Binling Chen

Zeolitic imidazolate framework materials: recent progress in synthesis and applications

Zeolitic imidazolate frameworks (ZIFs) represent a new and special class of metal organic frameworks comprised of imidazolate linkers and metal ions, with structures similar to conventional aluminosilicate zeolites. Their intrinsic porous characteristics, abundant functionalities as well as exceptional thermal and chemical stabilities have led to a wide range of potential applications for various ZIF materials. Explosive research activities ranging from synthesis approaches to attractive applications of ZIFs have emerged in this rapidly developing field in the past 5 years. In this review, the development and recent progress towards different synthesis strategies to generate both powder and membrane/film-based ZIF materials are analysed and summarised. Their attractive and potential applications in gas separation, catalysis, sensing and electronic devices, and drug delivery in the past years are discussed and reviewed. In addition, the prospects and potential new development of ZIF materials are presented.

Cobalt sulfide/N,S codoped porous carbon core-shell nanocomposites as superior bifunctional electrocatalysts for oxygen reduction and evolution reactions.

Exploring highly-efficient and low-cost bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) in the renewable energy area has gained momentum but still remains a significant challenge. Here we present a simple but efficient method that utilizes ZIF-67 as the precursor and template for the one-step generation of homogeneous dispersed cobalt sulfide/N,S-codoped porous carbon nanocomposites as high-performance electrocatalysts. Due to the favourable molecular-like structural features and uniform dispersed active sites in the precursor, the resulting nanocomposites, possessing a unique core-shell structure, high porosity, homogeneous dispersion of active components together with N and S-doping effects, not only show excellent electrocatalytic activity towards ORR with the high onset potential (around -0.04 V vs.-0.02 V for the benchmark Pt/C catalyst) and four-electron pathway and OER with a small overpotential of 0.47 V for 10 mA cm(-2) current density, but also exhibit superior stability (92%) to the commercial Pt/C catalyst (74%) in ORR and promising OER stability (80%) with good methanol tolerance. Our findings suggest that the transition metal sulfide-porous carbon nanocomposites derived from the one-step simultaneous sulfurization and carbonization of zeolitic imidazolate frameworks are excellent alternative bifunctional electrocatalysts towards ORR and OER in the next generation of energy storage and conversion technologies.

Controlled in situ synthesis of graphene oxide/zeolitic imidazolate framework composites with enhanced CO2 uptake capacity

A simple and controlled in situ synthesis method has been successfully used to produce graphene oxide/ZIF-8 composites from aqueous ammonia solution. A series of characterization techniques confirm the formation of strong interactions between ZIF-8 and graphene oxide in the synthesized composites. The crystal sizes of ZIF-8 and the textual properties of the composites can be tuned by the variable graphene oxide contents. The in situ synthesized composites exhibit enhanced CO2 adsorption energy and significant CO2 uptake capacity due to the synergistic effect between graphene oxide and ZIF-8. The synergistic interactions of ZIFs and graphene oxide may offer a new approach to produce novel graphene oxide/ZIFs composites for diverse applications.

Metal-organic-frameworks derived cobalt embedded in various carbon structures as bifunctional electrocatalysts for oxygen reduction and evolution reactions

A series of nanocomposites of cobalt embedded in N-doped nanoporous carbons, carbon nanotubes or hollow carbon onions have been synthesized by a one-step carbonization of metal-organic-framework ZIF-67. The effect of the carbonization temperature on the structural evolution of the resulting nanocomposites has been investigated in detail. Among the as-synthesized materials, the cobalt/nanoporous N-doped carbon composites have demonstrated excellent electrocatalytic activities and durability towards oxygen reduction reaction in alkaline medium. Compared to the benchmark Pt/C catalyst, the optimized Co@C-800 (carbonized at 800 °C) exhibited high oxygen reduction reaction activity with an onset potential of 0.92 V, and a half-wave potential of 0.82 V. Moreover, the optimized Co@C-800 also showed enhanced electrocatalytic activity towards oxygen evolution reaction from water splitting, with a low onset potential of 1.43 V and a potential of 1.61 V at 10 mA cm−2 current density. This work offered a simple solution to develop metal-organic-framework-derived materials for highly efficient electrochemical applications.

Fabrication of core–shell nanofibers by single capillary electrospinning combined with vapor induced phase separation

A water vapor induced phase separation (WVIPS) electrospinning process for the preparation of core–shell nanofibers with a single capillary is described. The PAN–PVP core–shell nanofibers were fabricated by WVIPS electrospinning a polyvinylpyrrolidone (PVP)–polyacrylonitrile (PAN) homogeneous solution. The solvent solubility parameter of the liquid electrospinning jets was altered by water vapor, which subsequently induced the phase separation before the solvent rapidly volatilized, and caused the formation of core–shell structured nanofibers. A scanning electron microscope (SEM) and transmission electron microscope (TEM) were applied to characterize the morphology. X-ray photoelectron spectroscopic analysis (XPS), water contact angle (CA) tests and thermogravimetry analysis (TGA) were used to confirm the composition of the fiber’s shell. The results of TGA also showed an improvement in the thermal stability of the fiber membranes.

Freeze-dried chitosan–sodium hyaluronate polyelectrolyte complex fibers as tissue engineering scaffolds

The present work was focused on the preparation and characterization of polyelectrolyte complex (PEC) fibers based on the natural oppositely charged biopolymers, chitosan and sodium hyaluronate, via a freeze-drying method. The physical structure and chemical properties of the freeze-dried fibers were characterized by means of Fourier transform infrared spectroscopy (FT-IR), solid-state 13C nuclear magnetic resonance (13C-NMR) and X-ray diffraction (XRD). The morphology, size, and surface structure of the freeze-dried PEC fibers were observed by means of scanning electron microscopy (SEM). An indirect in vitro cytotoxicity test showed the extracts of fibers had no significant effects on cell viability. Moreover, an in vitro cytocompatibility test exhibited cell population and spreading tendency, suggesting the fibers were non-toxic to L929 cells. All the results indicated that such freeze-dried PEC fibers might have potential applications in tissue engineering scaffolds.

Poly Aryl Ether Ketones (PAEKs) and carbon-reinforced PAEK powders for laser sintering

This paper discusses various methods of fabrication of plain and carbon-reinforced composite powders, as well as a range of powder characterisation test methods suitable for defining powders for laser sintering. Two milling processes (based on disc blades and rotatory cutting knives) were used as methods of fabrication of powders, starting from injection moulding granule grades, for comparison with current powders obtained directly from polymerisation processes. It was found that the milling process affects the particles properties. The rotary milling produced powders with superior properties in comparison with the disc milling method. Tests including particle size distribution, angle of repose, aspect ratio, sphericity and roundness of particles were employed to compare and assess the suitability of powders for laser sintering. The Brunauer–Emmett–Teller test was identified as a useful method to define surface roughness and porosity of the particles. The carbon fibre (Cf) Poly Ether Ketone (PEK) granules milled well and after an additional sieving process created a good quality powder. This is the first attempt to investigate properties of PEK powder with encapsulated Cf and follow their sintering profile through hot-stage microscopy. It is expected that this type of composite powder will create isotropic structures in comparison with the highly anisotropic properties given by the known dry mix composite powders, currently used in laser sintering.

Hofmeister anion effect on the formation of ZIF-8 with tuneable morphologies and textural properties from stoichiometric precursors in aqueous ammonia solution

In this report, a series of anions were demonstrated to remarkably affect and promote the formation of ZIF-8 from a stoichiometric molar ratio of precursors in aqueous ammonia solution at room temperature. The requirement of ammonia concentration for the formation of the pure ZIF-8 phase can be readily modulated by the anion. In addition, the anion types and concentrations can effectively promote the formation of the pure ZIF-8 phase with tuneable particle morphologies and textural properties. The anion effect capacity was revealed to be SO42− > CH3COO− > Cl− > Br− > NO3−, which follows the classic Hofmeister anion sequence.

Enhanced Ductility of PEEK thin film with self-assembled fibre-like crystals

Poly Ether Ether Ketone (PEEK) is a high temperature polymer material known for its excellent chemical resistance, high strength and toughness. As a semi-crystalline polymer, PEEK can become very brittle during long crystallisation times and temperatures helped as well by its high content of rigid benzene rings within its chemical structure. This paper presents a simple quench crystallization method for preparation of PEEK thin films with the formation of a novel fibre-like crystal structure on the surface of the films. These quenched crystallised films show higher elongation at break when compared with conventional melt crystallised thin films incorporating spherulitic crystals, while the tensile strength of both types of films (quenched crystallised and conventional melt) remained the same. The fracture analysis carried out using microscopy revealed an interesting microstructure which evolves as a function of annealing time. Based on these results, a crystal growth mechanism describing the development of the fibre-like crystals on the surface of the quenched crystallised films is proposed.