Composite Ultrafiltration Membranes Research Articles

Composite ultrafiltration membranes from polymer and its quaternary phosphonium-functionalized derivative with enhanced water flux

Novel ultrafiltration (UF) membranes were prepared by blending brominated poly(phenylene oxide) (BPPO) and its quaternary phosphonium derivative (TPPOQP-Br) as additive using a phase inversion method. The chemical structure and microstructure of the membranes were characterized by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The XPS results indicated that the BPPO/TPPOQP-Br composite membranes exhibited an increase in the concentration of TPPOQP-Br from the top surface to the bottom surface. In contrast, the composite membranes prepared from BPPO and its quaternary ammonium derivative (TPPOQA-Br) showed an opposite concentration gradient of TPPOQA-Br. This was attributed to the difference in wettability and hydration rate between TPPOQP-Br and TPPOQA-Br, leading to different membrane microstructure and chemical composition distributions. BPPO membrane showed a water flux of 215Lm−2h−1 at 100kPa and its molecular weight cut-off of PEG is 93.8kDa; the corresponding values of the optimal BPPO/TPPOQP-Br membrane are 873Lm−2h−1 and 111.3kDa, both of which are better than those of BPPO/TPPOQA-Br with the similar additive loading (381Lm−2h−1 and 150.2kDa). Therefore, the addition of TPPOQP-Br significantly enhances the water permeability while maintaining the excellent rejection properties in the resultant UF membranes. This work extends the choice of the additives in the UF membrane fabrication, and further proves that the addition of hydrophobic and charged polymer with slow hydration property is an effective strategy for improving flux and anti-biofouling properties of UF membranes.

Interfacial Polymerization of Reactive Block Polymers for the Preparation of Composite Ultrafiltration Membranes

Interfacial polymerization of an acid chloride-containing block polymer and a multivalent amine in the presence of a macroporous support was explored as a means to generate a nanoporous thin film composite (TFC) membrane potentially useful for ultrafiltration. When polylactide-b-poly(styrene-co-vinylbenzoyl chloride) (PLA-b-P(S-co-VBC)) in an organic phase and m-phenylenediamine (MPD) in an aqueous phase were used as the reactive block polymer and the amine, respectively, a block polymer thin film was successfully formed on a polysulfone support. This nanostructured film could be converted into a nanoporous layer by subsequent PLA etching under mild basic conditions. While most organic solvents used to dissolve PLA-b-P(S-co-VBC) damaged the support and decreased permeability of the resulting membrane, use of a mixture of methyl isobutyl ketone and acetonitrile produced a TFC membrane with high permeability.

Biocide modification of ultrafiltration membranes using nanofiber structures

Membrane biofouling has a negative effect on membrane performance. Commercial ultrafiltration (UF) membranes were therefore modified using polymeric nanofibers in order to gain additional water treatment functionality. In this case, membrane surface was modified using biocidal electrospun polyurethane nanofibers. It has been found that the inorganic silver in form of reduced silver nitrate is a feasible modification of nanofiber structure, and electrospinning conditions were optimized to maximize silver particle content. Two possible methods were verified for preparing composite UF membranes with antibacterial properties using: (a) direct nanofiber deposition and (b) thermal pressure lamination. Hydrodynamic properties of the developed membranes were tested on an AlfaLaval M10 unit. It has been found that the added functionality comes at the expense of lower permeability. Biocide properties over both short- and long-term operation were confirmed through cultivation techniques and respirometry with Escherichia coli while concurrently monitoring how the added silver leached from the nanofiber layer. The results indicate that UF membranes modification using silver-treated nanofibers is a promising technique worth future study and evaluation for advanced water treatment.

Preparation, characterization and performance enhancement of polysulfone ultrafiltration membrane using PBI as hydrophilic modifier

In this study, new type of polysulfone (PSf) composite ultrafiltration membranes were prepared by blending PSf with poly[2,2′-(m-phenylene)-5,5′-dibenzimidazole] (PBI). The prepared membranes were characterized by water contact angle, SEM, FTIR, DSC, TG/DTG and cross-flow filtration techniques. We demonstrated that membrane characteristics such as porosity, hydrophilicity and thermal stability of PSf can be significantly enhanced with the incorporation of PBI. The composite membranes exhibited comparable bovine serum albumin (BSA) retention (69% vs. 36%) and water fluxes (355 vs. 228L/m2h) against pristine PSf membranes.

Exploring the synergetic effects of graphene oxide (GO) and polyvinylpyrrodione (PVP) on poly(vinylylidenefluoride) (PVDF) ultrafiltration membrane performance

Membrane surface and cross-sectional morphology created during membrane formation is one of the most essential factors determining membrane separation performance. However, the complicated interactions between added nanoparticles and additives influencing membrane morphology and performance during building membrane architectures had been generally neglected. In this study, asymmetric PVDF composite ultrafiltration (UF) membranes containing graphene oxides (GO) were prepared by using N-methyl pyrrolidone (NMP) as solvent and polyvinylpyrrodione (PVP) as the pore forming reagent. In the first time, the effects of mutual interactions between GO and PVP on membranes surface compositions, morphology and performance were investigated in detail. The variation in chemical properties of different membranes and hydrogen bonds in the membrane containing GO and PVP were confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR). Atomic force microscopy (AFM), scanning electron microscopy (SEM), and contact angle (CA) were utilized to clarify the synergetic effects of GO and PVP on morphologies and surface hydrophilicity of membranes. Besides, water flux, bovine serum albumin (BSA) rejection and attenuate coefficient were also determined to investigate filtration performance of various membranes. Compared with pure PVDF membrane, the comprehensive performance of PVDF/GO/PVP membrane has been obviously improved. The surface hydrophilicity and anti-fouling performance were enhanced by the synergistic effects of incorporated GO and PVP. When the PVP content was 0.25wt.% and the GO content was 0.5wt.%, the optimized performance can be obtained due to the formation of hydrogen bonds between GO and PVP.

Fabrication of a low‐cost nano‐SiO2/PVC composite ultrafiltration membrane and its antifouling performance

ABSTRACTA novel low‐cost SiO2/Polyvinylchloride (PVC) membrane with different nano‐SiO2 particles loading (0–4 wt %) was prepared by the phase‐inversion process. The optimum nano‐SiO2 dosage was determined as 1.5 wt % based on the casting solution compositions, the membranes' mechanical properties and hydrophilicities, the pure water fluxes, microstructures, and absorption of protein. Compared with the bare membrane, the membrane with 1.5 wt % nano‐SiO2 addition presented better capabilities against the protein absorption and bacterial attachment, better antifouling performance, and higher flux recovery ratio in filtration of the supernatant liquor which collected from a secondary sedimentation tank in a municipal wastewater plant. The SiO2/PVC membranes have applicable potential in the municipal wastewater treatment for their low price, good antifouling performance and high removal efficiencies of SS (over 97.2%), COD (up to 82.9%) and total bacteria (more than 93.6%). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41267.

High flux PEO doped chitosan ultrafiltration composite membrane based on PAN nanofibrous substrate

A new method for fabrication of thin film nanofibrous composite (TFNC) ultrafiltration membrane with high flux containing a hydrophilic poly(ethylene oxide) (PEO) doped chitosan (CS) barrier layer and polyacrylonitrile (PAN) nanofibrous substrate was proposed in this study. First, PEO doped CS barrier layer was electrosprayed onto electrospun PAN substrate layer. Then, the deposited PEO doped CS layer was swollen to imperceptibly merge into an integrated barrier layer by acetic acid vapour treatment and chemically cross-linking in glutaraldehyde acetone/water solution to form a thin barrier film on the PAN substrate. The depositing time of electrospray and vapour treatment conditions were optimised to control the thickness of PEO doped CS layer. Oil/water emulsions system was used to evaluate the filtration performance of the as prepared composite membrane. It was shown that the TFNC membrane can perform well in the filtration of oil/water emulsions with permeate flux of 117·2 L m−2 h−1 and rejection rate of 99·0% at low pressure(0·2 MPa), and this membrane also exhibit good pressure resistance, for it showed higher flux (223·5 L m−2 h−1) with a high rejection rate (99·5%) at high operating pressure (0·6 MPa).

Organic fouling inhibition on electrically conducting carbon nanotube–polyvinyl alcohol composite ultrafiltration membranes

Robust and electrically conductive thin films (2500S/m) made of cross-linked poly(vinyl alcohol) and carboxylated multi-walled carbon nanotubes (PVA–CNT–COOH) were synthesized via a sequential deposition and cross-linking method. The PVA–CNT–COOH modified membranes were then used in an electrofiltration cell in which the effects of applied potentials on fouling of high concentrations (3–5g/L) of alginic acid (AA) were studied. It was demonstrated that after 100min of operation while applying −3V and −5V, the change in operating pressure was reduced by 33% and 51%, respectively, compared to application of no voltage. Increase in ionic strength resulted in overall higher fouling rates, where the application of −5V resulted in a pressure change reduction of 43% compared to no application of potential. A modified Poisson–Boltzmann equation used in a DLVO-type theory demonstrated that at the applied potentials, electrostatic interactions produced significant repulsive forces between the membrane surface and the charged organic foulant. Calculations at experimental conditions demonstrated the pure AA aggregates would be strongly repulsed away from membrane surface. In synthetic wastewater the repulsion force is greatly reduced, resulting in overall reduced fouling inhibition.

Efficacy of CNT-bound polyelectrolyte membrane by spray-assisted layer-by-layer (LbL) technique on water purification

This study demonstrates anti-fouling properties of surface-modified polyethersulfone composite ultrafiltration membranes prepared by a spray-assisted layer-by-layer technique.

Preparation and Characterization of Polysulfone/Polyphenylsulfone/Titanium Dioxide Composite Ultrafiltration Membranes for Palm Oil Mill Effluent Treatment

Palm oil mill effluent (POME) is the largest pollutant discharged into the rivers of Malaysia. An efficient treatment system is highly desirable in palm oil mills in order to control the effluent discharged to any water bodies. In this study, composite ultrafiltration (UF) membranes were successufully prepared by incorporating polysulfone (PSF)/polyphenylsulfone (PPSU) blend membranes with inorganic TiO2 nanoparticles in the range of 0–4 wt%. Prior to POME treatment process, the properties of the resulting membranes were first characterized with respect to pure water flux, BSA rejection, hydrophilicity and structural morphologies. Of the membranes tested, it is found that membrane without TiO2 incorporation demonstrated the highest pure water flux, i.e. 82.81 L/m2h with BSA rejection of 98% when tested at 2 bar. The decreasing water flux with increasing TiO2 loading in the membrane is mainly due to the high viscosity of the dope solution which delayed the phase inversion process and resulted in reduced surface pore size. For the POME treatment process, the results showed that UF membrane could effectively treat the wastewater by removing up to 87% BOD3, 90% COD and almost complete elimination of turbidity.

The characterization of polysulfone–Fe3O4 composite ultrafiltration membrane and its application

In this paper, a novel polysulfone (PSF)–Fe3O4 composite ultrafiltration membrane was prepared and employed to purify the flavonoids from the ginkgo biloba extraction (GBE). The mass susceptibility (χ) of the ginkgo flavonoids with 98% purity was tested to be greater than 0, so they showed paramagnetism. Hysteresis curve indicated that the composite membrane have superparamagnetism for the addition of nano-sized Fe3O4 particles. The process of ultrafiltration was performed without and in the magnetic field with different intensities, respectively. The flavonoids content in the products is much superior when performed in the magnetic field than that without magnetic field. In the absence of magnetic field, the flavonoids content in the products was purified to 30.16% from 15.60% in crude GBE. Once the magnetic field with 0.2 T was added in the process, the purity was enhanced to 35.24%. Furthermore, the purity was persistently increasing with the incremental magnetic intensity. When the magnetic intensity was strengthened to 1.0 T, the purity approaches saturation, with being up to 52.87%.

Novel Nanoparticles Incorporated Polyvinylidene Fluoride Ultrafiltration Membrane

In this study, polyvinylidene fluoride (PVDF) composite ultrafiltration membranes were prepared by a phase inversion method, N,N-dimethylacetamide (DMAc) was used as solvent and polyvinylpyrrolidone (PVP) was used as dispersant, nanoTiO2 and AgNO3 were used as addictive materials. With different doping content of nanoTiO2 and silver ions, those hybrid films have different functions and structure. The basic performance and photocatalytic properties of those ultrafiltration membranes were studied in detail. The experiment results show that adding nanosized TiO2 particles will make the porosity of PVDF membrane increase, adding silver ion with low content can not improve water flux and porosity of membranes, however, nanoTiO2 and silver ions doping together can effectively improve the photocatalytic degradation rate.

Preparation of Polypropylene and Polysulfone Composite Ultrafiltration Membrane though Physical Coating Method

Polypropylene/polysulfone composite ultrafiltration membrane was prepared though coating method using microporous polypropylene hollow fiber membrane as a support layer and polysulfone membrane as a functional layer. Membranes of different pore sizes were prepared by L-S phase translation though changing the concentration of PS. The properties of the composite membrane include water flux and rejections of PEG-2000 were studies. The flux of 78 L/m2h and 98 % rejection was achieved at PS concentration of 11%, Polyvinylpyrrolidone of 4 %, liquid phase coagulation time of 3 hours.

Preparation of polysulfone ultrafiltration membranes modified by silver particles

In this article, polysulfone–silver composite ultrafiltration membranes were successfully prepared with phase inversion technique through two steps. First, silver particles were prepared in N,N-dimethylformamide (DMF) through reducing silver nitrate via situ reduction method at 120°C. Then, the casting solution was prepared with polysulfone (PSF), N-methyl-2-pyrrolidone, polyvinyl pyrrolidone (PVP) (K10, K30, K50 and K70) and the DMF solution containing the formed silver particles. The effects of molecular weight of PVP on the separation performances and break strength of the membranes were investigated. As a result, for both of PSF membranes and silver composite membranes, with the increase in the molecular weight of PVP, the pure water flux and rejection ratio to bovine serum albumin (68 KDa) solution first increased and then decreased. When the same kind of PVP was added, the rejection ratio of all composite membranes was higher than the rejection ratio of PSF membranes. Moreover, when PVP K30 was added, the water flux and the rejection ratio of the silver composite membrane reached the maximum values, 159 L m-2 h-1 and 94%, respectively. It was also found that the break strength of all of the composite membranes was significantly improved by 38–48% compared with the PSF membranes.

Role of wettability in interfacial polymerization based on PVDF electrospun nanofibrous scaffolds

High flux composite filtration membrane based on electrospun poly(vinylidene fluoride) (PVDF) nanofibrous scaffold has been produced by interfacial polymerization. The liquid contact angles of the solvents used in the aqueous phase and the organic phase on the surface of PVDF nanofibrous scaffolds have been tested before interfacial polymerization. Three polymerization routes have been carried out and the wettability of the support layer in reactive phases has been proven to play an important role in the fabrication of a flawless thin barrier layer. Various parameters in interfacial polymerization were discussed and optimized to form a high performance composite ultrafiltration membrane. When the monomer concentration in the aqueous phase was 0.1%, and the monomer concentration in the organic phase was 0.2%, interfacial reaction time was 1min, the performance of the composite membrane was optimized. The pure water flux of the filtration membrane was 67L/m2h, and the BSA rejection was 98% under the pressure of 0.3MPa.

Preparation and Characterization of BaBi<sub>2</sub>Nb<sub>2</sub>O<sub>9</sub>/PVDF Inorganic-Organic Composite Ultrafiltration Membranes

BaBi2Nb2O9/PVDF (polyvinylidene fluoride) composite ultrafiltration (UF)membranes were prepared by alloying BaBi2Nb2O9 (BBN) particles uniformly in the PVDF solution (15% polymer weight) and used a phase-inversion method. This paper studied the effect of the concentration of BBN from 0% to 5% in 0.2Mpa on pure water flux and rejection rate to Bovine serum albumin (BSA). The cross-sectional structures of composite membranes were observed by scanning electron microscopy (SEM). Moreover, XRD results revealed the crystal structure of PVDF. The experimental results showed that the BBN/PVDF composite ultrafiltration membranes were superior in separation performances than the pure PVDF membranes due to the addition of BBN.

Thin Film Nanofibrous Composite Ultrafiltration Membrane for Oil Removal from Oilfield Wastewater

Nanofibrous substrate composite ultrafiltration membrane consisted of polyacrylonitrile (PAN) electrospun scaffold which was used as the substrate, and a thin crosslinked poly(vinyl alcohol) (PVA) barrier layer which was prepared by electrospinning technique combined with mixed solvent treatment. The thickness of PVA nanofibrous top layer was controlled by changing the electrospun depositing time. Through immersing PVA/PAN double-layer mats into water/acetone mixed solvent system, the PVA nanofibrous top layer was swollen to merge imperceptibly into an integrated barrier film on the surface of PAN substrate, and then chemically crosslinked by glutaraldehyde. The resultant PVA/PAN thin film nanofibrous composite (TFNC) membrane has high rejection rate (99.6%), high flux (410.5l/m2h) and good anti-fouling characteristic at very low operation pressure (0.2MPa) for separating oil from the oilfield wastewater. Additionally, the removal of TDS, suspended matter, total iron and sulfate reducing bacteria (SRB) showed high rejection rate with relatively stable PH.

Improved hydrophilicity, permeability, antifouling and mechanical performance of PVDF composite ultrafiltration membranes tailored by oxidized low-dimensional carbon nanomaterials

Polyvinylidene fluoride (PVDF)–oxidized carbon nanotubes (OMWCNTs), PVDF–graphene oxide (GO) and PVDF–OMWCNTs–GO composite ultrafiltration membranes were prepared by solution-blending the ternary mixture of PVDF–oxidized low-dimensional carbon nanomaterials–dimethylacetamide in combination with the phase inversion method. The microscope images of the PVDF matrix microstructure showed that the composite membranes exhibited a bigger mean pore size and higher roughness parameters than pristine membranes. The contact angle of the membranes decreased from 78.5° (PVDF) to 66.8° (PVDF–OMWCNTs), 66.4° (PVDF–GO) and 48.5° (PVDF–OMWCNTs–GO). For the PVDF–OMWCNTs, PVDF–GO and PVDF–OMWCNTs–GO composite membranes, there was a 99.33%, 173.03% and 240.03% increase in permeation flux and a 21.71%, 17.23% and 14.29% increase in bovine serum albumin (BSA) rejection, respectively, compared with those of the pristine membranes. The newly developed composite ultrafiltration membranes demonstrate an impressive prospect for the anti-irreversible fouling performance in multi-cycle operations from BSA treatment. Additionally, the addition of OMWCNTs and GO increased the tensile strength of composite membranes from 1.866 MPa to 2.106 MPa and 2.686 MPa, respectively. Conspicuously, the PVDF composite ultrafiltration membranes endowed with oxidized low-dimensional carbon nanomaterials demonstrated fascinating hydrophilicity, permeability, antifouling and mechanical performance and promising application prospects owing to the rich oxygen-containing functional groups, high specific surface and synergistic effect of inorganic additive.

Carbon nanotube/polyaniline nanofiber ultrafiltration membranes

Development of electro-ultrafiltration membranes is an attractive target. We report electrically conducting ultrafiltration membranes by blending single-walled carbon nanotube/polyaniline (SWCNT/PANi) nanofibers into a polysulfone (PSf) matrix. By selecting the amount of nanofibers and applying a flash welding technique, the chemical structure, porosity, thermal stability, conductivity, hydrophilicity, permeability, and bovine serum albumin (BSA) rejection of these composite ultrafiltration membranes can be controlled. Addition of SWCNT/PANi nanofibers to the composites enhances the initial water permeability by 2.5–7.3 times and increases the hydrophilicity, and maintains considerable rejection of BSA from 39.8–73.7%. An electrical conductivity between 0.1 and 3.4 × 10−6 S cm−1 can be maintained over a broad pH range from 0.52–10.2. By regulating the flash welding intensity, the conductivity, permeability, and BSA rejection can be enhanced up to 600, 2, and ∼1.5 times, respectively.

Carbon nanotube-templated polyaniline nanofibers: synthesis, flash welding and ultrafiltration membranes

Electro-active switchable ultrafiltration membranes are of great interest due to the possibility of external control over permeability, selectivity, anti-fouling and cleaning. Here, we report on hybrid single-walled carbon nanotube (SWCNT)-polyaniline (PANi) nanofibers synthesized by in situ polymerization of aniline in the presence of oxidized SWCNTs. The composite nanofibers exhibit unique morphology of core-shell (SWCNT-PANi) structures with average total diameters of 60 nm with 10 to 30 nm thick PANi coatings. The composite nanofibers are easily dispersed in polar aprotic solvents and cast into asymmetric membranes via a nonsolvent induced phase separation. The hybrid SWCNT-PANi membranes are electrically conductive at neutral pH and exhibit ultrafiltration-like permeability and selectivity when filtering aqueous suspensions of 6 nm diameter bovine serum albumin and 48 nm diameter silica particles. A novel flash welding technique is utilized to tune the morphology, porosity, conductivity, permeability and nanoparticle rejection of the SWCNT-PANi composite ultrafiltration membranes. Upon flash welding, both conductivity and pure water permeability of the membranes improves by nearly a factor of 10, while maintaining silica nanoparticle rejection levels above 90%. Flash welding of SWCNT-PANi composite membranes holds promise for formation of electrochemically tunable membranes.