W, and the ultrasonic time is 10-60 min.
(film formation of graphene oxide)
In the invention, the dispersion liquid containing graphene oxide obtained by the liquid phase regulation and control treatment is subjected to film forming treatment to obtain a graphene oxide film.
Film-forming means that can be used in the present invention include blade coating, casting, spray coating, spin coating, and vacuum filtration film-forming, and from the viewpoint of orientation to graphene oxide sheets, blade coating film-forming and vacuum filtration film-forming are preferable, and vacuum filtration film-forming is more preferable. Compared with other modes for film formation, the film formation by using the reduced pressure auxiliary suction filtration is more favorable for improving the mechanical property.
The conditions for the vacuum filtration are not particularly limited, and for example, the material of the filter membrane used in the vacuum filtration is one of nylon, polyvinylidene chloride, polytetrafluoroethylene, polycarbonate, and mixed cellulose.
In addition, when the reduced pressure filtration treatment is carried out, the solid content and the volume of the dispersion liquid containing the graphene oxide are preferably 0.5-2 mg/mL and 7-15 mL respectively; when casting treatment is carried out, the solid content and the volume of the graphene oxide-containing dispersion liquid are preferably 3-10 mg/mL and 5-50 mL respectively. When blade coating treatment is carried out, the solid content and the volume of the graphene oxide-containing dispersion liquid are preferably 10-30 mg/mL and 5-100 mL respectively.
The kind and the number of functional groups of the obtained graphene oxide thin film in the graphene oxide film formation step were determined by X-ray photoelectron spectroscopy (XPS).
In the liquid phase regulation, the oxygen-containing functional groups between the graphene oxide lamella layers are regulated, so that the binding force between the graphene oxide lamella layers can keep certain strength in the film forming process, and meanwhile, the graphene oxide lamella can be easily oriented in the film forming process.
In some processes for obtaining the graphene oxide thin film, a drying treatment step may be adopted. As the drying manner, oven heat drying or room temperature drying can be cited; more preferably, the graphene oxide thin film is dried at room temperature. The obtained graphene oxide film can be subjected to any washing treatment.
The present inventors have considered that, when a dispersion containing graphene oxide is subjected to vacuum filtration, casting or blade coating to form a graphene oxide film, the dispersion may undergo concentration and a process of increasing solid content, the distance between graphene oxide sheets decreases, the interaction with water molecules increases to cause formation of a gel network, and the apparent viscosity of the dispersion increases, at which time it is difficult for the graphene oxide sheets to adjust their positions and arrangement, thereby causing irregular stacking of the graphene oxide sheets in the resulting film, i.e., a decrease in the degree of orientation thereof.
In some specific embodiments, the invention reduces the interaction of sheets and water molecules and the viscosity of graphene oxide dispersion liquid under the condition of the same solid content by reducing the content of C ═ O functional groups (especially carboxyl groups) among graphene oxide sheets, so that the resistance of free rotation and conformation adjustment of the graphene oxide sheets in the assembling process is reduced, thereby relieving the wrinkle form of the graphene oxide film and improving the flatness and interlayer acting force of the graphene oxide film.
On the other hand, the reduction of the content of C ═ O functional groups (particularly carboxyl groups) contributes to the improvement of the crystalline state of the graphene oxide thin film and the reduction of the interlayer distance thereof, and therefore the structure is more dense. On the other hand, in the presence of water molecules, hydrogen bonds can be formed between graphene oxide sheets, so that the number of oxygen-containing functional groups between graphene oxide sheets also affects the mechanical properties of the graphene oxide film, and under the condition that the rest factors are consistent, the greater the number of oxygen-containing functional groups between graphene oxide sheets, the stronger the hydrogen bond interaction between sheets, and the better the mechanical properties of the graphene oxide film. Therefore, it is important to optimally adjust the composition of the oxygen-containing functional group.
Further, in the graphene oxide film obtained by the invention, the number ratio of carbon atoms to oxygen atoms is 1.8-3.4: 1, preferably 2.2-3.2: 1, more preferably 2.6 to 3.2: 1. in addition, the content of the OH functional group derived from the linkage with the non-carbonyl carbon is 30 to 80%, preferably 37 to 75%, and more preferably 39 to 70% based on the total number of atoms of the oxygen-containing functional group; the content of the C ═ O functional group is 5.0% or less, preferably 4.0% or less, and more preferably 2.5% or less.
Therefore, the orientation degree and the interlayer hydrogen bond interaction of the graphene oxide film can be synchronously enhanced, the crystallization state and the orientation degree of the graphene oxide film are improved based on a mechanism of reducing the content of C ═ O functional groups (particularly carboxyl) in the graphene oxide film, the content proportion of oxygen-containing functional groups of graphene oxide sheets is optimized through a dispersion liquid treatment process, the interlayer hydrogen bond interaction of the graphene oxide films is enhanced, the orientation degree and the interlayer hydrogen bond interaction of the graphene oxide film are comprehensively improved, and the mechanical property of the graphene oxide film is remarkably improved.
In addition, the graphene oxide film obtained according to the invention can have improved mechanical properties, wherein in some specific embodiments, the tensile strength can reach 750MPa at most, and can be regulated and controlled within the range of 150-750 MPa, preferably within the range of 200-700 MPa, and further preferably within the range of 300-700 MPa; the maximum fracture toughness can reach 8MJ/m3And can be between 1.0 and 8MJ/m3In the range of 2.0 to 7.9MJ/m, preferably3And regulating and controlling within the range.
In addition, the graphene oxide thin film of the present invention may have a (transverse) sheet diameter of a graphene oxide sheet of 0.8 to 20 μm, preferably 2 to 15 μm, and more preferably 3 to 10 μm. The size of the film is not particularly limited, and for example, the thickness of the film may be 0.01 to 50 μm, preferably 3 to 10 μm; the flat area may be greater than 0, preferably 80cm2The above.
The mechanical property provided by the graphene oxide film provided by the invention is widely applied to the fields of aerospace, packaging, filtering membranes and the like.
Examples
The present invention will be further illustrated by the following specific examples, wherein the raw materials used in the respective examples or comparative examples are commercially available.
Example one
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
the method comprises the steps of taking 300-mesh high-purity flake graphite as a raw material to prepare graphene oxide, controlling an oxidation method to be an improved Hummers method, adding 1.5g of sodium nitrate and 3g of high-purity flake graphite into 90mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, controlling the reaction temperature to be below 5 ℃, and then slowly adding 9g of potassium permanganate into a reaction solution. After the raw materials are added, the reaction liquid is heated to 35 ℃ for reaction for 3h, a certain amount of deionized water is slowly added into the reaction liquid, the reaction temperature is gradually increased to 80-95 ℃, the reaction temperature is kept for 15min, and the reaction liquid is added into 1000mL of deionized water to finish the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; and centrifuging the washed product at the rotating speed of 14000r/min for 5 times, removing supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid.
Controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1.5mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 2.9, and controlling the mode to be not adding an alkaline solution;
and (3) carrying out ultrasonic treatment on the obtained graphene oxide dispersion liquid for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 2.3, an OH functional group derived from a non-carbonyl carbon linkage accounted for 36.8% of the total oxygen-containing functional group, a C ═ O functional group accounted for 17.8% of the total oxygen-containing functional group, a thickness of 6 μm, a tensile strength of 169MPa, and a fracture toughness of 1.5MJ/m3。
Example two
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 3.54, and controlling the mode to be not adding an alkaline solution;
and (3) carrying out ultrasonic treatment on the obtained graphene oxide dispersion liquid for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 3.2, an OH functional group derived from a non-carbonyl carbon linkage accounted for 39.3% of the total oxygen-containing functional group, a C ═ O functional group accounted for 4.2% of the total oxygen-containing functional group, a thickness of 4 μm, a tensile strength of 494MPa, and a fracture toughness of 4.95MJ/m3。
EXAMPLE III
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 7.1, and adding 0.2mol/L sodium hydroxide alkaline solution in a control mode;
and (3) carrying out ultrasonic treatment on the obtained graphene oxide dispersion liquid for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 2.8, an OH functional group derived from a non-carbonyl carbon linkage accounted for 43.0% of the total oxygen-containing functional group, a C ═ O functional group accounted for 1.0% of the total oxygen-containing functional group, a thickness of 3 μm, a tensile strength of 543MPa, and a fracture toughness of 3.02MJ/m3。
Example four
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 8.43, and adding 0.2mol/L sodium hydroxide alkaline solution;
and (3) carrying out ultrasonic treatment on the obtained graphene oxide dispersion liquid for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 2.6, an OH functional group derived from a non-carbonyl carbon linkage accounted for 54.8% of the total oxygen-containing functional group, a C ═ O functional group accounted for 2.3% of the total oxygen-containing functional group, a thickness of 3 μm, a tensile strength of 616MPa, and a fracture toughness of 3.13MJ/m3。
EXAMPLE five
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 10.16, and adding 0.2mol/L sodium hydroxide alkaline solution in a control mode;
and (3) carrying out ultrasonic treatment on the graphene oxide dispersion liquid obtained in the step for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 2.7, an OH functional group derived from the linkage with the non-carbonyl carbon accounted for 46.9% of the total oxygen-containing functional group, a C ═ O functional group accounted for 2.4% of the total oxygen-containing functional group, a thickness of 3 μm, a tensile strength of 566MPa measured, and a fracture toughness of 3.12MJ/m3。
EXAMPLE six
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 8.44, and adding 0.2mol/L ammonia water alkaline solution;
and (3) carrying out ultrasonic treatment on the graphene oxide dispersion liquid obtained in the step (a) for 30min, wherein the ultrasonic power is 320W, carrying out vacuum-assisted suction filtration to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film has a carbon-to-oxygen ratio of 2.7, and OH functional groups connected with non-carbonyl carbon account for the total contentThe proportion of oxygen functional groups is 68.7 percent, the proportion of C ═ O functional groups to the total oxygen-containing functional groups is 0.1 percent, the thickness is 3 microns, the tensile strength is measured to be 695MPa, and the fracture toughness is 7.9MJ/m3。
EXAMPLE seven
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 3.54, and controlling the mode to be not adding an alkaline solution;
and (3) carrying out ultrasonic treatment on the graphene oxide dispersion liquid obtained in the step for 30min, controlling the solid content and the volume of the graphene oxide dispersion liquid to be 3mg/mL and 8mL respectively by centrifugal concentration, casting to obtain a graphene oxide film, and naturally drying.
The graphene oxide film had a carbon-to-oxygen ratio of 3.2, an OH functional group derived from a non-carbonyl carbon linkage accounted for 31.6% of the total oxygen-containing functional group, a C ═ O functional group accounted for 4.2% of the total oxygen-containing functional group, a thickness of 8 μm, a tensile strength of 358MPa, and a fracture toughness of 2.76MJ/m3。
Example eight
The embodiment relates to a high-strength graphene oxide film and a preparation method thereof, and the preparation method specifically comprises the following steps:
preparing graphene oxide by using 300-mesh high-purity flake graphite as a raw material, controlling an oxidation method to be an improved Hofmann method, mixing 30mL of 68 wt% concentrated nitric acid and 52.5mL of 98 wt% concentrated sulfuric acid under the conditions of ice-water bath and stirring, then adding 3g of high-purity flake graphite, and slowly adding 33g of potassium chlorate into the mixed solution; after uniform dispersion, removing the ice water bath, and carrying out reaction at 24 ℃ for 96 h; the reaction solution was poured into 1400mL of deionized water to terminate the reaction. Washing the reaction product by using 2000mL of 10 wt% hydrochloric acid solution and 2000mL of deionized water in sequence, and washing for 2 times respectively; centrifuging the washed product at the rotating speed of 14000r/min for 5-6 times, removing the supernatant after each centrifugation, collecting the precipitate at the lower layer, and finally obtaining the graphene oxide dispersion liquid;
controlling the solid content of the graphene oxide dispersion liquid obtained in the step to be 1mg/mL and the volume to be 10mL by using a water dilution mode, controlling the pH value of the graphene oxide dispersion liquid to be 3.54, and controlling the mode to be not adding an alkaline solution;
and (3) carrying out ultrasonic treatment on the graphene oxide dispersion liquid obtained in the step for 30min, controlling the solid content and the volume of the graphene oxide dispersion liquid to be 17mg/mL and 20mL respectively by centrifugal concentration, carrying out blade coating to obtain a graphene oxide film, and naturally drying the graphene oxide film.
The graphene oxide film had a carbon-to-oxygen ratio of 2.93, an OH functional group derived from a non-carbonyl carbon linkage accounted for 73.4% of the total oxygen-containing functional group, a C ═ O functional group accounted for 1.9% of the total oxygen-containing functional group, a thickness of 3 μm, a tensile strength measured as 287MPa, and a fracture toughness measured as 1.3MJ/m3。
See table 1 below for the above various example test data:
TABLE 1
| Example one | Example two | EXAMPLE III | Example four | EXAMPLE five | EXAMPLE six | EXAMPLE seven | Example eight | |
| Carbon to oxygen ratio | 23 | 3.2 | 2.8 | 2.6 | 2.7 | 2.7 | 3.2 | 2.93 |
| Ratio of OH functional groups | 36.8％ | 39.3％ | 43.0％ | 54.8％ | 46.9％ | 68.7％ | 31.6％ | 73.4％ |
| Ratio of C ═ O functional groups | 17.8％ | 4.2％ | 1.0％ | 2.3％ | 2.4％ | 0.1％ | 4.2％ | 1.9％ |
| Tensile Strength (MPa) | 169 | 494 | 543 | 616 | 566 | 695 | 358 | 287 |
| Fracture toughness (MJ/m)3) | 1.5 | 4.95 | 3.02 | 3.13 | 3.12 | 7.9 | 2.76 | 1.3 |
As can be seen from fig. 2, the carbon-to-oxygen ratio of the graphene oxide thin film obtained in the first example is 2.3, the carbon-to-oxygen ratio of the graphene oxide thin film obtained in the second example is 3.2, and the carbon-to-oxygen ratio of the graphene oxide thin film obtained in the fourth example is 2.6; from XPS C1s peak fitting results, it can be seen that the graphene oxide film obtained in example two has only a small amount of C ═ O bonds, accounting for 4.2% of the total amount of oxygen-containing functional groups, compared to the graphene oxide film obtained in example one, indicating that the content of C ═ O functional groups (especially carboxyl groups) is very low; in contrast, the content of C ═ O functional groups of the graphene oxide thin film obtained in example four was similar to that of example, and the number of OH functional groups was increased, which increased from 39.3% to 54.8%. As can be seen from the above analysis, the graphene oxide prepared by the modified Hofmann method has a smaller number of oxygen-containing functional groups than the graphene oxide prepared by the modified Hummers method, especially C ═ O functional groups (especially carboxyl groups), which helps it to achieve more regular graphene oxide stacking during drying; after liquid-phase regulation and control of the functional groups of the graphene oxide lamella, the number of oxygen-containing functional groups of the graphene oxide prepared by the improved Hofmann method is increased, which is beneficial to constructing stronger hydrogen bond interaction in the graphene oxide film.
As can be seen from the cross-sectional shapes of the graphene oxide films obtained in the first, second, and fourth embodiments in fig. 3, reducing the content of C ═ O functional groups between graphene oxide sheets helps to reduce the interaction between the sheets and water molecules, thereby reducing the viscosity of the dispersion liquid during the assembly process, facilitating the movement and conformation adjustment of the sheets, and the graphene oxide film obtained after drying has perfect layer arrangement and high orientation degree; and after the graphene oxide sheet layer is regulated and controlled by the functional group liquid phase of the graphene oxide sheet layer, the increase of the oxygen-containing functional group does not cause obvious change of the orientation degree of the graphene oxide sheet layer.
As can be seen from fig. 4, the degree of orientation of the graphene oxide film obtained in the first embodiment is the lowest, so that the tensile strength of the graphene oxide film is only 169MPa, the graphene oxide film obtained in the second embodiment has a higher degree of orientation, the mechanical properties of the graphene oxide film are greatly improved, the tensile strength is raised to 494MPa, and the graphene oxide film obtained in the fourth embodiment has a better orientation structure, and has stronger interlayer hydrogen bond interaction due to more oxygen-containing functional groups, so that the better mechanical properties are finally realized, and the tensile strength reaches 616 MPa.
To sum up, the mechanical properties of the graphene oxide film are mainly affected by the orientation degree and the strength of the interlayer hydrogen bond interaction, and the improvement of the orientation degree of the graphene oxide film and the enhancement of the interlayer hydrogen bond interaction are synchronously realized from the oxidation of graphite and the liquid-phase regulation of the functional groups of the graphene oxide, so that the mechanical properties of the graphene oxide film are improved by the synergistic effect, and the high-strength graphene oxide film is obtained.
It should be noted that, although the technical solutions of the present invention are described by specific examples, those skilled in the art can understand that the present disclosure should not be limited thereto.
Having described embodiments of the present disclosure, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen in order to best explain the principles of the embodiments, the practical application, or improvements made to the technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
Claims (12)
1. A graphene oxide thin film, wherein the graphene oxide thin film is formed of graphene oxide having a lamellar structure and has an oxygen-containing functional group in the lamellar structure, wherein,
the atomic ratio of carbon atoms to oxygen atoms in the graphene oxide film is 1.8-3.4: 1;
the oxygen-containing functional group at least comprises an OH functional group, an epoxy group and a C ═ O functional group, wherein the content of the OH functional group is 30-80% and the content of the C ═ O functional group is 5.0% or less based on the total number of atoms of the oxygen-containing functional group.
2. The film according to claim 1, wherein the atomic ratio of carbon atoms to oxygen atoms in the graphene oxide film is 2.6-3.2: 1.
3. the film according to claim 1 or 2, wherein the content of the OH functional group is 37 to 75%.
4. A film according to any one of claims 1 to 3, wherein the content of the C ═ O functional group is 4.0% or less.
5. The film according to any one of claims 1 to 4, wherein the graphene oxide sheets have a lateral dimension of 0.8 to 20 μm; the thickness of the graphene oxide film is 0.01-50 mu m.
6. A method for preparing a film according to any one of claims 1 to 5, comprising the steps of:
(1) treating graphite with an oxidant to obtain graphene oxide;
(2) a step of forming a dispersion liquid containing the graphene oxide, which includes adjusting a pH value of the dispersion liquid containing the graphene oxide;
(3) and a step of forming a graphene oxide film, in which the graphene oxide film is obtained by treating the dispersion liquid containing graphene oxide.
7. The method of claim 6, wherein the graphite is derived from flake graphite, expanded graphite, or artificial graphite; the graphite has a size of 100-1000 mesh.
8. The process according to claim 6 or 7, characterized in that the oxidation treatment is carried out in the presence of a strong acid solution containing a strong oxidizing agent.
9. The method according to any one of claims 6 to 8, wherein the method for adjusting the pH value of the dispersion comprises diluting or adding an alkaline substance, and the alkaline substance comprises one or more of water-soluble alkali metal, alkaline earth metal hydroxide or weak acid salt thereof, ammonia water and the like.
10. The method according to claim 9, wherein the pH of the dispersion liquid containing graphene oxide after the pH adjustment is 2.5 to 11.
11. The method according to any one of claims 6 to 10, wherein the condition for forming the graphene oxide thin film from the dispersion liquid containing the graphene oxide sheet layer is any one of vacuum filtration, casting, spray coating, spin coating, and blade coating molding.
12. The method according to any one of claims 6 to 11, further comprising a step of subjecting the dispersion liquid containing graphene oxide to ultrasonic treatment before the step of forming the graphene oxide thin film.
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