Forward osmosis (FO) has attracted wide attention in recent years. However, the FO performance may be restricted due to internal concentration polarization (ICP) and fast fouling propensity that ...occurs in the membrane sublayer. Particularly, these problems significantly affect the membrane performance when treating highly contaminated oily wastewater. Recently, double-skinned flat sheet cellulose acetate (CA) membranes consisting of two selective skins via the phase inversion method have demonstrated less ICP and fouling propensity over typical single-skinned membranes. However, these membranes exhibit low water fluxes of <12 LMH under 2 M NaCl draw solution. Therefore, a novel double-skinned FO membrane with a high water flux has been aimed for in this study for emulsified oil–water treatment. The double-skinned FO membrane comprises a fully porous sublayer sandwiched between (i) a truly dense skin for salt rejection and (ii) a fairly loose dense skin for emulsified oil particle rejection. The former dense skin is a polyamide synthesized via interfacial polymerization, while the latter one is a self-assembled sulfonated pentablock copolymer (Nexar copolymer) layer. The resultant double-skinned membrane exhibits a high water flux of 17.2 LMH and a low reverse salt transport of 4.85 gMH using 0.5 M NaCl as the draw solution and DI water as the feed. The double-skinned membrane outperforms the single-skinned membrane with much lower fouling propensity for emulsified oil–water separation.
A simple scalable strategy is proposed to fabricate highly permeable antifouling nanofiltration membranes. Membranes with a selective thin polyamide layer were prepared via interfacial polymerization ...incorporating building blocks of zwitterionic copolymers. The zwitterionic copolymer, poly(aminopropyldimethylaminoethyl methacrylate)-co-poly(sulfobetaine methacrylate) with an average molecular weight of 6.1 kg mol–1, was synthesized in three steps: (i) polymerization of dimethylaminoethyl methacrylate to yield the base polymer by atom transfer radical polymerization (ATRP), (ii) fractional sulfobetainization via quaternization, and (iii) amination via quaternization. The effect of the zwitterionic polymer content on the polyamide surface characteristics, fouling resistance, and permeance is demonstrated. The zwitterion-modified membrane becomes more hydrophilic with lower surface roughness, as the zwitterionic polymer fraction increases. The excellent fouling resistance of the zwitterion-modified membrane was confirmed by the negligible protein adsorption and low bacteria fouling compared to a pristine membrane without zwitterionic segments. In addition, the zwitterion-modified membranes achieve a water permeation around 135 L m–2 h–1bar–1, which is 27-fold higher than that of the pristine membrane, along with good selectivity in the nanofiltration range, confirmed by the rejection of organic dyes. This permeance is about 10 times higher than that of other reported loose nanofiltration membranes with comparable dye rejection. The newly designed membrane is promising as a highly permeable fouling resistant cross-linked polyamide network for various water treatment applications.
Large amounts of oily wastewater have been produced from various industries. The main challenge of oily wastewater treatments is to separate the stable emulsified oil particles from water. Therefore, ...the aim of this study is to investigate the effectiveness of forward osmosis (FO) processes to treat the stable oil–water emulsions. The FO technique has been demonstrated successfully for the treatment of a wide range of oil–water emulsions from a low to a very high concentration up to 200,000ppm. The dependence of separation performance on oily feed concentration and flow rate has been investigated. Water can be separated from oily feeds containing 500ppm or 200,000ppm emulsified oil at a relatively high flux of 16.5±1.2LMH or 11.8±1.6LMH respectively by using a thin film composite membrane PAN-TFC and 1M NaCl as the draw solution. Moreover, this membrane can achieve an oil rejection of 99.88% to produce water with a negligible oil level. Due to the presence of emulsified oil particles in the oily feed solutions, the membrane fouling has been addressed in this study. Better anti-fouling TFC FO membranes are needed.
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•Study the FO technique for the treatment of a wide range of oil–water emulsions.•Water flux as functions of feed flow rate and feed concentration has been studied.•Pure water can be separated from a 200,000ppm oily feed by FO technique.•A water flux of 11.8±1.6LMH can be obtained from a 200,000ppm oily feed.•The membrane fouling has been investigated in this study.
The preparation of membranes with high selectivity based on specific chemical properties such as size and charge would impact the efficiency of the world’s energy supply, the production of clean ...water, and many other separation technologies. We report a flexible synthetic protocol for preparing highly ordered two-dimensional nanoporous polymeric materials (termed covalent organic frameworks or COFs) that allow for placing virtually any function group within the nanopores. We demonstrate that membranes, fabricated with this new family of materials with carboxylated pore walls, are very water permeable, as well as highly charged and size selective.
A new carboxyl-functionalized covalent organic framework (referred to as COF hereafter, unless otherwise noted) contains aromatic backbones and carboxyl-functionalized nanopores has been synthesized ...and used as a two-dimensional (2D) nanofiller in polyacrylonitrile (PAN) polymer matrix of ultrafiltration (UF) membranes. A series of mixed-matrix UF membranes with various concentrations COF ranging from 0 to 0.8 wt% have been investigated using non-solvent induced phase separation (NIPS) method. The effect of COF concentration has been evaluated on the membrane morphology, intrinsic and mechanical properties, separation performance, and fouling propensity. Increasing COF concentration from 0 to 0.8 wt% could significantly enhance the rejection rate from 3.5 to 81.9 wt% for bovine serum albumin (BSA) and 65.0–99.4 wt% for γ-globulin. Moreover, membrane hydrophilicity greatly increased, with the decrease of water contact angle from 64.4° to 45.3°. Overall, compared to the pristine PAN membrane, the mixed-matrix PAN membrane with 0.8 wt% COF demonstrated high water flux of 940 L m−2 h−1 bar−1, better protein retention rate, thermal stability, mechanical properties, and fouling resistance.
•A new 2D COF was synthesized with carboxylated nanopores.•Mixed-matrix COF/PAN UF membranes were fabricated using non-solvent induced phase separation method.•The COF/PAN membranes showed rejection rate of BSA (81.9%) and γ-globulin (99.4%) along with excellent water permeance (940 L m2 h−1 bar−1).•Only 1.8% BSA was adsorbed on COF/PAN membrane with merely 0.8% COF as fillers, compared to 100% of BSA adsorption on pristine PAN membranes.•The COF/PAN membranes showed significantly enhanced thermal stability and mechanical properties.
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Layer-by-layer (LbL) deposition of polyelectrolytes onto a negative charge membrane has been investigated under a highly crosslinking condition for forward osmosis (FO). The influence of salt ...concentration and deposition time on LbL FO membranes performance has been investigated in order to optimize the deposition process, followed by the investigation of polyelectrolyte layer's crosslinking. In the crosslinking steps, polycation layers of the three bilayer LbL membrane were firstly crosslinked using glutaraldehyde (GA) as the crosslinker. Compared to a non-crosslinked membrane, the reverse salt fluxes were reduced by 63% and 58% under the PRO (pressure retarded osmosis) testing mode using 0.5M MgCl2 and 0.5M NaCl as draw solutions, respectively. Subsequently, the polyanion layer of that membrane was photo-crosslinked under ultraviolent (UV) at the wavelength of 254nm. The reverse salt flux of the resulting membrane was further reduced by 55% and 53% under the PRO testing mode using 0.5M MgCl2 and 0.5M NaCl as draw solutions, respectively. Specially, the LbL membrane with only one bilayer after cross-linking by both GA and 4h-UV could achieve a water flux of about 11LMH and a reverse flux of 8gMH under the PRO test using 0.3M NaCl as a draw solution. This is the first time, a LbL polyelectrolyte membrane has been successfully demonstrated as a FO membrane with good rejection toward NaCl while none of previously reported LbL polyelectrolyte membranes have achieved based on the best of our knowledge.
► Effects of salt concentration and deposition time on the FO performance of LbL membranes have been investigated. ► PAH and PSS layers were crosslinked using glutaraldehyde and ultraviolent, respectively. ► Crosslinking technologies have been proven to significant enhance the membrane's selectivity to NaCl. ► The crosslinked (PAH/PSS)1 membrane can achieve Jv at 11LMH and Js at 8g LM using 0.3M NaCl as the draw solution. ► The micro-structure of the membranes was examined using a positron annihilation spectroscopy (PAS).
Hydroxyl functionalized polytriazole-co-polyoxadiazole (PTA–POD) copolymers have been synthesized and cast as promising highly thermally stable, chemically resistant, and antiorganic/biological ...fouling porous substrates for the fabrication of thin-film composite (TFC) forward osmosis (FO) membranes. The roles of PTA/POD ratios in the membrane substrates, TFC layers, and FO membrane performance have been investigated. This study demonstrates that the substrate fabricated from the copolymer containing 40 mol % PTA is optimal for the TFC membranes. Compared to the POD–TFC membrane, the 40 mol % PTA–TFC membrane exhibits a remarkable decrease in structural parameter (S) of more than 3.3 times. In addition, the 40 mol % PTA–TFC membrane is characterized by high water fluxes of 24.9 LMH and 47.2 LMH using 1 M NaCl as the draw solution and DI water as the feed under FO and pressure retarded osmosis (PRO) modes, respectively. Compared to a polysulfone (PSU) supported TFC-FO membrane under similar fabrication conditions, the 40% mol PTA–TFC membrane shows better FO performance and enhanced antifouling properties on the support (lower protein binding propensity and improved bacterial inhibition). Moreover, the performance of the 40 mol % PTA supported TFC-FO membrane can be improved to 37.5 LMH (FO mode)/78.4 LMH (PRO mode) and potentially higher by optimizing the support morphology, the TFC formation, and the post-treatment process. Hence, the use of newly developed hydroxyl functionalized polytriazole-co-polyoxadiazole copolymers may open up a new class of material for FO processes.
Interactions among ions, molecules, and confining solid surfaces are universally challenging and intriguing topics. Lacking a molecular-level understanding of such interactions in complex organic ...solvents perpetuates the intractable challenge of simultaneously achieving high permeance and selectivity in selectively permeable barriers. Two-dimensional covalent organic frameworks (COFs) have demonstrated ultrahigh permeance, high selectivity, and stability in organic solvents. Using reactive force field molecular dynamics modeling and direct experimental comparisons of an imine-linked carboxylated COF (C-COF), we demonstrate that unprecedented organic solvent nanofiltration separation performance can be accomplished by the well-aligned, highly crystalline pores. Furthermore, we show that the effective, as opposed to designed, pore size and solvated solute radii can change dramatically with the solvent environment, providing insights into complex molecular interactions and enabling future application-specific material design and synthesis.
We report a new synthetic protocol for preparing highly ordered two-dimensional nanoporous covalent organic frameworks (2D-COFs) based on a quinoxaline backbone. The quinoxaline framework represents ...a new type of COF that enables postsynthetic modification by placing two different chemical functionalities within the nanopores including layer-to-layer cross-linking. We also demonstrate that membranes fabricated using this new 2D-COF perform highly selective separations resulting in dramatic performance enhancement post cross-linking.
Copolyamide films with a thickness from 50 to 780 nm were fabricated by interfacial polymerization between mixtures of m-phenylenediamine and primary amine-terminated polyamidoamine dendrimers ...(PAMAM) in the aqueous phase and trimesoyl chloride (TMC) in the organic phase. Different PAMAM generations (G0, d = 15 Å, Z = 4; G3, d = 36 Å, Z = 32; and G5, d = 54, Z = 128, where d is the measured diameter and Z is the number of terminal groups), and concentrations were used to obtain copolyamide films with different cross-linked structures. The influences of the concentration and degree of branching (PAMAM generation) on free volume were analyzed via positron annihilation spectroscopy (PAS) and correlated with the separation properties of copolyamide films. Besides, surface and intrinsic properties of copolyamide films prepared under different conditions were compared. The high hydrophilicity of PAMAM in the copolyamide network leads to the formation of a hydration layer on the copolyamide surface, which minimizes fouling. The separation performance of copolyamide membranes with various PAMAM networks was investigated in forward osmosis (FO) experiments. Understanding the correlation between the PAMAM structure/concentration, free volume, thickness, and surface intrinsic properties leads to the design of suitable fouling resistant thin-film composite membranes in a single interfacial polymerization process.
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