Investigating catechol adsorption to the ZnO (100) surface with and without an oxygen vacancies using the DFT-D2 method

Abstract

Functionalizing surfaces with different molecules can modulate their electronic properties and impart advantageous adsorption properties, which are crucial for various applications. For robust functionalization, chemisorption is required. Therefore, a molecular-level understanding of adsorption phenomena provides insight into the stability of the adsorbed molecule and its structure, crucial for designing catalysts, sensors, and other functional materials. This study employs detailed Density Functional Theory (DFT) calculations to investigate the adsorption behavior of catechol molecules on pristine ZnO and ZnOv (ZnO with oxygen-vacancy) (100) surfaces. Bader charge analysis and electronic structure calculations provide insights into adsorption mechanisms. Both half- and fully protonated catechol configurations were chemically adsorbed on the ZnO surface. The bond length between O of catechol and Zn of the surface obtained in the most stable configuration (E_ads = 2.14 eV) was 1.95 Å, which is close to the bond length between Zn and O of the surface of ZnO. Additionally, a significant change in bond angle was also observed. This clearly shows the chemisorption phenomenon of catechol on the surface of ZnO. Nevertheless, catechol showed weaker chemisorption to the ZnOv surface only in a fully protonated state. In this case, the bond length between the O of catechol and the Zn of ZnO surface was found to be 2.31 Å. In both the surfaces (ZnO and ZnOv), Bader analysis reveals a charge transfer from the surface to the catechol molecule, leading to a reduction in the surface's overall positive charge. Electronic structure changes observed in the valence and conduction bands upon adsorption corroborate these findings. Experimental adsorption kinetics on ZnO nanoparticles further benchmark the DFT results, confirming chemisorption of catechol on the ZnO surface. This combined theoretical and experimental approach advances the understanding of molecule–ZnO surface interactions for the design of functional materials.