Abstract
A new paradigm for photocatalysts based on two different hierarchically structured honeycomb and porous cylindrical Au-ZnO heterostructures was successfully developed via a straightforward and cost-effective hydrothermal method under different preparation conditions, which can be promising for industrial applications. The photocatalytic performance of all as-prepared samples under the illumination of sunlight was evaluated by the photocatalytic degradation of rhodamine B (RhB) and malachite green (MG) aqueous solutions. The results show that the photocatalytic degradation efficiency of RhB and MG was 55.3% and 40.7% for ZnO, 95.3% and 93.4% for the porous cylindrical Au-ZnO heterostructure, and 98.6% and 99.5% for the honeycomb Au-ZnO heterostructure, respectively. Compared with those from the ZnO, the results herein demonstrate an excellent reduction in the photoluminescence and improvement in the photocatalysis for the Au-ZnO hybrids with different morphologies. These results were attributed not only to the greatly improved sunlight utilization efficiency due to the surface plasmon resonance (SPR) absorption of Au nanoparticles in the visible region coupled with the UV light utilization by the ZnO nanostructures and multi-reflections of the incident light in the pore structures of their interior cavities but also to the high charge separation efficiency and low Schottky barrier generated by the combination of Au nanoparticles and ZnO micromaterials. Moreover, the honeycomb Au-ZnO heterostructure had a high Au content, surface area and surface oxygen vacancy (OV), which enabled photocatalytic properties that were higher than those of the porous cylindrical Au-ZnO heterostructures. In addition, two different formation mechanisms for the morphology and possible photocatalytic mechanisms are proposed in this paper.
Highlights
To overcome the aforementioned drawbacks, a workable solution to improve the optical absorption capacity and reduce charge recombination of ZnO is desired
The new Au-ZnO heterostructures were uncomplicated, inexpensive and easy to synthesize and showed decreased PL intensity and enhanced degradation efficiency, which can be promising for cost-efficient and uncomplicated ordinary laboratory research and industrial applications
The morphology evolution was investigated with Scanning electron microscopy (SEM) and BET tests were carried out to observe the amount of Au nanoparticles, morphology and specific surface area of the honeycomb and porous cylindrical Au-ZnO heterostructures
Summary
To overcome the aforementioned drawbacks, a workable solution to improve the optical absorption capacity and reduce charge recombination of ZnO is desired. The reported morphologies of Au-ZnO catalysts, including nanorods[32], nanopyramids[33], petal-like structures, urchin-like nanoflowers, nanomultipods, nanopyramids[30] and hollow doughnut-like Au-ZnO catalysts[29], are too complicated for ordinary laboratory research and industrial applications. To address this issue, we proposed a straightforward, cost-effective and uncomplicated hydrothermal method to synthesize Au-ZnO heterostructures. The new Au-ZnO heterostructures were uncomplicated, inexpensive and easy to synthesize and showed decreased PL intensity and enhanced degradation efficiency, which can be promising for cost-efficient and uncomplicated ordinary laboratory research and industrial applications
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