Water Transport with Ultralow Friction through Partially Exfoliated g‐C₃N₄ Nanosheet Membranes with Self‐Supporting Spacers

Abstract

Two-dimensional (2D) graphitic carbon nitride (g-C N ) nanosheets show brilliant application potential in numerous fields. Herein, a membrane with artificial nanopores and self-supporting spacers was fabricated by assembly of 2D g-C N nanosheets in a stack with elaborate structures. In water purification the g-C N membrane shows a better separation performance than commercial membranes. The g-C N membrane has a water permeance of 29 L m h bar and a rejection rate of 87 % for 3 nm molecules with a membrane thickness of 160 nm. The artificial nanopores in the g-C N nanosheets and the spacers between the partially exfoliated g-C N nanosheets provide nanochannels for water transport while bigger molecules are retained. The self-supported nanochannels in the g-C N membrane are very stable and rigid enough to resist environmental challenges, such as changes to pH and pressure conditions. Permeation experiments and molecular dynamics simulations indicate that a novel nanofluidics phenomenon takes place, whereby water transport through the g-C N nanosheet membrane occurs with ultralow friction. The findings provide new understanding of fluidics in nanochannels and illuminate a fabrication method by which rigid nanochannels may be obtained for applications in complex or harsh environments.

Nanofluidic Ion Transport and Energy Conversion through Ultrathin Free‐Standing Polymeric Carbon Nitride Membranes

“…[8] Recently,G eim et al described the ions transportation properties through angstrom-scale graphene slits. [10] Meanwhile,m embrane materials and methods based on carbon nitride have been developed to realize water transport, [11] actuators, [12] and separation, [13] all questions closely related to the present work. [6] Tw od imensional carbon nitride (C 3 N 4 ) materials are another obvious choice with inherent lateral porosity,and it already attracting broad interest with its broad applications in sensing,b io-imaging,n ovel solar energy exploitation, as well as photocatalysis.…”

A Regularly Channeled Lamellar Membrane for Unparalleled Water and Organics Permeation

“…[2,8] As calculated by this equation (Supporting Information, Note S4), MXene-230 yields the permeance of 1.3 10 À4 Lm À2 h À1 bar À1 for water and of 4.3 10 À4 Lm À2 h À1 bar À1 for acetone,s even orders of magnitude smaller than the experimental values.D ynamics simulations have shown that in confined space,p olar molecules adopt concerted orientations by forming intermolecular bonds. [2,8] As calculated by this equation (Supporting Information, Note S4), MXene-230 yields the permeance of 1.3 10 À4 Lm À2 h À1 bar À1 for water and of 4.3 10 À4 Lm À2 h À1 bar À1 for acetone,s even orders of magnitude smaller than the experimental values.D ynamics simulations have shown that in confined space,p olar molecules adopt concerted orientations by forming intermolecular bonds.…”

“…The K' value for MXene membrane (10 À8.5 )isover five orders of magnitude higher than that of GO membrane (10 À13.8 ), highlighting an ultralow transport barrier through MXene channels.C onsidering as harp decline in water permeance even after small disturbance of water-bonded flow, [4] these regular and straight channels have proven to be the most efficient transfer pathways to assure low-barrier molecular transfer. [5] As summarized in Figure 3dand the Supporting Information, Table S1, the MXene membrane exhibits an exceptional water separation performance,w hich outperforms almost all of the lamellar membranes including GO, WS 2 ,and MoS 2 , [2,15] highlighting the superiority of regular and straight transport channels. This observation can also be confirmed by the boosted K' value (10 À12.6 )o fG Om embrane when improving channel regularity (Supporting Information, Figure S23).…”

Endowing g‐C3N4 Membranes with Superior Permeability and Stability by Using Acid Spacers

“…[9] Searching for porous nanosheets to fabricate 2D laminates may be an alternative way to accomplish higher permeances,b ecause pores can offer additional routes for mass transport. [12] However, the resulting g-C 3 N 4 lamellar membrane only shows amoderate water flux of 29 Lh À1 m À2 bar À1 , which is even lower than those of 2D membranes stacked by dense nanosheets.W ec onsidered the narrow interlayer spacing with as ize of 0.32 nm in g-C 3 N 4 membranes is adverse for rapid water penetration. [11] In view of g-C 3 N 4 layered structures and porosity,W ang et al successfully assembled them into 2D membranes,a nd they discovered the water transport through the g-C 3 N 4 membrane occurred with ultralow friction, similar to water passing through graphene interlayers.…”