Structural Optimization And Modification Of Single Crystalline TiO₂ Nanorod Arrays And Their Influences On The Photocatalytic Performance

The rapid development of industrial civilization has improved the quality of human life, but also brought serious environment problems. Especially chemical materials using in decoration and paints release the volatile organic compounds such as benzene, formaldehyde which are difficult to degrade. Long-term exposed in the environment composed of organic pollutions, people are at risk of respiratory diseases, may even cancer and leukemia. For indoor air pollution treatment, TiO₂ is considered to be valuable in research and application due to its non-toxic, easy to prepare, excellent chemical stability, resistance to light corrosion, especially can degrade almost all kinds of organic pollutions.Traditional researches on TiO₂ are mostly in the form of nanoparticles. Thanks to its quantum effect and large surface area, it shows excellent photocatalytic performance, however it's not a perfect choice. High surface energy leads to the aggregation which reduces the effective light reaction area and helps the recombination of photo-induced carriers. By template-based method particle size can be controlled effectively to help avoid the aggregation, but the process is always complex and high-cost. Moreover, the internal mechanical adhesion is so weak that it's difficult for practical loading which limits its application. Therefore we choose the FTO conductive glass as substrate, using simple hydrothermal synthesis method to prepare single crystal TiO₂ nanorod arrays. Single crystal structure benefits the separation of the photo-induces carriers, it does help avoiding aggregation and is easy to load at the same time.First, in this paper, we adjusted the packing density of the TiO₂ nanorod arrays for the best photocatalytic performance. By decreasing the concentration of hydrochloric acid, we found that the packing density increased and the ratio of high energy?002? facets which were exposed on the top of nanorod increased too. However, the photocatalytic degradation of benzene didn't increase along with the increase of exposed?002? facets. Rods which are too thin or dense adverse light absorption, the moderate density enhances light absorption by strong light trapping effect and have higher light current value and weaker recombination, demonstrating the best photocatalytic performance.Then, we studied the photocatalytic performance of the TiO₂ nanorod arrays combined with heating. Results show that photothermocatalytic performance is obviously superior photocatalytic or thermocatalytic, it proves the existence of the synergetic mechanism of photothermocatalysis. The photothermocatalytic synergetic effect dramatically lowers the active energy of benzene oxidation and promoted the degradation. However, H₂ O dissociated from the surface of the TiO₂ along with the rise of temperature, thus minimized the ·OH interacted with benzene. As a result, the degradation rate increased first then decreased with temperature rising. But CO₂ increment kept increasing as the temperature rose. This can be ascribed to that H₂ O dissociated proved more reactive sites for the intermediates which can be degraded to CO₂ by photooxidation in the degradation process. Thereby the ultimate mineralization rate increased with temperature rising.Finally, we fabricated CeO₂ nanoparticles which were considered as efficient catalysts onto TiO₂ nanorods. We adjusted the proportion of CeO₂ nanoparticles on the nanorods by simple hydrothermal method. Variable valences of Ce provide more oxygen vacancies and Ce3+ reactive sites. Oxygen vacancies would react with H₂ O or OHadsorbed on the catalyst surface to generate hydroxyl radical?·OH?. Photoelectrons captured by Ce3+ reactive sites would react with hydroxyl oxygen to generate superoxide anion?O₂?-? in photocatalytic reaction. Another part of photo-induced electrons would be excited to migrate to single crystalline nanorod which had lower conduction value, and the recombination of photo-induced electrons and holes was reduced. As a result, the photocatalytic performance was improved with more CeO₂ nanoparticle on TiO₂ nanorods.