Hydrogen cold plasma for the effective reduction of graphene oxide.

Graphical abstract Highlights • H 2 plasma removes oxygen groups but not the sulfonyl and sulfonic groups. • Water treatment + H 2 plasma treatment removes 60% of oxygen and 100% of sulfur. • This methodology removes as much oxygen as NaBH 4 but is simpler, faster and cleaner. • The oxygen remaining after H 2 plasma reduction forms labile surface groups. • Three GOs were tested rendering similar results. Abstract We report the reduction of GO by hydrogen cold plasma as an effective alternative to the usual chemical (with harsh reducing agents) or physical (through high-temperature treatments) methods. The hydrogen plasma is generated through microwave radiation and the reduction is performed barely above room temperature, avoiding structural degradation of the graphene oxide. Three commercial GOs, with several oxygen and sulfur contents, have been used in this study. As a consequence of the exposure to the hydrogen plasma, the oxygen content is decreased in large extent while sulfur is scarcely removed. Thus a two-stage methodology consisting of a simple water treatment under reflux conditions of GO (to remove sulfur) and further treatment with H 2 plasma is proposed. The combination of both steps allows the total elimination of sulfur while achieving very high degrees of reduction, lowering the initial oxygen content by more than 60%. These degrees of reduction are comparable to those obtained when the reduction is carried out by using the standard procedure with NaBH 4 on the same materials. The reduction with hydrogen plasma clearly shows advantages over the conventional reduction procedures due to its simplicity: no chemicals or high temperatures are needed, and the procedure is very fast. [ABSTRACT FROM AUTHOR]