One-step in situ synthesis of CdS/SnO2 heterostructure with excellent photocatalytic performance for Cr(VI) reduction and tetracycline degradation

The heterointerface between different components of composite photocatalyst, which acts as the channel of charge transfer, is of crucial importance to photocatalytic performance. In this study, a series of tightly connected CdS/SnO2 heterojunction photocatalysts were prepared via simple hydrothermal process containing CdSnO3·3H2O as templates and thiourea as sulfur source. The crystal phase, morphology, interface structure, and composition of the obtained samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. It was found that the size and morphology of CdS/SnO2 composites can be conveniently controlled by using different CdSnO3·3H2O templates. The results of UV-vis diffuse reflectance spectrum (DRS), electrochemical impedance spectroscopy (EIS) and photoluminescence spectra (PL) demonstrated that the formation of ultrasmall CdS/SnO2 heterostructure remarkable enhance visible light absorption and effectively promote the separation of photogenerated charge carriers. Moreover, the formed intimate heterointerface can maximize the superior electron conductivity of SnO2 and thus, greatly speed up the transfer of photo-generated electron. Compared to the single CdS, the CdS/SnO2 composites exhibited excellent photocatalytic performance towards Cr(VI) reduction and tetracycline (TC) degradation under visible light irradiation, which was ascribed to the enhanced visible light absorption and rapid separation of electrons and holes. The trapping experiments and ESR proved that ·O2– and h+ are the primary reactive species involved in the photocatalytic degradation of TC. 3D EEMs results indicated that the CdS/SnO2 heterojuction photocatalysts owned strong mineralization ability on the TC molecules degradation. The energy band alignments of CdS/SnO2 heterostructure were determined by combining DRS and XPS results. Ultimately, a possible photocatalytic mechanism was proposed.