1 Ultrafast ion sieving in two dimensional

2025-04-30 0 0 982.55KB 12 页 10玖币

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Ultrafast ion sieving in two dimensional graphene oxide membranes

Junfan Liu1,3,†, Zonglin Gu1,†,*, Mengru Duan1, Pei Li2, Lu Li3, Jianjun Jiang1, Rujie

Yang3, Junlang Chen3, Zhikun Wang3, Liang Zhao1, Yusong Tu1,*, Liang Chen2,*

1College of Physical Science and Technology & Microelectronics Industry Research

Institute, Yangzhou University, Jiangsu, 225009, China

2School of Physical Science and Technology, Ningbo University, Ningbo 315211,

China

3 Department of Optical Engineering, Zhejiang Prov Key Lab Carbon Cycling Forest

Ecosy, College of Environmental and Resource Sciences, Zhejiang A&F University,

Hangzhou 311300, China.

Ultrahigh water permeance, together with a high rejection rate through

nanofiltration and separation membranes1,2, is crucial but still challenging for

multivalent ion sieving in water treatment processes of desalination, separation,

and purification3,4. To date, no theory or equation has ever been quantitatively

clarified the mechanism of water permeance in two-dimensional (2D) membranes,

despite intensive and prolonged searches. Here, we established a new general

equation of permeation through 2D membranes, and experimentally achieved

unprecedented advances in water permeance one to two orders of magnitude

higher than state-of-the-art membranes while simultaneously maintaining high

ion rejection rates for multivalent metal ions, by staking nano-sized reduced

graphene oxide (nano-rGO) flakes into nanofiltration membranes. The equation

is simply based on a fundamental steady-state flow assumption and provides an

essential description of water permeance through 2D membranes, demonstrating

that the ultrahigh water permeance is attributed to the high effective channel area

and shortened channel length elicited from the nano-sized-flake stacking effects in

nano-rGO membranes, consistent with our theoretical simulations and previous

experiments. These results pave the way for fabrication of advanced 2D

nanofiltration membranes to realize a breakthrough in water permeance with

exceptional ion sieving performance.

Removal of toxic heavy metal ions is important for water separation, recovery, and

purification from seawater, inland brackish water, and various waste water3,5 in order

for the water supply to cope with the growing freshwater crisis6,7. Nanofiltration

membranes offer significant advantages of high energy efficiency and low cost

effectiveness and have attracted increasingly extensive interest for ion removal

treatment processes4,8, particularly with the use of two-dimensional (2D) materials9,10,

such as graphene oxide (GO)-based membranes with precise ionic sieving1,11,12.

Currently, the development of membrane technologies with substantially improved

water permeance for effective removal of ions is considered one of the most important

objectives in nanofiltration separation applications6,9.

2D nanofiltration membranes have great potential for ultrafast water permeance with

effective ion rejection due to their atom-thick features1,4,13. Recently, numerous efforts

have been made to employ diverse 2D materials, such as the GO14,15, MoS2[16,17], and

MXene18,19 families, to fabricate 2D membranes and explore their relevant

characteristics to achieve ultrafast water permeance, including tuning porous

microstructures for water transport20,21, adjusting interfacial hydrophobicity for low

water friction22,23, and optimizing membrane parameters (e.g., thickness and material

lateral sizes)15,24. Despite these significant advances, water permeance through state-

of-the-art nanofiltration membranes tends to be on the order of a dozen or dozens L m-

2 h-1 bar-1 (LMH bar-1)[14,25] for multivalent metal ion removal, and the highest

permeance reported in the literature was just ~164.7 LMH bar-1, even with an ion

rejection rate of 85.2%22. Although very promising, further improvement in permeance

appears to be hindered, partially due to the lack of essential understanding of water

permeation through 2D membranes. Currently, no theory or equation is available to

quantitatively clarify the relationship between water permeance and relevant membrane

parameters. Hagen–Poiseuille equation is usually used to evaluate flow permeation

through nanofiltration membranes (including 2D membranes), but its permeance

predictions present a huge departure from experiments26-29 (i.e., four to six orders of

magnitude smaller than experimental values). Therefore, not only does it remain a great

challenge to substantially upgrade water permeance in nanofiltration membranes, but a

comprehensive theory or framework for guiding the development of filtration and

separation membranes is urgently expected, particularly in the arising field of 2D

membranes.

Here, we combined experimental and theoretical approaches to demonstrate ultrafast

multivalent ion sieving in nano-rGO membranes stacked with nano-sized rGO flakes.

The water permeance reached up to 1112 LMH bar-1 with a correspondingly high

rejection rate of 91.4%, which is one to two orders of magnitude higher than the

permeance of state-of-the-art membranes. Herein, a new general equation was

established to provide an essential description and accurate evaluation of water

permeance in 2D membranes that is consistent with our theoretical simulations and

filtration experiments and validated by a series of previous experiments.

We prepared a nano-rGO suspension from a GO suspension with micron-sized GO

flakes via a hydrothermal method. The nano-rGO membranes were prepared by

stacking the obtained nano-rGO suspension on a mixed cellulose ester (MCE) substrate

with a pore size of 0.22 μm (see Fig. 1a and Supplementary Information section PS1).

The nano-rGO flakes had an average lateral size of ~100 nm with a size distribution

range of ~50 nm to 250 nm and thickness of ~1.0 nm (AFM measurements, Fig. 1b).

The lateral size of the nano-rGO flakes was reduced by a factor of approximately 10

compared to the original GO flakes. The oxygen content of the nano-rGO membrane

decreased significantly from 35.5% to 26.5% (indicated by XPS measurements in Fig.

1d and Table S1), with the corresponding water contact angle increasing from 39.7º to

50.5º compared to the GO membrane (Fig. S1b), indicating that the nano-rGO

hydrophobicity was significantly enhanced. In previous work, it was difficult to form a

stable membrane directly with nano-sized GO flakes because the hydrophilic GO flakes

with lateral sizes less than the substrate pore sizes made them highly susceptible to

swelling and disintegration10,24. The enhanced hydrophobicity can lead to the formation

and stability of nano-rGO membranes stacked on the MCE substrate. Scanning electron

microscopy (SEM) images (Fig. 1c) showed that the stacked nano-rGO membrane is

continuous and free of macro pores or defects, which is critical for a highly efficient

separation process30.

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1UltrafastionsievingintwodimensionalgrapheneoxidemembranesJunfanLiu1,3,†,ZonglinGu1,†,*,MengruDuan1,PeiLi2,LuLi3,JianjunJiang1,RujieYang3,JunlangChen3,ZhikunWang3,LiangZhao1,YusongTu1,*,LiangChen2,*1CollegeofPhysicalScienceandTechnology&MicroelectronicsIndustryResearchInstitute,YangzhouUniversity,Ji...

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