Commercial Polyethersulfone Ultrafiltration Membrane Research Articles

Adsorption of steroid hormone micropollutant by polyethersulfone ultrafiltration membranes with varying morphology

The effective removal of micropollutants necessitates the use of dense membranes, such as thin-film composite (TFC) reverse osmosis (RO) and nanofiltration (NF) membranes. TFCs have a polyamide active layer interfacially polymerized on a support layer that is typically made of polysulfone (PSu) or polyethersulfone (PES). Retention by NF and RO is often incomplete because micropollutants are adsorbed to the polymer material and subsequently permeate via a combination of convection and diffusion, which evidences a breakthrough curve. When describing breakthrough phenomena, the role of the support membrane is commonly neglected, even though the adsorption in this layer can be significant. This work investigated the adsorption of steroid hormone micropollutants (17β-estradiol, E2) by fabricated and commercial PES ultrafiltration membranes with varying morphology.By increasing the coagulation bath temperature between 10 and 70 °C, the pure water permeability increased from 13 to 3800 L/m2·h−1·bar−1, and consequently, the average pore size rose from 12 to 191 nm. The fabricated membranes with smaller pore sizes showed higher E2 removal via adsorption which can be attributed to the higher internal surface area. The adsorbed mass of fabricated PES membranes (using dimethylformamide (coded as PDG) and N-methyl-2-pyrrolidone (coded as PNG) and PES (Istanbul Technical University (ITU), with non-woven supports) varies from 0.30 to 0.60, 0.27–0.60 and 1–1.2 ng·cm−2, respectively. These values are lower than the adsorbed masses with commercial Biomax (Millipore Inc.) membranes (0.5–2.0 ng·cm−2). Ultrafiltration membranes used as support for composite membranes, nanofiltration or as filters in sample preparation benefit from lower micropollutant adsorption.

Nanofiltration Performance of Poly(p-xylylene) Nanofilms with Imidazole Side Chains.

Herein, we report the nanofiltration performance of poly(p-xylylene) thin films with imidazole side chains that were deposited onto commercial polyethersulfone ultrafiltration membranes using a chemical vapor deposition process. The resulting thin films with a few tens of nanometers exhibited water permeation under a pressure difference of 0.5 MPa and selectively rejected water-soluble organic dyes based on their molecular sizes. Additionally, thin flaky ZIF-L crystals (Zn(mim)2·(Hmim)1/2·(H2O)3/2) (Hmim = 2-methylimidazole) formed on the surface of imidazole-containing poly(p-xylylene) films, and the composite films demonstrated the ability to adsorb methylene blue molecules within the cavities of ZIF-L.

Vanillin as an Antifouling and Hydrophilicity Promoter Agent in Surface Modification of Polyethersulfone Membrane.

Fouling as an intricate process is considered as the main obstacle in membrane technologies, and its control is one of the main areas of attention in membrane processes. In this study, a commercial polyethersulfone ultrafiltration membrane (MWCO: 4000 g/mol) was surface modified with different concentrations of vanillin as an antifouling and hydrophilicity promoter to improve its performance. The presence of vanillin and its increasing adsorption potential trends in higher vanillin concentrations were clearly confirmed by observable changes in FTIR (Fourier transform infrared) spectra after modification. Membranes with better hydrophilicity (almost 30% lower contact angle in the best case) and higher polyethylene glycol solution (PEG) permeability were achieved after modification, where a 35–38% increase in permeability of aqueous solution of PEG was perceived when the membrane was modified at the highest exposure concentration of vanillin (2.8 g/L). After filtration of wood extract, surface modified membrane (2.8 g/L vanillin) showed better antifouling characteristics compared to unmodified membrane, as indicated by approximately 22% lower pure water flux reduction, which in turn improved the separation of lignin from the other organic compounds present in wood extract.

Cell membrane mimetic coating immobilized by mussel-inspired adhesion on commercial ultrafiltration membrane to enhance antifouling performance

A facile method of modifying commercial polyethersulfone ultrafiltration membrane (PESUM) was developed based on mussel adhesive mimetic polydopamine (PDA) and cell membrane antifouling phosphorylcholine (PC). The PESUM was firstly coated with a thin PDA layer to confer the membrane adhesive property. A cell membrane mimetic and mussel adhesive mimetic random copolymer (PMEND) bearing both antifouling PC zwitterions and adhesive dopamine groups at different side chains was then immobilized onto the PDA surface by dopamine adhesion from the aqueous solution. The immobilized PMEND spontaneously formed a cell outer membrane mimetic film on the PESUM/PDA surface, which was stable in air, gasoline and pH 3–10 water for more than 2-weeks. Importantly, the water flux of this PESUM/PDA/PMEND membrane could be recovered up to 100% and 93% after one and three cycles of fouling by 1.0mg/mL BSA solution ultrafiltration, respectively. More importantly, the modified membrane could remove more than 99.99% of oil from an 80,000ppm gasoline/water emulsion. Furthermore, this PDA mediated cell outer membrane mimetic modification strategy is substrate independent and can be applied to other membranes and surfaces to enhance antifouling performance.

A study on the stability of polyethersulfone ultrafiltration membranes in a photocatalytic membrane reactor

To date no information about the stability of the polymer membranes in photocatalytic membrane reactors (PMRs) has been published. In order to implement this technology into the full scale the lifespan of the membranes should be assessed. In this paper the investigations on the influence of membrane properties, type of a TiO2 photocatalyst (P25, ST-01, A700, and A800), a presence of oxidative species and the process parameters such as feed cross flow velocity and transmembrane pressure (TMP) on the stability of commercial polyethersulfone ultrafiltration membranes with different cut-off in a PMR are presented. Under the conditions prevailing in the PMR all the tested membranes lost their separation properties towards dextrans. The membrane characterized by the finest pores and thus the most delicate skin layer was damaged to the highest extent. The small angular-shaped particles of ST-01 caused a more severe damage of the membrane surface than the large round-edge shaped particles of A800. The deterioration of the membrane separation properties was less severe at low (1bar) TMP value compared to that at TMP of 3bar. The loss of the separation properties of the membranes was caused to a greater extent by the abrasion of their surface by the photocatalyst particles than by the action of oxidative species.

Ultrafiltration membranes with markedly different pH- and ion-responsivity by photografted zwitterionic polysulfobetain or polycarbobetain

Stimuli-responsive ultrafiltration (UF) membranes were synthesized via photo-initiated “grafting from” of the zwitterionic monomers N-(3-sulfopropyl)-N-methacroyl-oxyethyl-N,N-dimethyl-ammonium betaine (sulfobetaine methacrylate, SPE) and 2-carboxy-N,N-dimethyl-N-(2′-(methacryl-oyloxy)ethyl)ethan-aminium inner salt (carbobetaine methacrylate, CBMA) onto commercial polyethersulfone UF membranes. The effects of kosmotropic and chaotropic potassium salts and pH on flux were determined in order to investigate the stimuli-responsive behavior of the polyzwitterion-grafted membranes. PolySPE showed the expected stimuli-responsiveness based on the “anti-polyelectrolyte” effect. The degree of swelling of grafted sulfobetaine polymer increased and water permeability decreased with increasing salt concentration; and the results can be related to the “Hofmeister series”, i.e. the magnitude of the effect increased with increasing chaotropic character of the anion, in the order: SO42−<H2PO4−<Cl−<ClO4−. However, the carbobetaine polymer (polyCBMA) did not show such anti-polyelectrolyte behavior at pH values in neutral and basic range. In contrast to the “strong–strong” type zwitterionic material polySPE, the swelling behavior of the “strong-weak” polyCBMA was significantly influenced by pH value because protonation of carboxylic acid side groups changes the grafted chains from net neutral zwitterionic into polycationic with ordinary polyelectrolyte properties. Hence, permeability of polyCBMA-grafted membranes increased with increasing salt concentration at pH=3. Furthermore, the rejection of dextrans as a function of electrolyte concentration and pH was determined and all results were in agreement with changes of water fluxes. For specific salt conditions, large and reversible changes of dextran rejection were found, confirming the possibilities of adjusting the sieving properties of the responsive zwitterionic membranes. Detailed studies by zetapotential measurements were also performed to investigate the specific effects of ion type, electrolyte concentration and pH onto the stimuli-responsive changes of surface charge of grafted membranes. All results support that the effects of the grafted zwitterionic polymers on the barrier properties of the UF membranes can be described with a pore-opening/-closing mechanism based on reversible deswelling/swelling of grafted chains on the pore walls in response to composition changes with respect to salt (for polySPE) or salt and pH value (polyCBMA).

Influence of sub-micron surface patterns on the deposition of model proteins during active filtration

In this study, the effects of sub-micron surface patterns on the fouling of a model protein solution (bovine serum albumin (BSA)), was investigated during active filtration and simple adsorption conditions. Surface patterns were created directly onto a commercial polyethersulfone ultrafiltration membrane using nanoimprint lithography, which resulted in a moderately reduced molecular mass cut-off (MWCO) but similar permeance as its non-imprinted counterpart as well as significantly improved resistance to BSA fouling. Staged filtration experiments, with backwash cleaning, revealed that the permeate flux of the imprinted membrane was considerably higher than that of the non-imprinted membrane, consistent with UV–vis measurements showing less protein deposition on the imprinted membranes. This improvement in anti-fouling characteristics for the imprinted membrane was universally observed for varying feed-solution chemistry including changes in both pH and ionic strength. From controlled protein-adsorption experiments under non-filtration conditions, it appears that the observed decrease in protein adsorption on the imprinted membranes is likely associated with altered hydrodynamics due to the presence of the sub-micron patterns.

Tuning the ultrafiltration properties of anti-fouling thin-layer hydrogel polyethersulfone composite membranes by suited crosslinker monomers and photo-grafting conditions

Anti-fouling composite membranes were prepared via photo-initiated “grafting-from” of the hydrophilic monomer poly(ethylene glycol) methacrylate on commercial polyethersulfone ultrafiltration membranes. A fine adjustment of the sieving properties of the modified membranes could be achieved by addition of suited crosslinker monomers in appropriate ratio to the reaction mixture. In this study, two crosslinkers were used: N,N′-methylene bisacrylamide (MBAA) and pentaerythritol triallyl ether (PETAE). Systematic variations of UV intensity and UV irradiation time in combination with varied monomer mixtures have been performed. The resulting membranes have been characterized with respect to degree of functionalization, contact angle and zeta potential as well as water flux and protein ultrafiltration performance with bovine serum albumin and myoglobin, yielding data for solute rejection and permeability loss due to membrane fouling. A minimum degree of functionalization was necessary to achieve fouling resistance, and especially in this range, the effects of the two crosslinker monomers were largely different. Crosslinking with the “two-armed” MBAA yielded denser hydrogel layers on the porous base membrane and, consequently, enhanced protein rejection with increasing crosslinker ratio. In contrast, on the same membrane pore size, hydrogel layers crosslinked with the “three-armed” PETAE yielded a more open barrier structure and the protein rejection decreased with increasing crosslinker ratio. Overall, this study delivered fundamental results for the preparation of high performance composite membranes with enhanced selectivity and anti-fouling properties for ultrafiltration.

Purification of aqueous solutions of metal ions by ultrafiltration

This study gathers experimental results that illustrate the efficiency of ultrafiltration in the purification of aqueous solutions of metal ions beforehand complexed on water-soluble macromolecular substrate. For this purpose, a commercial polyethersulfone ultrafiltration membrane is employed in a magnetic stirred cell operating in a batch mode. The metal ions Cu 2+, Co 2+, Ni 2+, Zn 2+, Fe 3+ and Ag + are removed from synthetic aqueous solutions which contain poly(vinyl alcohol) used as macromolecular complexing agent. It is, primarily, observed that, except silver ions, all the other studied metal ions are removed from monoionic solutions with a rejection higher than 97%. Moreover, the possibility to separate the cupric ions from the other metal ions is studied and the removal of silver ions from a diionic solution containing cupric and silver ions is achieved. The studied parameters are the effect of the pressure, the molecular weight of the sequestering agent and the nature of the ionic species in solution on the permeate flux through the ultrafilter and the rejection of the metal species by it.