Commercial Ultrafiltration Membranes Research Articles

Charge exclusion as a strategy to control retention of small proteins in polyelectrolyte-modified ultrafiltration membranes

While retention in commercial ultrafiltration membranes is commonly governed by size exclusion, addition of charged polyelectrolytes to the membrane surface has been proposed as a facile and inexpensive method to modulate retention during filtration of charged compounds, such as proteins. This study demonstrates that selected combinations of common polyelectrolytes can be efficiently used to control the retention of proteins. We show how the retention of positively charged lysozyme increased from ~7% to ~50% when a negatively charged polyelectrolyte was deposited on a commercial polysulfone membrane, most probably due to a combination of associated pore narrowing effect and protein adsorption onto the membrane. By contrast, the retention decreased again (from ~50% to ~30%) upon further addition of a positively charged polyelectrolyte onto the membrane. The electrostatic repulsion between the positively charged surface and proteins prevented protein adsorption onto the membrane, while pore size was still large enough that size exclusion was limited. The retention decreased further to ~22% when increasing amounts of polyelectrolytes of the same charge as the protein were deposited on the membrane. In addition, variations in pH revealed that the negative effect of polyelectrolytes of the same charge as the protein on lysozyme retention was reversed when the charge density of lysozyme reached a certain level beyond which the positively charged electrolyte promoted dramatic increases of rejection. The results of this study suggest that use of polyelectrolyte-modified ultrafiltration membranes with a much larger pore size than the charged solute to be filtered could be a strategy to control retention of such solutes by minimizing the effect of size exclusion and fouling.

Identification of Foulants on Polyethersulfone Membranes Used to Remove Colloids and Dissolved Matter from Paper Mill Treated Effluent

In this study, membrane fouling caused by paperboard mill treated effluent (PMTE) was investigated based on a dead-end ultrafiltration (UF) pilot-scale study. The membranes employed were commercial hydrophobic UF membranes made of polyethersulfone (PES) with a molecular weight cut-off of 10 kDa, 50 kDa, and 100 kDa. Membrane fouling mechanism during dead-end filtration, chemical analysis, field emission scanning electron microscopy (FESEM), energy-dispersive spectrophotometry (EDS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and 3D fluorescence excitation–emission matrix (3DEEM) analysis were applied to understand which fraction of the dissolved and colloidal substances (DCS) caused the membrane fouling. The results indicated that the phenomenon controlling fouling mechanism tended to be cake layer formation (R2 ≥ 0.98) for all membranes tested. The 3DEEM results indicate that the majority of the organic foulants with fluorescence characteristics on the membrane were colloidal proteins (protein-like substances I+II) and macromolecular proteins (soluble microbial products, SMP-like substances). In addition, polysaccharide (cellulosic species), fatty and resin acid substances were identified on the fouled membrane by the ATR–FTIR analysis and play an important role in membrane fouling. In addition, the FESEM and EDS analyses indicate that the presence of inorganic foulants on the membrane surfaces, such as metal ions and especially Ca2+, can accelerate membrane fouling, whereas Mg and Si are linked to reversible fouling.

Molecular-Sieving Membrane by Partitioning the Channels in Ultrafiltration Membrane by In Situ Polymerization.

Commercial ultrafiltration membranes have proliferated globally for water treatment. However, their pore sizes are too large to sieve gases. Conjugated microporous polymers (CMPs) feature well-developed microporosity yet are difficult to be fabricated into membranes. Herein, we report a strategy to prepare molecular-sieving membranes by partitioning the mesoscopic channels in water ultrafiltration membrane (PSU) into ultra-micropores by space-confined polymerization of multi-functionalized rigid building units. Nine CMP@PSU membranes were obtained, and their separation performance for H2 /CO2 , H2 /N2 , and H2 /CH4 pairs surpass the Robeson upper bound and rival against the best of those reported membranes. Furthermore, highly crosslinked skeletons inside the channels result in the structural robustness and transfer into the excellent aging resistance of the CMP@PSU. This strategy may shed light on the design and fabrication of high-performance polymeric gas separation membranes.

Preparation and Protein Separation Properties of the Porous Polystyrene/Ethylene-Vinyl Acetate Copolymer Blend Nanofibers Membranes.

To date, the preparation of a novel ultrafiltration membrane and the efficient separation and purification of protein solutions have gradually attracted widespread attention of many researchers. In this study, a hollow porous polystyrene/ethylene–vinyl acetate copolymer blend nanofibrous membrane (PS/EVA-BNM) was generated by electrospinning and chemical modification and then used to separate and purify proteins in solution. The BNM was characterized by scanning electron microscopy and specific surface area and pore size analyses. The membrane separation system was assembled using the BNM, which was overlaid to form the reaction layer. The optimal conditions for protein separation were determined by adjusting the operating pressure, filtration time, and pH. The results showed that the rejection rate of serum albumin and the membrane flux could reach 94.35% and 2.04 L/(m2 min), respectively, under the following conditions: the operating pressure was 0.10 MPa and the processing time was 1.5 h. By comparing the parameters of the polyethersulfone commercial ultrafiltration membrane with the PS/EVA-BNM system, it could be inferred that the rejection rate of the latter decreased slightly, whereas its transport flux improved several times. At the same time, the experimental results indicated that the PS/EVA-BNM possessed excellent reusability and mechanical properties. Additionally, the BNM could retain its nanofibrous morphological structure after the separation of serum albumin several times in an aqueous environment.

Morphological, Electrical, and Chemical Characteristics of Poly(sodium 4-styrenesulfonate) Coated PVDF Ultrafiltration Membranes after Plasma Treatment.

A commercial ultrafiltration (UF) membrane (HFM-183 de Koch Membrane Systems) made of poly(vinylidene fluoride) (PVDF), was recovered with a negatively-charged polyelectrolyte (poly(sodium 4-styrenesulfonate)) (PSS), and the effects on its electric, chemical, and morphological properties were analyzed. Atomic force microscopy (AFM), liquid–liquid displacement porometry, Electrical Impedance Spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy were used to investigate the modifications induced by the deposition of PSS on the PVDF positively-charged membrane and after its treatment by a radio frequency Ar-plasma. These techniques confirmed a real deposition and posterior compaction of PSS with increasing roughness and decreasing pore sizes. The evolution of the electric resistances of the membranes confirmed crosslinking and compaction with shielding of the sulfonated groups from PSS. In this way, a membrane with a negatively-charged active layer and a pore size which was 60% lower than the original membrane was obtained. The composition of the additive used by manufacturers to modify PVDF to make it positively charged was obtained by different procedures, all of which depended upon the results of X-ray photoelectron spectroscopy, leading to fairly consistent results. This polymer, carrying positive charges, contains quaternary nitrogen, as confirmed by XPS. Moreover, Raman spectroscopy confirmed that PVDF changes from mostly the β to the α phase, which is more stable as a substrate for the deposited PSS. The aim of the tested modifications was to increase the retention of divalent anions without reducing permeability.

Preparation and characterization of polylactic acid-modified polyvinylidene fluoride hollow fiber membranes with enhanced water flux and antifouling resistance

Although ultrafiltration (UF) membranes have gained considerable attention in water separation and purification process, most of the materials used for commercial UF membranes fabrication do not able to degrade/decompose easily and tend to cause severe environmental problem when they are discarded. In view of this, an environmentally friendly hydrophilic polymeric material - polylactic acid (PLA) has been considered in this work, aiming to reduce not only the environmental impacts caused by the existing membranes but also to improve membrane water flux and antifouling resistance. In this study, the effects of PLA quantity and air gap (during spinning process) on the morphology and liquid separation performance of polyvinylidene fluoride (PVDF) hollow fiber membranes were investigated. The membrane properties were characterised using scanning electron microscope, atomic force microscope Fourier transform Infrared spectrometer, tensile tester and contact angle goniometer before filtration experiment was conducted. Results showed that the incorporation of small quantity of PLA (with PLA/PVDF weight ratio of ≤ 1.0) could significantly improve membrane water flux from ˜30 to 376.7 L/m2.h.bar without compromising rejection (95–97%). More importantly, the PLA-modified PVDF membranes required much lower temperature to decompose which minimizes environmental impacts. Owing to the improved surface hydrophilicity (lower water contact angle), the PLA-modified PVDF membranes also exhibited higher flux recovery rate than that of pure PVDF membrane, revealing the improved antifouling resistance against bovine serum albumin. The findings of this work demonstrated that biodegradable PLA is potential to be used to modify the characteristics of UF membranes, leading to enhanced water treatment process.

Feasibility and Practicability of Magnetophoretic‐Augmented Composite Membrane in Treating Polluted River Water: Real Case Application

River water is a complex water system consisting of various foulants with different properties that affects the membrane removal efficiency as well as the fouling propensity. Present work aims to demonstrate the feasibility of an in‐house developed ultrafiltration (UF) magnetophoretic‐augmented composite (MAC) membrane in treating polluted river water for drinkable water production. Permeation and rejection performances of the commercial UF and UF MAC membranes were compared using cross‐flow recirculation unit. X‐ray photoelectron spectroscopy, vibrating sample magnetometer, and porometer analyses confirmed the end‐caped of magnetite colloids onto the surface of neat microfiltration (MF) polyethersulfone (PES) membrane. The laid magnetite layer on the surface of MF PES membrane has transformed it into UF MAC membrane. The commercial UF membrane suffered from greater amount of flux decline (27% of the initial flux) as compared with that of the developed UF MAC membrane (8% flux decline from the initial flux), after 48 h of filtration. Filtrates from both of the commercial UF and UF MAC membranes achieved the minimum requirement of local drinking‐water quality standards. The UF MAC membrane proved to effectively suppressed membrane fouling without jeopardizing the membrane rejection performances. © 2019 American Institute of Chemical Engineers Environ Prog, 38:e13146, 2019

Modification of commercial Ultrafiltration and Nanofiltration Membranes by UV-photografting Technique for Forward Osmosis Application

Abstract We introduce a novel approach to modify conventional pressure-driven membrane by ultraviolet (UV)-photografting technique for forward osmosis application. Both ultrafiltration polyethersulfone (UFPES) and nanofiltration polyethersulfone (NFPES) membranes were modified using two grafting parameters namely the grafting time and monomer concentration (acrylic acid). Evaluation and comparison were made on the performance in forward osmosis (FO) mode and reverse osmosis (RO) mode. The result shows that the effects of polyacrylic on the polyethersulfone (PES) can be conveniently controlled by controlling the grafting parameters via one factor at a time (OFAT). However, a detailed comparison between these two membranes has identified that only NFPES was suitable in FO application. Even the modified membranes exhibit greater water fluxes, the salt rejection for NFPES membrane is 59 % while the UF membrane produced less than 1 %. Moreover, we include the modelling of water flux at different osmotic pressure and feed concentration. Therefore, UV-photografting of NFPES membrane can be considered as an alternative technique to improve commercial membrane performance in FO application.

Rightsizing Nanochannels in Reduced Graphene Oxide Membranes by Solvating for Dye Desalination.

Membranes with high water permeance, near-zero rejection to inorganic salts (such as NaCl and Na2SO4), and almost 100% rejection to organic dyes are of great interest for the dye desalination (the separation of dyes and salts) of textile wastewater. Herein, we prepared reduced graphene oxide membranes in a solvation state (S-rGO) with nanochannel sizes rightly between the salt ions and dye molecules. The S-rGO membrane rejects >99.0% of Direct Red 80 (DR 80) and has almost zero rejection for Na2SO4. By contrast, conventional GO or rGO membranes often have channel sizes smaller than divalent ions (such as SO42-) and thus high rejection for Na2SO4. More interestingly, high salinity in typical dye solutions decreases the channel size in the S-rGO membranes and thus increases the dye rejection, while the Na2SO4 rejection decreases because of the negatively charged surface on GO and the salt screening effect. The membranes also show pure water permeance as high as 80 L m-2 h-1 bar-1, which is about 8 times that of commercial NF 90 membrane and 2 times that of a commercial ultrafiltration membrane (with a molecular weight cutoff of 2000 Da), rendering their promise for practical dye desalination.

Electro-Conductive Composite Gold-Polyethersulfone-Ultrafiltration-Membrane: Characterization of Membrane and Natural Organic Matter (NOM) Filtration Performance at Different In-Situ Applied Surface Potentials.

Next to the pore size distribution, surface charge is considered to be one main factor in the separation performance of ultrafiltration (UF) membranes. By applying an external surface potential onto an electro-conductive UF membrane, electrostatic induced rejection was investigated. This study introduces in a first part a relatively simple but yet not reported technology of membrane modification with direct current sputter deposition of ultrathin (15 nm) highly conductive gold layers. In a second part, characterization of the gold-coated UF flat sheet membrane with a molecular weight cut-off (MWCO) of 150 kDa is presented. Membrane parameters as contact angle (hydrophobicity), pure water permeability, MWCO, scanning electron microscopy imaging, zeta potential, surface conductivity and cyclic voltammetry of the virgin and the modified membrane are compared. Due to the coating, a high surface conductivity of 107 S m−1 was realized. Permeability of the modified membrane decreased by 40% but MWCO and contact angle remained almost unchanged. In a third part, cross-flow filtration experiments with negative charged Suwannee River Natural Organic Matter (SRNOM) are conducted at different cathodic and anodic applied potentials, different pH values (pH 4, 7, 10) and ionic strengths (0, 1, 10 mmol L−1). SRNOM rejection of not externally charged membrane was 28% in cross-flow and 5% in dead-end mode. Externally negative charged membrane (−1.5 V vs. Ag/AgCl) reached rejection of 64% which was close to the performance of commercial UF membrane with MWCO of 5 kDa. High ionic strengths or low pH of feed reduced the effect of electrostatic rejection.

Cross-flow-assembled ultrathin and robust graphene oxide membranes for efficient molecule separation

A graphene oxide (GO) membrane is promising for molecule separation. However, it is still a big challenge to achieve highly stable pristine GO membranes, especially in water. In this work, an ultrathin and robust GO membrane is assembled via the cross-flow method. The as-prepared 12 nm thick GO membrane (GOCF membrane) presents high stability with water permeance of 1505 ± 65 litres per hour per square meter per bar (LHM bar−1) and Evans Blue (EB) rejection of 98.7 ± 0.4%, 21-fold enhancement in water permeance compared with that of a pristine GO membrane (50–70 LHM bar−1) and 100 times higher than that of commercial ultrafiltration membranes (15 LHM.bar−1, GE2540F30, MWCO 1000, GE Co., Ltd) with similar rejection. Attributed to the surface cross-flow, the GO nanosheets will be refolded, crumpled, or wrinkled, resulting in a very strong inter-locking structure among the GO membrane, which significantly enhances the stability and facilitates their separation performance. This cross-flow assembling technique is also easily extended to assemble GO membranes onto other various backing filter supports. Based on the Donnan effect and size sieving mechanism, selective membrane separation of dyes with a similar molecular structure from their mixture (such as Rhodamine B (RhB) and Rose Bengal, and RhB and EB) are achieved with a selectivity of 133 ± 10 and 227 ± 15, respectively. Assembly of this ultrathin GO membrane with high stability and separation performance, via a simple cross-flow method, shows great potential for water purification.

Microscale stirred-cell filtration for high-throughput evaluation of separation performance

Membrane filtration is a key separations technique in downstream bioprocessing applications: for a commercial bioprocess operation, 10–20 membrane-related steps are typically required. At the laboratory scale, the evaluation of membrane separation performance often involves a ‘stirred cell device’; however, this simple tool is poorly suited for conducting high-throughput studies of separation performance. Here, we designed a high-throughput stirred cell (HTSC) device which is ideally suited for conducting optimization studies, especially at the early stages of bioprocess development when small volumes of feed material are available. The HTSC allows for up to six filtration experiments to be run simultaneously with continuous mixing above each membrane facilitated by suspended magnetic stir elements. Using fluorescently-labeled dextrans as model biomolecules and commercial ultrafiltration membranes, it was shown that the HTSC device gave the same separation performance as a traditional stirred cell, but with the added benefits of operating at a faster pace (due to its parallel nature) and requiring nearly an order of magnitude lower sample volumes. Furthermore, the utility of the HTSC was demonstrated by concurrently evaluating the performance of four different ultrafiltration membranes for the same model biomolecule and the membrane selectivity for a mixture of two model bio-macromolecules.

Roll‐to‐roll nanoimprint lithography of ultrafiltration membrane

ABSTRACTNanoimprinting of a commercial, as supplied, polyethersulfone ultrafiltration membrane has been carried out for the first time using a roll‐to‐roll (R2R) process. To support this processing approach, we also developed a reusable flexible polyetherimide mold. We were able to pattern membrane at room temperature (∼21 °C) due to the high pressures (22 MPa) applied during the low contact times (<2 s) inherent to R2R imprinting. N2 permeance (L m−2 h−1 bar−1) testing was used as an indicator to verify retention of membrane porosity and to guide selection of imprinting parameters during initial screening studies. Further measurements showed the N2 and (scaled) deionized water permeances to have a 0.97 correlation coefficient. We scaled up the size of patterned membranes to as large as 226 cm2 area, thereby demonstrating the plausibility of continuously patterning commercial ultrafiltration membranes. We also investigated pattern stability versus aqueous heat treatment and found that time, temperature, and imparted strain (during patterning) may all influence stability, but no evidence of pattern loss was observed in electron micrographs after our filtration experiments. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45993.

Antifouling, high-flux oil/water separation carbon nanotube membranes by polymer-mediated surface charging and hydrophilization

A facile approach to fabricating the antifouling, high-flux oil/water separation carbon nanotube (CNT) nanohybrid membranes was explored by polymer-mediated surface charging and hydrophilization through vacuum-assisted self-assembly process. The controlled stacking of CNT imparted the membranes hierarchical nanostructure and high water permeation reaching 4592Lm−2h−1bar−1, which was about 10 folds of commercial ultrafiltration membranes used for oil/water separation. Modifying CNT with a series of polymers endowed the membranes with different surface charge and hydrophilicity. The compact hydration layer was formed at the interface of water/membrane by the water trapped in the hierarchical nanostructure to prevent oil from adhering on the membrane surface. Hence, the polymer@CNT nanohybrid membranes possessed underwater superoleophobicity and low oil adhesive force. Moreover, the antifouling properties of as-prepared membranes were evaluated through filtration of oil-in-water emulsions with different surface charges and the results demonstrated that synergetically regulating the surface charge and hydrophilicity could tune the interactions between the foulants and membrane surface, which can efficiently inhibit the irreversible fouling, leading to 100% flux recovery ratio (FRR). The fabrication process of the polymer@CNT nanohybrid membranes with high water permeation, high separation efficiency and excellent antifouling properties may enlighten the great prospects for CNT-based materials in water separation and purification.

Treatment of textile dyes containing wastewaters with PES/PVA thin film composite nanofiltration membranes

Abstract Poly(ether sulfone) (PES) has been widely used in commercial ultrafiltration membranes. In the present work, the commercial PES ultrafiltration membrane is coated with poly(vinyl alcohol) (PVA) to make thin-film nanofiltration membranes by dip-coating method. PVA is a water soluble, hydrophilic polymer with the ability to form ultra thin films. Malic acid is used as the cross-linking agent to enhance thermal and chemical stability. The membrane performance is evaluated by cross-flow filtration of dyes – acid, reactive and disperse, which are commercially used in textile industries. The rejection and fouling characteristics of the membrane towards removal of different types of dyes from synthetic aqueous solutions were studied. Rejection towards salts like NaCl, Na 2 SO 4 and MgSO 4 were also studied. The membrane is characterized by FE-SEM, ATR-FTIR, TGA and contact angle measurements. It was observed that the permeate flux was almost same as that of pure water. A flux of 3.06 L/(m 2 h atm) was obtained with the membrane with 1 wt% PVA. Maximum dye rejection of about 97.7% was observed for disperse dyes. The influence of operating parameters on the membrane performance was studied. Combined film-theory solution-diffusion model was used to find mass transfer coefficients and solute transport parameters.

Preparation of PVDF hollow fiber membranes with high adsorption performance by one-step physical coating and chemical cross-linking

ABSTRACTIn this paper, PVDF hollow fiber membrane with high adsorption performance was prepared by coating polyvinyl alcohol on the surface of commercial PVDF hollow fiber ultrafiltration membrane and initiating partial hydroxyl acetalization. The modification effect was studied by scanning electron microscopy, infrared spectroscopy, contact angle test and organic dye adsorption capacity test. The results show that the polyvinyl alcohol is effectively fixed on the surface of PVDF hollow fiber membrane with polyvinyl alcohol used as coating agent to initiate partial acetalization reaction in the presence of glutaraldehyde and acid catalyst. The pure water contact angle of PVDF hollow fiber membrane decreases from 76.20° to 57.56°, which greatly improves the of PVDF hollow fiber membrane. The incorporation of the coating and cross-linked structure results in a decrease in the micro-porous permeability of the modified PVDF hollow fiber membrane. The adsorption performance of PVDF hollow fiber membrane modified by hydrophilic coating and cross-linked for organic dye Rhodamine B is significantly improved.

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.

Ultrathin and ordered stacking of silica nanoparticles via spin-assisted layer-by-layer assembly under dehydrated conditions for the fabrication of ultrafiltration membranes

Ultrafiltration (UF) membranes composed of an ultrathin and ordered layer of silica nanoparticles (NPs) was fabricated via spin-assisted layer-by-layer (LbL) assembly in dehydrated conditions. Anionic silica NPs and cationic sacrificial polymers were alternately stacked on an anodic aluminum oxide support membrane via electrostatic interactions. The assembly was then calcinated to remove the sacrificial polymers and form a stacked-NP membrane. The structure of the NP layers was controlled by altering the number of stacked-NP layers formed during the LbL assembly processes and performing an ethanol-based dehydration treatment. Increasing the number of NP layers increased the total thickness of the stacked-NP layer and decreased the water permeability. The rejection performance against dextran was improved by increasing the number of NP layers, indicating a decrease in the number of defects. The ethanol-based dehydration treatment successfully decreased the total thickness of the stacked-NP layer and improved the rejection performance against dextran. The surface morphology of the NP layers became smoother by the ethanol-based treatment. These results indicate that the ethanol-based treatment produces dense NP layers with an ordered structure by removing water molecules adsorbed on the sacrificial polymers and NPs. The performance of the stacked-NP membranes was superior to that of commercial UF membranes.

Novel low-fouling membrane bioreactor (MBR) for industrial wastewater treatment

A novel antifouling coating of ultrafiltration (UF) commercial membranes, based on a polymerisable bicontinuous microemulsion (PBM) technique, was developed and tested for the first time in a membrane bioreactor (MBR) using an artificial model textile dye wastewater and compared with a commercial uncoated UF membrane. The results showed that the commercial MBR module faced severe fouling problems whereas the novel coated PBM MBR module reduced the fouling significantly. The analysis of fouling rate using a resistance model confirms that PBM coated membrane has a higher antifouling effect. The antimicrobial properties of the PBM membrane contributed by polymerisable cationic surfactant acryloyloxyundecyltriethylammonium bromide (AUTEAB) guaranteed an anti-biofouling effect preventing the growth of microorganisms on the membrane surface. In addition, the PBM MBR module showed 10±1% higher blue dye removal efficiency and a similar rate of COD removal efficiency of about 95±1% compared to commercial module. However, water permeability was slightly lower due to extra resistance of the PBM coating. Root mean squared (RMS) roughness measurement and analysis of AFM images confirmed that the stable novel membrane coating still existed and showed antimicrobial effect even after 105 days of operation. The results obtained demonstrated the potential of the low fouling PBM membrane.

Synthesis of hyperbranched polymers towards efficient boron reclamation via a hybrid ultrafiltration process

Two hyperbranched polymers, hyperbranched polyglycidol (HPG) and 2, 3-Dihydroxypropyl-hyperbranched polyethylenimine (Diol-HPEI), were synthesized and studied as polychelatogens for boron reclamation via a hybrid ultrafiltration process, with the objectives of evaluating the key factors for polymer–boron chelation and improving boron rejection efficiency. Their chemical structures were unveiled by FTIR and XPS analyses whilst molecular weights were carefully tailored in order to be fully retained by a commercial ultrafiltration (UF) membrane. The chelation capacity of the two polymers was compared under different operating conditions i.e., chelating temperature, polymer loading and pH. It appears that Diol-HPEI prominently outperforms HPG because the tertiary amine group may be more competent than the ether group in terms of their protonation capability. Eventually, a rejection of 66–91% was achieved with a Diol-HPEI polymer loading of 100g per g boron in the pH range of 6.9–9.0. Besides, the effects of interfering ions, i.e., Na+, Mg2+, Cl− and SO42- on polymer–boron interactions were examined in the Diol-HPEI/boron solution at the neutral condition. Results reveal that divalent cations may exert more negative influence on boron rejection owing to the competition between them and boron to form complexes with chelating polymers. These findings may provide useful insights in design of efficient boron-chelating polymers.