Hydrothermal Synthesis of a Doped Mn‐Cd‐S Solid Solution as a Visible‐Light‐Driven Photocatalyst for H 2 Evolution

The effect of metal doping (i.e., with Cr, Fe, Ni, Cu, Zn, Ag and Sn) on the crystal structure of hydrothermally synthesized Mn 1− x Cd x S (where x ≈0.1) is studied with the aim of enhancing photocatalytic activity. In contrast to the low‐crystalline, undoped solid solution Mn 1− x Cd x S, Ni doping yields a well‐crystallized wurtzite‐type Mn‐Cd‐S solid solution, which precipitates as planar hexagonal facets of several hundred nanometers in size, together with much larger grains of α‐MnS (>10 μm). By removing inactive α‐MnS through sedimentation, a single phase with composition of Ni 0.01 Mn 0.56 Cd 0.43 S is obtained successfully. The Ni doping achieved a threefold higher photocatalytic activity for H 2 evolution from a 0.1  M Na 2 S/0.5  M Na 2 SO 3 solution under visible‐light irradiation ( λ ≥420 nm). The apparent quantum yield of 1 wt % Pt‐loaded Ni 0.01 Mn 0.56 Cd 0.43 S measured at λ =420 nm reached 25 %. The enhanced photocatalytic activity is most likely the result of a decreased concentration of defects, responsible for electron–hole recombination, in the active solid‐solution phase and a slightly higher bandgap energy (2.4 eV).