Mehl Sascha, Toghan Arafat, Bauer Tanja, Brummel Olaf, Taccardi Nicola, Wasserscheid Peter, Libuda Jörg
Chemistry Department, Faculty of Science, South Valley University , 83523 Qena, Egypt.
Erlangen Catalysis Resource Center and Interdisciplinary Center Interface-Controlled Processes, Friedrich-Alexander-Universität Erlangen-Nürnberg , 91058 Erlangen, Germany.
Langmuir. 2015 Nov 10;31(44):12126-39. doi: 10.1021/acs.langmuir.5b03386. Epub 2015 Oct 28.
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.
离子液体（ILs）是用于合成金属纳米颗粒（NPs）的灵活反应介质和溶剂。在此，我们描述了一种在超高真空（UHV）环境下，在超净离子液体的纳米厚膜中制备金属纳米颗粒的新方法。在低CO分压存在下，通过离子液体和金属的同时及顺序物理气相沉积（PVD）形成CO覆盖的Pd纳米颗粒。膜厚度和颗粒尺寸可通过沉积参数控制。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）跟踪纳米颗粒的形成及其热行为。在100 K下，Pd和[C1C2Im][OTf]在CO中共沉积导致在离子液体基质中形成CO覆盖的Pd聚集体的均匀多层膜。这些纳米颗粒的尺寸可通过共沉积物中的金属分数控制。随着金属分数增加，Pd纳米颗粒的尺寸也增加。在非常低的金属含量下，形成小的类似Pd羰基的物种，其仅以顶位构型结合CO。退火时，OTf阴离子共吸附在纳米颗粒表面并部分取代CO。CO和离子液体的共吸附由CO伸缩带的强烈红移表明。虽然弱结合的顶位CO主要在离子液体的熔化转变温度以下被取代，但具有桥式键合CO和离子液体的共吸附物壳在远高于熔点的温度下是稳定的。通过在100 K下将Pd物理气相沉积到固体[C1C2Im][OTf]膜上可制备更大的三维Pd纳米颗粒。退火时，顶位CO在200 K以下从这些纳米颗粒上解吸。离子液体膜熔化时，CO覆盖的Pd纳米颗粒浸入离子液体中并再次形成由桥式键合CO和离子液体组成的稳定共吸附物壳。
