Preparation Of The Heterostructured Composites Containing Cu-Compound For Photocatalytic Hydrogen Production

Photocatalytic hydrogen production from water splitting is a clean and renewable hydrogen production method, because it can convert the inexhaustible and low density solar energy to the chemical energy. Preparing highly efficient photocatalytsts is the key for developing the photocatalytic hydrogen production technology. So far, the applications of many photocatalytic materials in the photocatalytic hydrogen production field have been greatly limited due to the low efficiencies resulted from the easy recombination of photogenerated charge carriers. Therefore, seeking a suitable approach to effectively separate the photogenerated electrons and holes and increase the utilization of photogenerated charge carriers is significant for enhancing the photocatalytic activity for hydrogen production. Heterostructured materials have unique advantages for the transportation of carriers and exhibit potential values in the photocatalytic hydrogen production field. In this dissertation, the representative TiO2and ZnS were chose as the research objects and the fabrication of highly efficient Cu-cotaining composites heterostructured was as the research aim. We addict to develop highly efficient Cu-cotaining composites heterostructured photocatalysts with special morphology via increasing the driven force of the photogenerated charge carriers transfer. Main research topics are as follows:1. Based on the effect of the bandgap structure on the separation of photogenerated charges, we prepared q-Cu2O/TiO2heterojunction composites with excellent charges separation efficiency via ethanol induced method at low temperature followed by calcination. The Cu2O nanosize was controlled by adjusting the amount of Cu2O precursor. The qautum size effect maked the conduction band bottom of Cu2O shift up. This can efficiently increase the potential gradient between the conduction band bottom of Cu2O and that of TiO2, and thus enhance the driven force of the interfacial charges transfer. On the other hand, the energy band structure of Cu2O was tuned by the quantum size effect, which makes the electrons transfer from Cu2O to TiO2. The transfer was consistent with that in p-n junctions controlled by the built-in electrical field resulting in the enhanced photocatalytic activity for hydrogen production. This study not only provides a facial and green method to prepared Cu2O quantum dots on TiO2surfaces, but also supports an efficient approach to fabricate p-n heterojunctions with an increased interfacial charge transfer.2. Based on the relation between the charge separation of heterojuntions and the potentials of the insoluble non-semiconductor compounds, we find an facile method to develop efficient heterostructured composites. The separation of the photogenerated electrons and holes in the CuX/P25heteroj unctions was easily controlled by tuning the CuX/Cu electrode potentials, which was closely related to the solubility (Ksp) of insoluble non-semiconductor compounds. This can be achieved by simply changing the anion species in CuX (X:(OH)2CO32-、S2-、OH-、 C2O42-). According to this method, we have found that the Cu2(OH)2CO3/Cu reduction potential is between the conduction band bottom of P25and the redox potential of H+/H2with a relatively large potential gradient. Thus, Cu2(OH)2CO3can be used as an excellent co-catalyst to build heteroj unction composites with P25, which exhibited an excellent charge separation efficiency and photocatalytic hydrogen production activity. The photocatalytic activity for hydrogen production of the heteroj unction composites was up to0.51mmol h-1under the simulant solar light irradiation, and the quantum efficiency was up to31.2%which was485times higher than that of pure P25. This work develops an excellent cocatalyst-Cu2(OH)2CO3for photocatalytic hydrogen production as well as provides an facile and efficient method for fabricating heteroj unction composite photocatalysts.3. Considering the advantages of morphology control in photocatalytic hydrogen production, the flower-like ZnS/CuS heterostructured composites were prepared by the combination of microwave hydrothermal and cation exchange methods according to the interfacial charge transfer theory. The fabrication of the heterojunctions broadened the range of light response of ZnS. The photoexcited electrons of ZnS migrated to the redox potential of CuS/Cu2S under visible light irradiation, which can facilitate the effective separation of photogenerated electrons and holes in space. The visible photocatalytic activity towards hydrogen production for ZnS/CuS flower-like heterostructed composites without co-catalyst achieved0.33mmol h-1, and the quantum efficiency was up to22.8%under the wavelength with420nm visible light irradiation. Compared with the sheet-like photocatalyst composite, hydrogen production activity and quantum efficiency were improved. It proved that when both have photoinduced interfacial charge transfer (IFCT) effect, heterostructures photocatalyst composites with special morphology which possess high surface area and light absorption rate, have outstanding advantages in photoinduced charge separation. In addition, the formation mechanisms of the flakes and flower-like ZnS/CuS heterojunctions were also studied in detail by tuning the reaction time and temperature. Finally the relationship of the microstructure and the performance was revealed.