Mesostructured Pt/TiO2 Nanocomposites as Highly Active Photocatalysts for the Photooxidation of Dichloroacetic Acid

Mesoporous Pt/TiO2 nanocomposites have been synthesized by using two pathways: (1) the in-situ preparation of Pt/TiO2 nanocomposites was carried out using a one-step synthesis by dissolving the Pt and TiO2 precursors in the presence of a triblock copolymer as the structure-directing agent followed by drying, calcinations, and reduction under H-2 gas. (2) Platinum particles have been photochemically deposited onto mesoporous TiO2. The TEM images of the mesoporous Pt/TiO2 nanocomposites calcined at 450 degrees C demonstrate that the TiO2 nanoparticles with an average diameter of about 10 nm are not agglomerated and are quite uniform in size and shape. Following the photodeposition process, the Pt nanoparticles are well-dispersed and highly uniform, exhibiting diameters of similar to 3 nm; however, following the in situ preparation, the Pt particles are reaching diameters of approximately 15 nm, most likely as a result of the calcination and reduction at high temperatures. The photocatalytic activity of the newly synthesized mesoporous photocatalysts was measured and compared with that of nonporous commercial Aeroxide TiO2 P 25 and Pt/TiO2 P 25 by measuring the rate of H+ ion release during the photodegradation of dichloroacetic acid (DCA) and confirmed by measuring the concomitant total organic carbon removal. For both preparation routes the photonic efficiency of the mesoporous TiO2 photocatalysts is found to be increased by the addition of the Pt islands and to correlate with the size of the Pt particles. The mesoporous Pt/TiO2 nanocomposites showed 2 times higher activity for the photocatalytic DCA photodegradation than Aeroxide TiO2 P 25. The larger photoactivity of the mesoporous Pt/TiO2 nanocompositcs prepared by the photodeposition process is attributed to the higher dispersity and the small size of the Pt particles (3 nm). To the best of our knowledge, the measured photonic efficiency of xi = 7.95% for the photodeposited Pt/TiO2 nanocomposites is among the highest xi value reported up to now.