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Why does graphene prepared by different methods disperse?

May 23, 2019   Pageview:1053

The thickness of the two-dimensional material graphene is only a few nanometers, with high strength the adsorption performance of between nanomaterial particles, so it is difficult to be spread out completely, and due to the inherent in the hydrophobic pure carbon materials, graphene is not able to fully dispersed in other materials, which greatly limits the material performance of the play, so how to spread its become a bottleneck of graphene applications.

Graphene has excellent mechanics, electricity, magnetism, thermal and optical properties, its structure of hexagonal carbon ring in plane infinite extends, carbon sp2 hybridization formation of the hexagonal carbon ring plane direction has stable mechanical properties and electrical properties, the strength of the graphene can be up to 100 times the strength of steel and hardness can be comparable to the diamond. Electron mobility of graphene surface 2 x 105 cm2 / s. (V) is far higher than the conductivity of copper. These excellent performances make graphene become after the carbon nanotubes were found in 1991 more prospects of carbon materials.

Based on the many advantages of graphene, which can be used to improve other materials? By adding the graphene composite material, consisting of the mechanical and electrical performance are greatly improved in many studies. But the thickness of the two-dimensional material graphene is only a few nanometers, with high strength the adsorption performance of between nanomaterial particles, so it is difficult to be spread out completely, and due to the inherent in the hydrophobic pure carbon materials, graphene is not able to fully dispersed in other materials, which greatly limits the material performance of the play, so how to spread its become a bottleneck of graphene applications.

1, the influence of the preparation methods of graphene water dispersion

The mechanical stripping method, water dispersibility of graphene

Graphene has a lot of kinds of preparation methods, and the principle of various methods is very different, of graphene dispersion also exist differences in performance. Mechanical stripping method was initially made graphene, the method of minimum damage to the structure itself, the method of graphene materials complete structure, less defect. But there is little the graphene surface hydrophilic group, thus makes the water dispersion properties is poor. In addition, the mechanical stripping method cannot realize volume production of graphene, unable to be applied in actual production, so besides some microscopic studies of graphene, generally do not adopt this method.

Expansion of the legal system water dispersion of graphene

Raw materials more than the method of expanded graphite, expanded graphite has a relatively loose structure between the layers, by means of ultrasonic or high-speed shear method, makes the dispersed into the expanded graphite using solvent between layer and layer, and then under the electrostatic repulsion of ultrasonic and dispersant, the expanded graphite overcome interlayer van der Waals force, so that the separation layer and layer, and finally get single or less layers of graphene solution. PatonKR et al., using the similar principle, preparation of the graphene NMP dispersed solution, and through the X-ray spectra and Raman spectra, made by the method of graphene has the advantages of less defect.

XiumeiGeng, YufenGuo etc. are using H2O2 as the media, under the catalysis of FeCl3, with graphene dispersion, by SEM, TEM and AFM characterization, graphene has this kind of method, the thickness is small, the characteristics of the planar area is large, stable and easily in the water.

Chemical vapor deposition of water dispersion of graphene

Chemical vapor deposition (CVD), its principle is by high temperature gas, carbon and hydrogen atoms and then reduce the temperature of the gaseous atoms deposited on the metal grew out of graphene. This method was widely in the amount of carbon nanotubes during application. Graphene is of high quality, the method, however, compared to the graphene dispersion directly obtained in aqueous solution, its unique way of preparing the water dispersion is relatively less, so the production of graphene CVD method, such as the need to use into solution, it will need to deal with again.

REDOX legal water dispersion of graphene

The principle of oxidation reduction preparation of graphene for the use of concentrated sulfuric acid, nitric acid or other oxidants on graphite oxidation treatment, combined with ultrasonic treatment in order to increase the distance between the graphite layers, thus isolated graphene layers, get graphene oxide, finally through the back door of reductant will graphene oxide reduction, reduction of graphene oxide are formed. But the oxidation degree will not only major damage the structure of graphene, carbon ring on a lot of defects, but also bring many - COOH, making these defects - OH hydrophilic group, etc. Graphene has two sides, the method, the defects caused by oxidation, made of graphene quality is not high; Space, on the other hand defects with hydrophilic group if failed to fully restore, in the process of reduction will make of this method, the water dispersion of graphene is superior to other methods. The preparation method is easy to realize the mass production, but need to weigh the water dispersion performance and quality of graphene before you choose.

2, the influence of the type of dispersant on the graphene dispersion

The influence of ionic surfactant of graphene dispersion

Surfactant can be divided into ionic and nonionic, and ionic surfactants are the most common., DasS WajidAS etc., the study on anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in solution of graphene dispersion effect, obtained the ideal result. But the anionic surfactant in the electrolyte solution have unstable faults. Fernandez - MerinoMJ ParedesJI studied such as variety of ionic surfactant and nonionic surfactant in acidic solution and alkaline solution and dispersing properties, the results show that the nonionic surfactant on the acid alkali solution is not very sensitive, such as the dispersion effect of Brij700 almost no change, and in the case of high dosage of dispersants difference is smaller. Ionic surfactant, on the other hand, showed the characteristics of acid sensitive, many scattered good effect of dispersant in alkaline solution, almost no dispersion effect in the acidic environment, the typical representative have 1 - pyrene butyric acid, sodium deoxycholic acid and SDBS, etc. These findings suggest that in the actual preparation of graphene composites, the selection of dispersants and the solution of acid and alkali sex is very big.

Nonionic surfactant effects on graphene dispersion

PVP is a kind of polymer, is also a kind of non-ionic surface active agent, PVP as graphene dispersion has the very good effect. WajidAS et and Wei per capita studied the dispersant dispersion effect of graphene. Research shows that when the PVP solution for 10 mg/mL, diversifiable reached the maximum concentration of graphene., formation on the surface of this kind of dispersant can be adsorbed on the graphene layer, so as to prevent contact between graphene reunion, and WajidAS and others also studied this kind of dispersant of graphene in organic solvents such as DMF, NMP, ethanol and dispersing effect, the results showed that PVP in the high temperature about 100 ℃ and the conditions of low pH is about 2 can make graphene solution is stable, compared with other surfactants for the surfactant has obvious advantages, and further studies the average molecular weight is 10000400 00110 00110 after PVP dispersion effect, the smaller the relative molecular mass is obtained by PVP with dispersion effect is better.

3, summary

Studies of graphene dispersion in water method, has made a certain progress so far, each method has its own advantages and disadvantages, no defects in the graphene dispersion in water are difficult to implement, and when through certain methods, such as oxidation or surface modification, will introduce some more or less defects, or other functional groups. In addition, dispersant adsorbed on the surface of graphene will also affect its working performance of the play, such as lowering its original electric conductivity, etc. In the end, most of the graphene dispersion in water quantity under 10 mg/mL, the preparation of high concentration of graphene solution is still very difficult, hope that with the deepening of the research can get very good solution to these problems.

The page contains the contents of the machine translation.

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