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Theoretical calculation

Procedure

DFT calculation was performed by using the CP2K package. The Perdew-Burke-Ernzerhof functional with Grimme D3 correction was used to describe the system. Unrestricted Kohn-Sham DFT was used as the electronic structure method in the framework of the Gaussian and plane-wave method. The Goedecker-Teter-Hutter (GTH) pseudopotentials and DZVP-MOLOPT-GTH basis sets were used to describe the molecules. A plane-wave energy cutoff of 500 rydbergs was used.

The simulation was carried out in a 31.04 Å by 23.14 Å by 31.70 Å cubic box. A four-layer anatase TiO2 (101) surface, which contains 216 Ti atoms and 432 O atoms, was used in the simulation. A single layer of graphene was covered over the anatase (101) surface.

On the basis of our experiment results, where a Ti–O–C bond was observed, the oxidized graphene adsorbed on the TiO2 surface was modeled. For comparison, we also modeled the oxidized graphene. The molecule adsorbed on the oxidized graphene surface and the TiO2-supported graphene was first optimized.

The charge density difference is defined as$Δρ=ρmol/sur−ρmol−ρsur$(8)where ρmol/sur, ρmol, and ρsur are the electron density of the molecule adsorbed on the surface and the individual electron density of the molecule and the surface. Results show that when graphene was supported by the TiO2 surface, the CT was more pronounced.

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