Institut für Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str. 2, 24118 Kiel, Germany.
Dipartimento di Chimica Biologia e Biotecnologia, University of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy.
Inorg Chem. 2023 Apr 3;62(13):5176-5185. doi: 10.1021/acs.inorgchem.3c00049. Epub 2023 Mar 24.
The use of the V-shaped linker molecules 4,4'-oxydibenzoic acid (HODB) and 4,4'-carbonyldibenzoic acid (HCDB) led to the discovery of two isoreticular Ce(IV)-based metal-organic frameworks (MOFs) of composition [CeO(HO)(L)], L = ODB, CDB, denoted CAU-58 (CAU = Christian-Albrechts-University). The recently developed Ce-MOF synthesis approach in acetonitrile as the solvent proved effective in accessing Ce(IV)-MOF structures with infinite rod-shaped inorganic building units (IBUs) and circumventing the formation of the predominantly observed hexanuclear [CeO] cluster. For the structure determination of the isoreticular MOFs, three-dimensional electron diffraction (3D ED) and powder X-ray diffraction (PXRD) data were used in combination with density functional theory (DFT) calculations. [CeO(HO)(CDB)] shows reversible HO adsorption by stirring in water and thermal treatment at 190 °C, which leads to a unit cell volume change of 11%. The MOFs feature high thermal stabilities ( > 290 °C), which exceed those of most Ce(IV)-MOFs and can be attributed to the infinite rod-shaped IBU. Surface and bulk oxidation states of the cerium ions were analyzed X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). While Ce(III) ions are observed by the highly surface-sensitive XPS method, the bulk material contains predominantly Ce(IV) ions according to XANES. Application of the MOFs as catalysts for the catalytic degradation of methyl orange in aqueous solutions was also studied. While degradation activity for both MOFs was observed, only CAU-58-ODB revealed enhanced photocatalytic activity under ultraviolet (UV) light. The photocatalytic mechanism likely involves a ligand-to-metal charge transfer (LMCT) from the linkers to the Ce(IV) centers. Analyses by XANES and inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrate that leaching of Cerium ions as well as partial reduction of Ce(IV) to Ce(III) takes place during catalysis. At the same time, PXRD data confirm the structural stability of the remaining MOF catalysts.
使用 V 形连接分子 4,4'- 氧二苯甲酸（HODB）和 4,4'- 羰基二苯甲酸（HCDB），发现了两种同构的基于 Ce(IV)的金属-有机骨架（MOF）的组成[CeO(HO)(L)]，L = ODB，CDB，标记为 CAU-58（CAU = 克里斯蒂安-阿尔布雷希特-大学）。最近在乙腈溶剂中开发的 Ce-MOF 合成方法被证明是有效的，可获得具有无限棒状无机建筑单元（IBU）的 Ce(IV)-MOF 结构，并避免了主要观察到的六核[CeO]簇的形成。为了确定同构 MOF 的结构，使用了三维电子衍射（3D ED）和粉末 X 射线衍射（PXRD）数据，并结合密度泛函理论（DFT）计算。[CeO(HO)(CDB)]在水中搅拌和在 190°C 下热处理可实现可逆的 HO 吸附，导致单元体积变化 11%。MOF 具有高的热稳定性（>290°C），超过大多数 Ce(IV)-MOF，并可归因于无限棒状 IBU。通过 X 射线光电子能谱（XPS）和 X 射线吸收近边光谱（XANES）分析了铈离子的表面和体相氧化态。虽然 XPS 方法高度敏感地观察到 Ce(III)离子，但根据 XANES，块状材料主要包含 Ce(IV)离子。还研究了 MOF 作为催化剂在水溶液中催化降解甲基橙的应用。虽然两种 MOF 都观察到了降解活性，但只有 CAU-58-ODB 在紫外（UV）光下显示出增强的光催化活性。光催化机制可能涉及从配体到 Ce(IV)中心的配体到金属电荷转移（LMCT）。XANES 和电感耦合等离子体-光发射光谱（ICP-OES）分析表明，在催化过程中会发生 Cerium 离子浸出以及 Ce(IV)部分还原为 Ce(III)。与此同时，PXRD 数据证实了剩余 MOF 催化剂的结构稳定性。
