Study on a novel polyamide-urea reverse osmosis composite membrane (ICIC–MPD)I. Preparation and characterization of ICIC–MPD membrane

Tunable membranes incorporating artificial water channels for high-performance brackish/low-salinity water reverse osmosis desalination

Membrane-based technologies have a tremendous role in water purification and desalination. Inspired by biological proteins, artificial water channels (AWCs) have been proposed to overcome the permeability/selectivity trade-off of desalination processes. Promising strategies exploiting the AWC with angstrom-scale selectivity have revealed their impressive performances when embedded in bilayer membranes. Herein, we demonstrate that self-assembled imidazole-quartet (I-quartet) AWCs are macroscopically incorporated within industrially relevant reverse osmosis membranes. In particular, we explore the best combination between I-quartet AWC and m-phenylenediamine (MPD) monomer to achieve a seamless incorporation of AWC in a defect-free polyamide membrane. The performance of the membranes is evaluated by cross-flow filtration under real reverse osmosis conditions (15 to 20 bar of applied pressure) by filtration of brackish feed streams. The optimized bioinspired membranes achieve an unprecedented improvement, resulting in more than twice (up to 6.9 L⋅m^-2⋅h^-1⋅bar^-1) water permeance of analogous commercial membranes, while maintaining excellent NaCl rejection (>99.5%). They show also excellent performance in the purification of low-salinity water under low-pressure conditions (6 bar of applied pressure) with fluxes up to 35 L⋅m^-2⋅h^-1 and 97.5 to 99.3% observed rejection.

Cosolvent-Driven Interfacial Polymerization for Superior Separation Performance of Polyurea-Based Pervaporation Membrane

A thin-film composite (TFC) polyurea membrane was fabricated for the dehydration of an aqueous tetrahydrofuran (THF) solution through interfacial polymerization, wherein polyethyleneimine (a water-soluble amine monomer) and m-xylene diisocyanate (an oil-soluble diisocyanate monomer) were reacted on the surface of a modified polyacrylonitrile (mPAN) substrate. Cosolvents were used to tailor the membrane properties and increase the membrane permeation flux. Four types of alcohols that differed in the number of carbon (methanol, ethanol, isopropanol, and tert-butanol) were added as cosolvents, serving as swelling agents, to the aqueous-phase monomer solution, and their effect on the membrane properties and pervaporation separation was discussed. Attenuated total reflection Fourier transform infrared spectroscopy confirmed the formation of a polyurea layer on mPAN. Field emission scanning electron microscopy and surface water contact angle analysis indicated no change in the membrane morphology and hydrophilicity, respectively, despite the addition of cosolvents for interfacial polymerization. The TFC membrane produced when ethanol was the cosolvent exhibited the highest separation performance (permeation flux = 1006 ± 103 g·m⁻²·h⁻¹; water concentration in permeate = 98.8 ± 0.3 wt.%) for an aqueous feed solution containing 90 wt.% THF at 25 °C. During the membrane formation, ethanol caused the polyurea layer to loosen and to acquire a certain degree of cross-linking. The optimal fabrication conditions were as follows: 10 wt.% ethanol as cosolvent; membrane curing temperature = 50 °C; membrane curing time = 30 min.

Search for optimal monomers for fabricating active layers in thin-film composite osmosis membranes by conceptual density functional theory

This paper presented an effective way to select monomers to fabricate active layers for the thin-film composite (TFC) membrane at the molecular level. Five types of diamine monomers and six acid chloride monomers were firstly selected by a conformer search process. Then, the conceptual density functional theory (CDFT) method was adopted to examine the properties of these monomers. A few different molecular properties were calculated, including relative energy, hydrogen bond, global/local/difference local softness, hardness, chemical potential, and electrophilicity index. Similarly, polyamides that were the productions of interfacial polymerization reaction were also analyzed by CDFT. Our results showed that the mixture of trimesoyl chloride (TMC) and m-phenylenediamine (MPD) for the interfacial polymerization was ideal synthetic materials to fabricate the active layer of TFC membranes. Graphical abstract Polyamides synthesis by interfacial polymerization.

Modification of poly(amide-urethane-imide) (PAUI) thin film composite reverse osmosis membrane with nano-silver particles

A novel reverse osmosis (RO) composite membrane, poly(amide-urethane-imide@Ag) (PAUI@Ag), was prepared on a polysulfone supporting film through two-step interfacial polymerization. First, in the 1st interfacial polymerization procedure, a new tri-functional crosslinking agent with –OCOCl and –COCl groups, 5-choroformyloxyisophaloyl chloride (CFIC), was reacted with 4-methyl-phenylenediamine (MMPD) without curing treatment to obtain the poly(amide-urethane) base membrane with a CFIC–MMPD precursor separation layer. And then N,N′-dimethyl-m-phenylenediamine (DMMPD) with nano-Ag particle dispersion was introduced onto the base membrane to further construct a CFIC–DMMPD modified ultrathin separation layer via the 2nd interfacial polymerization. Thus, the PAUI@Ag RO membrane with poly(amide-urethane-imide) bi-layer skin was obtained. The membrane was characterized for the chemical composition of separation layer, the membrane cross-section structure and the membrane surface morphology. Permeation experiment was employed to evaluate the PAUI@Ag membrane performance including salt rejection rate and water flux. The results revealed that the PAUI@Ag membrane composed the highly cross-linked separation layer with entire ridges and valleys, small surface roughness, and well dispersed nano-Ag particles. Upon exposure of the membranes to high concentration of free chlorine solutions, the PAUI@Ag RO membrane showed a slightly less chlorine-resistant property compared with the nascent PAUI RO membrane, but was still superior to the conventional polyamide MPD-TMC RO membrane, meanwhile it processed higher anti-biofouling property.

A novel reverse osmosis (RO) composite membrane, poly(amide-urethane-imide@Ag) (PAUI@Ag), was prepared on a polysulfone supporting film through two-step interfacial polymerization.

Influence of l-lysine on the permeation and antifouling performance of polyamide thin film composite reverse osmosis membranes

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study. l-Lysine is used as a type of aqueous additive during interfacial polymerization. As a result, the pure water flux (PWF) of the resulting membranes increased by around 18% and their salt rejection improved from 98.17% to 98.40% at an optimum l-lysine dosage of 0.1 wt%. Additionally, the anti-fouling properties of the resulting membranes were enhanced. The chemical structure of the membranes was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The morphologies of the top surface and cross-section of the membranes were revealed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, contact angle (CA) and zeta potential measurements were carried out to determine the surface properties of the membranes. The results showed that the TFC RO membrane became thinner, smoother, smaller in surface area, more hydrophilic and more negatively charged after the introduction of l-lysine. Accordingly, the reason for the enhancement in the PWF and anti-fouling properties of the TFC RO membranes with the introduction of l-lysine was analyzed. The thinner selective layer (increase in concentration gradient across the membrane) with carboxyl groups (hydrogen bond interactions) and loose structure (greater free volume and sub-nanometer pores) resulted in low hydraulic resistance to the permeability of the polyamide selective layer, which led to the enhancement in PWF. Also, the smoother and more hydrophilic top surface and the increase in negative charges in the selective layer contribute to the improvement in anti-fouling property.

Polyamide thin film composite (TFC) reverse osmosis (RO) membranes were prepared in this study.

A novel semi-aromatic polyamide TFC reverse osmosis membrane fabricated from a dendritic molecule of trimesoylamidoamine through a two-step amine-immersion mode

In this work, a novel semi-aromatic polyamide RO membrane was fabricated from a new dendritic molecule of trimesoylamidoamine (TMAAM) combined 1,3-diamino-2-propanol (DAP) to react with trimesoyl chloride (TMC) via a new two-step amine immersion method.

A Novel Polyvinylidene Fluoride Tree-Like Nanofiber Membrane for Microfiltration

A novel polyvinylidene fluoride (PVDF) tree-like nanofiber membrane (PVDF-TLNM) was fabricated by adding tetrabutylammonium chloride (TBAC) into a PVDF spinning solution via one-step electrospinning. The structure of the prepared membranes was characterized by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR) and pore size analysis, and the hydrophilic property and microfiltration performance were also evaluated. The results showed that the tree-like nanofiber was composed of trunk fibers and branch fibers with diameters of 100-500 nm and 5-100 nm, respectively. The pore size of PVDF-TLNM (0.36 μm) was smaller than that of a common nanofiber membrane (3.52 μm), and the hydrophilic properties of the membranes were improved significantly. The PVDF-TLNM with a thickness of 30 ± 2 μm showed a satisfactory retention ratio of 99.9% against 0.3 μm polystyrene (PS) particles and a high pure water flux of 2.88 × 10⁴ L·m-2·h-1 under the pressure of 25 psi. This study highlights the potential benefits of this novel PVDF tree-like nanofiber membrane in the membrane field, which can achieve high flux rates at low pressure.

Structure-Property Relationships of Soluble Poly(ester-urea)s containing Naphthyl Groups

The preparation of new types of polyureas with good thermal properties and improved solubility was investigated. Two new bulky diamines as new monomers for the preparation of polyurea were synthesized via two steps. First, a nucleophilic reaction of 1-naphthol and 2-naphthol with 3,5-dinitrobenzoyl chloride and then the reduction of the nitro groups by hydrazine hydrate/Pd-C to produce the corresponding diamines (1NA and 2NA). The poly(ester-urea)s were synthesized through the polyaddition reaction of the diamines with various commercially available diisocyanates. The polymers were characterized using IR and 1H NMR spectroscopy, elemental analysis, viscometry, thermal analysis, gel permeation chromatography (GPC), and X-ray diffraction. The copolymers were amorphous and readily soluble in a wide range of organic solvents such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethyl sulfoxide, N, N-dimethylformamide, and m-cresol. Thermal analysis showed a glass transition temperature between 146 and 178 °C. Their decomposition temperatures were more than 180 °C, and their 10% weight losses were in the range 281—315 ° C in air. The weight average molecular weights ( Mw) of the polymers were about 32 200—40 500 g/mol.

The influence of antiscalants on biofouling of RO membranes in seawater desalination

Antiscalants are surface active polyelectrolyte compounds commonly used in reverse osmosis (RO) desalination processes to avoid membrane scaling. In spite of the significant roles of antiscalants in preventing membrane scaling, they are prone to enhance biofilm growth on RO membranes by either altering membrane surface properties or by serving as nutritional source for microorganisms. In this study, the contribution of antiscalants to membrane biofouling in seawater desalination was investigated. The effects of two commonly used antiscalants, polyphosphonate- and polyacrylate-based, were tested. The effects of RO membrane (DOW-Filmtec SW30 HRLE-400) exposure to antiscalants on its physico-chemical properties were studied, including the consequent effects on initial deposition and growth of the sessile microorganisms on the RO membrane surface. The effects of antiscalants on membrane physico-chemical properties were investigated by filtration of seawater supplemented with the antiscalants through flat-sheet RO membrane and changes in surface zeta potential and hydrophobicity were delineated. Adsorption of antiscalants to polyamide surfaces simulating RO membrane's polyamide layer and their effects on the consequent bacterial adhesion was tested using a quartz crystal microbalance with dissipation monitoring technology (QCM-D) and direct fluorescent microscopy. A significant increase in biofilm formation rate on RO membranes surface was observed in the presence of both types of antiscalants. Polyacrylate-based antiscalant was shown to enhance initial cell attachment as observed with the QCM-D and a parallel plate flow cell, due to rendering the polyamide surface more hydrophobic. Polyphosphonate-based antiscalants also increased biofilm formation rate, most likely by serving as an additional source of phosphorous to the seawater microbial population. A thicker biofilm layer was formed on the RO membrane when the polyacrylate-based antiscalant was used. Following these results, a wise selection of antiscalants for scaling control should take into account their contribution to membrane biofouling propensity.

Development of antifouling reverse osmosis membranes for water treatment: A review

With the rapidly increasing demands on water resources, fresh water shortage has become an important issue affecting the economic and social development in many countries. As one of the main technologies for producing fresh water from saline water and other wastewater sources, reverse osmosis (RO) has been widely used so far. However, a major challenge facing widespread application of RO technology is membrane fouling, which results in reduced production capacity and increased operation costs. Therefore, many researches have been focused on enhancing the RO membrane resistance to fouling. This paper presents a review of developing antifouling RO membranes in recent years, including the selection of new starting monomers, improvement of interfacial polymerization process, surface modification of conventional RO membrane by physical and chemical methods as well as the hybrid organic/inorganic RO membrane. The review of research progress in this article may provide an insight for the development of antifouling RO membranes and extend the applications of RO technology in water treatment in the future.

Covalent binding of single-walled carbon nanotubes to polyamide membranes for antimicrobial surface properties

We propose an innovative approach to impart nanomaterial-specific properties to the surface of thin-film composite membranes. Specifically, biocidal properties were obtained by covalently binding single-walled carbon nanotubes (SWNTs) to the membrane surface. The SWNTs were first modified by purification and ozonolysis to increase their sidewall functionalities, maximize cytotoxic properties, and achieve dispersion in aqueous solution. A tailored reaction protocol was developed to exploit the inherent moieties of hand-cast polyamide membrane surfaces and create covalent amide bonds with the functionalized SWNTs. The reaction is entirely aqueous-based and entails activation of the carboxylate groups of both the membrane and the nanomaterials to maximize reaction with ethylenediamine. The presence of SWNTs was verified after sonication of the membranes, confirming the strength of the bond between the SWNTs and the membrane surface. Characterization of the SWNT-functionalized surfaces demonstrated the attainment of membranes with novel properties that continued to exhibit high performance in water separation processes. The presence of surface-bound antimicrobial SWNTs was confirmed by experiments using E. coli cells that demonstrated an enhanced bacterial cytotoxicity for the SWNT-coated membranes. The SWNT membranes were observed to achieve up to 60% inactivation of bacteria attached to the membrane within 1 h of contact time. Our results suggest the potential of covalently bonded SWNTs to delay the onset of membrane biofouling during operation.