Tuning optical and electronic properties of graphene oxide by surface adsorption of molecular halogens (X₂ = I₂, Br₂, Cl₂, and F₂) for light harvesting

Surface adsorption of small molecules modulates both optical and electronic structure, which is beneficial for different applications. The molecular adsorption of halogens X₂ (X₂ = I₂, Br₂, Cl₂, and F₂) was investigated using density functional theory and the dispersion (Wb97xd) module. The electronic structure and optical properties of the pristine graphene oxide (GO) and its molecular complexes with halogens (GOI₂, GOBr₂, GOCl₂, and GOF₂) are explored. The adsorption of X₂ (X₂ = I₂, Br₂, and Cl₂) molecules were stabilized by non-covalent lone pair-π bonding, (O)lp… π, interactions and π-π interactions. The F₂ molecule were stabilized by lone pair-π bonding, (O)lp… π, as well as halogen bonding (XB). The GOX₂ complexes were energetically stable and optically red shifted in polar solvents. The simulated optical absorption spectra at TD-DFT calculations of GOX₂ complexes and TDOS uncover the presence of intermediate sates in the energy gap region, which is beneficial for harvest of visible light and photocatalysis.