The interactions between TiO2 and graphene with surface inhomogeneity determined using density functional theory

Abstract

TiO₂/graphene composites have shown promise as photocatalysts, leading to improved electronic properties. We have modeled using density functional theory TiO₂/graphene interfaces formed between graphene with various defects/functional groups (C vacancy, epoxide, and hydroxyl) and TiO₂ clusters of various sizes. We considered clusters from 3 to 45 atoms, the latter a nanoparticle of ∼1 nm in size. Our results show that binding to pristine graphene is dominated by van der Waals forces, and that C vacancies or epoxide groups lead to much stronger binding between the graphene and TiO₂. Such sites may serve to anchor TiO₂ to graphene. Graphene surfaces with hydroxyls however lead to OH transfer to TiO₂ and weak interactions between the graphene and the hydroxylated TiO₂ cluster. Charge transfer may occur between TiO₂ and graphene in various directions (graphene to TiO₂ or TiO₂ to graphene), depending on the state of the graphene surface, based on overlap of the density of states. Our work indicates that graphene surface defects or functional groups may have a significant effect on the stability, structure, and photoactivity of these materials.