Understanding the Electronic Structures of Graphene Quantum Dot Physisorption and Chemisorption onto the TiO2 (110) Surface: A First-Principles Calculation

We investigated the interfacial electronic structure and charge transfer properties of graphene quantum dot (GQD) physisorption and chemisorption on the TiO2 (110) surface from density functional theory calculations. The simulations show that a slight charge transfer occurs in physisorption case while a significant charge transfer takes place in chemisorption configuration. We present a detailed comparison of the similarities and differences between the electronic structures. The similarities originate from the positive work function difference in both the physisorption and chemisorption configurations, which is able to drive electron transfer from GQD into TiO2, leading to charge separation across the GQDTiO2 interface. The differences stem from the interaction between the GQD and TiO2 substrate. For example, GQD bounds to TiO2 surface through van der Waals interactions in the case of physisorption. In the chemisorption configuration, however, there exists strong covalent bonding between them. This leads to much more efficient charge separation for chemisorption than for physisorption. Furthermore, the GQDTiO2 composites show large band-gap narrowing that could extend the optical absorption edge into the visible-light region. This should imply that chemisorbed GQDs produce a composite with better photocatalytic and photovoltaic performance than composites formed through physisorption.