Rational Band Design in Metal Chalcogenide Ba6Zn6HfS14: Splitting Orbitals, Narrowing the Forbidden Gap, and Boosting Photocatalyst Properties

The insufficient light sources absorption often limits photocatalyst applications of metal chalcogenides because of their excessively broad band gap. Thus, it is necessary to discover and design a compound with a rational band gap. Here, a new visible-light photocatalyst, Ba6Zn6HfS14, is prepared through a traditional high temperature solid-state reaction. A set of experiments on the visible-light decomposition of methylene blue demonstrated that the photocatalytic efficiency of Ba6Zn6HfS14 (0.00761 min–1) is improved, compared to that of Ba6Zn6ZrS14 (0.00553 min–1), which proved to be a previously reported visible-light photocatalyst with a similar structure. The UV–visible reflection spectra demonstrated that the energy gap of Ba6Zn6HfS14 (E 1 = 1.45 eV; E 2 = 2.55 eV) is smaller than that of Ba6Zn6ZrS14 (E 1 = 1.78 eV; E 2 = 2.50 eV; E 3 = 2.65 eV). The Ba6Zn6HfS14 absorbs more visible light and exhibits preferably photocatalytic activity. The origin of split energy bands was elucidated via the first calculations.