Adsorption of Hydrogen Isotopes on Novel Nanomaterials

Abstract

We investigated the possibility of using various novel nanostructured carbon for control of hydrogen isotopes by exploring the adsorption, reflection, and penetration of hydrogen isotopes using molecular dynamics. Nanometer sized allotropes of nano-carbons have completely changed the research trend in carbon materials, and opened numerous exciting possibilities in many applications. Researchers started to pay attention to carbon nanomaterials when Fullerene C60 was discovered in 1985. The discovery of carbon nanotubes in 1991 and the first isolation of single layer of graphene from graphite in 2004 have encouraged researchers to measure the exciting thermal, electrical, and mechanical properties of these carbon nanomaterials computationally and experimentally. In the present research, we investigate graphene layers and nanostructured carbons with random configurations. The REBO and AIREBO potential are used alongside LAMMPS to simulate tritium interactions with sheets of graphene. Custom MATLAB codes were used to create the graphene structure as well as randomly distribute 100 tritium atoms along a plane above and parallel to the graphene sheet. The tritium atoms are held in place while the graphene sheets undergo multiple stages of equilibration. The velocities of tritium atoms are selected so that incident energies may be 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, or 500 eV during a single simulation. Reflection is shown to be the dominant interaction at low incident energy. Adsorption rates increase with increasing incident energy until energies reach 5 eV. After 5 eV, adsorption rates decrease as incident energy increases. At incident energies greater than 5 eV, adsorption rates increase with the number of graphene layers. At low incident energies (< 1 eV), no isotopic effects on interactions are observed since the predominant interaction is derived from the force of π electrons. Simulations were performed with different incident angles of tritium. Adsorption rates are always the highest when tritium atoms travel vertically towards graphene (θ = 0°) while they are the lowest when the angle is the largest (θ = 60°) with only a few exceptions (5 eV and 10 eV). AIREBO potential shows a significant difference in adsorption of tritium on graphene from REBO potential. AIREBO potential consistently showed lower adsorption rates and higher reflection rates when compared to REBO potential. The results obtained in this research study will be used to develop novel nanomaterials that can be employed for tritium control.