Preparation of PVC/PVP composite polymer membranes via phase inversion process for water treatment purposes

In this work, new composite membranes were successfully prepared via phase inversion technique using polyvinyl chloride(PVC) and polyvinylpyrrolidone(PVP) as polymers and tetrahydrofuran(THF) and N-methyl-2-pyrrolidone(NMP) as solvents. The prepared membranes have been characterized by scanning electron microscope(SEM), and fourier transforms infrared spectroscopy(FTIR). The scanning electron microscope results prove that the prepared membranes are smooth and their pores are distributed throughout the whole surface and bulk body of the membrane without any visible cracks. The stress–strain mechanical test showed an excellent mechanical behavior enhanced by the presence of PVP in the prepared membranes. The membranes performance results showed that the salt rejection reached 98% with a high flux. This, in turn, makes the prepared membranes can be applied for sea and brackish water treatment through membrane distillation technology.     

Flexible and robust YAG-Al2O3 composite nanofibrous membranes enabled by a hybrid nanocrystalline-amorphous structure

A flexible and robust YAG-Al₂O₃ composite nanofibrous membrane was fabricated by a combination of sol-gel and electrospinning methods, then a sintering at 900 °C. The effects of Al₂O₃ on the microstructure and mechanical performance of YAG nanofibrous membranes were investigated. The YAG nanofibrous membrane is brittle but the composite membranes exhibit a brittle-to-flexible transformation as the Al₂O₃ content reaches 30 wt.%, which can be attributed to an optimized dense hybrid microstructure consisting of finer YAG grain size surrounded by amorphous Al₂O₃. The YAG-30 wt.% Al₂O₃ nanofibrous membrane sintered at 900 °C shows a tensile strength of 3.52±0.31 MPa, three times of that of pure Al₂O₃ sintered at the same temperature. The membrane still presents a decent flexibility with a tensile strength of 0.75±0.25 MPa after sintering at 1000 °C, which is at least 100 °C higher than the sintering temperature of most reported ceramic nanofibrous membranes.     

A composite catalytic polymer membrane reactor using heteropolyacid-blended polymer membrane

The vapor-phase MTBE decomposition was examined in a shell and tube-type catalytic membrane reactor (CMR). 12-Tungstophosphoric acid (PW) was used as a catalyst and poly-2,6-dimethyl-1,4-phenylene oxide (PPO) was used as a polymer material. A single-phase CMR (PW-PPO/Al₂O₃, type-1) and a composite CMR (PW-PPO/ PPO/ Al₂O₃, type-2) were successfully designed and characterized. It was revealed that the single-phase PW-PPO/ Al₂O₃ showed perm-selectivities for reaction products. The selective removal of methanol through the catalytic membrane shifted the chemical equilibrium toward the favorable direction in the MTBE decomposition. The PWPPO/ PPO/ Al₂O₃ showed the better performance than PW-PPO/ Al₂O₃. The enhanced performance of PW-PPO/ PPO/ Al₂O₃ CMR was due to the intrinsic perm-selectivity of PW-PPO and the additional separation capability of sub-layered PPO membrane.     

Advanced functional polymer membranes

This feature article provides a comprehensive overview on the development of polymeric membranes having advanced or novel functions in the various membrane separation processes for liquid and gaseous mixtures (gas separation, reverse osmosis, pervaporation, nanofiltration, ultrafiltration, microfiltration) and in other important applications of membranes such as biomaterials, catalysis (including fuel cell systems) or lab-on-chip technologies. Important approaches toward this aim include novel processing technologies of polymers for membranes, the synthesis of novel polymers with well-defined structure as ‘designed’ membrane materials, advanced surface functionalizations of membranes, the use of templates for creating ‘tailored’ barrier or surface structures for membranes and the preparation of composite membranes for the synergistic combination of different functions by different (mainly polymeric) materials. Self-assembly of macromolecular structures is one important concept in all of the routes outlined above. These rather diverse approaches are systematically organized and explained by using many examples from the literature and with a particular emphasis on the research of the author's group(s). The structures and functions of these advanced polymer membranes are evaluated with respect to improved or novel performance, and the potential implications of those developments for the future of membrane technology are discussed.     

Flexible polymer composite electromagnetic crystals

The dielectric properties of a ceramic powder (BaTiO₃) filled thermoplastic elastomer (EPDM TPE) were investigated for use in a flexible electromagnetic crystal. Materials were produced that had a high dielectric constant (approximately 9) and low loss tangent (less than 0.01). Materials were extruded and injection molded so as to povide low‐cost processing. Mechanical and electromagnetic test results showed the effect of processing conditions on the final quality of the composite. The shear rate during processing and the number of mixing cycles were found to affect the final material characteristics significantly. An electromagnetic crystal woven from extruded rods showed good reflectivity in the 10–15 GHz region.     

Phase transformations in mesostructured vanadium–phosphorus-oxides

Mesostructured lamellar, hexagonal and cubic vanadium–phosphorus-oxide (VPO) phases were prepared employing cationic, anionic and alkylamine surfactants under mild conditions and low pH. The obtained mesophases displayed desirable vanadium oxidation states (+3.8 to +4.3) and P/V molar ratios 1.0 for the partial oxidation of n-butane to maleic anhydride. As-synthesized mesostructured VPO underwent phase transformations to various mesostructured and dense VPO phases depending on the post-synthesis treatment. The phase transformations of mesostructured VPO during Soxhlet extraction and thermal treatment in N₂ have been observed for the first time. These transformations were explained by the changes in the surfactant packing parameter, g. Calcination in air produced more disordered mesostructures and dense VPO phases such as γ-VOPO₄ and (VO)₂P₂O₇.     

无机层状矿物/聚合物高吸水性复合材料

综述了无机/聚合物高吸水性复合树脂的吸水机理,介绍了几种典型的无机层状矿物,重点对近年来通过添加不同无机层状矿物以改进聚合物高吸水性树脂性能研究进展进行了概述。最后对其发展方向进行了展望。     

功能化碳纳米管/聚合物复合分离膜

碳纳米管不仅具有优异的力学性质和超大的比表面积,同时具有优良的传输特性,将其添加到聚合物中制备复合分离膜,具有广阔的应用前景。通过化学改性将碳纳米管功能化,提高其在聚合物中的分散性,制备碳纳米管/聚合物复合膜。本文在介绍了碳纳米管功能化、碳纳米管/聚合物复合膜制备方法的基础上,综述了功能化碳纳米管的加入对复合分离膜亲水性、水通量、机械稳定性以及分离等性能的影响。总结了近年来对碳纳米管在聚合物膜内定向排列的研究进展及碳纳米管定向对复合膜相关性能的影响。由于碳纳米管材料的各向异性,利用电场、磁场及流场等对碳纳米管在聚合物膜内的分布进行定向,从而充分利用其优异的性能,是该类复合膜的研究方向。     

Effects of the nature of the aluminum source on the acidic properties of some mesostructured materials

Mesostructured aluminosilicates have been synthesized using gels prepared by reacting colloidal silica (Ludox AS) with Al(OH)₃, aluminum isopropoxide (Al(iPrO)₃) or NaAlO₂ in the presence of a surfactant. The hydrothermal transformation at 110°C of these gels produced solids with the hexagonal structure typical of MCM-41-type materials. These crystals have been characterized by X-ray diffraction, thermal analysis (TG/DTA), N₂ sorption and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The type, strength and density of acid sites have been studied using microcalorimetry and infrared (IR) spectroscopy.As a general trend, pore volume and average pore size decreased as the gel SiO₂/Al₂O₃ ratio decreased from 32–8, while the pore wall thickness remained in the 1.0–1.5 nm range. Except for one sample, Al was incorporated in tetrahedral coordination inside the pristine crystals. However, as expected, dealumination occurred upon calcination at 600°C/12 h, yielding materials having both tetrahedral and octahedral Al-species. Fourier transform infrared (FTIR) experiments with pyridine have indicated that these mesostructured aluminosilicates contain both Brönsted and Lewis acid sites and that acidity is strongest in samples prepared with NaAlO₂.Microcalorimetry experiments with ammonia as the probe molecule have shown that Al insertion into the mesoporous silicate framework affects acid site strength and distribution in a manner controlled by synthesis condition. Samples prepared with Al(OH)₃ contain a wide distribution of acid site strengths, indicating the absence of preferred locations of Si-O-Al groups within the pore walls. In contrast, distinct populations of acid sites with strengths in the 130–140 kJ mol⁻¹ range or near 150 kJ mol⁻¹, appear in materials prepared with Al(iPrO)₃ or with NaAlO₂, respectively. Al sites may be located at the surface of the pore wall, where they interact directly with the basic probe molecule. They may also be sandwiched between silica layers within the pore wall (3–4 Si layers thick), giving acid sites with a strength comparable with that of smectites. Finally, they may also be present in the pore (or within the pore walls) as extraframework Al(VI)-species. The nature, size, concentration, ease of hydrolysis and condensation of the aluminum precursors during synthesis control aluminum incorporation, distribution and location within the structure and with it the acidity of the resulting mesoporous aluminosilicate.     

Three-dimensional mesostructured binder-free nickel-based TiO2/RGO lithium-ion battery negative electrodes with enhanced volumetric capacity

Realization of high energy density Li-ion anodes is a significant challenge due to the volume changes generally exhibited by such systems during charge and discharge. Here, three-dimensional inverse opal (3D-IO) mesostructured Ni@TiO₂@RGO electrodes were fabricated by templating nickel electrodeposition with self-assembled, three dimensionally ordered polystyrene (PS) opals, followed by atomic layer deposition (ALD) of TiO₂ and spray coating of reduced graphene oxide (RGO). The electrode delivers initial discharge and charge volumetric capacities of 2082 mAh cm^-3 and 1873 mAh cm^-3 at 0.5 C, respectively. The composite electrode exhibits volumetric discharge and charge capacities of 1508 mAh cm^-3 and 1504 mAh cm^-3 at 0.5 C after 200 cycles and good rate capacity up to at least 10 C. The almost unbroken 3D-IO mesostructure after 200 lithiation and delithiation cycles demonstrates the excellent structural stability of the 3D-IO electrode design concept. The enhanced volumetric capacity and structural stability originate from high active materials loading, the short and efficient ion and electron pathways, and the composite structure provided by the nickel electrodeposition, ALD, and RGO spray coating electrode preparation process, as well as that both TiO₂ and RGO participate in lithium storage.     

Synthesis of stable mesostructured zirconia: Tween surfactant and controlled template removal

Mesostructured zirconia has been synthesized by using zirconium chloride and PEO nonionic ethoxylated sorbitan ester (Tween-20, -40, -60 or -80) as a zirconium source and structure-directing agent in an aqueous medium. To remove the occluded surfactants, UV/ozone treatment has been utilized instead of calcination due to thermal instability. This results from a special molecular structure of Tween surfactant. From XRD, SEM and TEM analyses, the materials treated with UV light and in-situ generated ozone has a wormhole structure and ill-defined or well-defined spherical particles.     

Fabrication and characterization of fullerene-Nafion composite membranes

Fullerene-Nafion composite membranes have been fabricated through a new solution casting for the first time. The fullerenes used for the composites included C₆₀ and polyhydroxy fullerene (PHF), C₆₀(OH)_n (n ∼ 12). The dispersion of the fullerene in the composite membrane was much more refined with smaller agglomeration particles, relative to the previously prepared fullerene-Nafion composites in which the fullerene was introduced through doping. The miscibility of the hydrophobic fullerene, C₆₀, in the Nafion matrix was further improved by a new fullerene dispersant, poly[tri(ethylene oxide)benzyl]fullerene, C₆₀[CH₂C₆H₄(OCH₂CH₂O)₃OCH₃]_n (n ∼ 5), synthesized in this work. The solution-cast fullerene composites also demonstrated a significant improvement in the physical stability relative to the fullerene-doped Nafion composites through a better integration of the fullerene into the Nafion matrix. Furthermore, increased loadings of the fullerene in Nafion were made possible through the new solution-casting method, compared to the previous doping method. The water characteristics in the fullerene composites have been examined by TGA and ¹H pulse NMR measurements. The interactions between the fullerene and the Nafion have been studied through ATR FT-IR and molecular dynamics simulations which suggested PHF resides primarily in the hydrophobic domain of Nafion when the loading was low. The voltammetric measurements also have shown that the fullerene composites have the reduced limiting current density, compared to Nafion membranes without fullerenes.     

Organic/inorganic composite membranes based on polybenzimidazole and nano-SiO2

Organic/inorganic composite membranes based on polybenzimidazole (PBI) and nano-SiO₂ were prepared in this work. However, the preparation of PBI/SiO₂ composite membrane is not easy since PBI is insoluble in water, while nano-SiO₂ is hydrophilic due to the hydrophilicity of nano-SiO₂ and water-insolubility of PBI. Thus, a solvent-exchange method was employed to prepare the composite membrane. The morphology of the composite membranes was studied by scanning electron microscopy (SEM). It was revealed that inorganic particles were dispersed homogenously in the PBI matrix. The thermal stability of the composite membrane is higher than that of pure PBI, both for doped and undoped membranes. PBI/SiO₂ composite membranes with up to 15 wt% SiO₂ exhibited improved mechanical properties compared with PBI membranes. The proton conductivity of the composite membranes containing phosphoric acid was studied. The nano-SiO₂ in the composite membranes enhanced the ability to trap phosphoric acid, which improved the proton conductivity of the composite membranes. The membrane with 15 wt% of inorganic material is oxidatively stable and has a proton conductivity of 3.9 × 10⁻³ S/cm at 180 °C.     

聚合物基纳米无机复合材料的最新研究进展

聚合物基纳米无机复合材料是一种性能优异的新型复合材料,已成为材料科学的新热点。本文综述了此种材料的特性、制备方法及应用,并概述了聚合物基纳米无机复合材料的发展前景及发展过程中应注意的问题。     

Influence of polarity of polymer on inorganic particle dispersion in dielectric particle/polymer composite systems

The influence of the polarity of polymers on the degree of dispersion of BaTiO₃ particles in BaTiO₃/polymer composite systems was investigated. The BaTiO₃ polymer composite systems were prepared from BaTiO₃ particles and low-density polyethylene (LDPE) or ethylene vinyl acetate copolymer (EVA) with 7 and 15 wt % vinyl acetate. Scanning electron microscopy observation showed that BaTiO₃ particles aggregated in the polymer matrices and dispersed more readily into the EVA matrix than into LDPE. The shift of the β-peak temperature by ca. +5°C in the temperature dispersion of the loss modulus was observed for EVA–BaTiO₃ composite systems in dynamic mechanical property measurement. On the other hand, the β-peak temperature of the polymers filled with graphite particles, which have hydrophobic surfaces, was almost constant in a volume fraction region of 0–0.3. The ellipsoidal axes' ratios given by comparison of experimental dielectric constant values and theoretical ones using the Maxwell equation were 4.2, 3.6, and 3.1 for LDPE/BaTiO₃, EVA(7%)/BaTiO₃, and EVA(15%)/BaTiO₃ composite systems, respectively. The axes' ratio decreased by the introduction of polar vinyl acetate groups into nonpolar LDPE. The results confirmed that the polarity of the polymers was one of the key factors governing the dispersibility of BaTiO₃ particles in the polymer matrix. © 1995 John Wiley & Sons, Inc.     

Novel composite polymer electrolyte comprising poly(ethylene oxide) and triblock copolymer/mesostructured silica hybrid used for lithium polymer battery

Ordered mesoporous materials, due to its potential applications in catalysis, separation technologies, and nano-science have attracted much attention in the past few years. In this work, a novel PEO-based composite polymer electrolyte by using organic-inorganic hybrid EO₂₀PO₇₀EO₂₀ @ mesoporous silica (P123 @ SBA-15) as the filler has been developed. The interactions between P123 @ SBA-15 hybrid and PEO chains are studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and FT-IR techniques. The effects of P123 @ SBA-15 on the electrochemical properties of the PEO-based electrolyte, such as ionic conductivity, lithium ion transference number are studied by electrochemical ac impedance spectroscopy and steady-state current method. The experiment results show that P123 @ SBA-15 can enhance the ionic conductivity and increase the lithium ion transference number of PEO-based electrolyte, which are induced by the special topology structure of P123 in P123 @ SBA-15 hybrid, at the same time. The excellent lithium transport properties and broad electrochemical stability window suggesting that PEO-LiClO₄/P123 @ SBA-15 composite polymer electrolyte can be used as candidate electrolyte materials for lithium polymer batteries.     

无机盐对聚二甲基硅氧烷/陶瓷复合膜渗透汽化性能的影响

将渗透汽化应用于醇/水体系的分离,具有诸多显著的优势。然而,目前的研究大都基于二元体系,而实际的应用体系是多元的,还包含少量无机盐和糖类等,它们的存在对膜的性能具有一定的影响。本文研究了NaCl、KCl和MgCl2 3种无机盐的加入对聚二甲基硅氧烷 （PDMS）/陶瓷复合膜渗透汽化性能的影响。结果表明,在313 K,无机盐的加入使复合膜的分离因子和通量均有所提高。其中二价盐MgCl2对渗透汽化性能的影响最为显著,分离因子最大提高到醇/水体系的2.8倍。而一价盐NaCl和KCl的加入,使分离因子分别提高为醇/水体系的2.5倍和2.4倍。同时借助于Setschenow扩展方程计算了乙醇活度,对实验结果进行了初步的解释。     

The effect of humidity on the durability of inorganic membranes

Porous oxide membranes of γ-alumina, zirconia and silica were prepared on porous α-alumina tubes by sol-gel processes. γ-Alumina and zirconia membranes impregnated with platinum were also prepared. The permeation properties of these membranes were investigated by using unary and binary feeds of H₂ and CO₂ at 423 K. After permeation for 5 h with humidification at a concentration of 3 mol%, no large changes were found for the zirconia and γ-alumina membranes, but the permeances to H₂ and CO₂ for the silica membrane were decreased by 10–20%. A 70-h exposure to humidified feeds showed that the zircomaand γ-alumina-based membranes were more resistant than the silica membrane. The decrease in H₂ permeance was only 5% for the zirconia-based membranes and 17.4% for the silica membrane. The Pt-loaded gg-alumina membrane remained defect-free after one-month of exposure to the humidified feeds at 423 K.     

An inorganic/organic self-humidifying composite membranes for proton exchange membrane fuel cell application

With an aim to operate the proton exchange membrane fuel cells (PEMFCs) with dry reactants, an inorganic/organic self-humidifying membrane based on sulfonated polyether ether ketone (SPEEK) hybrid with Cs_2.5H_0.5PW₁₂O₄₀ supported Pt catalyst (Pt-Cs2.5 catalyst) has been investigated. The Pt-Cs2.5 catalysts incorporated in the SPEEK matrix provide the site for catalytic recombination of permeable H₂ and O₂ to form water, and meanwhile avoid short circuit through the whole membrane due to the insulated property of Cs_2.5H_0.5PW₁₂O₄₀ support. Furthermore, the Pt-Cs2.5 catalyst can adsorb the water and transfer proton inside the membrane for its hygroscopic and proton-conductive properties. The structure of the SPEEK/Pt-Cs2.5 composite membrane was characterized by XRD, FT-IR, SEM and EDS. Comparison of the physicochemical and electrochemical properties, such as ion exchange capacity (IEC), water uptake and proton conductivity between the plain SPEEK and SPEEK/Pt-Cs2.5 composite membrane were investigated. Additive stability measurements indicated that the Pt-Cs2.5 catalyst showed improved stability in the SPEEK matrix compared to the PTA particle in the SPEEK matrix. Single cell tests employing the SPEEK/Pt-Cs2.5 self-humidifying membrane and the plain SPEEK membrane under wet or dry operation conditions and primary 100 h fuel cell stability measurement were also conducted in the present study.