Interfacial Ions Sieving for Ultrafast and Complete Desalination through 2D Nanochannel Defined Graphene Composite Membranes

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-oxide-based 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.