CN104058392A - Method for preparing graphene colloid dispersion liquid - Google Patents

Abstract

The invention relates to a preparation method of a graphene colloidal dispersion liquid, comprising the following steps: (1) adding graphite oxide into water and ultrasonically dispersing to obtain graphene oxide colloids uniformly dispersed in a single layer; (2) adding a surfactant (3) adding a reducing agent to the solution obtained in step (2), reacting until the pH rises to 10.5 to 11.5, and then placing the mixed solution at 70 to 90°C for reaction to obtain Graphene colloidal dispersion with stable dispersion. Compared with the prior art, the graphene dispersion prepared by the present invention can be used in the large-scale preparation, storage and transportation of graphene and the preparation of graphene composite materials and other fields; the graphene dispersion prepared by the present invention has high concentration, good dispersibility Good, can maintain the advantages of long-term stability, wherein the particle size distribution of graphene sheets is uniform, good peeling degree; low cost, simple preparation process, no environmental pollution, easy to realize large-scale industrial production.

Description

A kind of preparation method of graphene colloid dispersion liquid

technical field

The invention relates to a preparation method of a graphene colloidal dispersion liquid, belonging to the field of preparation of nanometer materials.

Background technique

Graphene is a two-dimensional honeycomb carbon material composed of a single layer of carbon atoms tightly packed. In 2004, British scientist Geim et al. successfully prepared graphene that existed stably at room temperature, which attracted widespread attention (Novoselov K, Geim A, et al. Science, 2004, v306: 666-669). Graphene has excellent electrical properties (conductivity up to 106S/cm), thermal properties (thermal conductivity 3000-5000J/m K s), mechanical properties (strength 110-130GPa, elastic modulus 1.0TPa) And optical properties (light transmittance can reach 97.7%), so it has broad application prospects in electronics, high-strength materials, energy conversion and storage, catalysis, sensors and other fields.

The methods for preparing graphene are mainly divided into two categories: bottom-up method and top-down method; the former includes micromechanical exfoliation method and chemical reduction graphene oxide method, etc., and the latter includes epitaxial growth method and chemical vapor deposition method, etc. . Among the many methods for preparing graphene, the chemical reduction of graphene oxide method is considered to be the most likely method to realize the industrial production of graphene; it has the advantages of low cost, high yield, and easy control. However, due to the gradual reduction of the hydrophilic oxygen-containing groups on the surface of graphene oxide during the reduction process, the electrostatic repulsion between the sheets is weakened, graphene will agglomerate, the dispersion will gradually decrease, and even precipitation will occur (Stankovich S, et al.Carbon , 2007, v45:1558-1565).

Due to the strong π-π bond interaction between graphene layers, graphene with a complete structure is easy to aggregate and precipitate in dispersion media such as water and organic solvents, which is not conducive to the large-scale preparation and application of graphene. In order to solve this problem, people functionalize graphene, which not only improves its solubility, but also uses a variety of chemical bonds to regulate the structure of graphene and endow graphene with new properties. According to whether new covalent bonds are introduced, graphene functionalization methods can be divided into covalent bond functionalization and non-covalent bond functionalization. The former is generally used to prepare graphene composite materials, in which graphene generally has good solubility; but due to the introduction of other functional groups, the large π bond conjugated structure of graphene is destroyed, making its conductivity and other properties significantly reduced. Non-covalent functionalization uses non-covalent bonds such as π-π interactions, ionic bonds, and hydrogen bonds to functionalize the surface of graphene with modified molecules, which not only maintains the properties of graphene itself, but also maintains the properties of graphene. Solubility. Li et al. studied the dispersed state of graphene and its charge repulsion. The results show that the reason why graphene oxide can dissolve in water is mainly due to the mutual repulsion of negative charges on its surface to form a stable colloidal solution, not just the hydrophilicity of oxygen-containing groups. They took advantage of this discovery to retain the carboxyl anions in graphene oxide when removing oxygen-containing functional groups such as hydroxyl groups and epoxy groups by controlling the degree of reduction, so that it can be stably dispersed in aqueous solution (Li D, et al.Nanotechnology , 2008, v3: 101-105).

At present, many important results have been achieved in the study of the dispersion of graphene. People such as Fu Honggang mix graphene and cyclodextrin and dissolve it in alcohol to prepare a graphene dispersion with good stability (preparation method of highly stable graphene dispersion; publication number: CN102515149A; publication date: 2012.06.27). Zhang Wen and others dispersed graphene oxide in organic solvents such as methanol, and then sprayed the dispersion into a liquid nitrogen container for quick-freezing treatment. After the product returned to room temperature, it was subjected to reduction treatment to obtain a black graphene slurry (a Preparation method of graphene dispersion; publication number: CN103496691A; publication date: 2014.01.08). Chen Guohua et al adopted the method of ball milling after blending reduced graphene oxide and a mixed solvent (such as N-methyl-2-pyrrolidone and water in a volume ratio of 9:1) to prepare 2.5-10 mg/ml Graphene dispersion (a method for preparing a high-concentration small-diameter graphene dispersion; publication number: CN103407998A; publication date: 2013.11.27). Xu Yan and others prepared the oligolayer graphene suspension, and used ultra-high pressure or supercritical equipment to carry out nano-fine dispersion treatment on the graphene solution (a preparation method of graphene dispersion; publication number: CN103253656A; publication date: 2013.08 .twenty one). People such as Sun Jing adopt the solution exchange method to disperse graphene oxide in N,N-dimethylformamide, make the graphene dispersion liquid (a kind of graphene colloidal dispersion liquid) of concentration about 0.5mg/ml after reduction. Preparation method; publication number: CN102633256A; publication date: 2012.08.15). However, in the existing research on the dispersion of graphene, toxic organic solvents are commonly used, the preparation process is complicated, the concentration of the stable dispersed graphene aqueous solution is low, the sheet size is small, and the conductivity of graphene after surface modification is reduced. And other issues. Therefore, it is of great significance to explore a method for preparing a graphene aqueous solution with high concentration, good dispersion and stability.

Contents of the invention

The purpose of the present invention is exactly to provide a kind of preparation method of high-quality graphene colloidal dispersion liquid in order to overcome the defective that above-mentioned prior art exists. It is characterized by using water as the dispersion system. Through the synergistic effect of ultrasound, surfactant and high temperature, the graphene can reach a higher quality and the stable dispersion concentration of graphene is higher. After drying into graphene powder and redissolving, it can still reach the same level. concentration and stability.

The purpose of the present invention can be achieved through the following technical solutions:

(1) According to the mass ratio of water to graphite oxide (400-1000): 1, add graphite oxide into water, ultrasonically disperse for 2-3 hours, and form a uniformly dispersed single-sheet layer with a concentration of 1-2.5mg/ml Graphene oxide colloid;

(2) Add the surfactant into the graphene oxide colloid in a ratio of 1: (50-100) according to the mass ratio with the graphene oxide colloid, and stir and mix evenly with a magnetic stirrer (rotating speed 100rmp-500rmp, 10-30 minutes ) after ultrasonic dispersion for 1 hour (working frequency ≥ 40kHz), the temperature is 40-50°C;

Wherein, the surfactant is at least one of sodium dodecylbenzenesulfonate and sodium dodecylsulfate.

(3) Add a reducing agent with a volume ratio of 1: (10-1000) to the liquid obtained in step (2), react at room temperature (20-25°C) for 1-3 hours until the pH rises to about 11, and place the mixed solution in After reacting at 80°C for 12 hours, a black reduced graphene oxide colloid with stable dispersion can be obtained, in which almost all (>90%) graphene exists in a single layer state. The graphene colloidal dispersion can still keep its dispersibility unchanged after standing for 1 month.

Wherein, the reducing agent is at least one of hydrazine, hydrazine hydrate, dimethylhydrazine, sodium borohydride, ascorbic acid, and gallic acid.

The hydrophobic group at one end of the surfactant molecule combines with graphene, and the hydrophilic group at the other end interacts with water, so that when graphene particles collide with each other, the entropy elasticity of the surfactant molecular layer and the protection of the hydration layer prevent Prevent their aggregation, resulting in steric hindrance, thereby improving the stability. In addition, the surfactant reduces the surface tension of the solvent, which can promote the stripping of graphene, so it can have a higher dispersion concentration.

Ultrasonic peeling method is a commonly used means of sheet peeling and crushing. Ultrasonic waves radiate densely and alternately in the graphite oxide suspension, making the liquid flow generate thousands of tiny bubbles, which form and grow in the negative pressure zone formed by the longitudinal propagation of ultrasonic waves, and quickly close in the positive pressure zone. Closure can create momentary high pressure and high temperature. The continuously generated high pressure and high temperature are like a series of small "explosions" that continuously impact the graphite oxide, causing the layers to peel off rapidly. The size of graphene oxide can be controlled by adjusting the ultrasonic power and ultrasonic time.

The function of ultrasound in the present invention is not only to peel off the graphene oxide, but also to fully disperse the surfactant in the graphene oxide colloid. Since the amount of surfactant used is higher than the critical micelle concentration, the surfactant molecules in the solution will inevitably form micelles, thereby reducing the efficiency of dispersing graphene as a whole. Ultrasound significantly inhibited the formation of micelles through the effect on the core water of micelles. When adding hydrazine hydrate for the reduction reaction, the pre-reaction in the middle temperature stage is beneficial to the dispersion of the reduced graphene oxide. Because the high-temperature reaction is carried out directly, the Brownian motion increases as the temperature increases, resulting in an increase in the flocculation speed of graphene sheets. In addition, increasing temperature will reduce the activity of surfactants, which is also not conducive to the dispersion of graphene.

(4) After the graphene colloidal dispersion liquid is placed in 80～100 ℃ degree of drying, obtain graphene powder; According to the mass ratio of water and graphene is (400～1000): 1 ratio, dry graphene powder is added into water After ultrasonic dispersion for 10-30 seconds, a uniformly dispersed graphene colloid with a concentration of 1-2.5 mg/ml is formed, and its dispersibility is the same as that of the graphene dispersion before drying;

The graphene dispersion prepared by the method can be used in the fields of large-scale preparation, storage and transportation of graphene, preparation of graphene composite materials and the like.

Compared with prior art, the present invention has following advantage:

1, the graphene dispersion prepared by the present invention has the advantages of high concentration, good dispersibility, and ability to maintain long-term stability, wherein the graphene sheet particle size distribution is uniform, and the peeling degree is good (almost all are monolayers);

2. Low cost, simple preparation process, no environmental pollution, and easy realization of large-scale industrial production.

Description of drawings

Fig. 1 is the schematic diagram of the principle of graphene dispersion in water;

Fig. 2 is the AFM figure of monolayer graphene in embodiment 1;

Fig. 3 is the particle size distribution figure of graphene in embodiment 1;

Fig. 4 is the XPS figure of graphene oxide (1) and graphene (2) in embodiment 1;

Fig. 5 is the Raman diagram of graphene in embodiment 1.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

2.0mg/ml graphite oxide dispersion liquid was prepared, and graphene oxide colloid was obtained by ultrasonication for 3 hours. The schematic diagram of the principle of graphene dispersion in water is shown in Figure 1. Add 1.0wt% sodium dodecylbenzenesulfonate, stir for 10 minutes to dissolve it completely, and ultrasonicate at 50°C for 1 hour; add 0.2vol% hydrazine hydrate, and let it stand at 25°C for 1h, the pH rises to 10.7.80 ℃ heating for 12h, a black graphene dispersion can be prepared. Take 200ml of graphene dispersion to form a film by vacuum suction filtration, and use four probes to test its sheet resistance after drying.

As shown in Figure 2, the graphene atomic force microscope (AFM) characterization diagram, it can be seen that the degree of exfoliation of reduced graphene oxide is better, and the sheet diameter is generally between 200-500nm; It can be seen that there is almost no agglomeration of graphene after reduction, the thickness is generally between 0.3-0.7nm, and it is mainly single-layer graphene. The oxidation-reduction process has little damage to the structure of graphene, and only a few holes are formed on the surface.

As shown in Figure 3, it is the dynamic light scattering-particle size distribution diagram of the obtained graphene dispersion liquid, as can be seen from the figure, the particle size distribution of graphene is uniform, mainly 150-450nm, which is consistent with the analysis data of AFM, The average particle size is 288.5nm, and the polydispersity coefficient is 0.265, indicating that the particle size analysis data has high reliability. Its zeta potential was tested to be -38 ~ -41.8mV, indicating that the dispersion liquid has good stability.

As shown in Figure 4, it is the X-ray photoelectron spectrum (XPS) figure of graphene after graphene oxide and its reduction, it can be seen that many oxygen-containing functional groups (-OH, 286.5eV;-C=O are contained in graphene oxide. , 287.5eV; -COOH, 289eV), but these oxygen-containing functional groups disappear after reduction, indicating that the reduction degree of graphene prepared by this method is good, and it also explains the reason why the prepared graphene has good conductivity.

As shown in Figure 5, it is the Raman spectrum (Raman) analysis diagram of graphene, the G peak due to E2g vibration is produced near 1576cm ^-1 , and the D peak is caused by defects at 1340cm ^-1 ; wherein, the G peak is obviously higher than The D peak (D/G=0.72) shows that the structural damage of graphene is small, which reflects that the reduction process in this method has good recoverability to the graphene sheet structure and few defects.

Example 2

Prepare a 1.0 mg/ml graphite oxide dispersion, and ultrasonicate for 3 hours to prepare graphene oxide colloids. Add 1.0wt% sodium dodecylbenzene sulfonate, stir for 10 minutes to dissolve it completely, ultrasonicate at 40°C for 1 hour; add 0.2vol% hydrazine hydrate, let it stand at 25°C for 2h, the pH rises to 11.80 ℃ heating for 12h, a black graphene dispersion can be obtained. Take 200ml of graphene dispersion to form a film by vacuum suction filtration, and use four probes to test its sheet resistance after drying.

Example 3

Prepare a 2.0 mg/ml graphite oxide dispersion, and ultrasonicate for 3 hours to prepare graphene oxide colloids. Add 2.0wt% sodium lauryl sulfate, stir for 30 minutes to dissolve it completely, ultrasonicate at 50°C for 1 hour; add 0.1vol% hydrazine hydrate, let it stand at 25°C for 2 hours, the pH rises to 11. Heat at 80°C 12h, a black graphene dispersion can be obtained. Take 200ml of graphene dispersion to form a film by vacuum suction filtration, and use four probes to test its sheet resistance after drying.

Example 4

Prepare a 2.0 mg/ml graphite oxide dispersion, and ultrasonicate for 3 hours to prepare graphene oxide colloids. Add 0.5wt% sodium lauryl sulfate, stir for 30 minutes to dissolve it completely, ultrasonicate at 50°C for 1 hour; add 0.2vol% hydrazine hydrate, let it stand at 25°C for 1 hour, the pH rises to 11. Heat at 80°C 12h, a black graphene dispersion can be obtained. Take 200ml of graphene dispersion to form a film by vacuum suction filtration, and use four probes to test its sheet resistance after drying.

The electrical conductivity of the graphene dispersion prepared in Examples 1 to 4 is shown in Table 1.

The electrical conductivity of table 1 embodiment 1～4

Example 5

Prepare a 2.5 mg/ml graphite oxide dispersion, and ultrasonicate for 2 hours to prepare graphene oxide colloids. Add 1.5wt% sodium lauryl sulfate, stir for 30 minutes to dissolve it completely, ultrasonicate at 50°C for 1 hour; add 0.2vol% hydrazine hydrate, let it stand at 25°C for 1 hour, the pH rises to 11. Heat at 80°C 12h, a black graphene dispersion can be obtained.

The above descriptions of the embodiments are for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative effort. Therefore, the present invention is not limited to the above-mentioned embodiments. Improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (9)

1. a preparation method for Graphene colloidal dispersion, is characterized in that, comprises the following steps:

(1) graphite oxide is added to the water, ultrasonic dispersion, obtains the homodisperse graphene oxide colloid of monolithic layer;

(2) tensio-active agent is joined in graphene oxide colloid, mix rear ultrasonic dispersion;

(3) in step (2) gained solution, add reductive agent, react to pH and rise to 10.5～11.5, then mixed solution is placed in to 70～90 ℃ of reactions, obtain having the Graphene colloidal dispersion of Investigation of stabilized dispersion of nano.

2. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, is characterized in that, in step (1), the mass ratio of water and graphite oxide is 400: 1～1000: 1.

3. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, is characterized in that, the tensio-active agent adding in step (2) and the mass ratio of graphene oxide colloid are 1: 50～1: 100.

4. according to the preparation method of a kind of Graphene colloidal dispersion described in claim 1 or 3, it is characterized in that, described tensio-active agent is Sodium dodecylbenzene sulfonate or sodium lauryl sulphate.

5. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, is characterized in that, the solution temperature in step (2) after ultrasonic dispersion is 40～50 ℃.

6. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, is characterized in that, the volume ratio of the reductive agent adding in step (3) and step (2) gained liquid is 1: 10～1: 1000.

7. according to the preparation method of a kind of Graphene colloidal dispersion described in claim 1 or 6, it is characterized in that, described reductive agent is at least one in hydrazine, hydrazine hydrate, dimethylhydrazine, sodium borohydride, xitix or gallic acid.

8. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, it is characterized in that, in step (2) gained solution, add reductive agent, 20～25 ℃ are reacted 1～3 hour, rise to 10.5～11.5 to pH, then mixed solution is placed in to 70～90 ℃ of reactions 10～14 hours, obtains having the Graphene colloidal dispersion of Investigation of stabilized dispersion of nano.

9. the preparation method of a kind of Graphene colloidal dispersion according to claim 1, is characterized in that, by Graphene colloidal dispersion be placed in 80～100 ℃ of degree dry after, obtain graphene powder; The ratio that according to the mass ratio of water and Graphene is 400: 1～1000: 1 is added to the water dry graphene powder, and ultrasonic dispersion is after 10～30 seconds, the homodisperse Graphene colloid of monolithic layer that to form concentration be 1～2.5mg/ml.