Fouling-resistant Ultrafiltration Research Articles

Experimental and theoretical investigations on fouling resistant cellulose acetate/SiO2 NPs/PEDOT ultrafiltration nanocomposite membranes

In the current work, we report the fabrication of a new fouling resistant ultrafiltration (UF) nanocomposite membranes by incorporating silicon oxide nanoparticles (SiO2 NPs) and poly(3,4-ethylene dioxythiophene) (PEDOT) into cellulose acetate (CA) matrix, taking advantage of the abundant surface-terminating groups on CA, SiO2 NPs, and PEDOT. The characteristics of the prepared materials and membranes were assessed experimentally and theoretically using molecular modeling concepts. The molecular modeling study manifested the stability of the proposed membrane structure which appeared to be slightly positive and had affinity to electrophilic addition reactions. The fabricated membranes exhibited both high flux and high bovine serum albumin (BSA) separation, ∼145 LMH/bar and 90%, respectively, as well as high fouling-resistant standards. Hence, it offers better solution in terms of performance, fouling, permeate quality, and longevity. Enhanced performance results were due to improving a range of membrane characteristic. Incorporation of PEDOT into CA matrix improved the hydrophilicity, porosity and fouling resistant of the nanocomposite membrane. Overall, this study opens an avenue for utilizing the biodegradable CA for the fabrication of robust UF nanocomposite membranes that do not need intensive physical and chemical cleaning which makes membrane technology more appealing for practical applications.

Antifouling Membranes Based on Cellulose Acetate (CA) Blended with Poly(acrylic acid) for Heavy Metal Remediation

Fouling has been widely recognized as the Achilles’ heel of membrane processes and the growing perception about the relevance of this critical issue has driven the development of advanced antifouling strategies. Herein, novel fouling-resistant ultrafiltration (UF) membranes for Cadmium (Cd) remediation were developed via a blending method by combining the flexibility of cellulose acetate (CA) with the complex properties of poly(acrylic acid) (PAA). A systematic characterization, based on differential scanning calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR), confirmed the homogeneity of the blend favored by hydrogen interconnections between CA and PAA polymeric chains. The concentration of PAA with respect to CA played a key role in tuning the morphology and the hydrophilic character of the novel UF membranes prepared via non-solvent-induced phase separation (NIPS). UF experiments revealed the tremendous advantages of the blend since CA/PAA membranes showed superior performance with respect to the neat CA membrane in terms of (i) water permeability; (ii) Cd rejection; and (iii) antifouling resistance to humic acid (HA). Concisely, the increasing of the concentration of PAA in the casting solution was found to be beneficial to improve the flux recovery ratio (FRR) coupled with the decline of the total fouling ratio (Rt). Overall, PAA is an effective additive to prepare CA membranes with enhanced antifouling properties exploitable for the remediation of water bodies contaminated by heavy metals via UF process.

A facile process to prepare fouling-resistant ultrafiltration membranes: Spray coating of water-containing block copolymer solutions on macroporous substrates

Ultrafiltration membranes derived from block copolymers (BCPs) are gaining much attention for their superiority in tunable pore structures and intrinsic surface functions. In terms of the practical applications of BCP membranes, simple and efficient manufacturing processes are essential and remain highly demanded. Herein, we propose a facile process to prepare BCP composite membranes by spray-coating polysulfone/poly(ethylene glycol) (PSF-b-PEG) solutions onto macroporous substrates. A small amount of nonsolvent (water) is added into the BCP solutions to act as the pore-forming agent. During spray coating, the evaporation of solvent and the rising water content lead to phase separation of BCP solutions in the atomized droplets. Subsequent drying removes water, and the volumes occupied by water are transformed into nanoscale pores, thus producing bi-layered composite membranes with the nanoporous BCP coatings as the selective layers atop the macroporous substrates. Water-affinitive PEG chains in PSF-b-PEG are crucial to adsorb and stabilize water droplets during pore formation. The thickness of the BCP selective layers is predominantly determined by the dosage of the sprayed BCP solutions, enabling tunable separation properties of the BCP membranes. In spite of the extremely simple preparation process, thus produced membranes exhibit good ultrafiltration performances, comparable or better than that of membranes prepared by much more complicated processes. Furthermore, PEG chains are enriched on pore walls, endowing the membranes an intrinsic fouling resistance.

Development of hydroxyl and carboxylic acid functionalized CNTs–polysulphone nanocomposite fouling-resistant ultrafiltration membranes for oil–water separation

Fouling-resistant composite ultrafiltration (UF) membranes of hydroxyl functionalized multi-walled carbon nanotubes (MCNTs) ( $$_{\mathrm {{OH}}}\text {CNT}$$ )/polysulphone (PSF)/polyvinylpyrrolidone (PVP) and carboxylic acid functionalized MCNTs ( $$_{\mathrm {{COOH}}}\hbox {CNT}$$ )/PSF/PVP in weight ratios of 0.7/86.1/13.2 and 1.3/85.5/13.2 were prepared by phase inversion process from dimethylformamide solution. These membranes were characterized by infrared, scanning electron microscopy, atomic force microscopy, differential scanning calorimetry and water contact angle measurements. The molecular weight cut off values of these membranes were measured by permeating aqueous solutions of different molecular weight PEGs and dextrans. Among the fabricated UF membranes, $$_{\mathrm {{COOH}}}\text {C}_{{{1.3}}}\text {PS}_{{{85.5}}}\text {PV}_{{{13.2}}}$$ composite membrane showed a lower average contact angle ( $$62^{\circ }$$ ). The $$_{\mathrm {{COOH}}}\text {C}_{{{0.7}}}\text {PS}_{{{86.1}}}\text {PV}_{{{13.2}}}$$ membrane exhibited higher flux (99 $$\hbox {l}~\hbox {m}^{-2}~\hbox {h}^{-1}$$ ) than all the fabricated membranes (62–78 $$\hbox {l}~\hbox {m}^{-2}~\hbox {h}^{-1}$$ ) at 2 bar pressure. The flux recovery ratio values for bovine serum albumin feed solution were in the range of 63–72% for $$_{\mathrm {{COOH}}}\hbox {CNTs}$$ containing membranes and 53–64% for $$_{\mathrm {{OH}}}\text {CNTs}$$ membranes, whereas PSF/PVP blend membrane exhibited 45% at 2 bar applied pressure. The membranes containing 0.7 and 1.3 wt% carboxylic acid functionalized MCNTs showed 100% oil rejection when tested with an oil–water emulsion containing 1000 ppm lube oil. Conversely, membranes containing hydroxyl functionalized MCNTs showed relatively lower oil rejection (86–90%), whereas the PSF/PVP membrane showed 86% oil rejection.

Fabrication of Low-Fouling Ultrafiltration Membranes Using a Hydrophilic, Self-Doping Polyaniline Additive

A simple, scalable method for fabricating fouling-resistant ultrafiltration membranes is described. A self-doped, sulfonated form of polyaniline was blended into polysulfone (PSf) ultrafiltration (UF) membranes to enhance hydrophilicity and fouling resistance. Polyaniline in its base form was sulfonated with fuming sulfuric acid, yielding sulfonated polyaniline (SPANi) with a degree of sulfonation of ∼0.5 confirmed by XPS. The SPANi polymer was dedoped and dissolved in a solution of polysulfone in N-methylpyrollidone at varying concentrations. During phase inversion to form membranes, SPANi is redoped and precipitated within the PSf membrane films in a facile one-step process. Composite membranes containing increasing amounts of SPANi were compared to the pure PSf membranes to determine changes in performance, hydrophilicity, and antifouling characteristics. The composite membranes exhibit fluxes similar to those of the pure PSf membrane and maintain rejection properties similar to those of current UF mem...

Composite Membranes Based on a Selective Chitosan−Poly(ethylene glycol) Hybrid Layer: Synthesis, Characterization, and Performance in Oil−Water Purification

A series of poly(ethylene glycol) diglycidyl ether−cross-linked chitosan (chi−PEG hybrid) films were prepared to elucidate their potential as fouling-resistant ultrafiltration (UF) membrane coating layers. Water permeability increased as the poly(ethylene glycol) diglycidyl ether to chitosan ratio in the prepolymerization mixture increased due to increased porosity in the polymer matrix resulting from phase separation during polymerization. Composite membranes for oil−water emulsion filtration were prepared by coating an optimized member of the chi−PEG hybrid family onto a commercial polysulfone ultrafiltration membrane. Scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), and pure water permeance measurements indicated that, depending on the concentration of chitosan in the coating solution, the coating layer thickness could be controlled, so water permeance could be optimized. These composite membranes exhibited water flux values more than 5 ti...

Highly fouling resistant ultrafiltration membranes for water and wastewater treatments

Control of fouling is a critical issue to increase the competitiveness of ultrafiltration (UF) membranes for drinking water and wastewater treatments. Highly fouling resistant UF membranes synthesized by photo-graft copolymerization of a water soluble monomer, poly(ethylene glycol) methacrylate (PEGMA), onto a polyethersulfone UF membrane have been evaluated with respect to the adsorptive as well as the ultrafiltration fouling. Protein, humic substance and polysaccharide solutions were used as the model for foulants occurring in the water sources for drinking water as well as in wastewater effluents. The results show that the modified membranes exhibited a much higher fouling resistance for all foulants than the unmodified membranes. Their combined high fouling resistance and high rejection suggests that the obtained modified membranes are very promising as a new generation of thin-layer composite low fouling UF membranes for drinking water and wastewater treatment applications.

Photografted Thin Polymer Hydrogel Layers on PES Ultrafiltration Membranes: Characterization, Stability, and Influence on Separation Performance

Highly fouling-resistant ultrafiltration (UF) membranes were synthesized by heterogeneous photograft copolymerization of two water-soluble monomers, poly(ethylene glycol) methacrylate (PEGMA) and N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPE), with and without cross-linker monomer N,N'-methylene bisacrylamide (MBAA), onto a polyethersulfone (PES) UF membrane. The characteristics, the stability, and the UF separation performance of the resulting composite membranes were evaluated in detail. The membranes were characterized with respect to membrane chemistry (by ATR-IR spectroscopy and elemental analysis), surface wettability (by contact angle), surface charge (by zeta potential), surface morphology (by scanning electron microscopy), and pure water permeability and rejection of macromolecular test substances (including the "cutoff" value). The surface chemistry and wettability of the composite membranes did not change after incubating in sodium hypochlorite solution (typically used for cleaning UF membranes) for a period of 8 days. Changes in water permeability after static contact with solutions of a model protein (myoglobin) were used as a measure of fouling resistance, and the results suggest that PEGMA- and SPE-based composite membranes at a sufficient degree of graft modification showed much higher adsorptive fouling resistance than unmodified PES membranes of similar or larger nominal cutoff. This was confirmed in UF experiments with myoglobin solutions. Similar results, namely, a very much improved fouling resistance due to the grafted thin polymer hydrogel layer, were also obtained in the UF evaluation using humic acid as another strong foulant. In some cases, the addition of the cross-linker during modification could improve both permeate flux and solute rejection during UF. Overall, composite membranes prepared with an "old generation" nonfouling material, PEGMA, showed better performance than composite membranes prepared with a "new generation" one, the zwitterionic SPE.

Fouling-resistant ceramic-supported polymer membranes for ultrafiltration of oil-in-water microemulsions

Fouling-resistant ultrafiltration ceramic-supported polymer (CSP) ultrafiltration membrane was developed for the treatment of oil-in-water (o/w) microemulsions. The CSP zirconia-based membrane was prepared via free-radical graft polymerization of vinylpyrrolidone onto the membrane surface. Pore reduction of about 25–28% was encountered upon modification as revealed by hydraulic permeability measurements. Oil rejection was higher for grafted membranes with smaller resultant pore size. Atomic force microscopy imaging of polymer-modified surfaces showed complete surface coverage by the polymer chains. The native zirconia membrane was irreversibly fouled after treating the o/w microemulsion for a brief period, while the CSP membranes maintained its pre-filtration hydraulic permeability even after many filtration runs. The present surface modification was found to be effective in preventing irreversible membrane fouling despite significant membrane surface roughness. Relative to the native membrane, oil rejection of the CSP membrane increased more than two-fold for the range of studied oil droplet size (18–66 nm), while surfactant rejection remained low for both the native and modified membranes.