1. Adsorption of Mixtures on Graphite Dominic Marco Millikin University
introduction
Methods
Currently the world is trying to find ways to create green energy and cut back on harmful emissions. Traditional methods of creating energy produce large amounts pollutants and researching clean energy can be expensive. Certain gases will adsorb to the surface of a slab under the right conditions.
Our goal is to find what conditions lead to the optimal adsorption of methane (CH4), in a mixture of nitrogen, on a slab of graphite.
L-J Potential curve follows this equation:
Epsilon is the depth of the well seen on the graph, and sigma is the cutoff of the interaction.
The values for mixed-pairs are the average of between their interaction strengths.
The interactions between the particle and the slab are calculated using the Leonard Jones 93 potential which represents the VdW force that pushes particles towards the slab.
The particles should form a monatomic film on the surface of the slab which represents the L-J potential well.
Each simulation contained 100 particles total, 50 CH4 and 50 N2 atoms.
The system was simulated at 100, 300, and 500 kelvin.  v
Sigma
Epsilon
N2-N2
3.7
0.1889
CH4-N2
3.699
0.2357
CH4-CH4
3.698
0.2941
conclusion
Lower temperatures aid the forming the film because they have less energy to escape the VdW forces that push them towards the wall.
Explore why the adsorption increases, then decreases at higher temperatures.
Methods
Our simulations will be conducted using a molecular dynamics software (MD) called LAAMPS. This program is free to use from Sandia National Laboratory.
Using LAMMPS we will simulate the particles on an infinite slab. To create this slab we will create a box with periodic side walls, and a top wall which will reflect the atoms. The floor of the simulation will be a graphite substrate. These conditions will allow the particles to move as if they were in an infinite box, without having a truly infinite space.
Each interaction in the system is calculated using the Leonard Jones potential curve.
References
Plimption,S. Et al, (2018). Sandia National Labs: LAMMPS. Available from
Naeem, R. (2019, June 05). Lennard-Jones Potential. Retrieved June 17, 2019, from  ry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistr y)/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolec ular_Forces/Specific_Interactions/Lennard-Jones_Potential
Results
After letting each system equilibrate for 1,000,000 steps the walls were activated and the number of particles in the film layer was recorded.
Mixtures had an inverse relationship between adsorption and temperature.
Atoms are not strongly bound in the film at higher temperatures. Seen by the large fluctuations in the adsorbed count.
Acknowledgements
Dr. Silvina Gatica​
Howard University NSF Award PHY
Hind ​
Dr. Misra​
Howard University​