Electrophoretically induced aqueous flow through single-walled carbon nanotube membranes

Wu, Ji; Gerstandt, Karen; Zhang, Hongbo; Liu, Jie; Hinds, Bruce J.

doi:10.1038/nnano.2011.240

Cited by 120 publications

(144 citation statements)

References 38 publications

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“…We found that ion mobility also scales inversely with membrane thickness (Extended Data Fig. 7a, b), which may conform to previous observations 25 . We then performed molecular-dynamics simulations of multilayer membranes of MoS 2 to investigate the power generated by those membranes.…”

Section: Letter Researchsupporting

confidence: 92%

Single-layer MoS2 nanopores as nanopower generators

Feng

Gräf

Liu

et al. 2016

Nature

983

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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Section: Letter Researchsupporting

confidence: 92%

Single-layer MoS2 nanopores as nanopower generators

Feng

Gräf

Liu

et al. 2016

Nature

983

855

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“…However, complex fabrication and the difficulty in obtaining CNTs with subnanometer diameters remain challenges. An alternative approach is to directly deposit CNTs onto a porous membrane and remove salt via capacitive electrostatic interactions [21][22][23] ; however, the salt adsorption capacity is limited 24,25 . Other methods, such as surface functionalization with carboxylic and alkoxysilane-based chemical groups, were also reported to enhance water flux and desalination efficiency of such CNT-based membranes, for example, as demonstrated in the case of membrane distillation 26 .…”

mentioning

confidence: 99%

Carbon nanotube membranes with ultrahigh specific adsorption capacity for water desalination and purification

et al. 2013

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Development of technologies for water desalination and purification is critical to meet the global challenges of insufficient water supply and inadequate sanitation, especially for pointof-use applications. Conventional desalination methods are energy and operationally intensive, whereas adsorption-based techniques are simple and easy to use for point-of-use water purification, yet their capacity to remove salts is limited. Here we report that plasma-modified ultralong carbon nanotubes exhibit ultrahigh specific adsorption capacity for salt (exceeding 400% by weight) that is two orders of magnitude higher than that found in the current stateof-the-art activated carbon-based water treatment systems. We exploit this adsorption capacity in ultralong carbon nanotube-based membranes that can remove salt, as well as organic and metal contaminants. These ultralong carbon nanotube-based membranes may lead to next-generation rechargeable, point-of-use potable water purification appliances with superior desalination, disinfection and filtration properties.

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“…As a result, the computed enhancement in potential barrier for trapping due to ion conductivity gradients at r m of 1 S/m continues to be significant in Figure 3(c) ($8-fold enhancement, with a conservative q c : 0.08 C/m 2 ), even though the EDL is not thick enough to ensure maximum coion exclusion and counter-ion surface conduction within the perm-selective region versus the respective level at r m of 0.2 S/m. However, while electro-osmotic effects on ion migration can be neglected at higher r m (!1 S/m), since electrophoretic ion mobilities are significantly greater than electro-osmotic mobilities in nanochannels [28][29][30] (see supplementary material, S3), this is not the case at r m of 0.2 S/m, where the two mobilities are comparable. 31 The inset (v) of Fig.…”

Section: Conductivity Of the Bulk Media (R M ) Determines The Electrimentioning

confidence: 99%

Nanoslit design for ion conductivity gradient enhanced dielectrophoresis for ultrafast biomarker enrichment in physiological media

et al. 2016

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Selective and rapid enrichment of biomolecules is of great interest for biomarker discovery, protein crystallization, and in biosensing for speeding assay kinetics and reducing signal interferences. The current state of the art is based on DC electrokinetics, wherein localized ion depletion at the microchannel to nanochannel interface is used to enhance electric fields, and the resulting biomarker electromigration is balanced against electro-osmosis in the microchannel to cause high degrees of biomarker enrichment. However, biomarker enrichment is not selective, and the levels fall off within physiological media of high conductivity, due to a reduction in ion concentration polarization and electro-osmosis effects. Herein, we present a methodology for coupling AC electrokinetics with ion concentration polarization effects in nanoslits under DC fields, for enabling ultrafast biomarker enrichment in physiological media. Using AC fields at the critical frequency necessary for negative dielectrophoresis of the biomarker of interest, along with a critical offset DC field to create proximal ion accumulation and depletion regions along the perm-selective region inside a nanoslit, we enhance the localized field and field gradient to enable biomarker enrichment over a wide spatial extent along the nanoslit length. While enrichment under DC electrokinetics relies solely on ion depletion to enhance fields, this AC electrokinetic mechanism utilizes ion depletion as well as ion accumulation regions to enhance the field and its gradient. Hence, biomarker enrichment continues to be substantial in spite of the steady drop in nanostructure perm-selectivity within physiological media. Published by AIP Publishing. [http://dx

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Electrophoretically induced aqueous flow through single-walled carbon nanotube membranes

Cited by 120 publications

References 38 publications

Single-layer MoS2 nanopores as nanopower generators

Single-layer MoS2 nanopores as nanopower generators

Carbon nanotube membranes with ultrahigh specific adsorption capacity for water desalination and purification

Nanoslit design for ion conductivity gradient enhanced dielectrophoresis for ultrafast biomarker enrichment in physiological media

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