Zinc hydroxystannate/zinc-tin oxide heterojunctions for the UVC-assisted photocatalytic degradation of methyl orange and tetracycline.

Partial phase modification of zinc hydroxystannate (ZHS) is an effective technique for improving its light absorption capacity. In this study, a zinc hydroxystannate/zinc-tin oxide (ZHS/ZTO) heterostructure was synthesized via chemical co-precipitation followed by annealing. The as-prepared heterostructure revealed cubic crystal morphology along with high-intensity diffraction peaks in the XRD pattern. The XPS analysis of ZHS/ZTO heterostructures demonstrated the presence of key elements (Zn, Sn, and O) in their most stable ionic forms. The photocatalytic degradation efficiencies of the prepared samples were tested against methyl orange (MO) and tetracycline (TC) in an aqueous medium under UVC (254 nm) radiation. Under optimized conditions, maximum degradation efficiencies of 99% for MO and 97% for TC were observed in 120 and 180 min, respectively. Further, the predominant role of OH˙ radicals in the photocatalytic removal of MO and TC was evident through scavenging experiments. 2nd order kinetic model was outperformed in simulating the degradation mechanism of both targets over 1st and zero-order kinetic models. Finally, a photocatalytic degradation mechanism is proposed based on the energy values estimated for the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) using UPS analysis.

Improved Photoresponse Characteristics of a ZnO-Based UV Photodetector by the Formation of an Amorphous SnO2 Shell Layer.

Although ZnO nanostructure-based photodetectors feature a well-established system, they still present difficulties when being used in practical situations due to their slow response time. In this study, we report on how forming an amorphous SnO2 (a-SnO2) shell layer on ZnO nanorods (NRs) enhances the photoresponse speed of a ZnO-based UV photodetector (UV PD). Our suggested UV PD, consisting of a ZnO/a-SnO2 NRs core-shell structure, shows a rise time that is 26 times faster than a UV PD with bare ZnO NRs under 365 nm UV irradiation. In addition, the light responsivity of the ZnO/SnO2 NRs PD simultaneously increases by 3.1 times, which can be attributed to the passivation effects of the coated a-SnO2 shell layer. With a wide bandgap (~4.5 eV), the a-SnO2 shell layer can successfully suppress the oxygen-mediated process on the ZnO NRs surface, improving the photoresponse properties. Therefore, with a fast photoresponse speed and a low fabrication temperature, our as-synthesized, a-SnO2-coated ZnO core-shell structure qualifies as a candidate for ZnO-based PDs.