Atomically thin membranes comprising nanopores in a 2D material promise to surpass the performance of polymeric membranes in several critical applications, including water purification, chemical and gas separations, and energy harvesting. However, fabrication of membranes with precise pore size distributions that provide exceptionally high selectivity and permeance in a scalable framework remains an outstanding challenge. Circumventing these constraints, here, a platform technology is developed that harnesses the ability of oppositely charged polyelectrolytes to self‐assemble preferentially across larger, relatively leaky atomically thin nanopores by exploiting the lower steric hindrance of such larger pores to molecular interactions across the pores. By selectively tightening the pore size distribution in this manner, self‐assembly of oppositely charged polyelectrolytes simultaneously introduced on opposite sides of nanoporous graphene membranes is demonstrated to discriminate between nanopores to seal non‐selective transport channels, while minimally compromising smaller, water‐selective pores, thereby remarkably attenuating solute leakage. This improved membrane selectivity enables desalination across centimeter‐scale nanoporous graphene with 99.7% and >90% rejection of MgSO4and NaCl, respectively, under forward osmosis. These findings provide a versatile strategy to augment the performance of nanoporous atomically thin membranes and present intriguing possibilities of controlling reactions across 2D materials via exclusive exploitation of pore size‐dependent intermolecular interactions.
Monodispersed angstrom-size pores embedded in a suitable matrix are promising for highly selective membrane-based separations. They can provide substantial energy savings in water treatment and small molecule bioseparations. Such pores present as membrane proteins (chiefly aquaporin-based) are commonplace in biological membranes but difficult to implement in synthetic industrial membranes and have modest selectivity without tunable selectivity. Here we present PoreDesigner, a design workflow to redesign the robust beta-barrel Outer Membrane Protein F as a scaffold to access three specific pore designs that exclude solutes larger than sucrose (>360 Da), glucose (>180 Da), and salt (>58 Da) respectively. PoreDesigner also enables us to design any specified pore size (spanning 3–10 Å), engineer its pore profile, and chemistry. These redesigned pores may be ideal for conducting sub-nm aqueous separations with permeabilities exceeding those of classical biological water channels, aquaporins, by more than an order of magnitude at over 10 billion water molecules per channel per second.
more » « less- PAR ID:
- 10153715
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Single‐layer graphene containing molecular‐sized in‐plane pores is regarded as a promising membrane material for high‐performance gas separations due to its atomic thickness and low gas transport resistance. However, typical etching‐based pore generation methods cannot decouple pore nucleation and pore growth, resulting in a trade‐off between high areal pore density and high selectivity. In contrast, intrinsic pores in graphene formed during chemical vapor deposition are not created by etching. Therefore, intrinsically porous graphene can exhibit high pore density while maintaining its gas selectivity. In this work, the density of intrinsic graphene pores is systematically controlled for the first time, while appropriate pore sizes for gas sieving are precisely maintained. As a result, single‐layer graphene membranes with the highest H2/CH4separation performances recorded to date (H2permeance > 4000 GPU and H2/CH4selectivity > 2000) are fabricated by manipulating growth temperature, precursor concentration, and non‐covalent decoration of the graphene surface. Moreover, it is identified that nanoscale molecular fouling of the graphene surface during gas separation where graphene pores are partially blocked by hydrocarbon contaminants under experimental conditions, controls both selectivity and temperature dependent permeance. Overall, the direct synthesis of porous single‐layer graphene exploits its tremendous potential as high‐performance gas‐sieving membranes.
-
more » « less
Summary Embolism spreading in angiosperm xylem occurs via mesoporous pit membranes between vessels. Here, we investigate how the size of pore constrictions in pit membranes is related to pit membrane thickness and embolism resistance.
Pit membranes were modelled as multiple layers to investigate how pit membrane thickness and the number of intervessel pits per vessel determine pore constriction sizes, the probability of encountering large pores, and embolism resistance. These estimations were complemented by measurements of pit membrane thickness, embolism resistance, and number of intervessel pits per vessel in stem xylem (
n = 31, 31 and 20 species, respectively).The modelled constriction sizes in pit membranes decreased with increasing membrane thickness, explaining the measured relationship between pit membrane thickness and embolism resistance. The number of pits per vessel affected constriction size and embolism resistance much less than pit membrane thickness. Moreover, a strong relationship between modelled and measured embolism resistance was observed.
Pore constrictions provide a mechanistic explanation for why pit membrane thickness determines embolism resistance, which suggests that hydraulic safety can be uncoupled from hydraulic efficiency. Although embolism spreading remains puzzling and encompasses more than pore constriction sizes, angiosperms are unlikely to have leaky pit membranes, which enables tensile transport of water.
-
Artificial water channels are a practical alternative to biological water channels for achieving exceptional water permeability and selectivity in a stable and scalable architecture. However, channel-based membrane fabrication faces critical barriers such as: (1) increasing pore density to achieve measurable gains in permeability while maintaining selectivity, and (2) scale-up to practical membrane sizes for applications. Recently, we proposed a technique to prepare channel-based membranes using peptide-appended pillar[5]arene (PAP[5]) artificial water channels, addressing the above challenges. These multi-layered PAP[5] membranes (ML-PAP[5]) showed significantly improved water permeability compared to commercial membranes with similar molecular weight cut-offs. However, due to the distinctive pore structure of water channels and the layer-by-layer architecture of the membrane, the separation behavior is unique and was still not fully understood. In this paper, two unique selectivity trends of ML-PAP[5] membranes are discussed from the perspectives of channel geometry, ion exclusion, and linear molecule transport.more » « less
-
Biomimetic and bioinspired membranes for water purification: A critical review and future directionsmore » « less
Various types of channel proteins, broadly named porins, present in the cell membrane of gram‐negative bacteria have specific functionalities depending on their selectivity toward different nutrients or toward water. The high selectivity of porins has led to their incorporation into synthetic systems, in a field called biomimetics. An example is the addition of water channel proteins, or aquaporins, to polymeric separations membranes in order to enhance their performance in terms of selectivity and permeability. The concept of incorporating aquaporins into synthetic membranes has been studied for the last 10 years; however, there are still limitations such as costs, alignment into the membrane assembly, and scalability of membrane fabrication. Therefore, in recent years, there has been an increase in the study of synthesizing molecules with similar structure–function relationships of porins. These artificial channels attempt to mimic the biological porins, while being synthesized using simpler chemistry, being solvent compatible, and requiring less space on the membrane surface which helps to incorporate more channels into the membrane assembly. In summary, the future of biomimetic and bioinspired membranes depends on the design strategies, level of nature imitation, and the performance of these systems on a commercial scale. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13215, 2019
