Composite Polyethersulfone Research Articles

Mitigating Membrane Fouling in Abattoir Wastewater Treatment: Integration of Pretreatment Step with Zwitterion Modified Graphene Oxide-Polyethersulfone Composite Membranes.

Composite polyethersulfone (PES) membranes containing N-aminoethyl piperazine propane sulfonate (AEPPS)-modified graphene oxide (GO) were integrated with either of the two pretreatment processes (activated carbon (AC) adsorption or polyelectrolyte coagulation) to assess their effectiveness in mitigating membrane fouling during the treatment of abattoir wastewater. The AEPPS@GO-modified membranes, as compared to the pristine PES membranes, showed improved hydrophilicity, with water uptake increasing from 72 to 118%, surface porosity increasing from 2.34 to 27%, and pure water flux (PWF) increasing from 235 to 673 L.m-2h-1. The modified membranes presented improved antifouling properties, with the flux recovery ratio (FRR) increasing from 59.5 to 93.3%. This study compared the effectiveness of the two pretreatment processes, AC, coagulation, and the integrated system (coagulation/AC-UF membrane), in the removal of natural organic matter (NOM) and improvement of abattoir wastewater's pH, electrical conductivity, TDS, and turbidity. The integrated systems produced improved water quality in terms of pH, EC, TDS, turbidity, and organic content. The fluorescence excitation-emission matrix (FEEM) analysis exhibited almost no fluorescence peak post-treatment following organic loading removal. The quality of the water met the South African non-potable water reuse standards. The sole membrane treatment systems exhibited good fouling resistance without the pretreatment systems; however, integrating these systems can offer extended longer filtration periods, thereby assisting in cost aspects of the abattoir wastewater treatment system.

High-performance of anti-bacterial composite membrane prepared from polyethersulfone-polyethylene glycol-silver nanoparticles

A bench-scale study of river water treatment using composite polyethersulfone (PES) membrane was carried out. Polyethylene glycol-silver nanoparticles (PEG-AgNPs) additive was designed to support the simultaneous filtration and disinfection performance of PES membranes via in situ incorporation. Significant improvements in the PES membranes after modification with PEG-AgNPs were observed. The experimental results showed that the PEG-AgNPs increased the PES membrane water flux from 2.87 to 172.84 L/m2·h. The anti-fouling test of the PES membrane toward humic acid molecules after the addition of PES/PEG-AgNPs increased the reversible fouling and decreased the irreversible fouling. In terms of filtration performance, the PES/PEG-AgNP membranes showed high filtration performance, with a water disinfection ability of 99.99 %. Moreover, the leach of silver particles from the PES membrane forced by ultrasonication was <50 ppb, indicating the security and stability of the PES/PEG-AgNP membrane.

Enhancing thin-film composite polyethersulfone hollow fiber membranes through alkali-induced interfacial polymerization modification for effective separation of monovalent/divalent salts

Amidst the escalating global water scarcity issues, finding better ways to sustainably treat brackish water and seawater while simultaneously recovering resources becomes increasingly important. In this work, we investigated the fabrication strategies to produce polyethersulfone hollow fiber membranes (PES HFMs) with robust characteristics and uniformly arranged shape. The presence of an air gap (AG) in the dry-wet spinning process facilitates the chain orientation due to the gravitational force and elongational stretch and moisture-induced early phase inversion, therefore preventing corrugations on the shell side. We extensively studied the correlation between HFM spinning parameters and the appearance and disappearance of buckling effects. Moreover, it was proven that the addition of N-methyl-2-pyrrolidone (NMP) to the bore fluid composition prolongs the demixing process, overcoming the HFMs' delamination issue. After optimizing the spinning conditions, a facile alkali-induced interfacial polymerization (IP) was employed to enhance the formation of a selective polyamide (PA) layer on PES HFM substrates. The final membrane made by this modification process, denoted as PES-IP-BOH, exhibits a Na2SO4 rejection higher than 96 %, while maintaining low rejections for other monovalent salts. Accordingly, it achieved a high ideal selectivity of >23 for the selective separation of monovalent and divalent salts.

Preparation and Characterization of Polyethersulfone/Activated Carbon Composite Membranes for Water Filtration.

Ultrafiltration membrane technology holds promise for wastewater treatment, but its widespread application is hindered by fouling and flux reduction issues. One effective strategy for enhancing ultrafiltration membranes involves incorporating activated carbon powder. In this study, composite polyethersulfone (PES) ultrafiltration membranes were fabricated to include activated carbon powder concentrations between 0 and 1.5 wt.%, with carbon size fixed at 200 mesh. The ultrafiltration membranes were evaluated in terms of membrane morphology, hydrophilicity, pure water flux, equilibrium water content, porosity, average pore size, protein separation, and E-coli bacteria removal. It was found that the addition of activated carbon to PES membranes resulted in improvements in some key properties. By incorporating activated carbon powder, the hydrophilicity of PES membranes was enhanced, lowering the contact angle from 60° to 47.3° for composite membranes (1.0 wt.% of activated carbon) compared to the pristine PES membrane. Water flux tests showed that the 1.0 wt.% composite membrane yielded the highest flux, with an improvement of nearly double the initial value at 2 bar, without compromising bovine serum albumin rejection or bacterial removal capabilities. This study also found that the inclusion of activated carbon had a minor impact on the membrane's porosity and equilibrium water content. Overall, these insights will be beneficial in determining the optimal concentration of activated carbon powder for PES ultrafiltration membranes.

Introducing self-healing properties to polyethersulfone (PES) membrane via poly(vinyl alcohol)/ polyacrylic acid (PVA/PAA) surface coating

During membrane filtration, it is inevitable that a membrane will experience physical damage, leading to a loss of its integrity and a decrease in separation efficiency. Hence, the development of a water-responsive membrane capable of healing itself autonomously after physical damage is significantly important in the field of water filtration. Herein, a water-enabled self-healing composite polyethersulfone (PES) membrane was synthesized by coating the membrane surface using a mixed solution composed of poly (vinyl alcohol) and polyacrylic acid (PVA-PAA). The self-healing efficiency of the coated PES membrane was examined based on the changes in water flux at three stages which are pre-damaged, post-damaged, and post-healing. The self-healing process was initiated by the swelling of the water-responsive PVA and PAA, followed by the formation of reversible hydrogen bonds, completing the self-healing process. The coated PES membrane with three layers of PVA-PAA coatings (at 3:1 ratio) demonstrated high water flux and remarkable self-healing efficiency of up to 98.3%. The self-healing capability was evidenced by the morphology of the membrane observed via scanning electron microscope (SEM). The findings of this investigation present a novel architecture approach for fabricating self-healing membranes using PVA-PAA, in addition to other relevant parameters as reported.

Preparation of pH-sensitive composite polyethersulfone membranes embedded by Ag(I) coordination polymer for the removal of cationic and anionic dyes

A pH-sensitive polyethersulfone (PES) membrane was prepared with the aid of newly synthesized Ag(I) coordination polymer (Ag(I)-CP) particles. Indicating obvious adsorptive property toward dyes, the Ag(I)-based metalorganic framework (MOF) was selected to be used as an additive to improve the dye selectivity of PES membranes for both cationic and anionic dyes. The performance examination and characterization of prepared membranes indicated the influence of Ag(I)-CP in PES membrane improvement. The effect of feed pH approved the membrane response to pH changes in dye removal results. By adjusting feed pH based on pHpzc of Ag(I)-CP, it is possible to remove both anionic and cationic dyes (97% of acid orange 7 (AO) & and 100% of methylene blue (MB)) from the effluent along with an enhanced permeated flux. The results offered a synergism in embedding Ag(I)-CP in PES membrane in dye removal efficiency. The additive particles can be applied with their natural size (200–300 nm) without severe influence on the uniformity of the membrane morphology if the optimum Ag(I)-CP content is considered.

Plasma surface modification of graphene oxide nanosheets for the synthesis of GO/PES nanocomposite ultrafiltration membrane for enhanced oily separation

AbstractIn this study, two different monomers, namely hexafluorobutyl acrylate (HFBA) and diethylaminoethyl methacrylate (DEAEMA) were individually used to modify graphene oxide (GO) nanosheets via environmentally friendly plasma enhanced chemical vapor deposition (PECVD) method. The results from instrumental analyses confirmed the successful deposition of respective functional material onto the nanomaterials. Modified GOs were used as the nano‐fillers to develop composite polyethersulfone (PES) ultrafiltration (UF) membrane with improved surface properties for oily solution treatment. All the developed membranes were characterized with a series of analytical instruments to support the findings of membrane filtration performance. The results indicated that the membrane incorporated with DEAEMA‐GOs (coated with hydrophilic polymer) could achieve better results in terms of oil rejection, antifouling resistance and water recovery rate than the membrane incorporated with HFBA‐GOs (coated with hydrophobic polymer). This is due to the reduced agglomeration between modified GOs as well as better interaction of hydrophilic‐coated GOs with polymer membrane. Compared to the pure water flux of the membrane incorporated with unmodified GO, the membrane incorporated with DEAEMA‐GO achieve approximately 85% higher value with oil removal rate remained almost unchanged (98.94% rejection).

Prepare of sunlight response NH2-MIL-125/PES composites ultrafiltration membrane for flux incrementation and fouling alleviation

In this paper, a novel hydrophilic composite polyethersulfone (PES) ultrafiltration membrane was prepared by blending sunlight response photocatalyst NH2-MIL-125 via the phase inversion method. The physical-chemistry performance of membrane was carried out by XRD, FTIR, UV-VIS/DRS, contact angle, and cross-section SEM images. The separation ability, anti-fouling ability, and self-cleaning efficiency of ultrafiltration membrane were analyzed by ultrafiltration experiment using the congo red solution. The results indicate that fouling resistance and the flux recovery ratio of ultrafiltration membrane is significantly improved, and it has higher solar response energy. There was no significant change in the rejection ratio of pollutants before and after illumination. For the pristine PES membrane and the 0.5% NH2-MIL-125/PES nanocomposite membrane, the water flux recovery ratio (FRR) could increase from 37.84% to 77.09%, and the Rr could increase from 22.22% to 44.09%, and the Rir could decrease from 67.11% to 47.09%. In a conclusion, the addition of NH2-MIL-125 at a low concentration could result in membranes with more pure water flux, better rejection, and good fouling resistance compared to the unfilled PES membrane.

Karakteristik Membran Komposit Polietersulfon, Polivinilpirolidon dan Kitosan

Polyethersulfone (PES) is a membrane forming material that has many advantages but is hydrophobic, so it is necessary to add other materials, such as composite PES with Polyvinylpyrrolidone (PVP) and chitosan. The addition of PVP aims to change the nature of the PES membrane to be hydrophilic and the addition of chitosan aims to improve the mechanical properties of the polymer. The purpose of this study was to study the effect of adding PVP and chitosan to the characteristics of PES membranes. The membranes were made using a phase inversion technique by immersion precipitation with a concentration of 20% PES, 1% PVP, and chitosan were varied, namely 0% (M0 membrane), 1.5% (M1), 2% (M2), and 3% (M3). The results of the permeability test showed that the membranes M0, M1, M2, and M3 are classified as nanofiltration membranes with Lp values of 9.1237, 7.618, 6.9651, and 4.4077 L/m2.h.bar. The swelling degree value is 61,512; 103.111; 145,564; and 158.610% and the overall porosity value is 22.892; 32.360; 80.726; and 117.016%. The SEM test showed that the morphology of the membrane changed its structure as the concentration of chitosan increased. The FTIR test on the membrane showed that there were absorption bands, each of which identified its functional group.

Synthesis and characterization of nano zerovalent iron-kaolin clay (nZVI-Kaol) composite polyethersulfone (PES) membrane for the efficacious As2O3 removal from potable water samples

In this study, Kaolin clay, a mining material, was used as an abundant and available mineral as zero-valent iron-kaolinite composites for As2O3 removal from the water samples. The composites were made by the sodium borohydrate reduction method. The existence of Fe0 in the produced composites was confirmed by X-ray diffraction (XRD) and Fourier-Transform Infrared Spectroscopy (FTIR) analysis. The membranes are prepared with zerovalent nano Iron–Kaolin and PES. The synthesized composites were then mixed with polyethersulfone to prepare the membranes S1, S2, and S3 with varying compositions. Field Emission Scanning Electron Microscopy (FESEM) analysis of the produced membranes showed the porous structure and the contact angle of membranes increased the hydrophilicity. The membranes were explored for the removal of As2O3 (AsIII) in potable water samples. The filtration studies were carried out using the syringe filtration setup. Analysis of the arsenic (III) solution was carried out, before and after the filtration process using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), which showed a maximum of 50% reduction in its original concentration. The filtered membrane is analyzed for arsenic by Energy Dispersive X-ray (EDX) technique. Thus, the synthesized membrane effectively sieves the arsenic in water samples.

Constructing porous channels in superhydrophilic polyethersulfone composite nanofibrous membranes for sustainably enhanced photocatalytic activities in wastewater remediation

Photocatalysis is regarded as one of the most promising technologies to remediate wastewater for environmental friendliness. However, most of the powder photocatalysts still suffer from poor hydrophilicity, easy aggregation and difficult recycling, which have restricted their further applications in wastewater treatment. In this study, we constructed porous and superhydrophilic composite polyethersulfone nanofibrous membranes to load titanium dioxide (TiO2) and graphitic carbon nitride (g-C3N4) photocatalysts to achieve the UV light and visible light driven photocatalytic degradation for organic contaminants, respectively. Particularly, the resultant mesopores in nanofibers could promote the diffusion of contaminant molecules, facilitate the exposure of photocatalytic active sites, improve the light absorption, and finally enhance the photocatalytic activities. Moreover, benefiting from the further removal of poly(vinylpyrrolidone) during the repetitive reuse process, it was provided with a sustainable enhancement of reusability for the composite nanofibrous membrane, which was superior to most of the traditional wastewater remediation materials. Overall, these encouraging features of porous and superhydrophilic composite nanofibrous membrane not only make it promising candidate for wastewater purification, but also offer new pathways to develop advanced nanofibrous materials for diverse catalysis, adsorption and separation applications in environment remediation.

Preparation of composite polyethersulfone membrane containing basalt powder and optimization of the parameters using response surface methodology

ABSTRACT In this study, environmental-friendly composite polyethersulfone (PES) membranes based on basalt powder were prepared by phase inversion method. The effects of polymer percentage, the basalt percentage, and the thickness of the membrane were investigated on the distilled water flux, compaction factor, bovine serum albumin (BSA) rejection, contact angle, fouling factor and the parameters were modelled by response surface methodology (RSM). The distilled water flux increased when the basalt was added to the membrane up to 6% percentage of the polymer amount. The blending of basalt also provided resistance against the membrane compaction. The BSA rejection experiments approved the positive effects of basalt on the rejections efficiencies. At higher basalt percentages, the rejection efficiencies increased from 78% at the raw membrane to 99% for the composite membranes had 10% basalt. The adding of basalt to the membranes decreased the contact angles. The hydrophilicity of the membranes contained basalt in their structures was higher than those which had not basalt. By comparison with the neat membranes and the basalt added membrane, it can be said that the basalt increased the flux recovery and decreased the irreversible fouling factors. The basalt increased the antifouling properties for the composite membranes. Finally, the prepared membranes were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).

Greywater reclamation: A comparison of the treatment performance of UiO-66-NH2@GO nanocomposites membrane filtration with and without activated carbon pretreatment

Composite polyethersulfone membranes incorporating UiO-66-NH2@GO were successfully prepared through phase inversion method. The membrane physico-chemical properties were established using a combination of techniques such as FTIR, SEM, TGA, AFM, and water contact angle whilst their performance was assessed using a benchtop membrane set-up. Important parameters such as pure water flux, fouling propensity as well as permeate were measured. Concomitant decrease in surface roughness, water contact angle, and porosity of the membranes improved with increasing UiO-66-NH2@GO filler content. The resulted modified membranes improved the antifouling properties. The quality of the treated greywater was upgraded to below minimum standards (SANS 1732: 2019) for reuse for pH, turbidity, electrical conductivity (EC), total dissolved solids (TDS). Integrating membranes with activated carbon pretreatment step further increased the antifouling profile of the membranes as seen through at least six greywater fouling-washing cycles. The current method, combination of activated carbon and ultrafiltration membranes, can be utilized to improve the greywater quality as an alternative cost-effective and simple treatment that meets the standards of non-potable water reuse.

Heparin-mimicking semi-interpenetrating composite membrane with multiple excellent performances for promising hemodialysis

Natural heparin macromolecule has been widely used to improve the hemocompatibility of biomaterials. However, heparin can cause spontaneous bleeding in some patients, which is troublesome for clinical applications. Fortunately, analogous heparin polymers have shown promise to replace heparin. Here a new class of composite polyethersulfone (PES) membranes were constructed, which offered tunable permeability together with excellent hemocompatibility via incorporating heparin-mimicking semi-interpenetrating polymer. The polyurethane macromer was synthesized as an effective cross-linker to incorporate functional polyacrylic acid and poly-2-acrylanmido-2-methylpropanesulfonic acid segments into PES solution through in-situ cross-linking polymerization. Then the heparin-mimicking semi-interpenetrating composite PES membranes were fabricated from the resulting casting solution via alkali-induced phase separation technique. The resulting composite membranes showed excellent inhibition of protein adsorption, suppression of platelet adhesion, reduction of hemolysis ratio and prolongation of clotting times, while displayed high hydrophilicity, permeability and clearance to urea, creatinine and lysozyme. Interestingly, the composite membranes also exhibited excellent mechanical properties due to the synergistic effect of polyurethane composition and in-situ cross-linking copolymerization. To further demonstrate the applicability and effectiveness of this method, a composite PES hollow fiber with excellent ultrafiltration and mechanical properties was also fabricated. This straightforward and facile method is constructed as an ideal candidate to suppress blood clotting for a range of blood purification membrane-related applications.

Effect of graphene oxide (GO) and polyvinylpyrollidone (PVP) additives on the hydrophilicity of composite polyethersulfone (PES) membrane

Membrane based separation system is considered as a promising technology to purify water, owing to its simplicity and efficiency in operation. However, the application is limited by membrane fouling, which can lead to the declination of water flux and premature failure of membrane. The fouling can be controlled through membrane surface modification by blending hydrophilic materials during the casting solution preparation. Polyethersulfone (PES) membrane is naturally hydrophobic due to lack of oxygen functional group, which limits its application in the filtration of water. Therefore, modification of PES-based membranes is required. In this work, modification of the PES membrane was carried out by incorporating carbon-based nanomaterials (graphene oxide (GO)) and a well-known organic polymer (polyvinylpyrrolidone (PVP)). The effect of each additive toward the hydrophilicity of composite PES membrane was then investigated. GO was synthesized using modified Hummers method due to its simpler and shorter process. Each additive was added during the casting solution preparation and the amount added was varied from 0.5 to 1.0 wt%. The resultant composite PES membranes were characterized using XRD, FTIR and TGA prior to hydrophilicity and pure water flux (PWF) measurement. It was observed that the additives (PVP and GO) have significantly affected the membranes hydrophilicity, resulting in lower contact angle and higher pure water flux. The highest value of PWF (230 L/m2.h) with lowest contact angle (42 °) were observed for PES-1.0GOPVP membrane due to high amount of GO and PVP. Improved PWF performance of composite PES-1.0GOPVP membrane was attributed to the better dispersibility of the PVP and GO and increased surface hydrophilicity of the modified composite membranes. This study indicated that PVP and GO are effective modifiers to enhance the performance of PES membrane

Polyethersulfone-carbon nanotubes composite hollow fiber membranes with improved biocompatibility for bioartificial liver

Carbon nanotubes (CNTs) blended hollow fiber membranes (HFMs) are a promising new material in the area of biomedical engineering because they simultaneously provide tunable hydrophilicity along with selective permeability. In the present study, composite polyethersulfone (P) HFMs were fabricated using d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS or T) as compatibilizer, and carboxylated multiwalled CNTs (MWCNTs or C) as filler. The amount of MWCNTs was optimized for the improved hemocompatibility, cell viability, and cellular functionality. An optimum was found with the composte HFMs (PTC-2), where MWCNTs were used at concentration of 0.030 wt.%, as it exhibited improved compatibility with human blood. Further, these PTC-2 HFMs showed enhanced liver (HepG2) cells growth with the enhanced cell functional activities, mainly albumin secretion and glucose consumption. These developed composite membrane can act as a membrane material for liver cell bioreactor and bioartificial liver development because of their 3D scaffold like characteristic which enables cell growth, and selective permeability which helps in immunoisolation.

Investigations of inorganic and organic fouling behaviors, antifouling and cleaning strategies for pressure retarded osmosis (PRO) membrane using seawater desalination brine and wastewater

By employing seawater desalination brine (SWBr) and wastewater brine (WWBr) as the feed pair, membrane fouling behaviors as well as antifouling and cleaning strategies for the state-of-the-art thin-film composite polyethersulfone (TFC-PES) hollow fiber membrane have been systematically investigated under pressure retarded osmosis (PRO) operations. Fouling on the polyamide selective layer induced by the SWBr draw solution is relatively mild because of the outstanding membrane rejection and the hydration antifouling layer formed by the permeating water. However, using WWBr as the feed causes fast and severe internal concentration polarization (ICP) and fouling within the porous PES substrate, which result in dramatic flux and power density declines. In addition, the PRO fouling upon and within the porous substrate is highly irreversible. Experimental data show that both anti-scalant pretreatment and pH adjustment of WWBr could effectively mitigate inorganic fouling, while increasing feed flow velocity along the substrate surface is ineffective for fouling control. To clean the fouled membranes, hydraulic-pressure induced backwash and flushing with alkaline and NaOCl solutions on the fouled surface are effective strategies to remove foulants and regenerate membranes with a flux recovery of 83–90%. However, osmotic backwash shows low cleaning efficiency in PRO. In summary, a proper combination of feed pretreatment and membrane cleaning strategies has been demonstrated in this study to sustain PRO operations with a high water flux and power density.

Membrane fouling and anti-fouling strategies using RO retentate from a municipal water recycling plant as the feed for osmotic power generation

RO retentate from a municipal water recycling plant is considered as a potential feed stream for osmotic power generation in this paper. The feasibility of using RO retentate from a municipal water recycling plant was examined from two aspects: (a) the membrane fouling propensity of RO retentate, and (b) the efficacy of anti-fouling strategies. The membranes used in this study were the inner selective thin film composite polyethersulfone (TFC/PES) hollow fiber membranes, which possessed a high water permeability and good mechanical strength. Scaling by phosphate salts was found to be one possible inorganic fouling on the innermost layer of the PES membrane, whereas silica fouling was observed to be the governing fouling on the outmost surface of the PES membrane. Two anti-fouling pretreatments, i.e., pH adjustment and anti-scalant pre-treatment for the feed stream, were studied and found to be straightforward and effective. Using RO retentate at pH 7.2 as the feed and 1 M NaCl as the draw solution, the average power density was 7.3 W/m2 at 20 bar. The average power density increased to 12.6 W/m2 by modifying RO retentate with an initial pH value of 5.5 using HCl and to 13.4 W/m2 by adding 1.1 mM ethylenediaminetetraacetic acid (EDTA). Moreover, the flux recovery of the fouled membranes, without the indicated pretreatments, reached 84.9% using deionized (DI) water flushing and 95.0% using air bubbling under a high crossflow velocity of 23.3 cm/s (Re = 2497) for 30 min. After pretreatment by pH adjustment, the flux recovery increased to 94.6% by DI water flushing and 100.0% by air bubbling. After pretreatment by adding 1.1 mM EDTA into RO retentate, flux was almost fully restored by physical cleaning by DI water flushing and air bubbling. These results provide insight into developing an effective pretreatment by either pH adjustment or EDTA addition before PRO and physical cleaning methods by DI water flushing and air bubbling for membrane used in osmotic power generation.

Thermo‐Responsive Polyethersulfone Composite Membranes Blended with Poly(N‐isopropylacrylamide) Nanogels

AbstractThermo‐responsive composite polyethersulfone (PES) membranes blended with monodisperse poly(N‐isopropylacrylamide) (PNIPAM) nanogels were prepared from blends of PES solution and PNIPAM nanogels by phase inversion. The monodisperse and spherical PNIPAM thermo‐responsive nanogels were synthesized by precipitation polymerization. The blended PNIPAM nanogels did not affect the formation of the finger‐like pore structure of the PES membrane but resulted in microporous structures. The water flux across the composite membrane at temperatures above the lower critical solution temperature (LCST) of PNIPAM was much higher than that below the LCST because of thermo‐responsive shrinking/swelling of the PNIPAM nanogels, and the thermo‐responsive permeation characteristics were affected by the content of blended PNIPAM nanogels. The thermo‐responsive permeation performance of the composite membranes was reversible and reproducible.

Development of antifouling properties and performance of nanofiltration membranes modified by interfacial polymerisation

Two types of bisphenol monomers, Bisphenol A (BPA) and Tetramethyl Bisphenol A (TMBPA), with different concentrations of bisphenol aqueous solution (0.5% to 2.%w/v) and various interfacial polymerisation times (10 s, 30 s and 60 s) in the fixed 0.15%w/v organic solution of trimesoyl chloride (TMC)-hexane were studied. Irreversible fouling of both unmodified polyethersulfone NFPES10 and modified polyester thin-film composite polyethersulfone membranes were studied using humic acid model solutions at two different pH values, pH 7 and pH 3. It was observed that polyester thin-film composite membranes prepared by BPA exhibited fewer tendencies for irreversible fouling by humic acid molecules at neutral environment compared to unmodified NFPES10 and TMBPA-polyester series. This is most probably due to high electrostatic repulsion force between negatively charged of BPA-polyester layer and highly negative charged of humic acid at pH7. However, some modified membranes with rougher surfaces were severely fouled by humic acid molecules at acidic environment, pH 3. Under this acidic environment, carboxylic acid groups of humic acid lost their charge and the macromolecules of humic acid have smaller macromolecular configuration due to the increased hydrophobicity and reduced inter-chain electrostatic repulsion. Thus the molecules of humic acid may be preferentially accumulated at the valleys of the rougher membrane surface blocking them and resulting in a more severe fouling. In addition, the modification also affected membrane pore size and pore size distribution as shown by AFM images. It was also observed that the smaller pore size generated after modification does not have significant effect on humic acid removal due to the larger size of humic acid molecules. All the modified membranes posses smaller pore size than the unmodified NFPES10 (1.47 nm) in the range of 0.8–1.34 nm.