Aqueous Phase Monomer Research Articles

N-Oxide Zwitterion Functionalized Positively Charged Polyamide Composite Membranes for Nanofiltration.

N-Oxide zwitterionic polyethyleneimine (ZPEI), a new kind of aqueous phase monomer synthesized by commercially branched polyethyleneimine (PEI) via oxidation reaction, was prepared for fabrication of thin-film composite (TFC) polyamide membranes via interfacial polymerization. The main factors, including the monomer concentration and immersion time of the aqueous phase and organic phase, were investigated. Compared with PEI-TFC membranes, the obtained optimal defect-free ZPEI-TFC membranes exhibited a lower roughness (3.3 ± 0.3 nm), a better surface hydrophilicity, and a smaller pore size (238 Da of MWCO). The positively charged ZPEI-TFC membranes (isoelectric point at pH 8.05) showed higher rejections toward both divalent cationic (MgCl2, 93.0%) and anionic (Na2SO4, 96.1%) salts with a water permeation flux of up to 81.0 L·m-2·h-1 at 6 bar, which surpassed currently reported membranes. More importantly, mainly owing to N-oxide zwitterion with strong hydration capability, ZPEI-TFC membranes displayed a high flux recovery ratio (97.0%) toward a model protein contaminant (bovine serum albumin), indicating good anti-fouling properties. Therefore, the novel N-oxide zwitterion functionalized positively charged nanofiltration membranes provide an alternative for water desalination and sewage reclamation.

Fabrication of highly positively charged nanofiltration membranes by novel interfacial polymerization: Accelerating Mg2+ removal and Li+ enrichment

Li+, a vital green energy source, is mainly extracted from salt lakes, which also contain high concentration of Mg2+. Therefore, there is an imminent need for separation of Li+ and Mg2+. Recent innovations highlight the great potential of positively charged nanofiltration (NF) membranes for separating Mg2+ and Li+. Typically, positively charged NF membranes are prepared by the interfacial polymerization approach, where the most commonly applied aqueous phase monomer is polyethyleneimine (PEI). In this work, a new class of polyallylamine (PAA)-based NF membrane with a high density of positive charge, was developed to achieve high perm-selectivity for separating Mg2+ and Li+. The results indicated that the abundant primary amine (-NH2) groups on the PAA molecular chain endowed the NF membrane with a highly hydrophilic and positively charged polyamide layer. The resulting NF membrane exhibited superior Mg2+/Li+ separation ability with a high separation factor SMg2+/Li+ of 82.8 and a water permeance of 7.39 L/(m2hbar). It is also noteworthy that the SMg2+/Li+ value is more than 4 times higher than that of the previously reported PEI-based membrane. Moreover, our work also provides a new potential candidate for the future development of positive charged NF membranes.

Novel macrocyclic polyamines regulated nanofiltration membranes: Towards efficient micropollutants removal and molecular separation

The discharge of wastewater containing organic micropollutants not only causes severe environmental pollution, but also exacerbates the scarcity of freshwater resources and poses a serious threat to human health. The nanofiltration (NF) membrane has unique advantages and obvious energy-saving effects in the demineralization of organic micropollutants. Poly(piperazine) amide NF membrane exhibits the poor organic micropollutants/salt selectivity and low water permeance. Therefore, developing a novel NF membrane with high water permeance and superior selectivity is of significance. In this study, a loose nanofiltration (LNF) membrane is fabricated by interfacial polymerization with 1, 4, 7, 10-tetraazacyclododecane (Cyclen) as a new aqueous phase monomer to modulate the polyamide microstructure. The steric structure of Cyclen is larger than that of PIP, and the steric hindrance increases, resulting in a low stacking density of the formed polyamide polymer. Compared with the PIP-based NF membrane, the fabricated Cyclen-TMC LNF membrane has a smoother surface, a higher density of carboxyl groups, and a lower degree of cross-linking. The Cyclen-TMC membrane exhibits the considerable water permeance, with the corresponding rejection of 99.9% and 92.7% for methyl blue and tetracycline (pH = 9), respectively, while maintaining a low rejection for monovalent salts (e.g., 4.5% for NaCl). Furthermore, the LNF membrane shows a superior anti-fouling performance with the relatively smooth, highly negatively charged surface and low operation pressure. The novel LNF membrane exhibits a high potential for textile and pharmaceutical wastewater treatment. This study provides a new candidate to regulate the separation performance of NF membranes using new aqueous monomers.

Regulation of interfacial polymerization process based on reversible enamine reaction for high performance nanofiltration membrane

The regulation of interfacial polymerization (IP) is the critical procedure for the preparation and industrialization of thin film composite (TFC) nanofiltration (NF) membranes. However, the IP control is still a huge challenge based on the extremely rapid reaction rate during the fabrication of the membrane. Herein, a new strategy was developed to modulate the IP process to increase the NF membrane performance. The aldehyde oxidized dextran (ODex) interlayer was deposited on the polysulfone ultrafiltration substrate, and the enamine would form between the secondary amines of aqueous phase monomer piperazine (PIP) and aldehyde groups of the ODex. Based on the by-products of IP, the enamine gradually decomposed reversibly in a hydrogen ion environment and the immobilized PIP was released and continued to react with organic phase monomer trimesoyl chloride (TMC). Accordingly, a thinner and exhibiting nanowire structures separation layer with fewer defects was obtained. The permeance of the optimal NF membrane with 0.7 wt% ODex interlayer deposition concentration could reach up to 208 ± 10.4 Lm−2h−1MPa−1, which was more than 2.5 times permeance of the ordinary NF membrane, and the rejection rate for Na2SO4 could reach 99.3 ± 0.3%. In addition, the mono- and divalent ion selectivity of the modified membrane was also greatly improved (αNaCl/Na2SO4 = 115). This study provides a new idea for the regulation of IP process, thereby suggesting a reasonable proposal for improving the performance of TFC NF membranes.

Synergistic regulation of macrocyclic polyamine-based polyamide nanofiltration membranes by the interlayer and surfactant for divalent ions rejection and mono-/di-ions sieving

For nanofiltration membranes, the selective separation of divalent/monovalent cations with high permeance is a desirable yet challenging demand due to the trade-off phenomenon between the perm-selectivity and permeance. In this study, a novel macrocyclic polyamine 1, 4, 7, 10-tetraazacyclododecane (Cyclen) is used as the aqueous phase monomer to construct a nanofiltration (NF) membrane with high permeance without sacrificing the perm-selectivity. The large molecular size of Cyclen greatly limits its interfacial mass transfer across the water/oil interface, resulting in the formation of many defects in the separation layer. Based on the widely applied interlayer technology in literature, a surfactant-assembly regulated interfacial polymerization (SARIP) is adopted to intensify the phase transfer process of the Cyclen. The interlayer accommodates enough Cyclen monomers and the surfactant acts as the phase transfer catalyst, which jointly enhance the monomer's phase transfer rate. The resultant polyamide membrane yields a uniform sub-nanometre pore size, and the combination of reduced pore size and charge distribution within the pores achieves high rejection for divalent ions and low rejection of monovalent ions, with the rejection order of LiCl (18.9 %) < NaCl (24.8 %) < MgSO4 (96.2 %) < MgCl2 (96.3 %) < Na2SO4 (97.0 %). The corresponding water permeance for MgCl2 reaches up to 18.5 L·m−2·h−1·bar−1 with the desirable Li+/Mg2+ and Na+/Mg2+ perm-selectivity of 21.9 and 20.3, respectively.

Enhancing the NaCl/Na2SO4 separation selectivity and chlorine resistance of nanofiltration membranes by incorporating novel designed starch nanoparticles

The challenge of poor compatibility between nanoparticles and separation layers in thin film nanocomposite (TFN) nanofiltration (NF) membranes has always plagued the researchers. In this work, a carboxylated starch nanoparticles (CSNPs) were introduced into the polyamide (PA) separation layer of NF membrane by the IP reaction between trimesoyl chloride (TMC) and piperazine (PIP). The agglomerated or large size CSNPs could transfer the reaction interface above the particles through the formation of a water template by adsorption of aqueous phase monomers, which shaped the defect-free separation layer. Furthermore, the reduced thickness and increased density of the separation layer greatly enhanced the separation selectivity of the nanofiltration membrane thanks to the introduction of hydrophilic groups of nanoparticles. The modified membrane achieved a nearly 5-fold improvement in separation selectivity for NaCl and Na2SO4 (SNaCl/Na2SO4 = 180) and a 2-fold increase in the water permeance. In addition, the modified NF membrane also possessed better chlorine-resistance property based on the formation of polyarylester between the reaction of hydroxyl groups in CSNPs and acyl chloride groups in TMC. Such novel aqueous-phase additives provide new insights to effectively solve the compatibility problem between the nanoparticles and separation layers, which is favorable for the commercial production of NF membrane.

Highly permeable composite nanofiltration membrane via γ-cyclodextrin modulation for multiple applications

The treatment of pharmaceutical wastewater has become a worldwide problem. Highly efficient treatment for wastewater is extremely critical for ecological environment. Herein, a thin-film nanofibrous composite (TFNC) nanofiltration (NF) membrane modulated by γ-cyclodextrin (γ-CD) was prepared via interfacial polymerization. The γ-CD and piperazine (PIP) were adopted and acting as the mixed reaction monomers in aqueous phase for the fabrication of the separation layer. Not only PIP, γ-CD units would also react with organic phase trimesoyl chloride (TMC) at the interface and participate into the polymerization network. Compared with pure polyamide TFNC membranes, the γ-CD modulated TFNC membranes demonstrated thinner skin thickness. Owing to the 3D hollow structure of γ-CD, the self-contained through cavities would provide additional direct nanochannels to facilitate the water transport. Under 0.5 MPa, the optimized PIP0.5γCD0.5 and PIP0.5γCD1.5 TFNC membranes showed much higher permeate flux of 23.27 and 26.34 L m-2h−1 bar−1, respectively, than that of pure polyamide membranes (9.13 and 9.85 L m-2h−1 bar−1) and the Na2SO4 rejection remained high (>98.7%). Moreover, both TFNC membranes exhibited extremely high rejection (>99%) for several pharmaceuticals (doxycycline hydrochloride, tetracycline, and amoxicillin), and the PIP0.5γCD0.5 TFNC membrane exhibited a good separation factor (31.8) for NaCl/tetracycline solution. In addition, both optimized TFNC membranes showed good pressure resistance and long-term operating stability. This research revealed a facile modulation strategy for the fabrication of high-performance NF membrane and indicated the great promise for desalination, pharmaceuticals wastewater treatment and antibiotics concentration.

Development of polymer-based new high performance thin-film nanocomposite nanofiltration membranes by vapor phase interfacial polymerization for the removal of heavy metal ions

The vapor phase interfacial polymerization is the new method for the development of thin-film nanocomposite (TFN) and thin-film composite (TFC) membranes. Generally, interfacial polymerization (IP) is done between aqueous phase monomers and organic phase monomers (containing organic solvent like n-hexane) but in this work, IP was done between aqueous phase monomer with vapour phase of organic monomer (TMC) which is the greener method. First time TFN membranes were prepared by vapour phase interfacial polymerization method. TiO2 nanoparticles act as very good nanofillers to prepare the polymeric nanocomposite membranes to tackle the problem of heavy metal pollution in water. However, their weak interaction with the matrix phase is an issue that causes them to leach out during the filtration process of pressure-driven nanofiltration membrane. Functionalizing the TiO2 nanoparticles with polar functional groups is a solution to this issue. After synthesizing carboxylic acid-functionalized TiO2 (COOH-TiO2) nanoparticles were incorporated in the TFN membranes while IP using DETA and TMC containing amine and acyl group monomers, respectively to modify the membrane surface. The effect of different loading concentrations of COOH-TiO2 nanoparticles in TFN has been studied and compared with the TFC membrane. The prepared membranes are subjected to a cross-filtration system for removing Na+, Cu+2, Hg+2, and Pb+2 from their respective Na2SO4, CuSO4, HgCl2, and Pb(NO3)2 feed solutions. The results of TFN membranes were compared with the TFC membrane. The outcomes have shown 87.03 ± 2% rejection of Na+, 86.89 ± 2% rejection of Cu+2, 77.01 ± 2% rejection of Hg+2 and 83.42 ± 1.5% rejection of Pb+2 ions by using TFN membranes. The effect of the monomeric concentration on the performance of the developed membranes was also studied. The antifouling tendency of the membranes was analysed as well by measuring different antifouling parameters like total fouling (FT), flux recovery ratio (FRR), reversible fouling (FR) and irreversible fouling (FIR). The results obtained are outstanding; incorporating nanomaterial results in lowering the irreversible fouling and enhancing the antifouling tendency.

Effects of alkali on the polyester membranes based on cyclic polyphenols for nanofiltration

To meet separation need under various conditions, a great variety of membranes have been fabricated via interfacial polymerization (IP), especially for the polyester membranes with intrinsic micro-porosity. However, the aqueous phase used for making those polyester membranes often requires alkaline environment, resulting in a quite different procedure compared with conventional polyamide membranes, which may alter IP process that have been widely studied. Here, the KOH, NaOH and LiOH were used respectively to create alkaline environment whereby the impact of alkali on polyester membranes were investigated systematically. It was found that the alkali not only showed influence on the IP process, but it also affected diffusion of monomers in aqueous phase across the water/hexane interface. When the concentration of alkali or pH of the aqueous phase were the same, the membranes using KOH as base were found to have the lowest permeability while the membranes using NaOH showed the highest permeability, and the membranes using LiOH showed the moderate permeability. The mechanism of the permeance trend was further investigated in detail, and it was found that the monomer containing hydroxyl not only could act as IP monomers, but also could play role as surfactant, thus affected its own diffusion to organic phase. This study paves the way for a wider integration of these macrocyclic polyphenols in the field of high-performance nanofiltration (NF) membranes, and also offers a new approach to optimize the performance of NF membranes based on polyester.

Nanofiltration membranes with enhanced performance by constructing an interlayer integrated with dextran nanoparticles and polyethyleneimine coating

The thin-film composite (TFC) nanofiltration (NF) membrane is a novel kind of membrane that has been extensively studied in recent years and broadly applied in desalination and wastewater treatment. The improvement of separation performance by optimizing the structure and morphology of NF membranes can significantly reduce energy consumption and bring more economic benefits. In this work, glutaraldehyde (GA) was used to crosslink polyethyleneimine (PEI) and dextran nanoparticles (DNPs) to construct an interfacial coating interlayer on polysulfone (PSF) ultrafiltration (UF) substrate. Subsequently, the polyamide (PA) NF membranes were fabricated by interfacial polymerization (IP) between piperazine (PIP) and trimesoyl chloride (TMC). DNPs were semi-encapsulated in the PEI coating and the exposed nanoparticles would be embedded in the PA layer for forming interfacial channels after IP. The interlayer not only affected the adsorption and diffusion of aqueous phase monomers to form a thin membrane, but also improved the membrane density to prevent selective defects associated with the incorporation of nanoparticles. The pure water permeance of the interlayered-TFC NF membrane was determined as 313.3 Lm−2h−1MPa−1, which was approximately four-fold that of the pristine membrane. The retention rate of various divalent salts of the NF membrane also significantly improved, and the retention rate of Na2SO4 exceeded 99%. This innovative method of interlayer modification has exhibited great potential in rapid desalination and wastewater recovery, providing new possibilities for the preparation of industrial high-performance NF membranes.

Composite membrane of polyguanidine cationic surface for desalination

Abstract Surface positve-charged composite membranes were prepared through two guanidine group containing polymers, polyhexamethylene guanidine (PHMG) and polyhexamethylene biguanidine (PHMB). They were used as aqueous phase monomers in an interfacial polymerization (IP) process reacting with trimesoyl chloride (TMC) on the surface of polysulfone (Psf) ultrafiltration membrane. Piperazine (PIP) provided the best pH adjustment among the chosen regulators. As guanidine groups dissociate in water and bring ammonium cations to membrane surfaces, both polyguanidine endowed membranes reacted with divalent metal cations better compared with Na+ and Li+. The rejection rates were more than 90% for all chosen divalent metal salts. PHMG membranes displayed excellent enrichment of Li+ from a mixed solution of Mg2+ and Li+ salts. The Mg2+/Li+ mass ratio decreased from 60 to 3.7, accompanying a −3.6% rejection to Li+. Although partial guanidine groups participated in the IP reaction, bactericidal rates of membranes were both higher than 99% in Gram-negative E. coli and Gram-positive S. aureus tests.

Extra-thin composite nanofiltration membranes tuned by γ-cyclodextrins containing amphipathic cavities for efficient separation of magnesium/lithium ions

Although nanofiltration (NF) membrane as a new frontier technique had made significant progress in the field of lithium extraction from salt lakes, they still suffered from the conventional permeability–selectivity trade-off effect. In this study, γ-cyclodextrins(CDs) containing amphipathic cavities and polyethyleneimine (PEI) acted as the aqueous phase monomer, which was carried out interfacial polymerization with the trimesoyl chloride (TMC) as the organic phase monomer to fabricate thin film composite (TFC) NF membranes with the extra-thin active layer. The hydrophilic surface and hydrophobic cavity of γ-CDs enhanced the hydrophilicity of the membrane surface and the water flux of the nanofiltration membrane. Moreover, the cavity size of γ-CDs also effectively screened magnesium and lithium ions to a certain extent. Under the best preparation conditions, the permeation flux of the PEI/γ-CDs-TMC nanofiltration membrane was 4.86 L⋅m−2⋅h−1⋅bar−1, SLi, Mg was 10.8. It was noteworthy that we used the molecular dynamics simulation method to confirm that the participation of γ-CDs led to the diffusion rate of the water phase monomers during the interfacial polymerization reaction slowed down. Thus, the thickness of the active layer of the nanofiltration membrane formed was also significantly reduced from 110.16 nm to 52.84 nm. This PEI/γ-CDs-TMC membrane provided a new strategy for preparing nanofiltration membranes with excellent overall magnesium-lithium separation performance.

Technological features of obtaining and properties of grafted polyvinylpyrrolidone copolymers

The impact of the vinyl monomers nature, concentration, and temperature on the kinetics of dispersion polymerization in the presence of polyvinylpyrrolidone was studied. The optimal technological parameters of the copolymer synthesis process are determined. It is defined that the properties of dispersion polymerization depend on the process conditions. Such conditions are temperature, monomer and aqueous phase ratio, monomer and initiator concentrations and as well as the amount of polyvinylpyrrolidone. Presented materials derived on the ground of the developed compositions are characterized by principally high working and physical-mechanical properties.

MOF laminates functionalized polyamide self-cleaning membrane for advanced loose nanofiltration

• High performance loose nanofiltration membrane was prepared by adding Zn-TCPP laminates to the interfacial polymerization of melamine and TMC. • The addition of Zn-TCPP laminates improved the permeance of membrane to 63.2 L m -2 h −1 bar −1 . • Zn-TCPP laminates enables the membrane superior dye degradation ability. Rational material design and controllable membrane preparation technology is essential to improve the separation performance and anti-fouling ability of a membrane. In this study, melamine is selected as the aqueous phase monomer of the interfacial polymerization and photocatalytic Zn-TCPP laminates are embedded into the membrane to develop a high performance self-cleaning loose TFN membrane. The melamine/TMC TFC membrane with a woven-like loose polyamide layer exhibits water permeance up to 30.1 L m -2 h −1 bar −1 and a good dye rejection (≥97%). With the addition of Zn-TCPP laminates, the membrane permeance is enhanced to 63.2 L m -2 h −1 bar −1 (TFN-2), which is twice than the TFC membrane. Furthermore, the dye rejection of TFN-2 remains high, and the rejection of salts (NaCl, Na 2 SO 4 ) is below 10%. Besides, the Zn-TCPP embedded TFN membrane can fully degrade the attached dye within 15 min under visible light, and the permeance of the treated membrane can be restored to its original state. The resultant Zn-TCPP/TFN loose nanofiltration membranes with excellent self-cleaning ability can not only provide a potential solution for the removal of organic pollutants, but also offer new inspiration for fabricating high performance self-cleaning loose nanofiltration membranes through a mature and facile interfacial polymerization method.

Thin-film composite polyester nanofiltration membrane with high flux and efficient dye/salts separation fabricated from precise molecular sieving structure of β-cyclodextrin

The treatment of dye pollutant and salts by nanofiltration membrane technology usually has the difficulty of low permeability and higher pressure in the case of maintaining a high rejection. In this study, high flux polyester membranes of β-cyclodextrin/trimesoyl chloride - multiwalled carbon nanotubes (β-CD/TMC-MWCNTs) were fabricated on a modified multiwalled carbon nanotubes (MWCNTs) substrate via interfacial polymerization (IP) process. The modified MWCNTs substrate was not only beneficial to modulating the permeation and distribution of aqueous phase monomer (β-cyclodextrin, β-CD), but also in favor of the formation of an ultrathin loose selective polyester active layer due to the porous network structure. The optimization experiments about the reaction time and monomer concentrations were conducted. The experimental results showed that the pure water flux of the as-prepared β-CD/TMC-MWCNTs membrane was 179.93 L m-2h-1 bar-1 (at the pressure of 0.1 MPa) when the reaction time of IP process was 5 min. The single dye removal efficiency of β-CD/TMC-MWCNTs membrane was 97.41% for Brilliant Green (BG) and 96.39% for Congo red (CR), respectively. The removal efficiency of dye/salt mixture by the membrane was above 84% for BG and over 98% for CR, respectively. The results indicated that the membrane had the efficient selective separation performance for the dye/salt mixture benefiting from the special molecular sieving architectures with the precisely intrinsic inner cavity of β-CD/TMC-MWCNTs membrane. Furthermore, the reusability, chlorine resistance, and antifouling ability of the β-CD/TMC-MWCNTs membrane was relatively excellent, and the membrane could effectively remove BG (>93%) and CR (>98%) simultaneously for mixed BG/CR dyes in real water body. These results suggested that the as-prepared β-CD/TMC-MWCNTs membrane had the potential of practical application in dye wastewater treatment.

High‐flux and solvent‐selective membranes with aromatic functionalities and dual‐layer structures

AbstractEfficient separation of aromatic‐aliphatic hydrocarbon mixtures has long been an important topic in chemical industries. Organic nanofiltration (OSN) has been revealing great promise in separating solvent mixtures that has not been effectively resolved by the state‐of‐the‐art technologies. Herein, novel OSN membranes are designed for the separation of toluene and n‐heptane. Polyamide active layer with diaminonaphthalene as the aqueous phase monomer is prepared by interfacial polymerization for the first time. The addition of polydimethylsiloxane gutter layer, as well as the combination of spin coating technique and macroporous substrate, renders the membranes with loose and defect‐free architectures. The as‐designed membranes achieve a rather high selectivity of toluene over n‐heptane (&gt;4) together with ultra‐high toluene permeance (&gt;180 L m−2 h−1 bar−1). These membranes also present excellent stability in the long‐term operation.

Tuning the pore size of graphene quantum dots composite nanofiltration membranes by P-aminobenzoic acid for enhanced dye/salt separation

Nanofiltration (NF) is a promising technology for fast molecular and ionic separation. Pore engineering is a critical but challenging strategy to fabricate NF membranes with high permeability and precise sieving ability. Herein, we proposed a post-modification approach to regulate the pore size of graphene quantum dots (GQDs) composite NF membranes by using a small molecule p-aminobenzoic acid (PABA) as a modifier. First, GQDs were used as the aqueous phase monomer of interfacial polymerization to react with trimesoyl chloride within the pores of the porous substrate, thereby fabricating large-pore-size GQDs composite NF membranes. After that, the self-polymerization of PABA within the pores of GQDs NF membranes would form nanoaggregates with different sizes, thus finely tuning the pore size of the as-prepared membrane. The PABA-modified membranes exhibited a range of pore sizes from 2.18 to 1.50 nm with the increased concentration of PABA. Specifically, the optimal PABA-modified membrane showed high water permeance of 128.1 L m−2 h−1 bar−1 and complete interception of 1000 Da-higher dye molecules, with desirable dye/salt selectivity factors of 877.0 and 175.4 for Alcian Blue/Na2SO4 and Evans Blue/Na2SO4 separation systems, respectively. Moreover, the membranes exhibited outstanding physicochemical stability. This study provides a facile method for pore size regulation of NF membranes.

A novel chlorine-resistant polyacrylate nanofiltration membrane constructed from oligomeric phenolic resin

Conventional water treatment polyamide nanofiltration (NF) membranes often suffer from the degradation of sodium hypochlorite (NaOCl) in sewage or during the process of membrane cleaning and deteriorate the separation performance, which significantly increases the treatment cost. Herein, a novel polyacrylate composite NF membranes were prepared by interfacial polymerization using oligomeric phenolic resin (OPR) and trimesoyl chloride (TMC) as aqueous and organic phase monomer respectively on the polyethersulfone (PES) ultrafiltration supporting membranes. The fabrication parameters, including the pH of the aqueous solution, reaction time and the concentration of the monomer, on the performance of the composite NF membranes were optimized. A series of characterization indicated that the surface of the NF membranes was negatively charged, the molecular weight cut-off (MWCO) and the pore diameter of the polyacrylate membrane were 400 Da and 0.47 nm, respectively. At the optimized preparation conditions, the NF membrane exhibited high Na2SO4 rejection of 98.2% and water flux of 2.42L·m−2·h−1·bar−1, which was superior to most of the polyacrylate NF membranes reported in recent years. Compared with the polyamide membrane, the prepared polyacrylate membrane demonstrated better chlorine-resistant property and still maintained 92.0% Na2SO4 rejection after being treated with NaOCl solution. Moreover, the NF membrane preserved excellent long-term operation stability. The chlorine-resistant NF membrane constructed from OPR monomer has a broad application prospect in the field of high chlorine wastewater treatment.

Intrinsic kinetics of interfacial polycondensation reactions– the reaction of mPDA with TMC

The performance of thin film composite membranes used in reverse osmosis is decided by the thickness and structure of the thin functional layer, which in turn depend on the kinetics of the interfacial polycondensation (IP) reaction which produces this layer. Quantitative determination of these kinetics has been a challenge. In the present study, we extend the method of pH-metry developed in our earlier work to the study of IP kinetics, in the presence of the side reaction of hydrolysis of the organic phase monomer. The method has been used to establish the kinetics of MPDA –TMC system in the presence and absence of a surfactant, Tween-85. The experimental method used eliminates all transport resistances, so that intrinsic kinetic control of the observed process is ensured. The hydrolysis reaction is studied separately by an adaptation of the same method, and those kinetics are systematically incorporated in the treatment of the data from the IP reaction. The observed kinetics have been fitted to a lumped kinetic form of the power law type, and show that the reaction is approximately first order in the acid chloride group concentration, and order 1.6 in the amine group concentration. The surfactant has been seen to influence the magnitude of the rate constant significantly. The reaction usually stops well short of 100% conversion of the stoichiometrically limiting monomer, because of the lowering of pH which restricts the availability of the aqueous phase monomer at the reaction locale.

Polyarylate membrane with special circular microporous structure by interfacial polymerization for gas separation

Microporous polymer membranes have received extensive attention in the membrane separation field based on the advantage of high gas permeance and low cost. However, there are a few reports of microporous polyacrylate membranes fabricated by interfacial polymerization (IP), and the formation mechanism and influence factor of the microporous structure is rarely illuminated. In this work, thin-film polyacrylate membrane with circular microporous morphology were prepared by IP method with cyclodextrin and acyl chloride as the aqueous and oil phase monomer respectively for effective gas separation. The effects of the aqueous and organic phase monomer structure and concentration, the concentration and type of alkali in the aqueous solution on the membrane morphology and gas separation performance were investigated in detail. As a result, the polyacrylate membrane fabricated by β-cyclodextrin (β-CD) and trimesoyl chloride (TMC) with optimal content of NaOH in the aqueous phase formed the special circular microporous structure by the scanning electronic microscope (SEM) characterization. The resulting membrane showed CO2 permeance of 200 GPU with CO2/N2 ideal separation selectivity of 10.53. This work provides an effective strategy to fabricate high performance polyacrylate membrane by regulating the monomer structure and the alkali concentration in the aqueous phenol solution with IP method, which would inspire the exploration of other phenolic monomer for the assembly of microporous polymer membranes for gas separation or seawater desalination.