Investigation of catalytic activity and atomic structure for core-shell nanoparticles

采用分析电子显微镜、正电子湮没光谱、Zeta电位、X射线衍射仪和催化活性反应实验对超声化学法制备的Au-Pd二元纳米粒子进行了表征。同时，对Au/Pd原子簇模型和纳米团簇进行了第一性原理计算，估算了Au/Pd界面的稳定性、电子密度和某些分子与纳米粒子Pd表面的反应能。通过添加另一种表面活性剂，还合成了具有相同尺寸的核壳纳米粒子的合金纳米粒子。此外，还进行了电子束、伽马射线、离子束等各种辐照还原实验，成功地合成了纯Au和Au-Pd NaN…结果表明，超声化学法合成的Au-Pd纳米粒子具有良好的相分离效果，表面Pd的薄晶格有膨胀的趋势。(3)通过正电子湮没和Zeta势实验发现，这种近表面的晶格膨胀与纯Au和Pd体相不匹配的表面电子态有关。在面心立方结构的Au晶格上生长的膨胀Pd晶格在Au/Pd界面附近是稳定的，其晶格空间随着Pd堆积层数的增加而变窄。(5)另一种计算结果表明：在核壳结构中表面周围的LDOS(局域态密度)电子态下，d带发生了收缩和上移。我们认为Pd晶格膨胀是核壳Au-Pd纳米粒子特有的催化活性的一个非常重要的因素。较少

Au-Pd binary nanoparticles prepared by sonochemical technique were investigated by the analytical transmission electron microscopy, positron annihilation spectroscopy, zeta-potential, X-ray diffraction and catalytic activity reaction experiments. Also, the first principle calculation of Au/Pd slub model and nano clusters have been performed in order to estimate the stability of Au/Pd interface, its electron density and reactive energy between some molecules and Pd surface of core-shell nanoparticles.Following conclusions we reached(1) Au-Pd nanoparticles of same diameter with different thickness ratio of Au-core and Pd-shell were successfully produced by sonochemical reduction method. Alloy nanoparticles with same size of core-shell nanoparticles also have been synthesized by addition of another type of surfactant. Moreover, various kind of irradiation reduction, such as electron, gamma-ray and ion beam, experiments have been performed and successfully synthesized pure Au and Au-Pd nan … More oparticles.(2) It makes clear that Au-Pd nanoparticles synthesized by sonochemical method have perfectly phase separation and surface Pd thin lattice tend to expand. Moreover, it found that expanded Pd-shell lattice epitaxially grows on the fcc Au lattice and with the coherent Au/Pd interface structure.(3) It found by positron annihilation and zeta potential experiments that this lattice expansion near the surface is related to the surface electronic state of which dose not match between pure Au and Pd bulk.(4) From the first principle calculations, expanded Pd thin lattice grow on fcc Au lattice is stable around Au/Pd interface and its lattice space becomes narrow as the stacked Pd layers increases.(5) Another calculation shows following result: in an electronic state of LDOS (local density of state) around surface in core-shell structure it appears that shrinking and up shift of d-band takes places.We proposed that Pd lattice expansion is a very important factor as the peculiar catalytic activity of core-shell Au-Pd nanoparticle. Less