Detection and characterisation of sub-critical nuclei during reactive Pd metal nucleation by X-ray absorption spectroscopy
Detection and characterisation of sub-critical nuclei during reactive Pd metal nucleation by X-ray absorption spectroscopy
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DOI：
10.1039/c5ce01883h
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发表时间：
2016-01-01
期刊：
影响因子：
3.1
通讯作者：
Schroeder, S. L. M.
中科院分区：
文献类型：
--
作者：
Chang, S. -Y.;Gruender, Y.;Schroeder, S. L. M.
本文用X射线吸收精细结构谱（XAFS）研究了[PdCl_4]（2-）水溶液与二茂铁有机溶液的界面还原反应。使用的液-液界面作为模型的均匀成核允许控制成核的热力学驱动力，通过变化的[PdCl 4]（2-）和二茂铁的浓度在大量的相邻相。我们证明，这种方法允许表征的条件下的系统（i）没有颗粒成核，（ii）快速自发成核的稳定的纳米粒子和（iii）的中间状态，在其中形成的亚稳态Pd亚临界核发生。在亚稳态的XAFS光谱分析表明，一个随机波动的平衡，其中钯核不断形成和重新溶解，明显的氧化态波动检测的Pd XAFS。过饱和度显然足以诱导纳米颗粒形成，但不足以使核生长超过临界簇尺寸。我们能够维持一个系统在亚稳态几个小时。这样的亚临界集群预测的经典成核理论，但没有被检测到，除了在液池TEM成像和扫描电化学显微镜的研究。
The interfacial reduction of aqueous [PdCl4](2-) at the interface with an organic solution of ferrocene has been characterised by X-ray absorption fine structure (XAFS) spectroscopy. Use of a liquid-liquid interface as a model for homogeneous nucleation permits control of the thermodynamic driving force for nucleation, through variation of the [PdCl4](2-) and ferrocene concentrations in the bulk of the adjacent phases. We demonstrate that this approach permits characterisation of the system under conditions of (i) no particle nucleation, (ii) fast spontaneous nucleation of stable nanoparticles and (iii) an intermediate state, in which formation of metastable Pd sub-critical nuclei takes place. Analysis of the XAFS spectra in the metastable state revealed a stochastically fluctuating equilibrium in which Pd nuclei are constantly formed and re-dissolved, as evident from oxidation state fluctuations detected by the Pd XAFS. Supersaturation was evidently sufficient to induce nanoparticle formation but insufficient for nuclei to grow beyond the critical cluster size. We were able to maintain a system in this metastable state for several hours. Such sub-critical clusters are predicted by classical nucleation theory, but have not been detected except in liquid-cell TEM imaging and scanning electrochemical microscopy studies.