Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584CG, Utrecht, The Netherlands.
Laboratory for Inorganic Materials and Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, P. O. Box 513, 5600, MB, Eindhoven, The Netherlands.
Chemistry. 2020 Jan 13;26(3):691-698. doi: 10.1002/chem.201903761. Epub 2019 Dec 13.
Metal-organic frameworks (MOFs) are a promising class of materials for many applications, due to their high chemical tunability and superb porosity. By growing MOFs as (thin-)films, additional properties and potential applications become available. Here, copper (II) 1,3,5-benzenetricarboxylate (Cu-BTC) metal-organic framework (MOF) thin-films are reported, which were synthesized by spin-coating, resulting in "nanowebs", that is, fiber-like structures. These surface-mounted MOFs (SURMOFs) were studied by using photoinduced force microscopy (PiFM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The optimal concentration of precursors (10 mm) was determined that resulted in chemically homogeneous, pure nanowebs. Furthermore, the morphology and (un)coordinated Cu sites in the web were tuned by varying the rotation speed of the spin-coating process. X-ray diffraction (XRD) analysis showed that rotation speeds ≥2000 rpm (with precursors in a water/ethanol solution) generate the catena-triaqua-μ-(1,3,5-benzenetricarboxylate)-copper(II), or Cu(BTC)(H O) coordination polymer. X-ray photoelectron spectroscopy (XPS) highlighted the strong decrease in number of (defective) Cu sites, as the nanowebs mainly consist of coordinated Cu Lewis acid sites (LAS) and organic linker-linker, for example, hydrogen-bonding, interactions. Finally, the Lewis-acidic character of the Cu sites is illustrated by testing the films as catalysts in the isomerization of α-pinene oxide. The higher number of LAS (≥3000 rpm), result in higher campholenic aldehyde selectivity reaching up to 87.7 %. Furthermore, the strength of a combined micro- and spectroscopic approach in understanding the nature of MOF thin-films in a spatially resolved manner is highlighted.
金属-有机骨架（MOFs）由于其高化学可调性和极好的多孔性，在许多应用中是一种很有前途的材料。通过将 MOFs 生长为（薄）膜，可以获得额外的性质和潜在的应用。本文报道了铜（II）1,3,5-苯三甲酸（Cu-BTC）金属-有机骨架（MOF）薄膜，通过旋涂法合成，得到“纳米网”，即纤维状结构。通过光致力显微镜（PiFM）和飞行时间二次离子质谱（ToF-SIMS）研究了这些表面安装的 MOFs（SURMOFs）。确定了最佳的前体浓度（10 mmol），得到了化学均匀、纯纳米网。此外，通过改变旋涂过程的转速来调节网络中的形貌和配位 Cu 位。X 射线衍射（XRD）分析表明，转速≥2000 rpm（前体在水/乙醇溶液中）生成链三 Aqua-μ-（1,3,5-苯三甲酸）-铜（II），或 Cu（BTC）（H2O）配位聚合物。X 射线光电子能谱（XPS）突出显示了配位 Cu 路易斯酸位（LAS）和有机配体-配体（例如氢键）数量的强烈减少，网络主要由路易斯酸位（LAS）和有机配体-配体组成。最后，通过将薄膜用作α-蒎烯氧化物异构化反应的催化剂来证明 Cu 位的路易斯酸性。LAS 的数量较多（≥3000 rpm），导致愈创木酚醛的选择性高达 87.7%。此外，还强调了微区和光谱相结合的方法在以空间分辨方式理解 MOF 薄膜的性质方面的强大作用。
