Structural characterization of heterogeneous RhAu nanoparticles from a microwave-assisted synthesis
Structural characterization of heterogeneous RhAu nanoparticles from a microwave-assisted synthesis
复制标题
微波辅助合成异质 RhAu 纳米粒子的结构表征
DOI：
10.1039/c8nr04866e
复制
发表时间：
2018
期刊：
影响因子：
6.7
通讯作者：
Frenkel, Anatoly I.
中科院分区：
文献类型：
--
作者：
Duan, Zhiyao;Timoshenko, Janis;Kunal, Pranaw;House, Stephen D.;Wan, Haqin;Jarvis, Karalee;Bonifacio, Cecile;Yang, Judith C.;Crooks, Richard M.;Frenkel, Anatoly I.
采用微波辅助法合成了铑金纳米粒子。表征，基于透射电子显微镜（TEM），能量色散光谱，和粉末X-射线衍射，提供了证据的单峰合金纳米颗粒的平均粒径分布在3和5纳米之间，这取决于组合物。扩展的X射线吸收精细结构光谱（EXAFS）也表明合金化的证据，但Rh和Au的配位数表明金属之间的显着偏析。更大的问题是Rh的配位数较低; ca的值。9表示小于2nm的NP，显著小于用TEM观察到的那些。此外，没有单粒子结构模型能够重现实验EXAFS数据。通过高分辨率像差校正扫描TEM成像实现了这种差异的解决方案，该成像显示存在超小（<2 nm）的纯Rh簇和具有富含Au的核和Rh修饰的壳的较大（约3-5 nm）的偏析颗粒。超小纯Rh簇和较大隔离Rh/Au NPs的混合物的非均相模型能够解释在测量的组合物范围内的NPs的实验测量。密度泛函理论，EXAFS和TEM的组合使我们能够量化的RhAu纳米颗粒的异质性。只有通过这种理论和实验技术的结合，才能得到能够解释所有实验表征数据的粒径双峰分布。
A microwave assisted method was used to synthesize RhAu nanoparticles (NPs). Characterization, based upon transmission electron microscopy (TEM), energy dispersive spectroscopy, and powder X-ray diffraction, provided the evidence of monomodal alloy NPs with a mean size distribution between 3 and 5 nm, depending upon the composition. Extended X-ray adsorption fine-structure spectroscopy (EXAFS) also showed evidence of alloying, but the coordination numbers of Rh and Au indicated significant segregation between the metals. More problematic were the low coordination numbers for Rh; values of ca. 9 indicate NPs smaller than 2 nm, significantly smaller than those observed with TEM. Additionally, no single-particle structural models were able to reproduce the experimental EXAFS data. Resolution of this discrepancy was achieved with high resolution aberration corrected scanning TEM imaging which showed the presence of ultra-small (<2 nm) pure Rh clusters and larger (∼3–5 nm) segregated particles with Au-rich cores and Rh-decorated shells. A heterogeneous model with a mixture of ultrasmall pure Rh clusters and larger segregated Rh/Au NPs was able to explain the experimental measurements of the NPs over the range of compositions measured. The combination of density functional theory, EXAFS, and TEM allowed us to quantify the heterogeneity in the RhAu NPs. It was only through this combination of theoretical and experimental techniques that resulted in a bimodal distribution of particle sizes that was able to explain all of the experimental characterization data.