Engineering nano-porous graphene oxide by hydroxyl radicals

Graphene oxide (GO) has recently been identified as an excellent candidate for membrane science, but the relatively small number of channels for species to transport across the laminated GO membranes is one of the major limitations for the membrane permeability. Thus, engineering porous structures on GO sheets, such as pores and notched edges, is a promising solution to increase channels across the laminate when GO sheets are stacked into membranes. However, a controllable approach for constructing porous GO sheets requires further development. Here, we demonstrated that nano-porous GO sheets with well-controlled nano-pores and 'lacelike' edges were generated after 'etching' GO sheets by hydroxyl radicals (OH), which were generated from water radiolysis by γ-irradiation. Furthermore, the average diameter of nano-pores can be easily tuned from 3.7 to 13.6 nm by varying the 'etching' time. Carbon atoms in GO sheets where oxygen-containing groups were bonded to could be oxidized and removed by OH radicals, leaving the defects in GO sheets. Then, the formation mechanism for the porous structures and the oxidation behavior of GO sheets are systematically investigated. These results should provide a new approach for engineering fluidic channels in GO membranes for future applications in nanofiltration and molecular separation.