d-Band Center Regulated O2 Adsorption on Transition Metal Single Atoms Loaded COF: A DFT Study

Abstract

Covalent organic framework (COF) materials are promising photocatalysts because of their fantastic structural and physicochemical features. To enhance photocatalytic performance, numerous metal single atoms (MSA) are loaded on COF to improve molecule adsorption. However, the inherent mechanisms and dominant factors of the heightened adsorption property are not deeply unveiled. Herein, four MSA-COF systems were constructed by severally introducing Fe, Co, Ni, and Cu single atoms in monolayer TpBpy-COF. The effect of various metal atoms modification on the electronic property and O₂ adsorption of COF was investigated using density functional theory calculations. The results show that the metal atoms are bonded to the pyridinic N atoms, forming stable MSA-COF configurations. The anchoring of metal atoms reduces the band gap and raises the Fermi level of COF. Moreover, as the atomic number of the metals increases, the d orbitals of the metal atoms gradually move to lower energy levels, manifesting a negative shift of the d-band centers. After metal atoms loading, the weak physical adsorption of O₂ on pristine COF is converted to robust chemisorption with the formation of M―O_ads bonds and intense electron transfer. Intriguingly, the adsorption energy presents a strong correlation with the d-band centers of the metal atoms. This finding is comprehended from the perspective of electron occupancy in antibonding orbitals in the adsorption systems. This work provides a feasible approach for modifying molecule adsorption on MSA-COF by regulating the d-band centers of metal atoms.

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