Synthesis And Catalytic Performance Of Heterojunction Nanomaterials Based On TiO₂ Aggregate Sphere

Since its commercial production in the early 1920 s, titanium dioxide(Ti O2) has succeeded in capturing the attention of scientists in exploring distinctive semiconducting and catalytic properties. Ti O2, as one of the representative semiconductive oxide, has been become one of most widely used semiconductor catalyst, which is due to its advantages such as environmental stability, high catalytic activity, non-toxic, photocorrosion resistance, easy-to-obtain and low-cost etc. However, there are some realities that can’t be ignored during the practical applications of Ti O2, including poor quantum efficiency, narrow range of photoresponse and recycling issue, which restrict the development of Ti O2. Therefore, surface loading and modification has been frequently used in practical applications of Ti O2, especially in the form of heterojunction structure. In this thesis, we mainly focus on the synthesis and catalytic performance of heterojunction nanomaterials based on Ti O2 aggregate sphere. There are six main parts in this thesis:1) The Ti O2 nanoparticle aggregated sphere(Ti O2 NPAS) was prepared by modified sol-gel method. A typical Ti O2 NPAS with diameter of 370-450 nm are packed of interconnected nanocrystals with a diameter of 19.0-21.0 nm. We also obtained the optimal parameter of the experimental condition through orthogonal experimental design. And then, the hierarchical structure and formation mechanism of Ti O2 NPAS were investigated.2) A series Ag2O/Ti O2 NPAS photocatalyst with different weight ratio of Ti O2/Ag2 O were prepared through a surface loading process with chemical precipitation method. The Ag2 O nanoparticles with a diameter of 10.0-60.0 nm are uniformly coated on the surface of the Ti O2 NPAS. The Ag2O/Ti O2 NPAS photocatalysts display a high activity for the degradation of MO under simulated sunlight irradiation, which could achieve the complete mineralization of 14mg/L MO aq. in 60 minutes. And then, the formation of heterojunction structure and the mechanism of degradation were discussed.3) A series plasmonic photocatalysis/Ti O2 NPAS photocatalyst which are Ag-Ag Cl@Ti O2 NPAS photocatalysts and Ag-Ag Br@Ti O2 NPAS photocatalysts were synthesized through a surface loading process with photochemical reduction reaction. The Ag-Ag Cl or Ag-Ag Br nanoparticles with a diameter of 5.0-15.0 nm are uniformly coated on the surface of the Ti O2 NPAS in both types of photocatalysts. Then, we studied the photocatalytic activity of these two types of photocatalysts under visible-light irradiation. With a large range of different Ti O2/Ag X(X=Cl, Br) theoretical weight ratio, both of the plasmonic photocatalysis/Ti O2 NPAS photocatalysts display a high activity for the degradation of MO under visible-light irradiation, which could obtain the complete mineralization of 14mg/L MO aq. in 60 minutes and 40 minutes, respectively. The differences and similarities of the mechanism of degradation with Ag-Ag Cl@Ti O2 NPAS and Ag-Ag Br@Ti O2 NPAS was studied.4) The preparation of the novel Pt/Ti O2 NPAS electrocatalysts was acquired by chemical precipitation method with minor modification. After being coated with Pt nanoparticles the diameter of Pt/Ti O2 NPAS samples are 450-600 nm. Pt nanoparticles about 8.0-20.0 nm in diameter are well supported on the surface of the Ti O2 NPAS samples. Comparing with the commercial Pt/CB electrocatalysts which are commonly used in industry, the Pt/Ti O2 NPAS electrocatalysts exhibits a higher catalytic oxidation activity to both methanol and ethanol in acidic and alkaline media. A series electrochemical measurement demonstrates that the Pt/Ti O2 NPAS structure provide larger three-phase interface and forms pores and channels for the liquid fuel to diffuse into inside and the gaseous product to escape from the catalyst layer more easily. In the meantime, the Pt/Ti O2 NPAS electrocatalysts retains faster electron-transfer speed on the interface between liquid and reaction surface of the electrode which is very pivotal for the enhancement of alcohol electrooxidation.5) The preparation of the Ti O2 nanosheet aggregated sphere(Ti O2 NSAS) which was self-assembled by Ti O2 nanosheets with anatase and Ti O2(B) containing mixed phases was acquired by solvothermal method. The diameter of Ti O2 NSAS samples are 2.5-4.5 μm. The formation of mixed phases structure and influencing factors in synthesis were discussed.6) A series Ag2O/Ti O2 NSAS photocatalysts with different weight ratio of Ti O2/Ag2 O which are with the same morphology of the Ti O2 NSAS samples were prepared by sol-gel assisted solvothermal method. The Ag2 O nanoparticles with a diameter of 5.0-15.0 nm are uniformly coated on the surface of the Ti O2 nanosheets within Ti O2 NPAS. The Ag2O/Ti O2 NSAS photocatalysts display a high activity for the degradation of MO under visible-light irradiation, which could achieve the complete mineralization of 14mg/L MO aq. in 55 minutes. The anatase phase within the three-phase heterojunction structure plays a critical role during the degradation. Under visible-light irradiation, the anatase phase Ti O2 was devoted to be the support materials for the heterojunction structure, meanwhile, it dominates the charge transfer processes during the whole photocatalysis degradation reaction. Simultaneously, both of the Ti O2(B) and Ag2 O nanoparticle act as visible-light photosensitizers which are very pivotal for the enhancement of photocatalysis activity.