Adsorption on Single-Walled Carbon Nanohorns Adam Scrivener.

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 Algorithm1. Start with an arbitrary configuration of particles.

The Grand Canonical Monte Carlo Algorithm1. 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 Algorithm1. 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 Algorithm1. 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 Algorithm1. 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

40K 60K 77.4K

Egg EggEgg

Egs

Egs

Egs

Krypton Adsorption - Pressure vs. Temperature

40K 60K 77.4K

Atoms inside

Krypton Adsorption - Pressure vs. Temperature

40K 60K 77.4K

Atoms insideand in between

nanohorns

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.