ZnGa<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>S<sub>4</sub> (0 ≤ <i>x</i> ≤
0.4) and Zn<sub>1–2<i>y</i></sub>(CuGa)<sub><i>y</i></sub>Ga<sub>1.7</sub>In<sub>0.3</sub>S<sub>4</sub> (0.1
≤ <i>y</i> ≤ 0.2): Optimize Visible Light
Photocatalytic H<sub>2</sub> Evolution by Fine Modulation of Band
Structures
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Abstract
Band structure engineering
is an efficient technique to develop desired semiconductor photocatalysts,
which was usually carried out through isovalent or aliovalent ionic
substitutions. Starting from a UV-activated catalyst ZnGa<sub>2</sub>S<sub>4</sub>, we successfully exploited good visible light photocatalysts
for H<sub>2</sub> evolution by In<sup>3+</sup>-to-Ga<sup>3+</sup> and
(Cu<sup>+</sup>/Ga<sup>3+</sup>)-to-Zn<sup>2+</sup> substitutions.
First, the bandgap of ZnGa<sub>2–<i>x</i></sub>In<sub><i>x</i></sub>S<sub>4</sub> (0 ≤ <i>x</i> ≤ 0.4) decreased from 3.36 to 3.04 eV by lowering the conduction
band position. Second, Zn<sub>1–2<i>y</i></sub>(CuGa)<sub><i>y</i></sub>Ga<sub>1.7</sub>In<sub>0.3</sub>S<sub>4</sub> (<i>y</i> = 0.1, 0.15, 0.2) provided a further
and significant red-shift of the photon absorption to ∼500
nm by raising the valence band maximum and barely losing the overpotential
to water reduction. Zn<sub>0.7</sub>Cu<sub>0.15</sub>Ga<sub>1.85</sub>In<sub>0.3</sub>S<sub>4</sub> possessed the highest H<sub>2</sub> evolution rate under pure visible light irradiation using
S<sup>2–</sup> and SO<sub>3</sub><sup>2–</sup> as sacrificial
reagents (386 μmol/h/g for the noble-metal-free sample and 629
μmol/h/g for the one loaded with 0.5 wt % Ru), while the binary
hosts ZnGa<sub>2</sub>S<sub>4</sub> and ZnIn<sub>2</sub>S<sub>4</sub> (synthesized using the same procedure) show 0 and 27.9 μmol/h/g,
respectively. The optimal apparent quantum yield reached to 7.9% at
500 nm by tuning the composition to Zn<sub>0.6</sub>Cu<sub>0.2</sub>Ga<sub>1.9</sub>In<sub>0.3</sub>S<sub>4</sub> (loaded with
0.5 wt % Ru)