Microwave-assisted preparation of graphene: principles, progress and challenges

<p indent="0mm">Graphene is a planar sheet composed of densely arranged sp²-bonded carbon atoms in a honeycomb lattice structure. It exhibits remarkable properties, including a high specific surface area <sc>(~2650 m²/g),</sc> excellent mechanical properties, and superior thermal and electrical conductivity. These characteristics make it an ideal candidate for applications in diverse fields such as electromagnetic interference shielding, sensors, advanced electronic devices, energy storage, water purification, gas separation, and biomedical applications. It is no exaggeration to say that the successful preparation of high-yield and high-quality graphene in future developments and utilizations is directly related to the extent of its in-depth expansion and application in various related fields. Microwave-assisted preparation of graphene has emerged as a burgeoning research direction in the field of graphene preparation due to its environmental friendliness, high efficiency, and convenient characteristics, and notable progress has been achieved in this area. Specifically, various methods such as microwave-assisted liquid-phase exfoliation, microwave-assisted reduction of graphene oxide, and microwave-assisted chemical vapor deposition can be employed to prepare graphene with diverse properties. These methods are capable of meeting the requirements of different application scenarios, thereby providing robust support for technological innovation and development in related fields. This review aims to offer a comprehensive view of the research advancements in microwave-assisted graphene preparation. First, we introduce the principle of microwave heating and briefly describe the characteristics and advantages of microwave-assisted graphene preparation. Subsequently, we summarize the current research progress in various microwave-assisted graphene preparation methods, mainly including two types: top-down and bottom-up. The principles, process parameters, advantages and disadvantages of each method are elucidated, as well as their applications in related fields. In the top-down approach, we elaborate on the utilization of microwaves in liquid-phase exfoliation and graphene oxide reduction methods. A notable feature of these methods is the significant shortening of the reaction time. Moreover, the merits of microwaves in solid-state reaction systems are emphasized during the microwave-assisted reduction of graphene oxide. This is because microwave heating depends on the wave penetration and the absorption properties of materials. In contrast, the presence of liquid-phase solvents may result in the dissipation of microwave energy. Consequently, the reduced graphene oxide (rGO) prepared by this approach exhibits qualities such as high quality, high purity, low oxygen content, and a limited number of layers. This effectively preserves the inherent characteristics of graphene and shows promise for the continuous large-scale production of high-quality rGO. In the bottom-up approach, the focus is mainly on presenting the microwave plasma vapor deposition technique for graphene preparation. Subsequently, the production of graphene is expounded upon from the aspects of both graphene thin films and powders, and the influence of certain pertinent parameters, such as gas source type, proportion, flow rate, reaction temperature, microwave power, etc on the quality of graphene is elaborated in detail. Additionally, a brief introduction is provided on the method of preparing graphene by microwave pyrolysis conversion of other carbon-containing waste materials, such as biomass, waste plastics, and waste batteries. We also review the related application fields of graphene prepared by microwave methods. Finally, the challenges and future development trends of microwave-assisted preparation of graphene are discussed, aiming to provide a reference for the large-scale production and further application research of graphene.