Significant Enhancement In Photoelectrochemical And Photocatalytic Activities Of ?GaN?_1-x?ZnO?_x Nanowires Via Solubility And Crystallographic Facet Tailoring

In recent years,energy shortage and environmental pollution have become two globaly concerned issues.Semiconductor photocatalysis is an ideal green technology which can convert solar energy into chemical energy through degradation of organic pollutants,water splitting and carbon dioxide reduction.Among the various semiconductor materials,gallium nitride and zinc oxide are two important photocatalytic materials.Although the band gap of these two materials is relatively wide and can only absorb UV light,they can form a solid solution with the same crystal structure.More interestingly,theoretical calculation has shown that the conduction band?CB?bottom of?GaN?_1-x?ZnO?_x solid solution is mainly composed of Ga 4s and 4p orbitals,while the valence band?VB?top consists of N 2p and Zn 3d orbitals,from which the p-d repulsion results in rising of the valence band top.Therefore,the energy band structure of?GaN?_1-x?ZnO?_x can be continuously regulated by adjusting the content of ZnO or GaN in the solid solution material.On the other hand,one-dimensional structure catalyst with large specific surface area,can provide more reactive sites in the photocatalytic reaction.In this thesis,we report on solubility and crystallographic facet tailoring of?GaN?_1-x?ZnO?_x solid solution nanowires for significant enhancement in photoelectrochemical and photocatalytic activities.?GaN?_1-x?ZnO?_x nanowires were fabricated via a simple chemical vapor deposition?CVD?method by using pre-synthesized ZnGa₂O₄ as precursor.The?GaN?_1-x?ZnO?_x nanowires with different ZnO concentrations were obtained by adjusting the growth temperature.With the decrease of the growth temperature,the content of ZnO in the synthesized nanowires gradually increased and the nanowires gradually changed from straight to zigzag morphology;meanwhile,the valence band top of the nanowires increased and the band gap decreased.When the growth temperature is as low as 900°C,the band edge was around 460 nm,corresponding to the band gap energy of 2.70 eV.Photocatalytic reactions for CO₂ reduction,water splitting and IPA degradation were comparatively carried out on?GaN?_1-x?ZnO?_x nanowires grown at three temperatures.It was found that the zigzag morphology of nanowires showed significantly enhanced photocatalytic performance in comparison with the straight nanowires.Similar results were also obtained from the photoelectrical experiment.The significantly improved photoelectrochemical properties of zigzag nanowires was more likely due to the enhanced charge carrier separation ability in addition to the stronger absorbance than the straight nanowires.