Transport and selectivity studies of protons across 2D membranes and molecules through angstrom-sized nanopores

Transport of molecules and ions across membranes has been a widely researched subject over the past few years due to its wide applications ranging from desalination, separation of molecules to batteries and energy storage. My research consists of three such topics, namely, understanding ion transport across 2D membranes with intrinsic defects and their potential application to desalination; and studying the selectivity of hard-to-separate liquids through precise control of the size of angstrom-sized nanopores and sequencing proteins using solid-state nanopores. These studies are performed using computational tools which include classical, ab-initio Molecular Dynamics(MD) and Density Functional Theory (DFT). Ab-initio MD makes use of Density Functional Theory (DFT) to calculate the electron charge distribution, after which the forces and energies are calculated from the resulting charge distribution. In the study of proton transport through 2D membranes, we show that water can dissociate on the surface due to the catalytic activity of 2D cubic Ti2 C membrane. The dissociated protons move into the interstitials present in the membrane and are able to transport across the membrane. We make use of this phenomena to demonstrate quantum desalination in a system where we have a nanopore in the membrane. We show that the pore facilitates the transport of OH− ions across the membrane and combining this with the interstitial transport of protons, we are able to generate water by transporting hydroxide ions and protons through two separate pathways. In addition to interstitial transport of protons, we also study the experimentally observed phenomenon of proton tunneling through hexagonal boron nitride (hBN), where the energy barriers of proton transport through pristine and defective hBN are evaluated. These energy barriers are used to estimate tunneling probabilities and fluxes of protons through the material, and the temperature dependence of these properties are studied. The second study consists of making use of angstrom-sized nanopores of precise diameter to sieve hard-to-separate liquids which have similar properties, for instance hexane and cyclohexane, and water and ethanol. In addition to MD (classical and ab-initio), time-dependent density functional theory (TD-DFT) simulations are used to show that ethanol is indeed excluded from the narrow pores chosen. We identify the diameter of the nanotube required for sieving water from ethanol-water mixtures through Potential of Mean Force (PMF) simulations and calculated the free energy barriers for water and ethanol filling the nanotubes. In the third study, we analyze the sequence of the β-amyloid protein through MD simulations, where we impel the amino acids through a sub-nm silica nanopore under the effect of an electric field. The effects of current, charge, number of water molecules, and radii of gyration of amino acids are leveraged to construct the sequence of β-amyloid.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Rayabharam, Archith

Contributors dc:contributor

• Aluru, Narayana R.
• Espinosa Marzal, Rosa M.
• van der Zande, Arend
• Zhang, Yingjie

• Molecular Sieving
• Carbon Nanotubes
• Mxenes
• Proton Transport
• Ab-initio Molecular Dynamics

Statement dc:rights

• Copyright 2023 Archith Rayabharam

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122197

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122197