Investigations of Functional Groups Effect on CO2 Adsorption on Pillar[5]arenes Using Density Functional Theory Calculations

Abstract

This study investigates how various functional groups affect the adsorption of carbon dioxide (CO2) in pillar[5]arenes (P[5]A) at the aim of enhancing CO2 capture in P[5]A for environmental applications. Density functional theory (DFT) and density-functional-based tight-binding (DFTB) methods were employed to investigate the adsorption behavior of CO2 in pillar[5]arenes (P[5]A) with various functional groups including P[5]A with methyl (P[5]A-OCH3), aldehyde (P[5]A-OCOH) functional groups and pillar[5]quinone (P[5]Q). Self-consistent charge DFTB calculations have been performed using the DFTB+ code, with dispersion corrections included for van der Waals interactions, to ensure accurate results at a lower computational cost. Bader charge analysis have been carried out with VASP code to understand the interaction mechanisms and charge transfer between P[5]A and CO2. The study demonstrates that changing the functional groups of P[5]A affects CO2 adsorption behavior. Specifically, CO2 adsorption is more favorable at the cavity site of P[5]A-OCH3 compared to other functional groups, due to the combined effects of weak hydrogen bonds and π-π interactions. The calculated results shows that the functionalization is one of the beneficial factors for CO2 capture in pillararenes, the adsorption energy and configuration of adsorbed CO2 at P[5]A are affected by both the polarization and geometry of the functional groups. Furthermore, the density of states (DOS) calculations confirm that CO2 is only physisorbed in P[5]A, ensuring the reusability of pillararenes after desorption. The findings of this study suggest that modifying the functional groups of pillararens is a promising strategy for developing high-efficiency CO2 capture materials.