Xiaoqin Zou

From metal–organic framework (MOF) to MOF–polymer composite membrane: enhancement of low-humidity proton conductivity

A chiral two-dimensional MOF, {[Ca(D-Hpmpc)(H2O)2]·2HO0.5}n (1, D-H3pmpc = D-1-(phosphonomethyl) piperidine-3-carboxylic acid), with intrinsic proton conductivity has been synthesized and characterized. Structure analysis shows that compound 1 possesses protonated tertiary amines as proton carriers and hydrogen-bonding chains served as proton-conducting pathways. Further, MOF–polymer composite membranes have been fabricated via assembling polymer PVP with different contents of rod-like 1 submicrometer crystals. Interestingly, the proton conductivity of this composite membrane containing 50 wt% 1 is rapidly increased, compared with that of pure submicrometer crystals at 298 K and ∼53% RH. Therefore, it is feasible to introduce humidification of PVP into composite membranes to enhance low-humidity proton conductivity; and humidified PVP with adsorbed water molecules plays an important role in proton conduction indicated by the results of water physical sorption and TG/DTG analyses. This study may offer a facile strategy to prepare a variety of solid electrolyte materials with distinctive proton-conducting properties under a low humidity.

Topology-directed design of porous organic frameworks and their advanced applications

Porous organic frameworks (POFs) as an important subclass of nanoporous materials are of great interest in materials science. In recent years, the discovery and creation of POFs with excellent properties for advanced applications have attracted much attention and intensive efforts have been contributed to this field. As a result, the design of materials with multi-functionalities is an ever-pursued dream of materials scientists and engineers. In this respect, a new concept based on topology chemistry is introduced for the rational and targeted synthesis of POF materials. The present feature article provides an overview of the relationship between building blocks or starting monomers, underlying topological nets, and pre-determined structures. Several important nets are included successively from one to three dimensions. In addition, special emphasis is given to the advanced applications of designed POF materials in the current paper.

Synthesis of a metal–organic framework film by direct conversion technique for VOCs sensing

For the first time, a metal-organic framework Zn(3)(BTC)(2) film has been successfully synthesized on the substrate of zinc wafer by a direct conversion technique. The obtained crystal densities and inter-growth of the film have been improved via the zinc wafer conversion method. The effect of synthesis conditions on the crystallization of Zn(3)(BTC)(2) and activation of the substrate were determined to optimize the strategies for the synthesis of continuous and stable layers. The crystallization took place by converting the activated zinc layer on the substrate. The reaction between the substrate-generated zinc source and the H(3)BTC clear solution yielded the best inter-growth of crystals and formed a high-density coating. More interestingly, the fluorescence emission of the Zn(3)(BTC)(2) film was found to be highly sensitive and selective sensing to dimethylamine among different VOCs. The fluorescence intensity decreased with increasing contents of dimethylamine in ethanol solution due to weak fluorescence quenching effect. This high-quality MOF film may find promising applications in sensors, especially in VOCs sensing.

Highly Selective and Permeable Porous Organic Framework Membrane for CO2 Capture

DOI: 10.1002/adma.201400020 polymer; providing abundant active sites (e.g. amino groups) for CO 2 sorption. The obtained SNW-1 exhibits a three-dimensional framework with major pore size falling in the molecular scale (5 Å). Polysulfone (PSF Udel P-3500) is chosen as the appropriate matrix thanks to its glassy and organic nature, high thermal/chemical stability, and commercial availability. SNW-1/PSF membrane is fabricated by fi lling SNW-1 nanoparticles into PSF matrix using a spin-coating method; and further applied for CO 2 capture from gas streams of CO 2 /CH 4 and CO 2 /N 2 . The extended aminal network of SNW-1 polymer is built up by forming C-N bonds between two monomers of melamine and terephthalaldehyde, the structure of which (Figure 1 a) is verifi ed by 13 C and 15 N NMR data (Figure S1). [ 5 ] Upon polymerization, many pores are generated by an elimination of water molecules; and the porosity is probed by the N 2 -sorption measurement (Figure 1 b). The adsorption isotherms show a steep uptake at low relative pressures, followed by nearly horizontal adsorption and desorption branches at high pressures, typical for microporous materials. The texture data is summarized in Table S1, Supporting Information. The specifi c Brunauer– Emmet–Teller surface area (S BET ) and micropore volume are 821 m 2 g −1 and 0.26 cm 3 g −1 , indicating a high degree of cross linking of monomers; which is in an agreement of the peak disappearance of C O vibration (1690 cm −1 ) from aldehydes (Figure S2, Supporting Information). To be noted, the major pore size of voids in SNW-1 is calculated to be around 5 Å using the NL-DFT method as seen from the pore size distribution curve (insert picture in Figure 1 b); which can be also visualized in a molecular model of a fragment of SNW-1 in Figure 1 a. The value of pore size corresponds to a small micropore (3∼20 Å for microporous materials from IUPAC). IR spectrum shows that SNW-1 network bears free N-H groups (Figure S2, Supporting Information). Small pores and available N-H groups in this POF material are benefi cial for CO 2 recognition, and thus selective diffusion of CO 2 (3.3 Å) through the pores would be expected. The morphology and size of as-synthesized SNW-1 particles are studied by SEM ( Figure 2 a). Spherical shape is observed for as-prepared nanoparticles, and the size of an individual one is about 100 nm. Small particles are superior for obtaining a homogeneous mixture with matrix for further membrane fabrication, which is evidenced by a stable suspension without any visible sedimentation after one month at static condition (see insert picture in Figure 2 a). SNW-1/PSF membrane is fabricated by spin coating SNW-1/PSF suspension in CHCl 3 onto a macroporous glass frit. The optical picture in Figure 2 b shows that the support is entirely covered by SNW-1/PSF layer homogeneously. Insight views of the membrane layer are inspected by SEM. Figure 2 c and d display the side views of a particular Microporous membranes with pore openings at a molecular level can exhibit size selectivity as molecular sieves, which are promising in membrane-based gas separations. [ 1 ] Between microporous materials, zeolites, metal organic frameworks (MOFs) and active carbons are widely used for this purpose. Very recently, porous organic frameworks (POFs or COFs) [ 2 ] as a new family member of molecular sieves have been a hot and frontier research theme in materials science and technology, and attracted increasing attentions. POFs are composed of different organic moieties linked by covalent bonds, resulted in diversifi ed structures with controllable pores ranging from 0.3 to 50 nm. The features of highly permanent porosity, exceptionally high thermal stability, and low framework density; make this class of porous materials as an ideal candidate in membrane applications. [ 3 ] Microporous POFs owing to their high surface areas and intrinsic polymer characteristics of the entirely covalent bonded networks, possess great advantages over classical inorganic porous counterparts of being easily processed into membranes. Thus, the preparation of POF membranes for gas separation has been proposed [ 3b-d ] since they provide an energy-effi cient and reliable technology in separating various gases including air purifi cation, hydrogen recovery and the upgrading of natural gas. CO 2 capture or separation from the fl ue gas or natural gas is of great interests from the energy and environmental perspective. [ 4 ] Currently, removal or purifi cation of CO 2 from gas streams of power plants and reservoirs is commonly accomplished by cryogenic method or sorption approach using different adsorbents; both of which are costly and ineffi cient. In order to search an effi cient technology with long-term viability for CO 2 removal, microporous membranes have been pursued as alternative means because it combines two merits of high CO 2 uptake and affi nity in porous materials, and operation fl exibility with membrane process. Based on the considerations above, an N-rich Schiff based POF (SNW-1) [ 5 ] is selected as a potential candidate for membrane fabrication. SNW-1 constructed from industrial chemicals of melamine and di-aldehydes (the chemical structure of a fragment of SNW-1 is shown in Figure 1 a), is a nitrogen-rich

Novel lithium-loaded porous aromatic framework for efficient CO2 and H2 uptake

Novel porous aromatic frameworks, PAF-18-OH and its lithiated derivative PAF-18-OLi, have been successfully synthesized. In particular, PAF-18-OLi displays significant enhancement of H2 and CO2 adsorption capacity, especially for CO2 uptake (14.4 wt%). More valuably, the stable PAF-18-OLi material exhibits high CO2/N2 selectivity, as high as 129 in the case of CO2 capture from simulated post-combustion flue gas mixtures (85% N2 and 15% CO2). Furthermore, the PAF-18-OLi has shown improved H2 storage capacity after lithiation.

Post-metalation of porous aromatic frameworks for highly efficient carbon capture from CO2 + N2 and CH4 + N2 mixtures

The development of microporous materials for carbon capture, especially for carbon dioxide and methane, is a rapidly growing field based on the increasing demand for clean energy and pressing environmental concerns of global warming effected by greenhouse gases. To achieve this goal of developing carbon selective porous materials, a new porous aromatic framework featuring carboxyl-decorated pores, PAF-26-COOH, has been synthesized successfully. The modification of PAF-26 materials with representative light metals is exemplified by Li, Na, K and Mg via a post-metalation approach. The obtained PAF-26 products exhibit moderate surface area and controllable pore size at the atomic level. Gas sorption of CO2, CH4 and N2 is carried out on as-prepared PAF-26 samples at mild temperatures (273 K and 298 K). It is found that the PAF-26 materials show high adsorption capacity for CO2 and CH4 and low ability toward N2. Particularly, as-synthesized PAF-26 compounds exhibit remarkably high isosteric heats of adsorption toward CO2 and CH4, indicating high affinity for CO2 and CH4 gases. The gas selectivity for CO2–N2 and CH4–N2 mixtures is predicted by the IAST model. High selectivity of 80 for CO2 over N2 is obtained for PAF-26-COOMg. In addition, high selectivity values of CH4 over N2 are observed. The high performance including high storage capacity and selectivity makes PAF-26 materials promising for carbon capture or sequestration.

Challenging fabrication of hollow ceramic fiber supported Cu3(BTC)2 membrane for hydrogen separation

High-performance and continuous Cu3(BTC)2 membranes have been successfully fabricated using a secondary growth approach on pre-seeded α-Al2O3 hollow ceramic fibers (HCFs) modified with chitosan. Facile synthesis of Cu3(BTC)2 nanocrystals can be achieved by a modified solvothermal protocol. A stable and homogeneous Cu3(BTC)2 seed precusor obtained with particle size of 300 nm, the size of which is suitable for seeding HCFs without any pore jam of HCFs supports (pore size of 200 nm for HCFs). A new substrate HCFs was introduced as the support of Cu3(BTC)2 membranes. Moreover, for the first time, chitosan is used to improve the binding force between seeds and the support owing to its abundance of both amino and hydroxyl groups. As-prepared Cu3(BTC)2 membrane is studied for hydrogen separation by binary gas permeation of H2/N2, H2/CO2 and H2/CH4. The synthesized membrane shows high H2 selectivity with separation factors of 8.66, 13.56 and 6.19 for the gas mixtures of H2/N2, H2/CO2 and H2/CH4 respectively. A preferred permeance for H2 in the binary gas mixture is obtained in the range of 3.23 × 10−8 to 4.1 × 10−8 mol m−2 s−1 Pa−1 due to the unique properties of the Cu3(BTC)2 MOF material, which is expected in the potential applications of industrial hydrogen recycling.

Defect-driven oxygen reduction reaction (ORR) of carbon without any element doping

A porous carbon (PC) material, containing carbon and oxygen only, was synthesized via carbonisation of a Zn-MOF (IRMOF-8) at 950 °C. Interestingly, the derived materials of this reaction exhibit excellent electrocatalytic activity, molecular selectivity and long-term durability. The fact that this material, which is effectively a “pure” carbon, lacking any elemental doping, exhibits excellent oxygen reduction reaction (ORR) activity suggests that a mechanism not dependent on elemental doping is being utilised. We suggest the formation of defects arising from the removal of Zn atoms as a consequence of the calcination procedure play the critical role in this process.

Microwave-assisted crystallization inclusion of spiropyran molecules in indium trimesate films with antidromic reversible photochromism

An indium trimesate metal–organic framework (JUC-120) which possesses a cubic zeolitic MTN topology, as a new analogue to MIL-100(Al, Fe or Cr) compounds, has been successfully synthesized. Its structure exhibits a mesoporous cage (26 A) and high thermal stability. The assembly of nitrobenzospiropyran derivatives (BSP) into JUC-120 nanocrystals (BSP/JUC-120) is achieved by a microwave-assisted crystallization inclusion approach. The BSP/JUC-120 films have been prepared on quartz wafers by a spin-coating method. The successful encapsulation of BSP molecules into the mesopores of the JUC-120 structure has been verified by N2 adsorption and TGA measurements. The photochromic properties of BSP/JUC-120 films are studied by the UV-Vis and fluorescence spectroscopies. More interestingly, metastable open merocyanine (OMC) species are directly generated from the closed spiropyran form (CSP) without photoirradiation and stabilized for a long period in the BSP/JUC-120 film. The open merocyanine isomer bleaches to the closed spiropyran form by ultraviolet or visible light, and the coloration is regained upon standing in the dark, exhibiting antidromic photochromism. Moreover, the BSP/JUC-120 film shows high reversibility and thermal stability of photochromism. This highly efficient MOF film is expected to be promising in the applications of optical devices.

Facile fabrication of metal–organic framework films promoted by colloidal seeds on various substrates

With the aid of In(OH)(BDC) colloidal seeds, metal–organic framework films (In(OH)(BDC)) have been fabricated by a simple solvothermal reaction of 1,4-benzenedicarboxylic acid (H2BDC) and In(NO3)3·xH2O in DMF on various substrates with different surface conditions.