Photocatalytic H2 evolution over basic zincoxysulfide (ZnS1−x−0.5yOx(OH)y) under visible light irradiation Original Research Article

A composite visible light photocatalyst was prepared through co-precipitation of Zn(NO3)2 in the mixed solution of aqueous Na2S and NaOH, and calcination in N2 atmosphere. The photocatalyst was characterized by thermogravimetric and differential thermal analysis (TG–DTA), X-ray diffraction (XRD), UV–vis diffusive reflectance spectroscopy (DRS), BET and electrochemistry measurements. Its activity was evaluated by hydrogen production from an aqueous solution containing Na2S and Na2SO3 as hole scavengers under visible light (λ ≥ 420 nm) irradiation. The photocatalyst is a mixture of basic zincoxysulfide (ZnS1−x−0.5yOx(OH)y) solid solution and ZnO or only the solid solution. ZnS1−x−0.5yOx(OH)y, which was visible light active, was a solid solution of ZnS with dissolved oxygen and hydroxide groups. Hydroxide groups are very important in the formation and stabilization of the solid solution. The precipitation and calcination temperatures as well as the precursor composition of ZnS1−x−0.5yOx(OH)y have great influence on the photocatalytic activity. With 1:1 calculated molar ratio of ZnS to ZnO (or Zn(OH)2), ZnS1−x−0.5yOx(OH)y photocatalyst prepared via co-precipitation at 373 K and calcination at 673 K under N2 atmosphere exhibits the highest activity. Its apparent quantum yield without noble metal cocatalyst is ca. 3.0% under visible light irradiation.