High Dye Rejection Research Articles

A new anti-fouling polysulphone nanofiltration membrane blended by amine-functionalized MCM-41 for post treating waste stabilization pond's effluent

Developing an effective and stable separation membrane for water treatment is of much interest while challenging because of the restrictions of membrane fouling and water flux reduction. To minimize this problem, in this work, highly porous and hydrophilic nanostructure of NH2-modified MCM-41 (NH2-MCM-41) was embedded successfully into the nanofiltration (NF) membrane body via commonly used phase inversion method. The unmodified and modified nanofiller was analyzed by Fourier Transform Infrared (FTIR) spectroscopy, X-Ray powder diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and nitrogen adsorption–desorption. Furthermore, the modified membranes were characterized through surface and cross section FE-SEM images, the membrane surface roughness, hydrophilicity, antifouling properties and dye rejection. Benefiting from porous networks and enhanced hydrophilicity, the mixed matrix membranes (MMMs) revealed more prominent hydrophilic property as well as higher pure water flux (PWF) compared with naked membrane. The polysulphone (PSf) membrane modified with NH2-MCM-41-1.0 exhibited the highest pure water flux (PWF) of 65.43 kg/m2.h and superior antifouling characteristics with a flux recovery ratio (FRR) of around 97.0% and an irreversible fouling resistance (Rir) of 3.2%. Furthermore, the optimal membrane possessed high dye rejection (100%) and antifouling capacity (FRR of 97%) while filtering a field sample, effluent from a local stabilization pond treating municipal wastewater. The fabricated membrane in this study is believed to pave pathways for constructing NF membranes with superior effectiveness for other municipal and industrial wastewaters treatment.

In situ assembly of a covalent organic framework composite membrane for dye separation

Covalent organic frameworks (COFs) are prominent candidates for water separations and treatment. They have ordered channel structures, low densities, large specific surface areas, and tunable pore sizes. These features can be used to construct advanced organic solvent nanofiltration and separation membranes. Here, membranes with high permeability and selectivity are prepared in situ with 10% 1,3,5‒triformylphloroglucinol (Tp) and 4,4′,4″- (1,3,5- triazine-2,4,6-triyl) trianiline (TTA) on a Noria−polyethyleneimine co-modified ultrafiltration membrane substrate. The membrane thickness is only 200 nm. Moreover, the loaded COF Tp-TTA significantly increases the chemical stability and solvent resistance of the membrane, which enables a high (Chrome black T) CB-T dye rejection rate (>94%) in water and ethanol. The COF-based membrane is superior to previously reported dye-separation membranes, and has great potential.

Zr-Porphyrin Metal–Organic Framework-Based Photocatalytic Self-Cleaning Membranes for Efficient Dye Removal

The self-cleaning ability and reusability of a membrane are critical in practical applications because they can severely affect the lifespan and the separation efficiency of the membranes. In this work, hydrophilic Zr-porphyrin metal–organic frameworks (MOFs) with different dimensions (2D or 3D) were embedded in the polyamide active layer to develop a self-cleaning membrane with enhanced separation performance. Zr-porphyrin MOF (3D) with excellent photocatalytic activity and uniform 1D open triangular channels can not only endow this membrane with visible-light photocatalytic ability for the degradation of organic dyes deposited on the membrane surface but also provide additional transport channels leading to a high membrane permeate flux. The optimum membrane exhibits a superior water permeate flux of 110.4 L m–² h–¹ (threefold higher than the pristine thin-film composite membrane) while maintaining very high dye rejection (close to 100%) for five dyes (anionic dyes: Congo red, Direct red 23, and Reactive Black 5 and cationic dyes: methylene blue and rhodamine B) and an outstanding photocatalytic degradation self-cleaning ability (the recovery of water permeate flux exceeds 97% after 4 cycles). Overall, this study may offer new inspiration for designing and tuning Zr-porphyrin MOF-based self-cleaning membranes with excellent dye removal ability.

Mesoporous silica thin films incorporated chitosan mixed matrix nanofiltration membranes for textile wastewater treatment

AbstractThe demand of nanofiltration (NF) membranes for practical and cost‐effective environmental treatment is exploding. Mixed matrix membranes (MMMs) have attracted tremendous interest on account of combining the benefits of polymer and inorganic fillers. In this study, mesoporous silica thin films with perpendicular nanochannels (SBA‐15(⊥)) incorporated in chitosan (CS) were fabricated for dye wastewater purification. Functional groups, such as amino or epoxy groups were introduced into SBA‐15(⊥) (SBA‐15(⊥)‐NH2, SBA‐15(⊥)‐Epo) for forming covalent bonds with chitosan matrix to improve their compatibility. The excellent performance in dye/salt fractionation in aqueous solution was demonstrated by SBA‐15(⊥)‐Epo/CS MMMs, which realized a cut off of 585 g/mol, 99.9% rejection of Congo red, while maintaining 85% permeation of NaCl. In addition, the separation mechanism of the resulting membrane was explored. The efficient NF performance of SBA‐15(⊥)‐Epo/CS membrane was attributed to its better compatibility between SBA‐15(⊥)‐Epo and chitosan matrix by virtue of the formation of covalent bonds thus to ensure the high dye rejection, and the vertically oriented nanochannels arrangement facilitated the molecule transportation. This work will inspire feasible synthesis of a new generation of MMMs membranes for dye wastewater purification.

Fabrication of highly permeable PVDF loose nanofiltration composite membranes for the effective separation of dye/salt mixtures

The separation of dyes and salts is very challenging in regards to treating high salinity textile wastewater. To effectively dispose dye/salt mixtures, it has become urgent to develop highly permeable and antifouling nanofiltration membranes. Herein, a novel loose nanofiltration membrane was fabricated by combining blending with interfacial polymerisation. Polyvinylidene fluoride (PVDF)/styrene-maleic anhydride (SMA) copolymer membranes with uniform microstructures were achieved via phase inversion by controlling the miscibility. Numerous carboxyl groups were gathered on the surface due to the amphiphilic SMA segregation during the membrane formation. Carboxylated carbon nanotubes (CNT-COOH) were used to further tune the membrane microstructures and promote the carboxyl groups segregation onto the surface. Ultimately, polyethylenimine (PEI) and triethanolamine (TEA) were co-deposited on the membrane surface by the amidation reaction and hydrogen bonding to form a loose structure. The optimized membrane exhibited high dye rejections to Congo red (99.9%), methyl blue (96.7%), acid fuchsin (96.1%), and low salt rejections to NaCl (1.7%), MgCl2 (4.5%), MgSO4 (1.2%). Significantly, it possessed a permeate flux of up to 251.6 L/m2·h·bar during the dye/salt mixtures filtration. Moreover, the optimized membrane also performed excellent antifouling properties toward proteins and dyes. Overall, this work provides a promising loose nanofiltration membrane for textile wastewater treatment.

Polypropylene non-woven supported calcium alginate hydrogel filtration membrane for efficient separation of dye/salt at low salt concentration

Calcium alginate hydrogel is an eco-friendly material, but its wide application as a self-supporting filtration membrane is severely limited by the weak mechanical properties, which makes it difficult for the large scale preparation and the fixation of the membrane in filtration equipment. In this work, a fiber-reinforced calcium alginate membrane (CaAlg-PP) was prepared by coating calcium alginate (CaAlg) hydrogel on the polypropylene (PP) non-woven fabric treated with ethanol/water (v:v = 1:1) solution. The CaAlg-PP filtration membrane was characterized and used for dye/salt separation under a series of operating conditions. The membrane exhibited the co-operativity of the porous support layer and the CaAlg hydrogel in the compositing process, and also exhibited good pressure resistance, pollution resistance and low anionic dye adsorption efficiency. The optimized CaAlg-PP membrane had a high permeance (e.g. 20.3 L·m−2·h−1 for methyl blue at 0.1 MPa) and high dye rejection (e.g. methyl blue 99.5%), while low salt rejection (e.g. NaCl 7.5%), and the selectivity of methyl blue/NaCl was up to 185. The CaAlg-PP membranes made with simple processes and low-cost materials may provide new strategies for environmentally-friendly and economical low salts-containing wastewater treatment and dye recycling.

Enhancing the permeability and antifouling properties of cellulose acetate ultrafiltration membrane by incorporation of ZnO@graphitic carbon nitride nanocomposite

This study reports the modification of cellulose acetate (CA) membrane with zinc oxide (ZnO)@graphitic carbon nitride (g-C3N4) nanocomposite to improve the antifouling and separation performance. Different combinations of the CA-based membranes such as CA/g-C3N4, CA/ZnO, and CA/ZnO@g-C3N4 were fabricated using the non-solvent induced phase separation (NIPS) method. Membranes were analyzed for their morphology (SEM), porosity, pore size, contact angle, permeability, rejection, and antifouling properties. According to the SEM images of CA/ZnO@g-C3N4, the formation of pear-shaped macro voids and finger-like canals originating from the top layer was evident. Nanocomposite blended membrane with 0.25 wt.% ZnO@g-C3N4 achieved the largest pore radius (3.05 nm) and the lowest contact angle (67.7°). With these characteristics, 0.25 wt.% ZnO@g-C3N4 membrane obtained a pure water flux of 51.3 LMH, which is 2.1 times greater than the bare CA and high BSA and dye rejections with 97.20% and 93.7% respectively. Finally, the antifouling resistance of the CA membrane was greatly improved with FRR increasing from 73.7% to 94.8%, which was accompanied by a significant decrease in the fouling resistance parameters.

Bioinspired modification of molybdenum disulfide nanosheets to prepare a loose nanofiltration membrane for wastewater treatment

Loose nanofiltration membrane (NFM) is suitable for wastewater treatment especially for dye solution desalination due to its high rejection of dyes and high permeance of salts. In this study, MoS2@PDA was prepared by modifying molybdenum disulfide (MoS2) nanosheets with polydopamine (PDA). Then, the loose nanofiltration membrane was prepared by the deposition of MoS2@PDA on hydrolyzed polyacrylonitrile (HPAN) ultrafiltration membrane with pressure-assisted self-assembly. The morphology and properties of MoS2@PDA and MoS2@PDA NFMs were analyzed by SEM, TEM, TGA, FT-IR, AFM, WCA, XRD, and ζ-potentials. The PDA nanoaggregates on the surface of MoS2 nanosheets interfered with the regular stacking of MoS2 nanosheets parallel to the membrane surface, so the resultant membranes showed irregular loose structure which could provide transmembrane channels along with the impermeable nanosheet surface for molecule diffusion. When the MoS2 loading was 0.116 mg/cm2 and the PDA modification time was 5 h, the pure water flux of MoS2@PDA NFM could reach 204.05 LMH/bar, the rejection of methylene blue was 99 %, and rejection of salts (NaCl, Na2SO4, MgCl2, MgSO4) were less than 12 %. And MoS2@PDA NFM exhibited satisfactory long-term operational stability. This study provides a new strategy for the design of loose nanofiltration membrane with high performance.

Fabrication of thin-film composite nanofiltration membranes with improved performance using β-cyclodextrin as monomer for efficient separation of dye/salt mixtures

Complete separation of dye/salt mixtures through nanofiltration (NF) membranes is of great significance for the sustainable development of salt-containing dye wastewater treatment. Herein, a novel hydrophilic thin-film composite NF membrane was fabricated using β-cyclodextrin (β-CD) and trimesoyl chloride (TMC) via interfacial polymerization on a commercial ultrafiltration membrane. The performance of the resultant β-CD/TMC membranes was optimized by altering the variables. The results showed that the optimized β-CD4.0/TMC membrane (4.0 wt% β-CD, 0.2 wt% TMC, and 0.5 mol L-1 NaOH) possessed a pure water flux of 207.8 L m-2h−1 at 2.0 bar. Meanwhile, the membrane exhibited efficient dye/salt separation with high rejection of dyes (e.g. 100.0% for congo red and 99.1% for rose bengal) and low salt rejection (e.g. 8.5% for NaCl). Congo red/NaCl mixtures achieved similar removal rates to those of dye or salt solutions (the congo red rejection over 99.0% and the rejection of NaCl was below 10.6%). Furthermore, the membrane showed desirable stability, the flux remained at 82.9% of the initial value after filtration for 16 h. We believe that the fabricated NF membrane has a great potential for application in the treatment of salt-containing dye wastewater with improved selectivity for dye/salt separation.

High-permeability graphene oxide and poly(vinyl pyrrolidone) blended poly(vinylidene fluoride) membranes: Roles of additives and their cumulative effects

We prepared poly (vinylidene fluoride) (PVDF) based membranes via the phase inversion method to investigate the individual and simultaneous effects of graphene oxide (GO) and poly (vinyl pyrrolidone) (PVP) additives. It was demonstrated that the noticeable contribution of GO was to lower membrane surface charge. The principal role of PVP was to enhance membrane porosity, α-to-β phase transformation and mechanical strength. PVP also assisted GO distribution in the membrane matrix owing to their hydrogen-bonding interactions. GO-PVP-PVDF membrane showed cumulative effects in membrane physicochemical properties. In both pure water and naphthol blue black (NBB) dye solutions at pHs 4–10, the filtrate permeance increased from the pure PVDF to GO-PVDF, PVP-PVDF and GO-PVP-PVDF membranes. Therein, GO and PVP introduction provided permeance increases by one order of magnitude. All the membranes exhibited high dye rejections of ≥80.0% due to the Donnan exclusion mechanism. The membranes showed negligible dye adsorption. The stable filtration performance was demonstrated over 24-h multi-cycle filtration. The GO-PVP-PVDF membrane achieved outstanding high permeance (953–1350 L m−2 h−1 MPa−1) and excellent dye removal efficiencies (83.2–87.5%), which opened an avenue for application of this PVDF composite membrane to actual dye wastewater treatment.

Erythritol-based polyester loose nanofiltration membrane with fast water transport for efficient dye/salt separation

Loose nanofiltration membranes with a remarkable water permeability are highly promising for the fractionation of dyes and salts in the treatment of textile wastewater. In this study, a novel polyester membrane with unprecedented water permeability was developed via interfacial polymerization (IP), in which meso-erythritol (ME) was utilized as an aqueous monomer. Instead of using toxic catalysts, sodium hydroxide was incorporated to the aqueous solution to catalyze the ester reaction between hydroxyl and acyl chloride. A series of characterizations demonstrated that the formed polyester film is hydrophilic and negatively charged, with microsphere structures on the surface. Due to the low-active hydroxyl groups of the aqueous monomers, the participation of ME could yield a coherent polyester film with slightly loose structure atop the polyethersulfone (PES) membrane. The resultant membrane with high water permeability exhibited both a high rejection of dyes and a high transmission of salts. The rejection of the LNFM-2 membrane with an excellent water permeability of 53.23 LMH bar−1 for Congo red (CR), direct red 23 (DR23), reactive blue 2 (RB2), Na2SO4, NaCl was 99.6%, 95.2%, 99.6%, 11.0%, and 5.6% respectively. Furthermore, LNFM-1 has a water permeability of up to 87.13 LMH bar−1 while maintaining a competitive dye/salt separation performance. In addition, this type of polyester membrane has a superior antifouling performance and long-term stability during the filtration of dye/salt mixtures.The newly developed polyester LNF membranes have great application potential in the treatment of textile wastewater. This study paves the way for applying hydroxyl monomers like polyols for constructing TFC membranes for diverse separations.

Green preparation of polyvinylidene fluoride loose nanofiltration hollow fiber membranes with multilayer structure for treating textile wastewater

In this work, polyvinylidene fluoride (PVDF) loose nanofiltration (NF) hollow fiber membranes with multilayer structure were prepared successfully based on a solvent-free process. Graphene oxide (GO) was used to cover the interface pores of the pristine PVDF membranes via vacuum filtration, and polypyrrole (PPy) was polymerized on the surface to further decorate the membrane structure. Interestingly, the modified membranes exhibited a multilayer structure due to synergistic effect of GO and PPy. The structure and property of PVDF loose NF membranes were investigated in detail. After modifying by GO and PPy, the hydrophilicity improved obviously. Moreover, the molecular weight cut off (MWCO) was about 3580 Da, and the smallest pore size of skin layer decreased to 2.5–4 nm. Furthermore, the PVDF loose NF hollow fiber membranes presented a high dye rejection (˃98.5%) for negative dyes, whereas a low salt rejection for NaCl (about 4%), showing a great potential for separating dye/salt accurately. Specifically, there were not any solvent used in all the preparation processes. The work offered a novel strategy for green preparation of loose NF membranes.

Smart covalent organic networks (CONs) with "on-off-on" light-switchable pores for molecular separation.

Development of the new-generation membranes for tunable molecular separation requires materials with abilities beyond strict separation. Stimuli response could remotely adjust the membrane selectivity. Azobenzene derivatives can be photo-switched between trans and cis isomers under ultraviolet or visible light. Here, the azobenzenes were implanted as light switches to bridge the flexible cyclen building blocks. The smart covalent organic network membranes fold and unfold as origami that can be photo-switched between on-state (large) and off-state (small) pores. The cis membranes with off state under ultraviolet (UV) light have higher dye rejection than trans membranes with on-state channels. By controlling the trans-to-cis azobenzene isomerization via UV/Vis light, the pore size can be remotely controlled at the molecular level and the solvent permeance and dye rejection can be dynamically tuned.

PIP/TMC Interfacial Polymerization with Electrospray: Novel Loose Nanofiltration Membrane for Dye Wastewater Treatment.

A loose nanofiltration (NF) membrane with excellent dye rejection and high permeation of inorganic salt is required to fractionate dye/salt mixture in dye wastewater treatment. In this study, we fabricated the loose NF membrane by using the electrospray interfacial polymerization (EIP) method. It is a novel and facile interfacial polymerization method, which controls the thickness of the poly(piperazine-amide) (PPA) layer in nanometers (1 nm/min) and changes cross-linking degree of PPA layer and pore size by varying the electrospray time; consequently, water permeance and dye/salt rejection ratio can be handled. The fabricated EIP membrane with an optimized fabrication condition (M30, electrospray time was 30 min) possessed excellent pure water permeance (20.2 LMH/bar), high dye rejection (e.g., 99.6% for congo red (CR)), and low salt rejection (e.g., 6.3% for NaCl). Moreover, the EIP membrane exhibited enhanced antifouling property than commercial NF membrane (NF90) with a high flux recovery rate (FRR) of 87.1% and low irreversible fouling (Rir) of 12.9% after fouled by bovine serum albumin (BSA) due to its great smooth surface (average roughness (Ra) is 12.2 nm), hydrophilicity property, enhanced zeta potential, and low protein adsorption. The results indicate that the EIP loose NF membrane had a high potential for dye wastewater treatment.

Completely green and sustainable preparation of PVDF hollow fiber membranes via melt-spinning and stretching method

In this work, the poly(vinylidene fluoride) (PVDF) hollow fiber membranes with switchable pore size were fabricated by melt-spinning and stretching (MS–S) process based on a completely green and sustainable route. The membrane preparation process and pore formation mechanism were discussed and investigated in detail. Meanwhile, the effect of stretching ratio on the membrane structure and property was studied based on scanning electron microscopy (SEM), pore size distribution, N2 flux, pure water flux, mechanical property and so on. The prepared membranes with different stretching ratios exhibited excellent tensile strength in the range from 23.0 to 62.6 MPa. The mean pore size of the prepared membranes with stretching 100 % (M-100) was about 0.317 μm, which showed a high dye rejection (<93.9 %) for Direct Black 19. Specifically, there were not any organic solvent and low-molecular-weight diluent used during the preparation process. The recycled PEO and water were obtained after treating the wastewater by membrane filtration. In addition, the recycled PEO could be reused as pore forming agent, which could achieve completely green and sustainable membrane preparation process.

Thin-film composite nanofiltration membranes with high flux and dye rejection fabricated from disulfonated diamine monomer

Novel nanofiltration (NF) membranes with improved flux, dye rejection, high pH and temperature resistance were developed using a disulfonated diamine co-monomer, disodium-3-3′-disulfone-4-4′-dichlorodiphenylsulfone (S-DADPS). Thin film composite (TFC) NF membranes were fabricated on a porous polysulfone-based ultrafiltration support layer via the interfacial polymerization between trimesoyl chloride (TMC) in the organic phase and S-DADPS/piperazine (PIP) mixture in the aqueous phase. The effect of S-DADPS content was investigated on the structure and properties of fabricated TFC-NF membranes by varying the ratio between S-DADPS and PIP from 0/100 to 100/0 (w/w). The chemical structure, surface properties and the morphology of TFC-NF membranes were characterized by Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM), optical profilometry, contact angle, and zeta potential measurements. Salt and dye rejection behaviors of fabricated TFC-NF membranes were evaluated using 2000 ppm MgSO4 and NaCl solutions and 100 ppm Setazol Red and Reactive Orange 16 dyes, respectively. Dyes were filtrated in acidic, neutral and alkaline conditions for pH resistance tests. The temperature resistance of membranes was evaluated using pure water and dye solutions at 15 °C, 25 °C, and 40 °C. Among all TFC-NF membranes fabricated by varying the S-DADPS/PIP ratio, the membrane with an 80/20 ratio of S-DADPS/PIP resulted in superior properties such as increased water flux without considerable salt and dye rejection loss compared to the neat TFC-NF membrane without S-DADPS. In addition, the variation of S-DADPS/PIP ratio was demonstrated as a powerful tool to tune the balance of flux, separation and rejection performance of NF membranes for custom purification purposes.

Preparation of highly permeable loose nanofiltration membranes using sulfonated polyethylenimine for effective dye/salt fractionation

The sulfonated polyethylenimine (SPEI) was designed and employed to prepare high-performance loose nanofiltration (NF) membranes. A simple ring-opening reaction of polyethylenimine with 1,3-propanesulfonate (1,3-PS) was firstly conducted to synthesize SPEI. Then NF membranes were obtained by the cross-linked reaction between SPEI and trimesoyl chloride (TMC) via interfacial polymerization. Thanks to the restraining effect on interfacial polymerization from the sulfonic acid groups of SPEI, NF membranes with loose structures of surface layers as well as more negatively-charged and hydrophilic surfaces were prepared. The optimized loose nanofiltration membrane (NF-SPEI) presented high dye rejections to Victoria blue B, Congo red, Methyl blue and Reactive red 120 (all >97%) and low salt rejections to Na2SO4 (8.40%) and NaCl (3.20%), meanwhile it presented a pure water flux as high as 411 L·m−2·h−1·MPa−1. The NF-SPEI membrane also performed a good anti-fouling ability towards bovine serum albumin (BSA), humic acid (HA) and sodiumalginate (SA). Moreover, a long-term performance stability of the membrane during the successive filtration process of dye/salt aqueous mixture was determined. Thus, this work offered a promising candidate SPEI for loose NF membrane’s development and application in textile wastewater treatment.

Development of nanofiltration PES membranes incorporated with hydrophilic para hydroxybenzoate alumoxane filler for high flux and antifouling property

The PES nanofiltration membranes incorporated with hydrophilic para hydroxybenzoate alumoxane (PHBA) filler were prepared with enhanced pure water flux, dye removal, and antifouling property. The fabricated membranes were characterized in terms of average pore radius, porosity, surface roughness, water contact angle, active layer thickness, and zeta potential. The surface roughness of the nanofiltration membranes decreased and the surface hydrophilicity of the nanofiltration membranes increased with the increase of the PHBA content. According to nanofiltration experiments, the highest pure water flux of the PES membranes incorporated with PHBA reached up to 80.47 kg/m2h under operation pressure of 0.4 MPa, which was nearly 5.8 times as much as that of the neat PES membrane. The PES membranes incorporated with PHBA filler also exhibited excellent antifouling performance and dye removal capability. In the best PHBA content with the P-PHBA 0.3 % membrane, the highest rejection of 99.21 and 98.53% were achieved for DR 16 and MB, respectively. Furthermore, the P-PHBA membranes exhibited good long-term operational pH stability for DR 16 rejection. P-PHBA 0.3 % membrane also exhibited the highest flux recovery ratio (98.50%) and the lowest irreversible fouling ration (1.50%). Moreover, the dominant fouling mechanism was determined using Hermia–"s model. This superior antifouling behavior and relatively high dye rejection combined with remarkable stability show the potential of the organic-inorganic fillers embedded nanofiltration membranes in sustainable water treatment technology.

Breaking through the selectivity-permeability tradeoff using nano zeolite-Y for micellar enhanced ultrafiltration dye rejection application

Membrane performance is a region of growing research interest, where new functional nanomaterials are continually sought. In this study, nano zeolite type-Y was prepared through a unique ball milling process. The produced zeolite has a high surface area, and abundant flow channels with a well-defined pore structure facilitating water passage, but at the same time restricting the passage of contaminants through the molecular sieving effect. Polysulfone (PSf) membranes were prepared through phase inversion with nano-Y loadings from 0.2 to 1.5 wt%. Membranes were characterized for their structure, morphology, thermal stability and porosity. The developed membranes were tested for micellar enhanced ultrafiltration (MEUF) cationic dye rejections. The addition of nano-Y affected both the flux and dye rejection of the membranes. Optimum performance was obtained at 0.4 wt% nano-Y loading, giving a rejection of 99.5% and a corresponding flux of 105 L m−2 h−1. The static contact angle measurements indicate that membrane hydrophilicity increased with progressive nano-Y additions until 0.4 wt%, after which the membrane showed no further change in hydrophilic character. The obtained effects of nano-Y addition on membrane performance was attributed to the well-connected 3-D microporous structure in which the nano zeolite provided preferential water pathways though its nanoporous hydrophilic channels. Whereas, the high dye rejection was attributed to the fact that nano-Y zeolite is negatively charged and, as a result, provided resistance to the negatively charged micelles, and further restricted its passage through the microporous zeolite structure.

A microporous polymer ultrathin membrane for the highly efficient removal of dyes from acidic saline solutions

Membranes with excellent water permeance and high dye removal efficiency are highly desired for textile industry wastewater treatment. However, the high acidity and salinity in such wastewater impose great challenges in dye removal efficiency for conventional polyamide-based membranes. This study presents a type of acid-tolerant polyarylate (PAR) nanofiltration (NF) membrane that tackles such challenges. The PAR active layer is produced via interfacial polymerization using 5,5′,6,6′-tetrahydroxy-3,3,3′,3′-tetramethyl-1,1′-spirobisindane (TTSBI) and isophthaloyl dichloride (IPC) as monomers, and formed on top of a single-walled carbon nanotube (SWCNT) nanofilm. The supporting SWCNT layer contributes to the ultrathin thickness of the PAR active layer and the extremely high membrane permeating flux of ~210 L m−2 h−1 bar−1, while the inclusion of TTSBI monomer grants the PAR active layer surface negatively charged that makes a high dye rejection of >99% at a wide range of feed solution pH and salinity possible. Furthermore, a high selectivity for dye and NaCl was observed with a stable NaCl retention of ~10%, when the membrane is tested at a pH ranging from 2 to 9 and feed NaCl concentration ranging from 1000 to 5000 ppm. The PAR NF membrane is therefore a promising tool for the highly efficient treatment of acidic and high salinity textile dye wastewaters.