Post-plasma oxidation in water of graphene paper surface

Abstract

Plasma activation is increasingly used to tailor the electronic properties of carbon materials by surface functionalization, especially with various oxygen groups. However, the actual application of these materials may be some time after the modification was performed, and what is more, in a different environment, e.g. in an aqueous solution. The presented research addresses the problem of instability of plasma-induced changes of graphene paper material where the desired surface property – work function – was verified just after plasma treatment and after bringing the plasma-treated surface to a stable state. In this study, we optimised plasma treatment for the maximum work function changes, and then we determined the speciation of the resulting oxygen groups before and after immersion of the plasma-treated samples in water. We found that the plasma-modified graphene paper's functionalization degree and electronic properties highly depend on the post-plasmatic reactions in water, which increase the concentration of surface oxygen groups. The observed reactivity is rationalized in terms of plasma-emitted irradiation in the ultraviolet range resulting in an enhanced delocalized radical species generation. These radicals react upon contact with water and increase the number of oxygen functional groups.