Improving the antifouling properties of ceramic membranes via chemical grafting of organosilanes

For enhanced antifouling surface properties, the alumina membranes were modified through a simple silanization process. Three organosilanes presenting neutral, positive, and negative charges were allowed to graft onto alumina membranes. A small decrease in the pore size and the successful chemical binding of organosilanes were confirmed, respectively. The membrane filtration test using humic acid (HA) was conducted to evaluate the effect of surface charges on fouling resistance. The neutral and negatively charged membranes achieved remarkable flux behaviour due to no charge interaction and electrostatic repulsion force, respectively. Especially, the negatively charged membranes presented the lowest flux decline, the highest flux recovery, and the lowest membrane fouling.     

Studies on fouling by natural organic matter (NOM) on polysulfone membranes: Effect of polyethylene glycol (PEG)

Polysulfone membranes were prepared via phase inversion technique by using polyethylene glycol with molecular weights of 400, 1500 and 6000 Da as pore forming agent in dope formulation. The performance of membrane was characterized using humic acid and water sample taken from Sembrong River, Johor, Malaysia was used as natural organic matter sources. Membrane properties were also characterized in terms of mean pore radius, pure water flux, humic acid rejection and fouling resistance. The results indicated that the pure water flux and mean pore radius of membranes increased with the increase of PEG content. Fourier transform infrared spectroscopy results revealed the presence of hydrophilic component in PSf/PEG blend with the significant appearance of O–H peak at 3418.78 cm^− 1. Scanning electron microscopy analysis revealed the presence of finger-like structure for all membranes and the structure intensified as PEG content was increased. The results obtained from the fouling study indicated that the membrane with the lowest PEG content and molecular weight has an excellent performance in mitigating fouling.     

Investigation of Fouling Mechanisms Using Surface Morphology and Physicochemical Membrane Features

The influences of membrane composition and surface morphology for membranes composed of polyethersulfone (PES) and fumarate alumoxane (Fum‐A) on fouling were investigated. Membrane fouling and blocking mechanisms were analyzed using the Hermia and combined pore blocking models. According to the Hermia fitted parameters, nanocomposite membranes revealed better antifouling properties. The lowest fouling coefficient belonged to the 2 wt % Fum‐A/PES membrane. In whey filtration, membrane surface morphology did not seem to have an important impact on the blocking mechanism as hydrophilicity. However, results clearly indicated a strong correlation between the surface morphology and the contribution of each individual fouling mechanism in the combined pore blocking/cake formation models.     

A novel method of surface modification on thin-film composite reverse osmosis membrane by grafting poly(ethylene glycol)

A novel method of surface modification by grafting hydrophilic poly(ethylene glycol) (PEG) chains onto the surface of a thin-film composite (TFC) polyamide reverse osmosis (RO) membrane was performed. Aminopolyethylene glycol monomethylether (MPEG-NH₂) was used as grafting monomer. The membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The changes in chemical composition and morphology of the membranes' surface indicated the successful grafting process. Furthermore, a preliminary experiment confirmed that the grafting of PEG chains improved membrane antifouling property.     

Photo‐induced grafting of poly(ethylene glycol) onto polyamide thin film composite membranes

In this study, the surface grafting of poly(ethylene glycol) (PEG) onto commercial polyamide thin film composite (TFC‐PA) membranes was carried out, using ultraviolet photo‐induced graft polymerization method. The attenuated total reflection Fourier transform infrared spectra verify a successful grafting of PEG onto the TFC‐PA membrane surface. The scanning electron microscope and atomic force microscope analyses demonstrate the changes of the membrane surface morphology due to the formation of the PEG‐grafted layer on the top. The contact angle measurements illustrate the increased hydrophilicity of the TFC‐PA‐g‐PEG membrane surfaces, with a significantly reduced water contact angles compared to the unmodified one. Consequently, the separation performance of the PEG‐grafted membranes is highly improved, with a significant enhancement of flux at a great retention for removal of the different objects in aqueous feed solutions. In addition, the antifouling property of the modified membranes is also clearly improved, with the higher maintained flux ratios and the lower irreversible fouling factors compared to the unmodified membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45454.     

Effects of the extractant on the hydrophilicity and performance of high‐density polyethylene/polyethylene‐b‐poly(ethylene glycol) blend membranes prepared via a thermally induced phase separation process

The blending of a block copolymer into the membrane matrix is a convenient and efficient way to modify membranes. In this study, high‐density polyethylene/polyethylene‐b‐poly(ethylene glycol) (PEG) membranes were prepared via a thermally induced phase separation process, and the extractant effect was investigated. An interesting finding was that the nonpolar extractant (n‐hexane) was more conducive to the surface enrichment of the PEG chains than the polar solvent (ethanol). The reason was deemed to be the combined effect of the entropy drive, interfacial energy, and swelling behavior. In addition, the membrane performance related to the surface chemical properties was studied. The results suggest that the prepared blend membranes extracted by n‐hexane showed enhanced the hydrophilicity, antifouling properties, and water flux. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3816–3824, 2013     

Influences of the chain structure of PE‐b‐PEG on the properties of PE/PE‐b‐PEG blend membranes prepared by TIPS

In this article, a series of diblock copolymer polyethylene‐b‐ poly(ethylene glycol)s (PE‐b‐PEGs) with various molecular weight of polyethylene segment was blended with linear low‐density PE. The PE/PE‐b‐PEG blend porous membranes with high porosity were obtained by thermally induced phase separation (TIPS) process. The isothermal crystallization kinetics of PE/LP/PE‐b‐PEG blends indicated that the introduction of PE‐b‐PEG could inhibit the growth rate of polyethylene crystals which could increase the pore size and porosity of the membranes. The PE/PE‐b‐PEG blend membranes with PE₁₃₀₀‐b‐PEG₂₂₀₀ showed the largest pore size and porosity due to its crystallization behavior during TIPS. The surface of the membranes became smoother and the morphology of the membranes could be effectively tuned by introducing PE‐b‐PEG. Compared with the PE membrane, the PE/PE‐b‐PEG blend membranes exhibited higher hydrophilicity (the water contact angle decreased from 112° to 84°), water permeability (the permeation flux increased from 80 to 440 L/m² h under 0.1 MPa), rejection performance (completely reject carbon particles in the filtration of carbon ink solution), and fouling resistance (the value of protein adsorption dropped from 0.25 to 0.05 mg/cm²). The hydrophilicity and fouling resistance of PE/PE‐b‐PEG blend membranes increased as the length of PE segment in PE‐b‐PEGs decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46499.     

Facile modification of aliphatic polyketone-based thin-film composite membrane for three-dimensional and comprehensive antifouling in active-layer-facing-draw-solution mode

The application of “active-layer-facing-draw-solution” (AL-DS) mode, which allows a considerably high water flux in forward osmosis (FO) processes, is hindered by severe fouling occurring within the porous support of the FO membranes. We designed a series of “three-dimensionally” antifouling FO membranes by an extremely convenient and scalable approach, by using in situ reduced aliphatic polyketone (PK) membranes (rPK) and the silver-nanoparticles-immobilized rPK-Ag membranes as the substrates for thin-film composite (TFC) FO membrane preparation. This modification imparted enhanced hydrophilicity compared with the original PK-TFC membrane, without affecting the morphology and transport properties. Benefiting from the three-dimensional antifouling structure, the modified TFC membranes (i.e., rPK-TFC and rPK-Ag-TFC membranes) demonstrated excellent and comprehensive fouling resistance towards a variety of organic foulants, as well as biofouling resistance towards Escherichia coli. These results provide useful insights into the fabrication of antifouling FO membranes for water purification purposes and pressure retarded osmosis (PRO) process.     

PA/PEG交联共聚反渗透膜的制备及耐污染性能

以聚丙烯腈（PAN）超滤膜为基底,在均苯三甲酰氯（TMC）和间苯二胺（MPD）界面聚合反应过程中引入聚乙二醇（PEG）,制备聚酰胺（PA）/PEG反渗透复合膜。利用傅里叶红外光谱（FTIR）、X射线光电子能谱（XPS）、场发射扫描电镜（FE-SEM）和原子力显微镜（AFM）等对膜的结构和物化性质进行了表征。考察了PEG分子量、PEG加入量、热处理温度及时间对膜反渗透性能的影响,并系统考察了膜对十二烷基硫酸钠（SDS）、十二烷基三甲基溴化铵（DTAB）以及牛血清蛋白（BSA）三种不同荷电性典型污染物的耐受性能。实验结果表明,相比于未改性的PA反渗透膜,PEG交联共聚反渗透膜的盐截留率和通量恢复率均有所提高。其中PA/PEG1000-0.1膜渗透通量为3.96kg/(m²?h),NaCl表观截留率为97.5%,并且对于SDS、DTAB和BSA都表现出较高的耐污染性,其中,SDS污染清洗后膜的通量恢复率可达89.4%。     

抗污染芳香聚酰胺反渗透膜研究进展

聚酰胺反渗透膜具有选择透过性高、化学稳定性好等优点,在水处理领域应用广泛。但膜污染导致的通量下降、寿命降低等问题严重制约了其发展与应用,开发抗污染反渗透膜是缓解膜污染的重要手段。本文根据抗污染膜作用机理将抗污染反渗透膜分为抗黏附型、污染驱除型和杀菌型,综述了近年来相关方面的研究成果,并对合理组合多种机制制备抗污染反渗透膜的进展进行简要概括,最后对抗污染反渗透膜的发展前景进行了展望。     

Surface modification of polyamide TFC membranes via redox‐initiated graft polymerization of acrylic acid

In this work, the redox‐initiated graft polymerization of acrylic acid (AA) onto the surface of polyamide thin film composite membranes has been carried out to enhance membrane separation and antifouling properties. The membrane surface characteristics were determined through the attenuated total reflection Fourier transform infrared spectra, scanning electron microscopy, atomic force microscopy, and water contact angles. The membrane separation performance was evaluated through membrane flux and rejection of some organic compounds such as reactive red dye (RR261), humic acid, and bovine serum albumin in aqueous feed solutions. The experimental results indicated that the membrane surfaces became more hydrophilic and smoother after grafting of AA. The modified membranes have a better separation performance with a significant enhancement of flux at a great retention. The fouling resistance of the modified membranes is also clearly improved with the higher maintained flux ratio and the lower irreversible fouling factor compared to the unmodified one. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45110.     

Preferable structure of poly(ethylene glycol) for grafting onto a cellulosic membrane to increase hemocompatibility without reduction in solute permeability of the membrane

Swelling layers formed by poly(ethylene glycol) (PEG) chains grafted onto surfaces of a cellulosic membrane are known to improve hemocompatibility of the membrane. Three types of hemodialysis membranes were derived from the same regenerated-cellulose hollow-fiber membrane by grafting PEG with different formulas onto the surfaces to clarify the influence of the grafted PEG chains on solute permeability of the membranes. Determination of volume fractions of nonfreezing water contained in the membranes by differential scanning calorimetry revealed that most of the PEG chains were grafted onto the external surfaces and less into the pores in the membranes. Permeability of vitamin B₁₂ for the PEG-grafted membranes except for the one with the shortest PEG chains was reduced as compared with the original membrane, while that of tritium-labeled water for all the PEG-grafted membranes was the same as that of the original membrane. Structural parameters only of the PEG-grafted membrane with the largest alkyl groups at the terminal of the PEG chains were different from those of the other PEG-grafted and original membranes. The shorter PEG chains with the larger terminal alkyl groups are suitable for grafting onto a cellulosic membrane to increase hemocompatibility of the membrane without significant reduction in the solute permeability of the membrane. © 1995 John Wiley & Sons, Inc.     

Influences of extractant on the hydrophilicity and performances of HDPE/PE‐b‐PEG blend membranes prepared via thermally induced phase separation (TIPS) process

Blending the block copolymer into the membrane matrix is a convenient and efficient way for membrane modification. In this study, HDPE/PE‐b‐PEG membranes were prepared via TIPS process, and the extractant effect was investigated. An interesting finding was that a non‐polar extractant (n‐hexane) was more conducive to the surface enrichment of PEG chains than a polar solvent (ethanol). The reason was deemed to be the combined effect of entropy drive, interfacial energy, and the swelling behavior. Besides, membrane performances related to the surface chemical properties were studied. Results suggested that the prepared blend membranes extracted by n‐hexane showed enhanced hydrophilicity, anti‐fouling property and water flux. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2680–2687, 2013     

Spray coating of polysulfone/poly(ethylene glycol) block polymer on macroporous substrates followed by selective swelling for composite ultrafiltration membranes

Polysulfone(PSF) is extensively used for the production of ultrafiltration(UF) membranes thanks to its high strength,chemical stability,and good processibility.However,PSF is intrinsically hydrophobic,and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems.Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded.Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes.The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol(PEG) on both ends,that is,PEG-b-PSF-b-PEG.We use the technique of spray coa ting to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports,instantly resulting in uniform,defect-free polymer coating layers with the thickness down to ～1.2 μm.The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation,thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers.This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods.The pore sizes,porositie s,hydrophilicity,and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath.This strategy combining spray coating and selective swelling is upscalable for the production of highperformance PSF UF membranes.     

Structure and Performance of Poly(vinylidene chloride‐co‐vinyl chloride) Porous Membranes with Different Additives

Poly(vinylidene chloride‐co‐vinyl chloride) (P(VDC‐co‐VC) membranes were prepared by non‐solvent‐induced phase separation and adjusted by adding water‐soluble polyethylene glycol (PEG) and water‐insoluble silicon dioxide (SiO₂) hydrophilic nanoparticles. The structure of pores and antifouling performance were investigated to illustrate the effect of these nanoparticles. The cross section of the P(VDC‐co‐VC) membrane exhibited more macropores and the typical finger‐like pores turned into more vertically interconnected ones with increasing PEG content, while the number and size of finger‐like pores became less with increasing SiO₂ content. Considering the filtration and antifouling experiments, the presence of hydrophilic PEG and SiO2 nanoparticles in the P(VDC‐co‐VC) polymer matrix improved the membrane performance in terms of high flux, high BSA rejection ratio, and fouling resistance.     

Effects of solubility parameter differences among PEG,PVP and CA on the preparation of ultrafiltration membranes: Impacts of solvents and additives on morphology,permeability and fouling performances

The effects of two different hydrophilic additives and two solvents on the membrane morphological structure,permeability property and anti-fouling performances of cellulose acetate (CA) ultrafiltration membranes were investigated.During the phase-inversion process,cellulose acetate was selected as a membrane forming polymer;polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as additives;acetone (Ac):N,N-Dimethylacetamide (DMAc) andN,N-Dimethylformamide (DMF) were used as solvents;and deionized (DI) water was used in the coagulation bath.All the prepared membranes were characterized in terms of hydraulic permeability (Pm),membrane resistance,average pore radius,and hydrophilicity.The top surface and crosssectional view of the prepared membranes were also observed by using field emission scanning electron microscopy.Membrane fouling and rejection experimentations were done using a stirred batch-cell filtration set-up.The experimental studies of fouling/rinsing cycles,rejection,and permeate fluxes were used to investigate the effect of PEG and PVP additives and effect of the two solvents on the fabricated membranes using bovine serum albumin (BSA) as a model protein.     

Self-doped sulfonated polyaniline ultrafiltration membranes with enhanced chlorine resistance and antifouling properties

Membranes heavily rely on chlorination to diminish (bio)fouling, but chlorination can also lead to membrane degradation. We developed sulfonated polyaniline (S-PANI) ultrafiltration (UF) membranes with improved chlorine resistance and intrinsic antifouling properties. The S-PANI membranes were synthesized through Non-solvent Induced Phase Separation (NIPS). Membrane performance was evaluated under harsh chlorine conditions (250 ppm sodium hypochlorite for 3 days under different pH conditions). The S-PANI membranes showed improved chlorine resistance including a stable performance without changes in model foulant BSA rejection. In contrast, PANI membranes suffered critical structural damage with complete leakage and commercial PES membranes showed a 76% increase in pure water flux and a noticeable change in BSA rejection. Small changes in S-PANI membrane performance could be linked to membrane structural changes with pH, as confirmed by SEM, IR spectroscopy, and contact angle measurements. Additionally, the S-PANI membranes showed better antifouling properties with a high flux recovery ratio in comparison to PANI membranes using alginic acid, humic acid, and BSA model foulants. Chemical cleaning by sodium hypochlorite re-instated the transport properties to its initial condition. Overall, the developed S-PANI membranes have a high chlorine tolerance and enhanced antifouling properties making them promising for a range of UF membrane applications.     

Improving the antifouling property of poly(vinyl chloride) membranes by poly(vinyl chloride)‐g‐poly(methacrylic acid) as the additive

To improve the antifouling property of poly(vinyl chloride) (PVC) membranes, a series of poly(methacrylic acid) grafted PVC copolymers (PVC‐g‐PMAA) with different grafting degree were synthesized via one‐step atom transfer radical polymerization process utilizing the labile chlorines on PVC backbones followed by one‐step hydrolysis reaction. PVC/PVC‐g‐PMAA blend membranes with different grafting degree and copolymer content were prepared by nonsolvent induced phase separation method. The surface chemical composition, surface charge, membrane structures, wettability, permeability, separation performances and the fouling resistance of blend membranes were carefully investigated. The results indicated that the PMAA chains were segregated towards the surface and the membranes were endowed with negative charge. The hydrophilicity and permeability of the blend membranes were obviously improved. Furthermore, the antifouling ability especially at neutral or alkaline environments was also significantly increased. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42745.     

Dendritic molecules give excellent long-lasting desalination fouling resistance to reverse osmosis membrane by generating an amine-rich layer

The organic fouling of polyamide membranes is one of the most serious problems in reverse osmosis fields such as sea water desalination and sewage disposal. In this study, poly(ethylene imine)–poly(ethylene glycol) dendrimer is used to improve the fouling resistance of polyamide reverse osmosis membranes. A crucial pretreatment is carried out with a reaction between poly(ethylene imine) and acyl chloride on the nascent polyamide surface, generating an amine-rich selective layer. Poly(ethylene glycol) diglycidyl ether is then attached to the primary amine group. The results illustrate a remarkable improvement in membrane surface hydrophilicity after modification (the contact angle decreases from 96.7° to 49.5°). Dynamic fouling tests are implemented with bovine serum albumin as a typical protein foulant, in which the membranes show very low protein adsorption (flux recovery ratio 96.9%). After 11-cycle fouling tests, the membranes show excellent long-term stability and remarkable antifouling property and cleaning performance. This approach of grafting a dendrimer might provide new insight for antifouling modifications for membranes. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47368.     

纳米SiO2-聚乙烯醇复合超滤膜的制备及应用

以水为溶剂，以聚乙二醇（PEG）为致孔剂，并通过向聚乙烯醇（PVA）溶液中添加纳米SiO2构成铸膜液。凝固浴为Na2SO4/KOH/N2O溶液。采用相转化过程制备纳米SiO2－PVA复合超滤膜。实验表明，膜孔径对压力是敏感的。考察了SiO2含量和PEG含量对膜性能的影响。该膜在含油废超滤实验中表现良好的抗污染性及稳定性。