Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C1C2Im][OTf] Monitored by In Situ IR Spectroscopy.
Ionic-Liquid-Modified Hybrid Materials Prepared by Physical Vapor Codeposition: Cobalt and Cobalt Oxide Nanoparticles in [C1C2Im][OTf] Monitored by In Situ IR Spectroscopy.
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DOI：
10.1021/acs.langmuir.6b02303
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发表时间：
2016-08
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通讯作者：
S. Mehl;T. Bauer;O. Brummel;Kaija Põhako‐Esko;P. Schulz;P. Wasserscheid;J. Libuda
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作者：
S. Mehl;T. Bauer;O. Brummel;Kaija Põhako‐Esko;P. Schulz;P. Wasserscheid;J. Libuda
离子液体修饰纳米材料的合成是近年来研究的热点。在这项研究中，我们探索的潜力，以超净的方式，通过物理气相共沉积（PVCD）准备这样的系统。我们在100 K下将金属钴和室温离子液体（IL）1-乙基-3-甲基咪唑三氟甲磺酸盐[C1 C2 Im][OTf]同时共沉积到Pd（111）表面。这个过程是在超高真空（UHV）条件下，在CO的存在下，或在O2和CO的存在下进行。我们使用时间分辨（TR）和程序升温（TP）红外反射吸收光谱（IRAS）调查的形成和稳定性的IL-改性的Co沉积物原位在基于PVD的合成。CO被用作探针分子来监测生长。在Pd（111）上初始生长平坦的Co膜之后，形成多层Co纳米颗粒（NPs）。CO和IL的振动带中观察到特征位移和强度变化，这源于IL/Co界面处的电场（斯塔克效应）和[OTf]（-）阴离子的特异性吸附。这些观察结果表明，Co聚集体是由CO和[OTf]（-）组成的混合吸附质壳稳定的。Co颗粒上的CO覆盖率随着温度的升高而降低，但一些CO被保存到IL的脱附温度（370 K）。此外，如果在PVCD工艺中引入氧，则IL壳抑制Co NP的氧化。只有在氧分压下才能形成化学吸附的氧，在没有IL的情况下（5 × 10（-6）mbar O2），这种氧分压会迅速导致Co 3 O 4的形成。发现这种化学吸附的氧使CO配体壳不稳定。如果IL和Co在其他相同的条件下顺序沉积，则Co的氧化不被抑制。在这种情况下，我们观察到完全氧化的钴氧化物颗粒的形成。
The synthesis of ionic-liquid-modified nanomaterials has attracted much attention recently. In this study we explore the potential to prepare such systems in an ultraclean fashion by physical vapor codeposition (PVCD). We codeposit metallic cobalt and the room-temperature ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [C1C2Im][OTf] simultaneously onto a Pd(111) surface at 100 K. This process is performed under ultrahigh-vacuum (UHV) conditions in the presence of CO, or in the presence of O2 and CO. We use time-resolved (TR) and temperature-programmed (TP) infrared reflection absorption spectroscopy (IRAS) to investigate the formation and stability of the IL-modified Co deposits in situ during the PVD-based synthesis. CO is used as a probe molecule to monitor the growth. After initial growth of flat Co films on Pd(111), multilayers of Co nanoparticles (NPs) are formed. Characteristic shifts and intensity changes are observed in the vibrational bands of both CO and the IL, which originate from the electric field at the IL/Co interface (Stark effect) and from specific adsorption of the [OTf](-) anion. These observations indicate that the Co aggregates are stabilized by mixed adsorbate shells consisting of CO and [OTf](-). The CO coverage on the Co particle decreases with increasing temperature, but some CO is preserved up to the desorption temperature of the IL (370 K). Further, the IL shell suppresses the oxidation of the Co NPs if oxygen is introduced in the PVCD process. Only chemisorbed oxygen is formed at oxygen partial pressures that swiftly lead to formation of Co3O4 in the absence of the IL (5 × 10(-6) mbar O2). This chemisorbed oxygen is found to destabilize the CO ligand shell. The oxidation of Co is not suppressed if IL and Co are deposited sequentially under otherwise identical conditions. In this case we observe the formation of fully oxidized cobalt oxide particles.