Charge Carriers Cascade in a Ternary TiO₂/TiO₂/ZnS Heterojunction: A DFT Study

Abstract

Composite materials whose band alignment induces a favorable separation of photogenerated electrons and holes often reveal a stronger photocatalytic activity compared to their separate components. As shown by experiments, titania composites display a heterojunction between the anatase (101)‐(001) surfaces, where the former stabilizes electrons and the latter the holes. In principle, an even more efficient carriers separation is achieved if a third component with high hole‐stabilizing capability, ZnS(110), is growth on anatase (001). However, even though this ternary TiO2/TiO2/ZnS composite material displays good photoactivity, it does not overperform the TiO2/TiO2 one. In this paper an explanation of this evidence is provided by means of periodic hybrid DFT calculations, showing how Coulomb forces play a role against the separation of charge carriers predicted based on the relative energy of the band edges. This highlights the necessity to explicitly account for structural and electronic junction's effects, as well as charge carriers’ localization.

LaFeO3 meets nitrogen-doped graphene functionalized with ultralow Pt loading in an impactful Z-scheme platform for photocatalytic hydrogen evolution

“…42,43 The band offsets were calculated by aligning the band edges of the composing units using as a reference the energy of the 1s core levels, as in XPS measurements, [44][45][46] and in DFT calculations of interfaces, see also the ESI. † [47][48][49][50][51] The calculated valence band offset (VBO), 0.74 eV, and conduction band offsets (CBO), 0.44 eV, are comparable to the measured ones, Fig. 3, with errors that are in the typical range of accuracy of band alignment approaches.…”

Nature and Role of Surface Junctions in BiOIO3 Photocatalysts

“…[ 48,54,58,65 ] In the explicit heterojunction model, the band edges are referred to the V TOP values calculated in independent slabs ( V TOP (010) , V TOP (100) ) and in the junction system ( V TOP (010),junc , V TOP (100),junc ). [ 54,58,66 ] In this way a direct comparison of experimental and calculated band alignment is possible.…”

Rational Design of Semiconductor Heterojunctions for Photocatalysis

“…This results in a ternary TiO 2 /TiO 2 /ZnS composite, investigated with the CRYSTAL code and the PBE0 functional. [117] New ZnÀ O and TiÀ S bonds form at the interface between TiO 2 and ZnS giving rise to non-negligible structural reconstruction, also beyond the interfacial region.…”

“…The resulting band alignment, obtained by considering electronic states on inner layers, is of Type‐II, Figure 9 , and is predicted also by the independent units model. [ 117 , 118 ] The picture provided by the band alignment was assessed by simulating the explicit formation of a hole in the VB and of an electron in the CB according to a singlet‐triplet excitation process. [119] The vertical excitation was followed by a structural relaxation that leads to hole and electron localization and polaron formation.…”