Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 3, D-91058 Erlangen, Germany.
Lehrstuhl für Chemische Reaktionstechnik, Friedrich-Alexander-Universität Erlangen-Nürnberg , Egerlandstraße 3, D-91058 Erlangen, Germany.
Langmuir. 2016 Aug 30;32(34):8613-22. doi: 10.1021/acs.langmuir.6b02303. Epub 2016 Aug 22.
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.
最近，离子液体修饰的纳米材料的合成引起了广泛关注。在这项研究中，我们探索了通过物理气相共沉积（PVCD）以超净方式制备此类系统的可能性。我们在 100 K 下将金属钴和室温离子液体（IL）1-乙基-3-甲基咪唑六氟磷酸盐[C1C2Im][OTf]同时共沉积在 Pd(111)表面上。在超真空（UHV）条件下，在 CO 存在或在 O2 和 CO 存在下进行该过程。我们使用时间分辨（TR）和程序升温（TP）红外反射吸收光谱（IRAS）原位研究了 IL 修饰的 Co 沉积物在基于 PVD 的合成过程中的形成和稳定性。CO 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 Co 纳米颗粒（NPs）的多层。在 CO 和 IL 的振动带中观察到特征的位移和强度变化，这源于 IL/Co 界面的电场（斯塔克效应）和 OTf阴离子的特定吸附。这些观察表明，Co 聚集体由 CO 和 OTf组成的混合吸附壳稳定。随着温度的升高，Co 颗粒上的 CO 覆盖率降低，但在 IL 解吸温度（370 K）之前仍保留一些 CO。此外，如果在 PVCD 过程中引入氧气，则 IL 壳抑制 Co NPs 的氧化。在不存在 IL（5×10(-6) mbar O2）的情况下，在氧气分压迅速导致 Co3O4 形成的情况下，仅形成化学吸附氧。发现这种化学吸附氧会破坏 CO 配体壳的稳定性。如果在其他条件相同的情况下顺序沉积 IL 和 Co，则 Co 的氧化不会受到抑制。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。
