| Cu2O is a typical p-type direct band gap semiconductor with a band gap of 2.17 eV and has potential applications in solar energy conversion, electrode materials, sensors, and catalysts. its potential application in catalysts was demonstrated by the discovery that Cu2O could act as a stable photocatalyst for the photochemical decomposition of water into O2 and H2 under visible light irradiation. In this thesis, we report a facile solution-phase route for the mass synthesis of Cu2O crystals with different morphologies, Cu2O nanoframes and nanocages, Cu2O nanospheres. And on the basis of experiment and characterization, we also did an in-depth study on shape, structure, growth, mechanism and catalytic and gas sensor properties. Some important results are obtained.We report a facile solution-phase route for the mass synthesis of Cu2O crystals with different morphologies in the presence of poly (vinyl pyrrolidone) (PVP) at relatively mild temperature of 80℃. In our system, the morphological evolution from cubes to truncated octahedral(R=1), runcated octahedral(R=1.15), octahedra and nanospheres has been investigated by using different amounts of PVP. As a well-known capping or stabilizing agent, PVP molecules with long chains can be adsorbed to the Cu2O particle surfaces via physical and chemical bonding. When we add PVP into reaction system, it is believed that PVP tends to suppress the growth rate of the {111} planes more than that of the {100} planes, since it interacts more strongly with the {111} facets than with the {100} facets. When the PVP concentration is 1.5 mM, this interaction strength is greatly enhanced, and it could efficiently lower the surface energies of {111} facets. The capping effect of PVP would block the growth on the {111} facets and facilitate the growth on the {100} facets. Further increasing the PVP concentration to 4.5 mM, perfect octahedral (R=1.73) are obtained due to the further increase of the growth rate on {100} facets relative to the {111} facets. Finally, spherical particles are generated only when the PVP concentration is 9 mM, owing to the high coverage of PVP on all the planes of Cu2O nanocrystals. Presumably, the steric effect of PVP against agglomeration and growth is fulfilled and the Cu2O particles are smaller, leading to an isotropic growth mode and loose spherical particles. A time-dependent morphology evolution experiments are performed by intercepting intermediate products in different reaction stages. The Cu2O crystals including smaller octahedra, star-shaped and star-shaped with six symmetric branches are obtained. Smaller particles are dissolved again and larger particles grow more, which is typical of Ostwald ripening. This preferential growth at six equivalent {100} facets eventually leads to the formation of six symmetric branch structures on the octahedra. A cut of the unit cell over one of its (111) planes reveals the presence of surface Cu atoms with dangling bonds. Thus, this simple comparison should indicate that the {111} faces are higher in surface energy and expected to be more catalytically active than the {100} faces. This series of experiments is the exceptionally high photocatalytic performance of the extended hexapods. This result suggests that Cu2O nanocrystals with more {111} facets can serve as more efficient photocatalysts. Furthermore, Cu2O crystals bounded by the {111} faces contain positively charged copper atoms at the surfaces, which facilitates the absorption of detected gases.We report low cost, simplicity, green synthetic and efficiency route for Cu2O nanoframes and nanocages with single-crystal walls. Our synthetic strategy involves following processes. First, polyhedra Cu2O particles were prepared by adding weak reductive agent (glucose) into copper citrate complex solution with the use of PVP as capping agents, and then Cu2O nanoframes and nanocages were obtained in situ via the oxidative etching at room temperature. During the hollowing step, the truncated octahedra are selectively etched on the {100} faces. With the increasing aging time, the interior of each truncated octahedra becomes empty increasingly, while the size of the hole in the surface starts to enlarge and to form a frame with relatively thick walls. An important feature of the as-synthesized products is that most of the surface of the six {100} faces is absent. Thus, the Cu2O nanoframes are constructed of hexagonal {111} skeletons. Our results also demonstrated that PVP has acted as a capping agent and that preferential adsorption occurred on the {111} faces of the Cu2O crystals, which'freeze'the {111} planes to facilitate the formation of hollow structure. It should be noted that, the photocatalytic activity of nanocages particles is higher than the nanoframes. This result further suggests that Cu2O particle with more {111} facets can serve as more efficient photocatalysts. Moreover, the photocatalytic activity of hollow particles is higher than the solid particles. This can be attributed to the hollow structure and higher surface area. The hollow structure can allow the appearance of multiple reflections of light within the interior hollow and lead to the more efficient use of light and improve the photocatalytic activity of Cu2O. Furthermore, the hollow structure particles result in larger surface area and much more capacious interspaces than any solid particles, which can provide sufficient space for the interaction between Cu2O and detected gases.We demonstrate a template-free hydrothermal method to synthesize Cu2O hollow spheres at 90℃. The key points of the successful realization are that we introduce PVP to improve the stabilization of crystalline phase occurred at a rate commensurate with localized Ostawald ripening and self-transformation for producting Cu2O hollow spheres. Compared with the conventional methods, the present synthetic procedure has the advantages of simplicity, low growth temperature, and efficiency. TEA may serve as surface modifier, which plays a role of "structure directing agent" which directed the aggregation of the building blocks. Furthermore, the observation on a blue-shift of Cu2O hollow spheres can be rationalized by considering that it is largely attributed to the hollowing of the spheres structures.
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