- Titanium dioxide, in the anatase form, is a photocatalyst and has applications in water pollution reduction. Efficiency can be improved with a graphene substrate, which delays electron-hole recombination and may reduce the band gap. In this work, we determine if graphene can also act as a morphactant, changing the shape of anatase particles to expose a larger area of catalytic surface.
Varying slabs of anatase planes – (001), (100), (101), and (110) – were uploaded into SIESTA, a program which undergoes an iterative process to determine the relaxed surface energy. Atom positions within the slab were adjusted slightly and the new surface energy was calculated using Density Functional Theory. A unit cell of graphene was constrained to fit each plane of anatase to reduce end effects. The overall slab energies of anatase (001), (100), (101), and (110) were -959.328, -959.472, -959.065, and -959.472 eV/atom, respectively. The resulting graphene strains produced energies of 0.451, 0.011, 0.044, and 0.022 eV/atom, respectively.
Graphene was then added to the anatase slabs to find relaxed energies of the combination, which are still in progress as they have not converged by the submission of this thesis.
Wulff constructions were created in Mathematica and revealed that lowering the (100) surface energy would yield the lowest overall energy and be the most favorable configuration. However, for the photocatalytic surface of (001) to be maximized, the surface energy of the (101) plane would need to be reduced. Future work should focus on making the addition of graphene, or another substrate, to the (101) anatase surface more favorable than addition to the (100) surface. The difference in overall energy between the two planes is only 0.1 J/m2, so the reduction in surface area of (101) by graphene does not need to be much larger than (100) to favor the best configuration for (001).