[[Frontiers in HaiChuan Chemical Technology]] Researchers make a key breakthrough in the mass production of graphene

Thread Content

Graphene is a two-dimensional material composed of sp²-hybridized carbon atoms, and it has attracted considerable attention due to its excellent physical and chemical properties. Thanks to its excellent thermal conductivity, graphene is considered an ideal material for heat management ； Its large specific surface area and excellent chemical stability also enable it to shine in energy storage systems. In particular, graphene’s low density, excellent corrosion resistance, and high electrical conductivity make it an extremely attractive candidate for next-generation electromagnetic interference (EMI) shielding materials. EMI shielding mechanisms typically include processes such as absorption, reflection, transmission, and multiple reflections, and the shielding efficiency (SE) mainly depends on the intrinsic properties of the material. In fields such as defense and military applications, particular emphasis is placed on EMI shielding performance that is primarily based on absorption in the 8.2–12.4 GHz frequency range. The preparation of high-quality graphene is crucial for achieving excellent EMI SE. In recent years, the preparation of graphene using microwave-assisted methods has received widespread attention. Compared with traditional thermal or chemical reduction methods, microwave reduction is not only fast and efficient but also more environmentally friendly. This method can reduce graphene oxide (GO) to structurally ordered and intact m-rGO (microwave-reduced graphene) within 1–2 seconds, without the need for a reducing agent, resulting in a significant increase in its electrical conductivity. Its reduction mechanism stems from the rapid heating caused by the interaction between microwaves and the material, the removal of oxygen-containing functional groups in GO at high temperatures, and the repair of structural defects by free carbon radicals during the reaction process. However, the uneven distribution of the microwave field in the reaction chamber makes it difficult to control the reduction process of GO, resulting in incomplete reduction or damage to the structural integrity of graphene, which fundamentally limits the application of the microwave method in the large-scale production of graphene. To address the issue of uneven heating caused by microwave field inhomogeneity, researchers have made numerous attempts. The most direct method is to rotate the sample in order to achieve uniform absorption of microwave energy; this approach is commonly used in food heating. Furthermore, methods such as using multiple microwave sources, frequency-adjustable microwave systems, and optimizing the cavity structure design have also been proposed to improve the uniformity of the field distribution. However, these strategies primarily focus on the microwave field itself, ignoring the fundamental coupling relationship between the material and microwave energy, and thus find it difficult to address the issue of uneven heating at its root. A team led by Academician Zhang Jin from Peking University and the Beijing Graphene Institute has proposed a new strategy to improve the consistency of the quality of m-rGO by adjusting the spatial distribution of GO within the waveguide cavity, in combination with the structural design of the containers for irregular-shaped samples; further improvements in its quality are achieved through systematic optimization of process parameters during the amplification process. Compared with graphene prepared by existing microwave reduction methods, the m-rGO obtained in this study exhibits excellent properties, with a conductivity as high as 13486 S·m⁻¹ and a Raman D-band intensity as low as ID/IG = 0.12; the yield per batch can reach 70 grams. Meanwhile, a flexible m-rGO/polyurethane (PU) composite film (A4 size, with a thickness of only 90 μm) was fabricated, which exhibits an electromagnetic shielding efficiency of up to 40 dB in the 8.2–12.4 GHz frequency range. The structural design concept proposed in this paper offers an innovative and practical approach for the large-scale industrial microwave preparation of high-quality m-rGO.