2D Material Nanofiltration Membranes: From Fundamental Understandings to Rational Design

Abstract

Since the discovery of 2D materials, 2D material nanofiltration (NF) membranes have attracted great attention and are being developed with a tremendously fast pace, due to their energy efficiency and cost effectiveness for water purification. The most attractive aspect for 2D material NF membranes is that, anomalous water and ion permeation phenomena have been constantly observed because of the presence of the severely confined nanocapillaries (<2 nm) in the membrane, leading to its great potential in achieving superior overall performance, e.g., high water flux, high rejection rates of ions, and high resistance to swelling. Hence, fundamental understandings of such water and ion transport behaviors are of great significance for the continuous development of 2D material NF membranes. In this work, the microscopic understandings developed up to date on 2D material NF membranes regarding the abnormal transport phenomena are reviewed, including ultrafast water and ion permeation rates with the magnitude several orders higher than that predicted by conventional diffusion behavior, ion dehydration, ionic Coulomb blockade, ion-ion correlations, etc. The state-of-the-art structural designs for 2D material NF membranes are also reviewed. Discussion and future perspectives are provided highlighting the rational design of 2D material membrane structures in the future.

Simultaneous Electrochemical Exfoliation and Covalent Functionalization of MoS2 Membrane for Ion Sieving

“…Freshwater scarcity has received more and more attention worldwide due to limited freshwater resources and increased environmental pollution. [ 1,2 ] Seawater desalination and water reuse are effective strategies to alleviate this problem. [ 3 ] Both approaches need to separate pollutant molecules and salt ions from water.…”

Covalently Functionalized Graphene for Black Liquor Concentration Membranes

“…8,11 Membrane-based separation is a promising alternative to thermal processing and offers the advantages of high energy efficiency, simplicity in the equipment, and the ability to be implemented as compact modules. [1][2][3][4][5][6][7]12 We have been interested in graphene oxide (GO)-based membranes, which have recently received significant attention as a result of their characteristics that include: high water permeability, two-dimensional structures, chemical resistance, mechanical strength, and tunable surface chemistry. 6−8,11, In GO-based separation membranes, the molecular transport pathways can be defined by different physical features: (i) defect pores in the basal plane, (ii) interedge gaps between the sheets, and (iii) interlayer space between the stacked planar sheets.…”

“…7,14,20,37−39 New methods for fine-tuning of the interlayer spacing are crucial to the capture, or exclusion, of target molecules and determining the separation performance of the GO membrane. 7,14,20,23,39 Our group has previously synthesized covalently functionalized graphenes from GO by a Claisen rearrangement. 40,41 Of particular relevance to the work we report herein, allylic alcohols found on the surface of GO are subjected to a Johnson−Claisen [3,3] sigmatropic rearrangement to produce ethyl esters attached to the basal plane via robust C−C bonds that can endure thermal and reductive conditions that degrade other GO derived materials.…”

“…The development of nonthermal separation technologies is imperative to reduce global energy requirements and to address environmental concerns in water purification in the industrial manufacturing, petroleum, chemicals, and paper sectors. − There is a particular need in paper manufacturing with the kraft pulping process, which generates weak black liquor (WBL) as a byproduct. WBL is often concentrated from total solids of ∼18% to ∼75%, which is important to make WBL suitable for combustion. − Since the combustion of the concentrated BL in a recovery boiler generates energy as steam and electricity, BL is regarded as one of the most critical renewable biofuels derived from wood. − However, a series of energy-intensive evaporation processes are used in the WBL concentration. − Besides, WBL is a corrosive high alkaline pH (∼12) complex aqueous fluid/dispersion that typically includes lignin, other organic materials separated from the wood, inorganic salts of Na 2 CO 3 and Na 2 SO 4 , and pulping chemicals of NaOH and Na 2 S and is processed at elevated temperatures (up to 95 °C). − Therefore, nonthermal methods that use separation materials that can endure the harsh separation conditions, have the prospects to significantly reduce energy consumption and bring economic and environmental benefits even with the partial concentration of WBL to a level of ∼30% solids. , Membrane-based separation is a promising alternative to thermal processing and offers the advantages of high energy efficiency, simplicity in the equipment, and the ability to be implemented as compact modules. − , We have been interested in graphene oxide (GO)-based membranes, which have recently received significant attention as a result of their characteristics that include: high water permeability, two-dimensional structures, chemical resistance, mechanical strength, and tunable surface chemistry. − ,,− …”

“…In GO-based separation membranes, the molecular transport pathways can be defined by different physical features: (i) defect pores in the basal plane, (ii) interedge gaps between the sheets, and (iii) interlayer space between the stacked planar sheets. ,, Although it is difficult to manipulate the defect and interedge pores precisely, ,, the interlayer spacing can be controlled by application of physical forces, , intercalation of carbon nanotubes and nanoparticles, − ionic interactions, and chemical modifications. − A narrowed interlayer spacing prevents the flux of molecules and results in low water permeation, and hence an enlargement of the interlayer spacing is vital to create free volume and enhance transport. ,,,− New methods for fine-tuning of the interlayer spacing are crucial to the capture, or exclusion, of target molecules and determining the separation performance of the GO membrane. ,,,, …”