Space-confined growth of nanoscale metal-organic frameworks/Pd in hollow mesoporous silica for highly efficient catalytic reduction of 4-nitrophenol.

The development of confined growth of metal-organic frameworks (MOFs) in a nano-space remains a challenge mainly due to the spatial size randomness and inhomogeneity of host materials and the limitation of MOF species. In this study, we developed a general "stepwise vacuum evaporation" strategy, which allows the nano-confined growth of MOFs in hollow mesoporous silica nanospheres (HMSN) by the vacuum forces and the capillary effect. A series of nanoscale MOFs including ZIF-8, ZIF-90, HKUST-1, MIL-53(Cr) and UiO-66-NH2 were confinely synthesized inside the cavities of HMSN, resulting in hierarchically porous composites with core-shell structures. Further functionalization was studied by anchoring Pd to obtain UiO-66-NH2/Pd@HMSN catalyst, which exhibited excellent activity in the catalytic reduction of 4-nitrophenol to 4-aminophenol under ambient condition.

Flexible Cuprous Triazolate Frameworks as Highly Stable and Efficient Electrocatalysts for CO2 Reduction with Tunable C2 H4 /CH4 Selectivity.

Cu-based metal-organic frameworks have attracted much attention for electrocatalytic CO2 reduction, but they are generally instable and difficult to control the product selectivity. We report flexible Cu(I) triazolate frameworks as efficient, stable, and tunable electrocatalysts for CO2 reduction to C2 H4 /CH4 . By changing the size of ligand side groups, the C2 H4 /CH4 selectivity ratio can be gradually tuned and inversed from 11.8 : 1 to 1 : 2.6, giving C2 H4 , CH4 , and hydrocarbon selectivities up to 51 %, 56 %, and 77 %, respectively. After long-term electrocatalysis, they can retain the structures/morphologies without formation of Cu-based inorganic species. Computational simulations showed that the coordination geometry of Cu(I) changed from triangular to tetrahedral to bind the reaction intermediates, and two adjacent Cu(I) cooperated for C-C coupling to form C2 H4 . Importantly, the ligand side groups controlled the catalyst flexibility by the steric hindrance mechanism, and the C2 H4 pathway is more sensitive than the CH4 one.

Hybrid Zeolitic Imidazolate Frameworks for Promoting Electrocatalytic Oxygen Evolution via a Dual-Site Relay Mechanism.

Developing efficient oxygen evolution reaction (OER) electrocatalysts is important for enhancing the water splitting efficiency. However, with the current catalysts containing one kind of active sites, it is challenging to achieve low overpotentials because of the four-electron transfer process. Herein is reported HZIF-2-CoMo, a new metal-organic framework with well-defined Co-Mo dual sites that can promote the OER process through an unconventional Mo6+/Co2+ dual-site relay mechanism. Theoretical calculations suggested that the Mo and Co sites stabilize the HO* and HOO* intermediates, respectively, and that the unique Co-O-Mo configuration induces the formation of a Co-O*-Mo transition intermediate, remarkably reducing the reaction free energy. As a result, HZIF-2-CoMo shows an overpotential of 277 mV at 10 mA cm-2 and a low Tafel slope of 70 mV dec-1 in alkaline solution, making it one of the best OER electrocatalysts reported to date.