To this end we have used geometrical criteria for identification of HBs. Specifically, we used for the donor-acceptor (i.e. O-O) distance (d don-acc ) ≤ 4 Å and for the acceptor-donor-H (i.e. ∕ O-O-H) angle (θ acc-don-H ) ≤ 30°. The selected criteria allow us to take into account strong to weak HBs. In order to facilitate the analysis, we categorized the HBs into three types displayed in the upper part of The maximum number of HBs of type O ep per epoxide group is two, whereas it is two and one per hydroxide for HO acc and HO don , respectively. The GO functions can form both intra-molecular HBs (i.e., HBs between two functional groups of the same GO layer)