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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. [ABSTRACT FROM AUTHOR]