Self-constructed facet junctions on hexagonal CdS single crystals with high photoactivity and photostability for water splitting

Crystal facets engineering of semiconductor catalysts with different exposed facets has been proven as a versatile approach to enhance their photocatalytic performance. Herein, for the first time, a facet junction engineered hexagonal CdS single crystal with exposing {0001} and {10 (1) over bar0} facets was synthesized by hydrothermal reaction via adjusting the molar ratio of S2-/Cd2+ precursor. The co-exposed {0001} and {10 (1) over bar0} facets on hexagonal CdS single crystals with continuous band bending and well-defined epitaxial interfaces showed highly efficient visible-light-induced H-2 evolution. The maximum photocatalytic H-2 production rate of 24.33 mmol h(-1) g(-1) is obtained over the facet-junction engineered hexagonal CdS-5 single crystals with an apparent quantum efficiency of 11.18% at 470 nm, which is about 5.27 times greater than CdS-1 nanoparticles. Also, superior photostability is also achieved, even after 25 consecutive cycles during 100 h light irradiation keeping impregnated in strong alkaline sacrificial agent beyond 20 days, the initial photoactivity is still remained. The enhanced photocatalytic H2 evolution activity and photostability can be ascribed to the type-II band alignment between the co-exposed {0001} and {10 (1) over bar0} facets that significantly promoted the separation rate of photo-generated electrons and holes. And the small amount of sulfur vacancies are also benefit for the photocatalytic hydrogen evolution activity of CdS-5. The time-resolved fluorescence (TRPL) decay and photoelectrochemical test further proved the effective spatial charge separation. This work provides a feasible and simple strategy for designing of facet-junction engineered CdS single crystals with highly efficient photocatalytic activity and unprecedented photostability.