A New Ti^(3+)-assisted Synthesis of Pd-supported TiO_2 Nanomaterial with Enhanced Photocatalytic Activity for Hydrogen Generation and Methyl Orange Degradation

Owing to the merits of high catalytic activity, Pd-supported materials have received extensive attention. However, those materials always require complex and high-cost synthetic processes such as high-temperature calcination or 1-12 reduction, which seriously hinder their wide applications. In this work, a novel Pd reduction method was developed for Pd-supported TiO2 catalysts, in which the Pd2~ ions were partly reduced and homogeneously loaded on the surface of 8 nm TiO2 with the assistance of pre-produced surface Ti3＋ ions. This facile preparation is calcination-free and cost-low. The excellent catalysts can produce H2 33 mmol/g/h under UV-vis light irradiation, and degrade nearly 10% methyl orange in 1 h visible-light irradiation, which is much higher than that of unloaded TiO2 or Pd/TiO2 prepared by traditional high-temperature calcination methods. Moreover, the resulting Pd-supported TiO2 nano-catalysts are also effective for colorless phenol degradation under visible-light. The reasons for these superior activities can be assigned to the co-existence of Pd~ and Pd2~ on the surface of TiO2 nanoparticles, which is closely related to the calcination-free synthetic process. UV-Vis absorbance spectra show that the obtained 0.53Pd/TiO2 is visible-light-driven and nitrogen physisorption isotherms indicate a high specific surface area of 203 m2/g. The preparation method reported herein may provide hints for obtaining other high photocatalytic activity Pd-based supported catalysts for hydrogen generation and methylene orange degradation.

Synthesis, Photoluminescence and Photocatalytic Performance of BiPO4 with Different Phase Structures

Three kinds of crystal phase BiPO4（HP, LTBP, and HTBP） were selectively synthesized by controlling the preparation conditions. Structures of the three samples are all constructed by PO4 and BiO8 polyhedra but with different geometric structures. Detailed characterization was carried out by X-ray diffraction（XRD）, scanning eletron microscopy（SEM） and Raman, UV-Vis, and luminescence spectrometries. Three samples exhibit huge distinctions in their photoluminescence（PL） lifetime： 0.68, 162 and 160 μs for HP, LTBP, and HTBP, respectively. More interesting, an outstanding photocatalytic activity is observed for as-prepared LTBP nanorod, which shows even higher activity for the degradation of MB solution than P25. In addition, experiments were carried out to clarify the role of hydroxyl （OH） and superoxide radicals（O2·） played in photocatalytic process and it was found O2·was the main active species in BiPO4 photocatalysts. Further comparison of structural and photocatalytic properties of the three samples finds that structure distortion is contributed to their property difference. A correlation was found between photocatalytic performance and the distortion of BiO8 dodecahedra. The internal field generated by the distortion of BiO8 dodecahedra was believed advantageous for the separation of electron and hole, which was in favor of the improvement of photocatalytic activity. This correlation may help to design other photocatalysts with high activity.