Pd Nanoparticle Formation in Ionic Liquid Thin Films Monitored by in situ Vibrational Spectroscopy.
Pd Nanoparticle Formation in Ionic Liquid Thin Films Monitored by in situ Vibrational Spectroscopy.
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DOI：
10.1021/acs.langmuir.5b03386
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发表时间：
2015-10
期刊：
影响因子：
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通讯作者：
S. Mehl;A. Toghan;T. Bauer;O. Brummel;N. Taccardi;P. Wasserscheid;J. Libuda
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作者：
S. Mehl;A. Toghan;T. Bauer;O. Brummel;N. Taccardi;P. Wasserscheid;J. Libuda
离子液体是合成金属纳米粒子的灵活反应介质和溶剂。在这里，我们描述了一种新的制备方法，金属纳米粒子在纳米厚膜的超净离子液体在超真空（UHV）的环境。CO覆盖的Pd纳米颗粒形成的同时和顺序的物理气相沉积（PVD）的IL和金属的存在下，低分压的CO。膜的厚度和粒度可以通过沉积参数控制。我们通过时间分辨红外反射吸收光谱（TP-IRAS）和程序升温红外光谱（TR-IRAS）跟踪了纳米粒子的形成及其热行为。共沉积的Pd和[C1 C2 Im][OTf]在CO中在100 K导致均匀的多层膜的CO覆盖的Pd聚集体在IL矩阵的生长。这些NP的尺寸可以通过共沉积物中的金属分数来控制。随着金属含量的增加，Pd纳米颗粒的尺寸也增加。在非常低的金属含量下，形成小的Pd羰基样物质，其仅以顶部几何形状结合CO。退火后，[OTf]（-）阴离子共吸附在NP表面和部分取代CO。CO和IL的共吸附由CO伸缩带的强红移表示。虽然弱结合的顶部CO主要是取代低于熔融转变的IL，共吸附壳与桥键合CO和IL是稳定的熔点以上。可以通过在100 K下将Pd PVD到固体[C1 C2 Im][OTf]膜上来制备更大的三维Pd NP。在退火时，在200 K以下，顶部CO从这些NP解吸。在IL膜熔化后，CO覆盖的Pd NP浸入IL中，并再次形成由桥键合的CO和IL组成的稳定的共吸附物壳。
Ionic liquids (ILs) are flexible reaction media and solvents for the synthesis of metal nanoparticles (NPs). Here, we describe a new preparation method for metallic NPs in nanometer thick films of ultraclean ILs in an ultrahigh vacuum (UHV) environment. CO-covered Pd NPs are formed by simultaneous and by sequential physical vapor deposition (PVD) of the IL and the metal in the presence of low partial pressures of CO. The film thickness and the particle size can be controlled by the deposition parameters. We followed the formation of the NPs and their thermal behavior by time-resolved IR reflection absorption spectroscopy (TP-IRAS) and by temperature-programmed IRAS (TR-IRAS). Codeposition of Pd and [C1C2Im][OTf] in CO at 100 K leads to the growth of homogeneous multilayer films of CO-covered Pd aggregates in an IL matrix. The size of these NPs can be controlled by the metal fraction in the co-deposit. With increasing metal fraction, the size of the Pd NPs also increases. At very low metal content, small Pd carbonyl-like species are formed, which bind CO in on-top geometry only. Upon annealing, the [OTf](-) anion coadsorbs at the NP surface and partially displaces CO. Co-adsorption of CO and IL is indicated by a strong red-shift of the CO stretching bands. While the weakly bound on-top CO is mainly replaced below the melting transition of the IL, coadsorbate shells with bridge-bonded CO and IL are stable well above the melting point. Larger three-dimensional Pd NPs can be prepared by PVD of Pd onto a solid [C1C2Im][OTf] film at 100 K. Upon annealing, on-top CO desorbs from these NPs below 200 K. Upon melting of the IL film, the CO-covered Pd NPs immerse into the IL and again form a stable coadsorbate shell that consists of bridge-bonded CO and the IL.