Ag₂O-assisted Synthesis Of Hollow Nanostructure Semiconductors And Their Photocatalytic Properties

Micrometer- and nanometer-sized hollow structures, especially hollow octahedral, have stimulated intense interest in photocatalytic fields during past decades, primarily owing to their high specific surface area and strong light absorption. Nevertheless, other than hollow spherical structures which have been obtained in most cases, fabricating well-defined hollow octahedron suffers from technological difficulties such as(i) the lack of proper and easily obtained octahedral templates,(ii) difficult formation of a uniform coating around high-curvature surfaces of the octahedral templates. Therefore, the controllable synthesis of hollow nanometer-sized photocatalyst with octahedral morphologies is recondite, challenging, and still much needed. On the other hand, the Ag-based materials have exhibit tremendously potential applications in photocatalytic field due to their excellently visible-light photocatalytic activity. To further enhance their photocatalytic activity, one of the most effective methodologies is to fabricate octahedral Ag-based photocatalyst with hollow interior. Herein, we construct a template-assisted approach to synthesize well-defined, octahedral Ag2 S and Ag Cl nanocages by using octaherdal Ag2 O nanocrystals as sacrificial templates. The main results were summarized as follows:First, we demonstrated that ultrathin octahedral Ag2 S nanocages with a wall thickness of 4 nm were successfully prepared through controlled displacement reaction between corresponding Ag2 O crystals and thiourea. The influenting factors for controlled synthesis of various Ag2 O morphologies and microstructures such as sulfur sources(thiourea and Na2S), solvents(water and alcohol), and reaction time were explored in detail. By following characterization(such as SEM, TEM, XRD, and UV-vis), the corresponding results indicated that the reaction medium and sulfur source were the two keys in the formation of the special nanostructures of Ag2 S in this case. The formation mechanism for different shaped Ag2 S hollow structure can be ascribed to different releasing ways of Ag+ and S2- in different sufur sources and solvent medium, which thus results in different nucleation and growth of Ag2 S. In following photocatalytic tests, Ag2O@Ag2S octahedron sample exhibits obviously higher photocatalytic activity(k = 0.04 /min) than Ag2 O octahedron by a factor of 3.6 for photocatalytic decolorization of MO. The enhanced photocatalytic activity of Ag2O@Ag2S could be attributed to the specific ultrathin octahedral structures of Ag2 O and good energy level match and coupling between Ag2 O and Ag2 S to promote effective separation of photogenerated electrons and holes.Second, porous octahedral Ag Cl hollow structure was prepared by Ag2 O crystals as sacrificial templates via Kirkendall diffusion. The influenting factors for controlled synthesis of various Ag2 O morphologies and microstructures such as the concentration of Ti Cl4, volum ratios of alcohol to water, and reaction time were explored in detail. By following characterization(such as SEM, TEM, XRD, and UV-vis), the corresponding results indicated that uniform, well-defined, and porous Ag Cl hollow octahedron was successfully synthesized under the optimum conditions. The formation mechanism of porous Ag Cl hollow octahedron is contributed by Kirkendall Effect(the different diffusion rate between Ag+ and Cl-). The porous Ag Cl hollow octahedron(k = 0.39 /min) is almost twice as fast as the simple precipitation of Ag Cl to decolorize MO solution, and the former is more stable in repeated cycles. Obviously,the porous Ag Cl hollow octahedron endows this material more efficient use of light source, higher specific surface area, and the plasmon resonance absorption of Ag nanoparticles, which results in excellent photocatalytic activity.In this paper, we construct a general route to prepare varieties of octahedral hollow structures of Ag based compounds. The present works can provide some novel insights into the smart design and preparation of other non-spherical hollow materials, and meanwhile, give an effecitve access to further enhance photocatalytic activity of Ag-based photocatalytic materials.