| Currently, among the semiconductor photocatalysts, metal oxide semiconductors have been widely investigated for degradation of organic pollutants due to its strong photocatalytic activity and photoelectrochemical stability in aqueous media. But as we know, many metal oxide semiconductors are only functional in the UV region owing to their large band gaps, for example,3.0 eV for TiO2 and for 3.2 eV for ZnO, which severely limits their practical applications. Semiconductors with narrow band gaps would be more favorable for the utilization of visible light. Cu2O is regarded as excellent candidates for visible-light photocatalysis because it is a p-type oxide semiconductor with a suitable band gap of 2.0-2.2 eV. In particular, it is inexpensive, ease in preparation, and good environmental acceptability. To date, various Cu2O nanostructured materials have been achieved and used for degradation of organic dyes. However, because of a short hole-diffusion length, there exists an easy recombination of photogenerated electron-hole pairs, which leads to a very low quantum efficiency and limits its promising applications in photocatalysis. Therefore, two kinds of Cu2O-based composite/hybrid materials were designed and fabricated for improving the photocatalytic activity. The main research contents are listed as follow:In chapter 2, spherical Ag-Cu2O/reduced graphene oxide (rGO) nanohybrids with an excellent hierarchical structures are developed through a facile one-pot, a two-stage reduction synthetic route. In the resulted complex heterostructures, both Ag and rGO are in direct contact with Cu2O, and Ag nanocrystals are mainly deposited on the surface of Cu2O spheres. The resultant ternary spherical Ag-Cu2O/rGO composite exhibited excellent photocatalytic activity in photocatalytic degradation of methyl orange (MO) under visible light irradiation, which was much higher than that of either the single component (Cu2O) or two components systems spherical Cu2O/rGO, and Ag-Cu2O. In particular, the recycling degradation experiments show that the stability of ternary composites is more excellent than Ag-Cu2O. The PL spectrum results demonstrated that not only Ag but also rGO could capture the photogenerated electrons from Cu2O, thus leading to effective separation of electrons and holes. Therefore, Ag-Cu2O/rGO composite exhibited enhanced photocatalytic activity. Further research indicates that the rGO-supported sphere-like Ag-Cu2O nanohybrids exhibited higher photoactivity than the sample Ag-rGO-Cu2O ternary composites (including more Ag nanoparticles in direct contact with rGO), indicating that the direct junction between Ag and Cu2O can more effectively separate the photogenerated charges due to the Schottky effects at the metal-semiconductor interface. This work provides an insight into designing and synthesizing new Cu2O-based hybrid materials for effectively improving the photocatalytic performance.In chapter 3, we successfully achieved a new method for preparing Zn0/Cu20 nanohybrids. The Zn(OH)42- was adsorbed on the surface of positively charged Cu2O as a substrate due to their electrostatic interactions. Zn0/Cu20 with hierarchical structures was synthesized by hydrothermal method. The control experiment show that the Zn0/Cu20 composite can be controlled by changing the concentration of base and reaction time. It is found that compared to pure ZnO and Cu2O, Zn0/Cu20 nanocrystals possess a higher catalytic efficiency in photocatalytic degradation of methyl orange (MO) under visible light irradiation. The enhanced photocatalytic performance of the composites was mainly attributed to the introduction of ZnO, which inhibit the recombination of photogenerated electron-hole pairs. Currently, electrochemical deposition method is extensively used to synthesize Zn0/Cu20. Therefore, this work provides an insight into designing and synthesizing Zn0/Cu20 hybrid materials for effectively improving the photocatalytic performance. |
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