Ultrafast Water Transport Research Articles

Graphene Oxide Membranes with Conical Nanochannels for Ultrafast Water Transport.

Membrane-based separations have been increasingly utilized to address global energy crisis and water scarcity. However, the separation efficiency often suffers from the trade-off between membrane permeability and selectivity. Although great efforts have been devoted, a membrane with both high permeability and high selectivity remains a distant prospect. Inspired by the hourglass structure and ultrafast water transport in aquaporins, we propose a novel approach to fabricating membranes with conical nanochannels to reduce the mass transfer resistance and to introduce Laplace pressure as the internal driving force, which successfully breaks the permeability/selectivity trade-off. First, sulfonated polyaniline (SPANI) nanorods were in situ-synthesized and vertically aligned on sulfonated graphene oxide (SGO) nanosheets, forming SGO-SPANI X composites. Then, the graphene oxide (GO) membranes were fabricated by assembling SGO-SPANI X composites through pressure-assisted filtration, in which the SPANI nanorods would bend and flatten on the SGO nanosheets under low shear force, forming stripe arrays on SGO nanosheets. The tilted stripe arrays between the adjacent SGO nanosheets form the conical nanochannels inside GO membranes. The conical nanochannels significantly decreased the steric hindrance and enabled the generation of Laplace pressure as the internal driving force within membranes. Consequently, the resulting membranes exhibit an ultrahigh water permeability of 1222.77 L·m-2·h-1·bar-1 and high efficiency in dye removal from water with a rejection of 90.44% and permeability of 528 L·m-2·h-1·bar-1.

Ultrafast water harvesting and transport in hierarchical microchannels.

Various natural materials have hierarchical microscale and nanoscale structures that allow for directional water transport. Here we report an ultrafast water transport process in the surface of a Sarracenia trichome, whose transport velocity is about three orders of magnitude faster than those measured in cactus spine and spider silk. The high velocity of water transport is attributed to the unique hierarchical microchannel organization of the trichome. Two types of ribs with different height regularly distribute around the trichome cone, where two neighbouring high ribs form a large channel that contains 1-5 low ribs that define smaller base channels. This results in two successive but distinct modes of water transport. Initially, a rapid thin film of water is formed inside the base channels (Mode I), which is followed by ultrafast water sliding on top of that thin film (Mode II). This two-step ultrafast water transport mechanism is modelled and experimentally tested in bio-inspired microchannels, which demonstrates the potential of this hierarchal design for microfluidic applications.

Graphene oxide-in-polymer nanofiltration membranes with enhanced permeability by interfacial polymerization

Membranes with high permeability and selectivity are desired for energy-efficient liquid separation. In the present work, a highly wrinkled surface and ultrafast water transport channels centered in a graphene oxide (GO)-in-polyamide membrane were prepared by in-situ embedding GO nanosheets into the separation layer of a nanofiltration (NF) membrane via an interfacial polymerization. The rough and hydrophilic surface enabled the attraction of large amounts of water molecules to the membrane, and the sub-20 nm membrane thickness and two-dimensional capillary network formed by the stacked GO nanosheets accelerated the transport of water molecules through the membrane. This wrinkled and sandwich structured ultrathin NF composite membrane gave a water flux up to 242 LMH/MPa (nearly four-fold higher than those of reported NF membranes) and an unchanged high salt rejection, simultaneously.

Ultrafast Water Permeation in Graphene Nanostructures Anomalously Enhances Two‐Phase Heat Transfer

AbstractThe unique property of ultrafast water transport in graphene nanoplatelets (GNPs) coating is attributed to the frictionless interaction between the smooth hydrophobic carbon nanostructures and the well‐ordered hydrogen bonds of water molecules, whereas the driving force originates from the randomly distributed hydrophilic functionalities. The anomalous two‐phase heat transfer enhancement that results from this distinctive property of GNPs‐coating is investigated. The fast water permeation property of graphene enables the formation of ultrathin water film that synergizes the evaporation and the circulation of water in a two‐phase closed thermosyphon (TPCT). In addition, the GNPs‐coating which performs as a hydrophilic surface, improves the droplet nucleation during condensation and its fast water permeation property augments the circulation of condensate back to the evaporator. Ultimately, the ultrafast water permeation property of GNPs‐coating enhances the efficiencies of all the three main processes taking place in a TPCT, namely, evaporation, condensation, and circulation of condensate, leading to a maximum enhancement of 80.7% in the effective thermal conductance and 116.3% in the evaporative heat transfer coefficient. The experimental results are supported by the molecular dynamics simulations. A great potential for the application of GNPs‐coating in the phase‐change heat transfer devices is envisaged.

Water/Alcohol Separation in Graphene Oxide Membranes: Insights from Molecular Dynamics and Monte Carlo Simulations

ABSTRACTGraphene-based membranes have been investigated as promising candidates for water filtration and gas separation applications. Experimental evidences have shown that graphene oxide can be impermeable to liquids, vapors and gases, while allowing a fast permeation of water molecules. This phenomenon has been attributed to the formation of a network of nano capillaries that allow nearly frictionless water flow while blocking other molecules by steric hindrance effects. It is supposed that water molecules are transported through the percolated two-dimensional channels formed between graphene-based sheets. Although these channels allow fast water permeation in such materials, the flow rates are strongly dependent on how the membranes are fabricated. Also, some fundamental issues regarding the nanoscale mechanisms of water permeation are still not fully understood and their interpretation remains controversial. In this work, we have investigated the dynamics of water permeation through pristine graphene and graphene oxide model membranes that have strong impact on water/alcohol separation. We have carried out fully atomistic classical molecular dynamics simulations of systems composed of multiple layered graphene-based sheets into contact with a pure water reservoir under controlled thermodynamics conditions (e. g., by varying temperature and pressure values). We have systematically analysed how the transport dynamics of the confined nanofluids depend on the interlayer distances and the role of the oxide functional groups. Our results show the water flux is much more effective for graphene than for graphene oxide membranes. These results can be attributed to the H-bonds formation between oxide functional groups and water, which traps the water molecules and precludes ultrafast water transport through the nanochannels.

Extremely Black Vertically Aligned Carbon Nanotube Arrays for Solar Steam Generation.

The unique structure of a vertically aligned carbon nanotube (VACNT) array makes it behave most similarly to a blackbody. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the highly efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and local temperature rise by the thin layer of VACNTs. We found that the evaporation rate of water assisted by VACNT arrays is 10 times that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and local temperature rise induced by the VACNT layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.

Tunable Ion Selectivity in Sub-Nanometer Diameter Carbon Nanotube Porins

Carbon nanotube porins (CNTPs), ultra-short carbon nanotubes (5-20nm) that can self-insert into lipid bilayers, allow single-channel planar lipid bilayer measurements of ionic transport through carbon nanotube (CNT) pores. CNTs with sub-nanometer diameters have been predicted to display ultra-fast water transport and high levels of ionic exclusion resulting from one-dimensional water wire transport through their hydrophobic cores. Here, we show that ultra-short 0.8-nm-diameter CNTPs, can spontaneously insert into lipid bilayers to form highly cation selective channels that exhibit low ionic conductance. Using reversal potential in various asymmetric salt conditions, we observe that these CNTPs exhibit large permselectivity values, corresponding to a high selectivity for both potassium and sodium over chloride. We also show evidence that neutralization of charges on the CNTs enhances ion selectivity. We also show that by using a solid-state nanopore to act as a support and form a completely solvent-free bilayer system, we can observe extremely stable ionic currents through these nanotubes, in contrast to previous reports with solvent containing bilayers. These results establish CNTPs as a promising biomimetic platform for developing cell interfaces, creating stochastic sensors, and water desalination.

Controlling water transport in carbon nanotubes

Water transport inside carbon nanotubes (CNTs) shows a wealth of unique nanofluidic phenomena, which can be exploited as solutions for many global challenges. However, translating this potential into practical applications remains questionable to date. Recently, a work by Secchi and coworkers provides confirmatory evidence of radius-dependent water slippage inside an individual CNT. This article therefore puts into perspective two key takeaways, namely, nanoconfinement and electronic structures of CNT, as promising approaches to control ultrafast water transport inside CNTs.

Ultrafiltration membranes with ultrafast water transport tuned via different substrates

A series of self-supporting and substrate-supporting polysulfone (PSf) ultrafiltration (UF) membranes was fabricated using various substrates including glass plates, polypropylene random plates (PPR) and three kinds of non-woven fabrics (NWFs) via a typical phase inversion technique. Effects of the substrate hydrophilicity and structure on the membrane characteristics, morphology, separation and anti-fouling performance were systematically investigated. For self-supporting membranes, compared to glass plates, PPR facilitated more porous membranes and higher pure water permeability (Lp), permeation flux as well as anti-fouling property. NWFs density played an important role in the separation performance of the NWFs-supporting membranes. The resulting membrane with loosest NWFs exhibited an ultrahigh Lp of approximate 13,572L/m2h per MPa without any sacrifice of rejection, which significantly outperformed almost all the PSf membranes with Lp of 1000–7000L/m2h per MPa in literature. In addition, fouling filtration tests were performed in dead-end mode using humic acids solution followed by physical washing. More reversible rather than irreversible fouling was found in the NWFs-supporting membranes, especially for the membrane with loosest NWFs, indicating an improved anti-fouling property. This work endows the conventional PSf membranes with the outstanding properties such as ultrafast water transport and high flux recovery in an efficient and facile way.

Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide.

Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in <5 s. Pressure driven transport data demonstrate high retention (>90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30–40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71±5 l m−2 hr−1 bar−1 for 150±15 nm thick membranes).

Ultrafast liquid water transport through graphene-based nanochannels measured by isotope labelling.

Based on isotope labelling, we found that liquid water can afford an ultrafast permeation through graphene-based nanochannels with a diffusion coefficient 4-5 orders of magnitude greater than in the bulk case. When dissolving ions in sources, the diffusion coefficient of ions through graphene channels lies in the same order of magnitude as water, while the ion diffusion is slightly faster than water, indicating that the ions are mainly transported by water flows and the delicate interactions between ions and nanocapillary walls also take effect in the accelerated ion transportation.

ChemInform Abstract: Carbon Nanofluidics of Rapid Water Transport for Energy Applications

AbstractReview: 55 refs.

Carbon nanofluidics of rapid water transport for energy applications

Fast transport of water inside nanoscale graphitic surfaces, namely carbon nanotubes and graphene, forms the basis of aqueous carbon nanofluidic phenomena for which there are numerous applications in energy and environmental fields. In this tutorial review, we provide the basic principles of nanofluidics using carbon materials. We also address thermodynamic and structural aspects of favourable water confinement between hydrophobic carbon surfaces. We outline the experimental and theoretical history and consider the current status of ultrafast water transport inside carbon nanotubes, together with recent applications of aqueous carbon nanofluidic phenomena for energy generation and energy storage. We briefly discuss the challenges and opportunities for utilization of fast water transport in the graphitic nanoenvironment as a means to offer a clean and sustainable source of energy technology.

High-performance hybrid pervaporation membranes with superior hydrothermal and acid stability

A new organic–inorganic hybrid membrane has been prepared with exceptional performance in dewatering applications. The only precursor used in the sol–gel synthesis of the selective layer was organically linked 1,2- bis(triethoxysilyl)ethane (BTESE). The microporous structure of this layer enables selective molecular sieving of small molecules from larger ones. In the dehydration of n-butanol with 5% of water, the membrane shows a high separation factor of over 4000 and ultra-fast water transport at a rate of more than 20 kg m −2 h −1 at 150 °C. This can be related to the high adsorption capacity of the material and the sub-micron thickness of the selective layer. The selectivity has now remained constant over almost one and a half years under continuous process testing conditions. Apart from the hydrothermal stability, the membrane exhibits a high tolerance for acid contamination. A slow performance decline in flux and separation factor is only observed at a pH lower than 2. The high stability and effective separation indicate a broad industrial application potential of the hybrid membrane material.