Effect of Calcination Temperature on the Structure of a Pt/TiO2 (B) Nanofiber and Its Photocatalytic Activity in Generating H2

[[abstract]]Hydrogen trititanate (H2Ti3O7) nanofibers were prepared by a hydrothermal method in 10 M NaOH at 403 K, followed by acidic rinsing and drying at 383 K. Calcining H2Ti3O7 nanofibers at 573 K led to the formation of TiO2 (B) nanofibers. Calcination at 673 K improved the crystallinity of the TiO2 (B) nanofibers and did not cause any change in the morphology and dimensions of the nanofibers. TiO2 (B) and H2Ti3O7 nanofibers are 10-20 nm in diameter and several micrometers long, but FE-SEM reveals that several of these nanofibers tend to bind tightly to each other, forming a fiber bundle. Calcination at 773 K transformed TiO2 (B) nanofibers into a TiO2 (B)/anatase bicrystalline mixture with their fibrous morphology remaining intact. Upon increasing the calcination temperature to 873 K, most of the TiO2 (B) nanofibers were converted into anatase nanofibers and small anatase particles with smoother surfaces. In the photocatalytic dehydrogenation of neat ethanol, 1% Pt/TiO2 (B) nanofiber calcined at 673 K was the most active catalyst and generated about the same amount of H2 as did 1 % Pt/P-25. TPR indicated that the calcination of 1 % Pt/TiO2 (B) nanofiber at 573 K produced a poor Pt dispersion and poor activity. Calcination at a temperature higher than 773 K (in ambient air) resulted in an SMSI effect similar to that observed over TiO2 in the reductive atmosphere. As suggested by XPS, such an SMSI effect decreased the surface concentration of Pt metal and created Ptδ- sites, preventing Pt particles from functioning as a Schottky barrier and leading to a lower activity. Because of the synergetic effect between TiO2 (B) and anatase phases, the bicrystalline mixture, produced by calcining at 773 K, was able to counter negative effects such as the reduction in surface area and the SMSI effect and maintained its photocatalytic activity