The water oxidation reaction involves a four electron–proton coupled process that is kinetically sluggish and has hindered the widespread application of water-splitting technology. Metal-MOF-coupled heterostructures serve as good OER electrocatalysts due to their endowed MOF frameworks and numerous transition metal active sites at the interface. In this study, a simple ultrasonic impregnation strategy was used to prepare CoOx/UiO-66-300 and NiO/UiO-66-300 heterostructures via the impregnation of Co and Ni ions into UiO-66 followed by roasting in air at 300 °C to obtain heterostructures with UiO-66-retained frameworks as revealed by SEM. The electrochemical results show that the respective impregnation successfully modulated the electronic charge at the interface of the heterostructures, leading to rapid electron transfer that enhanced the OER activity. CoOx/UiO-66-300 and NiO/UiO-66-300 heterostructures showed good oxygen evolution reaction activities of 283 mV and 291.6 mV, respectively, due to the retained UiO-66 framework, while CoOx/UiO-66-550 and NiO/UiO-66-550 heterostructures calcined at 550 °C showed a decrease in OER activities of 332.6 mV and 346.6 mV, respectively, due to the collapsed UiO-66 framework. This work gives insight into the development of heterostructures of MOF-retained frameworks for energy applications.
Rong Shang,Qizhao Zhang,Peng Lin,Bang Gu,Qinghu Tang,Qiue Cao,Wenhao Fang
Direct oxidative coupling of alcohols and amines is an environmental-benign and atomic-economy approach for imine synthesis. We disclosed that UiO-66 framework successfully confined Ru to single-atom scale with assistance of oxophilic Zn 2+ promoter. This RuZn@UiO-66 catalyst showed a highest TOF of 78 h -1 among all Ru catalysts in literature and attained > 99% yield to benzylideneaniline in the model reaction in an O 2 atmosphere at a low temperature without alkaline additives. In addition, this catalyst demonstrated satisfying gram-scale imine synthesis, wide substrate scope and stable reusability. Kinetic investigations and in situ characterizations allowed getting insights to active sites, amphoteric carrier and reaction mechanism. Dynamic interactions between Ru and Zn based on their ratios induced electron-deficient Ru 0 active sites promoted by oxophilic Zn 2+ species. Hence, primary alcohols can be efficiently converted to the corresponding aldehydes using molecular O 2 , i.e. , the rate-determining step. Besides, Zr 4+ -O 2- pairs on UiO-66 provided adequate acidic-basic sites for the tandem catalysis.
Ionic Liquids (IL) has been recently immobilized into the pores of metal-organic framework materials (MOFs) to prepare heterogeneous catalyst. However, the IL@MOFs composites are generally prepared by impregnation method, which is unstable in polar solvents. So, we design a new strategy to immobilize IL, and a novel Fenton-like catalyst [mim(CH 2 ) 3 COO]FeCl 4 @UiO-66 has been prepared based on the post-synthetic ligand exchange (PSLE) between MOFs and monocarboxylic functional IL. The [mim(CH 2 ) 3 COO]FeCl 4 @UiO-66 was exploited to act as an efficient heterogeneous catalyst for dibenzothiophene (DBT) oxidation in a biphasic system using H 2 O 2 as the oxidant. Based on optimal conditions, the DBT removal efficiency reached up to 99.1%. Moreover, the heterogeneous catalyst had a good thermal and chemical stability, and the DBT removal efficiency still exhibited over 95% after 6 recycle runs. It is worth noting that the high DBT removal efficiency could be attributed to the synergistic effect between adsorptive and oxidative desulfurization, where [mim(CH 2 ) 3 COO]FeCl 4 @UiO-66 is both an adsorbent and a catalyst.
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