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Fast reverse osmosis through nanotube-based membranes: molecular dynamics study

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Title: Fast reverse osmosis through nanotube-based membranes: molecular dynamics study
Author(s): Suk, Myung eun
Advisor(s): Aluru, Narayana R.
Contributor(s): Aluru, Narayana R.
Department / Program: Mechanical Sci & Engineering
Discipline: Mechanical Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: M.S.
Genre: Thesis
Subject(s): Reverse osmosis Carbon nanotube Boron nitride nanotube Water transport single-file water Electric field Molecular dynamis simulation
Abstract: Development of nanotechnology had led to novel and advanced methods in various fields of science and engineering, and its influence extended to the progress of water purification process. Development of novel membranes and modification of existing membranes for efficient water filtration can be studied based on the investigation of interactions between water and molecules constituting membranes. Also, water molecules confined in nano scale show different behavior from the bulk water, and the study of this behavior can contribute to enhance water flux and energy efficiency. Molecular dynamics simulation can be used in observing these features that experiments can not detect. In this work, we performed molecular dynamics simulation to investigate the methods to improve reverse osmosis process, which can produce high quality water by removing ions and emerging pollutants. In the first part, we investigate reverse-osmosis through commonly used polymeric and advanced inorganic nanotube based semi-permeable membranes by performing non-equilibrium molecular dynamics simulations. Simulations indicate that there is a significantly higher water flux through boron nitride (BNNT) and carbon nanotubes (CNT) compared to a polymethyl methacrylate (PMMA) pore, and a slightly higher water flux through BNNT as compared to CNT. The calculated permeation coefficient is in reasonable agreement with the theoretical single-file "hopping" model. Potential of mean force analysis indicates that the irregular nature of PMMA pore surface can cause significant localized energy barriers inside the pore, thereby reducing the water flux. In the second part, we investigated the effect of electric field on single-file reverse osmosis (RO) water flux. The electric field is generated by introducing oppositely charged biomolecules to the salt solution and pure water chambers attached to the nanopore. Simulation results indicate that an electric field in the direction of RO enhances the water flux while in the direction opposite to RO suppresses the water flux. When the RO water flux is enhanced, the single-file water dipoles are aligned in the direction of the electric field. The addition of an electric field in the direction of RO led to a flux of ~3 water molecules/ns by constantly maintaining water dipole vectors in the direction of electric field, and this water flux is superimposed on the pressure driven water flux.
Issue Date: 2010-01-06
URI: http://hdl.handle.net/2142/14675
Rights Information: Copyright 2009 Myung eun Suk
Date Available in IDEALS: 2010-01-06
Date Deposited: December 2
 

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