Microwave-assisted hydrothermal synthesis of copper oxide-based gas-sensitive nanostructures

Hydrothermal methods are widely used in chemical synthesis of target products with specific morphology and nanostructure. Those methods are very efficient for the preparation of well-controlled structures but the reaction time is usually long. The assistance of microwave makes the reaction system heat up faster, more uniformly and reactions are accelerated, it also can be utilized to change the morphology or structure of materials, which improves the physic-chemical properties of synthesized products and influences its gas-sensing performance. Copper oxide (CuO) is widely applied in semiconductor gas sensors because of its good reactivity and stability. This review article briefly introduces the principle, mechanism and recent development of CuO nanostructures obtained by microwave-assisted hydrothermal synthesis (MWHS) process. It also discussed the relation between endopathic factors of material and its gas-sensitive performance. The technical challenges and prospective solutions for high-performance CuO-based gas-sensitive materials with unique nanostructure are proposed. It is pointed out that the hierarchical CuO-based nanostructures and their composite materials prepared by MWHS process are efficacious methods to improve the gas-sensitive performance of the materials. On the basis of the morphology, the materials are divided into nanorods, nanoflowers, nanosheets, nanospheres and other nanostructures. The influence of microwave parameters on the properties of synthetic products is analyzed. The influence followed by metal element loading on the structure and properties of CuO-based materials by MWHS process is further discussed. Then this review summarizes the research progress of graphene-CuO and metal oxide-CuO composites prepared by MWHS process in recent years. Graphic abstract