Palladium Doped Porous Titania Photocatalysts: Impact of Mesoporous Order and Crystallinity

Herein, we report a facile synthesis method for highly ordered hexagonal P6m mesoporous palladium doped titania nanoarchitectures using the F127 triblock copolymer as a template. The mesoporous Pd/TiO 2 nanoarchitectures possess high surface areas of 223 m 2 g −1 and large pore volumes of 0.42 cm 3 g −1 at 300 °C that are reduced to 162 m 2 g −1 and 0.29 cm 3 g −1, respectively, as a result of calcination at 450 °C with their tunable mesopore diameter ranging from 5.7 to 8.3 nm. Transmission electron microscopy (TEM) measurements evince that the framework of the highly crystalline mesoporous Pd/TiO 2 is composed of aligned anatase phase grown along the [101] direction. The Pd nanoparticles are well dispersed and exhibit sizes of about 20 nm and they are separated by 1.95 Å, which agrees with the (200) lattice spacing of face-centered cubic Pd. The newly prepared photocatalysts have been compared with Pd photodeposited onto the commercial photocatalyst Sachtleben Hombikat UV-100 by the determination of the rate of HCHO formation generated by the photocatalytic oxidation of CH 3 OH. This study revealed that hexagonal P6m mesoporous Pd/TiO 2 nanoarchitectures possess a 2.5 times higher activity for the photooxidation of CH 3 OH than Pd/Hombikat UV-100. The photocatalytic oxidation of CH 3 OH using either highly ordered hexagonal networks in samples calcined at 350 °C, catalysts with randomly ordered mesoporous channels after calcinations at 450 °C or disordered mesostructures prepared at 550 °C are comparable although the crystallinity of the TiO 2 nanoparticles increases strongly only with calcination temperatures exceeding 500 °C. From the economic point of view, ordered mesochannels prepared upon calcination at 450 °C are considered to be the optimum for saving energy in the photocatalyst preparation without much loss of photocatalytic performance.