A novel In2S3/Gd2O3 p-n type visible light-driven heterojunction photocatalyst for dual role of Cr(VI) reduction and oxytetracycline degradation

Visible light-driven photocatalytic water and wastewater treatment presents a unique option towards combating organic, inorganic and microbial pollution. Herein, we report a novel In2S3/xGd(2)O(3) heterojunction (where x = 5, 10 and 15 wt% Gd2O3) photocatalyst obtained via a combination of hydrothermal and ultrasound assisted synthesis. Detailed characteristic properties of the prepared materials were studied using XRD, UV-Vis-DRS, SEM-EDX, TEM, BET, PL, EIS and XPS. The photocatalysts were investigated for photocatalytic degradation of oxytetracycline (OTC) and reduction of Cr(VI) in aqueous solutions under visible light illumination. Under optimised conditions the In2S3/10 wt%Gd2O3 photocatalyst showed the highest activity for both pollutants, reaching 80.0% OTC degradation and 96.3% Cr(VI) reduction, in just 50 min and 55 min, respectively. The improved activity could be linked to formation of a p-n heterojunction, resulting to more efficient visible utilisation, charge separation and transfer. Moreover, the photocatalyst could be recycled for 5 times with only 7 and 5% decline in activity after the 5th cycle for OTC and Cr(VI), respectively. A Gas chromatography-mass spectrometry (GC-MS) was used to identify the major intermediates during OTC degradation. A possible charge transfer pathway leading to the formation of the redox species was proposed based on the band structure and radical scavenging experiments. Finally, this work demonstrates the versatile nature of In2S3/xGd(2)O(3) nanostructures as promising tools for abatement of both emerging pollutants and Cr(VI) pollution in water.