Laboratoire de Chimie des Processus Biologiques, UMR 8229 CNRS, UPMC Univ Paris 06, Collège de France , 11 Marcelin Berthelot, 75231 Paris Cedex 05, France.
Institut de Chimie du Collège de France, Collège de France , 11 Marcelin Berthelot, 75231 Paris Cedex 05, France.
J Am Chem Soc. 2017 Jun 21;139(24):8222-8228. doi: 10.1021/jacs.7b02186. Epub 2017 Jun 7.
Despite the promise of utilizing metal-organic frameworks (MOFs) as highly tunable photocatalytic materials, systematic studies that interrogate the relationship between their catalytic performances and the amount of functionalized linkers are lacking. Aminated linkers are known to enhance the absorption of light and afford photocatalysis with MOFs under visible-light irradiation. However, the manner in which the photocatalytic performances are impacted by the amount of such linkers is poorly understood. Here, we assess the photocatalytic activity of MIL-125, a TiO/1,4-benzenedicarboxylate (bdc) MOF for the oxidation of benzyl alcohol to benzaldehyde when increasing amounts of bdc-NH linkers (0%, 20%, 46%, 70%, and 100%) are incorporated in the framework. Analytical TEM allowed assessing the homogeneous localization of bdc-NH in these mixed-linker MOFs. Steady state reaction rates reveal two regimes of catalytic performances: a first linear regime up to ∼50% bdc-NH into the hybrid framework whereby increased amounts of bdc-NH yielded increased photocatalytic rates, followed by a plateau up to 100% bdc-NH. This unexpected "saturation" of the catalytic activity above ∼50% bdc-NH content in the framework whatever the wavelength filters used demonstrates that amination of all linkers of the MOF is not required to obtain the maximum photocatalytic activity. This is rationalized on the basis of mixed-valence Ti/Ti intermediate catalytic centers revealed by electron spin resonance (ESR) measurements and recent knowledge of lifetime excited states in MIL-125-type of solids.
尽管金属-有机骨架（MOFs）作为高度可调的光催化材料具有广阔的应用前景，但缺乏系统研究来探究其催化性能与功能化连接体数量之间的关系。已知胺化连接体可以增强 MOFs 对光的吸收，并在可见光照射下提供光催化作用。然而，人们对这种连接体的数量如何影响光催化性能的了解甚少。在这里，我们评估了 MIL-125 的光催化活性，MIL-125 是一种 TiO2/1,4-苯二甲酸（bdc）MOF，用于氧化苄醇为苯甲醛，当框架中逐渐增加 bdc-NH 连接体的数量（0%、20%、46%、70%和 100%）时。分析性 TEM 允许评估 bdc-NH 在这些混合连接体 MOFs 中的均匀定位。稳态反应速率揭示了两种催化性能的模式：第一个线性模式持续到约 50%的 bdc-NH 进入混合框架，其中增加的 bdc-NH 数量会增加光催化速率，然后是直到 100% bdc-NH 的平台。这种在框架中 bdc-NH 含量超过约 50%时出现的催化活性“饱和”现象，无论使用何种波长滤光片，都证明了 MOF 的所有连接体的胺化并不需要获得最大的光催化活性。这可以基于电子自旋共振（ESR）测量揭示的混合价 Ti/Ti 中间催化中心和最近对 MIL-125 型固体中激发态寿命的认识来合理化。
