Preparation and performance of sulfonated polysulfone flat ultrafiltration membranes

Sulfonated polysulfone (SPSF) flat ultrafiltration membranes were successfully prepared by immersion precipitation phase inversion method. N‐Methyl pyrrolidone was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a polymeric additive in the casting solution. The effects of casting solution formulation and preparation conditions on membrane structure and properties were investigated in present study, and the morphology of the membranes was analyzed by scanning electron microscopy. The results indicated that the performances of SPSF membranes made by chemical modification were better than polysulfone membrane. The SPSF concentration played a vital role in restricting the pure water flux (PWF), promoting the rejection coefficient, and improving the hydrophilicity. A maximum PWF and minimum egg albumin rejection coefficient were obtained when the PVP content was 10%. When the coagulation bath temperature was set to 25°C, the PWF reached 480 L·m^?2·h^?1 and the ovalbumin rejection coefficient reached 92%. Longer evaporation times improved the PWF. Specifically, when the evaporation time was 70 s, the comprehensive performance was good. POLYM. ENG. SCI., 55:1003–1011, 2015. © 2014 Society of Plastics Engineers     

Aqueous dispersions of reduced graphene oxide and multi wall carbon nanotubes for enhanced glucose oxidase bioelectrode performance

Aqueous dispersions of reduced graphene oxide (rGO) and multi walled carbon nanotubes (MWCNT) were fabricated through a modified chemical reduction method. The significant advantage of the method developed here is the omission of any stabilising compound or organic solvent to obtain stable rGO–MWCNT dispersions. Significantly biological entities, in this case the enzyme glucose oxidase (GOx), can be successfully incorporated into the dispersion. These dispersions were characterised using XPS, SEM, zeta potential and particle size measurements which showed that the dispersion stability is not sacrificed with the addition of GOx, and significantly, the electrical properties of the rGO and MWCNTs are maintained. In this study, rGO acts as an effective dispersing agent for MWCNTs and does not affect the solubility or electroactivity of the GOx. Bioelectrodes fabricated from these rGO–MWCNT–GOx dispersions were characterised electrochemically to test their feasibility in facilitating direct electron transfer (DET) from the redox centre of the enzyme to the electrode. The DET results showed that the specific catalytic current generated at an optimised rGO–MWCNT–GOx electrode was 72 μA/μg GOx, which is 144 times more efficient than other literature values for similar systems. The remarkable specific catalytic current can be attributed to the use of purified enzyme, the efficiency of charge transfer within the rGO–MWCNT composite and the ability of the electrode to facilitate direct electron transfer.     

Gill inspired hierarchical wrinkles of reduced graphene oxide encapsulated carbon nanotubes with significantly boosted supercapacitor performance

It has long been pursued in the energy storage community that 3D carbon materials can be constructed with 1D carbon nanotubes and 2D graphene in a proper manner that fully develops their appealing synergistic effects of high conductivity and large surface area. However, the present hybrid nanostructures suffer from either weak bonding strength or heavy dependence on high cost processing techniques. Here we report a gill-inspired hierarchical structure created by a simple annealing strategy, where carbon nanotubes are encapsulated in the wrinkles made of reduced graphene oxide, in resemblance to the vessels embedded in the wrinkle-like gill lamellae. The wrinkled structure enables enriched micropore structures and improved specific surface area, while the embedded carbon nanotubes guarantee the enhanced electrical conductivity. Thus, rGO@CNTs@AC (1000) achieved a 75% increase in the specific capacity @ 1 A g⁻¹ (200 F g⁻¹ vs. 120 F g⁻¹) when compared to a commericial AC in 1 M Et₄NBF₄/PC. In addition, the encapsulation strategy improved the supercapacitor stability by preventing the electrode materials from falling apart during the cycling. After 1000 cycles @ 1 A g⁻¹, the capacity retention rate of rGO@CNTs@AC (1000) remained above 90% while that of AC only maintained around 60%. More importantly, the proposed strategy should be applicable to general electrode materials for further improvement as supercapacitors. This work offers a novel bio-inspired strategy to effectively improve the supercapacitor performance by rationally designed hierarchical nanostructures.     

Preparation of sulfonated polysulfone/polysulfone and aminated polysulfone/polysulfone blend membranes

Sulfonation and amination of polysulfone (PSf) were performed in this study to improve the hydrophilicity of PSf membranes. The sulfonated polysulfone (SPSf) and aminated polysulfone (APSf) membranes with a higher degree of reaction exhibited a higher water flux and worse mechanical strength than that of the original PSf membranes. Therefore, SPSf/PSf and APSf/PSf blended membranes were prepared in this study to improve their individual properties. By altering the formulations of casting solutions and forming conditions of the membranes (e.g., blending ratios of both polymers, additives, evaporation time, and gelation temperature), different SPSf/PSf and APSf/PSf blending membranes were prepared; and their performance in water flux and salt rejection were measured and are discussed. A difference in salt rejection was also observed between both SPSf/PSf and APSf/PSf blending membranes that rejected the various salts. Experimental results indicated that water flux increased and salt rejection decreased with an increase of the SPSf/PSf blending ratio from 1: 9 to 2: 1. The order of salt rejection, in which the SPSf/PSf blended membranes rejected four varieties of salts, was Na₂SO₄ > MgSO₄ > NaCl > MgCl₂. Furthermore, the opposite order was obtained by the APSf/PSf blended membranes. © 1996 John Wiley & Sons, Inc.     

Polymer electrolyte membranes based on blends of sulfonated polysulfone and PEO‐grafted polyethersulfone for low temperature water electrolysis

Polymer electrolyte membranes based on blends consisting of polyethylene oxide (PEO) grafted polyether sulfone (PES‐g‐PEO) and sulfonated polysulfone (SPSF(Na)) are prepared and their electrochemical and mechanical properties are investigated with respect to water electrolysis operation. The prepared blends are amorphous; they exhibit high glass transition temperatures and high thermal stability, thus ensuring the dimensional stability under electrolysis cell operation. Because of the presence of the water soluble constituent PES‐g‐PEO, the prepared blend membranes show very high water uptakes, reaching up to 370 wt %. Membrane electrode assemblies are fabricated and evaluated in single cells demonstrating that proton conductivity depends on the PEO‐g‐PES content as well as the PEO molecular weight. Namely, the increased concentration of PES‐g‐PEO leads to increased number of charge carriers, thus result in enhanced ionic conductivity. The use of longer PEO units (MW 5000), due to their improved chain mobility, facilitates the fast proton conduction as well. The maximum proton conductivity value is achieved (1.4 × 10^?2 S cm^?1, 80°C) for the blend with the higher PEO‐g‐PES content (20 wt %) and the higher PEO molecular weight (5000). Under electrolysis cell operation, the above‐mentioned membrane with the lower ohmic resistance shows the best performance, although it is still poor mainly due to the use of Pt as anode. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39922.     

聚砜/改性碳纳米管复合膜的制备及亲水性能

利用浸没沉淀相转化法,以聚砜(PSF)为膜材料,羧基化碳纳米管(MWCNTs-COOH)为添加剂,聚乙烯吡咯烷酮(PVP)为致孔剂,N,N-二甲基乙酰胺(DMAc)为溶剂,制备了聚砜/多壁碳纳米管复合膜,系统研究了制备复合膜时碳纳米管的添加量、预挥发时间以及凝固浴组成对其结构和性能的影响。实验结果表明,添加MWCNTs-COOH后,复合膜的亲水性能和抗污性能显著提高,同时复合膜的力学性能也明显增强。复合膜的 SEM 照片显示,随预挥发时间的延长和凝固浴中DMAc 质量分数的增加,复合膜断面由指状孔结构向海绵状孔结构过渡;复合膜的水通量下降,截留率上升。     

Fabrication of polysulfone nanocomposite membranes with silver‐doped carbon nanotubes and their antifouling performance

In this study, polysulfone (PSf)/silver‐doped carbon nanotube (Ag‐CNT) nanocomposite membranes were prepared by a phase‐inversion technique; they were characterized and evaluated for fouling‐resistant applications with bovine serum albumin (BSA) solutions. Carbon nanotubes were doped with silver nanoparticles via a wet‐impregnation technique. The prepared Ag‐CNT nanotubes were characterized with scanning electron microscopy (SEM)/energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Raman spectroscopy, and thermogravimetric analysis. The fabricated flat‐sheet PSf/Ag‐CNT nanocomposite membranes with different Ag‐CNT loadings were examined for their surface morphology, roughness, hydrophilicity, and mechanical strength with SEM, atomic force microscopy, contact angle measurement, and tensile testing, respectively. The prepared composite membranes displayed a greater rejection of BSA solution (≥90%) and water flux stability during membrane compaction with a 10% reduction in water flux values (up to 0.4% Ag‐CNTs) than the pristine PSf membrane. The PSf nanocomposite membrane with a 0.2% Ag‐CNT loading possessed the highest flux recovery of about 80% and the lowest total membrane resistance of 56% with a reduced irreversible fouling resistance of 21%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44688.     

Obtainment and prospects for the application of thin, multiwalled carbon nanotubes

Technology for obtaining thin, multiwalled carbon nanotubes developed at the Mendeleev University of Chemical Technology, as well as the morphology and certain properties of these tubes are characterized. Methods for activating, functionalizing, and solubilizing these nanotubes are enumerated. Promising directions of their application are characterized.     

Nanocrystalline transition metal oxides and their composites with reduced graphene oxide and carbon nanotubes for photocatalytic applications

Transition metal oxide nanoparticles (CuO, ZnO & Fe₂O₃) and mixed metal oxides CuO. ZnO.Fe₂O₃ were fabricated by facile co-precipitation approach for photocatalytic treatment of organic dyes. The structural features, phase purity, crystallite size and morphology of individual and mixed metal oxides were analysed by X-rays diffraction patterns (XRD) and scanning electron microscopic (SEM) analysis. Electrical behaviour of CuO, ZnO, Fe₂O₃ and mixed metal oxides CuO. ZnO.Fe₂O₃ was explored by current-voltage (I-V) measurements. Functional groups present in the synthesized metal oxides were investigated by Fourier transform infrared spectroscopy (FTIR) which ensures the existence of M-O functional groups in the samples. The optical bandgap analysis was carried out by UV–visible spectroscopic technique which revealed that the blend of three different transition metal oxides reduced the bandgap energy of mixed metal oxides. The reason behind this reduced bandgap energy is formation of new electronic state which arises due to the metal-oxygen interactions. Moreover, the nanocomposites of CuO.ZnO.Fe₂O₃ with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were prepared to study the effect of the carbonaceous materials on the rate of photodegradation. These carbonaceous nanomaterials have plethora properties which can bring advancement in sector of photocatalytic treatment of wastewater. The photocatalytic experiments were performed using methylene blue (MB) as standard dye for comparative study of metal oxides and their composites with rGO and CNTs. The percentage degradation of methylene blue (MB) by nanocomposite CuO.ZnO.Fe₂O₃/rGO is 87% which is prominent among all samples. This result ascribed the photocatalytic aspects of reduced graphene oxide along with mixed metal oxides.     

Preparation of sulfonated polysulfone/sulfonated titanium dioxide hybrid membranes for DMFC applications

Sulfonated titanium dioxide (STiO₂) was prepared by the reaction of TiO₂ with 1,3-propanesultone. Novel STiO₂ incorporated sulfonated poly(aryl ether sulfone) (SPAES) nanocomposite proton exchange membranes (PEMs) were made by solution casting. Fourier transform infrared, X-ray photoelectron spectroscopy, and proton nuclear magnetic resonance indicated the successful preparation of STiO₂ and SPAES. The thermogravimetric analysis and oxidative stability testing results implied that SPAES/STiO₂ membranes had better stability than pristine SPAES membrane. Meanwhile, the scanning electron microscopy spectra exhibited that the introduction of sulfonated groups on the surface of TiO₂ significantly improved its dispersibility in SPAES matrix. More specifically, SPAES membrane incorporated with 2%STiO₂ exhibited higher proton conductivity (60 mS cm⁻¹), lower methanol permeability (2.1 × 10⁻⁷ cm² s⁻¹) and better proton selectivity (28.0 × 10⁴ S s cm⁻³) than that of pure SPAES and SPAES/1%TiO₂ membrane. The SPAES-1%STiO₂ membrane showed better performance in direct methanol fuel cell (DMFC) test than SPAES and Nafion 117 due to the reduction of methanol crossover. From these results, it is evident that SPAES/STiO₂ nanocomposite PEMs have great potential for applications in DMFCs. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48938.     

Synthesis of hydrophobic carbon nanotubes/reduced graphene oxide composite films by flash light irradiation

Carbon nanotubes/graphene composites have superior mechanical, electrical and electrochemistry properties with carbon nanotubes as a hydrophobicity boosting agent. Their extraordinary hydrophobic performance is highly suitable for electrode applications in lithium ion batteries and supercapacitors which often employ organic electrolytes. Also the hydrophobic features enable the oil enrichment for the crude oil separation from seawater. The ever reported synthesis routes towards such a composite either involve complicated multi-step reactions, e.g., chemical vapor depositions, or lead to insufficient extrusion of carbon nanotubes in the chemical reductions of graphene oxide, e.g., fully embedding between the compact graphene oxide sheets. As a consequence, the formation of standalone carbon nanotubes over graphene sheets remains of high interests. Herein we use the facile flash light irradiation method to induce the reduction of graphene oxides in the presence of carbon nanotubes. Photographs, micrographs, X-ray diffraction, infrared spectroscopy and thermogravimetric analysis all indicate that graphene oxides has been reduced. And the contact angle tests confirm the excellent hydrophobic performances of the synthesized carbon nanotube/reduced graphene oxide composite films. This one-step treatment represents a straightforward and high efficiency way for the reduction of carbon nanotubes/graphene oxides composites.

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Thermal and electrical properties of carbon nanotubes based polysulfone nanocomposites

Carbon nanotubes (CNTs)-reinforced polysulfone (PSU) nanocomposites were prepared through solution mixing of PSU and different weight percent of multi-walled carbon nanotubes (MWCNTs). Thermal properties of nanocomposites were characterized using thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA studies revealed an increase in thermal stability of the PSU/MWCNTs nanocomposites, which is due to the hindrance of the nanodispered carbon nanotubes to the thermal transfer in nanocomposites and also due to higher thermal stability of CNTs. Morphological properties of nanocomposites were characterized by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscope (FESEM). The influence of CNTs loading on electrical properties of PSU/MWCNTs nanocomposites was studied by the measurement of AC and DC resistivity. Dielectric study of nanocomposites was carried out at different frequencies (10 Hz–1 MHz) by using LCR meter. An increase in dielectric constant and dielectric loss was observed with increase in CNTs content, which is due to the interfacial polarization between conducting CNTs and PSU.     

Preparation and performance testing of sulfonated poly(phenylene oxide) based composite membranes for nanofiltration

Sulfonated brominated poly(2,6‐dimethyl‐1,4‐phenylene oxide) (SPPOBr) was synthesized by a sequence of bromination and sulfonation. A thin film of SPPOBr was coated on top of a commercial poly(ether sulfone) membrane. Pure butoxyethanol (BE) solvent or a BE/isopropyl alcohol (IPA) solvent mixture was used to dissolve SPPOBr in the coating process. The thin film composite membranes so prepared were then tested for the separation of carbohydrate and electrolyte solutes. We found that the flux and the carbohydrate separation both increased significantly with increasing IPA content in the solvent mixture. However, the separation of electrolyte solutes did not change significantly. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2624–2628, 2004     

Mild sulfonated polyether ketone ether ketone ketone incorporated polysulfone membranes for microbial fuel cell application

To address the impediments of low power generation of Nafion, which is the main hurdle in the commercialization of microbial fuel cells (MFC), the current study focuses on developing a new PEM for MFC from mild sulfonation of PEKEKK with relatively improved physiochemical properties. In this study, mild post sulfonation of a polyether ketone ether ketone ketone (PEKEKK) has been successfully achieved using 98% H2SO4 at 90°C under reflux. 5%–30% (wt%) of sulfonated PEKEKK (SPEKEKK) loaded polysulfone (PSU) composite membranes were fabricated via a solution casting method. Ingeminating evidence of the sulfonation and structure of sulfonated polymer was proved by ¹H NMR peaks integration data and FTIR, respectively. The addition of SPEKEKK to PSU showed significant improvement in conductivity owing to the availability of more protonated sites ( SO3H) and water mediated pathways for the conduction of protons. The composite membrane containing 30 wt% SPEKEKK exhibits the highest conductivity of 0.12 S/cm at 90°C. The water uptakes and swelling ratio of the composite membranes are all higher than that of the pristine PSU membrane and show an increasing trend with increasing SPEKEKK content, thus validating the availability of water domains. Meanwhile, the lowest initial decomposition temperatures assigned to sulfonic acid groups and main chain degradation of the polysulfone/polyether ketone ether ketone ketone (PSU/SPEKEKK) composite membranes occurred at ~300°C and ~500°C respectively, which reflects an excellent thermal stability property. The experimental results indicate that the PSU/SPEKEKK membrane has the potential to greatly enhance the efficiency of MFCs.     

Far-infrared reduced graphene oxide as high performance electrodes for supercapacitors

We report a novel far-infrared (FIR) thermal reduction process to effectively reduce graphene oxide films for supercapacitor electrode applications. The binder-free graphene oxide films used in this study were produced by electro-spray deposition of a graphene oxide colloidal solution onto stainless steel current collectors. The reduction of graphene oxide was performed using a commercial FIR convection oven that is ubiquitous in homes for cooking and heating food. The reduction process incorporated a simple, one-step FIR irradiation carried out in ambient air. Further, the FIR irradiation process was completed in ∼3 min, wherein neither special atmosphere nor high temperature was employed, resulting in an economic, efficient and simplified processing technique. The as-produced FIR graphene electrode gave a specific capacitance of ∼320 F/g at a current density of ∼0.2 A/g with less than 94% loss in specific capacitance over 10,000 charge/discharge cycles. This is one of the best specific capacitances reported for all-carbon electrodes without any additives. Even at ultrafast charge/discharge rates (current densities as high as ∼100 A/g), the FIR graphene electrode still delivered specific capacitances in excess of 90 F/g. The measured energy and power densities of the FIR supercapacitors were found to be ∼3–6 times higher than commercial (activated carbon) supercapacitor devices. This excellent electrochemical performance of the FIR graphene coupled with its ease of production (in air at low temperatures) using a commercial home-use FIR convection oven indicates the significant potential of this concept for large-scale commercial electrochemical supercapacitor applications.     

Molecularly imprinted polymer based on multiwalled carbon nanotubes for ribavirin recognition

The polymorphic transformations (from form II to form I) of three kinds of isotactic poly(1-butene) were characterized by FTIR and by changes in their macroscopic physical and mechanical properties, including density and tensile characteristics. The kinetics of the form II to form I transformation were followed by performing FTIR measurements in real time. At 25?°C, as the crystallization time increased, the characteristic FTIR peak of form I of the poly(1-butene) increased, while that of form II diminished and finally disappeared. The polymorphic transformation from form II to form I of the poly(1-butene) obtained by the solution method (S-PB) occurred the most rapidly, followed by the corresponding transformation for the poly(1-butene) obtained from Mitsui Chemicals (M-PB) and then that for the poly(1-butene) produced using the high-pressure bulk polymerization method (B-PB). This transformation behavior is due to the higher isotacticity of the S-PB, as also demonstrated by the results of the density and tensile tests. The density of S-PB is higher than the densities of M-PB and B-PB due to its greater crystallinity.     

Graphene oxide & reduced graphene oxide polysulfone nanocomposite pellets: An alternative adsorbent of antibiotic pollutant-ciprofloxacin

Efficient nanocomposites, GO-Psf and RGO-Psf has been synthesised from polysulfone and graphene oxide. The synthesised nanomaterials were characterised using contact angle measurements, SEM, TEM, XRD, TGA, DSC, Raman and FT-IR analytical techniques. The reported polymeric nanomaterials are attractive due to their high surface area and thermal stability. The maximum adsorption capacity for ciprofloxacin is 82.781 mg/g and 21.486 mg/g on GO-Psf and RGO-Psf, respectively. The kinetic and adsorption analysis identifies the nanomaterials as attractive adsorbents for removal of antibiotic pollutant, ciprofloxacin from aqueous solution.     

Fabrication and characterization of sulfonated polybenzimidazole/sulfonated imidized graphene oxide hybrid membranes for high temperature proton exchange membrane fuel cells

The sulfonated polybenzimidazole (sPBI)/sulfonated imidized graphene oxide (SIGO) was evaluated to be a potential candidate for high temperature proton exchange membranes fuel cells (HT-PEMFCs). Multifunctionalized covalently bonded SIGO is incorporated in sPBI matrix to resolve the drawbacks such as low proton conductivity, poor water uptake, and ion-exchange capacity (IEC) of sPBI polymer, synthesized by direct polycondensation in phosphoric acid for the application of proton exchange membranes. Strong hydrogen bonding among multifunctional groups established a neighborhood of interconnected hydrophobic graphene sheets and organic polymer chains. It provides hydrophobic–hydrophilic phase separation and facile proton hopping architecture. The optimized sPBI/SIGO (15 wt %) revealed 2.45 meq g⁻¹ IEC; 5.81 mS cm⁻¹ proton conductivity [120 °C and 10% relative humidity (RH)] and 2.45% bound water content. The maximum power density of the sPBI/SIGO-15 membrane was 0.40 W cm⁻² at 160 °C (5% RH) and ambient pressure with stoichiometric feed of H₂/air. This recommends that sPBI/SIGO composite membranes are compatible candidate for HT-PEMFCs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47892.     

The morphology and gas‐separation performance of membranes comprising multiwalled carbon nanotubes/polysulfone–Kapton

The development of desirable chemical structures and properties in nanocomposite membranes involve steps that need to be carefully designed and controlled. This study investigates the effect of adding multiwalled nanotubes (MWNT) on a Kapton–polysulfone composite membrane on the separation of various gas pairs. Data from Fourier transform infrared spectroscopy and scanning electron microscopy confirm that some studies on the Kapton–polysulfone blends are miscible on the molecular level. In fact, the results indicate that the chemical structure of the blend components, the Kapton–polysulfone blend compositions, and the carbon nanotubes play important roles in the transport properties of the resulting membranes. The results of gas permeability tests for the synthesized membranes specify that using a higher percentage of polysulfone (PSF) in blends resulted in membranes with higher ideal selectivity and permeability. Although the addition of nanotubes can increase the permeability of gases, it decreases gas pair selectivity. Furthermore, these outcomes suggest that Kapton–PSF membranes with higher PSF are special candidates for CO₂/CH₄ separation compared to CO₂/N₂ and O₂/N₂ separation. High CH₄, CO₂, N₂, and O₂ permeabilities of 0.35, 6.2, 0.34, and 1.15 bar, respectively, are obtained for the developed Kapton–PSF membranes (25/75%) with the highest percentage of carbon nanotubes (8%), whose values are the highest among all the resultant membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43839.