Adsorption on Single-Walled
Carbon Nanohorns
Adam Scrivener
What are carbon nanohorns?
● Nanostructures made from graphene sheets,
forming a dahlia-like structure.
● Surface area is much
greater than graphene,
which makes nanohorns a
promising material for gas
adsorption.
What is adsorption?
● Adsorption is the adhesion of atoms or
molecules from a gas, liquid, or dissolved
solid to a surface.
● Caused by van der Waals force between an
adsorbate (gas molecules/atoms) and an
adsorbent (Carbon atoms).
Applications of adsorption
● Gas storage: gas particles can be stored at very high density using
nanohorns, due to the adsorption process and high surface area
per volume ratio.
● Gas separation: Several materials, including carbon nanohorns,
can be used as a filter in factories to reduce greenhouse gas
emissions such as methane and CO2.
● Gas sensing: The ability to monitor how much gas is in a system is
invaluable, and carbon-based materials such as carbon nanohorns
are perfect for this because of their large specific surface areas.
The van der Waals force
● The van der Waals force is the sum of the
attractive forces between molecules other
than those due to covalent bonds or
electrostatic interactions involving ions.
● There are no covalent bonds or ions
involved in the systems which we deal with,
so the electrostatic forces can be
disregarded.
The Lennard-Jones potential
● Approximates the interactions between the Carbon
atoms in the nanohorns and the gaseous adsorbate
● Incorporates the attractive portion of the van der
Waals force and the repulsive forces caused by
overlapping electron orbitals.
Monte Carlo Simulations
● An efficient method of observing the equilibrium properties of the
nanohorn/gas system.
● Simulations can be combined with experiments to make it easier to
interpret the results
● Using simulations, we can explore parameters that are not possible
in a real-world experiment. E.G., we can set any temperature or
pressure that we want, or add impurities to the adsorbent easily.
The Grand Canonical Monte
Carlo Algorithm
1. Start with an arbitrary configuration of particles.
The Grand Canonical Monte
Carlo Algorithm
1. Start with an arbitrary configuration of particles.
2. Randomly choose whether to:
a. Move a particle from the vapor into the system in a random
location.
The Grand Canonical Monte
Carlo Algorithm
1. Start with an arbitrary configuration of particles.
2. Randomly choose whether to:
a. Move a particle from the vapor into the system in a random
location.
b. Move a random particle from the system into the vapor.
The Grand Canonical Monte
Carlo Algorithm
1. Start with an arbitrary configuration of particles.
2. Randomly choose whether to:
a. Move a particle from the vapor into the system in a random
location.
b. Move a random particle from the system into the vapor.
c. Choose a random particle already in the system and move
it in a random direction within some fixed distance ∆.
∆
The Grand Canonical Monte
Carlo Algorithm
1. Start with an arbitrary configuration of particles.
2. Randomly choose whether to:
a. Move a particle from the vapor into the system in a random
location.
b. Move a random particle from the system into the vapor.
c. Choose a random particle already in the system and move it in
a random direction within some fixed distance ∆.
3. Repeat until the system is in equilibrium.
(After many iterations)
Energy of Krypton-nanohorn system
Egg
Egg
Egs
Egs
40K
60K
Egg
Egs
77.4K
Krypton Adsorption - Pressure vs.
Temperature
40K
60K
77.4K
Atoms inside
Krypton Adsorption - Pressure vs.
Temperature
40K
60K
77.4K
Atoms inside
and in
between
Krypton Adsorption - Pressure vs.
Temperature
40K
60K
77.4K
Atoms inside
and on surface
of nanohorns
Future plans
● Simulate Neon instead of Krypton
● Use Neon data to compare to already observed data
from real-world experiments.
● This will further affirm that our simulations accurately
represent the equilibrium state of the nanohorn
adsorption systems.
● We plan to simulate CO2 as well, and, similarly to
Neon, compare to data from real-world experiments.