Enhanced photo-reduction performance of CuInS2 for aqueous Cr(VI) via facile combining with Bi2S3: a direct Z-scheme mechanism

Recombination and redox energy declination of photo-induced carriers in their transfer over photocatalysts cause loss of efficiency in photodegradation of contaminants. Constructing a Z-scheme transfer mechanism of them is considered as a promising approach to boost the photocatalytic activity. Herein, direct Z-scheme CuInS2/Bi2S3 heterojunctions were successfully fabricated by a facile one-step hydrothermal method. The obtained photocatalysts were systematically characterized and used for the photo-reduction of aqueous Cr(VI) under visible light irradiation. The results showed that the optimal composite with a 24 wt% Bi2S3 content exhibited a superior photocatalytic activity, which was 4.12 times greater than that of pristine CuInS2, and subsequent cycling experiments demonstrated its excellent photocatalytic stability. Besides, the direct Z-scheme heterostructure of CuInS2/Bi2S3 was corroborated by trapping experiments and XPS measurement, which effectively facilitated the spatial charge separation and kept the photo-induced electrons with a strong reducing ability in the conduction band of CuInS2, thus resulting in its outstanding photocatalytic performance towards the reduction of Cr(VI). This study provides a feasible strategy to improve the photoreduction performance of CuInS2-based composites for Cr(VI)-containing wastewater treatment.