CN111285361B - High-performance liquid-phase mechanical preparation method of low-defect and high-dispersion graphene - Google Patents
High-performance liquid-phase mechanical preparation method of low-defect and high-dispersion graphene Download PDFInfo
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- C01B32/00—Carbon; Compounds thereof
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- C01B32/182—Graphene
- C01B32/184—Preparation
- C01B32/19—Preparation by exfoliation
Abstract
A high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene belongs to the field of graphene, and can solve the problems of low conversion rate, complex chemical method graphene preparation process, more defects and difficulty in redispersion of graphene powder in a mechanical stripping method, and comprises the following steps: graphite is used as a raw material, in-situ intercalation is adopted, an in-situ chemical reaction method is combined, bubbles are generated in situ between graphite layers, so that the spacing between the graphite layers is increased, and the expanded graphite with smaller van der Waals force between the layers is prepared; dispersing the expanded graphite in an alkaline aqueous solution containing a surfactant, and mechanically stripping the expanded graphite by adopting a high-speed shearing action to prepare a high-stability graphene dispersion liquid; the redispersible graphene powder is prepared by adopting a low-temperature spray drying method, and the redispersible graphene prepared by the invention has the advantages of simple operation process, high yield, low cost, few defects of graphene, redispersibility and wide application prospect in the fields of functional coatings, functional polymer composites and the like.
Description
Technical Field
The invention belongs to the technical field of graphene, and particularly relates to a high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene.
Background
Due to excellent physical and chemical properties, the graphene and the derivatives thereof have great potential to play roles in a plurality of fields, for example, the outstanding electrical properties can be applied to the fields of high-performance microelectronic devices, super capacitors, novel lithium ion batteries, functional coatings and the like; the excellent mechanical property is expected to be used as a reinforced complex to play the value in the fields of military and engineering, and the market prospect is wide. Thus, the problem to be solved in the field is the first one related to the production and preparation of graphene. At present, the preparation method of graphene can be mainly divided into the following 2 types: (1) Top-Down preparation method (Top-Down): preparing graphene by taking graphite or Carbon Nanotubes (CNTs) as a raw material through a physical and chemical method; (2) a preparation method from bottom to top (Bottomoup): namely, the growth of graphene is realized in space through chemical reaction by taking small molecules as basic raw materials. Compared with the two methods comprehensively, the Top-down preparation method (Top-down) requires simple equipment, is suitable for industrialization, has relatively low production stability and cost, and becomes a main preparation method of graphene powder. The current top-down preparation methods mainly comprise a mechanical stripping method and a redox chemical stripping method.
The mechanical stripping method belongs to a typical physical preparation method, and takes highly oriented pyrolytic graphite as a raw material to realize the stripping of the graphite under the physical action condition. The Geim group of the university of Manchester succeeded for the first time in 2004 in obtaining graphene sheets having 1 to 3 layers by using a "tape stripping method" using graphite as a raw material. Although the method can obtain high-quality graphene with a complete structure, the method is not suitable for large-scale preparation of graphene due to overlarge workload and low conversion rate. In addition to the tape stripping method, the mechanical stripping method includes a wet mechanical stripping method, i.e., mechanical stripping of graphite by a shear force supplied by a high-speed stirrer, a ball mill, or a sand mill. Although the process is simple, and the graphene sp hybridized structure remains relatively complete, the mechanical exfoliation efficiency and conversion rate are low due to van der waals force existing between graphites, and how to separate graphene or graphene-like from graphite which is not exfoliated or is exfoliated to a relatively low degree is also difficult. Thus, such methods are difficult to implement large-scale preparation of graphene. The oxidation-reduction chemical stripping method comprises the steps of using graphite as a raw material, firstly pretreating the graphite to obtain a precursor, namely, expanding the distance between graphite layers through acidification and an enhancer action and an intercalation principle to further reduce van der waals force between the graphite layers, then thoroughly destroying the van der waals acting force between the graphite layers under an ultrasonic action or a mechanical force to realize stripping of the graphite to prepare graphene oxide, and further reducing the graphene oxide through a chemical or physical method. The redox method is a main method for the industrial preparation of graphene at present because of high preparation efficiency and high conversion rate, and numerous patents and documents disclose the method. However, the product prepared by the method is graphene oxide, graphene can be obtained only by further reduction, the preparation process and the technology are complex, the batch stability is poor, and the cost is high; in addition, some irreparable defects are inevitably introduced in the graphite pretreatment process, so that the graphene loses many due characteristics, and the problems greatly limit the industrial application of the graphene.
It is well known that graphene prepared by a physical method or a chemical method is generally prepared in an aqueous phase, and the aqueous phase cannot exist in many applications of graphene, so that how to extract graphene from the aqueous phase and disperse the graphene again is a common problem in research and application in the field. At present, the simplest and most commonly adopted method is to remove water through a thermal drying method to obtain graphene powder, and then the graphene powder is applied to various downstream fields, but unrecoverable aggregates are easily formed in the graphene drying process, so that the physical characteristics of graphene are greatly reduced, and the problem of poor stability of downstream product structures and performance batches is caused due to uneven dispersion caused by the aggregates. This problem is also one of the bottleneck problems that graphene is difficult to be industrially applied.
Disclosure of Invention
Aiming at the problems of low conversion rate, complex chemical graphene preparation process, more defects and difficult redispersion of graphene powder, the invention newly develops a novel preparation process, namely a gas layer expansion-mechanical liquid phase stripping method, namely, the water solubility and the interlayer spacing of graphite are increased through simple acidification pretreatment, and the interlayer spacing (larger than 0.5 nm) of the graphite is further expanded by further adopting a method for generating bubbles in situ, so that the van der Waals force of the graphite interlayer spacing is greatly reduced; and finally, in the presence of a surface modifier with a specific structure, mechanically stripping the expanded graphite by an in-situ liquid phase to directly obtain the high-dispersity graphene, and combining a low-temperature drying process to obtain the redispersible graphene powder, thereby laying a solid foundation for accelerating and expanding the industrial application of the graphene.
The invention adopts the following technical scheme:
a high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene comprises the following steps:
step one, adding potassium permanganate (with the purity of more than 98%) into concentrated sulfuric acid (with the concentration of more than 98%) at room temperature, mechanically stirring the potassium permanganate to completely dissolve the potassium permanganate to form a homogeneous mixed solution, adding graphite powder into the mixed solution, stirring the mixed solution at the temperature of 25-35 ℃ at the speed of 500-1000 rpm for 0.5-1h, adding a layer expanding substance at the speed of 5-10 g/min at the speed of 500-1000 rpm, then adding acid, reacting the acid and the layer expanding substance to form a viscous mixed system at the speed of 1000-2000 rpm, finally continuously stirring the mixed solution at the temperature of 25-35 ℃ for 2-6h to obtain a layer expanding graphite slurry, adding the layer expanding graphite slurry into 2L of deionized water, adding hydrogen peroxide into the layer expanding graphite slurry at the speed of 10mL/min, stirring and mixing the mixture at the speed of 100-500 rpm at the temperature of 25-35 ℃, and filtering and washing the layer expanding graphite to be neutral by deionized water to obtain acid-free layer expanding graphite;
second, liquid phase mechanical stripping
Adding a surfactant into an alkaline aqueous solution with the pH value of 14, stirring at room temperature until the surfactant is dissolved, adding the expanded graphite obtained in the first step, and mechanically stripping in a sand mill or a high-speed stirrer to obtain a graphene dispersion liquid;
third, spray drying at low temperature
And (3) carrying out low-temperature spray drying on the graphene dispersion liquid with the concentration of 0.1-2.0 wt% obtained in the second step to obtain the redispersible graphene powder, wherein the inlet temperature is room temperature, the outlet temperature is 40-50 ℃, the drying room temperature is 60-70 ℃, and the feeding speed is 1.0-5L/h.
In the first step, the mass ratio of the graphite powder to potassium permanganate is 2-4.
In the first step, the layer-expanding substance comprises one or two of sodium carbonate and sodium bicarbonate, and the mass ratio of the graphite powder to the layer-expanding substance is 1.
The acid reacting with the coating material in the first step comprises any one or two of sulfuric acid (> 90%), phosphoric acid (> 70%) and nitric acid (> 40%), and the mass ratio of the acid to the coating material is 3 to 10.
In the second step, the surfactant is water-soluble imidazole ionic liquid, and the mass ratio of the graphite powder to the surfactant is 150-20.
In the second step, the surfactant includes any one of 1, 3-dimethylimidazole methanesulfonate, 1-ethyl-3-methylimidazole methanesulfonate, 1-propyl-3-methylimidazole acetate and 1-propyl-3-methylimidazole acetate.
In the second step, the rotational speed of the sand mill is 2000-2500 rpm, the sand milling time is 10-24h, the rotational speed of the high-speed stirrer is 15000-20000 rpm, and the stirring time is 0.5-2h.
According to the method, the graphite is intercalated in the mixed solution of concentrated sulfuric acid and potassium permanganate, sulfate radicals can enter between graphite layers to obtain the pre-intercalated graphite, so that the water solubility of the graphite is improved, the spacing between the graphite layers is enlarged, compared with the traditional acidification treatment, less concentrated sulfuric acid and potassium permanganate are used, the oxidation degree of the graphite is extremely low, and the excellent structural integrity is maintained. In the process of adding the layer expanding substance into the acid-containing intercalated graphite, because the acid-containing intercalated graphite is viscous, the layer expanding substance (sodium carbonate and sodium bicarbonate) is uniformly mixed in the acid-containing intercalated graphite at a high rotating speed and is diffused among graphite layers before reacting with residual acid. After acid which reacts with the layer expanding substance is added, the acid between the graphite layers reacts with sodium carbonate or sodium bicarbonate under high-speed stirring to generate gas, the gas is slowly and continuously generated to further expand the interlayer of the graphite to be increased to more than 0.5nm (according to calculation simulation, the interlayer spacing of the graphite is more than 0.5nm, the interlayer spacing acting force is small), the van der Waals force between the graphite layers is greatly reduced, and the efficient mechanical stripping of the subsequent graphene is facilitated. In addition, water-soluble imidazole ionic liquid is added in the liquid-phase mechanical stripping, and the water-soluble imidazole ionic liquid can form a physical adsorption effect with carbon atoms in graphite or graphene, so that the dispersion stability of the graphite and the graphene in water is improved, and the mechanical stripping efficiency is improved; in addition, the ionic liquid with a larger anion ratio is selected to prevent the ionic liquid from forming an ion pair, so that the surface of the ionic liquid modified on the surface of the graphene is positively charged, the generation of the graphene and the formation of unrecoverable aggregates in the drying process can be effectively prevented through the electrostatic repulsion, and meanwhile, the ionic liquid has higher temperature stability and further prevents the unrecoverable aggregates caused by the winding or bonding of the surface modifier in the drying process of the graphene. Through the control of the process, the beneficial effects of the invention are as follows:
1. according to the method, carbon dioxide is generated by reacting water-soluble carbonate with acid, the graphite layer is expanded by the generation of gas, compared with the traditional method for increasing the graphite layer spacing by an intercalation principle, the method is simpler, green and environment-friendly, the layer expansion effect is better (the layer spacing is increased more), compared with the traditional mechanical stripping method, the mechanical stripping time is shortened, the energy consumption is reduced, the preparation efficiency and the conversion rate of graphene are improved, and the application pace of the mechanical method in the field of graphene preparation is accelerated.
2. According to the method, the graphite after the layer expansion is used as a raw material, a mechanical stripping method is combined, the phenomenon that a large amount of concentrated sulfuric acid and strong oxidant are used in a traditional chemical method and a high-energy ultrasonic microwave stripping method is avoided, the process flow is simplified, and the structural defects of the graphene are reduced.
3. According to the invention, in the preparation process, the water-soluble imidazole ionic liquid is used as a dispersing agent, the structure of the dispersing agent is controlled, the interaction force with graphite or graphene is given, the dispersing agent has excellent water solubility and temperature stability, and the formation of ion pairs of positive ions and negative ions in an aqueous solution is avoided, so that the efficiency and the conversion rate of graphene liquid phase stripping are further improved, and the redispersible graphene powder can be prepared by combining a low-temperature spray drying process, thereby providing a new process for preparing the graphene composite material with uniform structure and performance by adopting a direct addition method in the downstream.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of exfoliated graphite prepared in example 1 of the present invention.
Fig. 2 is a Scanning Electron Microscope (SEM) image of exfoliated graphene prepared in example 1 of the present invention.
Fig. 3 is a Raman (Raman) spectrum of the exfoliated graphene prepared in example 1 of the present invention.
Fig. 4 is an X-ray diffraction (XRD) pattern of the exfoliated graphene prepared in example 1 of the present invention.
Fig. 5 is a projection electron microscope (TEM) image of the exfoliated graphene prepared in example 1 of the present invention.
Fig. 6 is an Atomic Force Microscope (AFM) image of exfoliated graphene prepared in example 1 of the present invention.
Detailed Description
Example 1
A low-defect and high-dispersion graphene and a high-efficiency liquid-phase mechanical preparation method thereof comprise the following steps:
in the first step, 20 g of graphite is added into a mixed solution containing 10g of potassium permanganate (purity > 98%) and 120 ml of concentrated sulfuric acid (concentration > 98%) at room temperature, and stirred for 1h at 35 ℃, then 40 g of sodium bicarbonate is added into the intercalated graphite containing acid at a speed of 5g/min at a speed of 1000 rpm, so that the sodium bicarbonate is uniformly mixed and inserted into the intercalated graphite containing acid, then 250 ml of phosphoric acid (concentration > 70%) is added into the intercalated graphite, and stirring is continued at a speed of 2000 rpm for 6h, so that the expanded graphite containing acid is obtained. Adding the acid-containing expanded graphite into 2 liters of deionized water, removing redundant sodium bicarbonate, adding 10 milliliters of hydrogen peroxide (30%) solution, removing redundant potassium permanganate, standing, removing supernatant, continuing to add deionized water, standing, removing supernatant, repeating the steps for several times until the pH value is 7, and obtaining the acid-free expanded graphite.
In the second step, 0.2 g of 1, 3-dimethylimidazole methanesulfonate was added to 800 ml of an aqueous sodium hydroxide solution with pH =14, and stirred at room temperature until dissolved. And adding the layer-expanded graphite in the first step into the alkaline solution containing the surfactant, and emulsifying for 2 hours at 15000 revolutions per minute to obtain a graphene dispersion liquid.
The graphene dispersion liquid prepared by the process is stably dispersed in an alkaline aqueous solution, the yield of the single-layer or multi-layer graphene is more than 90%, and the prepared graphene is thin like cicada's wing, has the thickness of 0.858 nanometer and is about 2-3 layers as can be seen from fig. 5 and 6.
And thirdly, adding 1.0L of 0.2wt% graphene solution into a container of a dryer, wherein the inlet temperature is room temperature, the outlet temperature is set to be 40 ℃, the temperature of a drying chamber is 60 ℃, the feeding speed is 1.0L/h, and the graphene powder can be prepared by spraying for 1 h.
Example 2
In the first step, 20 g of graphite is added into a mixed solution containing 10g of potassium permanganate (purity > 98%) and 120 ml of concentrated sulfuric acid (concentration > 98%) at room temperature, and stirred for 1h at 35 ℃, then 40 g of sodium bicarbonate is added into the acid-containing intercalated graphite at a speed of 5g/min at a speed of 1000 rpm, the sodium bicarbonate is uniformly mixed and inserted into the acid-containing intercalated graphite, then 250 ml of phosphoric acid (concentration > 70%) is added thereto, and stirring is continued for 6h at a speed of 2000 rpm, and the acid-containing exfoliated graphite is obtained. Adding the acid-containing expanded graphite into 2 liters of deionized water, removing excessive sodium bicarbonate, adding 10 milliliters of hydrogen peroxide (30%) solution, removing excessive potassium permanganate, standing, removing supernatant, continuing to add deionized water, standing, removing supernatant, repeating the steps for several times until the pH value is 7, and obtaining the acid-free expanded graphite.
In the second step, 0.2 g of 1, 3-dimethylimidazole methanesulfonate was added to 800 ml of an aqueous sodium hydroxide solution of pH =14, and stirred at room temperature until dissolved. And adding the layer-expanding graphite in the first step into the alkaline solution containing the surfactant, and sanding for 24 hours at 2400 revolutions per minute to obtain the graphene dispersion liquid.
And thirdly, adding 1.0L of graphene solution with the concentration of 1.0wt% into a dryer container, setting the inlet temperature to be room temperature, the outlet temperature to be 50 ℃, the drying chamber temperature to be 70 ℃, and the feeding speed to be 1.0L/h, and obtaining the graphene powder after 1 h.
Claims (7)
1. A high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene is characterized by comprising the following steps: the method comprises the following steps:
firstly, adding potassium permanganate into concentrated sulfuric acid at room temperature, mechanically stirring the potassium permanganate to completely dissolve the potassium permanganate to form a homogeneous mixed solution, adding graphite powder into the mixed solution, stirring the mixed solution at the temperature of 25-35 ℃ at the speed of 500-1000 rpm for 0.5-1h, then adding a layer expanding substance at the speed of 5g/min-10g/min at the speed of 500-1000 rpm, then adding acid, reacting the acid and the layer expanding substance to form a viscous mixed system at the speed of 1000-2000 rpm, finally continuing stirring the mixed solution at the temperature of 25-35 ℃ for 2-6h to obtain a layer expanding graphite slurry, adding the layer expanding graphite slurry into 2L of deionized water, adding hydrogen peroxide into the layer expanding graphite slurry at the speed of 10mL/min, stirring and mixing the slurry at the speed of 100-500 rpm at the temperature of 25-35 ℃, and cleaning the slurry to neutrality through filtration and deionized water to obtain acid-free layer expanding graphite;
the layer expanding substance comprises one or two of sodium carbonate and sodium bicarbonate;
second, liquid phase mechanical stripping
Adding a surfactant into an alkaline aqueous solution with the pH value of 14, stirring at room temperature until the surfactant is dissolved, adding the dissolved surfactant into the layer-expanding graphite slurry obtained in the first step, and mechanically stripping in a sand mill or a high-speed stirrer to directly obtain a graphene dispersion liquid;
thirdly, spray drying at low temperature
And (3) carrying out low-temperature spray drying on the graphene dispersion liquid with the concentration of 0.1-2.0 wt% obtained in the second step to obtain the redispersible graphene powder, wherein the inlet temperature is room temperature, the outlet temperature is 40-50 ℃, the drying room temperature is 60-70 ℃, and the feeding speed is 1.0-5L/h.
2. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, wherein the high-efficiency liquid-phase mechanical preparation method comprises the following steps: in the first step, the mass ratio of the graphite powder to potassium permanganate is 2-4.
3. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, wherein the high-efficiency liquid-phase mechanical preparation method comprises the following steps: in the first step, the mass ratio of the graphite powder to the layer-expanding substance is 1.
4. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, wherein the high-efficiency liquid-phase mechanical preparation method comprises the following steps: in the first step, the acid reacting with the coating material comprises any one or two of sulfuric acid, phosphoric acid and nitric acid, and the mass ratio of the acid to the coating material is (3) - (1).
5. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, wherein the high-efficiency liquid-phase mechanical preparation method comprises the following steps: in the second step, the surfactant is water-soluble imidazole ionic liquid, and the mass ratio of the graphite powder to the surfactant is 150-20.
6. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, wherein the high-efficiency liquid-phase mechanical preparation method comprises the following steps: in the second step, the surfactant includes any one of 1, 3-dimethylimidazole methanesulfonate, 1-ethyl-3-methylimidazole methanesulfonate, 1-propyl-3-methylimidazole acetate, and 1-propyl-3-methylimidazole acetate.
7. The high-efficiency liquid-phase mechanical preparation method of low-defect and high-dispersion graphene according to claim 1, characterized in that: in the second step, the rotating speed of the sand mill is 2000-2500 rpm, and the sand milling time is 10-24h; or the rotating speed of the high-speed stirrer is 15000 to 20000 revolutions per minute, and the stirring time is 0.5 to 2 hours.
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