Mineralization-inspired preparation of composite membranes with polyethyleneimine–nanoparticle hybrid active layer for solvent resistant nanofiltration

Fabrication of Organic Solvent Nanofiltration Membrane through Interfacial Polymerization Using N-Phenylthioure as Monomer for Dimethyl Sulfoxide Recovery

To recover dimethyl sulfoxide, an organic solvent nanofiltration membrane is prepared via the interfacial polymerization method. N-Phenylthiourea (NP)is applied as a water-soluble monomer, reacted with trimesoyl chloride (TMC) on the polyetherimide substrate crosslinked by ethylenediamine. The results of attenuated total reflectance-fourier transform infrared spectroscopy and X-ray electron spectroscopy confirm that N-Phenylthiourea reacts with TMC. The membrane morphology is investigated through atomic force microscopy and scanning electronic microscopy, respectively. The resultant optimized TFC membranes NF-1NP exhibited stable permeance of about 4.3 L m−2 h−1 bar-1 and rejection of 97% for crystal violet (407.98 g mol−1) during a 36 h continuous separation operation. It was also found that the NF-1NP membrane has the highest rejection rate in dimethyl sulfoxide (DMSO), and the rejection rates in methanol, acetone, tetrahydrofuran, ethyl acetate and dimethylacetamide(DMAc) are 51%, 84%, 94%, 96% and 92% respectively. The maximum flux in the methanol system is 11 L m−2 h−1 bar−1, while that in acetone, tetrahydrofuran, ethyl acetate and DMAc is 4.3 L m−2 h−1 bar−1, 6.3 L m−2 h−1 bar−1, 3.2 L m−2 h−1 bar−1, 4.9 L m−2 h−1 bar−1 and 2.1 L m−2 h−1 bar−1, respectively. It was also found that the membrane prepared by N-Phenylthiourea containing aromatic groups has lower mobility and stronger solvent resistance than that of by thiosemicarbazide.

Recent Advancements in the Recovery and Reuse of Organic Solvents Using Novel Nanomaterial-Based Membranes for Renewable Energy Applications

The energy crisis in the world is increasing rapidly owing to the shortage of fossil fuel reserves. Climate change and an increase in global warming necessitates a change in focus from petroleum-based fuels to renewable fuels such as biofuels. The remodeling of existing separation processes using various nanomaterials is of a growing interest to industrial separation methods. Recently, the design of membrane technologies has been the most focused research area concerning fermentation broth to enhance performance efficiency, while recovering those byproducts to be used as value added fuels. Specifically, the use of novel nano material membranes, which brings about a selective permeation of the byproducts, such as organic solvent, from the fermentation broth, positively affects the fermentation kinetics by eliminating the issue of product inhibition. In this review, which and how membrane-based technologies using novel materials can improve the separation performance of organic solvents is considered. In particular, technical approaches suggested in previous studies are discussed with the goal of emphasizing benefits and problems faced in order to direct research towards an optimized membrane separation performance for renewable fuel production on a commercial scale.

Design and Fabrication of Membranes Based on PAN Copolymer Obtained from Solutions in N-methylmorpholine-N-oxide

An original method is proposed for preparing highly concentrated solutions of PAN copolymer in N-methylmorpholine-N-oxide (NMMO) and forming membranes for nanofiltration from these solutions. The high activity of the solvent with respect to the polymer provides short preparation time of spinning solutions in comparison with PAN solutions obtained in other solvents. The use of the rheological approach made it possible to find the optimal concentration for obtaining membranes. The formation of PAN membranes from the obtained solutions is proposed by the rolling method. The morphology of the formed membranes depends on the method of removing the precipitant from the sample. The features of the formed morphology of PAN membranes were studied by scanning electron microscopy. It was revealed that the use of water as a rigid precipitant leads to the formation of a homogeneous and symmetric morphology in the membrane. The average pore sizes in the membrane have been obtained by porosimetry. The study of the separating properties of PAN membranes revealed noteworthy values of the permeability and rejection for the anionic dyes Orange II and Remazol Brilliant Blue (74 and 97%, respectively). The mechanical properties of PAN membranes from solutions in NMMO are not inferior to analogs formed from commercially used direct solvents.

Fabrication of Poly(amide-co-ester) Solvent Resistant Nanofiltration Membrane from P-nitrophenol and Trimethyl Chloride via Interfacial Polymerization

P-nitrophenol (PNP), a refractory hazardous substance, has not been efficiently utilized so far. In this paper, PNP is used as a membrane modification material for preparing poly(amide-co-ester) composite nanofiltration membrane. An organic solvent nanofiltration (OSN) membrane was prepared via interfacial polymerization reactionby using PNP and trimethyl chloride (TMC) on a ethylenediamine (EDA) crosslinked polyetherimide substrate. The results of ATR-FTIR and XPS show that interfacial polymerization occurs among with PNP and TMC and the terminal amine groups on the ethylenediamine crosslinked -PEI support forming a poly(amide-co-ester) toplayer. The NF-1PNP membrane maintained stable DMF performance permeance of 2.2 L m−2 h−1 bar−1 and rejection of 98% for Rose Bengal red (RB 1017.64 g mol−1) in 36 h continuous separation process. Furthermore, the average pore diameter of the two membranes including NF-1PNP and NF-1.25PNP, which is 0.40 and 0.36nm, respectively. This study not only provides a good way for the preparation of OSN membrane, but also provides a good demonstration for the comprehensive utilization of PNP and other toxic and harmful pollutants.

Nanometals-Containing Polymeric Membranes for Purification Processes

A recent trend in the field of membrane research is the incorporation of nanoparticles into polymeric membranes, which could produce synergistic effects when using different types of materials. This paper discusses the effect of the introduction of different nanometals such as silver, iron, silica, aluminum, titanium, zinc, and copper and their oxides on the permeability, selectivity, hydrophilicity, conductivity, mechanical strength, thermal stability, and antiviral and antibacterial properties of polymeric membranes. The effects of nanoparticle physicochemical properties, type, size, and concentration on a membrane's intrinsic properties such as pore morphology, porosity, pore size, hydrophilicity/hydrophobicity, membrane surface charge, and roughness are discussed, and the performance of nanocomposite membranes in terms of flux permeation, contaminant rejection, and antifouling capability are reviewed. The wide range of nanocomposite membrane applications including desalination and removal of various contaminants in water-treatment processes are discussed.

Syntheses of Colorless and Transparent Polyimide Membranes for Microfiltration

Herein, poly(amic acid) (PAA) was synthesized using 4,4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) as a dianhydride and 2,2-bis(3-aminophenyl)hexafluoropropane (6FAm) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAm-OH) as diamines. Poly(vinyl alcohol) (PVA) at various contents (0–5.0 wt%) was blended with PAA to prepare a composite material. Then, colorless and transparent polyimide (CPI) composite films were prepared by applying various stages of heat treatment using the PAA/PVA blend film as a precursor. These film-type composites were immersed in water to completely dissolve PVA, a water-soluble polymer, and their pore sizes were investigated to determine their potential as a porous membrane. According to the results of scanning electronic microscopy (SEM), as the concentration of PVA increased from 0 to 5.0 wt% in the CPI/PVA composite films, the size of the pores resulting from the dissolution of water-soluble PVA increased. Further, the micrometer-sized pores were uniformly dispersed in the CPI films. The thermal properties, morphology, and optical transparency of the two types of CPI membranes synthesized using 6FAm and 6FAm-OH monomers were examined and compared.

Flexible Aliphatic-Aromatic Polyamide Thin Film Composite Membrane for Highly Efficient Organic Solvent Nanofiltration

Membranes with strong solvent resistance and efficient molecular separation are desirable in industries. Especially the fractionation of organic molecules in harsh organic solvents still remains a challenge in the pharmaceutical industry. Here, we report a flexible aliphatic-aromatic polyamide thin-film composite (TFC) membrane with high stability, permeability, and precise selectivity in mild solvents as well as in polar aprotic solvents. This composite organic solvent nanofiltration (OSN) membrane integrates a cross-linked sub-100 nm nanofilm and a nanofibrous sublayer. The flexible aliphatic chains in the polyamide network render the selective layer with a tunable free volume in different organic solvents. Consistent with the solvent swelling degrees, the membrane shows a cutoff in a sequence of dimethyl sulfoxide (DMSO, MWCO: 814 g mol^-1) > N,N-dimethylformamide (DMF, MWCO: 648 g mol^-1) > methanol (MWCO: 506 g mol^-1, with DMF activation) > methanol (MWCO: 327 g mol^-1). The membrane can precisely fractionate two molecules with difference in molar mass of <166 g mol^-1 in a polar aprotic solvent, DMSO. Long-term filtration tests in DMF further demonstrate that the TFC membrane has an outstanding chemical stability and molecular selectivity in aggressive organic media. This work provides an efficient way to control OSN membrane separations by introducing flexible alkane chains into the rigid polymer structure followed by solvent activation. Additionally, the high permeance and excellent separation efficiency of the TFC membrane highlight its great potential for molecular separation in pharmaceutical and chemical industries.

Enhanced dispersibility of metal–organic frameworks (MOFs) in the organic phase via surface modification for TFN nanofiltration membrane preparation

The nanosized UiO-66-NH₂ metal–organic framework (MOF) material was synthesized and modified by palmitoyl chloride to enhance the dispersibility and restrain the aggregation of MOF particles in the organic phase. Then the above nanomaterial was introduced into interfacial polymerization to prepare thin film nanocomposite (TFN) nanofiltration membranes. The prepared membranes displayed “ridge-valley” shaped Turing structure surface morphology with membrane thickness around 380 nm. The FE-SEM, ATR-FTIR and XPS characterization showed the polyamide layer was fabricated on the substrate surface. The TFN membranes showed higher hydrophobicity, zeta potential and roughness than TFC membranes. Due to the introduction of MOF and the formation of MOF/polyamide interfacial passageways, the TFN membranes showed higher water permeability but slightly lower rejection properties than TFC membranes. Compared with the TFN membranes prepared from pristine UiO-66 and UiO-66-NH₂, the TFN membrane prepared from modified UiO-66-NH₂ showed better rejection properties because of its superior dispersibility in the organic phase.

The nanosized UiO-66-NH₂ metal–organic framework (MOF) material was synthesized and modified by palmitoyl chloride to enhance the dispersibility and restrain the aggregation of MOF particles in the organic phase.

In Situ Assembly of a Zeolite Imidazolate Framework Hybrid Thin-Film Nanocomposite Membrane with Enhanced Desalination Performance Induced by Noria-Polyethyleneimine Codeposition

Zeolite imidazolate framework-8 (ZIF-8) has emerged as an excellent candidate for the preparation of thin-film nanocomposite (TFN) membranes. Nevertheless, it still remains a great challenge to make the effective incorporation of ZIF-8 into the resulting TFN membrane feasible for facile application. Herein, we propose an in situ strategy to fabricate a ZIF-8 nanocrystal hybrid reverse osmosis membrane induced by the ultrafast surface modification of Noria-polyethyleneimine codeposition. By this method, ZIF-8 nanocubes with monodispersity were first formed on a modified support through the step-by-step deposition of precursor solutions. Afterward, a TFN membrane was fabricated by interfacial polymerization (IP) on a ZIF-8 loaded support. Due to the significantly altered IP process induced by the coexistence of Noria and ZIF-8 on the support surface, the TFN membrane depicts a distinct nanostrand-nanoparticle hybrid morphology, which endows the TFN membrane with excellent antifouling ability. Moreover, the permeance of the as-fabricated TFN membrane is up to 3.64 L·m^-2·h^-1·bar^-1, nearly 2.7-fold higher than that of the nascent membrane, while it still maintains a high rejection toward NaCl. The in situ assembly strategy reported here could also pave a promising way for the fabrication of TFN membranes with other nanomaterials in future.

Graphene Quantum Dots-Doped Thin Film Nanocomposite Polyimide Membranes with Enhanced Solvent Resistance for Solvent-Resistant Nanofiltration

The core of the organic solvent nanofiltration (OSN) technology is solvent-resistant nanofiltration (SRNF) membranes. Till now, relative poor performance of solvent resistance is still the bottleneck of industrial application of SRNF membranes. This work reports a novel polyimide (PI)-based thin-film nanocomposite (TFN) membrane which was embedded with graphene quantum dots (GQDs) and showed an improved solvent resistance for OSN application. This kind of SRNF membrane, termed (PI-GQDs/PI)_XA, was synthesized via serial processes of interfacial polymerization (IP), imidization, cross-linking, and solvent activation. The IP process was performed between an aqueous m-phenylenediamine solution doped with GQDs, having an average size of 1.9 nm, and an 1,2,4,5-benzenetetracarboxylic acyl chloride n-hexane solution on the PI substrate surface. The prepared (PI-GQDs-50/PI)_X SRNF membranes without organic solvent activation achieved an ethanol permeance of nearly 50% higher than those of the GQD-free membranes under the same preparation conditions, while no compromise of the dye rejection was observed. Further, after the solvent activation using N, N-dimethylformamide (DMF) at 80 °C for 30 min, the ethanol permeance achieved about an 8-folds increment, from 2.84 to 22.6 L m^-2 h^-1 MPa^-1. Interestingly, the rejection of rhodamine B also increased from 97.8 to 98.6%. A long-term permeation test of more than 100 h using rose bengal (RB, 1017 Da)/DMF solution at room temperature demonstrated that the synthesized (PI-GQDs-50/PI)_XA membranes could maintain the DMF permeance and the RB rejection as high as 18.3 L m^-2 h^-1 MPa^-1 and 99.9%, respectively. Moreover, the immersion test of the prepared (PI-GQDs-50/PI)_XA SRNF membranes in both DMF and ethanol at room temperature for about one year also demonstrated the long-term organic solvent stability, indicating their good potential for OSN application.

Polysulfone/Polyamide-SiO₂ Composite Membrane with High Permeance for Organic Solvent Nanofiltration

To improve the filtration performance and properties of organic solvent nanofiltration (OSN) membranes, we firstly introduce nanoporous silica (SiO₂) particles into the polyamide (PA) active layer of polysulfone (PSf) membrane via an interfacial polymerization process. Results from the study revealed that introduction of SiO₂ influenced the properties of PSf/PA-SiO₂ composite membranes by changing the surface roughness and hydrophilicity. Moreover, results also indicated that nanoporous SiO₂ modified membranes showed an improved performance of alcohols solvent permeance. The PSf/PA-SiO₂ composite membrane modified by 0.025 wt % of SiO₂ reached a permeance of 3.29 L m⁻² h⁻¹ bar⁻¹ for methanol and 0.42 L m⁻² h⁻¹ bar⁻¹ for ethanol, which were 20.0% and 13.5% higher than the control PSf membrane (permeance of 2.74 L m⁻² h⁻¹ bar⁻¹ for methanol and 0.37 L m⁻² h⁻¹ bar⁻¹ for ethanol). Conclusively, we demonstrated that the increase of membrane hydrophilicity and roughness were major factors contributing to the improved alcohols solvent permeance of the membranes.

Polydopamine Coatings with Nanopores for Versatile Molecular Separation

The demand for highly efficient and multifunctional membranes in various separation processes is increasing. Recently, mussel-inspired polydopamine (PDA) has provided a promising way to meet these requirements because of its surface-adhesive property and film-forming ability. However, traditional PDA coatings usually suffer from the disadvantages of nonuniformity, incompactness, and instability, leading to poor molecular separation and service performance. Herein, uniform, compact, and robust PDA coatings were fabricated on an ultrafiltration substrate via a reasonable screening of oxidants for the oxidized self-polymerization of dopamine. The as-prepared PDA coatings were nanoporous (0.56 ± 0.04 and 0.93 ± 0.04 nm) with a thickness of ∼75 nm, which endows the composite membranes with a high solute rejection and solvent permeability during molecular separation. They are useful in organic solvent nanofiltration because of their superior structural stability. Moreover, the composite membranes can be used for recycling the nanometer catalyst from organic solvents for the first time, which has significantly broadened the potential applications of these mussel-inspired coatings for versatile separation processes.

Oriented Clay Nanotube Membrane Assembled on Microporous Polymeric Substrates

Organized arrays of halloysite clay nanotubes have great potential in molecular separation, absorption, and biomedical applications. A highly oriented layer of halloysite on polyacrylonitrile porous membrane was prepared via a facile evaporation-induced method. Scanning electronic microscopy, surface attenuated total reflection Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy mapping indicated formation of the nanoarchitecture-controlled membrane. The well-ordered nanotube coating allowed for the excellent dye rejection (97.7% for reactive black 5) with high salt permeation (86.5% for aqueous NaCl), and thus these membranes were suitable for dye purification or concentration. These well-aligned nanotubes' composite membranes also showed very good fouling resistance against dye accumulation and bovine serum albumin adsorption as compared to the pristine polyacrylonitrile or membrane coated with disordered halloysite layer.