Lili Fan

Recent advances and challenges of metal–organic framework membranes for gas separation

Gas separation is one of the most critical and challenging steps for industrial processes, and metal–organic framework (MOF) membranes are potential candidates for this application. This review mainly focuses on the recent advances in improving the performance of MOF membranes, involving the issues faced with MOF designation and growth for practical applications. First, we discussed three strategies for permeability and selectivity enhancement of MOF membranes, in terms of obtaining ultra-thin two-dimensional (2D) MOF nanosheets, fine-tuning the pore size of the MOF framework and integrating with other species. Second, we reviewed the recent potential resolutions to the problems of MOF membranes for future practical applications including scale-up preparation and stability improvement. Finally, we summarized our work by providing some general conclusions on the state-of-the-art and an outlook on some development directions of molecule-sieving membranes.

Metal–Organic Framework Derived Porous Hollow Co3O4/N–C Polyhedron Composite with Excellent Energy Storage Capability

Metal-organic frameworks (MOFs) derived transition metal oxides exhibit enhanced performance in energy conversion and storage. In this work, porous hollow Co3O4 with N-doped carbon coating (Co3O4/N-C) polyhedrons have been prepared using cobalt-based MOFs as a sacrificial template. Assembled from tiny nanoparticles and N-doped carbon coating, Co3O4/N-C composite shortens the diffusion length of Li+/Na+ ions and possesses an enhanced conductivity. And the porous and hollow structure is also beneficial for tolerating volume changes in the galvanostatic discharge/charge cycles as lithium/sodium battery anode materials. As a result, it can exhibit impressive cycling and rating performance. At 1000 mA g-1, the specific capacities maintaine stable values of ∼620 mAh g-1 within 2000 cycles as anodes in lithium ion battery, while the specific capacity keeps at 229 mAh g-1 within 150 cycles as sodium ion battery anode. Our work shows comparable cycling performance in lithium ion battery but even better high-rate cycling stability as sodium ion battery anode. Herein, we provide a facile method to construct high electrochemical performance oxide/N-C composite electrode using new MOFs as sacrificial template.

Green Fabrication of Ultrathin Co3O4 Nanosheets from Metal–Organic Framework for Robust High-Rate Supercapacitors

Two-dimensional cobalt oxide (Co3O4) is a promising candidate for robust electrochemical capacitors with high performance. Herein, we use 2,3,5,6-tetramethyl-1,4-diisophthalate as a recyclable ligand to construct a Co-based metal-organic framework of UPC-9, and subsequently, we obtain ultrathin hierarchical Co3O4 hexagonal nanosheets with a thickness of 3.5 nm through a hydrolysis and calcination process. A remarkable and excellent specific capacitance of 1121 F·g-1 at a current density of 1 A·g-1 and 873 F·g-1 at a current density of 25 A·g-1 were achieved for the as-prepared asymmetric supercapacitor, which can be attributed to the ultrathin 2D morphology and the rich macroporous and mesoporous structures of the ultrathin Co3O4 nanosheets. This synthesis strategy is environmentally benign and economically viable due to the fact that the costly organic ligand molecules are recycled, reducing the materials cost as well as the environmental cost for the synthesis process.

In situ confinement of free linkers within a stable MOF membrane for highly improved gas separation properties

A stable MOF membrane with guest molecules encapsulated in the pores by in situ synthesis has been successfully fabricated. The in situ confinement of linkers in the channels of the MOF membrane improves its gas separation properties, which may provide a general method for fine-tuning the pore size of MOF membranes and develop the functional applications of porous MOF materials.

Bimetallic-MOF Derived Accordion-like Ternary Composite for High-Performance Supercapacitors

Supercapacitors are regarded to be highly probable candidates for next-generation energy storage devices. Herein, a bimetallic Co/Ni MOF is used as a sacrificial template through an alkaline hydrolysis and selective oxidation process to prepare an accordion-like ternary NiCo2O4/β-Ni xCo1- x(OH)2/α-Ni xCo1- x(OH)2 composite, which is composed of Co/Ni(OH)2 nanosheets with large specific surface as the frame and NiCo2O4 nanoparticles with high conductivity as the insertion, for supercapacitor application. This material exhibits both high specific capacitance (1315 F·g-1 at 5 A·g-1) and excellent cycle performance (retained 90.7% after 10 000 cycles). This hydrolysis-oxidation process, alkali hydrolysis followed by oxidation with H2O2, offers a novel approach to fabricate the Ni/Co-based electrode materials with enhanced supercapacitor performance.

In situ generation of intercalated membranes for efficient gas separation

Membranes with well-defined pore structure which have thin active layers may be promising materials for efficient gas separation. Graphene oxide (GO) materials have potential applications in the field of membrane separation. Here we describe a strategy for the construction of ultra-thin and flexible HKUST-1@GO intercalated membranes, where HKUST-1 is a copper-based metal–organic framework with coordinatively unsaturated metal sites, with simultaneous and synergistic modulation of permeance and selectivity to achieve high H2/CO2 separation. CuO nanosheets@GO membranes are fabricated layer-by-layer via repeated filtration cycles, then transformed to HKUST-1@GO membranes upon in situ reaction with linkers. The HKUST-1@GO membranes show enhanced performance for gas separation of H2/CO2 mixture. The number of filtration cycles is optimized to obtain H2 permeance of 5.77 × 10−7 mol m−2 s−1 Pa−1 and H2/CO2 selectivity of 73.2. Our work provides a facile strategy for the construction of membranes based on metal–organic frameworks and GO, which may be applied in the preparation of flexible membranes for gas separation applications.Graphene oxide membranes are promising materials for the separation of low molecular weight gases. Here, composite membranes comprising metal organic frameworks and graphene oxide show improved selectivity for the separation of hydrogen and carbon dioxide over graphene oxide alone.