Modification of ZnS1−x−0.5yOx(OH)y–ZnO photocatalyst with NiS for enhanced visible-light-driven hydrogen generation from seawater

• ZnS1−x−0.5yOx(OH)y–ZnO as photocatalyst, NiS as co-catalyst and S2− and SO32− as electron donors.
• NiS modification promotes activity of the photocatalyst for hydrogen evolution.
• The activity is dependant of the modification method, and method A is better than method B.
• Without NiS, the activity in seawater-ED (electron donors) is lower than that in water-ED.
• With NiS modification, the activity in seawater-ED is higher than that in water-ED.

NiS was loaded on ZnS1−x−0.5yOx(OH)y–ZnO photocatalyst by two methods (depositing NiS on the photocatalyst via impregnation with a NiS sol and via a precipitation reaction). The activity of the NiS-modified photocatalyst for hydrogen evolution from pure water and seawater was investigated using mixed electron donors (sulfide and sulfite). The activity (in pure water-electron donor solution) is dependant of the modification method and loading content of NiS. When Na2S·9H2O and Na2SO3 are added into seawater, a mixture precipitate (Mg(OH)2 and CaSO3) produces. The precipitate is detrimental to the photocatalytic hydrogen evolution over the unmodified ZnS1−x−0.5yOx(OH)y–ZnO. However, for the NiS-modified photocatalyst, the detrimental effect decreases notably. Interestingly, the activity of the modified photocatalyst in seawater-electron donor solution (with the precipitate) is higher than that in the pure water-electron-donor solution (without the precipitate). The possible mechanism was discussed.

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