N-doped anodic titania nanotube arrays for hydrogen production

Titanium dioxide (TiO₂) nanotube arrays are grown in a mixed electrolyte by anodizing process. The anodic nanotubes for N-doping were calcinated at 773 K in a tube furnace with a mixture of NH₃ and Ar gas. The photocatalytic activity of N-doped TiO₂ nanotubes was carried out in a water-splitting reaction under UV and visible light irradiation. Various characterization techniques (Scanning electron microscopy, X-ray diffractometry, X-ray photo-electron spectroscopy, etc.) are used to study the surface morphology, phase of structure, and binding energy.     

Mixed gas and pure gas transport properties of copolyimide membranes

Copolyimides were synthesized from dianhydride of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with various diamine contents of 4,4′‐oxydianiline (ODA) and 2,3,5,6‐tetramethyl‐1,4‐phenylenediamine (TeMPD) by chemical imidization in a two‐step procedure. Polyimides (PIs) were characterized using thermogravimetric analysis, Fourier transform infrared spectroscopy, differential scanning calorimetry, as well as specific volume and free volume. The gas transport properties for pure gas and blends of CO₂ and CH₄ for the homopolymers and 6FDA‐ODA/TeMPD copolymers were investigated at 35°C and 150 psi pressure. In pure gas permeation, permeability of CO₂ and CH₄ increased with increasing TeMPD content in the diamine moiety, whereas the ideal selectivity decreased with increasing TeMPD content. In the mixed gas permeation, permeabilities and separation factor were measured as a function of CO₂ feed molar fraction for five PI membranes. The behavior of pure gas and mixed gas permeabilities and separation factor of CO₂/CH₄ mixtures as the chemical nature of the diamine and the CO₂ molar fraction in the feed gas were varied and are discussed in detail. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Dopants for synthesis of stable bimodally porous titania

Bimodally porous titania powders doped with alumina, zirconia, and silica were made by wet precipitation from organometallic precursors (for Al/Ti=0.05-0.4, and Zr/Ti=Si/Ti=0.1). Doping retards not only the anatase-to-rutile phase transformation, but also the crystallite growth of titania. So it was used to control the powder phase composition and pore structure at high temperatures. The extent of the retarding effect on pore structure and phase transformation increased with increasing alumina concentration. The effectiveness of these dopants follows the order of: zirconia>silica>alumina. The dopants also reduce the loss of surface area of the calcined powders by decreasing the sintering and phase transformation rates. All powders exhibited bimodal pore size distributions (PSD) with fine intra-particle pores (1–4 nm) and larger inter-particle pores (10–120 nm). However, the intra-particle pores of the pure titania disappeared at 600°C, while the bimodal PSD of doped titania was maintained up to 750°C.     

Thermally stable and photocatalytically active titania for ceramic surfaces

The most photocatalytically active titania modification anatase must be stabilised to achieve high photocatalytic activity in ceramic processes at temperatures above 1000 °C. Thermally stable TiO₂ powders were prepared by the addition of silica and boehmite nanoparticles and deposited on corundum substrates and lead-free glazes. The powders and coatings were fired at increasing temperatures, and stabilisation of the anatase phase was achieved up to 1200 °C. In general, thermal stability was found to be lower when coated on substrates compared to the powder alone, and the extent of reduction depended on the chemical composition of the substrate. Only a slight modification of the titania electronic structure was found, indicating only weak interactions between silica and titania. Based on these results it is possible to assume an amorphous silica and alumina shell encases the titania particles which prevents grain growth and the anatase to rutile phase transformation.     

Preparation of composite membranes via interfacial polyfunctional condensation for gas separation applications

Composite membranes were prepared by interfacial polycondensation of a water-soluble diamine (4,4′;-methylene dianiline [MDA] or ethylene diamine [EDA]) with an organic solvent (hexane)-soluble 1,2,4,5-benzenetetra acyl chloride (BTAC) on top of a porous polysulfone (PSF) support. For both the poly(BTAC-MDA) and poly(BTAC-EDA) composite film systems, the permselectivity of these films increases only slightly with an increasing number of coatings. The poly(BTAC-MDA) composite membranes are treated at 135°C in a nitrogen atmosphere for 4 h, and they have a high selectivity [α^*(CO₂/CH₄) = 20.51] and permeability [P?(CO₂) = 44.12 Barrer]. This is due mainly to the great chain stiffness of the formed polyimide, which has high selectivity. The high permeability is due to a porous polysulfone support. The trend of the permeability for this composite film is P?(CO₂) > P?(O₂) > P?(N₂) > P?(CH₄). In poly(BTAC-EDA) composite membranes, the permeation of different gases decreases in the order of P?(CO₂) > P?(O₂) > P?(CH₄) > P?(N₂). As to the composite films being more permeable to CH₄ than to N₂, this is probably due to the presence of a considerable quantity of aliphatic chains (–CH₂–CH₂–) in the poly(BTAC-EDA) composite film caused by its particularly excellent solubility for methane.     

Mechanically stable membranes of polyacrylic acid-grafted chitosan-functionalized carbon nanotubes with remarkable water storage capacity in sandy soils

Polyacrylic acid (PAA) is one of the most exciting hydrophilic polymers for water control and conservation; however, it suffers from poor mechanical properties during the agricultural applications. For that purpose a series of PAA-based multiwalled carbon nanotubes (MWCNTs) membranes have synthesized via a grafting process of MWCNTs using chitosan (CS) polymer as a binder. The fabricated membranes have spectroscopically characterized by different techniques to confirm the composite structure. The MWCNTs content into the PAA membranes has played a pronounced effect on water absorptivity, swelling behavior, and mechanical properties. PAA membrane has showed a fourfold increase in yield-stress by the addition of 3 wt% PAA/CS/MWCNTs, while preserving a 91% of water absorptivity of PAA membrane. The soil applications of the PAA/CS/MWCNTs membranes have showed remarkable improvements in soil moisture content compared to the PAA membrane. This study provides a promising pathway for future field applications, especially in arid lands.     

Ceramic materials for H2 transport membranes applicable for gas separation under coal-gasification-related conditions

This work focuses on the synthesis, characterization and testing of mixed protonic–electronic conducting membrane materials for H₂ separation from gas mixtures capable of operating in a membrane reactor at temperatures higher than 600 °C. La_5.5WO_12−δ and selected substituted barium zirconates with stoichiometries BaCe_0.5Zr_0.4Y_0.1O_3−δ and BaCe_0.2Zr_0.7Yb_0.08Ni_0.02O_3−δ were therefore characterized and tested under coal-gasification-related conditions at 600–900 °C. Sintered samples of the synthesized substituted barium zirconates were characterized by measuring the total conductivity and the thermal expansion coefficients. Also particle size distributions, BET surface-areas and elemental analysis of the starting powders, including commercial La_5.5WO_12−δ were specified. The compounds were exposed to syngas with steam, as well as to an atmosphere mainly consisting of CO₂. The microstructure and phase composition of the membrane materials were studied by SEM, EDX and XRD before and after exposure. BaCe_0.2Zr_0.7Yb_0.08Ni_0.02O_3−δ shows a very promising chemical stability from 600 °C to 900 °C and La_5.5WO_12−δ at 900 °C.     

Mechanically strong shape memory polyurethane for water vapour permeable membranes

Water vapour permeable polymeric thin films possess significant importance in miscellaneous applications such as packaging, medical devices, controlled‐release systems, electronics and biosensors. In this work, a series of shape memory polyurethanes (SMPUs) were synthesized by a two‐step pre‐polymerization technique with variations in hard to soft segments and molecular weight of macroglycol. DSC, Fourier transform infrared spectra, dynamic TGA and tensile testing were carried out to characterize and evaluate the properties of these synthesized SMPUs. The effect of the soft segment and the molecular weight of macroglycol on the thermal properties, mechanical properties and water vapour permeability of the synthesized SMPUs were investigated to achieve a good water vapour permeable membrane. We found that the synthesized SMPUs demonstrated a good water vapour transmission rate of over 1460 g m^?2 day^–1 as well as robust mechanical properties with tensile strength 19.8 MPa indicating a promising permeable polymeric thin film for many potential applications, especially as protective clothing. © 2018 Society of Chemical Industry     

Perovskite foams used in combination with dense ceramic membranes for oxygen transport membrane applications

The future industrial implementation of membranes for oxygen transport requires new designs to increase oxygen semi-permeation, together with robust performance under operating conditions. This work describes the development of innovative membrane designs based on perovskite foams with a very large porosity (above 90%) supporting thin dense perovskite membranes (thickness of 50–100?µm). The preparation of such foam-supported membranes is described in this paper. The performances in terms of oxygen semi-permeation are also measured and compared with the best results reported in the literature up to date.     

Smart membranes for biomedical applications

Smart membranes with tunable permeability and selectivity have drawn widespread attention because of their unique biomimetic characteristics. Constructed by incorporating various stimuli-responsive materials into membrane substrates, smart membranes could self-adjust their physical/chemical properties(such as pore size and surface properties) in response to environmental signals such as temperature,pH, light, magnetic field, electric field, redox and specific ions/molecules. Such smart membranes...     

Use of mesoporous SBA-15 for nanostructuring titania for photocatalytic applications

SBA15–TiO₂ samples prepared by introducing titanium with a grafting method and having TiO₂ loadings below 15 wt.% have been characterized by XRF, XRD, IR, porosimetry, SEM, HRTEM, and UV–Visible diffuse reflectance. Differently from the samples reported in the literature characterized by a high TiO₂ loading, no evidences have been found for the presence of titania particles inside or outside the mesopores of SBA-15. Three different titanium species were instead evidenced to be present. The first two derive from the reaction of titanium with silanol groups in the corona area of inner SBA-15 walls leading to the formation of either TiO₄ tetrahedral sites (by reaction by hydroxyl nests of surface defect sites) and/or pseudo-octahedral surface sites anchored by two (or more) Si or Ti ions through bridging oxygens. The third species derives from the reaction of titanium in the regions with high sylanol density, e.g. in the micropores located in the corona of SBA-15 channels, leading to the formation of TiO₂-like nanoareas (probably Si-doped) with dimensions of around 1–2 nm maximum. The potential interest of these materials as photocatalysts, for the presence of a TiO₂-like nanoareas highly accessible by reactants, is discussed.     

Corrosion behavior of electrochemically assembled nanoporous titania for biomedical applications

Corrosion resistance of nanoporous titania was investigated in Hank’s solution using potentiodynamic polarization and electrochemical impedance spectroscopic techniques. The phase structure, surface morphology and elemental composition of the untreated, anodized heat treated and anodized heat treated titanium specimens immersed in Hank’s solution for seven days were characterized using X-ray diffraction, atomic force microscopy and scanning electron microscopy with energy dispersive X-ray spectroscopy techniques, respectively. The X-ray diffraction technique revealed that the anodized heat treated titanium exhibited anatase structure. The atomic force microscopic and scanning electron microscopic results showed that the titanium surface has transformed from a smooth to nanoporous surface depending on the anodization conditions. The energy dispersive X-ray spectroscopy results confirmed the formation of hydroxyapatite over the anodized titanium after immersion for seven days in Hank’s solution. The electrochemical results revealed that the anodized heat treated titanium after seven day immersion in Hank’s solution showed nobler shift in corrosion potential compared to untreated and anodized titanium. Hence, the results suggested that the nanoporous titania layer developed on titanium is a promising material for application as orthopaedic implants.     

金属有机框架材料中的质子传导及其在质子交换膜中的应用

质子交换膜（proton exchange membrane,PEM）是保证燃料电池安全、高效运行的关键部件。当前,Nafion及部分Nafion衍生物PEM被广泛应用于燃料电池、电解制氢、传感检测、液流电池等领域。但是,其仍存在制造成本过高、高效温度范围狭窄（\mathrm{约}\mathrm{20}~\mathrm{80}℃）等问题。近年来,部分金属有机框架材料（metal-organic frameworks,MOFs）因具有结晶性、可设计性和高比表面积等优点,作为潜在的新型质子导体,被用于修饰、改进现有高分子质子交换膜,或直接被作为主要质子传导介质制成质子交换膜,取得了一系列重要进展。本文详细介绍了在MOFs中五种质子传导的常见方式,综述了近年来国内外在高性能质子传导MOFs领域的代表性成果,总结了质子传导MOFs在质子交换膜中的三类常见应用方法,指出MOFs材料在提高PEM质子电导率、降低PEM成本、拓宽PEM高效工作区间等方面具有巨大的发展潜力。最后,本文提出现有MOFs在质子交换膜中的应用还存在稳定性、耐久性、有害物质逸出等方面的问题,这为新型MOFs质子交换膜的开发提供了参考与思路。     

Targetting membranes for gas separation

This paper describes a method of setting targets for the development of new membranes, such that the resulting membrane separator will be economically viable in a particular commercial process. The example used is the separation of carbon monoxide and hydrogen for the production of acetic acid. It is shown by an economic evaluation of the complete process, that the total cost of manufacturing acetic acid depends on the permeability and selectivity of the membrane. Costs upstream and downstream of the membrane separator are considered. The same production cost may be achieved by many different combinations of selectivity and permeability, and thus iso-cost lines may be generated which provide guidance for the development of new membranes.     

Synthesis and gas transport properties of new copolymer membranes with trimethylsilyl groups

Copolymers of 3-methacryloxypropyl tris(trimethylsiloxy) silane (SiMA) with methacrylate (MMA) and copolymers trimethylsilyl methyl methacrylate (TMSMMA) with vinyl acetate (VAc) were synthesized by radical polymerization. Membranes were cast from their solutions. Gas permeability, 10-1000 Barrer, of SiMA-MMA membranes was higher than that of TMSMMA-Vac membranes because of higher concentration of trimethylsilyl groups. Both apparent activation energies for gas permeability were very small compared to those of ordinary polymeric membranes. Poly(SiMA) is rubbery and poly(TMSMMA) is glassy at an ambient temperature. Copoly(SiMA-MMA) and copoly(TMSMMA-VAc) were shown to be random copolymers by the relationship between gas permeability coefficients and the molar ratio of each monomer. A series of copolymers in this investigation was shown to be a rare case of the polymer of which gas permeability increased in spite of the larger side chain, trimethylsilyl group, being introduced in the polymer chains.     

用于生物气提纯的促进传递膜

由生物气提纯获得的生物甲烷具有高热值,可作为天然气的替代品。生物气中除主要成分甲烷以外还含有大量的CO₂和少量的水、H₂S以及其他痕量杂质组分,需经过净化提纯方可获得高纯度的生物甲烷。膜分离技术用于生物气提纯具有绿色、高效、能耗低等特点,特别地,促进传递膜因其特殊的传质机制,对于生物甲烷系统提纯具有显著优势。综述了促进传递膜材料及其制备技术,讨论了生物气中水、H₂S杂质对膜过程的影响,同时尝试对膜法生物气提纯的经济性和发展前景进行了分析。     

用于气体净化的平板式固定床反应器

设计了一种用于气体净化的平板式固定床反应器,介绍了该反应器的结构、工作原理以及网板、导向板、气体收集箱、过滤盖等组件的功能。该反应器通过数片内置的装填有固体反应物的网板,在低功率风机作用下完成气-固反应和气体吸收,从而达到气体净化和处理的目的。应用结果表明,该反应器比直筒式反应器的净化效率高20％;用于吸收密闭空间内的酸性气体时,功率消耗较直简式反应器节省3.8 kW·h。     

Dimensionally stable polyimide copolymers for microelectronics applications

Polyimides are finding increased applications in microelectronics due to their high thermal stability, good chemical resistance, good adhesion, low moisture absorption, good mechanical properties, and low coefficient of thermal expansion (CTE). Four series of random copolyimides were synthesized and characterized for potential application as encapsulants, stress-relief layers, and interlevel dielectrics. Several candidates exhibited good combinations of physical and mechanical properties with inherent viscosities from 1.21 to 1.42 dL/g, T_g's ranging from 251 to 277°C, 10% weight loss temperatures between 503 and 527°C, and CTEs ranging from 33 to 39 ppm/°C. Mechanical properties at room temperature for the best candidates included tensile strengths of 17.8–21.3 ksi, moduli between 388 and 506 ksi, and elongations of 11–43%. Moisture absorption for these copolyimides ranged between 0.85 and 1.38 wt %. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2383–2393, 1998     

Polymeric mixed matrix membranes containing zeolites as a filler for gas separation applications: A review

Polymeric membrane technology has received extensive attention in the field of gas separation, recently. However, the tradeoff between permeability and selectivity is one of the biggest problems faced by pure polymer membranes, which greatly limits their further application in the chemical and petrochemical industries. To enhance gas separation performances, recent works have focused on improving polymeric membranes selectivity and permeability by fabricating mixed matrix membranes (MMMs). Inorganic zeolite materials distributed in the organic polymer matrix enhance the separation performance of the membranes well beyond the intrinsic properties of the polymer matrix. This concept combines the advantages of both components: high selectivity of zeolite molecular sieve, and mechanical integrity as well as economical processability of the polymeric materials. In this paper gas permeation mechanism through polymeric and zeolitic membranes, material selection for MMMs and their interaction with each other were reviewed. Also, interfacial morphology between zeolite and polymer in MMMs and modification methods of this interfacial region were discussed. In addition, the effect of different parameters such as zeolite loading, zeolite pore size, zeolite particle size, etc. on gas permeation tests through MMMs was critically reviewed.     

High performance carbon molecular sieve membranes derived from hyperbranched polyimide precursors for improved gas separation applications

A series of hyperbranched polyimides (HBPI) were selected as precursors for the production of carbon molecular sieve membranes (CMSMs) and the gas separation performance of the resultant CMSMs was explored. By varying the monomer compositions of HBPI precursor polymers, the influences of degree of branching on pore size and distribution of the CMSMs are investigated and examined. A CO₂ permeability of 1085 Barrer with CO₂/CH₄ selectivity of 52 is attained. Thermal analyses reveal that the chain rigidity of the precursors increases with the degree of branching, while the density of the CMSMs shows an opposite trend. In view of the unique network structure offered by the HBPI precursors, it is speculated that the rigid network of the HBPI with the highest degree of branching has facilitated the formation of ultra-micropores, giving rise to the more constrained structure and improved diffusivity selectivity. The unique hyperbranched network structure found in HBPI possesses great potential to producing CMSMs with superior performance.