Study on high efficiency fabrication and quality improvement of graphene oxide via Couette-Taylor flow

다국어 초록 (Multilingual Abstract)

In summary, a practical approach to bulk-scale graphene-based materials is critically important for their use in the industrial applications. Here, we describe a facile method to prepare graphite oxide using a Couette–Taylor flow reactor for the oxidation of bulk graphite flakes. We found that the turbulent Couette–Taylor flow in the reactor could be engineered to result in the efficient mixing and mass transfer of graphite and oxidizing agents (KMnO4 and H2SO4), thereby improving the efficiency of graphite into graphene oxide. As compared to the standard Hummers’ method, higher fraction of a single- and few-layer graphene oxide can be yielded in a dramatically shortened reaction time, by optimizing the processing parameters, we have shown that ~93% of graphene oxide yield could be achieved within 60 min of reaction time. This method also allowed for the in-situ functionalization of graphene oxide with metal oxide nanoparticles to give a nanoparticle-decorated graphene oxide hybrid material.
Furthermore, we describe a green method to prepare graphene oxide using a recycled sulfuric acid through filter process after oxidation of natural graphite in a Couette-Taylor flow reactor. The volume of water for the washing of graphite oxide was dramatically decreased. As compared to the conventional Hummers’ method, viscosity of the mixture containing graphite oxide and sulfuric acid after oxidation reaction using the Couette-Taylor flow was very low as 200 cP (25ºC), and it enabled the filtering process. In conclusion, although the recycled sulfuric acid was used for the fabrication of graphene oxide, high quality, a single- or few-layer, graphene oxide could be obtained at the same time while saving the process costs via reducing the washing water and reuse the sulfuric acid.
To utility in a range of applications of graphene oxide, high efficiency exfoliation of graphite oxide with controlled area is required. Here, we describe a facile method to prepare large-area and single layer graphene oxide using a Couette-Taylor flow reactor, a novel exfoliation method. The Couette-Taylor reactor consists of two concentric cylinders and the inner cylinder rotates at a controlled speed while the outer cylinder is kept stationary. We found that the formation of Taylor vortex flow with shearing stress in the reactor is effective for exfoliation of graphite oxide, which allows for the production of a more than 40μm in lateral size single or few-layer graphene oxide platelets at a high yield of 90% or above within 60 min of exfoliation reaction time. Moreover, we could control the lateral size of graphene oxide sheets through different rotation speed of the inner cylinder and reaction time.
Our method for facile and eco-friendly fabrication method of graphite oxide and their high efficiency exfoliation with controlled area may find utility in a range of applications including energy storage, conducting composite, electronic device and supporting frameworks of catalyst.

목차 (Table of Contents)

• SUMMARY ········································································ 1
• Chapter 1. Introduction ·························································· 3
• Chapter 2. Literature Review ··················································· 7
• 2.1 Overview of graphene ······························································ 7
• 2.2 Overview of graphene oxide ······················································· 10
• 2.3 Theory of Couette-Taylor flow ····················································· 18
• 2.4 Exfoliation of graphite oxide for graphene oxide ···································· 25
• Chapter 3. Facile synthesis of graphene oxide in a Couette-Taylor flow reactor ·············································································· 31
• 3.1. Experimental procedures ························································· 33
• 3.2. Results and discussion ···························································· 37
• 3.2.1. Synthesis of graphite oxide via Couette-Taylor flow ···························· 37
• 3.2.2. Synthesis of graphite oxide in a Couette-Taylor flow reactor for different reaction time ············································································· 41
• 3.2.3. Characterization of synthesized graphene oxide in a Couette-Taylor flow reactor ············································································ 46
• 3.2.4. Functionalization of graphene oxide in a Couette-Taylor flow reactor ············ 48
• Chapter 4. Green synthesis of graphene oxide using recycled sulfuric acid via Couette-Taylor flow ··················································· 50
• 4.1. Experimental procedures ························································· 52
• 4.2. Results and discussion ···························································· 57
• 4.2.1. Comparison of the viscosity and recovery rate of the Hummers’ method and the Couette-Taylor flow for GO synthesis ········································· 57
• 4.2.2. Filter process of reaction product from the Couette-Taylor flow reactor for recycling sulfuric acid ································································ 60
• 4.2.3. Characterization of graphene oxide using recycled sulfuric acid ·················· 62
• 4.2.4. Comparison the used volume of water for washing process of graphite oxide ····· 68
• Chapter 5. High efficiency exfoliation of large-area mono-layer graphene oxide with controlled size via Couette-Taylor flow ············ 70
• 5.1. Experimental procedures ························································· 72
• 5.2. Results & Discussion ····························································· 75
• 5.2.1. Characterization of graphite oxide via the oxidation reaction for 60 minutes in the Couette-Taylor flow reactor ·················································· 75
• 5.2.2. Exfoliation methods of graphite oxide ········································· 77
• 5.2.3. Production of GO via Couette-Taylor flow ····································· 79
• 5.2.4. Characterization of exfoliated graphene oxide ·································· 81
• Chapter 6. Conclusion ··························································· 91
• REFERENCE ···································································· 94
• 국문 초록 ······································································· 103