Lixiong Zhang

Influence of powder synthesis methods on microstructure and oxygen permeation performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite-type membranes

Abstract Ba0.5Sr0.5Co0.8Fe0.2O3−δ (designed as BSCF oxides) oxides prepared by different methods under the same sintering profile were examined in terms of microstructure and oxygen permeation performance. The oxide powders were synthesized by solid-state reaction, modified citrate and citrate–EDTA complexing method. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results revealed that the crystal structures of the powders synthesized by the three methods developed differently. Although the three kinds of powders have nearly the same particle size distributions, they showed different grain morphologies. Consequently, the membranes prepared from the three kinds of powders demonstrated different microstructures and different oxygen permeation fluxes. The membrane synthesized by the solid-state reaction method (designed as SS method) showed the highest oxygen permeability.

Preparation of supported carbon membranes from furfuryl alcohol by vapor deposition polymerization

Supported carbon membranes were prepared from furfuryl alcohol (FA) precursor by vapor deposition polymerization (VDP). For this purpose γ-Al_2O_3/α-Al_2O_3 or glass/α-Al_2O_3 support tubes were pretreated with an acid catalyst and exposed to FA vapors at 90°C. The tubes were then heated at 200°C to crosslink the poly(furfuryl alcohol) (PFFA) polymer and carbonized slowly to 600°C. The polymerization and carbonization cycle was repeated once to improve the permeation properties. The membranes were examined by scanning electron microscopy (SEM) and tested in a permeation cell with single gases (H_2, N_2, O_2, CO_2, CH_4) and with the mixture CO_2–CH_4. After the first polymerization/carbonization cycle the membranes had little selectivity for gas separations. After the second polymerization/carbonization cycle the membranes had ideal selectivities 10–13 for O_2:N_2, 80–90 for CO_2:CH_4, and 90–350 for H_2:N_2 at room temperature. The permeance was 0.6–2.5 for H_2, 0.27–0.58 for CO_2 and 0.08 for O_2, all in MPU (1 MPU=10^(−8) mol/m^2 Pa s). The permeances were sharply higher at 150°C but the selectivities were lower, e.g. one of the membranes had H2 permeance 10.6 MPU and H_2:N_2 ideal selectivity 30.

Investigation on efficient adsorption of cationic dyes on porous magnetic polyacrylamide microspheres.

We report here the preparation of porous magnetic polyacrylamide microspheres for efficient removal of cationic dyes by a simple polymerization-induced phase separation method. Characterizations by various techniques indicate that the microspheres show porous structures and magnetic properties. They can adsorb methylene blue with high efficiency, with adsorption capacity increasing from 263 to 1977 mg/g as the initial concentration increases from 5 to 300 mg/L. Complete removal of methylene blue can be obtained even at very low concentrations. The equilibrium data is well described by the Langmuir isotherm models, exhibiting a maximum adsorption capacity of 1990 mg/g. The adsorption capacity increases with increasing initial pH and reaches a maximum at pH 8, revealing an electrostatic interaction between the microspheres and the methylene blue molecules. The microspheres also show high adsorption capacities for neutral red and gentian violet of 1937 and 1850 mg/g, respectively, as well as high efficiency in adsorption of mixed-dye solutions. The dye-adsorbed magnetic polyacrylamide microspheres can be easily desorbed, and can be repeatedly used for at least 6 cycles without losing the adsorption capacity. The adsorption capacity and efficiency of the microspheres are much higher than those of reported adsorbents, which exhibits potential practical application in removing cationic dyes.

Influence of sintering condition on crystal structure, microstructure, and oxygen permeability of perovskite-related type Ba0.8Sr0.2Co0.8Fe0.2O3−δ membranes

Ba0.8Sr0.2Co0.8Fe0.2O3−δ (BSCF) membranes were prepared at different sintering conditions. X-ray diffraction (XRD) patterns revealed that the BSCF oxides had a perovskite-related structure with mixed-phase. Slight difference in crystal structures was found for membranes prepared at different sintering conditions including sintering temperature and dwell time. Compared with dwell time, sintering temperature was found to have more influence on the microstructure of membrane. Oxygen permeation flux did not increase directly with the relative density, which was considered to be the combinative result of the microstructure and the crystal structure.

Preparation of zeolite-A/chitosan hybrid composites and their bioactivities and antimicrobial activities

Zeolite-A/chitosan hybrid composites with zeolite contents of 20-55 wt.% were prepared by in situ transformation of silica/chitosan mixtures in a sodium aluminate alkaline solution through impregnation-gelation-hydrothermal synthesis. The products were characterized by X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, scanning electron microscopy, thermogravimetric analysis, and mercury penetration porosimetry. Their in vitro bioactivities were examined using as-synthesized and Ca(2+)-exchanged hybrid composites in simulated body fluid (SBF) for hydroxyapatite (HAP) growth. Their antimicrobial activities for Escherichia coli (E. coli) in trypticase soy broth (TSB) were evaluated using Ag(+)-exchanged hybrid composites. The zeolite-A/chitosan hybrid composites could be prepared as various shapes, including cylinders, plates and thin films. They possessed macropores with pore sizes ranging from 100 to 300 μm and showed compressive mechanical strength as high as 3.2 MPa when the zeolite content was 35 wt.%. Fast growth on the Ca(2+)-exchanged hybrid composites was observed with the highest weight gain of 51.4% in 30 days. The 35 wt.% Ag(+)-exchanged hybrid composite showed the highest antimicrobial activity, which could reduce the 9×10(6) CFU mL(-1)E. coli concentration to zero within 4h of incubation time with the Ag(+)-exchanged hybrid composite amount of 0.4 g L(-1). The bioactivity and antimicrobial activity could be combined by ion-exchanging the composites first with Ca(2+) and then with Ag(+). These zeolite-A/chitosan hybrid composites have potential applications on tissue engineering and antimicrobial food packaging.

Preparation of uniform nano-sized zeolite A crystals in microstructured reactors using manipulated organic template-free synthesis solutions

Zeolite A nanocrystals (100-240 nm) with well-developed crystal faces and uniform particle size distribution have been prepared at 80 degrees C for ca. 7.5 min in a two-phase liquid segmented microfluidic reactor using a manipulated organic template-free synthesis solution.

Role of ZrO2 addition on oxygen transport and stability of ZrO2-promoted SrCo0.4Fe0.6O3−δ

The crystal structure, oxygen permeation and stability of ZrO 2 -promoted SrCo 0.4 Fe 0.6 O 3-δ (SCFZ) were compared with those of SrCo 0.4 Fe 0.6 O 3-δ (SCF). X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis of SCFZ revealed that solubility of Zr into the SCF phase took place, resulting in a lattice expansion of SCF at high temperatures. SCFZ oxide showed enhanced structure stability compared to SCF without undergoing crystallographic phase transition when annealed in helium at high temperatures. The oxygen permeation experiments showed that long-term operation stability of the SCF membrane with addition of ZrO 2 was greatly improved, the oxygen permeation flux. however, was slightly reduced probably due to the Zr dissolution in SCF.

Amino‐Functionalized ZIF‐7 Nanocrystals: Improved Intrinsic Separation Ability and Interfacial Compatibility in Mixed‐Matrix Membranes for CO2/CH4 Separation

Highly permeable and selective, as well as plasticization-resistant membranes are desired as promising alternatives for cost- and energy-effective CO2 separation. Here, robust mixed-matrix membranes based on an amino-functionalized zeolitic imidazolate framework ZIF-7 (ZIF-7-NH2 ) and crosslinked poly(ethylene oxide) rubbery polymer are successfully fabricated with filler loadings up to 36 wt%. The ZIF-7-NH2 materials synthesized from in situ substitution of 2-aminobenzimidazole into the ZIF-7 structure exhibit enlarged aperture size compared with monoligand ZIF-7. The intrinsic separation ability for CO2 /CH4 on ZIF-7-NH2 is remarkably enhanced as a result of improved CO2 uptake capacity and diffusion selectivity. The incorporation of ZIF-7-NH2 fillers simultaneously makes the neat polymer more permeable and more selective, surpassing the state-of-the-art 2008 Robeson upper bound. The chelating effect between metal (zinc) nodes of fillers and ester groups of a polymer provides good bonding, enhancing the mechanical strength and plasticization resistance of the neat polymer membrane. The developed novel ZIF-7 structure with amino-function and the resulting nanocomposite membranes are very attractive for applications like natural-gas sweetening or biogas purification.

Zinc-substituted ZIF-67 nanocrystals and polycrystalline membranes for propylene/propane separation

Continuous ZIF-67 polycrystalline membranes with effective propylene/propane separation performances were successfully fabricated through the incorporation of zinc ions into the ZIF-67 framework. The separation factor increases from 1.4 for the pure ZIF-67 membrane to 50.5 for the 90% zinc-substituted ZIF-67 membrane.

Versatile Preparation of Nonspherical Multiple Hydrogel Core PAM/PEG Emulsions and Hierarchical Hydrogel Microarchitectures†

The preparation of nonspherical materials composed of separated multicomponents by droplet-based microfluidics remains a challenge. Based on polymerization-induced phase separation and droplet coalescence in microfluidics, we prepared emulsions of variously shaped PAM/PEG core/shell droplets and hydrogels composed of two separated components, which show flexible and transformable hierarchical structures and microarchitectures. We find that AM/PEG aqueous droplets form a core/shell structure after polymerization resulting from phase separation. Thus multicore/shell droplets are easily produced by coalescence of core/shell structures. By changing the polymerization temperature and the flow rate, the morphology of the multicore droplets and the hydrogel can be easily adjusted. The hydrogels exhibit apparent anisotropy and different protein release rates depending on their structures. The preparation technique is simple and versatile and the resulting hydrogels have potential applications in many fields.