Study of the Selectivity of SnO2 Supported Membranes Prepared by a Sol-Gel Route

In this work the sol-gel process was used to prepare SnO2 supported membranes with an average pore size of 2.5 nm. The effects of salt concentration (NaCl or CaCl2) and of the pH of the aqueous solutions used on the flux and selectivity through the SnO2 membrane were analyzed by permeation experiments and the results interpreted taking account of the zeta potential values determined from the electrophoretic mobility of the SnO2 powder aqueous dispersion. The results show that the ion flux (Na+, Ca2+ and Cl–) throughout the membrane is determined by the electrostatic repulsion among these species and the surface charge at the tin oxide-solution interface.     

Protein type effects on steady-state crossflow membrane ultrafiltration fluxes and protein transmission

The permeate fluxes and percent protein transmission were evaluated for steady-state crossflow ultrafiltration of two proteins of different composition: bovine serum albumin (BSA), containing fatty acid, and “fatty-acid-poor” BSA, from which most of the fatty acids had been removed (BSA/FAP). The influences of protein concentration up to 6.5 percent w/v, transmembrane pressure, ionic environment and membrane type (i.e. nominal molecular weight cut-off) were investigated. For both BSA and BSA/FAP, the fluxes and the protein transmission were dependent on the amount of salt present. The higher fatty acid content in the BSA apparently enhanced protein-protein interaction, resulting in a more cohesive and resistant fouling layer; permeate fluxes were lower with BSA/FAP than with BSA at otherwise corresponding operating conditions. A hysteresis behaviour of the flux (J)-transmembrane pressure (TMP) relationship was observed whenever the ultrafiltration unit was operated at a TMP less than some higher value to which the membrane previously had been exposed.     

微波辅助对生物溶液超滤过程的影响

为验证微波场强化植物提取的"膜超滤"假说机理,以聚醚砜超滤膜为研究对象,以膜通量为考察指标,结合膜和黄芪饮片显微结构的扫描电镜(SEM)表征,讨论了微波辐射对黄芪水提液超滤过程的影响。结果表明,驱动压力相同,微波辅助超滤30 min时,膜通量下降到初始值的57.36%,且膜表面观察不到凝胶层;而常规超滤30 min,膜通量已下降到初始值的30.29%,且膜表面覆盖一层约20μm的凝胶层。说明微波辐射能够减弱浓差极化现象,促进膜超滤过程中的物质传递。     

Water-Soluble Polymers and Their Polymer-Metal Ion-Complexes as Antibacterial Agents

Summary: Natural and synthetic polymers with heteroatom, such as oxygen, nitrogen, sulfur or phosphorous, potentially can efficiently remove metal ions from aqueous solutions. The ability of synthetic polymers derived from imino diacetic acid, acrylamido glycolic copolymer, and the natural polymer alginic acid to remove metal ions from dilute solution in conjunction with ultrafiltration membranes was studied. The maximum retention capacity was determined and its polymer-metal ion-complexes were studied as possible antibacterial agents.     

Fabrication,characterization, and performance evaluation of polyethersulfone/TiO2 nanocomposite ultrafiltration membranes for produced water treatment

In the present work, development of neat and nanocomposite polyethersulfone membranes composed of TiO₂ nanoparticles is presented. Membranes are fabricated using nonsolvent phase inversion process with the objective of improving antifouling, hydrophilicity, and mechanical properties for real and synthetic produced water treatment. Membranes are characterized using scanning electron microscopy, Fourier‐transform infrared, contact angle, porosity measurement, compaction factor, nanoparticles stability, and mechanical strength. The performance of prepared membranes was also characterized using flux measurement and oil rejection. Fourier‐transform infrared spectra indicated that noncovalence bond formed between Ti and polyethersulfone chains. The contact angle results confirmed the improved hydrophilicity of nanocomposite membranes upon addition of TiO₂ nanoparticles owing to the strong interactions between fillers and water molecules. The increased water flux for nanocomposite membranes in comparison with neat ones can be due to coupling effects of improved surface hydrophilicity, higher porosity, and formation of macrovoids in the membrane structure. The membrane containing 7 wt% of TiO₂ nanoparticles was the best nanocomposite membrane because of its high oil rejection, water flux, antifouling properties, and mechanical stability. The pure water flux for this membrane was twice greater than that of neat membrane without any loss in oil rejection. The hydrophilicity and antifouling resistance against oil nominates developed nanocomposite membranes for real and synthetic produced water treatment applications with high performance and extended life span.     

In vitro screening and isolation of human aromatase inhibitors from Cicer arietinum by a novel continuous online method combining chromatographic techniques

Ultrafiltration liquid chromatography with mass spectrometry can efficiently and rapidly screen and identify ligands from the seeds of Cicer arietinum for human aromatase. Using this method, we identified 11 major compounds, including organic acids, organic acid glycosides, flavone glycosides, isoflavones, and isoflavone glycosides, as potent human aromatase inhibitors. A continuous online method, including pressurized liquid extraction, countercurrent chromatography, and preparative liquid chromatography, was developed for scaling up the production of these compounds with high purity and efficiency. The bioactivity of the separated compounds was assessed by an in vitro enzyme inhibition assay. This novel approach using a combination of ultrafiltration liquid chromatography with mass spectrometry and pressurized liquid extraction with countercurrent chromatography and preparative liquid chromatography as well as an in vitro enzyme inhibition assay could be applied to efficiently screen and isolate human aromatase inhibitors from complex samples and to the large‐scale production of functional food and nutraceutical ingredients.     

Free-solvent model shows osmotic pressure is the dominant factor in limiting flux during protein ultrafiltration

In protein ultrafiltration (UF), the limiting flux phenomenon has been generally considered a consequence of the presence of membrane fouling or the perceived formation of a cake/gel layer that develops at high operating pressures. Subsequently, numerous theoretical models on gel/cake physics have been made to address how these factors can result in limiting flux. In a paradigm shift, the present article reestablishes the significance of osmotic pressure by examining its contribution to limiting flux in the framework of the recently developed free solvent osmotic pressure model. The resulting free-solvent-based flux model (FSB) uses the Kedem–Katchalsky model, film theory and the free solvent representation for osmotic pressure in its development. Single protein tangential-flow diafiltration experiments (30 kDa MWCO CRC membranes) were also conducted using ovalbumin (OVA, 45 kDa), bovine serum albumin (BSA, 69 kDa), and immuno-gamma globulin (IgG, 155 kDa) in moderate NaCl buffered solutions at pH 4.5, 5.4, 7 and 7.4. The membrane was preconditioned to minimize membrane fouling development during the experimental procedure. The pressure was randomly selected and flux and sieving were determined. The experimental results clearly demonstrated that the limiting flux phenomenon is not dominated by membrane fouling and the FSB model theoretically illustrates that osmotic pressure is the primary factor in limiting flux during UF. The FSB model provides excellent agreement with the experimental results while producing realistic protein wall concentrations. In addition, the pH dependence of the limiting flux is shown to correlate to the pH dependency of the specific protein diffusion coefficient.     

Copper recovery by polymer enhanced ultrafiltration (PEUF) and electrochemical regeneration

In this work, the removal of Cu²⁺ from a synthetic effluent has been tested by means of polymer enhanced ultrafiltration (PEUF), using partially ethoxylated polyethylenimine (PEPEI) as water-soluble polymer. Overall, the two necessary steps of a hypothetical continuous process, metal retention (in total recirculation and discontinuous mode) and polymer regeneration (in discontinuous mode), have been confronted individually. On the one hand, the values of temperature (T), transmembrane pressure (ΔP), metal–polymer ratio and pH that maximize both, permeate fluxes and rejection coefficients, have been obtained by ultrafiltration tests, reaching Cu²⁺ retention coefficients higher than 97%. On the other hand, the polymer regeneration step has been carried out by the electrochemical technique, which consists in the metal electrodeposition on the cathode of an electrochemical cell. In a first step, cyclic voltammetries have been carried out to assure the polymer does not suffer any oxidation or reduction process. From these tests, a cathodic working potential has been selected to minimize hydrogen evolution reaction (−0.7 V vs. Ag/AgCl). Working at this voltage in deposition tests, a pH of 3.3 has been selected from experiments at different pH values. This pH is less extreme than the pH necessary if this step was carried out chemically (pH 2).     

Performance improvement of polysulfone ultrafiltration membrane by blending with polyaniline nanofibers

Polyaniline (PANI) nanofibers were used to improve hydrophilic property and permeability of polysulfone (PS) membrane. PS membrane and PS/PANI nanofibers blended membranes with different PANI–PS mass ratios (1, 5, 10, and 15 wt.%) were prepared by phase inversion process. The blended membranes showed similar bovine serum albumin (BSA) and albumin egg (AE) rejections to PS membrane. The blended membranes had larger porosity and better hydrophilic property than PS membrane, which caused the improvement of their permeability. Pure water fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 1.6 and 2.4 times that of PS membrane, respectively. During the filtration of BSA solution, the blended membranes had slower flux decline rate than PS membrane. Moreover, stable permeate fluxes of the blended membranes with PANI–PS mass ratios of 1 and 15 wt.% were 2.0 and 2.5 times that of PS membrane, respectively. Compared with PS membrane, mechanical property and thermal stability of the blended membranes with less PANI–PS mass ratio, e.g. 1 wt.%, had no obvious change. For the blended membrane with PANI–PS mass ratio of 15 wt.%, breaking strength increased 28% and elongation at break decreased 30.6%.     

Double-pass casting: A novel technique for developing high performance ultrafiltration membranes

Double-pass casting was evaluated as a technique to overcome hard-to-cast membranes or hard-to-mix solutions. Two types of polyethersulfone (PES) membranes were tested, one incorporating a hydrophilic surface modifying additive and the other with a hydrophobic one. It was found that the morphological improvement was more obvious for hydrophobic membranes since their solutions were not completely homogenous and hard-to-cast. The double-pass hydrophobic membranes had smoother surfaces and more porous support layers, resulting in higher fluxes, higher volume of treated water (67.4% increase) but decreased natural organic matters (NOM) rejection. The new casting approach produced hydrophilic membranes having a spongy structure (as opposed to finger-like cavities), yet they had similar NOM rejection, a 12.4% higher flux than the single-pass membranes prepared from the same dope. This is attributed to the quite homogenous hydrophilic casting solutions and to the performance of the original hydrophilic membranes (single-pass casting) that was relatively good.