Preparation And Application Of Graphene And Graphene Dispersions

As one of the most promising materials in the 21th century, graphene has a very stable structure, ultrahigh carrier mobility, excellent electrical and thermal conductivity, high mechanical strength, high specific surface area, and good optical transparency and other excellent physical and chemical properties. As a result, graphene has exhibited appealing potential applications in many traditional and emerging fields such as electronics, aerospace, optics, energy, environment and new materials.Although graphene has many excellent physical and chemical properties, when a large number of single layer graphene sheets get together, it is prone to irreversibly aggregate due to the strong π-π stacking and van der Waals forces between adjacent graphene layers. As a result, it is difficult for graphene to stably disperse in a solvent, which greatly limits its application. In addition, large-scale preparation of graphene still has many difficulties, so it is very important to explore a large-scale and low-cost method to prepare high-quality and size-controlled graphene. To solve the above problems, the main contents are as follows:1. Preparation of RGO and RGO/Al(OH)3 nanocomposites by Red Al reduction. We describe, for the first time, a facile and efficient approach for selectively synthesizing reduced graphene oxide (RGO) and RGO/Al(OH)3 nanocomposites using Red Al as both the reducing agent and the precursor of Al(OH)3 by choosing different post-treatment processes. The structure and morphology of the products are elucidated using XRD, FT-IR, Raman, XPS, HRTEM and SAED analyses. It was found that the substantial oxygen functionalities on the graphene oxide were removed by Red Al, and RGO with a C/O ratio as high as 9.0 was yielded. The electrical conductivity of RGO could get to 90 S/cm, which was nearly 5 orders of magnitude higher than that of GO. The results also revealed that the RGO and Al(OH)3 formed a uniform nanocomposite with the Al(OH)3 absorbed on the RGO surface and/or filled between the RGO sheets in the form of round nanosheets with an average diameter of 200 nm. Plausible mechanisms of deoxygenation and formation of Al(OH)3 were discussed. This work not only provides a new reductant to effectively reduce graphene oxide, but also develops a facile route to prepare RGO/Al(OH)3 nanocomposites.2. Preparation of RGO in RPB by Red Al reduction. Here we demonstrate a simple and effective method for mass production of RGO by combining the fast and efficient reduction reaction based on Red Al with rotating packed bed (RPB). In this work, we use RPB as a reactor and Red Al as a reducing agent for large-scale preparation of RGO by choosing the post-treatment process of hydrochloric acid-washing. We compared the product named RPB-RGO prepared in RPB with the sample named STR-RGO prepared in STR (Stirred Tank Reactor, STR). At the same time, the structure, morphology and electrical performance of RPB-RGO and STR-RGO were characterized by XRD, SEM, TGA, Raman and Cyclic voltammetry. It was found that the reduction reaction of Red Al in RPB was more thoroughly than that in STR. Cyclic voltammetry showed that the specific capacitance of RPB-RGO ranged from 18.3 F/g to 43 F/g, depending on the potential scan rate from 10 mV/s to 100 mV/s, while the specific capacitance of STR-RGO ranged from 12.7 F/g to 28.3 F/g. This research might provide an effective and scalable route to prepare RGO.3. Preparation and application of edge-oxidized graphene and its aqueous dispersion. The current investigation showed that oxidation of graphite with low concentration KMnO4 and short oxidation time led to formation of edge-oxidized graphite (EOG) which preserved the sp2 hybrid structure on the basal planes while the edges were functionalized by oxygen-containing groups. Medium sonication of EOG in water using sodium cholate (SC) as a stabilizer could yield edge-oxidized graphene nanosheets (EOGNs) dispersion at a concentration of up to 0.59 mg/ml. This dispersion was stable at room temperature for more than 6 months. Later, the prepared EOGNs dispersion was used to produce transparent conducting EOGN films by vacuum filtration method. The resulting thin films are uniform and exhibit a transparency of 87.6%at 550 nm and a sheet resistance of-26.4 kΩ/□. Moreover, the prepared EOG was found to be dispersible in a wider variety of solvents than GO, which verifies wider application fields for EOG compared to GO. These results open up new possibilities for preparation of graphene dispersions with insignificant defects.4. Preparation and application of graphene and its organic phase dispersions. We use NG (HNO3-treated graphite, NG) as a strating material, polyvinylpyrrolidone (PVP) as a stabilizer, NaCl and oxalic acid as intercalants for preparation stable organic phase graphene dispersions. In this work, the aqueous mixtures of NG, NaCl, oxalic acid, and PVP were stirred under hydrothermal conditions, and subsequently washed by deionized water, and finally the mixtures were dispersed into organic solvents by ultrasonication and centrifugation. We optimized the hydrothermal exfoliation process. It was found that when the hydrothermal temperature was 240 ℃ and the hydrothermal time was 12 h, the exfoliation effect of NG was the best. Transparent and conductive graphene thin films can be fabricated from ethanol phase graphene dispersion by vacuum filtration method. The resulting thin films exhibited a transparency of ～81.2% at 550 nm and a sheet resistance of 28.0 kΩ/□. At last, the plausible mechanism of hydrothermal exfoliation process for NG was discussed. We believe that this method provide a good precursor material for graphene-based nanocomposites.