Morphological analysis and post processing of platinum-titanium nanoparticles

[摘要] In this thesis, the morphology of bimetallic Pt-Ti nanoparticles were investigated. Scanning Transmission Electron Microscopy (STEM) and X-ray Photoelectron Spectroscopy (XPS) was used to analyse the nanoparticles. Previously, it has been demonstrated that fully oxidised Pt-Ti nanoparticle form multi core morphology as the size of the nanoparticle increases. Here, the nanoparticles were investigated with minimal oxygen exposure and it was observed that the nanoparticle morphology prior to full oxidation is an amorphous alloy structure. Theoretical analysis through DFT calculation was also employed to investigate the addition of oxygen to the nanoparticle in a layer by layer manner. The theoretical results confirmed that the most stable structure after full oxidation is Pt core within the oxide Ti shell. The thermal energy provided by the electron beam was used to induce a single core formation in the larger 90 kDa nanoparticles. Then, annealing of the sample was used to investigate thermal processing of the nanoparticles. It was observed that single morphology can be achieved by heating to 600 ± 100 oC and increasing the temperature to 900 ± 100 oC induced the segregated morphology of Pt-Ti nanoparticle. Therefore, it was possible to post process the morphology of the nanoparticle through heat treatment. The results obtained from the XPS, demonstrated that the Ti shell is fully oxidised with mostly in TiO2 and small amount of Ti2O3. The Pt core consist of pure Pt as well as a layer of oxide Pt. Thermally heating the nanoparticles to 600 oC resulted in reduction of Pt core to fully metallic Pt state and also increased the Ti2O3 to TiO2 ratio of the Ti shell. The reduction was reverted to its original state after exposure to air. The XPS results were compared and confirm through Grazing Incidence X-ray Fluorescence Analysis (GIXRF) and Near-Edge X-ray Absorption Fine Structure (NEXAFS).

[发布机构] University:University of Birmingham;Department:School of Physics and Astronomy

[关键词] Q Science;QC Physics