Preparation Of Platinum Loaded TiO₂ Nanotubes And Its Photocatalytic Performance

Titanate nanotubes were synthesized via a typical hydrothermal method taking TiO₂ (Degussa P25) and NaOH as raw materials, and further core-shell titania nanotube (TiNTs) with intact morphology and anatase phase were obtained by chemical morphology freezing routes which consisted of carbon injection and silica-coated processes and high-temperature calcination treatment. On the one hand, Pt nanoparticles loaded titania nanotubes were prepared by photodeposition method using H₂PtCl6·6H₂O as a platinum source and methanol as a sacrificial electron donor and the finally obtained samples were referred as Pt/TiNTs; secondly, a combination processes of hydrothermal reactions and chemical morphology freezing method were also employed to synthesize Pt/TiNTs catalysis with titanate nanotubes as carriers and H₂PtCl6·6H₂O as a platinum source. The morphology, structures and compositions of the as-prepared TiNTs and Pt/TiNTs were investigated by TEM, FESEM, XRD and EDS spectrum; furthermore, the photo-catalytic activities of the samples were studied. The main content and key conclusions were summarized below:The titanate nanotubes were amorphous, and the structural formula was H₂Ti2O5·H₂O. With a unified shape and well-balanced size distribution, the nanotubes possessed an outstanding property of specific surface area and high length-diameter ratio structures; the nanotubes gradually transformed into anatase occurred as elevating the calcination temperature, however, the morphology of the nanotubes could easily be damaged with a rapid cut of structures in length, and finally became a mess of agglomerated nanorods or particles; But the thermally stable anatase TiNTs with undamaged morphology after 500℃calcination treatment could be achieved by adopting chemical morphology freezing method to protect the primary nanotubes against the possible shape deformation, and thus the prepared TiNTs maintained its advantages of large specific surface area and high pore volume. Calcinating at a higher temperature of 600℃, the TiNTs happened to be partially damaged, and the tube structure can hardly be found when the calcination temperature arrived at 700℃; the photo-catalytic activity tests were carried out with the participation of oxygen for the degradation of AcOH, and the increase of calcination temperature could significantly improve the catalytic performance of the samples, and the TiNTs calcined at 600℃acquired a better performance.For the catalysts prepared by photo-deposition method, the Pt nanoparticles on the surface of Pt/TiNTs were Pt metal and dispersed uniformly on the nanotubes, and the crystalline constitution of Pt/TiNTs was not apparently changed after a certain amounts of Pt loaded on the nanotubes; the photoreduction conditions such as irradiation time, intensity and pretreatment had a great impact on the performance and structures of the catalysts, and the optimal loading time were 1.5h; otherwise, the thermal treatment temperature also distinctively affected their photo-catalytic ability, and together with Pt loading amount determined the activities of the as-prepared Pt/TiNTs catalysts, among which Pt/TiNTs-600℃-1.5wt% exhibited the best performance, however, the excessive loading content of Pt particles would lower the photo-activities of the Pt/TiNTs.The Pt nanoparticles in the form of Pt metal deposited on the surface of Pt/TiNTs (low Pt loading amounts) neatly when a new hydrothermal-reduction method was employed to prepare the catalysts, and thereby the crystalline phase of Pt/TiNTs was not evidently changed; But the Pt particles started to appear even in the form of large spherical particles or agglomerations when the TiNTs loaded with a large quantity of Pt content which led to a pronounced variation of the phase composition of Pt/TiNTs and to damage catalyst's shape and microstructures; the specific surface area, phase composition as well as the form of Pt particle state jointly decided the photo-catalytic ability of the prepared materials. The Pt/TiNTs had a certain degree of photo-catalytic activity improvement after being loaded with an appropriate amount of Pt and results showed that Pt/TiNTs-600℃with a theoretical loading content of 2.0wt% Pt had the most satisfactory catalytic performance. In addition, it was also found that the activities of the Pt/TiNTs with excessive Pt loading amounts would be significantly reduced.