三乙酸纤维素正渗透膜的制备与性能

以三乙酸纤维素（CTA）为膜材料,1,4-二氧六环、丙酮为溶剂,甲醇、乳酸为添加剂,采用相转换法制备了三乙酸纤维素正渗透膜。研究了不同1,4-二氧六环/丙酮配比、添加剂乳酸含量、挥发时间、膜厚度、热处理温度条件下正渗透膜性能的变化规律。研究表明,当采用纯水为原料液,0.56mol/L CaCl2为汲取液时,优化制备的CTA正渗透膜的水通量达到14.10L/(m2?h),溶质反扩散量为0.031mol/(m2?h);采用0.1mol/L NaCl为原料液,4mol/L葡萄糖为汲取液时,优化制备的CTA正渗透膜的水通量保持在5L/(m2?h)以上,对NaCl的截留率大于99%。CTA正渗透膜相比于HTI膜,具有较高的亲水性、水通量、截留率,稳定性更好。     

The application of polyethyleneimine draw solution in a combined forward osmosis/nanofiltration system

The objective of this study is to investigate the effect of solution chemistry of branched polyethyleneimine (PEI) draw solute and to evaluate the PEI draw solute in a combined forward osmosis (FO)/nanofiltration (NF) system. Pure water was extracted from feed solution using the FO process, and the separation of pure water was achieved by the NF process. Lower molecular weight PEI showed higher water flux than higher molecular weight PEI, due to the lower internal concentration polarization caused by a higher diffusion rate and the easy permeation of pure water by lower viscosity of the draw solution (DS). The FO water flux was determined by the osmotic pressure induced by protonation/deprotonation of PEI, and the reverse draw solute flux was determined by the combination of PEI size due to the speciation and electrostatic interaction between the membrane and PEI. This study shows that the J_s/J_w value of PEI at pH 7 was smaller than those of sodium chloride and magnesium sulfate. The recovery of PEI DS using NF has a higher value (99.4%) than of sodium chloride (20.6%) and magnesium sulfate (97.0%); this means that PEI would be a promising draw solute in an FO–NF combined system for the saline water desalination. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42198.     

Unsupported electrospun membrane for water desalination using direct contact membrane distillation

In this project, an unsupported electrospun poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) membrane was used for water desalination using direct contact membrane distillation (DCMD). The membrane was electrospun using a laboratory-scale machine with multiple nozzles that was developed in-house. Critical process parameters, including the applied voltage and polymer concentration, were optimized to obtain bead-free electrospun membranes with fiber diameters less than 300 nm. To improve the membrane thermal stability and performance, the selected electrospun membrane was heat-pressed at 160°C. The untreated and heat-pressed membranes were tested in a DCMD setup at different feed temperatures (60, 70, and 80°C) and feed flow rates (0.4, 0.6, and 0.8 L/min), while maintaining the permeate temperature and flow rate at 20°C and 0.2 L/min, respectively. The modified electrospun membrane exhibited a very high permeate flux (>37.5 kg/m²/h) and a salt rejection rate of 99.99% at a feed temperature of 70°C. The performance of the heat-pressed unsupported PVDF-HFP electrospun membrane was nearly identical to a commercially available polytetrafluoroethylene (PTFE) supported membrane. These promising results demonstrate that relatively low-cost electrospun membranes can be easily produced and successfully used in DCMD to minimize the capital cost and increase the energy efficiency of the process.     

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.     

Low-cost and biodegradable cellulose/PVP/activated carbon composite membrane for brackish water treatment

A simple fabrication of a biodegradable membrane for use in water purification systems is presented in this work. Sodium carboxymethyl cellulose and PVP are dissolved in water and crosslinked with citric acid. The presence of glycerol has given immense flexibility and mechanical strength to the membrane. The addition of activated charcoal has enhanced its purification and dye adsorption capabilities at room temperature in dark and light conditions. The polymer semiconductor composites are completely soil degradable within a week and the membrane also exhibits good electrical conductivity when compared to the membrane without charcoal. The addition of glycerol has acted as molecular spacer between polymers composite's monomer backbone that allows good electron mobility of 9.9 cm² V⁻¹ s⁻¹. The dye adsorption efficiency of the material with two commonly used toxic textile dyes is found to be 100% for methyl orange and up to 57% for Rhodamine B within 3 h. The material shows good dye adsorption efficiency under dark and light conditions with acidic, neutral, and alkaline pH. Salt rejection was also found to increase from 25.3 to 64.4% with applied voltage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48746.     

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.     

Fabrication of anti-fouling thin-film composite reverse osmosis membrane via constructing heterogeneous wettability surface

Anti-fouling properties are tightly related to the surface properties of reverse osmosis (RO) membranes. In our study, fluorinated polyethyleneimine (FPEI) was synthesized by introducing perfluoroalkyl groups into a hydrophilic polyethyleneimine (PEI) matrix, and the heterogeneous wettability surface with hydrophilic and low-surface-energy properties was constructed by grafting FPEI on membrane surface via the carbodiimide-induced method. Verified by the result analysis of SEM, AFM, and zeta potentials measurements, the fluorinated RO membrane surface presented denser, smoother, and reduced negative charge. The surface free energy of RO membrane surface after grafting FPEI decreased from 45.5 to 38.7 mJ/m². By using bovine serum albumin (BSA), humic acid (HA), and dodecyltrimethyl ammonium bromide (DTAB) as model foulants, the fluorinated RO membrane exhibits optimal fouling resistance and fouling release properties compared to pristine membrane and membrane modified by surface grafting hydrophilic PEI. Especially, the high recovery ratio (99%) and low total flux decline ratio (17.2%) were acquired during the filtration of BSA solution. These results manifested that the construction of a heterogeneous wettability surface can further improve the anti-fouling properties of RO membranes compared to a pure hydrophilic surface, and the corresponding anti-fouling mechanism was put forward.     

Tris(hydroxymethyl)aminomethane polyamide thin‐film‐composite antifouling reverse osmosis membrane

For the applications of reverse osmosis (RO) process, membrane fouling caused by organic molecule adsorption is still a serious problem which significantly decreases membrane lifespan and increases operation costs. In this present article, we report the thin film composite (TFC) RO membrane functionalized with tris(hydroxymethyl)aminomethane (THAM) using one‐step method for improved antifouling property. The results of surface characterization indicated that THAM was successfully grafted onto the active layer of membrane by covalent linkage. Mult‐hydroxyl‐layer was generated and remained steadily on TFC membrane surface after modification. The contact angle decreased from 75.9 ± 3.0° to 46.9 ± 2.3°, which showed a distinct improvement of membrane surface hydrophilicity after modification. The grafted THAM improved water flux by 28.3%, while salt rejection was almost unchanged in membrane property tests. The modified membranes presented preferable antifouling property to foulants of bovine serum albumin, sodium alginate, and dodecyl trimethyl ammonium bromide than that of pristine membranes during dynamic fouling experiments. The method in this study provided an effective way to improve antifouling property of the polyamide thin‐film‐composite RO membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45891.     

Influence of support layer and PDMS coating conditions on composite membrane performance for ethanol/water separation by pervaporation

A systematic study was performed on the combination of support properties and polydimethylsiloxane (PDMS) coating conditions for the lab‐scale preparation of a defect‐free, thin film composite membrane for organophilic pervaporation. Support layers having comparable surface porosities were prepared from three polymers with different chemical composition (PVDF, PSF, PI). Their exact role on the deposition of the PDMS coating (i.e., wetting and intrusion) and the final membrane performance (i.e., effect on mass transfer of the permeants) was studied. The crosslinking behavior of dilute PDMS solutions was studied by viscosity measurements to optimize the coating layer thickness, support intrusion and wetting. It was found essential to pre‐crosslink the PDMS solution for a certain time prior to the coating. Dip time for coating the PDMS solution on the supports was varied by using automated dip coating machine. The performance of the synthesized membranes was tested in the separation of ethanol/water mixtures by pervaporation. Both flux and selectivity of the membranes were clearly influenced by the support layer. Resistance of the support layers increased by increasing the polymer concentration in the casting solutions of the supports. Increasing the dip time of the PDMS coating solution led to increased selectivity of the composite membranes. Scanning Electron Microscopy analysis of the composite membranes showed that this leads to a minor increase in the thickness of the PDMS top layer. Top layer thickness increased linearly with the square root of the dip time (t^0.5) at a constant withdrawal speed of the support. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43670.     

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.     

Preparation and characterization of a composite nanofiltration membrane interfacially polymerized from cis,cis‐1,3,5‐triaminocyclohexane and trimesoyl chloride

cis,cis‐1,3,5‐Triaminocyclohexane (TAC) was synthesized and used to prepare composite nanofiltration (NF) membranes by interfacial polymerization with trimesoyl chloride (TMC). The surface elemental composition, morphology, and hydrophilicity of the prepared NF membranes were characterized. The separation performances were examined with various salts and polyethylene glycol (PEG400, PEG600) solutions. The effects of preparation conditions were also systematically studied. The NF membrane was negatively charged and exhibited a salt rejection in the order Na₂SO₄ (98.2%) > MgSO₄ (90.8%) > MgCl₂ (84.5%) > NaCl (54.6%). The water permeability was 1.56 L m^?2 h^?1 bar^?1, and the molecular weight cutoff was 600 Da. The TAC/TMC membrane exhibited some characteristics that were different from the ones made from common diamines such as m‐phenylenediamine: (1) the surface was smoother, without a ridge‐and‐valley structure; (2) there were two kinds of crosslinking points in the polyamide chains; (3) the active layer was formed faster (only 5 seconds was required to reach a Na₂SO₄ rejection of 98%). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43511.     

Positively charged hollow‐fiber composite nanofiltration membrane prepared by quaternization crosslinking

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by interfacial polymerization to develop a positively charged dense network structure. According to this mechanism, a positively charged hollow‐fiber composite nanofiltration (NF) membrane was prepared by quaternization to achieve a crosslinked PDMAEMA gel layer on the outer surface of polysulfone hollow‐fiber ultrafiltration (UF) membranes with a PDMAEMA aqueous solution as a coating solution and p‐xylylene dichloride as an agent. The preparation conditions, including the PDMAEMA concentration, content of additive in the coating solution, catalyzer, alkali, crosslinking temperature, and hollow‐fiber substrate membrane, were studied. Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the structure of the membranes. This membrane had a rejection to inorganic salts in aqueous solution. The rejection of MgSO₄ (2 g/L aqueous solution at 0.7 MPa and 25°C) was above 98%, and the flux was about 19.5 L m^?2 h^?1. Moreover, the composite NF membranes showed good stability in the water‐phase filtration process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Spray-coated PDMS/PVDF composite membrane for enhanced butanol recovery by pervaporation

In this study, spray-coating was used to prepare dihydroxypolydimethylsiloxane (PDMS) composite membranes with high flux and separation factor for biobutanol recovery from aqueous solution. A thin, smooth, and defect-free PDMS layer was prepared by spray-coating on polyvinylidene difluoride ultrafiltration membrane with little PDMS penetration. The effects of process parameters for membrane fabrication and pervaporation on membrane performance were investigated. A membrane with 2 μm active layer was obtained with a high flux of 1306.9 g/m² h. The optimal membrane with the highest pervaporation separation index (PSI) (19.15 kg/m² h) showed a total flux of 530.6 g/m² h and a separation factor of 36.1 at 37°C, and a PSI of 65.61 kg/m² h and a flux of 1927.0 g/m² h at 70°C. Membrane performance was affected by feed composition and temperature. Acetone-butanol-ethanol solution and fermentation broth gave lower butanol fluxes and separation factors compared to butanol model solution.     

Effects of preparation parameters on CO2/N2 gas permselectivity of polyether thin film composite membrane

In this work, ether oxide (EO)-based multilayer composite membranes were prepared via interfacial polymerization (IP) of trimesoyl chloride (TMC) and polyetheramine (PEA) on polydimethylsiloxane precoated polysulfone support membrane. The effects of preparation parameters, such as monomer concentrations, reaction time, and heat-treatment temperature on the membrane performance were investigated. The optimal preparation parameters have been concluded. The results showed the increasing monomers concentration of both PEA and TMC can lead to the decrease of CO₂ permeance and increase of CO₂/N₂ selectivity. The optimal monomers concentration was found. When monomer concentrations are higher than the optimal values, the CO₂ permeance decreases continually while CO₂/N₂ selectivity only shows a very limited improvement with the further increase of monomers concentration. The reaction time has similar effects on membrane performance as the monomers concentration. The effect of heat-treatment temperature was also studied. With the increasing heat-treatment temperature, the CO₂ permeance shows a decrease tendency, while the CO₂/N₂ selectivity shows a maximum at 80 °C. When PEA is 0.013 mol L⁻¹, TMC is 0.020 mol L⁻¹, reaction time is 3 min, and heat-treatment temperature is 80 °C, the optimum preparation conditions are achieved with CO₂ permeance of 378.3 gas permeation unit (GPU) and CO₂/N₂ selectivity of 51.7 at 0.03 MPa. This work may help to design and fabricate gas separation membranes with desired performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47755.     

A solvent-resistance OTS/PDA/O-PASS composite membrane for water-in-oil emulsions separation

Water-in-oil emulsions separation plays a critical role in industrial wastewater treatment. Membrane technology has attracted much interest in water-in-oil emulsions separation field for its excellent separation performance and facile processing method. However, versatile membrane with better solvent-resistance is still absent in chemical industry. In this work, oxidized polyarylene sulfide sulfone (O-PASS) membrane was severed as substrate, on which a hydrophobicity surface was built via coating of octadecyltrichlorosilane (OTS). And polydopamine (PDA) layer was employed and acted as connector between OTS and O-PASS membrane due to its abundant active hydroxyl group. The maximum water contact angle was 132.6° indicating good hydrophobicity of the membrane. Finally, the OTS/PDA/O-PASS composite membranes showed good separation performance for corrosive emulsions: the rejection and flux were 93.0% and 10.0 L/m²h for water-in-dichloromethane emulsions, and the rejection and flux were 92.3% and 34.6 L/m²h for water-in-n-hexane emulsions. The OTS/PDA/O-PASS composite membrane is a new candidate membrane for water-in-oil emulsions separation. In addition, the superior performance of the composite membrane under harsh environment conditions ensures its usefulness in resistance aggressive solvent.     

超薄皮层反渗透复合膜制备技术的研究进展

聚酰胺皮层的物化性质是决定反渗透复合膜（TFC-RO膜）物质筛分和水透过效率的关键性因素。近年来,基于超薄皮层（通常<50nm）的高性能复合膜研究取得了重要的进展。本文总结并分析了超薄皮层反渗透复合膜的研究进展,如低单体浓度控制技术、分子层层自组装（mLBL）、静电打印技术、界面优化技术及新型纳米材料技术的成膜机理及特性,对比了各项制备技术的优缺点。总体来说,超薄皮层反渗透复合膜的研究为精细设计聚酰胺皮层的物化结构,进一步设计更高效率的反渗透复合膜提供了重要思路,但超薄皮层与聚酰胺层微纳结构之间的相互联系以及超薄皮层反渗透复合膜长期运行的稳定性仍需进一步探索。     

Superhydrophobic polytetrafluoroethylene nanofiber membranes prepared by vacuum sintering and their application in vacuum membrane distillation

Electrospinning-sintering is a general strategy to fabricate polytetrafluoroethylene (PTFE) nanofibrous membranes. In this study, vacuum atmosphere was created in the sintering process to obtain pure PTFE fibers. The effect of vacuum pressure on fiber morphology and material component of the sintered membrane was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterization. A proper vacuum condition was believed to be beneficial to decrease poly(vinyl alcohol) residual and creating nanosize structures on the fiber surface, as porous, which contributes to a secondary roughness, while insignificantly influence membrane strength. As a result, the prepared membrane was superhydrophobicity with enhanced liquid entry pressure value. The anti-wetting property of the vacuum sintered membranes was further evaluated by vacuum membrane distillation process, and ensured the superior wetting resistance of the vacuum sintered PTFE membranes.     

Complex membrane of cellulose and chitin nanocrystals with cationic guar gum for oil/water separation

In an effort to develop a membrane system with low cost and easy fabrication process for oil/water separation, cellulose nanocrystals (CNC), chitin nanocrystals (ChiNC), and cationic guar gum (CGG) are used to prepare a complex membrane on top of a poly(ethylene terephthalate) (PET) nonwoven fabric via a vacuum filtration method. The interactions among CNC, ChiNC, and CGG complexation are discussed, and the functionalization of the PET nonwoven fabric with these polysaccharide derivatives provides a high rate of water absorption and permeability on applying pressure. The morphology and wettability studies demonstrate that the as-prepared membrane has a porous structure and exhibits hydrophilic and underwater superoleophobic properties. The results of separation experiments show that the membrane can effectively separate oil/water emulsions with a relatively high flux and rejection ratio. This low-cost process can easily be scaled up to fabricate complex membranes for oil/water separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47947.     

Enhanced gas separation performance of PSF membrane after modification to PSF/PDMS composite membrane in CO2/CH4 separation

Asymmetric polysulfone (PSF) membrane was developed and modified to PSF/polydimethylsiloxane (PSF/PDMS) composite membrane by dip coating technique. Effect of PDMS coating time on membrane properties was examined by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, attenuated total reflectance‐Fourier transform infrared, and water contact angle. The increase in PDMS coating time resulted in a decrement in the thermal strength of PSF membrane. Surface contact angle values revealed that increase in PDMS coating time had increased the surface hydrophobicity in membranes. CO₂/CH₄ separation performance of membranes was evaluated, and an increase in CO₂/CH₄ ideal selectivity was observed with the increase of PDMS coating time. At feed pressure of 10 bar, the selectivity of PSF has increased up to 65% after dip coating with PDMS for 30 min. Modification of polymeric membrane into composite membrane provided a way forward towards the enhancement of gas separation performance in polymeric membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45650.     

Perfluorosulfonic acid—Tetraethoxysilane/polyacrylonitrile (PFSA‐TEOS/PAN) hollow fiber composite membranes prepared for pervaporation dehydration of ethyl acetate–water solutions

Preparation of organic‐inorganic composite membranes and their pervaporation (PV) permeation and separation characteristics for the aqueous solution of ethyl acetate were described. Polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane as support membrane, the mixtures of perfluorosulfonic acid (PFSA) and tetraethoxysilane (TEOS) by the sol‐gel reaction as the coating solution, the PFSA‐TEOS/PAN hollow fiber composite membranes by the different annealing conditions were prepared. The swelling of PFSA in ethyl acetate aqueous solutions was inhibited with addition of TEOS. The PFSA‐TEOS/PAN composite membranes containing up to 30 wt % TEOS in coating solution exhibited high selectivity towards water, then the selectivity decreased and permeation flux increased with increasing the TEOS concentration more than 30 wt %. When the PFSA‐TEOS/PAN composite membranes were annealed, the separation factor increased with increasing annealing temperature and time. Higher annealing temperature and longer annealing time promoted the crosslinking reaction between PFSA and TEOS in PFSA‐TEOS/PAN composite membranes, leading to the enhanced selectivity towards water. For the PFSA/PAN and PFSA‐TEOS/PAN composite membrane with 5 and 30 wt % TEOS annealed at 90°C for 12 h, their PV performance of aqueous solution 98 wt % ethyl acetate were as follows: the separation factors were 30.8, 254 and 496, while their permeation flux were 1430, 513 and 205 g/m² h at 40°C, respectively. In addition, the PV performance of PFSA‐TEOS/PAN composite membranes was investigated at different feed solution temperature and concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008