Highly Dispersed Platinum Nanoparticles on TiO2 Prepared by Using the Microwave-Assisted Deposition Method: An Efficient Photocatalyst for the Formation of H2 and N2 from Aqueous NH3

A simple and practical technique to synthesize nanosized platinum particles loaded on TiO2 (PtTiO2) by using a microwave (Mw)-assisted deposition method has been exploited in the development of a highly efficient photocatalyst for the formation of H2 and N2 gases from harmful nitrogen-containing chemical wastes, for example, aqueous ammonia (NH3). Upon Mw irradiation, a platinum precursor can be deposited quickly on the TiO2 surface from an aqueous solution of platinum and subsequent reduction with H2 affords the nanosized platinum metal particles with a narrow size distribution (Mw-PtTiO2). Characterization by CO adsorption, platinum LIII-edge X-ray absorption fine structure analysis, and TEM analysis revealed that the size of the metal nanoparticles strongly depended on the preparation methods. Smaller platinum nanoparticles were obtained by the Mw heating method than those obtained by conventional preparation techniques, such as photoassisted deposition (PAD), impregnation (Imp), and equilibrium adsorption (EA) deposition by conventional convective heating. The H2 and N2 formation rates increased with increasing dispersity of platinum. PtTiO2 prepared by the Mw heating method exhibited a specifically high H2 formation activity in the photocatalytic decomposition of aqueous NH3 in a nearly stoichiometric 3:1 (H2/N2) molar ratio under inert conditions. The present Mw heating method is applicable to a variety of anatase-type TiO2 species possessing different specific surface areas to provide small and highly dispersed platinum nanoparticles with a narrow size distribution.