Feasibility of using polycarbonate as a substrate of thin film composite membrane in forward osmosis

In the present study, thin film composite (TFC) forward osmosis (FO) membranes with polycarbonate (PC (and polyether sulfone (PES) as substrates were fabricated to investigate the impact of the structural parameters of substrate on the performance of the membranes. Firstly, the substrates were prepared by Loeb-Sourirajan method. Characterization techniques including FESEM, contact angle measurement, pure water flux, gas permeability test, and tensile test were applied to investigate the properties of the substrates. After preparing suitable substrates, active layers were fabricated via interfacial polymerization (IP) technique. The performance and characterization test showed that PC is a relatively hydrophilic polymer with a good property for using as a substrate of FO TFC membrane but as the result of gas permeability test show, this membrane has large surface pore size in comparison with PES membrane. Mean pore size of PC and PES membrane is 378 and 139 nm, respectively. Also, the results show that the effective surface porosity of PC (285, 1/m) is more than PES (213, 1/m) substrate.     

Developing thin‐film‐composite forward osmosis membranes on the PES/SPSf substrate through interfacial polymerization

A new scheme has been developed to fabricate high‐performance forward osmosis (FO) membranes through the interfacial polymerization reaction on porous polymeric supports. p‐Phenylenediamine and 1,3,5‐trimesoylchloride were adopted as the monomers for the in‐situ polycondensation reaction to form a thin aromatic polyamide selective layer of 150 nm in thickness on the substrate surface, a lab‐made polyethersulfone (PES)/sulfonated polysulfone (SPSf)‐alloyed porous membrane with enhanced hydrophilicity. Under FO tests, the FO membrane achieved a higher water flux of 69.8 LMH when against deionized water and 25.2 LMH when against a model 3.5 wt % NaCl solution under 5.0 M NaCl as the draw solution in the pressure‐retarded osmosis mode. The PES/SPSf thin‐film‐composite (TFC)‐FO membrane has a smaller structural parameter S of 238 μm than those reported data. The morphology and topology of substrates and TFC‐FO membranes have been studied by means of atomic force microscopy and scanning electronic microscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Selection of substrate manufacturing techniques of polyamine-based thin-film composite membranes for forward osmosis process

This paper is a comparative study on the preparation techniques used to make the support layer of polyamide-thin-film composite forward osmosis (TFC-FO) membranes. The role played by the support layer preparation technique in membrane performance is thoroughly investigated in this study. Electrospinning is shown to produce membranes of lower structural parameter compared to those obtained by conventional phase inversion techniques. The electrospun polyamide selective layer can also be tailored with the required properties. This makes electrospinning a promising process to design efficient FO membrane substrates. It is shown in this work that the FO water flux is more dependent on the internal structure of the support layer than the preparation materials. The main challenge remaining for substrates to operate in FO is to achieve simultaneously a low structural parameter, a high surface porosity, and the required mechanical properties. As most of today's approaches are not suitable, further materials development is essential in future investigations on TFC-FO membranes.     

Physical modification of polymeric support layer for thin film composite forward osmosis membranes by metal–organic framework-based porous matrix membrane strategy

Physical modification of support layers (SLs) for thin-film composite (TFC) forward osmosis (FO) membranes is the main goal of this study. Accordingly, the strategy of metal–organic framework (MOF)-based porous matrix membrane (PMM) was used for the fabrication of controllable SLs. Fourteen different TFC FO membranes were successfully fabricated by interfacial polymerization (IP) technique over the fourteen different SLs made of polyetherimide (PEI), polyethersulfone (PES), and twelve MOF-based PMM. The controllable MOF particles, fabricated SLs, and TFC membranes were characterized by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle (CA), inductively coupled plasma (ICP), and developed SHN1 method. The results showed that the PMM strategy can lead to an increase in the degree of crosslinking of polyamide (PA) as a result of physical modification of the original SLs. Also, the PMM strategy reduced the structural parameters and hence the internal concentration polarization (ICP) was controlled. However, according to the characteristic curve, physical modification of the structure of PES and PEI by MOF-based PMM strategy caused a small and dramatic effect (respectively) on the performance of the TFC FO membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48672.     

Polyethyleneimine-Mediated Polyamide Composite Membrane with High Perm-Selectivity for Forward Osmosis

Thin-film composite (TFC) membranes comprised of a polyamide (PA) selective layer upon a porous substrate dominate the forward osmosis (FO) membrane market. However, further improvement of perm-selectivity still remains a great challenge. Herein, a polyethyleneimine (PEI) interlayer is intentionally designed prior to interfacial polymerization (IP) to tailor the PA layer, which thus improves the separation performance. The PEI interlayer not only improves the substrate hydrophilicity for adsorbing more diamine monomer and controlling its release rate, but also participates in IP reaction by crosslinking with acyl chloride (TMC). Furthermore, it can decrease the electronegativity of the substrate for decreasing reverse salt diffusion. Consequently, a denser, thinner and smoother PA layer is formed due to the uniform distribution, controllable release of diamine monomer and the extra crosslinking between PEI and TMC. Furthermore, the PA layer becomes more hydrophilic with PEI involvement. As a result, the asprepared TFC membrane exhibits a favorable water flux of 16.1 L m⁻² h⁻¹ and an extremely low reverse salt flux (1.25 g m⁻² h⁻¹). Meanwhile, it achieves an excellent perm-selectivity with a ratio of water to salt permeability coefficient of 8.25 bar⁻¹. Moreover, it exhibits an outstanding antifouling capacity. The work sheds light on fabricating high perm-selective membranes for desalination.     

A design of composite hollow fiber membranes with tunable performance and reinforced mechanical strength

A new design of hollow fiber membranes with high mechanical strength, great surface area per volume ratio and tunable filtration performance is presented. This newly developed hollow fiber membrane was produced by an intensified production process, in which the processes of thermally induced phase separation (TIPS), non‐solvent induced phase separation (NIPS), and interfacial polymerization (IP) were combined. PVDF (polyvinylidene difluoride) hollow fiber membranes (produced by TIPS) were used as support substrates. Afterwards, PES (polyethersulfone) (made by NIPS) and PA (polyamide) layers (manufactured by IP) were coated one by one. The pure water permeability, molecular weight cut off (MWCO), salt rejection, tensile stress together with surface and cross‐sectional morphology indicate that the properties of the hollow fiber membranes can be easily adjusted from microfiltration‐like to nanofiltration‐like membranes only by varying the presence of the IP step and the concentration in the PES layer in the production system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41247.     

PA/PVA/PA多层交替复合分离膜的制备与表征

以工业应用的反渗透(RO)聚酰胺(PA)复合膜为支撑膜,通过组合浸涂法和界面缩聚(IP)法的两步成膜工艺,制备了分离层为交替复合的聚酰胺/聚乙烯醇/聚酰胺(PA/PVA/PA)多层复合膜(MLCM).用扫描电子显微镜(SEM)和原子力显微镜(AFM)分析了PA/PVA/PA MLCM的结构特征.结果表明,浸涂和IP的工艺条件是影响MLCM的分离性能以及微结构的主要因素.优化工艺制成的PA/PVA/PA MLCM,在实验温度20℃和下游真空度小于1000 Pa时,渗透汽化(PV)分离异丙醇(IPA)浓度为87.8%的水混合物,渗透通量(J)为60～80 g·m~(-2)·h~(-1),渗透物中水含量(CC_(p-H_2O))达99%以上.不同材料制成的多层交替复合的分离层具有显著的微结构形态和独特的双重选择性分离功能,其纳米-亚微米级厚度的多层结构强化了复合膜的水渗透性.     

刮刀厚度对聚酰胺正渗透复合膜性能的影响

为考察正渗透过程基膜厚度对膜水通量的作用,有效地提高膜的综合性能,采用浓度2 mol/L的NaCl作为汲取液、去离子水为原料液作为评价系统,考察了刮刀厚度不同对正渗透复合膜性能的影响。结果表明,以筛孔80μm的筛网作为支撑材料,当采用厚度为45μm的刮刀所制备的超滤膜作为支撑材料时,制备所得的正渗透复合膜性能为佳,结构参数S可低至1.086 mm;并具有最好的稳定性以及最佳的污染冲洗恢复效果。     

Synthesis and characterization of PVC-TFC hollow fibers for forward osmosis application

Forward osmosis (FO) is considered among the most encouraging water desalination processes as a result of its high performance and low energy demand. Thin-film composite (TFC) hollow fibers (HF) were synthesized and examined in the FO process. Three different concentrations of polyvinyl chloride (PVC) support polymer were fabricated via the phase inversion technique. The polyamide layer was synthesized on the outer surface of the PVC-HF substrate via interfacial polymerization (IP) reaction. To the best of our knowledge, PVC HF was used in this research for the first time as a support for TFC-FO membranes. PVC HFs have high-quality specifications that are expected to have outstanding performance in TFC-FO applications, especially for water desalination. The obtained membranes were characterized using contact angle measurement, scanning electron microscopy, atomic force microscope and Fourier-transform Infrared. The performance of the PVC-TFC HF was examined in the FO under standard conditions. Results showed that the membrane fabricated with a lower concentration of PVC substrate exhibited higher water flux in comparison to the higher concentration PVC membrane. Changing the concentration of PVC from 15% to 18% reduced water flux from 25 to 13 L m⁻² h⁻¹; however, salt flux also decreased from 8 to 3 g m⁻² h⁻¹.     

Thin film composite forward osmosis membranes with poly(2‐hydroxyethyl methacrylate) grafted nano‐TiO2 as additive in substrate

The poly(2‐hydroxyethyl methacrylate) grafted titanium dioxide nanoparticles were synthesized and added to the substrate of flat‐sheet thin film composite forward osmosis (TFC‐FO) membranes. The hydrophilicity of substrate was improved, which was advantageous to enhance the water flux of TFC‐FO membranes. The membranes containing a 3 wt % TiO₂‐PHEMA in the substrate exhibited a finger‐like structure combined with sponge‐like structure, while those with lower or without TiO₂‐PHEMA content showed fully finger‐like structures. As for FO performance, the TFC‐FO membranes with 3 wt % TiO₂‐PHEMA content achieved the highest water flux of 42.8 LMH and 24.2 LMH against the DI water using 2M NaCl as the draw solution tested under the active layer against draw solution (AL‐DS) mode and active layer against feed solution (AL‐FS) mode, respectively. It was proven that the hydrophilic property of membrane substrates was a strong factor influencing the water flux in FO tests. Furthermore, the structural parameter was remarkably decreased with an increase of TiO₂‐PHEMA content in membrane substrate, indicating the reducing of internal concentration polarization. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43719.     

Primary study of novel poly(acrylic sodium)/poly(ether sulfone) composite ultrafiltration membranes (I) the preparation of composite membrane

The poly(acrylic sodium) (PAS)/poly(ether sulfone) (PES) composite ultrafiltration membranes were prepared by coating PAS membrane solution on PES support membrane. The effects of substrate membrane, the composition of PAS solution such as PAS concentration, the choice of the solvent and the additive, and the thickness of PAS active layer on the performance of the composite membranes were extensively investigated. The experimental results have indicated the optimal PAS/PES composite membranes, containing a PES substrate with MWCO of 70,000, together with a PAS top layer having a thickness of about 20 μm, were tested at room temperature and under the pressure of 0.6 MPa with the mass concentration of 0.005 g/L poly(ethylene glycol) (PEG) (Mw = 1000 g/mol) solution, a flux of 32.6 L/(m² h) and a rejection of 92.2% were obtained, which are superior to those of the common commercial membranes reported.     

Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization

Polyamide(PA)-based thin-film composite membranes exhibit enormous potential in water purification, owing to their facile fabrication, decent performance and desirable stability. However, the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications. The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging. Herein,a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone(PES) substrate to reduce the thickness of PA active layer in interfacial polymerization. The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules, while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate. Arising from those synergetic effects, the PA active layer is effectively reduced from 200 nm to 120 nm. By optimizing TpPa-1 interlayer and PA active layer, the water flux of resultant membranes can reach 171.35 L·m~(-2)·h~(-1)·MPa~(-1), which increased by 125.4% compared with PA/PES membranes, while the rejection rates of sodium sulfate and dyes solution remained more than 90% and 99%, respectively. Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances.     

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.     

界面聚合中空纤维正渗透膜的制备和表征

以聚砜为原料,通过浸没沉淀法制备中空纤维基膜,然后采用界面聚合法制备出中空纤维正渗透膜。考察了制膜参数、基膜结构和FO性能三者之间的关系。结果表明基膜的厚度为影响FO性能的主要因素之一。基膜的厚度越厚,FO过程中渗透效率越低。制得PSF中空纤维正渗透膜的厚度为0.129 mm,断裂拉伸力为2.48 N,FO通量为10.3 L·m^-2·h^-1,逆向盐扩散性能为0.15 g·L^-1。     

Improved separation performance of polyamide based reverse osmosis membrane incorporated with poly(dopamine) coated carbon nanotubes

A series of polyamide thin-film nanocomposite (PA TFN) membranes have been fabricated by incorporating hydrophilic poly(dopamine) (PDA) coated carbon nanotubes (CNTs@PDA) into the PA selective layer via interfacial polymerization. The effects of PDA coating thickness on surface characteristics and separation performances of membranes are studied in detail. The PDA coating makes the surface of PA TFN membrane more hydrophilic, smoother and less electronegative. The desalination performance is obviously influenced by the coating thickness of PDA and the loading concentration of PDA@CNTs. The water fluxes of PDA@CNTs incorporated PA TFN membranes have been improved without sacrificing NaCl rejections. When the loading concentration is 0.0010%, the maximum water flux is 48.1 L m⁻² h increasing by 45% compared with that of pristine PA membrane. Meanwhile, the NaCl rejection is up to 99.8%. The CNTs@PDA incorporated PA TFN membranes exhibit better anti-fouling property and separation performance durability. This work proves that CNTs@PDA has great potential application in PA TFN membranes.     

商业正渗透膜的改性及其用于处理焦化废水的研究

正渗透技术是一种新兴的膜分离技术，在处理有机废水方面具有广阔的应用前景。分别对Poten以及HTI商业正渗透膜进行改性，并用于对焦化废水中难降解毒性小分子(吲哚和吡啶)的截留测试。探究了水相单体PIP浓度、膜朝向、汲取液浓度对改性前后两种膜水通量、J_s/J_w比值、有机物截留率的影响，以及改性前后两膜特征参数的变化。结果表明：对Poten膜和HTI膜进行界面聚合改性后，膜水通量以及J_s/J_w比值都不同程度地降低；改性后的两正渗透膜水渗透系数A、盐渗透系数B均降低，而膜结构参数S以及对NaCl和有机物的截留率均提高；其中HTI-IP复合膜对有机物的截留率(81%)明显高于IP-2(改性Poten膜)复合膜；与FO模式相比，IP-2复合膜在PRO模式下(汲取液面向活性层)具有更高的水通量及反向盐通量。此外，在两种膜朝向下，水通量及反向盐通量都随汲取液浓度的增大而增大，但是在FO模式下(料液面向活性层)，通量呈现非线性增长。     

The influence of membrane formation parameters on structural morphology and performance of PES/PDMS composite membrane for gas separation

In this study, influence of membrane preparation parameters on structural morphology and performance of polyethersulfone/polydimethylsiloxane (PES/PDMS) composite membrane was investigated for gas separation. Asymmetric PES flat sheet membranes were composed by phase inversion method and used as supports. PES composite membranes were fabricated by coating silicone rubber as selective layer on the top surface of support. Effects of different concentrations of PES and PDMS, solvent type, and support thickness on membrane performance were investigated for separation of oxygen from nitrogen. The optimized superior membrane was further modified using polyvinylidenfluoride, methanol and ethanol as additives in PES solutions and/or in water coagulation bath to promote the membrane capability. The results showed that addition of ethanol and methanol in cast solution and coagulation bath can greatly affect the morphology and hence the performance of the prepared membranes. The permeance changes have the contrary trend with solubility parameter difference between solvent and nonsolvent mixture, for instance when this parameter difference was lowest, higher permeance was obtained. Support and coating polymer concentration can control the permeance. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thin-film composite forward osmosis membrane prepared from polyvinyl chloride/cellulose carbamate substrate and its potential application in brackish water desalination

Synthesized by the reaction between α-cellulose and m-tolyl isocyanate (MTI), cellulose carbamate (CC) was blended with polyvinyl chloride (PVC) to fabricate substrates for thin-film composite (TFC) forward osmosis (FO) membranes. The introduction of CC into substrates improved both membrane structure and performance. The substrates exhibited higher porosity and hydrophilicity, and better connective pore structure; while rejection layer exhibited better morphology but limited cross-linked degree decrease after the introduction of CC. According to the results, the CC blend ratio of 10% was the optimal ratio. With this blend ratio, the TFC-10 membrane presented favorable water permeability (1.86 LMH/bar) and structure parameter (337 μm), which resulted in excellent FO performance (water flux with a value of 40.40 LMH and specific salt flux with a value of 0.099 g/L under rejection layer faces draw solution [DS] mode when 1 M NaCl and deionized water were utilized as DS and feed solution). In addition, the TFC-10 membrane showed good water flux and low-sulfate ion leakage in the potential application of brackish water desalination.     

聚醚砜中空纤维膜的制备

讨论了在二次成形聚醚砜(PES)中空纤维膜的制备中,PES浓度和不同的填充液对中空纤维膜结构和性能的影响。结果发现:随着PES浓度的增大,中空纤维膜的水通量呈下降的趋势,确定了二次成形PES中空纤维膜制备中PES最佳浓度为24%;不同填充液与溶剂之间的相互扩散速率不同,得到了具有不同结构的聚醚砜中空纤维膜。随着填充液压力的提高,纤维的内径、外径增加,壁厚减小,水通量增大,一般填充液压力为0.020MPa。     

Effect of the manufacturing conditions on the structure and performance of thin-film composite membranes

A systematic investigation of the influence of the manufacturing conditions on the structure and performance of thin-film composite (TFC) membranes is presented for polyamide (PA) supported by poly(ether sulfone) (PES). The TFC membranes were composed of an ultrathin PA layer synthesized by interfacial polymerization on top of a porous PES support layer formed by immersion precipitation. For the PES support layer, the role of the wetting pretreatment, initial casting film thickness, and relative air humidity were studied. Assuming a strong correlation between the thermodynamics and the hydrodynamics of the casting process, we derived new insights from scanning electron microscopy images and the experimental data. In view of optimization of the flux through the membranes, a wetting pretreatment should be avoided. Important polymer savings were obtained without a loss of performance through a decrease in the casting thickness in combination with the use of a very smooth support. Last but not least, a high air humidity during casting was found to inhibit the formation of a dense, defect-free skin layer. For the PA layer, the interfacial polymerization method, the drying method, and the curing time were studied. The clamping of the membrane in a frame with one side in contact with the piperazine (PIP) solution and the other side to the air yielded the highest membrane flux and rejection with the lowest use of PIP and trimesoylchloride solution. Because of the absence of a uniform PIP solution layer for some drying methods, nodular PA structures could be observed in the macrovoids of the underlying PES layer because of hexane intrusion; this resulted in a dramatic decrease in the flux. Moreover, the omission of the drying step did not result in a significant loss of performance and enhanced the ease of operation. Finally, a curing time of 8 min was found to be optimal. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012