Effect of a crystalline phase of TiO2 photocatalysts on the photodeposition of Rh metal nanoparticles

• Photodeposited Rh species are an aggregate of primary Rh nanoparticles.
• Photodeposited Rh species on anatase TiO2 are decorated with TiO2 due to strong metal-support interaction (SMSI).
• Photodeposited Rh species on rutile TiO2 are not decorated with TiO2.
• The crystalline phase of TiO2 (anatase and rutile) affects the appearance rate of Rh nanoparticles.
• Rh nanoparticles with a uniform size appear one after another in the photodeposition process on both anatase and rutile TiO2.

Effect of a crystalline phase of TiO2 is investigated in the photodeposition processes of Rh metal nanoparticles on TiO2 photocatalysts having anatase and rutile phase by means of in situ time-resolved energy dispersive X-ray absorption fine structure spectroscopy (DXAFS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The important factor was neither its crystallite size nor its specific surface area, and was the crystalline phase. In situ time-resolved DXAFS analysis clarified that the Rh metal nanoparticles with a uniform size appear on both anatase and rutile phases of TiO2, whereas the appearance rate of Rh metal nanoparticles decreases with the photoirradiation time only on the rutile phase of TiO2. The TEM observation and XPS depth analysis revealed that the bare surface of photodeposited Rh metal nanoparticles on the rutile is exposed, although that on the anatase is partially covered with TiO2 due to strong metal-support interaction (SMSI) between Rh metal nanoparticle and TiO2−δ.

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