Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session H9: Nanoscale Flows: Membranes for Filtering and Separation |
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Chair: Rohit Karnik, MIT Room: 109 |
Monday, November 23, 2015 10:35AM - 10:48AM |
H9.00001: Ultra-high Burst Strength of CVD Graphene Membranes Luda Wang, Michael Boutilier, Piran Kidambi, Rohit Karnik Porous graphene membranes have significant potential in gas separation, water desalination and nanofiltration. Understanding the mechanical strength of porous graphene is crucial because membrane separations can involve high pressures. We studied the burst strength of CVD graphene membrane placed on porous support at applied pressures up to 100 bar by monitoring the gas flow rate across the membrane as a function of pressure. Increase of gas flow rate with pressure allowed for extraction of the burst fraction of graphene as it failed under increasing pressure. We also studied the effect of sub-nanometer pores on the ability of graphene to withstand pressure. The results showed that porous graphene membranes can withstand pressures comparable to or even higher than the \textgreater 50 bar pressures encountered in water desalination, with non-porous CVD graphene exhibiting even higher mechanical strength. Our study shows that porous polycrystalline CVD graphene has ultra-high burst strength under applied pressure, suggesting the possibility for its use in high-pressure membrane separations. [Preview Abstract] |
Monday, November 23, 2015 10:48AM - 11:01AM |
H9.00002: Development of macroscopic nanoporous graphene membranes for gas separation. Michael Boutilier, Nicolas Hadjiconstantinou, Rohit Karnik Nanoporous graphene membranes have the potential to exceed permeance and selectivity limits of existing gas separation membranes due to their atomic thickness and ability to support sub-nanometer pores for molecular sieving, while offering low resistance to flow. Gas separation by graphene nanopores has been demonstrated experimentally on micron-scale membranes, but scaling-up to larger sizes is challenging due to graphene imperfections and control of the selective nanopore size distribution. Using a model we developed for the inherent permeance of graphene, we designed a macroscopic graphene membrane predicted to be selectively permeable despite material imperfections. Micrometer-scale defects are sealed by interfacial polymerization and nanometer-scale defects are sealed by atomic layer deposition. The underlying support structure is tuned to further reduce the effects of leakage. Finally, ion bombardment followed by oxidative etching is used to create a high density of selective nanopores. SEM and TEM imaging are used to characterize the resulting membrane structure, and its performance is assessed by gas permeance and selectivity measurements. This work provides insight into gas flow through nanoporous graphene membranes and guides their future development. [Preview Abstract] |
Monday, November 23, 2015 11:01AM - 11:14AM |
H9.00003: Chemical vapor deposition of atomically thin materials for membrane dialysis applications Piran Kidambi, Alexander Mok, Doojoon Jang, Michael Boutilier, Luda Wang, Rohit Karnik Atomically thin 2D materials like graphene and h-BN represent a new class of membranes materials. They offer the possibility of minimum theoretical membrane transport resistance along with the opportunity to tune pore sizes at the nanometer scale. Chemical vapor deposition has emerged as the preferable route towards scalable, cost effective synthesis of 2D materials. Here we show selective molecular transport through sub-nanometer diameter pores in graphene grown via chemical vapor deposition processes. A combination of pressure driven and diffusive transport measurements shows evidence for size selective transport behavior which can be used for separation by dialysis for applications such as desalting of biomolecular or chemical solutions. 1. O'Hern et al. Nano Letters (2015). 2. Boutilier et al. ACS Nano (2014). 3. O'Hern et al. Nano Letters (2013). 4. O'Hern et al. ACS Nano (2012). 5. Kidambi et al. Chemistry of Materials (2014). 6. Kidambi et al. Nano Letters (2013). [Preview Abstract] |
Monday, November 23, 2015 11:14AM - 11:27AM |
H9.00004: Application of Solution-blown 20-50 nm Nanofibers in Filtration of Nanoparticles: The Efficient van der Waals Collectors Sumit Sinha-Ray, Suman Sinha-Ray, Alexander Yarin, Behnam Pourdeyhimi Filtration efficiency of commercially available filter media with fiber/pore sizes on the scale of 10 $\mu $m can be dramatically increased by adding a layer of ultrafine supersonically-blown 20-50 nm nanofibers. Different commercial filters were modified with (i) electrospun nanofibers alone, (ii) solution-blown 20-50 nm alone, and (iii) the dual coating with electrospun nanofibers deposited first and the solution-blown 20-50 nm nanofibers deposited on top of them. Detailed observations of nanoparticle removal revealed that the above-mentioned modified filters, especially those with the dual nanofiber coating with the 20-50 nm nanofibers deposited on top, are the most effective in removing the below-200 nm Cu nanoparticles/clusters from aqueous suspensions, in particular at the lowest concentrations of 0.2-0.5 ppm. The theory developed in the present work dealing with convective transport of nanoparticles in the fluid flow along with diffusion of nanoparticles and the van der Waals attraction explains and describes how the smallest solution-blown nanofibers introduce a novel physical mechanism of nanoparticle interception (the attractive van der Waals forces) and become significantly more efficient collectors compared to the larger electrospun nanofibers. The theory also elucidates the morphology of the nanoparticle clusters being accumulated at the smallest nanofiber surfaces, including the clusters growing at the windward side, or in some cases also on the leeward side of a nanofiber. [Preview Abstract] |
Monday, November 23, 2015 11:27AM - 11:40AM |
H9.00005: Molecular level water and solute transport in reverse osmosis membranes Richard M. Lueptow, Meng Shen, Sinan Keten The water permeability and rejection characteristics of six solutes, methanol, ethanol, 2-propanol, urea, Na$^{+}$, and Cl$^{-}$, were studied for a polymeric reverse osmosis (RO) membrane using non-equilibrium molecular dynamics simulations. Results indicate that water flux increases with an increasing fraction of percolated free volume in the membrane polymer structure. Solute molecules display Brownian motion and hop from pore to pore as they pass through the membrane. The solute rejection depends on both the size of the solute molecule and the chemical interaction of the solute with water and the membrane. When the open spaces in the polymeric structure are such that solutes have to shed at least one water molecule from their solvation shell to pass through the membrane molecular structure, the water-solute pair interaction energy governs solute rejection. Organic solutes more easily shed water molecules than ions to more readily pass through the membrane. Hydrogen-bonding sites for molecules like urea also lead to a higher rejection. These findings underline the importance of the solute's solvation shell and solute-water-membrane chemistry in solute transport and rejection in RO membranes. [Preview Abstract] |
Monday, November 23, 2015 11:40AM - 11:53AM |
H9.00006: Water and Molecular Transport across Nanopores in Monolayer Graphene Membranes Doojoon Jang, Sean O'Hern, Piran Kidambi, Michael Boutilier, Yi Song, Juan-Carlos Idrobo, Jing Kong, Tahar Laoui, Rohit Karnik Graphene's atomic thickness and high tensile strength allow it to outstand as backbone material for next-generation high flux separation membrane. Molecular dynamics simulations predicted that a single-layer graphene membrane could exhibit high permeability and selectivity for water over ions/molecules, qualifying as novel water desalination membranes. However, experimental investigation of water and molecular transport across graphene nanopores had remained barely explored due to the presence of intrinsic defects and tears in graphene. We introduce two-step methods to seal leakage across centimeter scale single-layer graphene membranes create sub-nanometer pores using ion irradiation and oxidative etching. Pore creation parameters were varied to explore the effects of created pore structures on water and molecular transport driven by forward osmosis. The results demonstrate the potential of nanoporous graphene as a reliable platform for high flux nanofiltration membranes. [Preview Abstract] |
Monday, November 23, 2015 11:53AM - 12:06PM |
H9.00007: Water Purification across MoS$_{2}$ Nano-porous Membranes Mohammad Heiranian, Amir Barati Farimani, Narayana R. Aluru A 2D material, molybdenum disulfide (MoS$_{2})$, is proposed as a nano-porous membrane for water desalination. By performing detailed molecular dynamics simulations, we find that salt ions are rejected efficiently across a single-layer MoS$_{2}$ while water permeates at high rates. Depending on the pore area, which ranges from 20 to 60 {\AA}$^{2}$, the nanopore allows less than 12{\%} of ions to pass through even at theoretically high pressures of 350 MPa. Water permeation across the MoS$_{2}$ membrane is found to be as high as 12 L/cm$^{2}$/day/MPa which is at least two orders of magnitude higher than that of other existing nano-porous membranes. Pore chemistry is shown to be one of the important factors leading to large water fluxes. MoS$_{2}$ pore edges terminated with only molybdenum atoms result in higher fluxes which are about 70{\%} higher than that of graphene nanopores. These findings are explained and supported by the permeation coefficients, energy barriers, water density and velocity distributions in the pores. [Preview Abstract] |
Monday, November 23, 2015 12:06PM - 12:19PM |
H9.00008: Active osmotic exchanger for advanced filtration at the nano scale Sophie Marbach, Lyderic Bocquet One of the main functions of the kidney is to remove the waste products of an organism, mostly by excreting concentrated urea while reabsorbing water and other molecules. The human kidney is capable of recycling about 200 liters of water per day, at the relatively low cost of 0.5 kJ/L (standard dialysis requiring at least 150 kJ/L). Kidneys are constituted of millions of parallel filtration networks called nephrons. The nephrons of all mammalian kidneys present a specific loop geometry, the Loop of Henle, that is believed to play a key role in the urinary concentrating mechanism. One limb of the loop is permeable to water and the other contains sodium pumps that exchange with a common interstitium. In this work, we take inspiration from this osmotic exchanger design to propose new nanofiltration principles. We first establish simple analytical results to derive general operating principles, based on coupled water permeable pores and osmotic pumps. The best filtration geometry, in terms of power required for a given water recycling ratio, is comparable in many ways to the mammalian nephron. It is not only more efficient than traditional reverse osmosis systems, but can also work at much smaller pressures (of the order of the blood pressure, 0.13 bar, as compared to more than 30 bars for pressure-retarded osmosis systems). We anticipate that our proof of principle will be a starting point for the development of new filtration systems relying on the active osmotic exchanger principle. [Preview Abstract] |
Monday, November 23, 2015 12:19PM - 12:32PM |
H9.00009: ABSTRACT WITHDRAWN |
Monday, November 23, 2015 12:32PM - 12:45PM |
H9.00010: Particle Dynamics in Tangential Flow Filtration Mike Garcia, Sumita Pennathur Tangential Flow Filtration (TFF) is a rapid and efficient method for filtration and separation of solutions containing particles such as viruses, bacteria or cellular material. Enhancing the efficiency of TFF not only requires a detailed understanding of the individual mechanisms behind particle transport, but the interaction between these transport mechanisms and a porous wall. In this work, we numerically and experimentally explore how inertial migration is affected by the presence of a permeate flow through the porous walls of a microchannel in order to develop a platform for further studies of particle transport in a TFF device. Numerically, we use COMSOL multiphysics to model the large parameter space of permeate versus inertial forces. Experimentally, we develop a MEMS fabricated TFF device to confirm the results of the numerical model, where the permeate flow is controlled using multiple pumps and pressure transducers regulated by a feedback loop. Experimental and numerical results reveal interesting dynamics, including the competition between permeate and inertial forces and the consequences of this competition on particle trajectories and equilibrium location. [Preview Abstract] |
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