Structure and dynamics of water confined in graphene oxide

Graphene oxide (GO) is among the most promising platforms for studying confined water and for engineering applications. The lamellar stacking of GO flakes, tunable sub-nanometer interlayer spacings, confining wall chemistry, and hydrophilicity favour a remarkable modulation in the arrangement and motion of water molecules. This promise comes with a challenge: hierarchical microstructure and structural and morphological disorder are ubiquitous in GO. The interpretation of several experimental outcomes is therefore quite challenging, and this also renders the simulations made on idealised systems rather inadequate. Here, we present a detailed overview of the recent developments in the structure and dynamics of confined water in GO. Sorption properties providing phenomenological insight into water's interactions and dielectric properties related to water's arrangement and reorientation are included within the scope. Comparisons with the parent graphene system are made throughout to place the results in the context of the defining features of GO. Particular emphasis is given to the super-permeation of water in GO, whose origin has been the subject of extensive debate and recent developments. A critical account of several experimental efforts on water in the flow and sorption-diffusion regimes is presented along with the findings from simulation studies. Finally, environmental applications that leverage the sorption capacity and rapid water transport in GO are discussed. The ion rejection performance, along with the challenges for utilising GO in desalination, is presented. Furthermore, the latest developments in atmospheric water harvesting and dehumidification applications of GO are discussed.