The poor mechanical strength of graphene oxide (GO) membranes, caused by the weak interlamellar interactions, poses a critical challenge for any practical application. In addition, intrinsic but large-sized 2D channels of stacked GO membranes lead to low selectivity for small molecules. To address the mechanical strength and 2D channel size control, thiourea covalent-linked graphene oxide framework (TU-GOF) membranes on porous ceramics are developed through a facile hydrothermal self-assembly synthesis. With this strategy, thiourea-bridged GO laminates periodically through the dehydration condensation reactions via NH and/or SH with OCOH as well as the nucleophilic addition reactions of NH to COC, leading to narrowed and structurally well-defined 2D channels due to the small dimension of the covalent TU-link and the deoxygenated processes. The resultant TU-GOF/ceramic composite membranes feature excellent sieving capabilities for small species, leading to high hydrogen permselectivities and nearly complete rejections for methanol and small ions in gas, solvent, and saline water separations. Moreover, the covalent bonding formed at the GO/support and GO/GO interfaces endows the composite membrane with significantly enhanced stability.

The layered graphene membrane has high potential for efficient desalination owing to its frictionless surface and hydrophobic nature. However, it has not been demonstrated so far due to the challenges related to controlling membrane microstructure. Herein, we develop a facile and simple thiol−ene click method to prepare a perfluoro-alkyl grafted graphene (fGraphene) membrane on porous ceramic, which features an ultrahigh antiwetting surface, oriented mesoporous surface entrances, and a well-defined interlamellar spacing of ∼1.1 nm. With vacuum membrane distillation, the fGraphene membranes post ∼100% rejections to the small ions of seawater, at least 1 order of magnitude higher water fluxes than those of commercial membranes and graphene-oxidebased membranes, as well as robust stability in the desalination. Fast NaCl desalinations on the fGraphene membrane were also confirmed by the reverse/forward osmosis tests. The complete rejection of ions and high flux are attributed to the interfacial sieving effect over the 2D nanochannels as well as the vapor-phase transport in the mesoscale channels, which is fundamentally different from the solution−diffusion mechanism of dense polymeric membranes and the size-sieving mechanism of microporous membranes. This work not only demonstrates a special separation effect for complete desalination over the layered graphene-based membrane but also offers a reliable method to functionalize and structure graphene membranes for other potential applications.

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