Towards full-spectrum photocatalysis: Achieving a Z-scheme between Ag2S and TiO2 by engineering energy band alignment with interfacial Ag

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Abstract
A Z-scheme is a promising approach to achieve broad-spectrum photocatalysis. Integration of TiO2 with another semiconductor with a band gap of ∼1.0 eV would be ideal to harvest both ultraviolet and visible-near infrared light for photocatalysis; however, most narrow-bandgap semiconductors have straddling band structure alignments with TiO2, constituting an obstacle to forming the Z-scheme for photocatalytic hydrogen production. In this communication, we demonstrate Ag2S as a model system where the energy band upshift of the narrow-bandgap semiconductor that shares an interface with a metal can overcome this limitation. To fabricate the design, we developed a unique approach to synthesize Ag2S–Ag–TiO2 hybrid structures. The obtained ternary hybrid structures exhibited dramatically enhanced performance in photocatalytic hydrogen production under full-spectrum light illumination. The activities were significantly higher than the sum of those of Ag2S–Ag–TiO2 structures under λ < 400 nm and λ > 400 nm irradiation as well as those of their counterparts under any light illumination conditions.

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