Ming Xue

Porous ZnCo2O4 nanoparticles derived from a new mixed-metal organic framework for supercapacitors

Cobalt-based oxides have been shown to be promising materials for application in high-energy-density Li-ion batteries and supercapacitors. In this paper, we report a new and simple strategy for the synthesis of a mixed-metal spinel phase (ZnCo2O4) from a zinc and cobalt mixed-metal organic framework (JUC-155). It is important to rationally design a MOF with a precise ratio (Co/Zn) and a synthetic process that is simple and time saving. After solid-state annealing of the mixed-metal MOF precursor at 400 °C for two hours, a pure ZnCo2O4 phase with a high surface area (55 cm2 g−1) was obtained. When used as electrode materials for supercapacitors, an exceptionally high specific capacitance of 451 F g−1 was obtained at the scan rate of 5 mV s−1. The capacitance loss after 1500 cycles was only 2.1% at a current density of 2 A g−1, indicating that this phase has an excellent cycling stability. These remarkable electrochemical performances suggest that this phase is potentially promising for application as an efficient electrode in electrochemical capacitors.

Rational design and synthesis of NixCo3−xO4 nanoparticles derived from multivariate MOF-74 for supercapacitors

Mixed transition metal oxides have attracted much attention recently due to their potential application in energy and environmental sciences. The emergence of multivariate MOFs recently has attracted great research attention and provides an opportunity for multivariate mixed-metal oxides. In this work, five isostructural, single-phase MOF-74 structures with different divalent metals (MOF-74–Co, MOF-74–Ni, MOF-74–NiCo1, MOF-74–NiCo2 and MOF-74–NiCo4) were synthesised by varying the mole ratios of Ni/Co mixed-metal ions. After annealing at the appropriate temperature, Co3O4, NiO and three kinds of NixCo3−xO4 mixed-metal oxide nanoparticles with high surface area were easily obtained and the metal ratio was readily controlled, enabling us to systematically investigate the effect of different metal species amounts on the electrochemical properties of the mixed-metal oxide materials. When these metal oxides were used as electrode materials for supercapacitors, we found that the mixed-metal oxides NixCo3−xO4 obtained from bimetallic MOF-74–NiCo structures had obvious advantages compared with the monometallic oxides of MOF-74–Ni and MOF-74–Co. In particular, the NixCo3−xO4-1 with the Ni/Co metal ratio 1 : 1 exhibited the highest capacitance of 797 F g−1 and excellent cycling stability.

Highly selective sieving of small gas molecules by using an ultra-microporous metal–organic framework membrane

Two tailor-made microporous metal–organic framework (MOF) membranes were successfully fabricated on nickel screens by secondary growth. The effect of pore structures on gas separation was examined by means of single and binary gas permeation tests. The MOF JUC-150 membrane with its ultra-micropores showed marked preferential permeance to H2 relative to other gas molecules. The selectivity factors of this membrane were 26.3, 17.1 and 38.7 for H2/CH4, H2/N2 and H2/CO2, respectively, at room temperature. To the best of our knowledge, these values represent unprecedentedly high separation selectivity among those for all MOF membranes reported to date. The JUC-150 membrane also shows high thermal stability and outstanding separation performance at a high temperature of 200 °C. The separation performance of these membranes persists even after more than 1 year exposure to air. The superiority of the tailored pore size, high selectivity for H2 over other gases, significant stability and recyclability make these materials potential candidates for industrial H2 recycling applications.

Electrospinning technology applied in zeolitic imidazolate framework membrane synthesis

For the first time, an electrospinning technique has been introduced into the synthesis of supported microporous membranes. This new approach is suitable for various substrates, especially tubes, with the possibility of large-area processing. We can precisely control the thickness of the seed layer and obtain a continuous and uniform seed coating on the support surface. The zeolite imidazolate framework-8 was selected as a candidate to demonstrate the effectiveness of this method, by which, defect-free and well-intergrown ZIF-8 membranes have been successfully synthesized. Single gas permeance of H2, N2, CH4, CO2 and binary mixtures experiments for H2–CO2, H2–CH4, H2–N2 were carried out. The results indicated that the ZIF-8 membrane prepared through this new approach had better H2 selectivity and gas permeability.

A chiral layered Co(II) coordination polymer with helical chains from achiral materials

A layered coordination polymer Co(PDC)(H2O)2.H2O containing two helical chains was synthesized, and the resultant crystals were not racemic as evidenced by the observation of strong signals in vibrational circular dichroism (VCD) spectra.

Porous coordination polymers with zeolite topologies constructed from 4-connected building units

Two novel 3D coordination polymers, Cd(CTC)(H2O).(H2PIP)(0.5)(H2O) (1) with zeolite ABW topology and Cd(CTC).(HIPA) (2) with zeolite BCT topology, have been synthesized by constructing inorganic and organic 4-connected building units and using the organic bases as templates, and the frameworks of and not only expand the original structures of zeolites ABW and BCT, but also exhibit significant advantages over them in terms of thermal stability, ion exchange and adsorption.

Cation exchanged MOF-derived nitrogen-doped porous carbons for CO2 capture and supercapacitor electrode materials

A new strategy was developed to introduce active site K+ into the pores of MOF precursors, and various N-doped hierarchical porous carbons were prepared in a one-step synthetic route. The effect of K+in situ activation on the textural properties of the derived porous carbons was studied systematically, and the CO2 capture properties and electrochemical performance of these porous carbons were enhanced for their application in supercapacitors. The KBM-700 sample derived from K@bio-MOF-1 (potassium-ion-exchanged bio-MOF-1), which had high nitrogen content (10.16%) and micropore volume (73%), exhibited good CO2 uptakes (4.75 mmol g−1), and high adsorption selectivity for CO2/N2 at 298 K and 1 bar (Sads = 99.1) as well as high specific capacitance (230 F g−1) and excellent electrochemical cycling stability (97% retention after cycling 10 000 times).

Direct observations of the MOF (UiO-66) structure by transmission electron microscopy

As a demonstration of ab initio structure characterizations of nano metal organic framework (MOF) crystals by high resolution transmission electron microscopy (HRTEM) and electron diffraction tomography methods, a Zr-MOF (UiO-66) structure was determined and further confirmed by Rietveld refinements of powder X-ray diffraction. HRTEM gave direct imaging of the channels.

ZIF-derived in situ nitrogen decorated porous carbons for CO2 capture

Various N-doped hierarchical porous carbons were prepared by using a new mixed-ligand ZIF (zeolitic imidazolate framework) (JUC-160) as the precursor in a one-step synthetic route without any additional carbon sources or purification steps. The effect of the ZIF precursor crystal size on the textural properties of the derived porous carbons was systematically studied. Microporosity was dominant in micron-sized JUC-160 crystal derived porous carbons, while more mesopore volume was present in porous carbons obtained from nanometre-sized JUC-160 crystals. The mJUC160-900 sample, which had a high nitrogen content and micropore volume, exhibited the highest CO2 uptake, which is 5.50 and 3.50 mmol g−1 at 273 and 298 K, respectively. Moreover, the analysis based on the ideal adsorbed solution theory (IAST) exhibited a high adsorption selectivity for CO2/N2 at 298 K and 1 bar (Sads = 29). Introduction to the international collaboration State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, at Jilin University China, has a long term cooperation with the Laboratory of Catalysis and Spectroscopy in Caen, at CNRS-France. Recently, Prof. Shilun Qius group and Prof. Valentin Valtchevs group had an international collaborative researching project entitled “Microporous materials: green synthesis for green applications”, which was supported by the National Natural Science Foundation of China (21261130584) and the French Science Foundation (ANR-12-IS08-0001-01). This project is focused on the design and synthesis of porous materials such as zeolites, metal organic frameworks (MOFs), covalent organic frameworks (COFs), porous aromatic frameworks (PAFs) and porous carbon materials that can find applications for clean energy storage, carbon capture, catalysis, and molecular selective sorption and separation.

Three-Dimensional Ionic Covalent Organic Frameworks for Rapid, Reversible, and Selective Ion Exchange

Covalent organic frameworks (COFs) have emerged as functional materials for various potential applications. However, the availability of three-dimensional (3D) COFs is still limited, and nearly all of them exhibit neutral porous skeletons. Here we report a general strategy to design porous positively charged 3D ionic COFs by incorporation of cationic monomers in the framework. The obtained 3D COFs are built of 3-fold interpenetrated diamond net and show impressive surface area and CO2 uptakes. The ion-exchange ability of 3D ionic COFs has been highlighted by reversible removal of nuclear waste model ions and excellent size-selective capture for anionic pollutants. This research thereby provides a new perspective to explore 3D COFs as a versatile type of ion-exchange materials.