On the Possibility of Helium Adsorption in Nitrogen Doped Graphitic Materials

Sudhir K Sahoo,Nadezda V Tarakina,Zhenzhe Zhang,Sam Azadi,Thomas D Kühne,Julian Heske,Markus Antonietti,Rustam Z Khaliullin,Martin Oschatz

doi:10.1038/s41598-020-62638-z

Abstract

The potassium salt of polyheptazine imide (K–PHI) is a promising photocatalyst for various chemical reactions. From powder X–ray diffraction data an idealized structural model of K–PHI has been derived. Using atomic coordinates of this model we defined an energetically optimized K–PHI structure, in which the K ions are present in the pore and between the PHI–planes. The distance between the anion framework and K+ resembles a frustrated Lewis pair-like structure, which we denote as frustrated Coulomb pair that results in an interesting adsorption environment for otherwise non-adsorbing, non-polar gas molecules. We demonstrate that even helium (He) gas molecules, which are known to have the lowest boiling point and the lowest intermolecular interactions, can be adsorbed in this polarized environment with an adsorption energy of − 4.6 kJ mol−1 per He atom. The interaction between He atoms and K–PHI is partially originating from charge transfer, as disclosed by our energy decomposition analysis based on absolutely localized molecular orbitals. Due to very small charge transfer interactions, He gas adsorption saturates at 8 at%, which however can be subject to further improvement by cation variation.

Highlights

Materials based on carbon-nitride (CN) have received huge attention in the scientific community for their large variety of applications in catalysis[1,2,3,4,5], gas storage and separation[6], battery research[7,8,9], and other energy storage devices[10]
We investigate whether K–PHI could be used for He gas adsorption and storage by employing density functional theory (DFT) and quantum Monte Carlo calculations
Images from high-resolution transmission electron microscopy (HRTEM), which are shown in Fig. 1, shows the crystalline nature of K–PHI

Summary

Introduction

Materials based on carbon-nitride (CN) have received huge attention in the scientific community for their large variety of applications in catalysis[1,2,3,4,5], gas storage and separation[6], battery research[7,8,9], and other energy storage devices[10]. Assuming that charge transfer effects due to the FCP structure of K–PHI are essential for the adsorption of He, this would explain, why the adsorption energies for K–PHI a systematically higher than for Au–PHI and H–PHI, respectively, where the Au and H atoms are located in the same plane as the 2D PHI scaffold and create less frustration.

Results

Conclusion