Water desalination using nanoporous single-layer graphene

Surwade, Sumedh P.; Smirnov, Sergei; Vlassiouk, Ivan; Unocic, Raymond R.; Veith, Gabriel M.; Dai, Sheng; Mahurin, Shannon M.

doi:10.1038/nnano.2015.37

Cited by 1,514 publications

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“…As a comparison, the pore density of the nanoporous graphene membrane recently achieved experimentally by Surwade et al is estimated to be ~10 12 pores per cm 2 . 11 In addition, our calculations predict that the CTF--1 membrane is able to reject salt at a rate of 91%, which provides opportunities in brackish water desalination or multi--stage sea water desalination. This salt rejection rate, however, is not high enough to meet the requirements of widely used one--step sea water RO processes (i.e., ~99% is needed), indicating the membrane's pore is still marginally too large.…”

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confidence: 81%

“…10 Moreover, recent work of Surwade et al has further experimentally realized such single--layered nanoporous graphene membranes and demonstrated their potential in desalination at the lab scale. 11 However, the production of nanoporous graphene membranes with perfectly sized nanopores still remains a great challenge. Moreover, to allow unprecedentedly high water fluxes, it is of great importance to achieve a pore density as high as possible while preventing pores from overlapping, a goal best achieved with a well--ordered pore structure.…”

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Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination

2015

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We computationally demonstrate that two--dimensional covalent traizine frameworks (CTFs) provide opportunties in water desalination. By varying the chemical building blocks, the pore structure, chemistry, and membrane performance can be designed, leading to two orders of mangnutide higher water permeability than polyamide membranes while maintaining excellent ability to reject salts.Water scarcity is one of the most prominent challenges in modern society. 1,2 Due to the rapid growth of the world population and the accelerated industrialization of developing countries, fresh water has become increasingly scarce. Although 75% of the earth's surface is covered with water, more than 97% of it is seawater that cannot be used directly. Much of the remaining fresh water is locked in glaciers and snowfields, leaving less than 1% of the world's water available for human consumption. Despite the vast availability of seawater, the production of fresh water using processes that separate salt ions from saline water (i.e., desalination) remains negligible (less than 1%) when compared to global demand, primarily due to high costs and large energy consumption. 3 To facilitate clean water production via desalination, much recent attention has been given to improving the cost--effectiveness and energy--efficiency of reverse osmosis (RO) desalination processes, which account for roughly two thirds of installed capacity. In particular, new membranes with enhanced water permeability compared to currently available polyamide--based membranes may have an important role to play in lowering energy consumption. 4 Several nanostructured materials have been previously investigated as promising membrane candidates such as carbon nanotubes (CNTs) 5,6,7 and zeolites 8,9 . Despite CNTs' high water permeability, 5 membranes based on CNTs exhibit poor salt rejection, and it remains challenging to fabricate membranes with dense, well--aligned nanotubes. 6,7 Zeolite membranes, on the other hand, possess three--dimensional networks that can effectively reject salt ions 8 but show relatively low water permeability. 9 Recently, nanoporous one--atom--thick graphene, the thinnest possible membrane made from matter, has drawn considerable attention and been shown computationally to provide significantly enhanced permeability compared to polyamide while maintaining excellent ability to reject salt. 10 Moreover, recent work of Surwade et al. has further experimentally realized such single--layered nanoporous graphene membranes and demonstrated their potential in desalination at the lab scale. 11 However, the production of nanoporous graphene membranes with perfectly sized nanopores still remains a great challenge. Moreover, to allow unprecedentedly high water fluxes, it is of great importance to achieve a pore density as high as possible while preventing pores from overlapping, a goal best achieved with a well--ordered pore structure. Seeking membranes with naturally ordered pores of an ideal size presents an important alternative to nanoporous graphene m...

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Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination

2015

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“…8d). Considerable energy could also be generated by exploiting parallelization, with multiple small pores or even a continuous porous structure within a large area of single-layer MoS 2 membrane 26 , which could be scaled up for mass production using the ECR pore-fabrication technique 16 or plasma-based defect creation 27 .The use of individual nanopores as a micro/nano power source has long been expected 22 . We find here that an individual osmotic generator can also serve as a nanopower source for a self-powered nanosystem, owing to its high efficiency and power density.…”

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Single-layer MoS2 nanopores as nanopower generators

Feng

Gräf

Liu

et al. 2016

Nature

978

855

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Making use of the osmotic pressure difference between fresh water and seawater is an attractive, renewable and clean way to generate power and is known as 'blue energy' 1-3 . Another electrokinetic phenomenon, called the streaming potential, occurs when an electrolyte is driven through narrow pores either by a pressure gradient 4 or by an osmotic potential resulting from a salt concentration gradient 5 . For this task, membranes made of two-dimensional materials are expected to be the most efficient, because water transport through a membrane scales inversely with membrane thickness 5-7 . Here we demonstrate the use of single-layer molybdenum disulfide (MoS 2 ) nanopores as osmotic nanopower generators. We observe a large, osmotically induced current produced from a salt gradient with an estimated power density of up to 10 6 watts per square metre-a current that can be attributed mainly to the atomically thin membrane of MoS 2 . Low power requirements for nanoelectronic and optoelectric devices can be provided by a neighbouring nanogenerator that harvests energy from the local environment 8-11 -for example, a piezoelectric zinc oxide nanowire array 8 or single-layer MoS 2 (ref. 12). We use our MoS 2 nanopore generator to power a MoS 2 transistor, thus demonstrating a self-powered nanosystem.MoS 2 nanopores have already demonstrated better water-transport behaviour than graphene 13,14 owing to the enriched hydrophilic surface sites (provided by the molybdenum) that are produced following either irradiation with transmission electron microscopy (TEM) 15 or electrochemical oxidation 16 . The osmotic power is generated by separating two reservoirs containing potassium chloride (KCl) solutions of different concentrations with a freestanding MoS 2 membrane, into which a single nanopore has been introduced 13 . A chemical potential gradient arises at the interface of these two liquids at a nanopore in a 0.65-nm-thick, single-layer MoS 2 membrane, and drives ions spontaneously across the nanopore, forming an osmotic ion flux towards the equilibrium state (Fig. 1a). The presence of surface charges on the pore screens the passing ions according to their charge polarity, and thus results in a net measurable osmotic current, known as reverse electrodialysis 1 . This cation selectivity can be better understood by analysing the concentration of each ion type (potassium and chloride) as a function of the radial distance from the centre of the pore, as we show here through molecular-dynamics simulations (Fig. 1b).We fabricated MoS 2 nanopores either by TEM 13 (Fig. 1c) Distance from the centre of the pore (Å)C max /C min = 1,000C max /C min = 500C max /C min = 100 LETTER RESEARCHosmotic current can be expected, owing to the long time required for the system to reach equilibrium. We measured the osmotic current and voltage across the pore by using a pair of Ag/AgCl electrodes to characterize the current-voltage (I-V) response of the nanopore.To gain a better insight into the performance of the MoS 2 nanopore power generator, ...

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“…Reporting in this issue of Nature Nanotechnology, Ivan Vlassiouk, Shannon Mahurin and colleagues have now shown that a single layer of nanoporous graphene can be used to desalinate water 10 . The pores are created in the graphene layer by exposing the material to short bursts of oxygen plasma, a process that allows holes of precise dimensions to be controllably etched in the layer.…”

Section: Editorialmentioning

confidence: 99%

Graphene opens up to new applications

2015

Nature Nanotech

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Water desalination using nanoporous single-layer graphene

Cited by 1,514 publications

References 41 publications

Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination

Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination

Single-layer MoS2 nanopores as nanopower generators

Graphene opens up to new applications

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