One-Pot Synthesis of a CoS_X@Ag₂S/CdS Z-Scheme Photocatalyst for RhB Photodegradation and Cr(VI) Photoreduction

A ternary metal sulfide was designed as a photocatalyst for removal of pollutants. CoS_X@Ag₂S/CdS nanostructures were prepared using ZIF-67 derived for CoS_X via a one-pot solvothermal method. It is noteworthy that the partial formation of the hollow structure occurred concurrently with the generation of bimetallic sulfide particles on the surface of CoS_X particles. The synthetic conditions were optimized by controlling the temperature, time, and ZIF-67 amount. The resulting structure showed high photoactivity and was used for remediation of a water pollutant. The photocatalyst successfully degraded rhodamine B (RhB) with a 96% degradation rate within 90 min. Additionally, Cr(VI) could be efficiently reduced with 100% efficiency within 50 min at pH 5 under exposure to visible light (light-emitting diode, 100 W). The photocatalyst also demonstrated excellent activity in the remediation of a mixture of RhB and Cr(VI). Such photoactivity was attributed to the unique architecture of CoS_X@Ag₂S/CdS in generating the n-n-n type I hybrid Z-scheme, compared to single and double components. It also results in a synergistic effect between metal sulfides and the hollow structure, which enhances the light absorption, surface area, and active sites. It is proposed that the photocatalytic mechanism relies on a combination of a Z-scheme and a type I mechanism.