Adsorption on Single-Walled Carbon Nanohorns

1. Adsorption on Single-Walled Carbon Nanohorns Adam Scrivener

2. 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.

3. 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).

4. 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.

5. 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.

6. 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.

7. 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.

8. The Grand Canonical Monte Carlo Algorithm • Start with an arbitrary configuration of particles.

9. The Grand Canonical Monte Carlo Algorithm • Start with an arbitrary configuration of particles. • Randomly choose whether to: • Move a particle from the vapor into the system in a random location.

11. The Grand Canonical Monte Carlo Algorithm • Start with an arbitrary configuration of particles. • Randomly choose whether to: • Move a particle from the vapor into the system in a random location. • Move a random particle from the system into the vapor.

13. The Grand Canonical Monte Carlo Algorithm • Start with an arbitrary configuration of particles. • Randomly choose whether to: • Move a particle from the vapor into the system in a random location. • Move a random particle from the system into the vapor. • Choose a random particle already in the system and move it in a random direction within some fixed distance ∆.

14. ∆

15. The Grand Canonical Monte Carlo Algorithm • Start with an arbitrary configuration of particles. • Randomly choose whether to: • Move a particle from the vapor into the system in a random location. • Move a random particle from the system into the vapor. • Choose a random particle already in the system and move it in a random direction within some fixed distance ∆. • Repeat until the system is in equilibrium.

16. (After many iterations)

17. Energy of Krypton-nanohorn system Egg Egg Egg Egs Egs Egs 60K 77.4K 40K

18. Krypton Adsorption - Pressure vs. Temperature 60K 77.4K 40K

19. Atoms inside

20. Krypton Adsorption - Pressure vs. Temperature 60K 77.4K 40K

21. Atoms inside and in between nanohorns

22. Krypton Adsorption - Pressure vs. Temperature 60K 77.4K 40K

23. Atoms inside and on surface of nanohorns

24. 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.