Oxygen permeability and CO_2-tolerance of Ce_(0.8)Gd_(0.2)O_(2-δ)-Ln BaCo_2O_(5+δ) dual-phase membranes

A series of oxygen permeable dual-phase composite oxides 60 wt% Ce0.8Gd0.2O2-δ-40 wt% LnBaCo2O5＋δ （CGO-LBCO, Ln = La, Pr, Nd, Sin, Gd and Y） were synthesized through a sol-gel route and effects of the Ln3＋ cations on their phase structure, oxygen permeability and chemical stability against CO2 were investigated systemically by XRD, SEM, TG-DSC and oxygen permeation experiments. XRD patterns reveal that the larger Ln3＋ cations （La3＋, Pr3＋ and Nd3＋） successfully stabilized the double-layered perovskite structure of sintered LBCO, while the smaller ones （Sm3＋, Gd3＋, and Y3＋） resulted in the partial decomposition of LBCO with some impurities formed. CGO-PBCO yields the highest oxygen permeation flux, reaching 2.8× 10^-7 mol.s-1.cm-2 at 925 ℃ with 1 mm thickness under air/He gradient. The TG-DSC profiles in 20 mol% CO2/N2 and oxygen permeability experiments with CO2 as sweep gas show that CGO-YBCO demonstrates the best chemical stability against CO2, possibly due to its minimum basicity. The stable oxygen permeation flux of CGO-YBCO under CO2 atmosphere reveals its potential application in the oxy-fuel combustion route for CO2 capture.

Total conductivity,oxygen permeability and stability of perovskite-type oxide BaCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ)

The total conductivity,oxygen sorption property,oxygen permeability and stability of pure perovskite-type oxide BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) in real operating conditions were investigated. Its total conductivity was measured to be 3.6 S·cm-1 at 600°C. Though the total conductivity of the BCFNO membrane is much smaller than that of the Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCFO) membrane,the oxygen permeability of the BCFNO membrane is similar to that of the BSCFO membrane. SEM observation and EDX analysis of the BCFNO and BSCFO membranes indicated that no segregation of metal ions was found for the used BCFNO membrane while the original perovskite phase of BSCFO decomposed under the experimental condition. The experimental results of oxygen permeability and stability were consistent with the analysis on the oxygen sorption property of perovskites.

Oxygen permeability of soft contact lenses in different pH, osmolality and buffering solution

AIMTo determine the effect of pH, osmolality, and buffering system on the oxygen permeability (Dk) of soft contact lenses.METHODSTwo hydrogel lenses (nelfilcon A and etafilcon A) and 2 silicone hydrogel lenses (lotrafilcon A and balafilcon A) were used in the study. These lenses were incubated in phosphate-buffered saline (PBS) and borate-buffered saline (BBS) solutions adjusted by 0.8 pH increments to a pH in the range of 5.8-9.0 or in hypotonic (280 mOsmol/kg), isotonic (310 mOsmol/kg) and hypertonic (380 mOsmol/kg) PBS solutions. Polarographic method was used for measuring the Dk and lenses were stacked as 4 layers to correct the boundary effect.RESULTSDk values of all contact lenses measured in BBS solutions were more stable than those in PBS solutions. Especially the etafilcon A lens showed a relative big change compared with other types of contact lenses at the same conditions. When the osmolality of PBS solution increased from hypotonic to hypertonic, Dk of all contact lenses decreased. Variations in Dk existed depending on lens materials, etafilcon A lens was the most affected and nelfilcon A was the least affected by osmolality.CONCLUSIONFrom the result obtained, it is revealed that Dk of contact lenses is changed by the pH, osmolality, and buffering condition of tear. Thus, Dk of contact lens can be varied by the lens wearers' physiological and/or pathological conditions.

Effect of dopant valence on the oxygen desorption and oxygen permeability of SrCo_(0.4)Fe_(0.5)M_(0.1)O_(3-δ)(M=Ni, Al and Zr) mixed-conducting oxides

The effect of dopant valence on oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M = Ni, Al and Zr） mixed-conducting oxides were investigated in detail by O2-TPD and oxygen permeation measurement. The SrCo0.4Fe0.5M0.1O3-δ for M = Fe, Ni, Al and Zr were denoted as SCF, SCFN, SCFA and SCFZ, respectively. O2-TPD analysis revealed that the amount of α oxygen desorption decreased with increasing the valance of doped metal elements （SCFN 〉 SCFA SCF 〉 SCFZ）. The oxygen permeation flux at the temperature ≈igher than 1148 K decreased in the order of SCFN 〉 SCF 〉 SCFZ 〉 SCFA. Single activation for oxygen permeation was observed for SCFZ oxide and the activation energies of SCF and SCFA change at around 1073 K, while the change temoerature of SCFN was about 1173 K.

Oxygen Permeability of Polypropylene Containing Polyisobutene with Magnesium Acetate

The oxygen permeabilities of polypropylene films are reduced by adding a minor percentage of a polyisobutene ionomer. The polyisobutene ionomers were prepared by in situ salt exchange of magnesium acetate with maleated polyisobutenes of commercially available low relative molecular mass. The more polar magnesiurn salts aided phase separaion during crystallization from the molten polypropylene mixtusre. Scanning electron microscope photographs revealed that the polyisobotene ionomer is largely concentratd in the amorphous regions between the polypropylene spherulites, where the ionomer tends to concentrate during crystallization. The influence of the polyisobutene ionomer on the oxygen permeability of polypropylene was found to be slightly dependent upon the relative molecular mass of the polyisobutene precursor. Under optimum conditions, the oxygen permeability of polypropylene is reduced by 20%with only 1% additive.

Effect of Cooling Rate on Morphology and Oxygen Permeability of Polypropylene

The influence of different cooling rates on the morphology and oxygen permeabilityr of polypropylene containing ferrocene has been investigated. The spherulitic crystalline size and structure, which can affect the oxygen permeability are dependent upon the heating temperature, annealing time and cooling rate. The modulus of the composite was measured b}' dynamic mechanical analysis.

IMPROVED OXYGEN PERMEABILITY AND MECHANICAL STRENGTH OF SILICONE HYDROGELS WITH INTERPENETRATING NETWORK STRUCTURE

The interpenetrating polymer network(IPN) silicone hydrogels with improved oxygen permeability and mechanical strength were prepared by UV-initiated polymerization of monomers including methacryloxypropyl tris(trimethylsiloxy)silane(TRIS),2-hydroxyethylmethacrylate(HEMA) and N-vinyl pyrrolidone(NVP) in the presence of free radical photoinitiator and cationic photoinitiator.The polymerization mechanism was investigated by the formation of gel network.The structure of IPN hydrogels was characterized by Fourier transform infrared spectroscopy(FTIR), differential scanning calorimetry(DSC) and transmission electron microscopy(TEM).The results showed that the IPN hydrogels exhibited a heterogeneous morphology.The mechanical properties,surface wettability and oxygen permeability were examined by using a tensile tester,a contact angle goniometer and an oxygen transmission tester,respectively.The equilibrium water content of the hydrogels was measured by the gravimetric method.The results revealed that the IPN hydrogels possessed hydrophilic surface and high water content.They exhibited improved oxygen permeability and mechanical strength because of the incorporation of TRIS.

Fluorite Ce_(0.8)Sm_(0.2)O_(2-δ) porous layer coating to enhance the oxygen permeation behavior of a BaCo_(0.7)Fe_(0.2)Nb_(0.1)O_(3-δ) mixed conductor

Fluorite Ce0.8Sm0.2O2-δ（SDC） nanopowder with a crystallite size of 15 nm was synthesized by a co-precipitation method. An SDC porous layer was coated onto a BaCo0.7Fe0.2Nb0.1O3-δ（BCFN） mixed conductor to improve its oxygen transport behavior. The results show that the SDC-coated BCFN membrane exhibits a remarkably higher oxygen permeation flux（JO2） than the uncoated BCFN in the partial oxidation of coke oven gas（COG）. The maximum JO2 value of the SDC-coated BCFN is 18.28 mL ·min^-1·cm^-2 under a COG/air flux of 177 mL ·min^-1/353 mL ·min^-1 at 875℃ when the thickness of the BCFN membrane is 1 mm; this JO2 value is 23% higher than that of the uncoated BCFN membrane. This enhancement is likely because of the higher oxygen ionic conductivity of SDC, which supplies oxygen vacancies and accelerates oxygen exchange on the membrane/coating layer/gas three-phase boundary.

Environmentally regulated intrinsic oxygen-ion transport for oxideion conductors

Oxide-ion conductors have been widely used as catalytic,conductive,detecting and other materials under oxidizing,reducing,inert,mixed environments and the like.However,so far the evaluation of their oxygen-ion transport(such as oxide-ion conductivity and oxygen permeability)either is extrinsic or is limited only in oxidizing or inert environment.Herein,the evaluation of intrinsic oxygen-ion transport for oxide-ion conductors in all environments seems especially important.In this work,a new test system was designed to enable the oxide-ion conductors placing in single oxidizing,reducing,inert or mixed environment separately,which also realized all the oxygen-vacancy concentrations of oxide-ion conductors are in equilibrium in all environments.The intrinsic oxide-ion conductivity and oxygen permeability were evaluated in all environments,and the influencing factors regulated by environments also were analyzed to correlate the variation of oxygen-ion transport.

Pigment epithelium-derived factor protects retinal ganglion cells from hypoxia-induced apoptosis by preventing mitochondrial dysfunction

AIM： To investigate the potential of pigment epitheliumderived factor（PEDF） to protect the immortalized rat retinal ganglion cells-5（RGC-5） exposed to Co Cl2-induced chemical hypoxia. METHODS： After being differentiated with staurosporine（SS）, RGC-5 cells were cultured in four conditions： control group cells cultured in Dulbecco ＇s modified eagle medium（DMEM） supplemented with 10% fetal bovine serum, 100 μmol/m L streptomycin and penicillin（named as normal conditions）; hypoxia group cells cultured in DMEM containing 300 μmol/m L Co Cl2; cells in the group protected by PEDF were first pretreated with 100 ng/m L PEDF for 2h and then cultured in the same condition as hypoxia group cells; and PEDF group cells that were cultured in the presence of 100 ng/m L PEDF under normal conditions. The cell viability was assessed by MTT assay, the percentage of apoptotic cells was quantified using Annexin V-FITC apoptosis kit, and intra-cellar reactive oxygen species（ROS） was measured by dichloro-dihydro-fluorescein diacetate（DCFH-DA） probe. The mitochondria-mediated apoptosis was also examined to further study the underlying mechanism of the protective effect of PEDF. The opening of mitochondrial permeability transition pores（m PTPs） and membrane potential（Δψm） were tested as cellular adenosine triphosphate（ATP） level and glutathione（GSH）. Also, the expression and distribution of Cyt C and apoptosis inducing factor（AIF） were observed.RESULTS： SS induced differentiation of RGC-5 cells resulting in elongation of their neurites and establishing contacts between outgrowths. Exposure to 300 μmol/m L Co Cl2 triggered death of 30% of the total cells in cultures within 24 h. At the same time, pretreatment with 100 ng/m L PEDF significantly suppressed the cell death induced by hypoxia（P〈0.05）. The apoptosis induced by treatment of Co Cl2 was that induced cell death accompanied with increasing intracellar ROS and decreasing GSH and ATP level. PEDF pretreatment suppressed these effects（P〈0.05）. Additionally, PEDF treatment inhibited the opening of m PTPs and suppressed decreasing of Δψm in RGC-5 cells, resulting in blocking of the mitochondrial apoptotic pathway.CONCLUSION： Pretreatment of RGC-5 cells with 100 ng/m L PEDF significantly decreases the extent of apoptosis. PEDF inhibits the opening of m PTPs and suppresses decreasing of Δψm. Moreover, PEDF also reduces ROS production and inhibits cellular ATP level＇s reduction. Cyt C and AIF activation in PEDF-pretreated cultures are also reduced. These results demonstrate the potential for PEDF to protect RGCs against hypoxic damage in vitro by preventing mitochondrial dysfunction.

Influence of MoSi_(2) on oxidation protective ability of TaB_(2)-SiC coating in oxygen-containing environments within a broad temperature range

TaB_(2)-SiC coating modified by different content of MoSi_(2) was fabricated on graphite substrate with SiC inner coating by liquid phase sintering to elevate the anti-oxidation capability of the TaB_(2)-SiC coatings.As compared to the sample with the TaB_(2)-40wt% SiC coating,the coating sample modified with MoSi_(2) exhibited a weight gain trend at lower temperatures,the fastest weight loss rate went down by 76%,and the relative oxygen permeability value reduced from about 1% to near 0.More importantly,the large amount of SiO_(2) glass phase produced over the coating during oxidation was in contact with the modification of MoSi_(2),which was proved to be beneficial to the dispersion of Ta-oxides.A concomitantly formed continuous Ta-Si-O-B compound glass layer showed excellent capacity to prevent oxygen penetration.However,when the TaB_(2) content was sacrificed to increase the MoSi_(2) content,the relative oxygen permeability of the coating increased instead of decreased.Thus,on the basis of ample TaB_(2) content,increasing the MoSi_(2) content of the coating is conducive to reducing the relative oxygen permeability of the coatings in a broad temperature region.

High-performance oxygen permeation membranes:Cobalt-free Ba_(0.975)La_(0.025)Fe_(1-x)Cu_(x)O_(3)-δceramics

A new group of cobalt-free perovskite oxides,Ba_(0.975)La_(0.025)Fe_(1-x)Cu_(x)O_(3-δ)(BLFC,x=0.05-0.15),was designed,characterized and applied as oxygen permeation membranes.It was found that BLFC oxides with Cu doping range of 0.075-0.15 maintain cubic perovskite phase in a wide range of temperatures.More Cu introduced at the B-site results in a gradual increase of the electrical conductivity,which is attributed to the denser overlapping of electron clouds of CueO bonds.With increasing Cu content,the oxygen vacancy concentration increases and the oxygen ion migration energy decreases,leading to the highest oxygen permeation flux of 1.59 mL cm^(-2)min^(-1)recorded for Ba_(0.975)La_(0.025)Fe_(0.9)Cu_(0.1)O_(3-δ)1mm thick membrane at 950℃.However,the oxygen permeability decreases with further Cu doping,which may be correspond to a presence of defect association.Ba_(0.975)La_(0.025)Fe_(0.9)Cu_(0.10)O_(3-δ)membrane with 0.7mm thickness delivers stable oxygen permeation flux of 1.57 mL cm^(-2)min^(-1)for 200 h at 900℃.All of the obtained results indicate that the developed BLFC with optimized Cu content(i.e.x=0.1)is a very promising material for usage in oxygen separation applications.

Thermal and Oxygen Barrier Properties of Chitosan Bionanocomposites by Reinforcement of Calcium Carbonate Nanopowder

Chitosan and calcium carbonate nanopowder（chitosan/CaCO3） bionanocomposites were prepared by solution method.Interaction between chitosan and CaCO3 was studied by Fourier transform infrared spectroscopy（FTIR）.Structure and surface morphology of chitosan/CaCO3 bionanocomposites were investigated by X-ray diffraction（XRD） and field emission scanning electron microscopy（FESEM）,respectively.The energy dispersive X-ray spectroscopy（EDS） of chitosan/CaCO3 bionanocomposites was studied in order to establish the elements of composition.Thermal stability of prepared bionanocomposites was studied by thermogravimetric analysis（TGA） and a substantial increase of thermal stability of virgin chitosan was noticed due to incorporation of CaCO3 nanopowder.The oxygen permeability was reduced by three times as compared to the raw chitosan due to the dispersion of nano CaCO3 filler.Biodegradability and resistance towards dilute acid and alkali of the prepared bionanocomposite were investigated.The bionanocomposite having gas barrier and thermal stable property may be suitable for packaging and biomedical applications.

Effects of Boron Nitride Nanopowder on Thermal, Chemical and Gas Barrier Properties of Starch

Starch/boron nitride （starch/BN） bionanocomposites were prepared with the reinforcement of boron nitride nano powder by solution technique. The dispersion of BN in the starch was achieved by a continuous sonication process. The interaction between starch and boron nitride nanopowder was investigated by Fourier transform infrared （FTIR） spectroscopy. The structural properties of starch/BN bionanocomposites was studied by X-ray diffraction （XRD）. The high resolution transmission electron microscopy （HRTEM） was used for the study of dispersion of boron nitride in starch matrix and diffraction patterns were studied by selected area electron diffraction （SAED）. Thermal stability of the starch was increased with rising concentrations of boron nitride due to incorporation of rigid nano BN with starch matrix. The substantial reduction in oxygen permeability was obtained by increasing the concentration of BN. The biodegradability of synthesized bionanocomposites was measured by using activated sludge water. Further, it was noticed that, starch/BN bionanocomposites are resistant towards inorganic acids and bases. The tensile strength of starch/BN bionanocomposites was increased whereas; the water resistance property of the materials was decreased with increasing BN loading.

POLY(METHYL METHACRYLATE)/SOY PROTEIN GREEN COMPOSITES AS GAS BARRIER MATERIALS

Poly（methyl methacrylate）/soy protein （PMMA/SP） composites were prepared by emulsion polymerization method using potassium persulphate （KPS） as the radical initiator. The interaction of soy protein with PMMA was evidenced by Fourier transformed infrared （FTIR） spectroscopy. The structure of PMMA/SP composite： was investigated by X-ray diffraction （XRD） study and scanning electron microscopy （SEM）. The thermal properties of soy protein and PMMA/SP composites were compared with soy protein and virgin PMMA sample. PMMA/SP composites were found to be flame retardant materials from the measurement of limiting oxygen index （LOI） of samples. The oxygen permeability of PMMA/SP composites was substantially decreased as compared to virgin PMMA.