Research Of TiO₂ Modification

It is well known that the properties of materials are closely related to its composition, structure and preparation process. In functional nanomaterials research areas, to achieve the better performance of materials, it is important to design and control the properties by fusion of small size effect, morphology control and defect design.The energy and environment problems are two of the most serious challenges in today’s life. Ti O2 nanomaterials are drawing great interest in the field of hydrogen energy production and pollution treatment due to its excellent photocatalytic activity. However, its application is severely limited by the poor respond to the visible light and the fast recombination rate of electron-holes.To solve the above problems, this paper was focused on the modification of Ti O2 nanomaterials, and guided by the theory of crystal defects and growth. The main work and achievement are as follows:(1) Ag modified Sn O2/ Ti O2 nanoparticles were successfully prepared by vapor transport method and the solid state reaction method. The as prepared samples were well dispersed and were with an appropriate diameter of 10-15 nm. The real photocatalytic efficiency does not increase with the increase of Ag proportions as expected. And among all the samples, the one which content 1% Sn and 0.5% Ag calcined at 400 ℃ showed the best photocatalytic activity. The EPR pattern shows that the synergistic effect of Ag and Sn will create more crystal defects-oxygen vacancies, and the amount of oxygen vacancies rose along with the content of Ag. According to the catalytic mechanism, the oxygen vacancies created by doping with Sn and modified with Ag have two opposite influences on the decomposition of MB. They would prevent the recombination of electron-hole pairs, which is beneficial to the improvement of the photocatalytic activity. At the same time, they would capture the photogenerated electrons, and the amount of electrons reacting with O2 will decrease, which will result in the decrease of photocatalytic activity.(2) Rod-like N-doped Ti O2/ Ag composites were successfully synthesized by a modified sol-gel method, without adding any surfactants. The entire preparation differs from the traditional sol-gel synthesis of Ti O2 that the reaction can get controlled by adjusting the flow speed of water vapor and NH3. Characterization results show that as-prepared samples were uniform nanorods with an average length of ca. 3 mm and across section diameter of ca. 150 nm. The rod-like structure was formed during the annealing process. A possible mechanism was proposed to illustrate the formation of rod-like Ag-N-Ti O2. The degradation of methylene blue performed under visible light with the prepared nanorods as the photocatalyst demonstrated the photocatalytic activities of Ti O2 can be improved by the synergistic effect of N doping and Ag modification. In addition, as-prepared Ti O2-based photocatalyst exhibits a significantly enhanced photo-chemical stability after 5 catalytic cycles mainly due to the rod-like morphology.(3) N-doped mesoporous Ti O2 nanorods were fabricated by a modified and facile sol-gel approach without any templates. Ammonium nitrate was used as a raw source of N dopants, which could produce a lot of gases such as N2, NO2 and H2 O in the process of heating samples. These gasses were proved to be vitally important to form the special mesoporous structure. The samples were characterized by the powder X-ray diffraction, X-ray photoelectron spectrometer, nitrogen adsorption isotherms, scanning electron microscopy, transmission electron microscopy, and UV-visible absorption spectra. The average length and the cross section diameter of the as-prepared samples were ca. 1.5 μm and ca. 80 nm, respectively. The photo-catalytic activity was evaluated by photodegradation of methylene blue(MB) in aqueous solution. The N-doped mesoporous Ti O2 nanorods showed an excellent photo-catalytic activity, which may be attributed to the enlarged surface area(106.4 m2g-1) and the narrowed band gap(2.05 e V). Besides, the rod-like photocatalyst was found to be easy to recycle.In our research, to achieve the better properties of Ti O2, the work fused small size effect, morphology control and crystal defect design together, which is helpful for carrying out intercross among subjects in nanomaterials preparing field.