Fig 3A shows that the GO powder used in this study is composed of unfolded GO nanosheets of approximately 100–200 nm in length forming aggregates stacked together mainly on its planar surface by van der Waals forces and π-π interactions. However, GO crosslinked with any divalent cation shows a very different structure of folded GO nanosheets (Fig 3B–3D) linked via divalent atoms. These images show very irregular morphology where the bridging of the GO sheets can be appreciated in the cGO samples in comparison with GO.