Catalytic synthesis of graphite oxide and graphite nanostructures in transient glow-to-arc plasma discharge

Carbon and carbon-based materials like graphene and graphene oxide exhibit a constantly expanding field of applications in science, medicine, and industry. However, their implementation is still hindered by the absence of a reliable, flexible, and highly productive method of synthesis. Most of the existing methods rely on the use of chemical reagents potentially dangerous for the environment. In this paper, a physical method based on the use of a transient glow-to-arc discharge is developed, and the carbon nanostructures are obtained during a single-step production in a plasma reactor. Argon and oxygen are used to grow either carbon or carbon oxide nanostructures on the surfaces of expanded graphite samples. To enhance the growth of the carbon nanostructures, an anode made of copper is employed in the setup, to serve as a source of the copper catalyst. As a result, complex three-dimensional carbon nanostructures with a density of about 0.01 μm-2 were detected using scanning electron microscopy (SEM) on the entire surface of the sample after the oxygen plasma treatment. An enlarged view of nanostructures shows that they are a composition of 2D and 1D nanostructures connected by jumpers, as well as the presence of tree-like and petal nanostructures with dimensions of approximately 3 μm in length and 30 nm in diameter. The replacement of oxygen with argon led to a significant change in the appearance of nanostructures. Layered 2D graphene-like and tree-like carbon nanostructures capped with copper particles of diameters up to 10 μm were found. The obtained nanostructures suggest that expanded graphite is an excellent source for the production of two-dimensional nanostructures, like graphene and graphene oxide, which can be used as components for field-effect transistors, nanofluidic applications, supercapacitors, and electromagnetic absorbers.