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The present study highlights the influence of support and monomer properties on the performance of thin-film composite (TFC) membranes. For this purpose, a series of polyamide-cellulose acetate thin-film composite nanofiltration (TFC-NF) membranes were prepared by interfacial polymerization technique using cellulose acetate (CA) membrane as support and the monomer of cyclohexane-1,3,5 tricarbonylchloride (HTC) as an organic phase. The effect of the cellulose acetate concentration on the pore size of the membrane support was investigated using 15%, 16.5%, 18%, 19.5%, and 21.5% of cellulose acetate. m-phenylenediamine (MPD), piperazidine (PIP), and 1,3- cyclohexanebis (methylamine) (CHMA) were studied as monomers. Results displayed that PIP/HTC membrane is more hydrophilic and has more intense granular and convex structure with rougher surface compared to the other prepared membranes. The water flow and the porosity depended on the cellulose acetate concentration. The decrease in porosity complied well with permeability, contact angle, and SEM analysis. The membrane performances were evaluated for the retention of NaCl, CaCl, and NaSO retention. Comparing the NaSO rejection with CaCl and NaCl, the former is higher than the latter.

Fluoropolymer membranes are applied in membrane operations such as membrane distillation and membrane crystallization where hydrophobic porous membranes act as a physical barrier separating two phases. Due to their hydrophobic nature, only gaseous molecules are allowed to pass through the membrane and are collected on the permeate side, while the aqueous solution cannot penetrate. However, these two processes suffer problems such as membrane wetting, fouling or scaling. Membrane wetting is a common and undesired phenomenon, which is caused by the loss of hydrophobicity of the porous membrane employed. This greatly affects the mass transfer efficiency and separation efficiency. Simultaneously, membrane fouling occurs, along with membrane wetting and scaling, which greatly reduces the lifespan of the membranes. Therefore, strategies to improve the hydrophobicity of membranes have been widely investigated by researchers. In this direction, hydrophobic fluoropolymer membrane materials are employed more and more for membrane distillation and membrane crystallization thanks to their high chemical and thermal resistance. This paper summarizes different preparation methods of these fluoropolymer membrane, such as non-solvent-induced phase separation (NIPS), thermally-induced phase separation (TIPS), vapor-induced phase separation (VIPS), etc. Hydrophobic modification methods, including surface coating, surface grafting and blending, etc., are also introduced. Moreover, the research advances on the application of less toxic solvents for preparing these membranes are herein reviewed. This review aims to provide guidance to researchers for their future membrane development in membrane distillation and membrane crystallization, using fluoropolymer materials.

Membrane separation has been widely used for various applications including microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) processes in the fields of biomedicine, food, and water purification. In this work, a facile synthesis of new polyamide thin-film composite nanofiltration membranes (NF-TFC) for water purification was described. The polyamide thin film was deposed over a synthetic cellulose acetate (CA) support by interfacial polymerization method. 1,3 cyclohexane bis (methylamine) (CHMA) and trimesoyl chloride (TMC) were used as monomers. The membranes were characterized using Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FT-IR), water uptake, porosity, contact angle, water permeability and rejection towards specific salt and dye molecules. The effect of the variation of the CHMA concentration (0.2–2 wt.%) on the morphology, porosity, water permeation and rejection properties of the prepared membranes was studied. SEM results displayed the growth of the membrane thickness when the CHMA concentration increased from 0.2 to 2 wt.%. The strong adhesion between the cellulose acetate substrate and the polyamide layer explained by the formation of the polyamide film in the substrate surface and inside the pores. The water permeability varied from 36.02 to 17.09 L h−1 m−2 bar−1. The salt rejection of Na2SO4 and NaCl increased from 9 to 68% and from 38.41% to 89.4%, respectively, when the CHMA concentration was changed from 0.2 to 2 wt.%. The prepared membranes were further applied successfully for the removal of malachite green and congo red. The results indicated that the maximum rejection reached 89% and 85% for malachite green and congo red, respectively.

Water contamination by traces of heavy metals is a global issue causing serious environmental and health concerns and, as a consequence, an increasing of demand for water remediation technologies. Nowadays, membranes, defined as a selective barrier that permit the separation of molecules or ions in a liquid by a combination of sieving and diffusion mechanisms, have more attention due to their several advantages. In particular, ultrafiltration (UF) is a well-established membrane technology for purification of contaminated water bodies enabling an efficient and cost-saving low-pressure filtration. However, UF membranes possesses a pore size ranging from 20 nm to 0.1 µm, ineffective in rejecting small molecules and ions, such as heavy metals. In this work, a new generation of antifouling UF membranes able to heavy metals remediation has been developed [1]. Specifically, poly (acrylic acid) (PAA) as ideal complexing agent for heavy metals, was blended with cellulose acetate (CA), polymer extensively studied in UF membranes preparation. The novel membranes were prepared via non solvent-induced phase separation (NIPS). These new membranes combine the use of carboxyl group of the PAA that allowing one to efficiently adsorb or chelate heavy metal ions with the processability/biocompatibility/hydrophilicity of the CA. The membranes were produced varying the PAA concentration from 0 to 15wt. %. The homogeneity of the blend was evaluated via differential scanning calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FTIR). Mitigation of the fouling phenomena and the improvement of the efficiency of the CA membrane on heavy metal rejection was studied and evaluated. The experiments results revealed the important advantages of the blend, since CA/PAA membranes showed superior performance with respect to the neat CA membrane, in terms of: (i) water permeability (20% higher than the neat CA membrane); (ii) Cd rejection (83% at pH 6.5); and (iii) antifouling resistance to humic acid (HA) (R% of 99.9 and 95.3% of flux recovery ratio FRR). [1] I. Ounifi, Y. Guesmi, C. Ursino, S. Santoro, S. Mahfoudhi, A. Figoli, E. Ferjanie, A. Hafiane, Antifouling Membranes Based on Cellulose Acetate (CA) Blended with Poly(acrylic acid) for Heavy Metal Remediation, Appl. Sci. 2021, 11, 4354. https://doi.org/10.3390/app11104354

Membrane separation has been widely used for various applications including microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) processes in the fields of biomedicine, food, and water purification. In this work, a facile synthesis of new polyamide thin-film composite nanofiltration membranes (NF-TFC) for water purification was described. The polyamide thin film was deposed over a synthetic cellulose acetate (CA) support by interfacial polymerization method. 1,3 cyclohexane bis (methylamine) (CHMA) and trimesoyl chloride (TMC) were used as monomers. The membranes were characterized using Scanning Electron Microscopy (SEM), Fourier Transform Infrared spectroscopy (FT-IR), water uptake, porosity, contact angle, water permeability and rejection towards specific salt and dye molecules. The effect of the variation of the CHMA concentration (0.2-2 wt.%) on the morphology, porosity, water permeation and rejection properties of the prepared membranes was studied. SEM results displayed the growth of the membrane thickness when the CHMA concentration increased from 0.2 to 2 wt.%. The strong adhesion between the cellulose acetate substrate and the polyamide layer explained by the formation of the polyamide film in the substrate surface and inside the pores. The water permeability varied from 36.02 to 17.09 L h-1 m-2 bar-1. The salt rejection of Na2SO4 and NaCl increased from 9 to 68% and from 38.41% to 89.4%, respectively, when the CHMA concentration was changed from 0.2 to 2 wt.%. The prepared membranes were further applied successfully for the removal of malachite green and congo red. The results indicated that the maximum rejection reached 89% and 85% for malachite green and congo red, respectively.

Polyamide thin film composite nanofiltration (NF-TFC) membranes were prepared by interfacial polymerization (IP) method using synthetic cellulose acetate membranes as support. M-phenylenediamine (MPD) and trimesoyl chloride (TMC) were used as monomers in water and hexane solution respectively. The effect of different monomers concentrations varying from 0.1 to 0.25 wt.% and IP times from 15 to 90 s were investigated. The surface of different produced membranes were characterized using the scanning electron microscopy, atomic force microscopy, Fourier-transform infrared, contact angle (CAw) and porosity. Water permeability and salts rejection (NaCl, Na SO) were determined for testing the membranes performances. The permeation studies showed that depending on TMC concentration and IP reaction time, the water permeabilities were 23.57 and 10.44 (L m h bar), respectively. Na SO and NaCl rejections were varying from 69.23% to 92.43% and from 19% to 55.54%, respectively, when TMC concentration was between 0.1% and 0.25% (w/v). The results of cadmium solution retention indicated that these novel membranes could be successfully applied for the heavy metals removal. The maximum of cadmium rejection at 0.25% (v/w) TMC concentration is 97.76% for CdSO. This cadmium rejection depend on the nature of associated anion: R(Cd(NO)) < R(CdCl) < R(CdSO).

An easy method to prepare hydrophilic PES membranes with anti-fouling properties was developed by UV-polymerization of poly vinyl pirrolidone (PVP) on membrane surfaces. The modified membrane surfaces were analyzed by ATR-FTIR, and the new hydrophilic nature of the membranes was determined by contact angle measurements. The novel membranes were prepared using Rhodiasolv&reg, Polarclean as a green solvent and compared with a control PES membrane, without the exposure at the hydrophilization procedure. The influences of the UV lamp distance (15 and 30 cm) and the exposure time (0 cm to 60 cm) were evaluated. All membranes were characterized in terms of surface morphology, porosity, pore size, and pure water permeability (PWP). The treated membranes resulted in an increase in hydrophilicity and in improved performances in terms of PWP and foulant rejection. In particular, an anti-fouling test was performed using a solution of 100 mg/L of humic acid (HA) as a model foulant. The UV-treated membrane efficiency, compared with a commercial PES membrane, showed a recovery of about 97%, confirming that these membranes can be applied in wastewater treatment.

In this work, Rhodiasolv® PolarClean was employed as a more sustainable solvent for the preparation of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) flat sheet membranes via phase inversion technique by coupling vapour induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) processes. Preliminary calculations based on Hansen solubility parameters well predicted the solubilization of the polymer in the selected solvent. The effect of exposure time on humidity and the influence of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and sulfonated polyether sulfone (S-PES) on membrane properties and performance, were evaluated. Three different coagulation bath compositions were also explored. The obtained membranes, prepared using a more sustainable approach, were compared with those produced with the traditional toxic solvent N-methyl-2-pyrrolidone (NMP) and characterised in terms of morphology, porosity, wettability, pore size, surface roughness and mechanical resistance. The potential influence of the new solvent on the crystallinity of PVDF-HFP-based membranes was also evaluated by infrared spectroscopy. The adjustment of the parameters investigated allowed tuning of the membrane pore size in the microfiltration (MF) and ultrafiltration (UF) range resulting in membranes with various morphologies. From the water permeability and rejection tests, performed with methylene blue dye, the prepared membranes showed their potentiality to be used in MF and UF applications.

Electrospinning is an emerging technique for the preparation of electrospun fiber membranes (ENMs), and a very promising one on the basis of the high-yield and the scalability of the process according to a process intensification strategy. Most of the research reported in the literature has been focused on the preparation of poly (vinylidene fluoride) (PVDF) ENMs by using N,N- dimethylformamide (DMF) as a solvent, which is considered a mutagenic and cancerogenic substance. Hence, the possibility of using alternative solvents represents an interesting approach to investigate. In this work, we explored the use of dimethyl sulfoxide (DMSO) as a low toxicity solvent in a mixture with acetone for the preparation of PVDF-ENMs. As a first step, a solubility study of the polymer, PVDF 6012 Solef&reg, in several DMSO/acetone mixtures was carried out, and then, different operating conditions (e.g., applied voltage and needle to collector plate distance) for the successful electrospinning of the ENMs were evaluated. The study provided evidence of the crucial role of solution conductivity in the electrospinning phase and the thermal post-treatment. The prepared ENMs were characterized by evaluating the morphology (by SEM), pore-size, porosity, surface properties, and performance in terms of water permeability. The obtained results showed the possibility of producing ENMs in a more sustainable way, with a pore size in the range of 0.2-0.8 &micro, m, high porosity (above 80%), and water flux in the range of 11.000&ndash, 38.000 L/m2&middot, h&middot, bar.

In this work, for the first time, Polarclean® was used as eco-friendly sustainable solvent for preparing Polyethersulfone (PES) hollow fiber membranes via non-solvent induced phase separation (NIPS) technique. After a preliminary study on the dope solution viscosity, the hollow fibers were prepared by non-solvent induced phase separation (NIPS) technique by varying polymer concentration and bore fluid composition. The obtained fibers were fully characterized in terms of morphology, mechanical properties, porosity, pore size and water permeability. A cost analyses evaluation was also carried out based on the use of the green solvent Polarclean®.

For the first time the chemical profile, physico-chemical parameters, inhibition of carbohydrate hydrolysing enzymes associated with type 2 diabetes, and radical scavenging properties of Sambucus nigra L. (elderberry) juice treated by nanofiltration (NF) were investigated. Three commercial NF membranes with different molecular weight cut-off (MWCO) (400 and 1000 Da) and polymeric material (composite fluoro-polymer and polyethersulphone) were tested. According to HPLC analyses, most part of bioactive compounds were retained by the NF membranes producing a retentate fraction of interest for the production of functional foods. The NP030 membrane, a polyethersulphone membrane with a MWCO of 400 Da, exhibited the highest rejection towards phenolic compounds when compared with the other selected membranes. Accordingly, the produced retentate fractions exhibited the highest radical scavenging activity.

A novel catalytic membrane has been synthesised, characterised and evaluated for the selective hydrogenation of furfural to furfuryl alcohol. Unlike conventional methods, involving high pressure and high H2 : feed ratios, this work proposes an innovative ruthenium based Catalytic Membrane Reactor (CMR) to overcome mass transfer limitations, resulting in low H2 requirements, high catalytic activity and high selectivity towards furfuryl alcohol. A UV-curable hydrophilic anionic monomer acrylic acid was used as a coating material on a commercial PES membrane and subsequently Ru nanoparticles were added. The hydrogenation of furfural was carried out in a customised catalytic membrane reactor under mild conditions: 70 °C and 7 bar, exhibiting high catalytic activity towards furfuryl alcohol (selectivity >99%) with turnover frequency (TOF) as high as 48 000 h-1, 2 orders of magnitude higher than those obtained so far.

This study aimed at evaluating and comparing the chemical profile as well as the antityrosinase and antioxidant activities of ethanol (EtOH) and methanol (MeOH) extracts of Sambucus nigra L. (Adoxaceae) flowers and leaves in order to discover new candidates for food additives and cosmetic and pharmaceutical products. For this purpose, a novel lower-melting-point ethylene-chlorotrifluoroethylene (LMP ECTFE) nanofiltration (NF) membrane was employed in order to produce the concentrated fractions of S. nigra. Floral extracts were richer in phytochemicals in comparison to the leaf extracts. The High-performance liquid chromatography (HPLC) profile revealed rutin, quercetin, protocateuchic acid, 3,5-dicaffeoylquinic acid, and neochlorogenic acid as the most abundant compounds. Ferric reducing antioxidant power (FRAP), 2,2&rsquo, diphenil-1-picrylhydrazil (DPPH) radical scavenging, and 2,2&rsquo, azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) tests were used to investigate the antioxidant properties. NF retentate fractions of floral ethanol extracts exerted the highest tyrosinase inhibitory activity with an IC50 of 53.9 &micro, g/mL and the highest ABTS radical scavenging activity (IC50 of 46.4 &micro, g/mL). In conclusion, the present investigation revealed the potential benefits of NF application in S. nigra extracts processing, suggesting the use of retentate fractions as a promising source for antioxidant and tyrosinase inhibitory compounds which could pave the way for future applications

A novel method to prepare hydrophilic/hydrophobic membranes via dip-coating and UV in situ polymerization was presented. Fluorolink® MD700, a UV-curable perfluoropolyether (PFPE) hydrophobic compound, was employed as surface modifier via coating technique on two different commercial hydrophilic membranes with different pore size (0.1-0.2-0.45 μm): polyamide (PA), and polyethersulfone (PES). The influence of starting membrane material (PA-PES) was studied and all coated membranes were characterized in terms of surface morphology, water and oil contact angle, porosity, pore size, liquid entry pressure and mechanical tests. The coating resistance and stability in time with salty solution NaCl 0.6 M and chemicals cleaning agents, such as KMnO4 0.1 wt%, Hypochlorite NaClO pH 4.25, HCl pH 2.5, NaOH pH 11.5, were evaluated. Membranes performance was tested in direct contact membrane distillation (DCMD) configuration, using deionized water and salty solution 0.6 M (NaCl) as feed. The effect of the starting material on the permeate fluxes was investigated. The measured permeate water fluxes ranged between 3 and 22 kg/m2h and 2.9–19.5 kg/m2 h for PA and PES respectively, at different feed temperatures (40–60 °C). Both flux (∼8.3 kg/m2 h) and salt rejection (∼99.95%) were kept constant during a prolonged test (158 h) carried out at 50 °C on the coated PA 0.45 μm membrane.

Keratin proteins extracted from wool fibers by sulfitolysis were electrospun for the production of active nanofiber membranes (NFMs). The keratin NFMs were composited with nylon woven fabric for improving their mechanical properties as a filtration material. The prepared membranes were characterized in terms of morphology, pore size, contact angle, and performance of water and air permeability. Experimental data showed that most of investigated parameters were affected by the electrospinning time: that is, roughness rose by increasing the electrospinning time, while the narrowest pore size distribution was obtained at the longest electrospinning time (2 h). The pure water permeability (PWP) was greater for the produced NFMs than for the commercial microfiltration membranes and decreased by increasing the electrospinning time. At the longest electrospinning time, the produced NFMs showed a PWP of about 45.7 m3/m2 h bar, which is a value greater than those obtained by conventional materials used in water filtration, including microfiltration membranes. According to the data of contact angle measurements, the high hydrophobicity of NFMs membranes could reinforce their stability in water. Other potential applications could be venting, adsorption of VOCs, and separation of oils from oil/water emulsions.

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.

In this work, a lower melting point of HALAR® Ethylene-Chlorotrifluoroethylene (LMP ECTFE) was used to prepare non-woven fabric-based porous membranes, using a polyester non woven (NWPET) as support, via dip-coating. Di-ethyl Adipate (DEA) and di-ethylene Glycol (DEG) were selected as primary and secondary diluent, respectively. SEM analyses showed that in all cases the coating layer was homogeneous, covering all the NWPET support and leading to an interconnected sponge-like microstructure. Membrane characterization evidenced the effects of the DEG concentration, which plays the role of pore former. The effect of the immersion time was examined and studied, too. The produced membranes were fully characterized in terms of water contact angle, porosity and pore size. Direct contact membrane distillation (DCMD) experiments using water and salty solution 0.6 M (NaCl) as feed, were performed for selected supported membranes. The obtained fluxes ranged between 3 and 22 kg/m2h, depending on DEG concentration, at the same immersion time, and on the feed temperatures (40–60 °C). Rejection (R%) was comprised from 94.95 to 99.82%. In particular, the N-ECTFE 7-0-7 membrane, with the highest R%, showed a stable deionized water flux before and after the experiments, indicating its ability to recover its original performance.

The use of membrane-based technologies has been applied for water treatment applications; however, the limitations of conventional polymeric membranes have led to the addition of inorganic fillers to enhance their performance. In recent years, nanocomposite membranes have greatly attracted the attention of scientists for water treatment applications such as wastewater treatment, water purification, removal of microorganisms, chemical compounds, heavy metals, etc. The incorporation of different nanofillers, such as carbon nanotubes, zinc oxide, graphene oxide, silver and copper nanoparticles, titanium dioxide, 2D materials, and some other novel nano-scale materials into polymeric membranes have provided great advances, e.g., enhancing on hydrophilicity, suppressing the accumulation of pollutants and foulants, enhancing rejection efficiencies and improving mechanical properties and thermal stabilities. Thereby, the aim of this work is to provide up-to-date information related to those novel nanocomposite membranes and their contribution for water treatment applications.

Innovative hydrophobic coated membranes have been prepared and characterised in Direct Contact Membrane Distillation (DCMD) for potential water treatment applications. A UV-curable perfluoropolyether (PFPE) hydrophobic compound (Fluorolink® AD 1700) was used as coating material to tailor the surface of commercial microfiltration hydrophilic polyamide (PA) membranes with different pore sizes. The coated membranes consisted of a top thin hydrophobic porous layer overlying the hydrophilic commercial membrane support. Produced membranes were fully characterised in terms of surface and cross-section morphology, water contact angle, porosity, pore size and liquid entry pressure. The innovative coated hydrophobic membranes were tested in DCMD configuration, using deionized water and salty solution 0.6 M (NaCl) as feed. In particular, the effect of the coating concentration on the permeate fluxes was investigated for different hydrophilic pore size commercial membranes (0.1–0.22–0.45 μm). The measured permeate fluxes ranged between 4.56–22.81 kg/m2 h at different feed temperatures (40–50–60 °C) keeping constant the permeate temperature at 14 °C, for deionized water, whereas an average value of 11 kg/m2 h, at 50 °C was found in case of the salty solution.

A new grade of ethylene-chlorotrifluoroethylene, low melting point HALAR (R) ECTFE (LMP ECTFE), was studied and used as a polymer for the preparation of solvent-resistant flat-sheet membranes. Among the different types of non-toxic solvents tested, di-ethyl adipate (DEA) was selected for preparing flat sheet membranes via thermally induced phase separation (TIPS). The morphology of the membranes has been analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dense and porous membranes have been obtained and characterized by contact angle, pore size and porosity tests. Porous membranes showed an asymmetric structure made of a denser top-side and a spherulitic porous structure on the bottom side. Membrane resistance was studied using the dense membrane in contact with most aggressive organic solvents, such as polar protic, polar aprotic and non-polar solvents. The results suggest that the newly developed LMP ECTFE membranes are very promising candidates for organic solvent separation. Ultrafiltration (UF) and nanofiltration (NF) tests with alcohols and di-methyl formamide (DMF) demonstrated their solvent separation potential.

The replacement of commonly-used substances with non-toxic equivalents is attracting a great amount of attention in membrane preparation processes. In order to address this issue, we prepared poly(vinylidene fluoride) (PVDF) flat membranes via thermally-induced phase separation using non-toxic citrate-based solvents (Citroflex): acetyl tributyl citrate (ATBC); acetyl triethyl citrate (ATEC); and triethyl citrate (TEC). It was found that the three kinds of Citroflex showed the different solubility with PVDF: the solubility was improved in the following order of ATBC