Remarkably efficient charge transfer through a double heterojunction mechanism by a CdS-SnS-SnS2/rGO composite with excellent photocatalytic performance under visible light.

In this work, a novel CdS-SnS-SnS2/rGO photocatalyst with two tin valence states (Ⅱ and IV) was successfully synthesized by a one-pot solvothermal method. For comparison, CdS-SnS2/rGO (GCS2) with tin in only the IV valence state was made by the same method. Based on a series of characterizations, CdS, SnS and SnS2 were shown to be successfully loaded onto the rGO surface. The introduction of rGO may increase charge carrier separation. The degradation efficiency increased gradually with increasing rGO loading content, and the optimum photocatalytic activity was observed at 6.0 wt% rGO loading content (GCS1), which achieved the efficient removal (84.46%) of ibuprofen over 60 min. Compared with GCS2, the CdS-SnS-SnS2/rGO composite exhibited significantly improved photocatalytic performance, which can be ascribed to the formation of a double heterostructure. rGO worked as a transfer mediator to transfer electrons from the conduction band (CB) of SnS to the CB of SnS2 at the heterointerface, which then flowed to the CB of CdS because of another heterojunction, further enhancing the separation efficiency of photogenerated carriers. Therefore, this study highlights a novel double heterojunction system with a facial preparation method, visible light response and good recyclability, which is beneficial for environmental remediation.