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ZIF-8 membranes have emerged as the most promising candidate for propylene/propane (C3 H6 /C3 H8 ) separation through its precise molecular sieving characteristics. The poor reproducibility and durability, and high cost, thus far hinder the scalable synthesis and industrial application of ZIF-8 membranes. Herein, we report a semi-solid process featuring ultrafast and high-yield synthesis, and outstanding scalability for reproducible fabrication of ZIF-8 membranes. The membranes show excellent C3 H6 /C3 H8 separation performance in a wide temperature and pressure range, and remarkable stability over 6 months. The ZIF-8 membrane features dimethylacetamide entrapped ZIF-8 crystals retaining the same diffusion characteristics but offering enhanced adsorptive selectivity for C3 H6 /C3 H8 . The ZIF-8 membrane was prepared on a commercial flat-sheet ceramic substrate. A prototypical plate-and-frame membrane module with an effective membrane area of about 300 cm2 was used for efficient C3 H6 /C3 H8 separation.

Metal-organic frameworks (MOFs) have been recently proposed as supports for biomolecules immobilization, particularly for enzymes. However, their stability under the high ionic strength aqueous solutions required for practical applications of these biocatalysts have not been evaluated. Here, it is shown that surface modifications and a careful analysis and selection of the buffer components must be accomplished to ensure the resistance of the MOF to hydrolysis, even for the previously assumed robust Zeolitic Imidazole Frameworks (ZIFs). By taking into account these considerations, and introducing polyvinylpyrrolidone (PVP) as a surfactant in the synthetic process, a resistant and stable magnetic MOF (Fe3O4@ZIF-8/PVP) was obtained. Further, the loading capacity of the stabilized synthetized structures for the immobilization of a model protein, such as bovine serum albumin (BSA), was analyzed. It was found that physical interaction provides an efficient and suitable method to immobilize this biomolecule without evidence of leaching.

Good oxygen permeability and stability of oxygen transport membrane are highly necessary for practical applications. Herein, through different theories, the oxygen transport limitation step through the Ruddlesden-Popper (Pr0.9La0.1)1.9Ni0.74Cu0.21Ga0.05O4+δ ((PL)1.9NCG) membrane was demonstrated firstly, which suggest surface modification can be an effective approach to improve the oxygen separation performance. After coating, various influences of different side surface modification on permeability and phase stability were observed. The sweep-side coated membrane exhibits largely enhanced permeation fluxes than feed-side coated membrane, and the feed-side coated membrane shows better phase stability under the same conditions (these results reveal that the sweep side is the permeability limitation side and the feed is the phase stability limitation side). The both side coated membrane combines abovementioned advantages which shows 57% enhanced and stable oxygen permeation flux at 800 °C. The observed various modification effects on the permeation performance are discussed based on the surface exchange properties and the mechanism of the oxygen transporting membrane in detail.

Hybrid semiconductor-based nanocrystals (NCs) are generally synthesized in organic media prior to their assembly into catalytically promising nanostructures via multistep methods. Here, a tunable, easy-to-adapt and versatile approach for the preparation of hybrid nanoparticle networks from aqueous nanocrystal solutions is demonstrated. The networks consist of interconnected semiconductor NC backbones (made of CdSe/CdS dot-in-rods or core/crown nanoplatelets) decorated with noble metal (Au and Pt) or with metal-based domains (Co2+ and Ni2+) demonstrating a powerful synthetic control over a variety of hybrid nanostructures. The deposition of the domains and the formation of the network take place simultaneously (one-step method) at room temperature in dark conditions without any external trigger. Beside the in-depth structural characterization of the gel-like hybrid networks, the wavelength-dependent optical features are studied to reveal an efficient charge carrier separation in the systems and a controllable extent of fluorescence quenching through the domain sizes. Photoluminescence quantum yields and decay dynamics highlight the importance of fine-tuning the conduction band/Fermi level offset between the semiconductors and the various deposited metals playing central role in the electron–hole separation processes. This procedure provides a novel platform toward the preparation of photo(electro)catalytically promising hybrid nanostructures (acetogels and xerogels) without the need of presynthetic hybrid particle design.

The impact of low-pressure treatment on the crystal structure, morphology, and chemical composition of ettringite, due to their major importance with respect to processability (i.a., drying conditions) and to the analysis of ettringite-containing samples, is examined utilizing X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and environmental scanning electron microscopy. Synthetic ettringite was treated for various durations (5 min up to 72 h) and at two different levels of low-pressure (4.0 mbar and 60 µbar). Evaluation showed a correlation between the procedural parameters (time and pressure), the chemical composition, and the morphology of ettringite. The experiments reveal that, when exposed to 4 mbar pressure, nearly no changes occur in the ettringite’s morphology, whereas the crystals undergo swelling and slight deformations at very low pressures (60 µbar and 35.3 nbar), which is attributed to the loss of bound water and the partial transformation from ettringite to quicklime, anhydrite, and calcium aluminate. Furthermore, the strongly dehydrated ettringite shows the same morphology.

Poly(3,4-ethylenedioxythiophene) (PEDOT) plays a key role in the field of electrically conducting materials, despite its poor solubility and processability. Various molecules and polymers carrying sulfonic groups can be used to enhance PEDOT’s electrical conductivity. Among all, sulfonated polyarylether sulfone (SPAES), prepared via homogenous synthesis with controlled degree of sulfonation (DS), is a very promising PEDOT doping agent. In this work, PEDOT was synthesized via high-concentration solvent-based emulsion polymerization using 1% w/w of SPAES with different DS as dopant. It was found that the PEDOT:SPAESs obtained have improved solubility in the chosen reaction solvents, i.e., N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone and, for the first time, the role of doping agent, DS and polymerization solvents were investigated analyzing the electrical properties of SPAESs and PEDOT:SPAES samples and studying the different morphology of PEDOT-based thin films. High DS of SPAES, i.e., 2.4 meq R-SO3−g−1 of polymer, proved crucial in enhancing PEDOT’s electrical conductivity. Furthermore, the DMSO capability to favor PEDOT and SPAES chains rearrangement and interaction results in the formation of a polymer film with more homogenous morphology and higher conductivity than the ones prepared from DMAc, DMF, and NMP.

In this work, mixing and co-gelation of Au nanoparticles (NPs) and highly luminescent CdSe/CdS core/shell nanorods (NRs) are used as tools to obtain noble metal particle-decorated macroscopic semiconductor gel networks. The hybrid nature of the macrostructures facilitates the control over the optical properties: while the holes are trapped in the CdSe cores, the connected CdSe/CdS NRs support the mobility of excited electrons throughout the porous, hyperbranched gel networks. Due to the presence of Au NPs in the mixed gels, electron trapping in the gold NPs leads to a suppressed radiative recombination, namely, quenches the fluorescence in certain fragments of the multicomponent gel. The extent of fluorescence quenching can be influenced by the quantity of the noble metal domains. The optical properties are monitored as a function of the NR:NP ratio of a model system CdSe/CdS:Au. By this correlation, it demonstrates that the spatial extent of quenching initiated by a single Au NP exceeds the dimensions of one NR, which the Au is connected to (with a length of 45.8 nm ± 4.1 nm) and can reach the number of nine NRs per Au NP, which roughly corresponds to 400 nm of total electron travel distance within the network structure.

For practical application in syngas production, the oxygen permeable membranes should possess both high oxygen permeation flux and good stability in harsh environment (CO2-containing reductive atmosphere). Under the premise of keeping stability, anion-doping method was applied to improve the oxygen permeability of the CO2-stable (Pr0.9La0.1)2.0(Ni0.74Cu0.21Ga0.05)O4+δ ((PL)2.0NCG) membrane. The developed (Pr0.9La0.1)2.0(Ni0.74Cu0.21Ga0.05)O4+δCl0.1 ((PL)2.0NCGCl0.1) exhibited three times higher oxygen permeation fluxes, similar CO2-tolerance and long-term stability compared with its parent one. Furthermore, the (PL)2.0NCGCl0.1 membrane was constructed to be used in reactors for the syngas production through partial oxidation of methane, which showed an oxygen permeation flux of 5 mL/min cm2, a methane conversion of 99.9%, and a CO selectivity of 97.5% at 900 °C, and no any degradation was observed during 100 h.

Covalent organic frameworks (COFs) have been proposed as alternative candidates for molecular sieving membranes due to their chemical stability. However, developing COF membranes with narrowed apertures close to the size of common gas molecules is a crucial task for selective gas separation. Herein, we demonstrate a new type of a two-dimensional layered-stacking COF–COF composite membrane in bilayer geometry synthesized on a porous support by successively regulating the growth of imine-based COF-LZU1 and azine-based ACOF-1 layers via a temperature-swing solvothermal approach. The resultant COF-LZU1–ACOF-1 bilayer membrane has much higher separation selectivity for H2/CO2, H2/N2, and H2/CH4 gas mixtures than the individual COF-LZU1 and ACOF-1 membranes due to the formation of interlaced pore networks, and the overall performance surpasses the Robeson upper bounds. The COF-LZU1–ACOF-1 bilayer membrane also shows high thermal and long-time stabilities.

Due to high figure of merit, Ca3Co4 − xO9 + δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 °C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (∼970 °C) than in air (∼930 °C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 °C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.

In this study, dual-phase membranes 60 wt % Ce0.8M0.2O2–δ (M = La, Pr, Nd, Sm, Gd) - 40 wt % La0.5Sr0.5Fe0.8Cu0.2O3–δ (CMO-LSFCO) were prepared via a combination of EDTA-citric acid complexing sol-gel and mechanical mixture method. Their chemical compatibility, CO2 tolerance, oxygen permeability, conductivity, and long-term regenerative durability regarding the phase structure and composition were systematically studied. Among the studied CMO-LSCFO dual-phase membranes, CGO-LSFCO shows the highest oxygen permeability under air/He and air/CO2 gradients, which can be associated with the small particle size and high electronic conductivity of the CGO phase resulting in a good percolation with different transfer paths based on the correlations between membrane material characterization and oxygen permeability. The comprehensive comparative study presented in this work identifies the critical factors influencing the oxygen permeability, which may provide guidelines for designing further high performance dual-phase oxygen transport membranes.

A porous Ag network has been deposited on laser structured Ni supports by using the dynamic hydrogen template deposition (DHTD) technique. For a better hydrogen evolution, a 10 nm Pt layer has been sputtered on the Ni supports before Ag deposition. In a subsequent step, the Ag network has been modified by electrochemical Pt deposition in a replacement reaction forming a porous Pt@Ag network. Different Pt species are formed at different positions of the Ag network: Pure Pt on top and Ag1Pt1 alloy at the interface between the Ag network and the deposited Pt film. Laser structuring the substrate in advance can facilitate mass transport, especially for the galvanic Pt replacement reaction, and improves the performance of the electrode. As a result, the performance of the Pt@Ag network on laser structured electrodes is significantly higher compared to a non-structured electrode.

Metal-organic framework (MOF) glasses are promising candidates for membrane fabrication due to their significant porosity, the ease of processing, and most notably, the potential to eliminate the grain boundary that is unavoidable for polycrystalline MOF membranes. Herein, we developed a ZIF-62 MOF glass membrane and exploited its intrinsic gas-separation properties. The MOF glass membrane was fabricated by melt-quenching treatment of an in situ solvothermally synthesized polycrystalline ZIF-62 MOF membrane on a porous ceramic alumina support. The molten ZIF-62 phase penetrated into the nanopores of the support and eliminated the formation of intercrystalline defects in the resultant glass membrane. The molecular sieving ability of the MOF membrane is remarkably enhanced via vitrification. The separation factors of the MOF glass membrane for H2 /CH4 , CO2 /N2 and CO2 /CH4 mixtures are 50.7, 34.5, and 36.6, respectively, far exceeding the Robeson upper bounds.

Partial internal reduction is observed of NiO precipitates in a matrix of a Ruddlesden-Popper type mixed ionic-electronic conducting ceramic with composition of (Pr 0.9 La 0.1 ) 2.0 Ni 0.74 Cu 0.21 Ga 0.05 O 4+δ during the cooling from sintering temperature to room temperature in ambient air. A metallic Ni interlayer between NiO and the oxide matrix is demonstrated using scanning transmission electron microscopy combined with electron energy-loss spectroscopy. The possible formation mechanism for the metallic Ni is discussed in light of the partial internal reduction during the cooling process in ambient air. The drop of temperature during cooling process in ambient air causes a drop of the oxygen chemical potential in the Ruddlesden-Popper type oxide ceramic, which acts as an oxygen absorber. Thus, the local oxygen chemical potential at the internal interface between Ruddlesden-Popper type matrix and NiO precipitate can fall below the stability limit of the later. As consequence, NiO is partially reduced to metallic Ni at the interface.

Hydrogen production by catalytic steam reforming of renewable hydrocarbons like bio-methane or bio-ethanol has become an attractive goal of sustainable chemistry. Side reactions as in ethanol steam reforming decrease the hydrogen selectivity. A low-temperature catalytic membrane reactor with a hydrogen-selective membrane is expected to solve this problem. Three different carbon membranes are investigated with respect to their performance to extract hydrogen selectively from the binary and ternary reaction mixtures (H2/CO2), (H2/CO2/H2O), and (H2/ethanol) as model systems for bio-ethanol steam reforming. The three carbon membranes under study are (i) an amorphous carbon layer prepared by physical vapour deposition (PVD) of carbon on an porous alumina support using a carbon fibre yarn, (ii) a turbostratic carbon layer obtained by pyrolysis of a supported organic polymer blend as precursor, and (iii) a crystalline carbon prepared by pressing of graphite flakes into a self-supporting disc. For the equimolar binary feed mixture (H2/CO2) all carbon membranes were found to be hydrogen selective. For the ternary feed mixture (41vol.-% H2/41vol.-% CO2/18vol.-% H2O), in the case of the amorphous and crystalline carbon membrane, the hydrogen selectivity remains also in the presence of steam. The turbostratic carbon membrane separates preferentially steam (H2O) from the ternary feed mixture (H2/CO2/H2O).

The performance of a dense ceramic hydrogen-permeable membrane reactor for the nonoxidative methane dehydroaromatization (MDA), according to the equilibrium reaction 6CH4 ⇆ C6H6 + 9H2 with a 6 wt % Mo/HZSM-5 bifunctional catalyst was investigated. A U-shaped ceramic hollow fiber membrane of the composition La5.5W0.6Mo0.4O11.25−δ (LWM0.4) has been used for the in situ removal of H2 to overcome thermodynamic constraints. The yield of aromatics (benzene, toluene, naphthalene) in the MDA could be increased in the beginning of the aromatization reaction by ∼50%–70%, in comparison with the fixed-bed reactor, because 40%–60% of the H2 abstracted have been extracted at 700 °C with a weight hourly space velocity (WHSV) of 840 cm3 gcat–1 h–1. These advantages of the membrane reactor operation decrease with time on stream, since the removal of H2 boosts not only CH4 conversion and yield of aromatics, but also catalyst deactivation by deposition of carbonaceous deposits. However, the catalyst system could be regenera...

Membrane-based separation technology has evolved as a competitive approach for CO2 capture from flue gas (mainly N2). To achieve high separation performance, three partially NH2-, OH- and CH3OH- functionalized mixed-linker-ZIF-7 were successfully synthesized, and incorporated into polyether-block-amide (Pebax® 2533) polymer to form mixed-matrix membranes (MMMs). As evidenced by the CO2 adsorption isotherms, introducing functional groups in the ZIF-7 framework was indeed beneficial for CO2 adsorption. All MMMs composed of ZIF-7-NH2, ZIF-7-OH and ZIF-7-CH3OH offered better CO2/N2 separation performance than the parent ZIF-7-Pebax® 2533 membrane, suggesting the positive effect of functionalized ZIF-7 fillers on the gas separation performance. Among the three functionalized ZIF-7 based MMMs, the ZIF-7-OH-Pebax MMMs exhibited the best performance for CO2/N2 separation, which might be ascribed to the highest adsorption selectivity of CO2 over N2 predicted by ideal adsorbed solution theory (IAST) for ZIF-7-OH fillers. The 14% ZIF-7-OH-Pebax MMM showed high CO2 permeability of 273 Barrer and CO2/N2 separation factor of 38, which increased by 60% and 145% as compared with the neat Pebax membrane. The strategy of preparing functionalized MOFs with strong affinity for CO2 provides an effective method to develop MMMs for highly efficient CO2 separation.

A series of novel dense, CO2-tolerant, oxygen permeable, dual-phase membranes made of Ce0.9Pr0.1O2–δ - La0.5Sr0.5Fe0.9Cu0.1O3–δ (CPO-LSFCO) with different CPO : LSFCO weight ratios (2:8, 4:6, 6:4 and 8:2) was prepared by an one-pot EDTA-citric acid method. Their chemical compatibility, oxygen permeability, CO2 tolerance and long-term stability regarding the phase structure and composition in different atmospheres were studied. A direct dependency of the oxygen permeation flux through the membranes on the CPO : LSFCO weight ratio was obtained. The highest permeation fluxes of 0.93 mL min−1 cm−2 and 0.71 mL min−1 cm−2 under an air/He and an air/CO2 gradient, respectively, through a 0.5 mm thick membrane at 1173 K were measured for a weight ratio of 4:6. Especially, the membranes showed excellent chemical resistance towards CO2 for more than 2050 h and CO2 plasma for more than 20 h. This work demonstrates that dual-phase CPO-LSFCO membranes are promising, chemically stable candidates as oxygen suppliers or oxygen distributors for industrial applications.

Ba2In2O5 is a mixed ionic–electronic conducting (MIEC) ceramic-based material offering a large number of oxygen vacancies to become an alternative material for oxygen separation membranes from gas mixtures or even a CO2 plasma. This material was selected as model system to deeper analyze the structure-property relations, while making use of a promising structure stability. In this study, partial substitution of In3+ by Cr3+ yielded single-phase Ba2In2–xCrxO5–δ (x = 0, 0.2, 0.25). This forced an altered arrangement of the oxygen vacancies and a structural change from orthorhombic (Ibm2) to tetragonal (I4cm). The highest oxygen permeability of P(O2) = 1.4 ± 0.1 mL min−1·cm−2·mm at 1223 K among all tested samples was obtained for x = 0.2. A precise adjustment of the degree of oxygen vacancy ordering and the unit cell volume in this material reduced the activation energy EA and enhanced the self-diffusion coefficient D0 of the oxygen ions boosting the oxygen permeability as demonstrated by the superior oxygen permeability at lower temperatures (~1000 K), still reaching an oxygen permeability of P(O2) = 0.72 ± 0.04 mL min−1·cm−2·mm at 773 K. This concept seems plausible for an adaption to other structurally related membrane materials.

The Ruddlesden-Popper type oxide (Pr0.9La0.1)2.0Ni0.74Cu0.21Ga0.05O4+δ ((PL)2.0NCG) is important for oxygen separating membranes and intermediate temperature solid-oxide fuel cell (SOFC) cathodes if the high chemical stability of CO2 is required. This oxide exhibits good phase stability in the air at high temperatures, whereas at intermediate temperatures it demonstrates a reversible decomposition into Pr4Ni3O10+δ′ (a higher member of the Ruddlesden-Popper series) and praseodymium oxide phases, which are barriers to the oxygen transport. The phase decomposition conditions of (PL)2.0NCG, as a function of temperature and oxygen pressure, have been examined. The defined phase stability window of temperature and oxygen partial pressure for (PL)2.0NCG can be the instruction for practical applications. The influence of calcination temperature and A-site deficiency on the material’s phase stability are discussed to guide the development of Ruddlesden-Popper type materials with improved stability.

Most of the alkaline earth-containing perovskite-based oxygen-transporting membranes (OTMs) have insufficient tolerance toward CO2 that potentially limits their commercial applications, for example, oxy-fuel combustion processes with CO2 capture. One concern regarding the chemical potential of oxygen that may influence the CO2 tolerance of perovskites, however, is lacking effective investigations. In the present work, we demonstrate that the approach to increase the chemical potential of oxygen at the feed side contributes to stabilize the oxygen permeation fluxes of the fluorite–perovskite dual-phase OTM under CO2-rich atmosphere, and we further verify that oxygen can effectively act as a “buffer” to prevent the carbonate formation. Remarkably, we achieve high and stable oxygen permeation fluxes over 0.84 mL cm–2 min–1 during long-term operation at 900 °C with a 0.5 mm thickness 80 wt % Ce0.8Gd0.15Cu0.05O2−δ-20 wt % SrFeO3−δ (CGCO-SFO, nominal composition) dual-phase membrane using oxygen-enriched air as...

The membrane microstructure and phase composition of Ruddlesden–Popper-type La 2 NiO 4+ δ ceramics, which were prepared by field-assisted sintering technique/spark plasma sintering (FAST/SPS) process or by conventional pressing and pressureless sintering were investigated. As starting material, a La 2 NiO 4+ δ powder, with an average particle size of 0.2 μm was used. The grain-size distribution of the resulting membranes varied from 0.015 μm 2 for FAST/SPS sintered ceramic to 6.11 μm 2 for pressureless sintered membrane. The microstructure analysis of membranes was performed by transmission and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy. Phase transition from orthorhombic to tetragonal crystallographic structure in FAST/SPS material was investigated by temperature-dependent X-ray powder diffraction. The effect of sintering technique and grain size on the oxygen permeation performance of the membranes is discussed with respect to impurities in the material.

The initial stages of the formation of anatase nanotubes starting from TiO2 microparticles are studied theoretically at density-functional theory (DFT) level. Several formation mechanisms proposed in the literature are discussed. In the present study a mechanism is adapted that starts with NaOH adsorption on the anatase (101) surface. A phase transition from NaOH:anatase to sodium titanate is thermodynamically favorable but does not lead to the formation of sodium titanate nanotubes. Instead it is shown that anatase nanotubes with NaOH adsorbed on the inner surface are stabilized with respect to the unmodified 2D-periodic anatase surface structure. The structure and stability of selected intermediates of the nanotube formation process are investigated. In the experimental part we investigated the initial step of the nanotube formation and characterized the crystal structure of the as prepared titanate nanotubes.

The U-shaped alkaline-earth metal-free CO2-stable oxide hollow-fiber membranes based on (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ (PLNCG) are prepared by a phase-inversion spinning process and applied successfully in the partial oxidation of methane (POM) to syngas. The effects of temperature, CH4 concentration and flow rate of the feed air on CH4 conversion, CO selectivity, H2/CO ratio, and oxygen permeation flux through the PLNCG hollow-fiber membrane are investigated in detail. The oxygen permeation flux arrives at approximately 10.5 mL/min cm2 and the CO selectivity is higher than 99.5% with a CH4 conversion of 97.0% and a H2/CO ratio of 1.8 during 140 h steady operation. The spent hollow-fiber membrane still maintains a dense microstructure and the Ruddlesden-Popper K2NiF4-type structure, which indicates that the U-shaped alkaline-earth metal-free CO2-tolerant PLNCG hollow-fiber membrane reactor can be steadily operated for POM to syngas with good performance. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3587–3595, 2014

Most of the currently used perovskite-based oxygen-transporting membranes have insufficient resistance towards CO2 and high material costs that potentially limit their commercial applications. In the present work, a highly CO2-tolerant oxygen permeation membrane based on La0.6Ca0.4Co1–xFexO3−δ (x = 0, 0.3, 0.5, 0.7, 1) was designed and prepared by a scalable reverse co-precipitation method. The oxygen permeation flux through the dense membranes was evaluated and found to be highly dependent on the Co/Fe ratio. La0.6Ca0.4Co0.3Fe0.7O3−δ possessed the highest permeation flux among the investigated samples, achieving 0.76 ml min−1 cm−2 under an Air/He gradient and 0.5 ml min−1 cm−2 under an Air/CO2 gradient at 1173 K for a 1 mm thick membrane. A combination study of first principles calculations and experimental measurements was conducted to advance the understanding of Co/Fe ratio effects on the oxygen migration behavior in La0.6Ca0.4Co1–xFexO3−δ. The observed oxygen permeability is three times higher than that reported in literature under similar conditions. The presented results demonstrate that this highly CO2-tolerant membrane is a promising candidate for high temperature oxygen separation applications.

In this work, the ZnO spherical nanoparticles with a diameter in the range of 10–30 nm have been prepared via mechanochemical oxidation of metallic Zn powders treated in a vibratory ball mill in the presence of air and liquid nitrogen. The as-prepared nanocrystals were characterized by XRD, HR-TEM, FTIR, XPS, and UV–vis spectroscopy. The results show that metallic zinc powder is completely converted to nanocrystalline ZnO within 48 h of cryomilling. The XPS analysis confirms the presence of incorporated nitrogen as well as Zn(OH)2 and carbonate species formed on the reactive structurally-disordered surface shell of the as-prepared nanoparticles. Compared with the pure ZnO, the light absorption by the as-prepared ZnO nanocrystals was shifted to longer wavelengths.

Micro-hybrid vehicles with stop–start function and regenerative braking lead to higher requirements on flooded lead-acid batteries. A promising approach to improve the cycleability of flooded lead-acid batteries is the use of carbon additives in the negative active mass. In this study different carbons (carbon blacks and a lamp black) were studied by transmission electron microscopy and Raman spectroscopy. Furthermore, batteries containing carbon blacks and lamp black in the negative active material were cycled with 17.5% depth of discharge. Morphology, surface functionalisation, and the degree of order were correlated with the cycle life. In cycling tests, batteries with highly ordered carbon blacks increase the lifetime of the corresponding battery by up to a factor of two.

A novel concept for the preparation of multiphase composite ceramics based on demixing of a single ceramic precursor has been developed and used for the synthesis of a dual-phase H2 -permeable ceramic membrane. The precursor BaCe0.5 Fe0.5 O3-δ decomposes on calcination at 1370 °C for 10 h into two thermodynamically stable oxides with perovskite structures: the cerium-rich oxide BaCe0.85 Fe0.15 O3-δ (BCF8515) and the iron-rich oxide BaCe0.15 Fe0.85 O3-δ (BCF1585), 50 mol % each. In the resulting dual-phase material, the orthorhombic perovskite BCF8515 acts as the main proton conductor and the cubic perovskite BCF1585 as the main electron conductor. The dual-phase membrane shows an extremely high H2 permeation flux of 0.76 mL min(-1) cm(-2) at 950 °C with 1.0 mm thickness. This auto-demixing concept should be applicable to the synthesis of other ionic-electronic conducting ceramics.

Water splitting coupled with partial oxidation of methane (POM) using an oxygen-transporting membrane (OTM) would be a potentially ideal way to produce high-purity hydrogen as well as syngas. Over the past decades, substantial efforts have been devoted to the development of supported membranes with appropriate configurations to achieve considerable performance improvements. Herein, we describe the design of a novel symmetrical membrane reactor with a sandwich-like structure, whereby a largescale production (>10 mL min(-1) cm(-2) ) of hydrogen and syngas can be obtained simultaneously on opposite sides of the OTM. Furthermore, this special membrane reactor could regenerate the coke-deactivated catalyst in situ by water steam in a single unit. These results represent an important first step in the development of membrane separation technologies for the integration of multiple chemical processes.

Ordered mesoporous TiO2 nanoparticles with amorphous pore walls were synthesized by a facile one pot template synthesis. The samples were heat treated at different temperatures under oxidizing (air), inert (N2), and reducing (N2/H2) conditions before removing the template under air atmosphere at 350 °C. The use of N2/H2 or N2 atmospheres can effectively reduce the crystallite size by 2 nm compared to the calcination in air, leading to a better ordering of the mesoporous system than in the case of the calcination under air. The phase analysis of the powder diffraction data shows that the anatase content remains constant with temperature and is fed by an amorphous precursor and consumed by rutile when it is formed.

This study presents a new approach to enhance the corrosion resistance of tungsten inert gas (TIG) welded AZ31 magnesium alloys by using nanocrystalline magnesium fluoride suspensions in a suspension plasma spray (SPS) process. We have developed a synthesis for the preparation of nanocrystalline magnesium fluoride suspensions, which delivers nearly monodisperse nanoparticles in a gram scale yield. The particles were analyzed with transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). Stable suspensions of magnesium fluoride nanoparticles in water were characterized by dynamic light scattering (DLS), zeta-potential, and viscosity measurements. Such suspensions were deposited with an SPS torch onto TIG welded seams of the magnesium alloy AZ31, thus producing a protective magnesium fluoride layer. Magnesium fluoride covered welded seams were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectroscopy (EDXS). In order to introduce a simple method for sensoring the deposited magnesium fluoride coatings, the magnesium fluoride nanoparticles can also be fluorescence-labeled by co-doping with cerium(III) and terbium(III), the respective optical properties were characterized by reflection and luminescence spectroscopy. The deposited layers can, thus, be inspected by illumination with an UV lamp, because of their bright green emission. The corrosion properties of the magnesium fluoride layer on the welded seams were studied by means of potentiodynamic potential measurements.

Nanocrystalline ZnSe was prepared by mechanochemical synthesis in a laboratory mill and an industrial mill from the mixture of Zn and Se powdered precursors. XRD measurements indicate the formation of the cubic and hexagonal modifications of ZnSe during mechanochemical synthesis in the laboratory mill. Hexagonal modification disappears with increasing time of mechanochemical reaction. XPS analysis was applied to study the surface composition of mechanosynthesized ZnSe. The reaction products were also characterized by TEM. An application of the industrial mill verified the possibility of a large-scale mechanochemical production of ZnSe semiconductor at ambient temperature and in a relatively short reaction time (15–60 min).

Mechanochemical synthesis of lead selenide PbSe nanoparticles was performed by high-energy milling of lead and selenium powder in a laboratory planetary ball mill and in an industrial eccentric vibratory mill. Structural properties of the synthesized lead selenide were characterized using X-ray diffraction that confirmed crystalline nature of PbSe nanoparticles. The average size of PbSe crystallites of 37 nm was calculated from X-ray diffraction data using the Williamson – Hall method. The methods of particle size distribution analysis, specific surface area measurement, scanning electron microscopy and transmission electron microscopy were used for characterization of surface, mean particle size, and morphology of PbSe. An application of industrial mill verified a possibility of the synthesis of a narrow bandgap semiconductor PbSe at ambient temperature and in a relatively short reaction time.

A highly oriented zeolitic imidazolate framework 8 (ZIF-8) composite membrane was prepared by seeding and secondary growth. By dip-coating, preformed ZIF-8 nanocrystals were attached to the surface of a porous α-alumina support using polyethyleneimine as the coupling agent. After solvothermal treatment, a continuous and well-intergrown ZIF-8 layer was obtained. X-ray diffraction analysis of the membrane showed preferred orientation of the {100} plane parallel to the support. Further time-dependent investigations by scanning and transmission electron microscopy as well as X-ray diffraction indicated that the preferred orientation develops during an evolutionary growth process. In gas mixture permeation experiments, the membrane showed good performance in H2/hydrocarbon separation. A sharp molecular sieve separation is observed for an equimolar H2/C3H8 mixture with a separation factor above 300.

We report on a simple and straightforward method that enables the rapid room-temperature production of nanocrystals (finely tuned in size between ∼10 and 65 nm) and microcrystals (∼1 μm) of the prototypical microporous zeolitic imidazolate framework (ZIF) material ZIF-8. Control of crystal size is achieved in a novel approach by employing an excess of the bridging bidentate ligand and various simple auxiliary monodentate ligands with different chemical functionalities (carboxylate, N-heterocycle, alkylamine). The function of the monodentate ligands can be understood as a modulation of complex formation and deprotonation equilibria during crystal nucleation and growth. Using time-resolved static light scattering, the functioning of modulating ligands is monitored for the first time by in situ experiments, which offered significant insight into the crystal growth processes. Formation of nanocrystals is characterized by continuous, comparatively slow nucleation and fast crystal growth occurring on a time sca...

Phase stability and oxygen permeation behavior of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) dead-end tube membranes were investigated in long-term oxygen production at 950 and 750 °C. At 950 °C, the BSCF tube membranes exhibit good long-term phase stability and a stable oxygen permeation flux. However, at the intermediate temperature of 750 °C, both the oxygen permeation flux and the oxygen purity decrease continuously. This behavior is related to the formation of two secondary phases that are a hexagonal perovskite, Ba0.5±xSr0.5±xCoO3−δ, and a trigonal mixed oxide, Ba1–xSrxCo2–yFeyO5, that evolved in the ceramic membrane made of cubic BSCF perovskite during the dynamic flow of oxygen through it. Tensile stress as a result of phase formation causes the development of cracks in the membrane, which spoil the purity of the permeated oxygen. The partial degradation of cubic BSCF perovskite in the intermediate temperature range (750 °C) was more pronounced under the strongly oxidizing conditions on the oxygen supply (fe...

The bulk and surface properties of magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals synthesized by solid state route in a planetary mill were studied. XRD, SEM, TEM (HRTEM), low-temperature N 2 sorption, nanoparticle size distribution as well as SQUID magnetometry methods have been applied. The measurements identified the aggregates of small nanocrystals, 5–10 nm in size. The homogeneity of produced particles with well developed specific surface area (15–66 m 2 g −1 ) was documented. The transition from the paramagnetic to the spin-glass-like phase has been observed below ∼40 K. The changes in the magnetic behaviour at low temperatures seem to be correlated with the formation of the new surface area as a consequence of milling. The magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals are obtained in the simple synthesis step, making the process attractive for industrial applications.

TiO2 rutile nanorods either decorated with anatase nanoparticles or pure have been prepared via a facile single-step hydrothermal method using commercially available aqueous solutions of titanium bis(ammonium lactate) dihydroxide at natural pH (∼8.0) without any additives. The obtained powders have been characterized by X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, UV−vis diffuse reflectance spectroscopy, and nitrogen adsorption. The photocatalytic activities have been evaluated for the gas-phase decomposition of acetaldehyde under UV(A) illumination. The results revealed that TiO2 rutile nanorods decorated with anatase nanoparticles exhibit a higher photocatalytic activity than those embedded in anatase nanoparticles or without any anatase contact. This behavior is explained by the better charge carrier separation in the case of anatase rutile mixtures.

High quality brookite TiO2 nanorods have been obtained by the thermal hydrolysis of commercially available aqueous solutions of titanium bis(ammonium lactate) dihydroxide in the presence of high concentrations of urea (≥6.0 M) as an in situ OH− source. Biphasial anatase/brookite mixtures are obtained at lower urea concentrations. The ratios between anatase and brookite can readily be tailored by the control of the urea concentration. The obtained powders have been characterized by X-ray diffraction, Raman spectroscopy, field emission-scanning electron microscopy, high-resolution transmission electron microscopy, UV−vis diffuse reflectance spectra, and nitrogen adsorption. The photocatalytic activity of pure anatase nanoparticles, of anatase/brookite mixtures, and of pure brookite nanorods has been assessed by hydrogen evolution from aqueous methanol solution as well as by the degradation of dichloroacetic acid (DCA) in aqueous solution. The results indicate that the photocatalytic hydrogen evolution activ...

Cobalt-free perovskite with the novel composition (Ba0.5Sr0.5)(Fe0.8Cu0.2)O3-δ (BSFCu) was synthesized via a sol−gel method and studied with respect to the crystallographic structure as well as the oxygen ionic and the electronic conductivity. In situ X-ray diffraction (XRD) was applied to investigate the thermal dilatation and the phase stability of the BSFCu at high and intermediate temperatures. Additionally, time-dependent oxygen permeation performance measurements were carried out for BSFCu and Co-based (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ membranes at 1023 K for 200 h. The BSFCu phase was found to be a cubic perovskite by XRD and transmission electron microscopy. The BSFCu membrane exhibits a very high oxygen permeation and electrical conductivity as compared to known perovskite membranes. The oxygen permeation of the BSFCu membrane maintains its value for 200 h at 1023 K unlike (Ba0.5Sr0.5)(Co0.8Fe0.2)O3-δ, whose oxygen flux was reduced by one-half during the same interval.

In this work, the preparation of three-dimensional hierarchical pore structures by a combination of laser-based templates and the self-organization process of mesostructured titania is presented. For this purpose macrostructured polymers produced by two-photon polymerization act as a template for the deposition of a mesostructured titania film from a solution containing an amphiphilic block copolymer by dip coating. A carefully applied calcination procedure removes both the macrotemplating polymer and the mesotemplating surfactant molecules so that a replica of the initial polymer structure with a hierarchical (macro- and meso-) pore system is obtained. In addition, the titania, which is amorphous after deposition, is transferred into crystalline anatase during calcination. Materials with dual pore systems are interesting for possible applications in catalysis and sorption, and three-dimensional crystalline structures from materials with high refraction index are attractive for photonic applications, for example as photonic crystals.

Microporous membranes with pore apertures below the nanolevel can exhibit size selectivity by serving as a molecular sieve, which is promising for overcoming Robeson s “upperbound” limits in membrane-based gas separation. Zeolites, polymers of intrinsic microporosity (PIMs), metal oxides, and active carbon are the typical materials used for this purpose. Metal–organic frameworks (MOFs) have attracted much research interest in recent years, and are emerging as a new family of molecular sieves. MOFs are novel porous crystalline materials consisting of metal ions or clusters interconnected by a variety of organic linkers. In addition to promising applications in adsorptive gas separation and storage or in catalysis, their unique properties, such as their highly diversified structures, large range in pore sizes, very high surface areas, and specific adsorption affinities, make MOFs excellent candidates for use in the construction of molecular sieve membranes with superior performance. The preparation of MOF membranes for gas separation is rapidly becoming a research focus. A number of attempts have been made to prepare supported-MOF membranes; however, progress is very limited and so far there are only very few reports of continuous MOF films on porous supports being used as separating membranes. Recently, Guo et al. reported a copper-net-supported HKUST-1 (Cu3(BTC)2; BTC= benzene-1,3,5-tricarboxylate) membrane exhibiting a H2/N2 selectivity of 7 [13] (separation factor of H2 over N2 is calculated as the permeate-to-retentate composition ratio of H2, divided by the same ratio for N2 as proposed by IUPAC) ; this is the first MOF membrane to show gasseparation performance beyond Knudsen diffusion behavior. Very recently, Ranjan and Tsapatsis prepared a microporous metal–organic framework [MMOF, Cu(hfipbb)(H2hfipbb)0.5; hfipbb= 4,4’-(hexafluoroisopropylidene)bis(benzoic acid)] membrane by seeded growth on an alumina support. The ideal selectivity for H2/N2, based on single permeation tests, was 23 at 190 8C. This higher selectivity, compared to the report from Guo et al., might be a result of the smaller effective pore size (ca. 0.32 nm of MMOF versus 0.9 nm of HKUTS-1), which results in a relatively low H2 permeance of this MMOF membrane (10 9 molm 2 s Pa 1 at 190 8C). The authors attributed this finding to the blockage of the onedimensional (1D) straight-pore channels in the membrane. Therefore, with regard to H2 separation, small-pore MOFs having three-dimensional (3D) channel structures are considered to be ideal membrane materials. Zeolitic imidazolate frameworks (ZIFs), a subfamily of MOFs, consist of transition metals (Zn, Co) and imidazolate linkers which form 3D tetrahedral frameworks and frequently resemble zeolite topologies. A number of ZIFs exhibit exceptional thermal and chemical stability. Another important feature of ZIFs is their hydrophobic surfaces, which give ZIF membranes certain advantages over zeolite membranes and sol–gel-derived silica membranes in the separation of H2 in the presence of steam. Very recently we reported the first result from permeation measurements on a ZIF-8 membrane. The ZIF-8 membrane showed a H2/CH4 separation factor greater than 10. Whereas the ZIF-8 pores (0.34 nm) are slightly larger than the kinetic diameter of CO2 (0.33 nm), and are very flexible, the H2/CO2 separation on this ZIF-8 membrane showed Knudsen selectivity. In the current work, we therefore chose ZIF-7 as a promising candidate for the development of a H2-selective membrane to satisfy the above requirements. ZIF-7 (Zn(bim)2) is formed by bridging benzimidazolate (bim) anions and zinc cations with soladite (SOD) topology. The pore size of ZIF-7 (the hexagonal window size in the SOD cage) estimated from crystallographic data is about 0.3 nm, which is just in between the size of H2 (0.29 nm) and CO2 (0.33 nm). We could therefore expect a ZIF-7 membrane to achieve a high selectivity of H2 over CO2 and other gases through a molecular sieving effect. In many cases, it was reported that the heterogeneous nucleation density of MOF crystals on ceramic supports is very low, 14] which makes it extremely difficult to prepare supported-MOF membranes by an in situ synthesis route. Chemical modifications of substrate surfaces have been proposed to direct the nucleation and orientation of the deposited MOF layers. Based on our knowledge in the development of zeolite membranes, we adopted a seeded secondary growth method for the ZIF-7 membrane prepara[*] Prof. Dr. Y.-S. Li, F.-Y. Liang, H. Bux, A. Feldhoff, Prof. Dr. J. Caro Institute of Physical Chemistry and Electrochemistry and the Laboratory for Nano and Quantum Engineering (LNQE) in cooperation with the Center for Solid State Research and New Materials, Leibniz Universit t Hannover Callinstrasse 3A, 30167 Hannover (Germany) Fax: (+49)511-762-19121 E-mail: yanshuo.li@pci.uni-hannover.de juergen.caro@pci.uni-hannover.de

A BaCoxFeyZrzO3−δ (BCFZ) perovskite hollow fiber membrane was used to construct reactors for the partial oxidation of methane (POM) to syngas. The performance of the BCFZ fibers in the POM was studied (i) without any catalyst, (ii) with catalyst-coated fibers, and (iii) with catalyst packed around the fibers. In addition to the performance in the POM, the stability of the BCFZ hollow fiber membranes was investigated for the different catalyst arrangements. Best stability of the BCFZ hollow fiber membrane reactor in the POM could be obtained if the reforming catalyst is placed behind the oxygen permeation zone. It was found that a direct contact of the catalyst and the fiber must be avoided which could be achieved by coating the fiber with a gold film. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Zinc-doped (BaSr)FeO3-δ perovskite-type membranes were found to exhibit an excellent long-term stability at high and intermediate temperatures under an oxygen partial pressure gradient. With carbon dioxide as sweep gas, the oxygen permeation diminishes almost completely. By X-ray diffraction a phase mixture of hexagonal, tetragonal and cubic perovskite with a (Ba0.4{plus minus}0.1Sr0.6{plus minus}0.1)CO3 layer and some zinc oxide was found. Transmission electron microscopy showed that the dense perovskite membrane is decomposed into phases with different morphologies accompanied by pore and crack formation in a surface layer of 5 µm. After switching to helium as the sweep gas, a hexagonal perovskite phase is still present, which reduces the oxygen permeation flux. A short heating to 950 {degree sign}C regenerates the oxygen permeation flux. The appearance of the carbonate structure leads to a breakdown of the oxygen permeation ability, but the effect of the carbon dioxide is totally reversal after a short high temperature treatment.

Dense mixed proton and electron conducting membrane made of BaCe 0.95 Nd 0.05 O 3− δ (BCNd5) was prepared by pressing followed by sintering. X-ray diffraction (XRD) was used to characterize the phase structure of both the powder and the sintered membranes. The microstructure of the sintered membranes was studied by scanning electron microscopy (SEM). Hydrogen permeation through the BCNd5 membrane was studied using a high temperature permeator. The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions, which is due to H + hopping via surface OH groups. At 925 °C, a hydrogen permeation flux of 0.02 mL/min cm 2 was obtained under wet condition, which recommends BCNd5 as a potential material for hydrogen-selective membranes.