Indium sulfide-based photocatalysts for hydrogen production and water cleaning: a review

Solar illumination is a promising source of primary energy to reduce global warming and to clean polluted waters, thus fostering research of the design of efficient photocatalysts for hydrogen production by water splitting and for contaminant degradation. In particular, photocatalysis by indium sulfide (In₂S₃) is drawing attention due to its suitable narrow bandgap of 2.0–2.3 eV for visible light harnessing, yet large-scale application of unmodified In₂S₃ is limited. Here we review the photocatalyst criteria for water splitting, the synthesis and morphological manipulations of In₂S₃, the synthesis of heterojunctions by coupling semiconductors to increase performance, and doping In₂S₃. In₂S₃-based heterojunctions, i.e., traditional type II, all-solid-state, and direct Z-scheme photocatalytic systems show benefits such as larger charge separation, broad solar spectrum absorption, and amended conduction band and valence band edge potentials for maximum pollutant removal and H₂ production. The effect of dopant incorporation on electronic modulations of In₂S₃ is explained by the density functional theory.