Changing the Microstructural and Chemical Properties of Graphene Oxide Through a Chemical Route

The aim of this work is to investigate the possibility of engineering desired molecular sp² structures in graphene oxide, via controlled oxidation of graphite powder, in order to achieve tunable chemical and microstructural properties useful for optoelectronics or sensing applications. Specifically, GO powder is obtained by a modified Hummers method, by using different concentrations of potassium permanganate (KMnO₄) in order to change the number of oxygen functionalities in the graphitic structure. Then, a successive alkaline treatment is performed by increasing the KOH concentration. The alkaline treatment induces a noticeable variation of the GO microstructural and chemical properties, which is accompanied by a strong enhancement of photoluminecence. PL and PLE measurements reveal that the configuration of electronic energy states changes as a function of the KMnO₄ and KOH concentration, by introducing further electronic n levels available for n→π* transitions. In particular, the number of sp² small domains embedded among oxygen-sp³ domains, increases under the KOH treatment, due to the addition of OH groups. Most of these sp² domains are lifted-off from GO and thrown away in the surnatant giving it high blue photoluminescence excited at λ_exc ∼ 319 nm. The employ of combined spectroscopy techniques allows a deep investigation of the microstructural and chemical changes induced by chemical treatments, opening the way to the fine tuning of GO functional properties.