Fouling mechanisms in y shaped carbon nanotubes
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Fouling Mechanisms in Y-shaped Carbon Nanotubes. Jason Myers, SeongJun Heo, and Susan B. Sinnott Department of Materials Science and Engineering University of Florida. Funded by the Network for Computational Nanotechnology at Purdue University, NSF Grant No. EEC -02288390. Outline.

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Fouling Mechanisms in Y-shaped Carbon Nanotubes

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Fouling mechanisms in y shaped carbon nanotubes

Fouling Mechanisms in Y-shaped Carbon Nanotubes

Jason Myers, SeongJun Heo, and Susan B. Sinnott

Department of Materials Science and Engineering

University of Florida

Funded by the Network for Computational Nanotechnology at Purdue University, NSF Grant No. EEC-02288390


Outline

Outline

  • Background

  • Computational Methods

  • System Design

  • Results

  • Conclusions


The need for filtration

The Need for Filtration

The chemical and biomedical fields have a constant demand for solutions of greater purity.

Current filtration methods (zeolites) do not offer uniform pore size, and are susceptible to fouling.

Carbon nanotubes (CNTs) have the potential to be custom designed for optimal molecular filtration.


Carbon nanotubes

Nanofluidics: Confinementof fluids to nanopores

Carbon nanotubes (CNTs):

Honeycomb graphene lattice rolled

into a cylinder

Ajayan and

Zhou (2001)

Sinnott et al. (2002)

Carbon Nanotubes

  • Discovered by Ijima, et al in 1991

  • Outstanding mechanical properties

  • Nanometer size enables precise molecular transport


Carbon nanotubes cont

Zigzag (10,0)

Chiral

(7,4)

Armchair (6,6)

Analagous to a rolled graphene sheet.

- One-dimensional axial symmetry.

- Spiral conformation: Chirality

Carbon Nanotubes, cont.

Chiral vector Ch = (n,m) = na1 + ma2


Y shaped cnts

Small arm – large molecule is energetically discouraged from entering

Y-shaped CNTs

Large arm – no similar barrier for large molecules

Result? Only the small molecule will pass through the small arm.


Outline1

Outline

  • Background

  • Computational Methods

  • System Design

  • Results

  • Conclusions


Molecular dynamics

Classical molecular dynamics (MD) simulations (numerically integrating F = ma)

Reactive Empirical Bond Order (REBO) Potential

Lennard-Jones (LJ) Potential

van der Waals Interaction

Covalent Interaction

Molecular Dynamics

  • For more details on REBO-MD, see Wen-Dung Hsu’s Breeze presentation.


Outline2

Outline

  • Background

  • Computational Methods

  • System Design

  • Results


Y shaped cnts1

Y-shaped CNTs

“Ytube1”

“Ytube2”

CNT

Diameter, Å

CNT

Diameter, Å

Branch:

Big arm:

Small arm:


Reservoirs

Reservoirs

Three different molecules:

Methane

N-butane

Rigid Argon Box

Isobutane

Push-plate

10, 5, 3, and 0 m/s


System design

Rigid

Active

Thermostat

Reservoir

Branch

Arms

Direction of Flow

Each system consists of a Y-shaped CNT and reservoir.

System Design


Outline3

Outline

  • Background

  • Computational Methods

  • System Design

  • Results

    • Methane

    • Isobutane + Methane

    • N-butane + Methane

  • Conclusions


Methane

Methane

Ytube1

Ytube2

6.35 Å

6.92 Å


Isobutane methane

Isobutane + Methane

Ytube1

Ytube2

Filtered methane

Blocking Isobutane


N butane methane

Ytube2, 10 m/s at…

N-butane + Methane

0.48ns

0.27ns

Stationary n-butane

Aligned n-butane


Summary

Summary

Ytube1 shows no tendency for filtration. There is evidence of size-based diffusion in the methane systems. Ytube2 shows no similar behavior.

The isobutane + methane systems exhibit fouling. This is attributed to the steric interactions of the isobutane molecule with the junction area, and is not due to a potential energy well. Prior to the formation of the block, filtration occurred in ytube2.

There is neither fouling nor filtration in the n-butane + methane systems. Once the driving force is sufficient, the n-butane aligns itself to pass easily down both arms.


Outline4

Outline

  • Background

  • Computational Methods

  • System Design

  • Results

  • Conclusions


Conclusions

Conclusions

  • Y-shaped carbon nanotubes exhibit promising signs of filtration.

  • However, they tend to clog due to molecular steric interactions.

  • Linear molecules (n-butane) avoid fouling, but prevent filtration.

  • System redesign with these factors in mind is needed.


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