(644g) Structure Design of Nanoporous Multilayer Graphene Membrane for Organic Solvent Nanofiltration

Graphene-based membranes are promising candidates for efficient organic solvent nanofiltration (OSN) processes because of their unique structural characteristics, such as mechanical/chemical stability and precise molecular sieving enabled by nanopore and interlayer spacing. Recently, to improve organic solvent permeance and selectivity, nanopores have been fabricated on graphene planes via chemical and physical methods. The nanopores serve as an additional channel for facilitating ultrafast solvent permeation while filtering organic molecules by size exclusion.

For single-layer graphene prepared by chemical vapor deposition, various top-down methods, such as focused ion beam, focused electron beam, ultraviolet-induced oxidative etching, ion bombardment followed by chemical etching, and oxygen plasma etching, have been used. Because single-layer or few-layer graphene is used as the selective layer, the membrane thickness can be significantly decreased to the atomic scale. However, as such processes are performed under high-vacuum conditions and post-treated in a chamber and graphene is required to be transferred on a porous support. Therefore, large-scale fabrication is still challenging with precise pore-size control.

As an alternative method, the nanopores can be generated in graphene oxide (GO) on a large scale by post-treatment of GO powder and GO film. Intrinsic defects and holes are present in the original GO, formed during the synthesis of GO, but the size and density of the pores are negligible and not controlled. Because post-treatments generate nanopores by the decomposition of oxygen-functional groups or defective sp2 carbon on the GO plane, dense sp3 carbons are formed near the pores, and oxygen-functional groups are also partially present. The defective structure is critical to tuning the interlayer spacing to enable the permeation of large organic solvents through the nanochannel. Moreover, because nanoporous graphene is soluble in water and organic solvents, it is beneficial to fabricate laminated membranes by solution processes such as vacuum filtration, spin coating, bar coating, spray coating, and slot-die coating.

In this talk, the post-thermal treatment method will be discussed to generate nanopores in graphene, and the membrane fabrication method will be handled as well. Particularly, nanopores can be generated on the basal plane of graphene by rapid thermal annealing of GO. The size of the nanopores is also tuned from micropores to nanopores by adjusting the activation temperatures. And the density of sp² domains can be controllable by additional microwave-assisted reduction. The optimized nanoporous graphene membranes show ultrafast alcohol and organic solvent permeance and a sharp molecular weight cut-off for molecules in nanoscale dimension. The membrane is feasible to separate mixed organic molecules dissolved in various organic solvents.

[REFERENCES]

Kim, D.W. et al., Carbon, 191, 563 (2022)

Kim, D.W. et al., J. Membr. Sci. 637, 119620 (2021)

Kim, D.W. et al., J. Membr. Sci. 618, 118638 (2021)

Kim, D.W. et al., J. Membr. Sci. 612, 118454 (2020)

Kim, D.W. et al., J. Mater. Chem. A 8, 8292 (2020)