Gholhaki Saeed, Hung Shih-Hsuan, Cant David J H, Blackmore Caroline E, Shard Alex G, Guo Quanmin, McKenna Keith P, Palmer Richard E
School of Physics and Astronomy, University of Birmingham Birmingham B15 2TT UK.
National Physical Laboratory Hampton Road Teddington Middlesex TW11 0LW UK.
RSC Adv. 2018 Jul 31;8(48):27276-27282. doi: 10.1039/c8ra02449a. eCollection 2018 Jul 30.
The response of nanoparticles to exposure to ambient conditions and especially oxidation is fundamental to the application of nanotechnology. Bimetallic platinum-titanium nanoparticles of selected mass, 30 kDa and 90 kDa, were produced using a magnetron sputtering gas condensation cluster source and deposited onto amorphous carbon TEM grids. The nanoparticles were analysed with a C-corrected Scanning Transmission Electron Microscope (STEM) in High Angle Annular Dark Field (HAADF) mode. It was observed that prior to full Ti oxidation, Pt atoms were dispersed within a Ti shell. However, after full oxidation by prolonged exposure to ambient conditions prior to STEM, the smaller size 30 kDa particles form a single Pt core and the larger size 90 kDa particles exhibit a multi-core structure. Electron beam annealing induced a single core morphology in the larger particles. First principles density functional theory (DFT) calculations were employed to calculate the lowest energy structure of the Pt-Ti nanoparticles with and without the presence of oxygen. It was demonstrated that, as the concentration of oxygen increases, the lowest energy structure changes from dispersed Pt to multiple Pt cores and finally a single Pt core, which is in good agreement with the experimental observations.
纳米颗粒对暴露于环境条件尤其是氧化的响应对于纳米技术的应用至关重要。使用磁控溅射气体冷凝团簇源制备了选定质量（30 kDa和90 kDa）的双金属铂钛纳米颗粒，并将其沉积在非晶碳透射电子显微镜（TEM）网格上。使用C校正扫描透射电子显微镜（STEM）在高角度环形暗场（HAADF）模式下对纳米颗粒进行分析。观察到在钛完全氧化之前，铂原子分散在钛壳内。然而，在STEM分析之前通过长时间暴露于环境条件进行完全氧化后，较小尺寸的30 kDa颗粒形成单个铂核，而较大尺寸的90 kDa颗粒呈现多核结构。电子束退火在较大颗粒中诱导出单核形态。采用第一性原理密度泛函理论（DFT）计算有氧气和无氧气存在时铂钛纳米颗粒的最低能量结构。结果表明，随着氧浓度的增加，最低能量结构从分散的铂变为多个铂核，最终变为单个铂核，这与实验观察结果高度吻合。
