Flux Recovery Ratio Value Research Articles

Designing of a novel polyethersulfone (PES) ultrafiltration (UF) membrane with thermal stability and high fouling resistance using melamine-modified zirconium-based metal-organic framework (UiO-66-NH2/MOF)

A novel polyethersulfone (PES) ultrafiltration (UF) membrane, with thermal stability and high permeability, was synthesized using melamine-modified zirconium-based metal-organic framework (MOF), UiO-66-NH2. The surface roughness and textural property of the as-prepared membranes were studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The wettability of the membranes was measured by water contact angle (WCA). Membrane performance was investigated by pure water flux (PWF), flux recovery ratio (FRR), fouling resistance, and antifouling ability. An improvement in the performance of the membrane was observed by introducing the MOF to the PES matrix. A considerable decrease in the WCA and roughness and a notable increase in porosity were found in the modified membranes compared to the bare membrane. By adding the MOF (in the optimal percentage of 0.1 wt%) into the polymer matrix the FRR value was increased from 59.2 to 95.22%. The UF membranes were tested by oily wastewater in different conditions (500 and 300 ppm at 25 and 60 °C). Moreover, the antifouling property of the membranes was found to be greatly improved by the incorporation of the MOFs for long-term filtration.

The Construction of a Hydrophilic Inorganic Layer Enables Mechanochemically Robust Super Antifouling UHMWPE Composite Membrane Surfaces.

In this study, a facile and effective method is adopted to prepare mechanochemically robust super antifouling membrane surfaces. During the process, vinyl trimethoxy silane (VTMS) was used as the reactive intermediate for coupling the hydrophilic inorganic SiO2 nanoparticle layer on to the organic ultra-high-molecular-weight polyethylene (UHMWPE) membrane surface, which created hierarchical nanostructures and lower surface energy simultaneously. The physical and chemical properties of the modified UHMWPE composite membrane surface were investigated. FTIR and XPS showed the successful chemical grafting of VTMS and SiO2 immobilization, and this modification could effectively enhance the membrane’s surface hydrophilicity and filtration property with obviously decreased surface contact angle, the pure water flux and bovine serum albumin (BSA) rejection were 805 L·m−2·h−1 and 93%, respectively. The construction of the hydrophilic nano-SiO2 layer on the composite membrane surface for the improvement of membrane antifouling performance was universal, water flux recovery ratio values of BSA, humic acid (HA), and sodium alginate (SA) were all up to 90%. The aim of this paper is to provide an effective approach for the enhancement of membrane antifouling performance by the construction of a hydrophilic inorganic layer on an organic membrane surface.

Self-cleaning properties of L-Histidine doped TiO2-CdS/PES nanocomposite membrane: Fabrication, characterization and performance

The polyethersulfone (PES) membrane incorporated with L-Histidine doped TiO2-CdS photocatalytic nanocomposite is fabricated to improve the membrane performance and its antifouling properties. The L-Histidine doped TiO2-CdS/PES nanofiltration membrane was characterized by scanning electron microscopy (SEM), contact angle and atomic force analysis (AFM) analyses. SEM images and contact angle results are demonstrated that membrane porosity and its hydrophilic properties increase with adding of L-Histidine doped TiO2-CdS photocatalytic nanocomposite. Moreover, AFM images of the modified membranes indicate favorable changes in surface roughness resulting in the improvement of antifouling properties. The pure water flux, flux recovery ratio (FRR) during filtration of milk powder and activated sludge suspension were also measured in a dead end cell. Increasing membrane permeability and FRR value approved its effective role of the added nanoparticles into the PES matrix. The M3 (0.5 wt% of NPs) membrane is selected as an optimal nanocomposite membrane which exhibits a much higher pure water flux (42.1 kg/m2 h) and FRR value (90 and 97% during filtration of milk powder and activated sludge suspension, respectively). The photocatalytic capability and antifouling properties of the M3 membrane as an optimum membrane were also investigated in a cross flow cell under continuous visible light irradiation. As a result, the high permeation flux (34.7 kg/m2 h), COD removal (100%) and FRR value (99%) was achieved during filtration of biologically treated palm oil mill effluent (POME) with COD concentration of 1000 mg/L at feed flow rate of 150 L/h and pressure of 5 bar. Effect of feed flow rate (50 and 150 L/h) and COD concentration (1000, 3000 and 5000 mg/L) on the membrane performance and its fouling resistance was also evaluated. Increasing feed concentration shows a negative effect on the membrane performance while feed flow rate increases separation performance and self-cleaning properties of the M3 membrane.

Clarification of Apple Juice Using New Generation Nanocomposite Membranes Fabricated with TiO2 and Al2O3 Nanoparticles

To enhance anti-fouling properties of polymeric membranes during apple juice clarification, PSF/PEI (20/2 wt%) ultrafiltration (UF) membranes were modified with TiO2 and Al2O3 nanoparticles using the phase inversion method. Turbid apple juice samples were clarified using cross-flow membrane filtration system. All fabricated nanocomposite UF membranes had higher apple juice flux values than PSF/PEI membrane. Membrane prepared with 0.01% TiO2 (UFT1) had the highest apple juice flux (at steady state, 44.6 L/m2h). The FRR (%) value of TiO2 and Al2O3 incorporated UF membranes was between 90.9–94.0% and 79.6–97.6%, respectively, and these FRR values were higher than that of PSF/PEI membrane (UF2, 60.3%). Porosity and hydrophilicity of the UF membranes significantly increased with the addition of nanoparticles and the highest porosity and hydrophilicity was achieved in the 0.01% TiO2 incorporated UF membrane (UFT1) membrane. Higher flux recovery ratio (FRR) and lower relative flux reduction (RFR) values of Al2O3 and TiO2 incorporated nanocomposite membranes, compared with the unmodified membrane, demonstrated the enhancement in the anti-fouling properties of the PSF/PEI membrane. SEM images of the nanocomposite membranes also proved the nanoparticle incorporation to the PSF/PEI matrix. Color, turbidity, total soluble solid, total phenolic content, and antioxidant capacity of the samples using nanocomposite membranes were better than that of clarified using both commercial and unmodified membranes. TiO2 incorporated nanocomposite membranes had superior performance than Al2O3 incorporated nanocomposite membranes and among these membranes, the ones prepared with the addition of 0.01 wt% TiO2 exhibit the best performance in terms of clarification of apple juice.

Influence of TiO2 nanoparticles loading on permeability and antifouling properties of nanocomposite polymeric membranes: experimental and statistical analysis

Influence of the dope solution concentration on final membrane properties, regarding TiO2 role, was investigated. For this purpose, blended flat sheet poly(vinylidene fluoride) (PVDF)-based membranes with different proportions of poly(vinyl pyrrolidone) (PVP)/TiO2 ratios were prepared via phase inversion process. The final application of the membranes was evaluated, especially in contact with vital microbial mixed liquor, in membrane bioreactors due to antibacterial properties of TiO2 and environmentally concern of nanoparticles application. Response surface methodology (RSM) was used as a precise and multivariate technique to estimate and navigate the system performance at any experimental point within the investigation domain. Filtration properties, flux recovery ratio and (Protein flux / pure water flux: Jp/Jw) ratio of the membranes were investigated statistically to propose the formulations for the optimal performance. The correlation showed good agreement with the measured pure water flux and flux recovery ratio values of the fabricated membranes, with R2 values higher than 90%. The findings are significant since demonstrating that the loaded nano TiO2 particles around 0.5 wt% improve pure water flux, however, based on the Pareto analysis, experimental values and environmental safety concern, nanoparticles loading can be neglected in comparison with the other factors investigated in this study.

High-hydrophilic and salt rejecting PA-g/co-PVP RO membrane via bionic sand-fixing grass for pharmaceutical wastewater treatment

In this study, a novel PA-g/co-PVP reverse osmosis (RO) composite membrane with high-hydrophilic, antifouling, high salt rejection properties, was prepared according to the principle of sand-fixing grass effect for pharmaceutical wastewater treatment. N-vinyl-2-pyrrolidone (NVP) was used as a “seed agent” that was seeped into a low cross-linked polyamide (PA) film. A hydrophilic molecular brush of polyvinylpyrrolidone (PVP) grafted on the PA surface (PA-g-PVP) similar to grass growing on sand and a cross-linked copolymer layer of PA and NVP (PA-co-NVP) similar to grass roots distributed in sand, as well as an interlayer cross-linking between PA separation layer and PES ultrafiltration membrane with a highly stable interfacial structure, synchronously occurred through γ-ray radiation. Upon incorporation of 1.0% of NVP, the resultant PA-g/co-PVP membrane achieved 18.8° water contact angle and high flux recovery ratio (FRR) values of 91.23%, 96.28%, and 93.67% for the foulants of bovine serum albumin (BSA), sodium alginate (SA), and sodium dodecyl sulfate (SDS), respectively. The FRR value of pharmaceutical wastewater-polluted membrane after cleaning was 94.30%. The PA-g/co-PVP RO membrane showed outstanding separation stability due to the radiation cross-linking reactions, which limit matrix swelling and interface delamination similar to the action principle of sand-fixing grass. These merits prove that the RO membrane developed in this study can be used in many applications, including small organic molecular wastewater separation.

Membrane bioreactors troubleshooting through the preparation of a high antifouling PVDF ultrafiltration mixed-matrix membrane blended with O-carboxymethyl chitosan-Fe3O4 nanoparticles

ABSTRACTPolymeric ultrafiltration (UF) membranes often used in membrane bioreactor (MBR) prone to be fouled by fouling agents. Therefore, in this paper, the antifouling characteristics of polyvinylidene fluoride (PVDF) UF membranes for wastewater treatment are improved through modifying membranes by O-carboxymethyl chitosan (OCMCS)-functionalized Fe3O4 nanoparticles (OCMCSFe3O4). The modifier agent was manufactured by the adsorption of OCMCS on Fe3O4 nanoparticles, which were synthesized via co-precipitating method. Antifouling performance of membranes was assessed by permeation tests done using activated sludge suspension as a biological foulant, then the calculation of the pure water flux recovery ratio (FRR) and fouling resistance parameters. Also, to investigate the protein rejection of membranes, permeation tests were conducted by the bovine serum albumin (BSA) solution. According to the obtained results, surface hydrophilicity of the embedded membranes was improved in the low concentrations of the modified nanoparticles. However, the high quantity of the OCMCS-Fe3O4 nanoparticles (>0.1 wt. %) in the casting solution lessened membrane performance owing to the agglomeration of the nanoparticles in the polymer matrix. Although, the 1 wt. % OCMCS-Fe3O4 membrane revealed considerably higher PWF and permeation than that of the other membranes. It was because of defects and cracks in the membranes. The 0.05 wt. % OCMCS-Fe3O4/PVDF membrane exhibited the highest FRR (95.7%) and protein rejection value (48%) and the lowest irreversible fouling resistance (Rir) value (4.2%). It is concluded that the blended membranes with modified nanoparticles resulted in a high-flux ultrafiltration membrane comparable with microfiltration membrane, while its separation properties remained similar to UF membrane.

TMU-5 metal-organic frameworks (MOFs) as a novel nanofiller for flux increment and fouling mitigation in PES ultrafiltration membrane

Abstract In this study, a novel hydrophilic polyethersulfone (PES) ultrafiltration membrane was synthesized by blending of TMU-5 Metal-Organic frameworks (MOFs) via the phase inversion method. The sequel of the incorporated MOFs on the morphology and efficiency of the constructed neoteric membranes was investigated in terms of pure water flux, and fouling parameters. The microstructure of the fabricated membranes was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle. The antifouling process using a feed solution of 40,000 ppm engine oil/water mixtures leads to a well performance of the newly interconnected structure membranes (>98%) which possess great advantages for oil-water separation. The SEM photographs demonstrated an increase in pore size and porosity of the prepared membranes with blending of the MOF that reflected the symptoms in the pure water flux increased up to 182 (kg/m2 h). Furthermore, surface hydrophilicity of the reclaimed membranes was improved due to water tendency improvement of the membrane surface. The antifouling properties of the membranes were assessed by powder milk solution and measuring the flux recovery ratio (FRR). The 0.1 wt% MOF NPs–PES membrane displayed the highest FRR value (98.74%) and the lowest irreversible fouling resistance (Rir) value (1.25%). As a conclusion, the addition of MOF nano particles (NPs) at a low concentration (0.1 wt%) could result in membranes with more pure water flux, higher rejection and good fouling resistance compared to the unfilled PES membrane.

Custom-made PEI/exfoliated-MoS2 nanocomposite ultrafiltration membranes for separation of bovine serum albumin and humic acid

Herein, we report the effect of the exfoliated molybdenum disulfide (eMoS2) nanosheets in improving the permeability and anti-fouling properties of the PEI ultra-filtration (UF) membrane using bovine serum albumin (BSA) and humic acid (HA) as model fouling agents. The PEI/eMoS2 nanocomposite membranes were prepared via phase inversion method using three different eMoS2 concentrations (0.5, 1 and 2wt%) designated as PEI-0.5, PEI-1 and PEI-2, respectively. Fourier transform infra-red spectroscopy employed to probe the surface functionalities on the membranes. Contact angle measurement, pure water flux, swelling rate and solute rejection studies confirmed the improved hydrophilicity of the PEI/eMoS2 nanocomposite membranes than the individual entities. Flux recovery ratio (FRR), reversible and irreversible fouling results evidenced the improved fouling resistance of PEI/eMoS2 modified membranes than the individual counterparts. SEM results evidenced that the nanoscale eMoS2 significantly altered the membrane morphology by causing increased porosity and larger macrovoids formation on the surface as well as in the bulk of the membrane. PEI-1 membrane showed an increased pure water flux (52.54Lm−2h−1) and water content (74.8%) whereas lesser contact angle (69.2°) and hydraulic resistance (1.85kPa/Lm−2h−1). Resistance to fouling performance of PEI-1 membrane was evident from the FRR values of 95.3 and 90.2% and rejection values of 94.5 and 92.4% for BSA and HA respectively. PEI-2 membrane agglomerates with eMoS2 and hindered the membrane permeability by blocking the macrovoids in the bulk which restricted the permeation and fouling resistance of the membrane. Amongst various nanocomposite membranes investigated, the PEI-1 membrane exhibited better hydrophilicity and fouling resistance properties due to the availability of the favorable surface and bulk characteristics.

Preparation and Characterization of an Antifouling Polyethersulfone Nanofiltration Membrane Blended with Graphene Oxide/Ag Nanoparticles

Graphene oxide/Ag nanoparticles (Ag/GO) was prepared and employed to synthesize antifouling polyethersulfone (PES) mixed matrix membranes. The performance of the membranes was evaluated in terms of flux, hydrophilicity and anti-biofouling properties. With increment of the Ag/GO from 0 to 0.1 wt.%, the pure water flux increased from 24.7 up to 54.1 kg/m2 h. The flux recovery ratio (FRR) of the membranes was performed using milk powder solution and the results illustrated that the 0.1 wt.% Ag/GO membrane had the best fouling resistance with the FRR value of 95.45%. The performance of the nanofiltration was assessed using the retention of Direct Red 16. It was indicated that the Ag/GO-PES membranes have remarkable dye removal (98.38% rejection). The anti-biofouling activities of the 0.1 wt.% Ag/GO mixed matrix membrane was also investigated using activated sludge and the results showed a notable improvement.

Versatile polyvinylidene fluoride hybrid ultrafiltration membranes with superior antifouling, antibacterial and self-cleaning properties for water treatment

Novel ultrafiltration membranes with both superior antibacterial and self-cleaning properties were fabricated. By using a non-solvent induced phase separation method (NIPS), N-halamine epoxide and siloxane were grafted onto the multi-walled carbon nanotubes (N-Si-MWNTs) to fabricate polyvinylidene fluoride (PVDF) hybrid membranes. The membrane morphology was observed under a field emission scanning electron microscopy. The results demonstrated that the PVDF hybrid membranes had an asymmetrical structure, and their hydraulic permeability was evidently enhanced with the addition of modified MWNTs. When compared with the primitive PVDF membrane, the hybrid membranes presented improved surface hydrophilicity. After three ultrafiltration–regeneration cycles with bovine serum albumin as model biofoulant and pure water as detergent, the PVDF hybrid membranes exhibited a high flux recovery ratio (FRR). Furthermore, when compared with other membranes, the membrane containing N-Si-MWNTs displayed the highest FRR value of above 96.5% after the entire fouling and cleaning experiment. The fabricated PVDF/N-Si-MWNTs hybrid membranes had excellent antibacterial efficacy, presenting maximum antibacterial efficacy of 98.0% and 95.6% against Staphylococcus aureus and Escherichia coli, respectively. Thus, the PVDF/N-Si-MWNTs membranes fabricated in this study are environment-friendly with both benign antibacterial and self-cleaning properties.

Amphiphilic ABA‐type triblock copolymers for the development of high‐performance poly(vinylidene fluoride)/poly(vinyl pyrrolidone) blend ultrafiltration membranes for oil separation

ABSTRACTABA‐type amphiphilic triblock copolymers (TBCs) were synthesized by a reversible addition fragmentation chain transfer (RAFT) process with a telechelic polystyrene macro‐RAFT agent and 4‐[n‐(acryloyloxy)alkyloxy]benzoic acid monomers. Ultrafiltration (UF) membranes were fabricated by a phase‐inversion process with blends of the TBC, poly(vinylidene fluoride) (PVDF), and poly(vinyl pyrrolidone) (PVP) in dimethylformamide. The UF‐fabricated membranes were characterized by scanning electron microscopy, atomic force microscopy, water contact angle measurement, thermogravimetric analysis, and differential scanning calorimetry. Pure water permeation, molecular weight cutoff values obtained by the permeation of different molecular weight polymers as probe solutes, bovine serum albumin (BSA) solution permeate flux, and oil–water emulsion filtration tests were used to evaluate the separation characteristics of the fabricated membranes. The tripolymer blend membranes exhibited a higher flux recovery ratio (FRR) after the membrane was washed with sodium lauryl sulfate (0.05 wt %) solution for a BSA solution (FRR = 88%) and oil–water emulsion (FRR = 95%) feeds when than the PVDF–PVP blend membrane (57 and 80% FRR values for the BSA solution and oil–water emulsion, respectively). The pendant carboxylic acid functional moieties in this ABA‐type TBC have potential advantages in the fabrication of high‐performance membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45132.

Cellulose acetate ultrafiltration membranes reinforced by cellulose nanocrystals: Preparation and characterization

ABSTRACTCellulose nanocrystals (CNCs) were used as a sustainable additive to improve the hydrophilicity, permeability, antifouling, and mechanical properties of blend membranes. Different CNC loadings (0–1.2 wt %) in cellulose acetate (CA) membranes were studied. The blend membranes were prepared by a phase‐inversion process, and their chemical structure and morphological properties were characterized by attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy, porosity, and mean pore size and contact angle measurement. The blend membranes became more porous and more interconnected after the addition of CNCs. The thickness of the top layer decreased and a few large holes in the porous substrate appeared with increasing CNC loading. In comparison with the pure CA membranes, the pure water flux of the blend membranes increased with increasing CNC loading. It reaches a maximum value of 76 L m−2 h−1 when the CNC loading was 0.5 wt %. The antifouling properties of the CA membrane were significantly improved after the addition of CNCs, and the flux recovery ratio value increased to 68% with the addition of 0.5 wt % CNCs. In comparison with that of the pure CA membranes, the tensile strength of the composite membranes increased by 47%. This study demonstrated the importance of using sustainable CNCs to achieve great improvements in the physical and chemical performance of CA ultrafiltration membranes and provided an efficient method for preparing high‐performance membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43946.

Fabrication and characterization of anti-fouling and anti-bacterial Ag-loaded graphene oxide/polyethersulfone mixed matrix membrane

Partially reduced graphene oxide/Ag nanocomposite (rGO/Ag) was fabricated via a green and facile method, from graphite oxide, AgNO3 as a precursor of Ag0, and sodium citrate as a reducing and stabilizing agent. The synthesized rGO/Ag nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy techniques (SEM). The influence of rGO/Ag nanocomposite as a new nanofiller on the preparation of polyethersulfone (PES) mixed matrix membranes was evaluated in the cases of permeation performance, hydrophilicity, anti-fouling and anti-bacterial properties. Water flux of the mixed matrix membranes was increased up to 0.2wt% rGO/Ag, reaching to 429.8 (kg/m2h), and then reduced. The anti-bacterial activities of rGO/Ag mixed matrix membranes were investigated using Gram-negative bacteria of Escherichia coli and Pseudomonas aeruginosa, and Gram-positive bacteria of Staphylococcus aureus. The amount of Ag0 in the surface of GO sheets was about 34.24wt%. Addition of rGO/Ag nanosheets induced anti-bacterial properties to the membranes, leading to the increase in the zone of inhibition. The flux recovery ratio (FRR) study of the membranes using bovine serum albumin (BSA) solution revealed that 0.2wt% rGO/Ag membrane had the best fouling resistance with the FRR value of 67.2%.

Novel high flux antifouling nanofiltration membranes for dye removal containing carboxymethyl chitosan coated Fe3O4 nanoparticles

In this study, polyethersulfone (PES) nanofiltration membranes were synthesized by blending of O-carboxymethyl chitosan/Fe3O4 nanoparticles via the phase inversion method. O-carboxymethyl chitosan bound Fe3O4 magnetic nanoparticles (CC–Fe3O4 NPs) were synthesized by the binding of carboxymethyl chitosan (CC) onto the surface of Fe3O4 magnetic nanoparticles via co-precipitating method. The modified membranes had considerably higher pure water flux and permeation compared to the unfilled PES membrane. Surface hydrophilicity of the modified membranes was improved due to water affinity improvement of the membrane surface. However, high content of CC–Fe3O4 NPs (>0.5%) in the casting solution diminished membrane performance due to agglomeration of the nanoparticles in the polymer matrix. The antifouling properties of the membranes were evaluated by powder milk solution and measuring the pure water flux recovery ratio (FRR). The 0.5wt.% CC–Fe3O4 NPs–PES membrane exhibited the highest FRR value (91.7%) and the lowest irreversible fouling resistance (Rir) value (8.33%). Nanofiltration performance was also examined by retention of Direct Red 16 dye. As a conclusion, the addition of CC–Fe3O4 NPs at lower concentration could result in membranes with superior pure water flux, higher rejection and good fouling resistance compared to the unfilled PES membrane.

Tailoring the molecular weight cut off values of polyacrylonitrile based hollow fibre ultrafiltration membranes with improved fouling resistance by chemical modification

Chemical modification was employed for tuning the molecular weight cut off (MWCO) values of poly(acrylonitrile-co-methacrylic acid) hollow fibre ultrafiltration membranes by treating them with aqueous NaOH solutions of different concentration (0.25, 0.75, 1.25 and 1.75M) separately for 1, 3, 6 or 9h and then with 0.1M HCl solution for 2h at room temperature. This has resulted in the decrease of MWCO values of the fibres from the initial 92kDa to the range of 9–75kDa. The flux was decreased from 215 to 28–150L/m2h at 1.5kg/cm2. NaOHHCl treated fibres exhibited somewhat higher MWCO value and permeate flux than those of the fibres which were treated with NaOH only. Modified fibres exhibited lower fouling tendency for the ultrafiltration of aqueous solutions of polyethyleneoxide and bovine serum albumin, as indicated by their flux recovery ratio values of 91%–93%, when compared to the 53%–58% for virgin fibres. IR spectra of NaOH treated fibres showed a new peak at about 1580cm−1 due to the conversion of nitrile group to cyclic CN naphthyridine structure. HCl treatment was resulted in the disappearance of the peak at 1580cm−1 and appearance of a new peak around 1695cm−1 due to the amide carbonyl group that was generated by the hydrolysis of naphthyridine structure. The fibres were characterized by scanning electron microscopy, contact angles and zeta potential measurements.

Boehmite nanoparticles as a new nanofiller for preparation of antifouling mixed matrix membranes

Abstract The influences of boehmite nanoparticles as innovative nanofiller on fabrication of polyethersulfone (PES) blended membranes were investigated in terms of hydrophilicity, permeation performance, membrane morphology and antifouling property. Boehmite is an aluminum oxide hydroxide (γ-AlOOH) particle, containing extra hydroxyl groups on its surface. The hydrophilicity and pure water flux of the membranes were improved by incorporating of boehmite nanoparticles. Scanning electron microscopic (SEM) images showed that the nanoboehmite embedded membranes possessed a typical asymmetric structure similar with the bare PES membrane. In other words, embedding of the nanoboehmite did not change the finger-like structure of the membranes. Moreover, the high resolution SEM images revealed agglomeration of the nanoparticles at high concentrations. This reduced the pure water flux and increased the membrane resistances. The whey filtration results indicated that by addition of the low quantity of nanoboehmite, the fouling resistance parameters were significantly declined due to lower roughness and higher hydrophilicity of the surface of the modified membranes. These changes in the membrane characteristics improved the flux recovery ratio ( FRR ). Comparison of the nanoboehmite embedded membranes with the γ-Al 2 O 3 /PES membranes demonstrated superior characteristics and antifouling properties of the nanoboehmite mixed matrix membrane. The 1 wt.% nanoboehmite/PES membrane exhibited the highest FRR value of 96.1% and the lowest irreversible fouling resistance ( R ir ) value of 3.9%.

Preparation, characterization, acid stability and organic fouling of poly(acrylonitrile-co-methacrylic acid) ultrafiltration membranes

Poly(acrylonitrile-co-methacrylic acid) (PANMA) ultrafiltration membranes were prepared according to phase-inversion method using a semi-automatic mechanical casting unit. Membranes were made using casting dopes containing PANMA (16–22%) and polyvinylpyrrolidone (0–2%) in dimethylformamide or the mixture of dimethylformamide (DMF) and tetrahydrofuran (THF). SEM micrographs showed the presence of finger-like macrovoids and tear drop shape-like cavities under the dense skin layer for the membranes prepared using the casting dope containing 16–18% and 20–22% PANMA, respectively. The pure water fluxes were in the range of 756–78 and 246–52 L/m 2.h at 3 kg/cm 2, and the molecular weight cut off values were found to be in the range of 96–112 kDa and 92–102 kDa, respectively, for the membranes prepared using the casting dope in DMF and DMF + THF. Fouling tendency of the membranes was studied by permeating aqueous solution of PEO-100 kDa and measuring the trend in the flux with time. The flux recovery ratio values were in the range of 93–99%, thus indicating that the membranes have excellent fouling resistant nature. Acid stability measurements have shown that the flux was decreased by 13–16% while, there was no significant change in the rejections of the membranes which were immersed in 5–20% sulphuric acid solution for 12 months.

PSf/PANI nanocomposite membrane prepared by in situ blending of PSf and PANI/NMP

A simplified method to prepare polysulfone (PSf)/polyaniline (PANI) nanocomposite membrane was proposed. With this method, aniline was polymerized using ammonium peroxydisulfate as oxidant and N-methyl-2-pyrrolidone (NMP) as solvent, which was also the solvent of PSf. The mixture after aniline polymerization containing PANI nanospheres, PANI oligomers, NMP and inorganic ions, named PANI/NMP, was added directly into the solution consisting of PSf and NMP without any post-processing to form membrane casting solution. Then, PSf/PANI nanocomposite membranes were prepared via immersion phase inversion process using the casing solution. This method is called in situ blending method. PANI oligomers were soluble in both water and organic solvent while PANI nanospheres were dispersed in both water and organic solvent. The behaviors of PANI oligomers and PANI nanospheres during membrane formation were investigated and analyzed. A large portion of PANI oligomers and a small portion of PANI nanospheres would be leached out of the casting film during the phase separation and act as pore formers, inducing the enhancement of membrane porosity and surface pore size. A large portion of PANI nanospheres and a small portion of PANI oligomers residing in the prepared membranes favored the enhancement of membrane hydrophilicity, breaking strength and thermal stability. Compared with PSf membrane, PSf/PANI nanocomposite membranes obtained with this method had more hydrophilic surface, higher porosity, larger surface pore size, less acicular pores, thicker skinlayer, wider pores beneath the skinlayer, better vertically interconnected finger-like pores and less macrovoids. Pure water fluxes of PSf/PANI nanocomposite membranes were 1.7–4.1 times that of PSf membrane and BSA rejections of the membranes were all above 96%. During BSA ultrafiltration, PSf/PANI nanocomposite membranes showed slower flux decline rate and higher flux recovery ratio values after simple water flushing than PSf membrane.