Sisal-like Sn2+ doped ZnO hierarchical structures: synthesis, growth mechanism, and their application in photocatalysis

By introducing SnCl2 into the reaction system, the sisal-like Sn doped ZnO hierarchical structures were prepared by the hydrothermal method without employing templates or matrices. Based on the electron microscope observations, the growth of such hierarchitectures has been proposed as a self-assembly followed by Ostwald ripening process. The effects of the reaction time and dosage of SnCl2 on the morphology, structure, and performance of the samples were systematically investigated. With the increase of SnCl2 dosage from 0 to 10 mmol, the band gap value of the as-synthesized samples decreased from 3.14 to 2.73 eV, and then increased again to 2.77 eV. The photocatalytic activities of the as-prepared sisal-like Sn doped ZnO hierarchical structures were about 1.64 times higher than that of the pure ZnO samples. The results showed that the photocatalytic activity of ZnO can be improved by appropriate Sn doping. In addition, the sisal-like Sn doped ZnO hierarchical structures were recyclable and showed very small change in activity after five consecutive cycles, which might be due to their small band gap, large surface area, as well as the unique morphology.