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  • Construction of SiO2@MWNTs incorporated PVDF substrate for reducing internal concentration polarization in forward osmosis
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Xuan Zhang, Liang Shen, Chen-Yu Guan, Chu-Xuan Liu, Wan-Zhong Lang, Yan Wang

    This work provides a facile and effective way of incorporating SiO2@MWNTs in polyvinylidene fluoride (PVDF) substrate to alleviate the internal concentration polarization (ICP) impact of the resultant thin film composite forward osmosis (TFC-FO) membranes for the first time. The in-situ decoration of multi-walled carbon nanotubes (MWNTs) using tetraethyl orthosilicate (TEOS) as precursor was conducted, resulting in improved hydrophilicity and the excellent dispersion of synthesized SiO2@MWNTs in PVDF membrane substrates accordingly. Effects of the SiO2@MWNTs concentration on the morphologies and properties of the modified substrates, and further impact on the polyamide (PA) layer structure are investigated via various characterizations. Besides, the intrinsic separation properties and forward osmosis performance of resultant TFC-FO membranes are also systemically studied. In comparison with the control TFC membrane, SiO2@MWNT-modified TFC membranes exhibit higher water fluxes with the enhanced membrane selectivity, as indicated by the decreased JS/JV values (from 1.1 to 0.19 g/L). This work therefore presents an alternative approach to prepare TFC-FO membranes with enhanced water flux as well as increased selectivity.

    更新日期:2018-07-18
  • Solvent-Thermal Induced Roughening: a Novel and Versatile Method to Prepare Superhydrophobic Membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Weihua Qing, Xiaonan Shi, Weidong Zhang, Jianqiang Wang, Yifan Wu, Peng Wang, Chuyang Y. Tang

    Surface roughness enhancement by fabricating multi-scale nano/microstructure is an effective strategy to prepare superhydrophobic membranes. Here we report a novel solvent-thermal induced roughening (STIR) method. The method involves the swelling of a polymer surface to create a soft shell/hard core structure under the combined action of solvent and heating, followed by a controllable surface roughening as a result of mismatched thermal expansion between the shell and the core. We show a significant increase of surface roughness for a STIR-treated polyvinylidene fluoride nanofibrous membrane, whose nanofibers were covered with densely-packed nanofins. The treated membrane had greatly enhanced hydrophobicity, resulting in improved anti-wetting performance to low-surface-tension feed water in a membrane distillation process. The STIR method was capable of treating membranes with various pore structures. The novel surface roughening strategy opens up new directions to fabricate superhydrophobic surfaces and membranes, which can greatly benefit a wide range of applications such as membrane distillation, oil/water separation.

    更新日期:2018-07-18
  • Pervaporative Efficiency of Organic Solvents Separation Employing Hydrophilic and Hydrophobic Commercial Polymeric Membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Katarzyna Knozowska, Wojciech Kujawski, Paulina Zatorska, Joanna Kujawa

    Performances of various hydrophilic and hydrophobic commercial membranes were evaluated in the pervaporative separation of binary organic-organic mixtures. The research was performed for the following binary mixtures: acetone-ethanol, ethanol-butanol, and acetone-butanol using chosen commercial membranes: DuraMem™150 (polyimide), Pervap 1060 (poly(dimethylsiloxane)) and Pervap 2216 (poly(vinyl alcohol)). For the assessment of membrane performance, in organic-organic pervaporation, transport and separation features (pervaporative separation index and separation factor) were taken into account. Regardless the membrane nature, the same component of the separated mixture was preferentially transported across the membrane. The assessment of membrane performance was additionally discussed by using Hansen's Solubility Parameters. The detailed physicochemical analyses focused on contact angle, spreading pressure and surface free energy with their components calculation were performed. The established physicochemical parameters were in a good accordance with the observed changes during pervaporative separation of organic-organic mixtures. Furthermore, an investigation of traces of water presence in feed of organic-organic mixtures on the membrane performance was done.

    更新日期:2018-07-18
  • Anion exchange membranes with well-developed conductive channels: effect of the functional groups
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Fang Hua Liu, Chen Xiao Lin, En Ning Hu, Qian Yang, Qiu Gen Zhang, Ai Mei Zhu, Qing Lin Liu

    To explore the alkaline stability of cationic groups, several investigations have been reported via small molecule model compounds, theoretical calculations or grafting cations to the benzylic positions of the polymer backbones. In this work, anion exchange membranes (AEMs) with various head groups of trimethylammonium (TMA), 1-methylpyrrolidinium (MPY), 1-methylpiperidinium (MPRD), 1-methylimidazolium (Im1) and 1,2-dimethylimidazolium (Im1,2)) flexibly linked to poly(ether sulfone) (PES) backbones are prepared to explore the effect of pendent functional groups. The AEMs tethering MPRD groups are found to exhibit the highest Br− conductivity of 60.4±2.1 mS cm−1 at 80 °C. PES-MPY exhibits the best relative stability and maintains 90.7% and 83.1% of the original ionic exchange capacity (IEC) and conductivity, respectively, after immersed into 2 M NaOH at 60 °C for 672 h. Meanwhile, the alkaline stability is in the order of PES-MPY > PES-MPRD > PES-TMA > PES-Im1,2 > PES-Im1. The maximum power density of a H2/O2 fuel cell using PES-MPRD (109.0 mW cm−2) and PES-MPY (106.5 mW cm−2) is larger than that using PES-Im1 (65.1 mW cm-2). The results provide a guidance for designing high-performance AEMs.

    更新日期:2018-07-18
  • Crosslinked poly (2,6-dimethyl-1,4-phenylene oxide) polyelectrolyte enhanced with poly (styrene-b-(ethylene-co-butylene)-b-styrene) for anion exchange membrane applications
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Zhihua Wang, Ziming Li, Nanjun Chen, Chuanrui Lu, Fanghui Wang, Hong Zhu

    Poly (styrene‑b‑(ethylene-co-butylene)‑b‑styrene) (SEBS) shows great potential in anion exchange membranes (AEMs) due to its high chemical stability and flexible mechanical properties, but the trade-off between the ion conductivity and gelation issues greatly impedes further applications. To address this dilemma, we present an effective strategy to enhance comprehensive properties of AEMs by fabricating a crosslinking structure between SEBS and poly (2,6-dimethyl-1,4-phenylene oxide) (PPO). Grafting multiple cations as the side chains ensures the highly efficiently transport of hydroxide. With the addition of SEBS, the crosslinked membranes (T3PPO-c-SEBS) show enhanced physical and chemical properties, such as restrained swelling behavior, firm mechanical properties, great chemical and dimensional stabilities. Obvious hydrophilic/hydrophobic microphase separation morphology is designed to form effective ionic channels for transmitting hydroxide. The T3PPO-c-30%SEBS membrane with 30 wt% content of SEBS exhibits relatively high hydroxide conductivity (24.0 mS/cm at 30 °C) but low swelling ratios (15.6% at 30 °C). Moreover, after the long-time alkaline test (1 M NaOH, 80 °C, 500 h) and antioxidative test (Fenton solution, room temperature, 150 h), the T3PPO-c-30%SEBS membrane shows much better alkaline stability (57.8% retention vs. 24.5%) and oxidative stability (92.0% retention vs. 85.8%) than the pristine T3PPO membrane does. Therefore, T3PPO-c-SEBS can be regarded as promising candidates for AEM applications.

    更新日期:2018-07-18
  • Multi-block Sulfonated Poly(arylene ether nitrile) Polymers Bearing Oligomeric Benzotriazole Pendants with Exceptionally High H2/O2 Fuel Cell Performance
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Huayuan Hu, Yuqian Sui, Mitsuru Ueda, Jieshu Qian, Lianjun Wang, Xuan Zhang

    Aromatic ionomers have emerged as promising alternatives to perfluorosulfonic acid polymers to be applied as proton exchange membranes in fuel cells. However, the paradox between the ion conductivity and stability is still a challenge precluding the commercialization of aromatic ionomers. In this paper, we report the design of a novel sulfonated poly(arylene ether nitrile) multi-block structure by introducing a key component, alkyl benzotriazole (Bt) side chains, into the hydrophobic segments. The modified structure could facilitate polymer phase-separation and generate self-standing films with excellent mechanical properties, and it effectively suppresses the excessive swelling of the membrane owing to strong electrostatic interactions between the Bt chains and sulfonic acid groups. Moreover, the Bt unit could act as both a proton acceptor and proton donor, causing a dramatic increase in the ion conductivity of the membrane. The most optimal membrane possesses an ion-exchange capacity of 2.15 meq g-1 and exhibits a weaker relative humidity (RH) dependence and higher proton conductivity than the commercial Nafion 212 over the entire RH range. Remarkably, the maximum power output of the fuel cell based on the most optimal membrane reaches 1090, 856, and 451 mW cm-2 at 95, 70, and 30% RH, respectively, which are more than 2 times higher than those of the non-Bt analogue. Further, the current densities (I0.6) ranging up to 1500 and 1000 mA cm-2 (0.6 V) at 95 and 70% RH are both much higher than those of the Nafion. Our study provides a novel methodology for the design of aromatic ionomer structures with excellent performances for practical fuel cell application.

    更新日期:2018-07-18
  • Removal of Disinfection Byproducts in Forward Osmosis for Wastewater Recycling
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Jiale Xu, Thien Ngoc Tran, Haiqing Lin, Ning Dai

    Forward osmosis (FO) is an emerging membrane technology for wastewater recycling. However, its performance in removing disinfection byproducts (DBPs), a critical aspect of wastewater recycling, has not been investigated. This study systematically investigated the rejection of sixteen neutral DBP that are relevant to wastewater recycling in two commercial FO membranes (Aquaporin and CTA). Clean Aquaporin membrane displayed higher rejection for all DBPs than clean CTA membrane. For N-nitrosodimethylamine (NDMA) and haloacetonitriles (HANs), the most prevalent and toxic DBPs in wastewater recycling, the rejection by Aquaporin was 31% and 48%–76%, respectively. The rejection of DBPs in FO positively correlated with their size across different DBP groups but did not correlate with their hydrophobicity. Organic fouling by alginate and bovine serum albumin (BSA) decreased the rejection and transmembrane fluxes of most DBPs. The DBP transport and the influence of fouling were discussed using a solution-diffusion model incorporating size exclusion, the surface interaction between membrane and DBPs, and DBP diffusion within the membrane. Lastly, the rejection of NDMA and HANs in FO membranes determined in this study was compared with that in reverse osmosis (RO) membranes reported in the literature.

    更新日期:2018-07-18
  • Poly (maleic anhydride-alt-1-alkenes) directly grafted to γ-alumina for high-performance organic solvent nanofiltration membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Mohammad Amirilargani, Renaud B. Merlet, Arian Nijmeijer, Louis Winnubst, Louis C.P.M. de Smet, Ernst J.R. Sudhölter

    In this study we describe a novel and simple method to couple covalently poly (maleic anhydride-alt-1-alkenes) to γ-alumina nanofiltration membranes for the first time. The 1-alkenes varied from 1-hexene, 1-decene, 1-hexadecane to 1-octadecene. The grafting reaction was between the reactive anhydride moieties of the polymer and surface hydroxyl groups, resulting in highly stable bonds. The modified membranes were investigated for their permeation and rejection performance of Sudan Black (SB, Mw 457 Da) in either toluene or ethyl acetate (EA) solution, and very high rejections (>90%) and high permeation flux were observed compared to unmodified membranes. Initially, the SB in toluene solution was found to bind strongly to the surface hydroxyl groups of the unmodified membranes, an effect not observed in EA solution.

    更新日期:2018-07-18
  • Preparation of Proton Permselective Composite Membrane and Its application in Waste Acid Reclamation by Ion Substitution Electrodialysis
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Feng-jiao Li, Yu-xiang Jia, Ting-ting Bai, Meng Wang

    Nowadays, the reclamation of industrial waste acid characterized with low acid concentration and high metal ion content has attracted much attention. How to carry out effectively a separation between protons and metal ions becomes a top priority. In this report, a so-called proton permselective composite membrane was prepared specifically for waste acid reclamation by electrodialysis. Above all, a porous supporting membrane was prepared from polysulfone via classical wet phase inversion technology. Therein appropriate amount of sulfonated polysulfone (SPSF) was added to adjust its microstructure. Subsequently, a hydrophilic composite layer, such as Poly(ethylene imine) layer or Poly(vinyl alcohol) layer, was used to endow the proton permeability based on the unique transport mechanism of protons in which water molecules play an important role. ATR-FTIR and SEM were employed to monitor the changes in chemical composition and microstructure of as-prepared membranes, respectively. Furthermore, their electrodialytic transport properties, including electrical resistance, limiting current, water transport behaviors, proton permselectivity and anion-blocking ability, were investigated and compared with those of typical commercial cation-exchange membrane. As confirmed by series of electrochemical characterizations, as-prepared composite membranes, especially PVA-Series membranes, exhibited outstanding work performances and remarkable practical value in the acid recovery. At last, the ion substitution electrodialysis for waste acid reclamation in which typical composite membranes were assembled were also conducted to examine the process energy consumption, the concentration and purity of the produced acid.

    更新日期:2018-07-18
  • Enhanced separation performance of PES ultrafiltration membranes by imidazole-based deep eutectic solvents as novel functional additives
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Bin Jiang, Na Zhang, Luhong Zhang, Yongli Sun, Zhaohe Huang, Baoyu Wang, Haozhen Dou, Hongfang Guan

    Herein, high performance polyethersulfone (PES) membranes were fabricated by introducing a series of imidazole-based deep eutectic solvents (DESs) as functional additives, which could tailor membrane structure due to the synergetic effect between DES components in phase inversion process. The addition of those DESs to the casting solutions all improved membrane porous structure, which contributes to a remarkably enhanced permeability and a high selectivity of the resultant membranes. Especially, the PES membrane with tetrabutylammonium chloride/imidazole as additive had a maximum water flux of 781 L/(m2·h), which was about 6.45 times that of the additive-free membrane, and a high BSA rejection of 97.7% at 2 bar. Moreover, the antifouling performance as well as thermal and mechanical properties of the prepared membranes was investigated. Overall, this work indicates the promise of imidazole-based DESs as alternative pore-forming additives for the fabrication of ultrafiltration membranes with superior performance.

    更新日期:2018-07-18
  • Dual functional membrane with multiple hierarchical structures (MHS) for simultaneous and high-efficiency removal of dye and nano-sized oil droplets in water under high flux
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-17
    Zhenxing Wang, Shengqiang Ji, Jin Zhang, Fang He, Zhaodi Xu, Shaoqin Peng, Yuexiang Li

    Dual functional membranes with super-wetting and adsorption capacity have drawn great attentions owing to their good application prospect in the treatment of mixed wastewater containing oil and dyes. Despite recent development in such functional membranes, there are still some obstacles need to be resolved. The one is how to further improve the dye adsorption capacity to realize the high-efficiency removal of dye under high permeation flux. The other is to improve the rejection towards nano-sized oil droplets in water. Herein, with porous polypropylene (PP) membrane as substrate, we show that constructing multiple hierarchical structures (MHS) on membrane surface is an effective way to solve the above mentioned problems. The MHS prepared by low-cost tannic acid, 3-Aminopropyltriethoxysilane (APTES), and polyethyleneimine (PEI) are composed of rough layer, nanospheres, and nano nodes with abundant amine groups. On the one hand, the MHS can endow the membrane with high adsorptive capacity (480 mg g-1 toward methyl blue). On the other hand, the MHS can also decrease the pore size of the membrane, making it suitable for separation of nano-sized oil droplets. Moreover, the MHS can also render the membrane superhydrophilicity and excellent anti-oil-adhesion properties. Thanks to these advantages derived from MHS, the obtained dual functional membrane can realize high-efficiency and simultaneous removal of high concentrated dye (10–50 ppm, removal efficiency>95%) and nano-sized oil droplets (about 50–300 nm, oil rejection>99%) from mixed wastewater under high flux (1680 L m-2 h-1). Considering the significantly enhanced performance, as well as the facile and cost-effective process, the as-prepared functional membrane with MHS has good application prospects. Besides, a new insight on the influence of hydrodynamic conditions on membrane fouling during emulsion separation is also proposed, which may guide better design of anti-fouling membranes.

    更新日期:2018-07-18
  • Porous organic polymer as fillers for fabrication of defect-free PIM-1 based mixed matrix membranes with facilitating CO2-transfer chain
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-10
    Chenhui Wang, Fangyuan Guo, He Li, Jian Xu, Jun Hu, Honglai Liu

    Considering both molecular sieving effect and compatibility of filler-polymer interface, the main challenges in the fabrication of excellent mixed matrix membranes (MMMs) are the selection of fillers. Here, porous organic polymer (POP) is chosen as fillers to fabricate a series of novel PIM-1 based MMMs for CO2 separation. TPFC-based POPs showed highly selective CO2 adsorption capacity and good interfacial compatibility with PIM-1 matrix. Moreover, amine modified POPs in MMMs can provide specific transfer chains for facilitating CO2 molecules separation. As a result, the obtained PIM-TPFC-CH2NH2 MMM exhibited excellent CO2 permeability of 7730 barrer and selectivity of 45.9 and 36.4 for CO2/N2 and CO2/CH4 gas pairs, far beyond the 2008 Robeson upper bound and surpassed most reported state-of-the-art MMMs.

    更新日期:2018-07-12
  • Experimental and modeling study of blended membranes for direct methanol fuel cells
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-10
    Deuk Ju Kim, Chi Hoon Park, Elena Tocci, Sang Yong Nam

    The dynamics of hydronium ions and methanol molecules in hydrated SPAES and blend membranes are investigated via molecular dynamics simulations using the COMPASS force field. In addition to calculating the diffusion coefficients as a function of the hydration level, an amorphous cell with a specific composition of H2O molecules and H3O+ determined from the experimental data is constructed and tested. The water and methanol diffusion coefficients are considerably smaller at lower hydration levels and room temperature. The diffusion coefficient of the water and methanol molecules increases with increases in the hydration level, and this is in good agreement with experiment data. Analysis of the pair correlation functions supports the experimental observations of the membrane performance with hydration related to the water and methanol diffusion behavior in hydrated SPAES and blend membranes.

    更新日期:2018-07-12
  • Tailoring the nanophase-separated morphology of anion exchange membrane by embedding aliphatic chains of different lengths into aromatic main chains
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-11
    Xiaoming Yan, Baolin Zhao, Jiafei Liu, Xinyue Zhang, Gaohong He

    Tuning the hydrophilic/hydrophobic nanophase-separated morphology to enhance the conductivity is a considerable challenge in the field of anion exchange membranes (AEMs). Here, a series of novel aliphatic-aromatic copolymer AEMs were designed by embedding flexible alkyl chains of different lengths into rigid main chain of poly(ether sulfone). Compared to traditional aromatic polymer, the aliphatic-aromatic copolymers had more flexible main chains and longer hydrophobic segments, both of which promoted the nanophase separation and the formation of ionic clusters. Increasing aliphatic chain length made the ionic clusters larger and more interconnected, but too long aliphatic chain led to the formation of smaller ionic clusters because the ionic groups were far away from each other. An optimum length of the aliphatic chain (8 C) existed for the nanophase-separated morphology with the biggest ionic clusters (around 8 nm), with which the membrane showed the highest conductivity. A peak power density of 159 mW cm−2 was obtained for the cell incorporating the 8 C membrane. Based on these, this study reveals a new direction to create a tunable nanophase-separated morphology for high-performance AEMs.

    更新日期:2018-07-12
  • Polyvinyl Chloride (PVC) Ultrafiltration Membrane Fouling and Defouling Behavior: EDLVO Theory and Interface Adhesion Force Analysis
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-11
    Wanyi Fu, Lan Wang, Fangjuan Chen, Xuezhi Zhang, Wen Zhang

    To unravel fouling and defouling mechanisms of protein, saccharides and natural organic matters (NOM) on polymeric membrane during filtration, this study investigated filtration characteristics on polyvinyl chloride (PVC) ultrafiltration membranes with bovine serum albumin, dextran, humic acid as model foulants. Membrane fouling and defouling performances were analyzed through monitoring the flux decline during filtration and flux recovery during physical backwash. Physico-chemical properties (e.g., hydrophobicity and surface charge) of PVC membrane and foulants were characterized, which were used in the extended Derjaguin–Landau–Verwey–Overbeek (EDLVO) theory to calculate the interaction energies between membrane-foulant and foulant-foulant. The results showed that at the later filtration stages the fouling rate was strongly correlated with the deposition rate, which was determined by the interaction energy profile calculated by EDLVO. Moreover, the adhesion forces of membrane−foulant and foulant−foulant were further measured by atomic force microscopy (AFM) with modified colloidal probes. A positive correlation (R2=0.845) between particle detachment rate (determined by adhesion force) and defouling rate was developed for BSA and HA foulants that led to cake layer formation. By contrast, dextran defouling rate was off this correlation as dextran partially clogged membrane pores due to its smaller size.

    更新日期:2018-07-12
  • On the rejection and reversibility of fouling in ultrafiltration as assessed by hydraulic impedance spectroscopy
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-11
    M.C. Martí-Calatayud, S. Schneider, M. Wessling

    The manifestation of critical fluxes in membrane filtration has typically served to set an upper value above which detrimental fouling events and a substantial increase of membrane resistance occurs. Despite the usefulness of critical flux concepts for conducting sustainable membrane processes, the specific phenomena causing them cannot be easily identified via conventional membrane filtration modes. Usually arbitrary fouling rates are selected to delimit the boundary between under- and over-critical flux operation. Timescales respective for colloidal matter accumulation are overlooked. Frequency response analysis of transmembrane pressures has been recently presented as a highly-sensitive method to track fouling in ultrafiltration. This hydraulic impedance spectroscopy method allows not only measuring membrane resistances but also corresponding time constants related to colloidal matter accumulation. In this work, hydraulic impedance spectra are gained for the ultrafiltration of different model foulants to assess the origin of critical fluxes for two different membranes. A correlation among characteristic impedance features and the type of fouling could be established: the evolution of phase shift between flux and pressure at increasing fluxes allows identifying the formation of external fouling layers, while registering of hysteresis loops at reversed frequency sequences signals the development of irreversible internal fouling. The hydraulic impedance method emerges as a precise and more sensitive monitoring tool to diagnose the beginning and nature of critical fouling.

    更新日期:2018-07-12
  • Discrimination among gas translation, surface and Knudsen diffusion in permeation through zeolite membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-11
    Pasquale F. Zito, Alessio Caravella, Adele Brunetti, Enrico Drioli, Giuseppe Barbieri

    Gas translation diffusion is proposed to compete with surface diffusion for describing the permeation of light gases (He, H2, CO2 and CO) through zeolite membranes. The analysis for both DD3R and NaY zeolite membranes shows some differences in H2, CO and CO2 permeation for both binary/ternary gas mixture and single gas. The permeation description through gas translation of weakly adsorbed species such as, e.g., H2, specifically at low temperatures, is more accurate than that obtained by Knudsen diffusion in a previous work. Gas translation paired to surface diffusion well reproduces the maximum in H2 flux, which was missed by the Knudsen diffusion [Caravella et al., Micropor. Mesopor. Mater. 235 (2016), 87–99]. The strongly adsorbed species are less dependent on gas translation or Knudsen diffusion since the surface diffusion is very significant in the whole temperature range investigated. The gas translation was demonstrated to reproduce the permeation through zeolite membranes better than Knudsen diffusion. This paper attempts to discriminate the operating mechanisms among gas translation, surface and Knudsen diffusion in gas mixture permeation through zeolite membranes.

    更新日期:2018-07-12
  • CT scanning of membrane feed spacers – Impact of spacer model accuracy on hydrodynamic and solute transport modeling in membrane feed channels
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-05
    Nils Horstmeyer, Thomas Lippert, David Schön, Felizitas Schlederer, Cristian Picioreanu, Klaus Achterhold, Franz Pfeiffer, Jörg E. Drewes

    This study evaluated the impact of precise representation of spacer geometry on numerical simulations of hydrodynamics and solute transport in feed channels of membrane processes. Three levels of increasing geometry accuracy were assessed: i) cylindrical filaments, ii) filaments with circular sections of variable diameter based on microscopic measurements, and iii) geometries obtained from X-ray computed tomography (CT scans) in three resolutions (22 µm, 11 µm, and 5.5 µm). The three-dimensional CT scans revealed quasi-elliptic, not circular, cross-sections of the filaments. Microscopic measurements fail to account for this ellipticity, resulting in overestimation of pressure drop calculated at industry-typical average velocities (0.07–0.15 m s-1) by a factor of 1.8 compared to CT-based geometries. On the other hand, the cylindrical spacer filaments representation overestimates concentration polarization at the membrane surface compared to CT-based geometries. Experimental results of pressure drop and particle deposition were in close agreement with simulations using CT scanned geometries. This work demonstrates that modeling results depend significantly on the spacer geometry accuracy. Within the investigated CT scan accuracies 20 µm was found sufficient for modeling hydrodynamics and solute transport in spacer-filled feed channels. The results may be useful for reliable investigation and development of novel spacer geometries.

    更新日期:2018-07-08
  • Kinetic Model for Surfactant-Induced Pore Wetting in Membrane Distillation
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-06
    Zhangxin Wang, Yuanmiaoliang Chen, Shihong Lin

    Membrane pore wetting is a unique and important technical challenge for membrane distillation (MD). While the general principle of pore wetting is well known, the detailed mechanism of pore wetting induced by surfactants that can actively adsorb onto membrane pore surface has not been theoretically elucidated. In this study, we developed a theoretical model, based on surfactant transport in a partially wetted membrane pore under the pseudo-steady state assumption, to quantify the kinetics of pore wetting. The theoretical model predicts several key dependences of wetting kinetics on operating parameters and solution properties, which are highly consistent with results from MD experiments using feed solution containing sodium dodecyl sulfate. It was found that kinetics of pore wetting is strongly dependent on vapor flux, surfactant concentration, but relatively independent of the transmembrane hydraulic pressure. The critical surfactant concentration below which pore wetting does not occur was also predicted by the wetting model. Finally, impact of surfactant species on wetting kinetics was also discussed.

    更新日期:2018-07-08
  • Bioinspired Dual Stimuli-Responsive Membranes with Enhanced Gating Ratios and Reversible Performances for Water Gating
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-06
    Huawen Liu, Junbin Liao, Yan Zhao, Arcadio Sotto, Jiajie Zhu, Bart van der Bruggen, Congjie Gao, Jiangnan Shen

    Self-regulation of membrane permeability performance is highly desirable for porous membrane applications. Inspired by the stomatal closure behavior of plant leaves in response to environmental changes, here we report a series of dual thermo- and pH-responsive membranes based on the poly(4-vinyl pyridine) (P4VP) core/poly(N-isopropylacrylaminde) (PNIPAM) shell microgels. The stimuli-responsive microgels underwent in situ surface segregation and uniformly decorated on the surface of internal channels during the phase inversion process. The hydraulic permeability performance of the dual responsive membranes (DRMs) has been investigated within a temperature range of 20–50 °C and a wide pH range (spanning pH 2–6). The water flux of optimized membrane (M2) varied from 1.94 kg m−2 h−1 at 20 °C/pH 2 to 474.91 kg m−2 h−1 at 50 °C/pH 6 with a high gating ratio of 245. Investigations revealed that microgels based on different thickness of PNIPAM shell conferred different thermo-/pH-responsive properties to the DRMs. For example, the thicker PNIPAM shell enhanced the thermo-response performance, while the pH-response performance was restrained. These optimum smart gating membranes with enhanced gating coefficient and reversibility are potential for the applications in water gating and controlled release systems.

    更新日期:2018-07-08
  • CO2 permeation through asymmetric thin tubular ceramic-carbonate dual-phase membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-06
    Xueliang Dong, Han-Chun Wu, Y.S. Lin

    Ceramic-carbonate dual-phase dense membrane is a promising high temperature CO2 separation membrane with remarkable CO2 permeance and theoretically infinite CO2 selectivity. This paper reports synthesis and CO2 permeation properties of asymmetric tubular dual-phase membranes with a thin samarium doped ceria (Ce0.8Sm0.2O1.9, SDC)-carbonate separation layer and a thick porous SDC-Bi1.5Y0.3Sm0.2O3-δ (BYS) support. The asymmetric tubular thin (0.12 mm) dual-phase membrane has much higher CO2 permeance and lower activation energy for permeation than the thick (1.0–1.5 mm) membranes. At 900 °C with 50%CO2/N2 feed at 1 atm, the CO2 permeation flux and permeance for the thin membrane reach 1.53×10−2 mol·m−2·s−1 (or 2.05 mL(STP)·cm−2·min−1) and 3.16×10−7 mol·m−2·s−1·Pa−1, respectively, with activation energy for permeation of 62.5 kJ/mol. These dual-phase membranes exhibit slightly higher CO2 permeance with essentially same activation energy for permeation, and stable operation, for CO2 permeation with simulated syngas (with the composition of 49.5%CO, 36%CO2, 4.5%N2, 10%H2) feed. The CO2 permeation fluxes of the tubular asymmetric membranes can be well described by the power-function flux equation. The analysis of CO2 permeation data with the model shows that the CO2 separation performance of the tubular asymmetric membranes can be further improved by optimizing the microstructure of ceramic porous supports. This work demonstrates that asymmetric SDC-carbonate dual-phase membrane has high potential for practical application in high temperature CO2 separation.

    更新日期:2018-07-08
  • Water permeation in polymeric membranes: Mechanism and synthetic strategy for water-inhibiting functional polymers
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-07
    Yusuke Araki, Yusei Kobayashi, Touru Kawaguchi, Takashi Kaneko, Noriyoshi Arai

    The prediction and control of penetration in a polymeric membrane is of critical importance in green chemistry and energy technology, including gas separation, water purification, and desalination. We performed molecular simulations of water transport through a polymeric membrane to clarify the key factors that dominate water permeation. The effects of additives and chemical interaction (solubility) on water inhibition were investigated. We found that additives reduce water permeability into the membrane. Upon incorporation of the additive, strength of coordination of water molecules near the membrane surface increases. Thus, the penetration frequency of water molecules into the membrane decreases. It is suggested that the local environment near the membrane surface plays a significant role in controlling water permeability. In order to gain deeper insights into the polymer design, we discussed the chemical interaction (solubility) parameter change between polymer chains and additives. Using a repulsive chemical species of a polymer chain for additives can lead to higher water inhibition. The ability to control water permeability into the membrane by polymer design can be exploited for applications in water separation technology.

    更新日期:2018-07-08
  • Mesoscale Modeling of Sulfonated Polyimides Copolymer Membranes: effect of sequence distributions
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-07
    Chenchen Hu, Teng Lu, Hongxia Guo

    We adopt dissipative particle dynamics simulation technique and systematically study the effect of sequence distributions of hydrophobic and hydrophilic segments in individual sulfonated polyimide (SPI) copolymer on the micro-phase separated structure and the performance of proton exchange membranes (PEMs) under various water contents. The phase morphology as well as the shape and size of water channels is affected by sequence distributions. Compared to the di-block copolymer and the alt-copolymer, water channels in the multi-block copolymer are more homogenous. Additionally, the copolymer sequence distributions affect the water transport which is closely related to the proton conductivity, the dimensional stability and the mechanical properties of PEMs via tuning the phase structure. Generally, the more homogenous water channels the faster water transport. As for the dimensional stability, unlike the other two copolymers the unique shrinkage behavior of multi-block copolymer can resist the membrane swelling induced by water uptake. Moreover, the system with short block has relatively large Young's modulus and the influence of sequence distributions on Young's modulus weakens with the addition of water. Consequently, the multi-block SPI copolymer possesses fast water transport, low dimension-swelling and relatively high Young's modulus, which will make it a potentially huge application in PEM.

    更新日期:2018-07-08
  • Enhanced sulfur tolerance of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite for hydrogen separation membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-07
    C. Mortalò, E. Rebollo, S. Escolástico, S. Deambrosis, K. Haas-Santo, M. Rancan, R. Dittmeyer, L. Armelao, M. Fabrizio

    Thanks to its high hydrogen permeability and good chemical stability in moist CO2 environments, BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ mixed conducting material is considered one of the most promising candidates for hydrogen separation ceramic membranes. In this work, its chemical stability under H2S-rich atmosphere was systematically investigated by in-situ electrochemical characterizations and ex-situ structural, chemical and morphological analyses. A performance degradation of the total conductivity depending on the H2S content was observed: at 700 °C and under 1500 and 700 ppm of H2S the conductivity drop was 15% and 2% respectively. The complementary information gathered by morphological and chemical analyses showed that the changes responsible for the total conductivity degradation are mainly confined to the surface of the membrane. Indeed, after the exposure to the H2S-containing atmosphere, some traces of sulfur-related compounds were detected only on the top of the membrane while the bulk preserved a fully dense structure with well-defined grain boundaries and no evidence of cracks. However, no evidence of S-based compounds were revealed by structural investigations, probably due to the detection limit of these techniques and/or to the low crystallinity of the secondary phases. Contrary to Pd-based membranes that are severely deteriorated by a few ppm of sulfur, this material shows an acceptable stability even under 700 ppm of H2S and could be attractive for tailored applications such as, for example, operations related to steam reforming of methane often containing 10–300 ppm of H2S.

    更新日期:2018-07-08
  • A novel non-woven fabric supported gel polymer electrolyte based on poly(methylmethacrylate-polyhedral oligomeric silsesquioxane) by phase inversion method for lithium ion batteries
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-07
    Bo Liu, Yun Huang, Lei Zhao, Yixuan Huang, Amin Song, Yuanhua Lin, Mingshan Wang, Xing Li, Haijun Cao

    A novel non-woven fabric supported polymer membrane based on poly(methyl methacrylate-polyhedral oligomeric silsesquioxane) (P(MMA-POSS)) copolymer is prepared by phase inversion method. The difficulty in preparing PMMA membrane by phase inversion method is solved. Further, the P(MMA-POSS) based gel polymer electrolyte (GPE) is prepared by absorbing liquid electrolyte. The morphology structure and properties of the P(MMA-POSS) membrane and electrochemical performance of P(MMA-POSS) GPE are investigated. The results of the analysis exhibit that the P(MMA-POSS) membrane possesses a significant pore structure, and P(MMA-POSS) membrane containing 10 wt.% POSS in polymerization presents the optimal electrolyte uptake of 275 wt.%. Compared with pure PMMA GPE without introducing POSS, the excellent electrochemical performances of P(MMA-POSS) GPE are demonstrated: a higher ionic conductivity of 3.41 mS cm−1 at room temperature, a wider electrochemical stability window of 5.01 V (vs. Li/Li+), the excellent interface compatibility with anode and a satisfactory lithium ion transference number of 0.49. The lithium ion battery with the P(MMA-POSS) GPE also exhibits a higher charge-discharge capacity of 151.9 mAh g−1 at 0.2 C, and a capacity retention rate of 99.8% at 0.5 C is confirmed after 100 cycles.

    更新日期:2018-07-08
  • Nanostructure Depositions on Alumina Hollow Fiber Membranes for Enhanced Wetting Resistance during Membrane Distillation
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-07
    Liang-Hsun Chen, Yi-Rui Chen, Allen Huang, Chien-Hua Chen, Dung-Yue Su, Che-Chen Hsu, Feng-Yu Tsai, Kuo-Lun Tung

    Omniphobic alumina hollow fiber membranes were developed for direct contact membrane distillation (DCMD) with a low surface tension feed in this study. Alumina hollow fiber (HF) membranes were prepared as the membrane substrates, and chemical bath deposition methods were applied to deposit ZnO nanorods and nanoparticles on the HF membranes. The SEM, EDX, and AFM analyses showed that the ZnO nanostructures were effectively deposited on the membrane surfaces and able to increase the surface roughness. After surface fluorination by FAS17, the HF membranes deposited by ZnO nanorods and nanoparticles demonstrated contact angles of 128.7° and 138.1° for a 90% v/v ethanol/water mixture, both of which were higher than 114.8° for the pristine HF membrane without ZnO nanostructures. In the DCMD experiments with the sequential addition of SDS from 0.2 to 2.0 mM, the HF membranes with ZnO nanostructures exhibited superior wetting resistances with low surface tension feeds compared to that of the pristine HF membranes. Moreover, the HF membranes with the deposited ZnO nanoparticles had the best wetting resistance, and the permeate water flux was maintained for 24 h using a 2.0 mM SDS (70 °C 1 M NaCl) solution as an initial feed. The results not only suggested that the deposition of nanostructures enhanced the wetting resistance of the alumina hollow fiber membranes to low surface tension liquids but also showed the promise of utilizing these membranes for the desalination of low surface tension wastewaters.

    更新日期:2018-07-08
  • A simple model for the response of an anion-exchange membrane to variation in concentration and pH of bathing solution
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-04
    A.E. Kozmai, V.V. Nikonenko, S. Zyryanova, N.D. Pismenskaya, L. Dammak

    Swelling is an important property of charged gels and membranes. The size of pores and, therefore, membrane properties such as conductivity, diffusion and hydraulic permeability, permselectivity depend on water content and degree of swelling. In this paper we propose a simple model for equilibrium swelling of an ion-exchange membrane, allowing calculation of water content and membrane thickness as functions of the concentration and pH of the bathing solution. The model parameters include the equivalent volume of dry polyelectrolyte gel, the volume fraction of macropores and others. Three types of ion-exchange functional groups, namely, the secondary, tertiary and quaternary amino groups in an anion-exchange membrane are taken into account. The osmotic pressure exerted by micro- and mesopores, appearing in the gel when swelling, is expressed using the Gregor equation, which employs the mole fractions of free and bound water. The equilibria between protonated and deprotonated amino groups are assumed as well as the Donnan and ion-exchange equilibria between the membrane and bathing solution. The results of calculations are compared with experimental data on the membrane thickness and effective exchange capacity obtained for two heterogeneous anion-exchange membranes MA-40 and MA-41 (Shchekinoazot) differed by the composition of functional groups. The procedure of determining membrane structural and thermodynamic parameters is described. A good quantitative agreement between the theory and experiment is found for both membranes using the same set of ion hydration numbers and chemical equilibrium constants for secondary and tertiary amino groups. In particular, it is shown that with increasing pH of the bathing solution, the membrane thickness (and, hence, water content) pass through a local maximum and a local minimum. The simplicity of the model, which does not reduce adequacy, would enable it to be included later in other models describing the transport of ions and water to account for the swelling and change in the membrane structure with a change in pH and concentration of the bathing solution.

    更新日期:2018-07-05
  • Scalable graphene composite membranes for enhanced ion selectivity
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-03
    Siying Li, Jung-Hun Lee, Qicheng Hu, Tae-Sik Oh, Ji-Beom Yoo

    Unintended defects are a significant problem for mass production of graphene membranes. Herein, we report a method to fabricate scalable CVD graphene polymer membranes through the formation of a polysulfone (PSf) supporting layer, which is capable of duplicating the Cu morphology. Unintended defects were limited by minimizing defects associated with graphene wrinkles and eliminating polymer residues used in the transfer process. Consequently, the KCl leakage by diffusion of raw graphene membranes fabricated with this method was only ~0.5% that of the supporting membrane; there was also no water flux under a pressure of 20 bar. Excellent ion selectivity was achieved by controlling the duration of H2 plasma treatment. The selectivity of KCl over NaCl was 2.61, the selectivity of KCl over MgCl2 was 15.62, and the selectivity of NaCl over MgCl2 was 5.98.

    更新日期:2018-07-04
  • Synthesis of SGO Composite Interpenetrating Network (CIPN) Cation Exchange Membranes: Stability and Salt Removal Efficiency
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-03
    Abhishek Rajput, Vikrant Yadav, Prem P. Sharma, Vaibhav Kulshrestha

    Current study demonstrate the alternative route for synthesis of interpenetrating network (IPN) type composite cation exchange membranes (CEM) based on PVC-St/DVB, with different content sulfonated graphene oxide (SGO) via simple solution casting method. First the synthesis of GO was confirmed by TEM and XRD analysis. Functional group of GO and SGO was done by using FT-IR spectroscopy. Water content related assets like water uptake, linear expansion ratio, and ion transport properties like: ion exchange capacity, ionic conductivity of composite IPN membranes were evaluated. Ion exchange capacity and ionic conductivity for PM-5 was found to highest with values of 1.76 meq/g and 4.7 ×10-3 S/cm, respectively. Thermal and mechanical stabilities of prepared membrane were checked by TGA, DSC, DMA and UTM analysis. Composite interpenetrating network cation exchange membranes (IPN CEM) show better thermal and mechanical stability on comparison with virgin membrane. The suitability of synthesized composite IPN membranes towards electro-membrane processes was checked against salt removal by electrodialysis for water desalination. Power consumption and current efficiency during salt removal for PM-5, composite membrane was found to be 1.07 kWh/kg and 82%, respectively, which is most efficient among the IPN membrane.

    更新日期:2018-07-04
  • Cellulose - Polyethyleneimine Blend Membranes with Anomalous Nanofiltration Performance
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-03
    Tiara Puspasari, Tiefan Huang, Burhannudin Sutisna, Klaus-Viktor Peinemann

    A unique method for the preparation of cellulose-polyethyleneimine (PEI) blend membranes for nanofiltration is presented. Trimethylsilyl cellulose was used as a precursor for the blend membrane fabrication followed by a simple hydrolysis to regenerate the cellulose structure. The resulting homogeneous blend membranes exhibited high neutral solute rejection in water, which was surprisingly better than the performance of the individual membranes due to the strong interactions between the blended polymers. More interestingly, the same membrane demonstrated over five times higher flux of methanol after solvent activation with water as compared to the fluxes of the pure membranes, attributed to formation of nanocracks. High rejection of negatively charged dyes in this solvent with around 450 Da molecular weight cut-off was obtained at an exceptionally high flux of 160 Lm−2h−1 at a 4.5 bar filtration. The membranes will be beneficial in nanofiltration of polar solvents containing neutral and charged molecules.

    更新日期:2018-07-04
  • Influence of feed flow rate, temperature and feed concentration on concentration polarization effects during separation of water-methyl acetate solutions with high permeable hydrophobic pervaporation PDMS membrane
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-03
    Ilya L. Borisov, Anna Kujawska, Katarzyna Knozowska, Vladimir V. Volkov, Wojciech Kujawski

    A novel and efficient method is proposed to evaluate the concentration polarization (CP) effect in pervaporation process. The novelty of the method results from the approach towards the CP phenomenon, that proposes the calculation algorithm on the basis of permeate fluxes and feed/permeate compositions as a function of the feed flow velocity only. The main advantage of the method over the approaches available in the literature is that the intrinsic enrichment factor is calculated directly from the experimental data instead of being found as one of the regression parameters. To prove this approach, pervaporation experiments were carried out using commercial hydrophobic composite PDMS based membrane Pervatech for the recovery of methyl acetate (MeAc) from diluted aqueous solutions (0–1.5 wt% MeAc in feed mixture). Pervaporation performance of PDMS membrane was investigated at various feed flow rates in the range 4.8–70 dm3 h−1 and at three different temperatures of feed mixture (i.e. 30 °C, 40 °C, and 50 °C). It was shown that the intrinsic enrichment factor changes noticeably when the process parameters are altered and this change is one of the key factors affecting the concentration polarization modulus value during pervaporative removal of organic compounds from diluted aqueous solutions. With increasing temperature and feed flow rate, the concentration polarization modulus increases, reaching the value close to 1 at temperature of 50 °C and at the average feed flow rate equal to 1.34 cm s−1. Moreover, under these conditions, the thickness of the boundary layer tends to zero.

    更新日期:2018-07-04
  • Fouling Resistant 2D Boron Nitride Nanosheet – PES Nanofiltration Membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-07-03
    Ze-Xian Low, Jing Ji, David Blumenstock, Yong-Min Chew, Daniel Wolverson, Davide Mattia

    A novel fouling-resistant nanofiltration mixed-matrix membrane was obtained by the incorporation of 2D boron nitride nanosheets (BNNS) in polyethersulfone (PES). The addition of just 0.05 wt% of BNNS into the PES matrix led to a 4-fold increase in pure water permeance with a 10% decrease in the rejection of the dye Rose Bengal; up to 95% rejection of humic acid and nearly 100% flux recovery over two cycles in cross-flow fouling tests without the need for chemical cleansing. This performance is attributed to the uniform distribution of the BNNS in the PES matrix, observed via Raman mapping, and the surface chemistry and structure of the BNNS, which hydrophilised the polymer matrix and reduced its surface roughness. The low amount of BNNS filler needed to render the mixed-matrix membrane fouling-resistant opens the way to its use in waste-water treatment applications where organic fouling remains a major challenge.

    更新日期:2018-07-03
  • Graphene Oxide Quantum Dots Incorporated Nanocomposite Membranes with High Water Flux for Pervaporative Dehydration
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-30
    Manru Wang, Fusheng Pan, Leixin Yang, Yimeng Song, Hong Wu, Xuanxuan Cheng, Guanhua Liu, Hao Yang, Hongjian Wang, Zhongyi Jiang, Xingzhong Cao

    Graphene oxide quantum dots (GOQDs), which inherit the monolayer of sp2 carbon atoms structure and hydrophilic groups as graphene oxide (GO) sheets, but with a quantum lateral size less than 100 nm, may hold great promise in membrane preparation. In this study, a novel nanocomposite membrane by mixing GOQDs with sodium alginate (SA) matrix was prepared for ethanol dehydration. GOQDs with an average lateral dimension around 3.9 nm provided additional shorter and less tortuous transport pathways for water molecules to penetrate the membrane compared to microsized GO sheets. Benefiting from the nanosize and high hydrophilicity of GOQDs, the nanocomposite membrane exhibited favorable ethanol dehydration performance with a total permeation flux of 2432±58 g m-2 h-1, which was 60% higher than that of pristine alginate membrane, and a separation factor of 1152±48. Incorporating GOQDs into the membranes can be an effective approach to improving the water permeation for water-permselective pervaporation membranes.

    更新日期:2018-07-01
  • Nucleophilic-functionalized β-cyclodextrin-polyethersulfone structures from facile lamination process as nanoporous membrane active layers for wastewater post-treatment: Molecular implications
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-30
    Adewale Giwa, Shadi W. Hasan

    Nanocomposite membranes consisting of functionalized β-cyclodextrin (fβ-CD) and polyethersulfone (PES) were fabricated, characterized, and used for low-pressure wastewater post-treatment. The impact of nucleophilic functionalization of β-CD on the performance of these membranes was evaluated via three substitution routes: Crosslinking with nucleophilic dicarboxyl groups (M1) in maleic acid; co-polymerization with excess amino group (M2) in hyperbranched polyethyleneimine (HPEI); and nucleophilic modification with amino and hydroxyl groups (M3) in chitosan. All fβ-CD-incorporated membranes were hydrophilic as a result of the highly populated –OH groups at the exterior of β-CD. Although there are higher-energy intermolecular C–O bonds in M1 membrane, less degree of nucleophilic crosslinking restricted kinetic hindrance and led to an increase in the mean pore size of M1 membrane to 52 nm. A dense structure, the lowest mean pore size of 22 nm, and the highest porosity of 45% was imparted to M2 membrane by the flexible C–N linkages provided by HPEI. Nucleophilic attack by the abundant N–H groups in HPEI also improved the tensile strength of M2 membrane reaching 20 MPa. Consequently, the water permeability of M2 membrane was significantly enhanced via β-CD's solution-diffusion property. M1, M2, and M3 membrane water permeability were 61, 239, and 167 LMH bar−1, respectively. M3 membrane showed the highest removal efficiencies for heavy metal ions (92% of Cr6+, 90% of Zn2+, 82% of Fe2+, and 87% of Cd2+) since it is the most hydrophilic membrane with abundant –OH groups in chitosan. However, M2 membrane displayed the highest removal efficiencies for residual organics, i.e. 67% chemical oxygen demand (COD) and 84% bacteria due to the hydrophobic interior of its dense fβ-CD.

    更新日期:2018-07-01
  • Catalytic palladium membrane reactors for one-step benzene hydroxylation to phenol
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-30
    Xiaobin Wang, Yiming Zou, Bo Meng, Xiaoyao Tan, Shaobin Wang, Shaomin Liu
    更新日期:2018-07-01
  • One-step fabrication and characterization of reinforced microcomposite membranes for polymer electrolyte membrane fuel cells
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-30
    Seol Jang, Young-Gi Yoon, Youn-Sik Lee, Young-Woo Choi

    The mechanical durability of hydrocarbon membranes in polymer electrolyte membrane fuel cells remains insufficient. To resolve this issue, in contrast to the conventionally used method, reinforced composite membranes were fabricated by simultaneous electrospinning and spraying. A hydrophobic polysulfone (PSf) was used as a non-conducting substrate to increase the membrane's mechanical strength, and hydrophilic sulfonated poly(arylene ether sulfone) (sPAES) was used as an electrolyte. The properties and performance of a reinforced microcomposite membrane comprising electrospun PSf/sprayed sPAES were compared with those of (i) sPAES homogeneous membrane, (ii) sprayed PSf/electrospun sPAES membrane, and (iii) PSf/sPAES blend membrane. Although the electrospun PSf/sprayed sPAES membrane was slightly more durable than the others, we think that the developed membrane fabrication method holds great promise and can be further improved by utilising more compatible materials.

    更新日期:2018-07-01
  • 更新日期:2018-07-01
  • Single-nanoparticle tracking reveals mechanisms of membrane fouling
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-28
    Yu Cai, Daniel K. Schwartz

    While membrane fouling has been studied for decades, it remains challenging to obtain direct information about the dominant mechanism of fouling in a specific scenario. Here, we employed a high-throughput particle-tracking approach, which enabled the visualization of particle transport in actual microfiltration membranes under flow conditions and provided direct evidence for distinct fouling mechanisms under different operating conditions. Our results suggest that the “stickiness” of particles can qualitatively change the dominant fouling mechanism. In particular, the evolutions of effective flux, particle velocity and pathway tortuosity were found to be systematically different under “sticking” vs “reduced-sticking” conditions in two different microfiltration membranes, composed of PVDF and PTFE, respectively. Under “sticking” conditions, fouling was rapid, and individual pathways were observed to disappear with the reduction of flux. However, the average particle velocity and the tortuosity of particle trajectories were unchanged throughout the fouling process, consistent with the complete blocking of random pathways. Conversely, under “reduced-sticking” conditions, the average particle velocity decreased and the tortuosity of particle pathways increased systematically with fouling, consistent with the gradual narrowing of pathways causing increased resistance. The comprehensive information about particle dynamics in membranes achieved with this approach will assist design and optimization of reduced-fouling separation processes as well as advance the understanding of complex mass transport.

    更新日期:2018-06-30
  • Quaternary Ti3C2Tx enhanced ionic conduction in Quaternized polysulfone membrane for alkaline anion exchange membrane fuel cells
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-28
    Xiaole Zhang, Chanchan Fan, Naiyuan Yao, Peng Zhang, Tao Hong, Chenxi Xu, Jigui Cheng
    更新日期:2018-06-30
  • Solvent and pH-stable poly(2,5-benzimidazole) (ABPBI) based UF membranes: Preparation and characterizations
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-27
    Harshada R. Lohokare, Harshal D. Chaudhari, Ulhas. K. Kharul
    更新日期:2018-06-28
  • Optimizing electrospinning parameters for piezoelectric PVDF nanofiber membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-27
    S. Gee, B. Johnson, A.L. Smith
    更新日期:2018-06-28
  • Dual-layered nanocomposite membrane incorporating graphene oxide and halloysite nanotube for high osmotic power density and fouling resistance
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-27
    Sungil Lim, Myoung Jun Park, Sherub Phuntsho, Anne Mai-Prochnow, Anthony B. Murphy, Donghan Seo, Hokyong Shon
    更新日期:2018-06-28
  • Gravity-driven Ultrafast Separation of Water-in-Oil Emulsion by Hierarchically Porous Electrospun Poly(L-lactide) Fabrics
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-27
    Jingxin Zhao, Wao Wang, Cuicui Ye, Yongjin Li, Jichun You
    更新日期:2018-06-28
  • Model-Guided Design of High-Performance Membrane Distillation Modules for Water Desalination
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-28
    Mahdi Mohammadi Ghaleni, Mona Bavarian, Siamak Nejati

    The significance of geometrical and physical parameters of hollow fiber membrane modules in the membrane distillation process has not been fully evaluated. In this study, we develop a three-dimensional multi-physics model of a hollow fiber membrane module in order to investigate the effect of operating and design parameters on the module performance. The permeate flux and thermal efficiency of the system are considered as the characteristic parameters of the module, operated in direct contact membrane distillation mode (DCMD). The simulation results indicate that the permeate flux for the module can be enhanced by 54% when 1) the hollow fibers are in close-packed configuration, and 2) the interspacing parameter, the ratio of a fiber radius to the center-to-center distance between neighboring fibers, is adjusted properly. We identify the fiber interspacing parameter as a critical parameter for the module design. The permeate flux significantly drops when the interspacing parameter is equal to a value of 0.5, implying that the fibers are adjacent to each other. Moreover, the results indicate that, in our system, the time constant for the mass transfer process through the membrane is higher than that of heat transfer, meaning that the DCMD process for a hollow fiber membrane module under parallel flow condition is a mass transfer limited process.

    更新日期:2018-06-28
  • Performance of a polypropylene membrane contactor for the recovery of dissolved methane from anaerobic effluents: mass transfer evaluation, long-term operation and cleaning strategies
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-25
    María Henares, Pablo Ferrero, Pau San-Valero, Vicente Martínez-Soria, Marta Izquierdo

    A polypropylene membrane contactor was used for the recovery of dissolved methane from an anaerobic reactor effluent. Effect of operational parameters, operation mode and fouling on long-term operation was studied using vacuum pressure or N2 as sweep gas. Results were analyzed based on the mass transfer estimations. Lower performance was observed in the shell-side mode due to the lower liquid velocity and the probable channeling. Membrane pore wetting was observed with the increase in QL in the vacuum-pressure mode. This was confirmed with mass transfer resistance analysis, resulting in an estimated wetted pore fraction of between 0.25 and 0.53. The highest removal efficiencies were obtained with the liquid flowing in the lumen side and sweep-gas operation (between 98% and 67% for QL between 4.1 and 27.2 L h–1), with negligible effect of the N2 flow rate. In the long-term operation, the impact of membrane fouling was less intense in the lumen side, with longer operation time and more reversible fouling. A complete characterization of the fouling based on water sample analysis concluded that both inorganic and organic foulants were present, probably with higher biofouling presence. A combination of water and chemical cleanings resulted in a recommended protocol based on daily water cleaning.

    更新日期:2018-06-27
  • Negatively charged polyimide nanofiltration membranes with high selectivity and performance stability by optimization of synergistic imidization
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-26
    Chenjie Wei, Zhifu He, Ligang Lin, Qi Cheng, Kai Huang, Sisi Ma, Li Chen
    更新日期:2018-06-27
  • 更新日期:2018-06-27
  • Integrated Fe-based floc-membrane process for alleviating ultrafiltration membrane fouling by humic acid and reservoir water
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-26
    Baiwen Ma, Wenjing Xue, Wenjiang Li, Chengzhi Hu, Huijuan Liu, Jiuhui Qu
    更新日期:2018-06-27
  • Characteristics and formation mechanism of membrane fouling in a full-scale RO wastewater reclamation process: Membrane autopsy and fouling characterization
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-26
    Libing Zheng, Dawei Yu, Gang Wang, Zenggang Yue, Chun Zhang, Yawei Wang, Junya Zhang, Jun Wang, Guoliang Liang, Yuansong Wei

    Membrane fouling is the bottleneck of stable operations for reverse osmosis (RO), which is the key technology for reclaimed water reuse in thermal power plants. The foulant composition, formation mechanism, and key contributors were analyzed in this study. The primary scaling substances are Ca, Mg, Al, Fe, and Si, and Ca accounts for 1.49 wt%. Humic substances, proteins, and polysaccharides are the primary organic constitutes, and among them bio-derivatives were main composition revealed by FTIR, EEM, and SEC. Thus, bio-fouling was believed to be the key contributor together with the results of the SEM and the microbial community analysis. The three leading bacteria were α-, β-, γ-proteobacteria at class levels, 38.11%, 14.19%, and 34.31%, respectively, while starkeya, acidovorax, luteimonas, and pseudoxanthomonas were the leading bacteria at the genus level. Among these bacteria, the one with metabolic processes related to nitrogen fixation and proteolysis showed higher abundance for the high concentrations of nitrogen and protein. Foulants on the endcap and membrane entrance also indicated severe bio-fouling, where Acidovorax presented significant abundance. A Vertical distribution of the microbial community was found in the cross-section of the foulant, in particular, a significant decrease of starkeya (from 48.4% to 4.65%) and acidovorax (from 17.64% to 5.61%) and an increase of pseudoxanthomonas (from 1.04% to 12.89%) from the top layer to the bottom layer were observed. The γ-proteobacteria was recognized as the pioneering bacteria for its significantly higher abundance in the deeper layer. This study helps to elucidate the RO membrane fouling composition and its key contributors, and improves our understanding of the membrane fouling mechanism and a controlling strategy.

    更新日期:2018-06-27
  • Effects of organic fouling and cleaning on the retention of pharmaceutically active compounds by ceramic nanofiltration membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-26
    Yang-ying Zhao, Xiao-mao Wang, Hong-wei Yang, Yue-feng F. Xie
    更新日期:2018-06-27
  • The role of MOFs in Thin-Film Nanocomposite (TFN) membranes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-22
    Cédric Van Goethem, Rhea Verbeke, Martin Pfanmöller, Tönjes Koschine, Marcel Dickmann, Tanja Timpel-Lindner, Werner Egger, Sara Bals, Ivo F.J. Vankelecom

    Incorporation of MOFs in interfacially polymerized Thin-Film Nanocomposite (TFN) membranes has widely been shown to result in increased membrane performance. However, the exact functioning of these membranes is poorly understood as large variability in permeance increase, filler incorporation and rejection changes can be observed in literature. The synthesis and functioning of TFN membranes (herein exemplified by ZIF-8 filled polyamide (PA) membranes prepared via the EFP method) was investigated via targeted membrane synthesis and thorough characterization via STEM-EDX, XRD and PALS. It is hypothesized that the acid generated during the interfacial polymerization (IP) at least partially degrades the crystalline, acid-sensitive ZIF-8 and that this influences the membrane formation (through so-called secondary effects, i.e. not strictly linked to the pore morphology of the MOF). Nanoscale HAADF-STEM imaging and STEM-EDX Zn-mapping revealed no ZIF-8 particles but rather the presence of randomly shaped regions with elevated Zn-content. Also XRD failed to show the presence of crystalline areas in the composite PA films. As the addition of the acid-quenching TEA led to an increase in the diffraction signal observed in XRD, the role of the acid was confirmed. The separate addition of dissolved Zn2+ to the synthesis of regular TFC membranes showed an increase in permeance while losing some salt retention, similar to observations regularly made for TFN membranes. While the addition of a porous material to a TFC membrane is a straightforward concept, all obtained results indicate that the synthesis and performance of such composite membranes is often more complex than commonly accepted.

    更新日期:2018-06-22
  • Modification of Nafion with silica nanoparticles in supercritical carbon dioxide for electrochemical applications
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-22
    Anton S. Simonov, Mikhail S. Kondratenko, Igor V. Elmanovich, V.E. Sizov, Elena P. Kharitonova, Sergei S. Abramchuk, Alexandr Yu. Nikolaev, Daniil A. Fedosov, Marat O. Gallyamov, Alexei R. Khokhlov

    In this paper a promising approach to implement the hydrolysis/condensation of tetraethoxysilane (TEOS) inside Nafion membrane using supercritical carbon dioxide as a solvent is suggested. Since sc CO2 is a non-polar fluid, TEOS transport towards the hydrophilic channels of the Nafion should occur mostly through hydrophobic fluorinated domains of the Nafion swollen in CO2. Therefore, unlike using conventional more polar liquid solvents for TEOS, silica phase growing in the channels does not block the transport of the precursor, which impregnates the polymer matrix uniformly. As a result, silica nanoparticles having size in the range from 2 to 5 nm are formed inside the Nafion membranes. The methanol permeability is decreased from 16 × 10-7cm2/s for pristine membranes to about 9 × 10-7 cm2/s for the modified ones, while the proton conductivity is not affected by the silica incorporation. Thermomechanical analysis revealed that water retention at elevated temperatures is improved by the silica incorporation. Yet, the general water uptake is reduced in comparison to the pristine samples. These results have been interpreted as an evidence for advanced performance of the composite films at high temperatures or at low humidity conditions.

    更新日期:2018-06-22
  • Molecular design of sulfonated polyphenylsulfone /polybenzimidazole blend membranes using a double cross-linking technique towards an efficient hydrogen purification
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-22
    Ali Naderi, Akbar Asadi Tashvigh, Tai-Shung Chung, Martin Weber, Christian Maletzko

    This study, for the first time, demonstrates a new double-crosslinking approach to manipulate the microstructure and gas separation performance of PBI membranes for H2/CO2 separation at 150 °C. The PBI membranes were firstly blended with sulfonated polyphenylsulfone (sPPSU) as an ionic-crosslinker and then α,α′-dibromo-p-xylene (DBX) as a covalent crosslinker with the aid of thermal annealing. Experiments show that PBI and sPPSU interact on the molecular level. Different from conventional blends, the PBI/sPPSU blend membranes show both enhanced chemical resistance and greater fractional free volume (FFV) after annealing at elevated temperatures because of chain motion and ionic crosslinking. As a result, the blend membranes maintain their high permeability after annealing. The DBX addition further improves the chemical resistance and tightens the inter-chain spacing that results in membranes with a small FFV and pore size. Consequently, the DBX cross-linked blend membranes retain their high gas pair selectivity at high temperatures. The 50/50 PBI/sPPSU blend membrane crosslinked by 0.7 wt% DBX at 300 °C possesses the best separation performance surpassing the Robeson's upper bound. It has an impressively H2 permeability of 46.2 Barrer and a high H2/CO2 selectivity of 9.9 at 150 °C.

    更新日期:2018-06-22
  • Thermal rearranged poly(imide-co-ethylene glycol) membranes for gas separation
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-19
    Colin A. Scholes, Benny D. Freeman

    Thermal rearrangement of α-functional polyimide membranes into poly(benzoxazole) improves the permselectivity performance compared to the precursor polymer. This is due to the bimodal cavity size distribution generated through the TR process. The cavity volume can be further increased by including segments within the polyimide that undergo degradation at a lower temperature than the TR process. The loss of these segments leaves behind cavity space that can be used to increase gas permeability. This is achieved here for copolymers based on 4,4’-hexafluoroisopropylidene diphthalic anhydride (6FDA) and 3,3’-dihydroxy-4,4’-diamino-biphenyl (HAB) with poly (ethylene glycol) segments, where the PEG segments undergo thermal degradation below the PI to PBO transition temperature. HAB-6FDA-PEG copolymer membranes, with different weight % PEG, had poor permselectivity for CO2-N2 and CO2-CH4 separation. Undertaking thermal treatment to degrade the PEG segments but retaining the PI polymer resulted in an increased fractional free volume of the resulting membrane and higher gas permeability, but a corresponding loss of CO2 selectivity. Producing TR-PBO from the copolymers through thermal rearrangement at 450 °C, improved the gas permeability of the resulting membranes by over an order of magnitude, as well as improving the CO2 selectivity. This was attributed to the degradation of the PEG segments increasing the FFV of the membranes, resulting in over a third of the polymers’ morphology being free volume. The resulting TR-PBO membranes formed from copolymers with PEG segment had enhanced permselectivity performance compared to TR-PBO formed from the polyimide homopolymer.

    更新日期:2018-06-22
  • 更新日期:2018-06-22
  • Nanopore charge inversion and current-voltage curves in mixtures of asymmetric electrolytes
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-19
    Patricio Ramirez, José A. Manzanares, Javier Cervera, Vicente Gomez, Mubarak Ali, Isabelle Pause, Wolfgang Ensinger, Salvador Mafe
    更新日期:2018-06-22
  • Water and salt dynamics in multilayer graphene oxide (GO) membrane: role of lateral sheet dimensions
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-19
    Abhijit Gogoi, Tukhar Jyoti Konch, Kalyan Raidongia, K. Anki Reddy

    Dependence of salt rejection efficiency and water permeability of layered graphene oxide (GO) membranes on the lateral dimension of constituting sheets are studied through equilibrium molecular dynamic (MD) simulation and experiments. This study suggests that with increasing sheets dimension permeability of the GO membranes decreases but its selectivity increases. The velocity and permeation time of the water molecules while permeating through the membrane are influenced to a greater extent by the pore offset distance (W) of the membranes. More over the larger pore offset distance increases the path length that the water molecules and ions have to traverse for permeating through the layered GO membranes. Based on the simple technique discussed in this work, one can construct GO membranes of required water permeability and salt rejection without the application of any foreign nanomaterials with the GO membrane, which retains the inherent selectivity of the GO membranes. This work also provides the effect of internal structure of GO membrane on the atomistic level details of the solvation shell of ions while they are permeating through the membrane.

    更新日期:2018-06-22
  • 更新日期:2018-06-22
  • GAS PERMEABLE MEMBRANE BIOREACTOR FOR THE CO-CULTURE OF HUMAN SKIN DERIVED MESENCHYMAL STEM CELLS WITH HEPATOCYTES AND ENDOTHELIAL CELLS
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-20
    Simona Salerno, Efrem Curcio, Augustinus Bader, Lidietta Giorno, Enrico Drioli, Loredana De Bartolo
    更新日期:2018-06-22
  • Water/salt transport properties of organic/inorganic hybrid films based on cellulose triacetate
    J. Membr. Sci. (IF 6.578) Pub Date : 2018-06-20
    Meng You, Jian Yin, Rongbo Sun, Xingzhong Cao, Jianqiang Meng

    The synergized optimization of water flux and salt rejection by blending with inorganic fillers has been achieved for the polyamide (PA) thin film nanocomposite (TFN) membrane. However, it is difficult to characterize its mass transport properties due to the very thin and heterogeneous PA film. In this work, we select cellulose triacetate (CTA) as the base to prepare hybrid films and their transport properties were studied according to solution-diffusion theory. A series of inorganic fillers, such as reduced graphene oxide (RGO), zeolites, ZIF-8, SiO2 and graphene oxide (GO) were incorporated. The SEM and EDX results indicate a less than 1 wt% filler content for a uniform dispersion. The blending of inorganic fillers leads to enhanced glass transition temperature (Tg) and density, little effect on the water transport property but dramatically decreased salt permeability values, which are nearly ten-fold of that of the CTA film. The blending of GO can densify and hydrophilize CTA simultaneously, which is most promising for a desalination application. The increased water uptake should contribute to its increased water permeability, while the decreased free volume size and FFV value and various interactions between the ions (Na+, Cl-) and GO sheets account for salt permeability decrease.

    更新日期:2018-06-22
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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