Polyacrylonitrile Composite Membranes Research Articles

Highly adherent Ti3C2Tx nanosheet-loaded amidoxime polyacrylonitrile composite membrane for uranium extraction

Uranium is the main element of nuclear energy production, so the current global energy scarcity can be solved by uranium enrichment. The total amount of uranium in the ocean is huge, but how to extract uranium from the ocean efficiently and conveniently has become a hot issue nowadays. Polydopamine (PDA) from the self-polymerization of the mussel substance dopamine (DA) improved the adhesion of Ti3C2Tx (MXene) nanosheets to amidoxime polyacrylonitrile (PAO) support membrane to form amidoxime polyacrylonitrile composite membrane loaded with MXene nanosheets for uranium capture (PDA@M/PAO). The obtained maximum uranium adsorption capacity of PDA@M/PAO composite membrane can reach up to 14.85 g/m2 (499.9 mg/g), which was significantly higher than that of single PAO membrane. Kinetic fitting indicated that the adsorption was chemical adsorption, and isothermal model indicated that the adsorption was consistent with Langmuir adsorption, which was monolayer adsorption. After eight adsorption–desorption cycles, the adsorbent still retained 83 % of the elution rate, indicating that the adsorbent had great stability and recyclability. Due to its high adsorption capacity and excellent cycling stability, PDA@M/PAO composite membrane will provide a new strategy for uranium enrichment.

Tuning In‐Plane Wicking Properties of Hydrophilic Fibrous Membranes Using Hydrophobic Fibrous Cover Layers

AbstractThis study elucidates the effect of thin porous hydrophobic covering layers on the in‐plane wicking properties of a hydrophilic fibrous membrane. Polyacrylonitrile (PAN) fibrous membrane is used as the hydrophilic membrane model and poly(vinylidene fluoride‐hexafluoropropylene) (PVDF‐HFP) fibrous membranes as hydrophobic covers, both prepared by electrospinning. The vertical wicking height is measured to express the in‐plane wicking properties. The results show that the PVDF‐HFP fibrous layer profoundly impacted the in‐plane wicking properties. When the PVDF‐HFP layer is 5.00–7.05 µm in thickness, the PVDF‐HFP/PAN composite membranes show a directional water transport property. The wicking height is higher than the other composite membranes with either a thinner PVDF‐HFP layer (<5.00 µm), which causes a two‐way liquid transport, or a thicker PVDF‐HFP layer (>7.05 µm), which stops water permeation from both sides. Such a trend happened no matter whether the PVDF‐HFP layer covered one or both PAN membrane sides. The composite membranes with a PVDF‐HFP layer thicker than 7.05 µm show the smallest wicking height. By changing PVDF‐HFP layer thickness, the wicking height can be adjusted by 50–110%. Such thickness‐dependent wicking capability is novel, having not been reported in the previous literature. It comes from the combined action of hydrophobic and hydrophilic surfaces on water. The tunable wicking properties combined with the water‐absorbing and transport properties enabled the PVDF‐HFP/PAN fibrous membranes to exhibit different functions. They offer opportunities to develop novel “smart” membranes for various applications.

A novel nanofibrous PAN ultrafiltration membrane embedded with ZIF-8 nanoparticles for effective removal of Congo red, Pb(II), and Cu(II) in industrial wastewater treatment.

A novel Polyacrylonitrile (PAN) composite membrane involving ZIF-8 nanoparticles, named as ZIF-8/PAN membrane, was obtained via electrospinning to remove the Congo red (CR), Pb(II) and Cu(II) ions in industrial wastewaters, during which the adsorption mechanisms were examined in this study. The adsorption efficiency of the electrospun ZIF-8/PAN membrane was as high as 89%, 92% and 76% for CR, Pb(II) and Cu(II), respectively. Comparative analysis showed that ZIF-8 nanoparticles embedded in the ZIF-8/PAN membrane accounted for these enhanced adsorption capabilities. The adsorption behaviors of the ZIF-8 nanoparticles were investigated through experiments and theoretical analysis, and the results unraveled that the adsorption for CR by the ZIF-8 was mainly including electrostatic interaction, hydrogen bonding and π-π interaction, while those for Pb(II) and Cu(II) were mainly caused by ion-exchange and chemical adsorption. Parametric studies were conducted to optimize the conditions for removing CR, Pb(II), and Cu(II) by ZIF-8 nanoparticles, during which all of pollutants showed different reactions to the solution pH. This work not only develops a novel ZIF-8/PAN composite membrane for effective removals of pollutants, but also reveals the underlying mechanisms of pollutants adsorption in terms of molecular interactions, providing important understandings on fibrous materials design for efficient heavy metals and dyes removals in industrial wastewater treatment.

Interfacial polymerization of a covalent organic framework layer on titanium dioxide@graphene oxide/polyacrylonitrile mixed-matrix membranes for high-performance dye separation

Interfacial polymerization of imine-linked covalent organic frameworks (COFs) on support membranes is one of the most promising routes for realizing COF composite membranes for industrial applications. In the present work, first, the influences of the pore structure, microtopography, and chemical structure of TiO 2 @graphene oxide (GO)/polyacrylonitrile (PAN) support membranes on the structure and performance of 1,3,5-triformylphloroglucinol (Tp)– p -Phenylenediamine (Pa) COF composite membranes were studied. The results showed that the hydrophilic and smooth top surface, homogenous pore distribution, and large pore size of TiO 2 @GO/PAN support membranes enabled them to be easily infiltrated by aqueous-phase solutions. These features promoted the homogenous diffusion of an aqueous solution from the bottom surface to the top surface of the TiO 2 @GO/PAN membranes, which generated a stable interface between the organic and aqueous phases. A thin, crystalline TpPa layer with a mean pore size of 1.78 nm on the top surface of TiO 2 @GO/PAN endowed the COF composite membranes with excellent filtration performance, including a pure-water permeance of 89.08 L m −2 h −1 bar −1 (testing pressure = 1.0 bar) and the Congo red dye rejection rate of 94.83%. Membranes that displayed steady filtration properties for a 300-h filtration test will be given greater attention, as they will be suitable for industrial applications. • Synergestic effects of GO and TiO 2 in TiO 2 @GO/PAN membrane were proved. • Thin and crystalline TpPa layer was generated on the top surface of TiO 2 @GO/PAN membrane. • Influences of support membranes on TpPa COF layer have been investigated. • Synergestic effects promototed the generation and quality of the TpPa layer. • TpPa/TiO 2 @GO/PAN composite membrane exhibit great potential to dye separation.

The dehydration performance and sorption behavior of PVA/silica hybrid pervaporative membrane

A polyvinyl alcohol (PVA)/SiO2 organic-inorganic hybrid membrane was fabricated, using PVA as the basic material, SiO2 nanoparticles as the inorganic material, γ-(2,3)-glycidoxy propyl trimethoxysilane (GPTMS) and 3-aminopropyl triethoxysilane (APTEOS) as the second modified agents. The dehydration performance of PVA-SiO2/polyacrylonitrile (PAN) composite membrane to ethyl acetate (EA)/H2O, EA/ethanol (EtOH)/H2O and EA/EtOH/acetic acid (HAc)/H2O solutions was investigated. After modification of the second coupling agent of APTEOS or GPTMS, PVA-SiO2/PAN composite membrane had the better dehydration performance to these aqueous solutions. When dehydrating PVA-SiO2/PAN composite membrane modified by GPTMS (M5 membrane) in EA/H2O binary solution (98/2, wt%) at 40°C, the separation factor and the total permeation flux were 5245 and 293.9 g m−2 h−1, respectively. The preparation method of PVA/SiO2 membrane through adding the second coupling agent was simple, it had good dehydration performance and has excellent application prospects. The sorption behavior of PVA/SiO2 hybrid membrane was systematically studied, providing sufficient data for studying the separation mechanism of pervaporative membrane. The degree of swelling (DS) and the sorption selectivity of the membrane in different feed compositions and temperatures were measured to determine the static sorption of membrane. Dynamic sorption more clearly reflects the sorption and swelling processes of the membrane, and the dynamic sorption curves of the membrane in EA aqueous solutions were obtained. The sorption behavior of membrane to permeate components was studied by ATR-FTIR. Changes in the characteristic peaks for the permeate components and membrane indicated the sorption behavior of the membrane.

Carbon Nanotube Scaffolds Entrapped in a Gel Matrix for Realizing the Improved Cycle Life of Zinc Bromine Redox Flow Batteries.

Herein, we have successfully demonstrated a nanofiller (such as multiwalled carbon nanotubes (MWCNT)) dispersed in a polymer matrix (such as polyacrylonitrile (PAN)) as an effective pore filling agent to a microporous Daramic membrane for inhibiting bromine diffusion in zinc bromine redox flow batteries. A simple protocol of the MWCNT/PAN-Daramic membrane renders a major benefit for inhibiting bromine diffusion relative to the conventional microporous membrane. As a result, the MWCNT/PAN composite Daramic membrane exhibits remarkable electrochemical performance in zinc bromine redox flow batteries at various current densities. More impressively, the MWCNT/PAN composite Daramic membrane shows a 90% Coulombic efficiency compared to the pristine Daramic membrane and the PAN composite Daramic membrane with only 68.53 and 71.20% efficiencies at 160 mA cm-2, respectively. Moreover, the MWCNT/PAN composite Daramic membrane displays an extraordinary long cycling performance with a >97% Coulombic efficiency, whereas the Daramic membrane withstands only 200 cycles due to severe water transport from the catholyte to the anolyte. The zinc bromine redox flow battery assembled with the MWCNT/PAN composite Daramic membrane significantly reduces the self-discharge rate and retains an open circuit voltage of 1.69 V for 13.40 h in comparison to the Daramic membrane (10.83 h) and the PAN composite membrane (11.13 h). Thus, the extraordinary flow cell performance and stability of the MWCNT/PAN composite Daramic membrane lead to the development of an alternative to the microporous Daramic membrane in zinc bromine redox flow batteries.

Membranes with selective laminar nanochannels of modified reduced graphene oxide for water purification

Developing graphene-based membranes is important for a wide range of applications such as in desalination, wastewater treatment, separation and purification. Herein, a novel graphene-based nanofiltration (NF) membrane was fabricated by depositing the magnesium silicate modified reduced graphene oxide (MgSi@RGO) nanosheets on a polyacrylonitrile (PAN) ultrafiltration membrane via a vacuum filtration method. The MgSi@RGO/PAN composite membrane exhibits special selectivities for separation of organic molecules. Molecule permeation through the MgSi@RGO selective skin layer was observed with the broadened nanochannels propped up by MgSi nanosheets. The rejections of different PEG molecules (PEG200, PEG400, PEG600 and PEG1000) were tested, and the experimental results and theoretical calculations showed high consistency, which means the theoretical model can be effectively used for calculating the real diameter of “pore” in NF membrane. Additionally, three dye molecules were selected to investigate the NF membrane performance, and the MgSi@RGO/PAN composite membrane showed different separation characteristics of charged molecules.

Mussel-inspired fabrication of structurally stable chitosan/polyacrylonitrile composite membrane for pervaporation dehydration

The structural stability of chitosan (CS)/polyacrylonitrile (PAN) composite membrane for pervaporation dehydration was improved by the introduction of mussel-adhesive-mimetic molecule, carbopol (CP). The composite membranes were simply fabricated by layer-by-layer technique, in which CP as an intermediate layer bridging the CS active layer and the PAN support layer. The structure and morphology of composite membranes were characterized by Fourier transform infrared spectroscopy (FT-IR) and field emission scanning electron microscope (FESEM). The methylene iodide contact angle measurement, T-peel test and molecular dynamics (MD) simulation were employed to analyze the wetting characteristics, adhesion strength and interaction at the interface. Positron annihilation lifetime spectroscopy (PALS) was employed to probe the fractional free-volume properties of the CS active layer. The membrane pervaporation performance was investigated by varying the molecular weight (CP981, 940, 974) and concentration of CP as well as the cross-linking degree of the CS active layer. When the concentration of CP974 was 0.5 wt.%, GCCS(60)/CP(0.5)/PAN composite membrane displayed the permeation flux of 1247 g/(m 2 h) and separation factor of 256 for ethanol dehydration at 353 K. Furthermore, the enhancement of the long-term operation stability of membrane by incorporating the CP layer was also verified.

Perfluorosulfonic acid—Tetraethoxysilane/polyacrylonitrile (PFSA‐TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate–water solutions

AbstractPreparation of organic‐inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol‐gel reaction as the coating solution, the PFSA‐TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA‐TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA‐TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA‐TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA‐TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m2 h at 40°C, respectively. In addition, the PV performance of PFSA‐TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Hybrid sol–gel membranes of polyacrylonitrile–tetraethoxysilane composites for gas permselectivity

AbstractSol–gel reaction of tetraethoxysilane (TEOS) with fumed silica–polyacrylonitrile (PAN) membrane was carried out to prepare hybrid gas permeable membranes for oxygen and nitrogen separation. Various amounts of fumed silica microparticles with a few μm diameters were compounded in PAN–dimethylsulfoxide (DMSO) solution. After casting of the viscous compound solution on a flat sheet with 100 μm thickness, DMSO was evacuated under vacuum at 80°C. Then, the silica–PAN composite membranes were treated with TEOS for 1 day at 40°C in methanol. Air permeation was examined and compared in silica–PAN composite membranes with and without TEOS treatment. The latter hybrid membranes showed selective oxygen permeability, which depended on amounts of fumed silica in the membrane. The TEOS hybrid PAN membranes have a high ability of oxygen permselectivity for O2/N2 gas mixture with α(O2/N2) = 13–17, when the silica content was in the range of 13–20 wt %. This is attributed to siloxane network formation in hybrid silica–PAN composite membranes. Favorable siloxane network formation resulted in high oxygen permeability of the hybrid composite membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1752–1759, 2003

The Structure and Hydration of Composite Membranes Based on Polyacrylonitrile

The morphology of polyacrylonitrile composite membranes containing microdispersions of ion exchange resins was investigated by gas adsorption, mercury porosimetry, and scanning and transmission electron microscopy. The relation between the structure, hydration and permeability of composite membranes at the transmembrane difference of pH and pNa was studied.