Key Takeaways & Executive Findings
- •• • Complete oxidation of large graphite flakes (up to 1 mm) achieved without fragmentation, as directly evidenced by in-situ monitoring, enabling production of LGO with average lateral sizes up to 116.2 μm. • • Minimizing H2SO4 volume to create a semi-solid state elevates oxidizer concentration, reducing reagent consumption while achieving full oxidation of 200-, 100-, and 50-mesh graphite. • • Optimized reaction temperature balances Mn(VII) self-decomposition and graphite oxidation, ensuring complete oxidation with 100% conversion and yield exceeding 165%. • • Scalable and cost-effective synthesis route for LGO, with average sizes of 27.3, 58.7, and 116.2 μm from 200-, 100-, and 50-mesh graphite, respectively, suitable for industrial production.
Abstract
Large graphene oxide (LGO) sheets offer significant advantages over smaller ones in various applications, yet their production via Hummers-type oxidation of large natural graphite flakes remains challenging due to difficulties in achieving full oxidation and avoiding fragmentation. This study provides the first direct evidence that large graphite flakes (up to 1 mm) can be completely oxidized without fragmentation under static conditions, as revealed by in-situ monitoring. The oxidation process is governed by diffusion of the oxidizer between layers, described by Fick's law, where a high oxidizer concentration gradient increases the diffusion rate. By minimizing the amount of concentrated H2SO4 solvent, we achieved a semi-solid state that elevates oxidizer concentration, facilitating Mn(VII) diffusion and enabling complete oxidation of gram-scale large flakes with significantly reduced reagent consumption. Reaction temperature was optimized to balance graphite oxidation and Mn(VII) self-decomposition. Using this approach, 200-, 100-, and 50-mesh natural graphite were fully oxidized with reduced H2SO4 and KMnO4 usage. After exfoliation, LGO with average lateral sizes of 27.3, 58.7, and 116.2 μm were obtained, respectively, with 100% conversion and yield over 165%. This work not only provides a scalable, cost-effective strategy for LGO production but also advances the fundamental understanding of Hummers-type oxidation.
1. Introduction
The production of large graphene oxide (LGO) flakes has been a persistent bottleneck in the scalable manufacturing of high-performance graphene-based materials. Conventional Hummers-type oxidation of large natural graphite flakes typically results in incomplete oxidation, leaving unoxidized cores that compromise the quality of the final graphene oxide. This incomplete oxidation arises from the long diffusion path for oxidizer molecules from the flake edges to the interior, a process governed by Fick's law. Additionally, the mechanical fragility of large flakes during oxidation often leads to fragmentation, further reducing the lateral dimensions of the resulting GO. These challenges have historically limited the production of LGO to small-scale or low-yield processes, hindering its application in industries requiring large-area films, membranes, and composites.
This study addresses these limitations by demonstrating that large graphite flakes can be fully oxidized without fragmentation under static conditions, provided sufficient time and an optimized oxidizer concentration. By reducing the volume of concentrated H2SO4 to create a semi-solid reaction medium, the concentration of the active oxidizer (Mn(VII)) is significantly increased, accelerating diffusion and enabling complete oxidation of gram-scale flakes. The reaction temperature is carefully controlled to balance the competing reactions of graphite oxidation and Mn(VII) self-decomposition. This approach not only achieves full oxidation of 200-, 100-, and 50-mesh graphite with reduced reagent consumption but also yields LGO with average lateral sizes ranging from 27.3 to 116.2 μm, offering a scalable and cost-effective route for industrial LGO production.
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ZHANG Yuanyuan, MAI Jianbin, CHEN Wei, ZHANG Wenlong, LIU Jing, LIAO Huaping, AN Junwei, WANG Jionghui, HUANG Dongmei, LV Wei, DU Hongda, KANG Feiyu (2026). Low-cost synthesis of large graphene oxide flakes by the total oxidation of large natural graphite flakes. New Carbon Materials. https://doi.org/10.1016/S1872-5805(25)61036-5
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Frequently Asked Questions
What is the maximum lateral size of graphene oxide flakes that can be produced using this method, and what is the yield?
The method produces LGO with average lateral sizes up to 116.2 μm from 50-mesh graphite, with 100% conversion and yield over 165%.
How does reducing the amount of H2SO4 affect the oxidation process and reagent consumption?
Reducing H2SO4 volume elevates the oxidizer concentration, facilitating Mn(VII) diffusion and enabling complete oxidation. This reduces both H2SO4 and KMnO4 consumption, lowering costs.
What is the role of temperature control in achieving complete oxidation without fragmentation?
Temperature is optimized to balance graphite oxidation and Mn(VII) self-decomposition, ensuring that the oxidizer remains active for complete oxidation while minimizing side reactions that could cause fragmentation.
Can this method be scaled up for industrial production of LGO?
Yes, the method is scalable as it uses gram-scale graphite flakes and a semi-solid state that reduces reagent usage, making it cost-effective for industrial production.
What are the key differences between this method and traditional Hummers methods in terms of oxidation completeness?
Traditional methods often result in incomplete oxidation of large flakes due to diffusion limitations. This method ensures complete oxidation by increasing oxidizer concentration and optimizing temperature, as confirmed by in-situ monitoring.
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