Electronic Structure and Charge Transfer in the TiO₂ Rutile (110)/Graphene Composite Using Hybrid DFT Calculations

Abstract

Composite systems of TiO 2 with nanocarbon materials, such as graphene, graphene oxide and carbon nanotubes, have proven to be e cient photocatalyst materials. However, detailed understanding of their electronic structure and the mechanisms of the charge transfer processes is still lacking. Here, we use hybrid density functional theory calculations to analyse the electronic properties of the ideal rutile (110)-graphene interface, in order to understand experimentally observed trends in photoinduced charge transfer. We show that the potential energy surface of pristine graphene physisorbed above rutile (110) is relatively at, enabling many possible positions of graphene above the rutile (110) surface. We verify that tensile and compressive strain has negligible e ect on the electronic properties of graphene at low levels of strain. By analysing the band structure of this composite material and the composition of the valence and conduction band edges, we show that both the highest occupied states and the lowest unoccupied states of this composite are dominated by graphene, and that there is also a signi cant contribution of Ti orbitals to the two lowest unoccupied bands. We suggest that a transition from graphene-dominated occupied bands to mixed graphene and TiO 2 -based unoccupied bands is responsible for the experimentally observed photoinduced charge transfer from graphene to TiO 2 under visible light irradiation; however, the most stable state for an excess (e.g. photoexcited) electron is localised on the carbon orbitals, which make up the lowest-energy conduction band. This separation of photogenerated electrons and holes makes TiO 2 -graphene an e cient photocatalyst material.

Electronic Structure of Graphene/TiO$_2$ Interface: Design and Functional Perspectives

“…This observation is also supported theoretically, in the case of graphene/rutile(110) interface, using non-adiabatic MD (NAMD) simulations where the photoexcited electron transfer is reported to be several times faster than the electron-phonon energy relaxations [27]. Similar results on charge transfer from C-p to Ti-3d states have also been reported for G/A(101) [18,24,25] and G/R(110) interfaces [26,28]. Irrespective of the orientation of the surface, it is expected that similar kind of charge transfer should occur for G/A(001) interface as well.…”

“…In fact, there are a number of first principle electronic structure calculations that have reported graphene as an overlayer on anatase TiO 2 (001) surface leads to a finite bandgap of 0.45−0.65 eV [21][22][23]. Interestingly, similar calculations report that the graphene does not exhibit any bandgap when it becomes an overlayer on other surfaces such as anatase(101) [24,25] and rutile(110) [26][27][28]. Therefore, it raises two valid possibilities.…”

A Theory/Experience Description of Support Effects in Carbon-Supported Catalysts

“…457 As far as (photo-induced) charge transfer is concerned, both electron transfers from graphene to TiO2 and from TiO2 to graphene have been proposed, according to the energy of the incoming photons (see Figure 34). 669,670 Under visible light, electron excitation occurs from carbon-based states to both C-and Ti-based states (overall electron transfer is from graphene to TiO2). UV photons may produce excitations from Ti-based states again to both C-and Ti-based states (overall electron transfer from TiO2 to graphene).…”

Smart Coatings with Carbon Nanoparticles

“…Modifying these nanofillers with graphene or its derivatives can enhance their visible light response. Hybrid TiO 2 /graphene nanofillers can exhibit strong electronic overlap and high interfacial binding energy; thus, photoexcited carriers can transfer from TiO 2 to graphene, and its band gap is reduced, improving the visible light photoresponse [69,70]. Nevertheless, graphene enhances the photocatalytic efficiency of ZnO due to that graphene accepts the electron from ZnO nanoparticles, preventing the recombination of photo-generated electron hole in the semiconductor.…”