High flux nanofiltration membranes based on interfacially polymerized polyamide barrier layer on polyacrylonitrile nanofibrous scaffolds

Electrospun polyacrylonitrile (PAN) nanofibrous scaffold was used as a mid-layer support in a new kind of high flux thin film nanofibrous composite (TFNC) membranes for nanofiltration (NF) applications. The top barrier layer was produced by interfacial polymerization of polyamides containing different ratios of piperazine and bipiperidine. The filtration performance (i.e., permeate flux and rejection) of TFNC membranes based on electrospun PAN nanofibrous scaffold was compared with those of conventional thin film composite (TFC) membranes consisting of (1) a commercial PAN ultrafiltration (UF) support with the same barrier layer coating and (2) two kinds of commercial NF membranes (i.e., NF90 and NF270 from Dow Filmtec). The nanofiltration test was carried out by using a divalent salt solution (MgSO₄, 2000 ppm) and a cross-flow filtration cell. The results indicated that TFNC membranes exhibited over 2.4 times more permeate flux than TFC membranes with the same chemical compositions, while maintaining the same rejection rate (ca. 98%). In addition, the permeate flux of hand-cast TFNC membranes was about 38% higher than commercial NF270 membrane with the similar rejection rate.     

The role of bentonite addition in UF flux enhancement mechanisms for oil/water emulsion

The main problem in treating oil/water emulsion from car wash waste-water by ultrafiltration (UF) is fouling caused by oil adsorption on the membrane surface and internal pore walls. This study demonstrates that the addition of bentonite clay can reduce the adsorption layer on cellulose acetate UF membrane, resulting in a reduction of total membrane resistance (R_t). Experiments were conducted to identify and describe three possible mechanisms: (i) bulk oil emulsion concentration reduction; (ii) particle aggregation and (iii) detachment of the adsorbed gel layer by shear force. Adsorption of oil emulsion by bentonite can lead to a significant reduction of bulk oil emulsion concentration, one of the major causes of flux enhancement. Results show that contact of oil emulsion with bentonite forms larger particles resulting in flux increment. An optimum particle size of 37 μm, corresponds with a bentonite concentration of 300 mg/l and provided the highest flux. Beyond this limiting concentration, flux improvement gradually declined, possibly due to the formation of packed cake of particles on the membrane surface. The presence of bentonite in the oil emulsion promotes high shear stress which acts against the gel layer. This high shear stress, caused by bentonite particles and cross-flow velocity, reverses the adsorbed gel layer to the bulk of the liquid phase.     

Hydrophilic nanofiltration membranes with self-polymerized and strongly-adhered polydopamine as separating layer

Inspired by the self-polymerization and strong adhesion characteristics of dopamine in aqueous conditions,a novel hydrophilic nanofiltration（NF） membrane was fabricated by simply dipping polysulfone（PSf） ultrafiltration（UF） substrate in dopamine solution.The changes in surface chemical composition and morphology of membranes were determined by Fourier transform infrared spectroscopy（FTIR-ATR）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM） and atomic force microscopy（AFM）.The experimental results indicated that the self-polymerized dopamine formed an ultrathin and defect-free barrier layer on the PSf UF membrane.The surface hydrophilicity of membranes was evaluated through water contact angle measurements.It was found that membrane hydrophilicity was significantly improved after coating a polydopamine（pDA） layer,especially after double coating.The dyes filtration experiments showed that the double-coated membranes were able to reject completely the dyes of brilliant blue,congo red and methyl orange with a pure water flux of 83.7 L/（m²·h） under 0.6 MPa.The zeta potential determination revealed the positively-charged characteristics of PSf/pDA composite membrane in NF process.The salt rejection of the membranes was characterized by 0.01 mmol/L of salts filtration experiment.It was demonstrated that the salts rejections followed the sequence:NaCl2SO₄422,and the rejection to CaCl₂ reached 68.7%.Moreover,the composite NF membranes showed a good stability in water-phase filtration process.     

Tailoring polyethersulfone/quaternary ammonium polysulfone ultrafiltration membrane with positive charge for dye and salt selective separation

Polyethersulfone (PES)/quaternary ammonium polysulfone (QAPSf) blend ultrafiltration (UF) membranes with positive charge were fabricated by nonsolvent induced phase separation (NIPS) for use in dye and salt selective separation. QAPSf was synthesized by nucleophilic substitution with chloromethylated polysulfone (CMPSf). The effect of the PES/QAPSf mass ratio on the morphology and performance of blend UF membranes were studied. The membranes' zeta potentials gradually changed from negative to positive with decreases in the PES/QAPSf mass ratio. At PES/QAPSf mass ratios of 30:70 and 10:90, the zeta potentials of the membranes reached +1.8 mV and + 5.9 mV, respectively. Additionally, the contact angles of the membranes decreased from 74° to 52° as the QAPSf content increased from 0 wt% to 90 wt%. Furthermore, the membrane with a PES/QAPSf mass ratio of 30:70 showed a high water permeance (181.4 LMH bar⁻¹) and excellent dye and salt selective separation performance. The rejection ratios reached 99.1%, 87.8%, 99.6%, and 92.4% for dyes Congo red, methyl blue, Alixin blue 8GX, and basic blue 24, respectively, while those for salts Na₂SO₄, MgSO₄, MgCl₂, and NaCl were ≤ 10%. In addition, the PES/QAPSf membranes showed excellent antifouling performance and good operating stability with dye-salt mixtures of various pHs and salt concentrations.     

Structure and properties of gel-spun ultra-high molecular weight polyethylene fibers with high gel solution concentration

The gel-spun ultra-high molecular weight polyethylene(UHMWPE) fibers were prepared at the industrial production line with different gel solution concentrations of 15 wt%, 18 wt% and 24 wt%. The difference in ultimate structure and mechanical properties of UHMWPE fibers for different gel solution concentrations were analyzed by tensile testing, differential scanning calorimetry(DSC), wide angle X-ray diffraction(WAXD) and small angle X-ray scattering(SAXS). With the increase of gel solution concentration, the ultimate mechanical properties of UHMWPE fibers were decreased and the crystallization and orientation of UHMWPE fibers became inferior. Besides, both the average shish length(〈L _(shish)〉) and shish misorientation(B_φ) of UHMWPE fibers were decreased with the increase of gel solution concentration. In addition, the appropriate increase of spinning temperature led to the further optimization of the ultimate structure and mechanical properties of UHMWPE fibers.     

Effect of gelatin on properties of <Emphasis Type="Italic">Luciola mingrelica</Emphasis> firefly luciferase

An ATP-reagent containing thermostable mutant of Luciola mingrelica firefly luciferase, MgSO₄, components of buffer solution, and stabilizers, which is widely used to detect nano- and picomolar concentrations of adenosine-5′-triphosphate (ATP) in various biological samples, is been object of this study. The activity, stability, and analytical characteristics of the ATP-reagent have been assessed in the presence and absence of 5% gelatin and in gelatin gel. The solution of ATP-reagent was obtained at 30°C and a gelatin concentration of 5%, while gel formation occurred at 22°C. The gelatin addition decreased the activity and stability of luciferase slightly. The sensitivity of ATP detection (above 0.96) did not depend on the gelatin presence and the aggregate state of the disperse system. Limits of detection were 2 × 10⁻¹², 7 × 10⁻¹³, and 7 × 10⁻¹⁴ M ATP, when the ATP-reagent was used in gelatin films and in the solution in the presence of 5% gelatin and in the absence, respectively. It was shown that the storage of ATP-reagent in gelatin gel not only preserved enzymatic activity, but protected the enzyme from bacterial contamination, which was the cause of the enzyme activity loss.     

GelatinnZn(CF3SO3)2 Polymer Electrolytes for Electrochromic Devices

The present work is focused on gelatin‐based electrolytes doped with a range of concentration of zinc triflate (Zn(CF₃SO₃)₂). The transparent‐thin‐film samples have been represented by the notation Gelatin_nZn(CF₃SO₃)₂, where n represents the zinc triflate salt concentration in the electrolyte membranes from 0.00 wt% to 10.93 wt% . The samples have been characterized by conductivity measurements, thermal analysis, cyclic voltammetry, X‐ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The gelatin‐based electrolytes were also tested as ionic conductors in electrochromic devices with the glass/ITO/WO₃/gelatin‐based electrolyte/CeO₂‐TiO₂/ITO/glass configuration.     

Drying dissipative structures of arrowroot starch

Macroscopic and microscopic drying patterns of arrowroot starch (ARS) in diluted aqueous solution and gel state were investigated on a cover glass in order to know the molecular information of ARS and their interaction with the substrate. Thickness profiles of the dried film showed coexistence of the rather sharp broad ring and the very broad accumulation at the outside edge and the inner region, respectively. The sharpness parameters, S values from the outside peaks decreased sharply from 100 to 3 as initial concentration increased from 0.04 to 3 wt%. Furthermore, very low S values between one and two originating from the round hills were also observed at low concentrations, 0.04 to 0.2 wt%. The results support that stable gelation of ARS molecules does not take place at the ARS concentrations lower than ca. 2 wt% at 20 °C. It is highly plausible that ARS molecules existing near the substrate surface are adsorbed strongly on the substrate. Gelation of ARS molecules took place rapidly above 2 wt%. The S values increased sharply from 3 to 15 with increasing temperature from 5 to 20 °C, and kept constant around 15 at the higher temperatures up to 50 °C. Convectional diffusion of ARS decreased in the order of ARS > gelatin > poly (N-butyl acrylate), when comparison was made at the same weight percent at the lower concentrations than ca. 2 wt%. Above the concentration, stable gel structures of ARS were formed.     

Effect of engineered PLGA‐gelatin‐chitosan/PLGA‐gelatin/PLGA‐gelatin‐graphene three‐layer scaffold on adhesion/proliferation of HUVECs

A three‐layered fibrous scaffold composed of fibers of different diameters in each layer was fabricated in correspondence with the structure of the blood vessels. Effect of solution and electrospinning parameters on morphology and diameters of the fibers were investigated by scanning electron microscopy (SEM), for each layer. The SEM images showed that 18% poly (lactic‐co‐glycolic acid) (PLGA)‐gelatin‐chitosan in 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP)/acid acetic solution resulted in bead‐free fibers for the outer layer. For the middle layer, 18% PLGA‐gelatin in HFIP at 13 kV with 13 cm needle to collector distance was chosen as the optimum condition. SEM imaging demonstrated that by increasing graphene content from 0.5 to 2 wt% in the inner layer (as an electrically conductive/platelet anti‐adhesion material), the fiber diameter decreased from 324.01 ± 58.90 to 288.59 ± 70.77 nm. The effect of gelatin crosslinking on the microstructure of the fibers was also examined. Shrinkage ratio decreased from 57 to below 21% upon crosslinking of the three‐layered scaffold in exposure to vapor of 50% glutaraldehyde solution for 2 hours. Mechanical test showed that tensile strength of the crosslinked three‐layer scaffold in the longitudinal direction was 2.90 MPa which is comparable to that of the vein and artery. The MTT [3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide] assay displayed cell viability of above 96% for the PLGA‐gelatin containing 2 wt% graphene. SEM analysis revealed that the addition of graphene to PLGA‐gelatin (up to 2%) causes a remarkable improvement in cell adhesion.     

Concentration of potassium cations in the permeate solution in the presence of N,N-dimethyl-N-2-propenyl-2-propen-1-aminium chloride homopolymer using dead-end nano-or ultrafiltration

The investigation is based on the nano-or ultrafiltration of inorganic salts in the presence of a polyelectrolyte in the feed solution. Cellulose acetate membranes are selected with a pore size of 10–20 nm. The membranes are imaged using atomic force microscope. The membrane is completely impermeable to the polyelectrolyte. Polyelectrolyte concentrations are taken in the range of 0.5–1 g/l to avoid a gel layer formation over the membrane. It is discovered that, at such low polyelectrolyte concentration, inorganic salt concentration in the permeate is higher than in the feed solution. This process therefore deviates from conventional membrane separation processes, where the permeate salt concentration is lower or equal to the salt concentration in the feed solution. It is shown that during the nano-or ultrafiltration of inorganic salts in the presence of polyelectrolyte, the ratio of salt concentration in the permeate to feed increases when the initial salt concentration in the feed solution is low. Concentration polarization has a negative impact on this concentrating effect. In the case of this investigation, KCl, KNO₃, K₂SO₄ are taken as inorganic salts, N,N-dimethyl-N-2-propenyl-2-propen-1-aminium chloride homopolymer is selected as a polyelectrolyte. The text was submitted by the authors in English.     

A unified model for flux prediction during batch cell ultrafiltration

An analysis of the flux decline encountered during ultrafiltration (UF) in a batch cell is presented by including the combined influence of the osmotic pressure and the gel layer. A predictive model for the flux decline in unstirred and stirred batch cell UF processes is developed by unifying the osmotic pressure and gel layer models. UF experiments were performed in a batch cell with polymeric solutes (PEG, dextran and PVA) and a protein (BSA), ranging widely in molecular weights and physico-chemical properties, under various operating conditions (pressure, solution pH, and stirrer speed). The present unified model predictions match closely with the experimental flux behaviour for all cases, while individual osmotic pressure and gel layer models are found to be inadequate.     

Cutoff performance of Escherichia coli by charged and noncharged polyacrylonitrile ultrafiltration membranes

Cutoff performance of Escherichia coli (E. coli) was studied by three types of polyacrylonitrile (PAN) ultrafiltration (UF) membranes without and with charge groups of sulfonate sodium salt (SSS) and trimethylammonium chloride (TMA). These UF membranes were prepared by phase inversion method in water coagulation bath with various concentrations of dimethylsulfoxide (DMSO) and used for the E. coli cutoff experiments under 2.5 kPa applied pressure. With the increase of the polymer concentration in the DMSO cast solution, the pore size of the molecular size exclusion effect of the resultant UF membrane decreased. For UF experiments of E. coli suspension solution with 10⁷ colony forming unit/unit volume (cfu/ml), the permeability of the bacteria through the membrane was in the range of about 10⁻³% in PAN homopolymer membranes. It was found that E. coli permeation through copolymer UF membranes with SSS and TMA groups was completely restricted. Difference of the E. coli cutoff performance in these UF membranes was discussed in comparison with membrane filtration properties such as molecular sieve effect, permeation rate of solute and membrane morphology.     

Cloud points and phase separation of aqueous poly(N-vinylacetamide) solutions in the presence of salts

Aqueous poly(N-vinylacetamide) (PNVA) solution was found to exhibit the cloud point in the presence of salt. This cloud point was shown to correspond to a liquid-liquid phase separation, as confirmed when the PNVA-salt solutions were maintained at a temperature above the cloud point. The upper layer had a higher polymer concentration and a lower salt concentration than those in the lower layer. Thus interaction between PNVA and salts are repulsive. The lower critical solution temperatures were estimated to be 18±1°C for 1.25 molal (NH₄)₂SO₄ and 25±1°C for 0.76 molal Na₂SO₄. Divalent anions such as SO _2– ⁴ , SO _2– ³ , HPO _2– ⁴ and CO _2– ³ were effective in causing turbidity when examined at 25°C. Dependence of the effect on the cationic species was similar to but significantly different from that for acetyltetraglycine ethylester. The cloud points of PNVA decreased linearly with the increase of the polymer concentration at a fixed salt concentration or with the increase of the salt concentration at a fixed polymer concentration. A parameter analogous to the salting-out constant was empirically derived from the dependencies of the cloud points on the concentrations of polymer and salt.     

Effect of preparation variables on morphology and pure water permeation flux through asymmetric cellulose acetate membranes

In this study, cellulose acetate (CA) ultrafiltration (UF) membranes were prepared using the phase inversion method. Effects of CA and polyethylene glycol (PEG) concentrations in the casting solution and coagulation bath temperature (CBT) on morphology of the synthesized membranes were investigated. Based on L₉ orthogonal array of Taguchi experimental design 18 membranes were synthesized (with two replications) and pure water permeation flux through them were measured. It was found out that increasing PEG concentration in the casting solution and CBT, accelerate diffusional exchange rate of solvent 1-methyl-2-pyrrolidone (NMP) and nonsolvent (water) and consequently facilitate formation of macrovoids in the membrane structure. Increasing CA concentration, however, slows down the demixing process. This prevents instantaneous growth of nucleuses in the membrane structure. Hence, a large number of small nucleuses are created and distributed throughout the polymer film and denser membranes are synthesized. Rate of water flux through the synthesized membranes is directly dependent on the size and number of macrovoids in the membrane structure. Thus, maximum value of flux is obtained at the highest levels of PEG concentration and CBT (10 wt.% and 23 °C, respectively) and the lowest level of CA concentration (13.5 wt.%). Analysis of variance (ANOVA) showed that all parameters have significant effects on the response. However, CBT is the less influential factor than CA and PEG concentrations on the response (flux).     

Hierarchical Tubular Structures Grown from the Gel/Liquid Interface

Three dimensional hierarchical materials are widespread in nature but are difficult to synthesize by using self‐assembly/organization. Here, we employ a gel–liquid interface to obtain centimeter‐long ～100 μm diameter tubes with complex mineral wall structures that grow from the interface into solution. The gel, made from gelatin, is loaded with metal chloride salt, whereas the solution is a high pH anion source. Tubes were obtained with a range of cations (Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺, and Zn²⁺) and anions (CO₃^2? and PO₄^3?). The crystalline phases found in the tube walls corresponded to expectations from solution chemistries and phase solubilities. The growth mechanism is found to be akin to that of chemical gardens. The divalent cations modify the strength of the gelatin gel in a manner that involves not only simple electrostatic screening, but also ion‐specific effects. Thus, tubes were not obtained for those ions and/or concentrations that significantly changed the gel’s mechanical structure. At high Cu²⁺ loading, for example, vertical convection bands, not Liesegang bands, were observed in the gels.     

Diffusion of sodium dodecyl sulfate micelles in agarose gels

The gradient diffusion of ionic sodium dodecyl sulfate micelles in agarose gel was investigated at moderate concentrations above the CMC. Of particular interest were the effects of micelle, gel, and sodium chloride concentration on the micelle diffusivity. Holographic interferometry was used to measure the gradient diffusion coefficient at three sodium chloride concentrations (0, 0.03, 0.10 M), three gel concentrations (0, 1, 2 wt%), and several surfactant concentrations. Time-resolved fluorescence quenching was used to measure aggregation numbers both in solution and gel. The micelle diffusivity increased linearly with surfactant concentration at the two larger sodium chloride concentrations and all gel concentrations. In general, the strength of this effect increased with decreasing sodium chloride concentration and increased with gel concentration. This behavior is evidence of decreasing micelle-micelle electrostatic interactions with increasing sodium chloride concentrations, and increasing excluded volume effects and hydrodynamic screening with increasing gel concentration, respectively. The only exception was at 0.1M sodium chloride and 2 wt% agarose, which showed a slight reduction in the slope compared to 1 wt% agarose. It was found that the concentration effect is quite strong for charged solutes: at a NaCl concentration of 0.03 M in a 2% agarose gel, in a solution with 3% SDS micelles by volume, the micelle diffusion coefficient is doubled relative to its value in the same gel at infinite dilution. The extrapolated, infinite-dilution diffusion coefficients and the rate at which the micelle diffusivity increased with surfactant concentration were compared with predictions of previously published theories in which the micelles are treated as charged, colloidal spheres and the gel as a Brinkman medium. The experimental data and theoretical predictions were in good agreement.     

Unsteady state flux response: a method to determine the nature of the solute and gel layer in membrane filtration

The unsteady-state permeate flux response to a step change in transmembrane pressure is shown to result in unique flux–pressure profiles for the three types of solutes common in membrane ultrafiltration (UF): (a) solutes which exert an osmotic pressure but do not form a ‘gel’; (b) solutes which do not exert an osmotic pressure but form a ‘gel’ and (c) solutes which exert an osmotic pressure and also form a ‘gel’. It is also shown that for stirred cell UF, changes in the bulk feed solution properties (concentration, volume) are negligible on the time scale needed to attain a stable permeate flux. Unsteady-state permeate flux measurements could therefore be made at short filtration times so that the results would not be masked by changes in bulk properties.     

Synthesis of nanosized BaSO4 particles with a membrane reactor: effects of operating parameters on particles

Nanosized BaSO₄ particles were synthesized successfully by a membrane reactor, in which Na₂SO₄ solution permeated through the micropores of ultrafiltration (UF) membrane gradually into BaCl₂ solution to control the saturation ratio, nucleation and growth rates. The effects of membrane molecular weight cut-off (MWCO), temperature, transmembrane pressure and reactant concentration on the particles morphology were investigated. The results reveal that the products tend from nanoparticles towards aggregates with the increase in membrane MWCO and reactant concentrations. Higher temperature favors the synthesis of regular particles. Transmembrane pressure does not show significant influences on the particles under the experimental conditions.     

Dispersion stability and aggregation behavior of TEMPO-oxidized cellulose nanofibrils in water as a function of salt addition

Dispersion stability of TEMPO-oxidized cellulose nanofibrils (TOCNs) in water was investigated through both experimental and theoretical analyses to elucidate the critical aggregation concentration of different salts. The 0.1 wt% TOCN/water dispersions with various NaCl concentrations were evaluated by measuring light transmittance, viscosity under steady-shear flow, and the weight fraction of TOCN that had aggregated. Homogeneous TOCN/water dispersion turned to gel as the NaCl concentration increased. The TOCN dispersion maintained its homogeneous state up to 50 mM NaCl, but aggregated gel particles were formed at 100 mM NaCl. The mixture became separated into two phases (gel and supernatant) at ≥200 mM NaCl. Theoretical analysis using ζ-potentials of TOCN elements in the dispersions revealed that the aggregation behavior upon NaCl addition could be explained well in terms of the interaction potential energy between two cylindrical rods based on the Derjaguin–Landau–Verwey–Overbeek theory. The experiments were extended to analyze critical aggregation concentrations of MgCl₂ and CaCl₂ for the 0.1 wt% TOCN dispersion. In the case of divalent electrolytes, TOCN elements began to form aggregated gel particles at salt concentrations of 2–4 mM, corresponding to the critical aggregation concentration predicted by the empirical Schultz-Hardy rule.     

Enhancing the performance of TFC nanofiltration membranes by adding organic acids in polysulfone support layer

Throughout this study, the effect of certain organic acids, methacrylic acid, lactic acid and tartaric acid, doped in polysulfone (PSF) casting solution onto the performance of nanofiltration (NF) membranes was investigated. Different NF membranes have been prepared from m-phenylenediamine and trimesoylchloride onto the top surface of the acid-modified PSF membranes through regulating the concentration and contact time of the conventional interfacial polymerization process. The study of scanning electron microscopy (SEM) was used to investigate the influence of acids on the morphology of membranes and cross-sectional structures. The functional groups, hydroxyl and carboxylic acid, of the acids have resulted in a significant increase in membrane thickness, porosity and hydrophilicity, with a decrease in macrovoid capacity of the PSF layer. The acid-modified PSF/TFC membranes showed higher rejection of salt, with an increment in water flux compared to the neat membrane. Water flux and salt rejection (R_s %) of the control membrane was 7.6 L/m² h and 65.4%, whereas polysulfone/methacrylic acid (PSF/MAAc), polysulfone/tartaric acid (PSF/TAc), and polysulfone/lactic acid (PSF/LAc) were 16.8, 18.5, and 20.2 L/m² h and 88, 88.2 and 94.1%, respectively. Efficiency of prepared NF membranes under various inlet pressures and specific salts was investigated with selectivity and salt rejection. The salt rejection of a mixed salt solution was found to meet the order of R_s % CaSO₄ ≥ R_s % Na₂SO₄ ˃ R_s % MgSO₄ ˃ R_s MgCl₂ ˃ Rs % NaCl.