Ionic Hyperbranched Poly(amido-amine)-Incorporated Nanofiltration Membranes for High-Efficiency Dye Desalination.

High-efficiency dye desalination is crucial in the textile industry, considering its importance for human health, safe aquatic ecological systems, and resource recovery. In order to solve the problem of effective separation of univalent salt and ionic dye under the condition of high salt, ionic hyperbranched poly(amido-amine) (HBPs) were synthesized based on a simple and scalable one-step polycondensation method and then incorporated into the polyamide (PA) selective layers to construct charged nanochannels through interfacial polymerization (IP) on the surface of a polyvinyl chloride ultrafiltration (PVC-UF) hollow fiber membrane. Both the internal nanopores of HBPs (internal nanochannels) and the interfacial voids between HBPs and the PA matrix (external nanochannels) can be regarded as a fast water molecule transport pathway, while the terminal ionic groups of ionic HBPs endow the nanochannels with charge characteristics for improving ionic dye/salt selectivities. The permeate fluxes and dye/salt selectivities of HBP-TAC/PIP (57.3 L m-2 h-1 and rhodamine B (RB)/NaCl selectivity of 224.0) and HBP-PS/PIP (63.7 L m-2 h-1 and lemon yellow (LY)/NaCl selectivity of 664.0) membranes under 0.4 MPa operation pressure are much higher than PIP-only and HBP-NH2/PIP membranes. At the same time, this project also studied the membrane desalination process in a simulated high-salinity dye/salt mixture system to provide a theoretical basis and technical support for the actual dye desalination process.

Cross 1,3-dipolar cycloadditions of C,N-cyclic azomethine imines with an N-benzyl azomethine ylide: facile access to fused tricyclic 1,2,4-hexahydrotriazines.

A cross 1,3-dipolar cycloaddition of two different ylides between C,N-cyclic azomethine imines with an in situ-generated nonstabilized azomethine ylide from an N-benzyl precursor was realized. The reactions afforded a clean and facile access to diverse fused tricyclic 1,2,4-hexahydrotriazines in high yields (up to 96%). The chemical structures of the typical compounds were confirmed by X-ray single-crystal structure analysis.

Enhancing the antifouling property of polymeric membrane via surface charge regulation.

In this study, positively charged monomers were grafted onto negatively charged membranes via UV radiation to improve the antifouling/antibiofouling properties of the polymeric membrane and the stability of the modification layer. The surface properties, morphologies, antifouling and antibiofouling properties, and stability of the modified membranes were systematically characterized. Results indicated that the introduction of [2-(methacryloyloxy) ethyl] trimethylammonium chloride (MTAC) monomers onto polyethersulfone (PES)/sulfonated polyethersulfone (SPES) membranes effectively increased the surface hydrophilicity. Meanwhile, the surfaces were neutralized with ~0 mV zeta potential in pH 3-10. Moreover, the formation of a polyampholytic copolymer and the antibacterial ability of MTAC considerably improved the antibiofouling properties of the modified membranes. The MTAC-grafted PES/SPES membranes showed excellent antifouling/antibiofouling properties during the treatment of various types of wastewater, including bovine serum albumin solution, oil/water emulsion, and bacterial suspension. Therefore, this study provides a simple and effective method of constructing stable and antifouling membranes for sustainable water treatment.

Ionic Dendrimer Based Polyamide Membranes for Ion Separation.

Separating low/high-valent ions with sub-nanometer sizes is a crucial yet challenging task in various areas (e.g., within environmental, healthcare, chemical, and energy engineering). Satisfying high separation precision requires membranes with exceptionally high selectivity. One way to realize this is constructing well-designed ion-selective nanochannels in pressure-driven membranes where the separation mechanism relies on combined steric, dielectric exclusion, and Donnan effects. To this aim, charged nanochannels in polyamide (PA) membranes are created by incorporating ionic polyamidoamine (PAMAM) dendrimers via interfacial polymerization. Both sub-10 nm sizes of the ionic PAMAM dendrimer molecules and their gradient distributions in the PA nanofilms contribute to the successful formation of defect-free PA nanofilms, containing both internal (intramolecular voids) and external (interfacial voids between the ionic PAMAM dendrimers and the PA matrix) nanochannels for fast transport of water molecules. The external nanochannels with tunable ionizable groups endow the PA membranes with both high low/high-valent co-ion selectivity and chemical cleaning tolerance, while the ion sieving/transport mechanism was analyzed by employing the Donnan steric pore model with dielectric exclusion.

Antifouling and antibacterial behavior of membranes containing quaternary ammonium and zwitterionic polymers.

To overcome the organic-/bio- fouling of the membrane, a dual-functional ultrafiltration membrane containing quaternary ammonium and zwitterionic polymers via quaternization and surface radical polymerization was designed, and its antifouling and antibacterial behavior was studied. In this work, poly(vinylidene fluoride)/poly(methyl methacrylate-co-dimethylamino-2-ethyl methacrylate) (PVDF/P(MMA-co-DMAEMA)) blend membrane was quaternized by p-chloromethyl styrene (p-CMS), and the double bonds were introduced onto the membrane surface, which further participated in the polymerization of zwitterionic monomers on the membrane surface. The results indicated that the resultant membrane exhibited obviously improved hydrophilicity and weak positive charge (isoelectric point, 7.49). The membrane presented higher flux recovery ratio and lower protein adhesion compared with the pure PVDF membrane. Meanwhile, the membrane showed high-efficiency broad-spectrum antibacterial performance, that is, the bacteria killing efficiency of S. aureus and E. coli reached 98.2% and 97.0%, respectively. Moreover, the membrane effectively inhibited bacterial adhesion, which is important for the long-term antibacterial properties of membrane. This antifouling and antibacterial PVDF membrane may have potential in the long-term filtration process, especially when dealing with microbiologically contaminated water.

Improved permeability and antifouling properties of polyvinyl chloride ultrafiltration membrane via blending sulfonated polysulfone.

To improve the permeability and antifouling properties of polyvinyl chloride (PVC) ultrafiltration (UF) membrane, amphiphilic sulfonated polysulfone (SPSF) was introduced into PVC matrix. Three types of PVC/SPSF blend membranes containing different SPSF with the sulfonation degree (SD) of 20%, 30%, and 50% were fabricated by non-solvent induced phase separation (NIPS) process. The excellent compatibility between PVC and SPSF was confirmed by differential scanning calorimetry (DSC). Surface chemical compositions, morphology, roughness, charge, hydrophilicity, permeability and antifouling properties of the pristine PVC membrane and the PVC/SPSF blend membranes were systematically compared and characterized. Due to the improved hydrophilicity and endowed negative charge, the blend membrane showed high water permeability (i.e. 880 L m-2h-1 bar-1), high bovine serum albumin (BSA) rejection (i.e. 95.7%), and high flux recovery ratio (i.e. 96%), which outperformed ever reported and commercialized PVC membranes. Furthermore, the permeability and rejection properties of PVC/SPSF UF membranes were maintained after soaking in acidic and alkaline solutions for 30 days, indicating their outstanding acid and alkali tolerance. Therefore, SPSF was expected as a potential versatile modifier for fabricating high performance UF membranes.

A positively charged tight UF membrane and its properties for removing trace metal cations via electrostatic repulsion mechanism.

The development of highly efficient membranes technology using low-pressure driven filtration process, is one of the principal challenges in the wastewater treatment field, especially those aimed at the removal of trace heavy metals. In this work, a novel positively charged tight ultrafiltration (PCTUF) membrane was developed to remove heavy metal cations (Mn2+, Co2+, Ni2+, Zn2+ and Cd2+) from contaminated waters via electrostatic repulsion mechanism. The PCTUF membrane was fabricated from a new polymer with poly (vinyl chloride co dimethylaminoethyl methacrylate), P (VC-co-DMA) via a nonsolvent induce phase separation (NIPS) process and following facile surface quaternization. The quaternization conditions, the pore structures and chemical properties of the membranes were investigated in detail. The optimally quaternized membrane possessed a positively charged surface and 3.27 nm charged channel with the water permeability of 84 L m-2 h-1 bar-1. The rejections of heavy metal cations surpassed 95% for feed solutions containing 10 ppm heavy metal. Moreover, the influences of feed concentrations and the operating condition with pressure and pH on the membrane performances were also investigated. The results revealed that the prepared PCTUF membrane with its high perm-selectivity performance provides a worthy reference for highly efficient removal of heavy metal cations.

Negatively-charged nanofiltration membrane and its hexavalent chromium removal performance.

To enhance hexavalent chromium (Cr(VI)) removal performance under acidic conditions, the nanofiltration (NF) membrane with enhanced negative charge was fabricated via introducing 2, 5-diaminobenzenesulfonic acid (DABSA) into polyamide layer. The control membrane (NF-P) was directly prepared from piperazine and 1, 3, 5-benzenetricarbonyltrichloride. Surface chemical compositions, morphology, surface charge, pore size, permeability and pH-dependent separation performance of the fabricated membranes were characterized. The membranes showed the similar water permeance (∼11.5 L m-2 h-1 bar-1) and Na2SO4 rejections (∼98%) under neutral environments. The DABSA introduced NF membrane (NF-PD) was negatively charged in the pH range of 2.5-11, while the isoelectric point for NF-P was ∼pH 4.0. Cr(VI) removal ability was then evaluated under various concentrations and pH environments. The results indicated that NF-PD showed the better Cr(VI) rejection performance in all tested conditions than NF-P, especially under acidic environments (e.g., pH 4 and pH 5). Moreover, there was a fluctuation of the rejection with the increase of Cr(VI) concentration under acidic environments, which was mainly caused by the formation of Cr2O72- species. The harmful Cr(VI) was efficiently removed by the NF membrane with enhanced negative charge under acidic environments, which indicated the wider application range of the NF membrane.

Improved protein-adsorption resistance of polyethersulfone membranes via surface segregation of ultrahigh molecular weight poly(styrene-alt-maleic anhydride).

A styrene-maleic anhydride (SMA) alternating copolymer with ultrahigh molecular weight (M(w)>10(6)) synthesized in super critical carbon dioxide (SC CO(2)) medium was used as hydrophilic polymeric additive in the preparation of polyethersulfone (PES) membranes. The PES/SMA blend membranes were prepared by immersion precipitation process. X-ray photoelectronic spectroscopy (XPS) measurements confirmed that the hydrolyzed SMA preferentially segregated to membrane-coagulant interface during membrane formation. For the PES/SMA blend membranes, no big change was observed in the cross-sectional structure and the mechanical properties were well maintained after SMA addition except that a thicker top layer was formed. The surface morphology analysis by atomic force microscopy (AFM) showed that the membrane surface roughness increased with the added SMA amount. The results of water contact angle, water absorbance measurements and static protein adsorption experiments revealed that the surface enrichment of SMA endowed PES/SMA blend membranes with significantly improved surface hydrophilicity and protein-adsorption resistance.

Surface zwitterionicalization of poly(vinylidene fluoride) membranes from the entrapped reactive core-shell silica nanoparticles.

We demonstrate the preparation and properties of poly(vinylidene fluoride) (PVDF) filtration membranes modified via surface zwitterionicalization mediated by reactive core-shell silica nanoparticles (SiO2 NPs). The organic/inorganic hybrid SiO2 NPs grafted with poly(methyl meth acrylate)-block-poly(2-dimethylaminoethyl methacrylate) copolymer (PMMA-b-PDMAEMA) shell were prepared by surface-initiated reversible addition fragmentation chain transfer (SI-RAFT) polymerization and then used as a membrane-making additive of PVDF membranes. The PDMAEMA exposed on membrane surface and pore walls were quaternized into zwitterionic poly(sulfobetaine methacrylate) (PSBMA) using 1,3-propane sultone (1,3-PS) as the quaternization agent. The membrane surface chemistry and morphology were analyzed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), respectively. The hydrophilicity, permeability and antifouling ability of the investigated membranes were evaluated in detail. It was found that the PSBMA chains brought highly-hydrophilic and strong fouling resistant characteristics to PVDF membranes due to the powerful hydration of zwitterionic surface. The SiO2 cores and PMMA chains in the hybrid NPs play a role of anchors for the linking of PSBMA chains to membrane surface. Compared to the traditional strategies for membrane hydrophilic modification, the developed method in this work combined the advantages of both blending and surface reaction.

Synergistic strengthening of polyelectrolyte complex membranes by functionalized carbon nanotubes and metal ions.

Hydrophilic polymers have garnered much attention due to their critical roles in various applications such as molecular separation membranes, bio-interfaces, and surface engineering. However, a long-standing problem is that their mechanical properties usually deteriorate at high relative humidity (RH). Through the simultaneous incorporation of functionalized carbon nanotubes and copper ions (Cu(2+)), this study introduces a facile method to fabricate high strength polyelectrolyte complex nanohybrid membranes resistant to high RH (90%). For example, the tensile strength of the nanohybrid membranes is 55 MPa at 90% RH (80% of the original value at 30% RH). These results are explained by copper ions depressing the swelling degree of the membrane, and functionalized carbon nanotubes promoting stress transfer between the polymer matrix and them. The nanohybrid membranes are efficient in separating water/alcohol mixtures containing relatively high water content (up to 30 wt%), whereas common hydrophilic polymer membranes usually suffer from excessive swelling under this condition.

Preparation and properties of PEC nanocomposite membranes with carboxymethyl cellulose and modified silica.

Carboxymethyl cellulose (CMC)-modified silica nanocomposites were prepared via in situ incorporation of modified silica during the ionic complexation between CMC and poly(2-methacryloyloxy ethyl trimethylammonium chloride) (PDMC). Ionic bonds were introduced between the poly(2-acrylamido-2-methylproanesulfonic acid) modified silica (SiO2-PAMPS) and the polyelectrolyte complex (PEC) matrix. The PEC nanocomposites (PECNs) and their membranes (PECNMs) were characterized with Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and tensile testing. PECNM containing 5 wt.% SiO2-PAMPS showed a tensile strength of 68 MPa and elongation at break of 7.1%, which were 1.9 and 2.6 times as high as those of pristine PEC membranes, respectively. Moreover, the pervaporation performance of as-prepared PECNMs was evaluated with dehydration of 10 wt.% aqueous isopropanol mixtures, and the PECNMs exhibited a flux of 2,400 gm(-2)h(-1) with a high separation factor of 4491 at 70°C.

Hemocompatible and antibacterial porous membranes with heparinized copper hydroxide nanofibers as separation layer.

Here we report the fabrication of a novel heparinized copper hydroxide (Cu(OH)2) nanofiberous membrane with satisfying hemocompatibility and antibacterial properties. The positively charged Cu(OH)2 nanofibers were prepared in a weakly alkaline copper nitrate solution in the presence of 2-aminoethanol. A heparin (Hep) solution was then added dropwise into the solution of nanofibers to immobilize negatively charged heparin onto the Cu(OH)2 nanofibers by electrostatic interaction. A composite Hep@Cu(OH)2 nanofiberous membrane was prepared by filtration and deposition of the heparinized nanofibers onto a polysulfone (PSF) porous membrane. Chemical composition analysis of membrane surface using X-ray photoelectron spectroscopy (XPS) confirmed the successful immobilization of heparin on Cu(OH)2 nanofibers. The amount of immobilized heparin on nanofiberous membrane was determined by a colorimetric assay of toluidine blue dye and the results showed that the amount of immobilized heparin was strongly dependent on the heparin dosage in reaction solution. The results of contact angle measurement indicated that the hydrophilicity of Cu(OH)2 nanofiberous membranes was enhanced by the immobilization of heparin. The adhesion, activation and transmutation of platelets on Hep@Cu(OH)2 membrane were suppressed remarkably due to the introduction of heparin, which suggested that the Hep@Cu(OH)2 membranes had good hemocompatibility. In addition, Cu(OH)2 and Hep@Cu(OH)2 nanofiberous membranes exhibited very good antibacterial activities against Escherichia coli and Staphyloccocus aureus.

Fabrication of superhydrophilic poly(styrene-alt-maleic anhydride)/silica hybrid surfaces on poly(vinylidene fluoride) membranes.

Superhydrophilic organic/inorganic hybrid surfaces have been fabricated on blend membranes of poly(vinylidene fluoride) (PVDF) and poly(styrene-alt-maleic anhydride) (SMA). The blend membranes were prepared from PVDF/SMA mixed solution with N,N-dimethylacetamide (DMAc) as solvent by immersion-precipitation phase inversion process. The gained blend membranes were immersed into γ-aminopropyltriethoxysilane (APTS) solution to generate SMA/silica hybrid surfaces by the reaction between anhydrides and APTS. The hybrid surfaces chemical compositions, morphologies and hydrophilicity were investigated in detail. It demonstrates that the hybrid surfaces possess micro-nano hierarchical structure and display superhydrophilicity property and good stability. Finally, the reaction and formation mechanism of the superhydrophilicity hybrid surface was discussed.

Immobilization of bovine serum albumin onto porous polyethylene membranes using strongly attached polydopamine as a spacer.

Based on the self-polymerization and strong adhesion characteristics of dopamine in aqueous solution, a novel and convenient approach was developed to immobilize protein onto porous polyethylene (PE) membranes. A thin polydopamine (pDA) layer was formed and tightly coated onto PE membrane by dipping simply the membrane into dopamine aqueous solution for a period of time. Subsequently, bovine serum albumin (BSA) was bound onto the obtained PE/pDA composite membranes via the coupling between BSA and the reactive polydopamine layer. The firm immobilization of polydopamine layer and BSA was verified by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The results of water contact angle measurement showed that the hydrophilicity of PE membrane was significantly improved after coating polydopamine and binding BSA. The experiments of blood platelet adhesion indicated that BSA-immobilized PE membrane had better blood compatibility than the unmodified PE and the PE/pDA composite membranes. The investigations on hepatocyte cultures and cell viability revealed that the polydopamine coating endowed PE membrane with significantly improved cell compatibility. Compared to BSA surface, polydopamine surface is more favorable for cell adhesion, growth, and proliferation.

[Membrane fouling control in a free-end comb-like hollow fiber membrane bioreactor].

A free-end comb-like hollow fiber membrane bioreactor was applied to treat wastewater. The results clearly showed that membrane fouling, defined as permeate flux decline, was greatly influenced by membrane module configuration. The permeate flux decline was much less for module b, demonstrating the superiority of module b over module a. Its permeate flux could be maintained in the range of 4.0 to 8.0 L x (m2 x h)(-1) under the operating conditions that temperature was 22-26 degrees C, the mixed liquor suspended solids (MLSS) concentration was 7500-10500 mg/L, aeration intensity was 200 L/h, suction time/ suspended time ratio was 9 min/1 min and suction pressure was 0.02 MPa. As this novel kind of membrane module resulted in high air scouring efficiency, relatively low aeration intensity was needed for the MBR maintenance. In addition, the permeate flux varied a little when suction time/ suspended time ratio changed from 12 min/1 min to 6 min/1 min. The performances of several different cleaning methods were tested and the results indicated that water cleaning + chemical cleaning + ethanol soaking had the best cleaning efficiency. SEM images clearly showed that the membrane surface became cleaner and the membrane holes became more visible after water cleaning + chemical cleaning, compared with water cleaning solely.

Surface modification of PVDF porous membranes via poly(DOPA) coating and heparin immobilization.

Based on the strong adhesive behavior of poly(3,4-dihydroxy-l-phenylalanine) (or poly(DOPA)) on solid surface, poly(vinylidene fluoride) (PVDF) microporous membranes were surface-modified by the self-polymerization of DOPA in aqueous solution. Subsequently, heparin was immobilized covalently onto the obtained PVDF/poly(DOPA) composite membranes by the coupling between heparin and poly(DOPA) coating. The modified membranes were subjected to a long-term washing, and the firm immobilization of poly(DOPA) and heparin was confirmed by X-ray photoelectron spectroscopy (XPS). The results of water contact angle measurements showed that the hydrophilicity of PVDF membranes was significantly improved by the incorporation of poly(DOPA) and heparin. The effects of poly(DOPA) and heparin on membrane surface morphologies were also investigated by scanning electron microscopy (SEM).

Improving hydrophilicity and protein resistance of poly(vinylidene fluoride) membranes by blending with amphiphilic hyperbranched-star polymer.

To endow hydrophobic poly(vinylidene fluoride) (PVDF) membranes with reliable hydrophilicity and protein resistance, an amphiphilic hyperbranched-star polymer (HPE-g-MPEG) with about 12 hydrophilic arms in each molecule was synthesized by grafting methoxy poly(ethylene glycol) (MPEG) to the hyperbranched polyester (HPE) molecule using terephthaloyl chloride (TPC) as the coupling agent and blended with PVDF to fabricate porous membranes via phase inversion process. The chemical composition changes of the membrane surface were confirmed by X-ray photoelectron spectroscopy (XPS), and the membrane morphologies were measured by scanning electron microscopy (SEM). Water contact angle, static protein adsorption, and filtration experiments were used to evaluate the hydrophilicity and anti-fouling properties of the membranes. It was found that MPEG segments of HPE-g-MPEG enriched at the membrane surface substantially, while the water contact angle decreased as low as 49 degrees for the membrane with a HPE-g-MPEG/PVDF ratio of 3/10. More importantly, the water contact angle of the blend membrane changed little after being leached continuously in water at 60 degrees C for 30 days, indicating a quite stable presence of HPE-g-MPEG in the blend membranes. Furthermore, the blend membranes showed lower static protein adsorption, higher water and protein solution fluxes, and better water flux recovery after cleaning than the pure PVDF membrane.

Novel, fluorescent, magnetic, polysaccharide-based microsphere for orientation, tracing, and anticoagulation: preparation and characterization.

A fluorescent, magnetic composite poly(styrene-maleic anhydride) microsphere, suitable for conjugation with polysaccharide, was synthesized using magnetite/europium phthalate particles as seeds by copolymerization of styrene and maleic anhydride. The magnetite/europium phthalate particles were wrapped up by poly(ethylene glycol), which improved the affinity between the seed particles and the monomers. The composite microspheres obtained, with a diameter of 0.15-0.7 microm, contain 586-1013 microg of magnetite/g of microsphere and 0.5-16 mmol surface anhydride groups/g of microsphere. Heparin was conjugated with the reactive surface anhydride groups on the surface of the microspheres by covalent binding to obtain a fluorescent, magnetic, polysaccharide-based microsphere. The microspheres not only retain their bioactivities but also provide magnetic susceptibility and fluorescence. They can be used as a carrier with magnetic orientation and fluorescence tracer for potent drug targeting. The orientation, tracer, and anticoagulation of the fluorescence, magnetic, polysaccharide-based microspheres were studied. The anticoagulant activity of the microspheres and heparin binding capacity reached 54,212.8 U and 607.1 mg/g of dry microspheres. The activity recovery was 50.2%. The anticoagulant activity of the microspheres increases with the increase of the conjugated heparin on the surface of the microspheres and the decrease of the microsphere size. Furthermore, The fluorescent, magnetic, polysaccharide-based microspheres can be easily transported to a given position in a magnetic field and traced via their fluorescence.