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Current thin film nanocomposite membranes incorporated with microporous particles are demanding for improving membrane performance. In this study, carbon nanotubes (CNTs)-modified poly(ethyleneimine) (PEI)/sodium lignosulfonate (SL) membranes were prepared through layer-by-layer assembly by dispersing CNTs into PEI and/or SL solutions, in order to investigate the effects of CNTs on membrane structure and forward osmosis performance. The characterization results indicated that the CNTs can be well-incorporated in the PEI/SL membranes, which contribute to a slightly lower hydrophilicity of membrane surface and different membrane morphology. The forward osmosis performance of the PEI/SL and CNTs-modified PEI/SL membranes were investigated for application in separating NaCl from water. Compare with the PEI/SL membrane, PEI/(SL–CNTs) membrane prepared by dispersing CNTs into the SL solution exhibited the best water flux and membrane selectivity. The increase in the CNTs content of the PEI/(SL–CNTs) membrane can enhance the water flux, but cannot significantly impact on the reverse salt flux, resulting in the improvement in membrane selectivity. The PEI/(SL–CNTs) membrane containing 0.075 g L−1 CNTs in SL showed a 66.3% higher water flux of 7.32 LMH, also exhibited better antifouling and foulant-release properties. This study offers a new method to design novel FO membranes for desalination and water purification.

Pulping and papermaking generate large amounts of waste in the form of lignosulfonates which have limited valorized applications so far. Herein, we report a novel lignosulfonate‐based nanofiltration membrane, prepared by using polyethylenimine (PEI) and sodium lignosulfonate (SL) via a layer‐by‐layer (LbL) self‐assembly. As a low‐cost and renewable natural polyelectrolyte, SL is selected to replace the synthetic polyelectrolyte commonly used in the conventional LbL fabrication for composite membranes. The prepared LbL (PEI/SL)7 membranes were crosslinked by glutaraldehyde (GA) to obtain (PEI/SL)7‐GA membranes with compact selective layer. We characterized (PEI/SL)7 and (PEI/SL)7‐GA membranes to study the chemical compositions, morphologies, and surface hydrophilicity. To improve the nanofiltration performances of the (PEI/SL)7‐GA membranes for water desalination, we investigated the effects of the crosslinking time, GA concentration and the NaCl supporting electrolyte on membrane structure and performance. The optimized (PEI/SL)7‐GA membrane exhibited a permeating flux up to 39.6 L/(m2·h) and a rejection of 91.7% for the MgSO4 aqueous solution 2.0 g/L concentration, showing its promising potential for water desalination. This study provides a new approach to applying the underdeveloped lignin‐based biomass as green membrane materials for water treatment.

Constructing efficient and continuous transport pathways in membranes is a promising and challenging way to achieve the desired performance in the pervaporation process. The incorporation of various metal–organic frameworks (MOFs) into polymer membranes provided selective and fast transport channels and enhanced the separation performance of polymeric membranes. Particle size and surface properties are strongly related to the random distribution and possible agglomeration of MOFs particles, which may lead to poor connectivity between adjacent MOFs-based nanoparticles and result in low-efficiency molecular transport in the membrane. In this work, ZIF−8 particles with different particle sizes were physically filled into PEG to fabricate mixed matrix membranes (MMMs) for desulfurization via pervaporation. The micro-structures and physi-/chemical properties of different ZIF−8 particles, along with their corresponding MMMs, were systematically characterized by SEM, FT-IR, XRD, BET, etc. It was found that ZIF−8 with different particle sizes showed similar crystalline structures and surface areas, while larger ZIF−8 particles possessed more micro-pores and fewer meso-/macro-pores than did the smaller particles. ZIF−8 showed preferential adsorption for thiophene rather than n−heptane molecules, and the diffusion coefficient of thiophene was larger than that of thiophene in ZIF−8, based on molecular simulation. PEG MMMs with larger ZIF−8 particles showed a higher sulfur enrichment factor, but a lower permeation flux than that found with smaller particles. This might be ascribed to the fact that larger ZIF−8 particles provided more and longer selective transport channels in one single particle. Moreover, the number of ZIF−8−L particles in MMMs was smaller than the number of smaller ones with the same particle loading, which might weaken the connectivity between adjacent ZIF−8−L nanoparticles and result in low-efficiency molecular transport in the membrane. Moreover, the surface area available for mass transport was smaller for MMMs with ZIF−8−L particles due to the smaller specific surface area of the ZIF−8−L particles, which might also result in lower permeability in ZIF−8−L/PEG MMMs. The ZIF−8−L/PEG MMMs exhibited enhanced pervaporation performance, with a sulfur enrichment factor of 22.5 and a permeation flux of 183.2 g/(m−2·h−1), increasing by 57% and 389% compared with the results for pure PEG membrane, respectively. The effects of ZIF−8 loading, feed temperature, and concentration on desulfurization performance were also studied. This work might provide some new insights into the effect of particle size on desulfurization performance and the transport mechanism in MMMs.

Volatile organic compounds (VOCs) are important sources of atmospheric pollutants on account of their high recycling value. The membrane of dense silicone rubber polydimethylsiloxane (PDMS) has wide-ranging prospects for the separation and recovery of VOCs. In this study, PDMS membrane body models were established in BIOVIA Materials Studio (MS) to simulate VOCs with C3/N2 gases, and to study the structure of PDMS membranes and the dissolution and diffusion process of gas in the membranes. The free volume fraction (FFV), cohesive energy density (CED), radial distribution function (RDF), diffusion coefficient and solubility coefficient of C3H8, C3H6 and N2 in PDMS membranes were calculated, and the permeability coefficients were calculated according to these values. At the same time, the effects of temperature and mixed gas on the dissolution and diffusion of C3/N2 in PDMS membranes were investigated. The results show that the mass transfer process of C3 in PDMS membranes is mainly controlled by the dissolution process, while that of N2 is mainly controlled by the diffusion process. In a C3/N2 mixed gas system, there is a synergistic relationship between gases in the diffusion process, while there is competitive adsorption in the dissolution process. With an increase in temperature, the diffusion coefficients of the three gases in PDMS gradually increase, the solubility coefficients gradually decrease, and the overall permeability selectivity coefficients of the gases gradually decrease. Therefore, low-temperature conditions are more conducive to the separation of C3/N2 in PDMS membranes. The simulation results of the permeability selectivity coefficients of pure C3 and N2 in PDMS are similar to the experimental results, and the relationship between the micro- and macro-transport properties of PDMS membranes can be better understood through molecular simulation.

Polyaluminum chloride with a dominant species of Al30 (PAC-Al30) was prepared in laboratory and used for humic acid (HA) removal from water. The action properties and mechanisms of PAC-Al30, HA, calcium, and kaolin were tested and discussed. The results showed that the existence of calcium or kaolin contributed to the HA removal when the PAC-Al30 dosage was deficient and had no obvious effect when the amount of PAC-Al30 was sufficient. When the PAC-Al30 dosage was 0.01 and 0.02 mmol/L, the HA removal rate was increased by 66.59 and 42.20%, respectively, with a calcium concentration of 2.0 mmol/L, or increased by 53.31 and 40.92%, respectively, with the kaolin particle concentration of 150 mg/L. Calcium could compress the double electrical layers or complex with HA to neutralize a part of the surface negative charge of HA, but could not make the water system reach its isoelectric point. The mechanisms of calcium and kaolin’s promoting coagulation effect were adsorption neutralization and collision aggregation respectively, but these actions were much weaker than that of PAC-Al30 with HA. The adsorption neutralization capacity of PAC-Al30 was calculated to be nearly 60 times than that of calcium, and the higher γ value of calcium modified by the Sips equation may indicate that the adsorption or neutralization sites of calcium on HA were pickier than PAC-Al30.

In this study, zeolite molecular sieve SAPO-34/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) were prepared to recover propane. n-Octyltrichlorosilane (OTCS) was introduced to improve compatibility between SAPO-34 and PDMS, and enhance the separation performance of the MMMs. Physicochemical properties of the MMMs were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and water contact angle (WCA). Results showed that, after modification, alkyl chains were successfully grafted onto SAPO-34 without changing its crystal structure, particles in the MMMs were evenly distributed in the base film, and the hydrophobicity of the MMMs was enhanced. Moreover, the effects of SAPO-34 filling content, operating pressure, and feed gas concentration on the separation performance was explored. This indicated that the modification with OTCS effectively enhanced the separation performance of SAPO-34/PDMS MMMs. When the filling content of modified SAPO-34 was 15%, the maximal separation factor of 22.1 was achieved, and the corresponding propane permeation rate was 101 GPU.

Two different types of 2D nanosheets, including hydrophobic graphene (GR) and hydrophilic graphene oxide (GO), were filled into poly (vinyl alcohol) (PVA) polymers to prepare mixed matrix membranes (MMMs) for ethanol dehydration via pervaporation. The relationship between the physical/chemical properties of graphene and pervaporation performance of MMMs was investigated by a comparison of GR/PVA and GO/PVA MMMs in microstructure and PV performance. The incorporation of GO nanosheets into PVA reduced PVA crystallinity and enhanced the membrane hydrophilicity, while the incorporation of GR into PVA led to the opposite results. The incorporation of GR/GO into PVA depressed the PVA membrane swelling degree, and the incorporation of GR showed a more obvious depression effect. GR/PVA MMMs showed a much higher separation factor than GO/PVA MMMs, while they exhibited a much lower permeation flux than GO/PVA MMMs and pristine PVA membranes. The huge difference in microstructure and performance between GO/PVA and GR/PVA MMMs was strongly associated with the oxygen-containing groups on graphene lamellae. The higher permeation flux of GO/PVA MMMs was ascribed to the facilitated transport of water molecules induced by oxygen-containing groups and exclusive channels provided by GO lamellae, while the much lower permeation flux and higher separation factor GR/PVA MMMs was resulted from the smaller GR interplanar spacing (0.33 nm) and hydrophobicity as well as barrier effect of GR lamellae on the sorption and diffusion of water molecules. It was presumed that graphene intercalated with an appropriate number of oxygen-containing groups might be a good choice to prepare PVA-based MMMs for ethanol dehydration, which would combine the advantages of GR’s high interlayer diffusion selectivity and GO’s high permeation properties. The investigation might open a door to achieve both of high permeation flux and separation factor of PVA-based MMMs by tuning the microstructure of graphene.

Although several strategies have been developed to improve the efficiency of heterogeneous Fenton-like reactions, investigating the relationship among the electronic properties of the catalyst surface, the complex water matrix and catalytic activity remains challenges. Herein, the electron density of the active site Co(II) in Co Prussian blue analogs (Co-PBAs) is proved to be modulated by the anion source method. The elevated electron density of Co(II) and the higher metallicity of the catalyst lead to an increase in electron transport efficiency as revealed by X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and density functional theory (DFT) calculations. Furthermore, the negative shift of the D-band center of Co(II) can effectively release intermediates to avoid catalyst poisoning. Bicarbonate has been demonstrated to activate peroxymonosulfate (PMS) by weakening the peroxide bond. Its activation mechanism involves free radical mechanism and non-radical mechanism: the first step is the generation of HCO

Graphene oxide (GO), owing to its atomic thickness and tunable physicochemical properties, exhibits fascinating properties in membrane separation fields, especially in water treatment applications (due to unimpeded permeation of water through graphene-based membranes). Particularly, GO-based membranes used for desalination via pervaporation or nanofiltration have been widely investigated with respect to membrane design and preparation. However, the precise construction of transport pathways, facile fabrication of large-area GO-based membranes (GOMs), and robust stability in desalination applications are the main challenges restricting the industrial application of GOMs. This review summarizes the challenges and recent research and development of GOMs with respect to preparation methods, the regulation of GOM mass transfer pathways, desalination performance, and mass transport mechanisms. The review aims to provide an overview of the precise regulation methods of the horizontal and longitudinal mass transfer channels of GOMs, including GO reduction, interlayer cross-linking, intercalation with cations, polymers, or inorganic particles, etc., to clarify the relationship between the microstructure and desalination performance, which may provide some new insight regarding the structural design of high-performance GOMs. Based on the above analysis, the future and development of GOMs are proposed.

In this article, ZIF-8 nanoparticles were synthesized in water and directly added to a polyethyleneglycol (PEG) aqueous solution (water-based mixing process) to prepare ZIF-8/PEG mixed matrix membranes (MMMs) for pervaporation desulfurization. The structure and properties of ZIF-8 particles were characterized by Fourier Transform-Infrared Spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and BET analysis. The surface composition and structural morphology of all ZIF-8/PEG MMMs were systematically investigated by FT-IR and SEM. The effect of ZIF-8 content on the pervaporation performance of ZIF-8/PEG membranes was investigated. Versus pure PEG membranes, both the total flux and the sulfur enrichment factor of the ZIF-8/PEG MMMs were remarkably increased. This phenomenon is attributed to the good compatibility between PEG and ZIF-8 particles and the high thiophene selective sorption of ZIF-8 particles (confirmed by molecular simulation). Optimal pervaporation performance was achieved at a 4 wt% loading of ZIF-8 particles with the flux of 1.96 kg/(m2 h) and the sulfur enrichment factor of 8.93. These increased by 397.46% and 18.75% versus pristine PEG membrane, respectively. In addition, the effect of operation temperature and feed sulfur content on membrane performance were also systematically investigated.

A homogeneous distribution of inorganic fillers and their integration with polymer matrix is the primary challenge for advancement of mixed matrix membranes (MMMs) in pervaporation. Due to well-defined structure and multi-functional groups attached to the apex silicon atoms, polyhedral oligomeric silsesquioxane (POSS) provides a high possibility of good compatibility with diverse polymer matrix at the molecular level. In this work, soluble and reactive octa[(trimethoxysilyl)ethyl]-POSS(OPS) was synthesized, which was used as macro-crosslinker and reinforced porous fillers of polydimethylsiloxane (PDMS) synchronously to prepare a series of OPS/PDMS MMMs. The OPS/PDMS MMMs were characterized by FT-IR, XRD, SEM, TGA, DSC, PALS, vapor adsorption measurement and tensile test. It was found that OPS dispersed homogeneously in PDMS matrix and achieved good integration with PDMS based on SEM and DSC characterization. PALS results indicated that compared with pure PDMS membrane, OPS/PDMS MMMs with proper OPS loading showed much larger radii of free volume cavities (r3, r4) and fractional free volumes (fv3, fv4 and fv). The numerous hydrophobic POSS cages and enlarged PDMS’ free volume would effectively improve the diffusion selectivity towards ethanol. Vapor adsorption results showed that the chemical incorporation of moderate amount OPS into PDMS not only improved ethanol vapor adsorption amount, but also depressed water adsorption amount in PDMS, which would obviously improve PDMS’ sorption selectivity to ethanol. As applied to the bio-ethanol recovery from aqueous solutions, the prepared OPS/PDMS MMMs exhibited a simultaneous increase in permeation flux and separation factor, breaking the permeation flux-separation factor trade-off limitation. As OPS loading was 7.5 wt%, the separation factor of OPS/PDMS MMMs reached the maximum value of 16.4 (109% higher than that of pure PDMS membrane), with permeation flux of 253.1 g/m2h (32% higher than that of pure PDMS membrane). Experimental results showed that an increase in operation temperature resulted in an increase in permeation flux, but decrease in permeability, separation factor and selectivity. The pervaporation performance of OPS/PDMS MMMs kept stable during two days operation time. This work may provide useful insights of high-performance MMMs with a POSS embedded selective layer for biofuel separation.

The lack of fresh water in the world makes the search for an effective method to decontaminate water an urgent priority. An important step is to remove different multivalent ions in salt treatment. Nanofiltration (NF) has been used for treating water containing different kinds of salts. In this work, sulfonate group-modified graphene oxide (SGO) was prepared, and added during the interfacial polymerization (IP) reaction to prepare SGO-modifiedNF membranes (PA-SGO). The chemical composition, structure and surface properties of PA and PA-SGO membranes were characterized by FT-IR, XPS, SEM, AFM, contact angle and zeta potential measurements. Their water flux, salt rejection and anti-fouling abilities were investigated systematically. The testing results showed that the water flux of PA-SGO (0.03% SGO) was 45.85 LMH under a pressure of 0.2 MPa, and the salt rejection varied in the order of Na2SO4 (98.99%) > MgSO4 (91.25%) > MgCl2 (42.27%) > NaCl (21.96%). An anti-fouling experiment indicated that the PA-SGO membrane had good anti-fouling properties because of its decreased roughness and increased hydrophilicity and electronegativity. The PA-SGO membrane has good potential for use in removing salt ions from water.

Although poly(vinyl alcohol) (PVA) membranes are widely used in solvent dehydration by pervaporation, the separation factor is rather limited. Considering this, novel PVA mixed matrix membranes with graphene oxide (GO) nanosheets were prepared. poly(acrylonitrile) ultrafiltration (PAN) membrane was used as support layer. The PVA/GO composite membranes were characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy, thermogravimetric analysis and water contact angle. We also explored the pervaporation performance of the membrane for ethanol dehydration. GO slightly improves the thermal stability and crystallinity of the composite membranes. In addition, the hydrophilicity of the composite membranes is weakened after GO addition, but the crosslinking degree is increased, resulting a significant increase in the separation factor and a certain decrease in the total flux. With the amount of GO addition increases, the total flux of the PVA/GO composite membrane decreases, while the separation factor increases first and then decreases, and the preferred amount of GO addition is 2.0 wt%. Especially, the separation factor of the composite membranes with 2.0 wt% GO addition could reach 3 059, which is 16 times higher than PVA membranes, with the corresponding permeability flux is 145 g m−2 h−1.

In this paper, copper benzene-1,3,5-tricarboxylate (CuBTC) was incorporated into polyethylenglyol (PEG) to prepare a mixed matrix membrane (MMM) for pervaporation desulfurization. The characterization results showed that the prepared CuBTC particles had an ideal octahedral shape and micropores. The Cu2+ in CuBTC interacts with thiophene via &pi, complexation, thus enhancing the separation performance of the hybrid membranes. The effect of CuBTC content and the operating condition on the pervaporation performance of the MMMs was investigated. An optimal pervaporation separation performance was acquired with a permeation flux of 2.21 kg/(m2&middot, h) and an enrichment factor of 8.79, which were increased by 100% and 39% compared with the pristine PEG membrane. Moreover, the CuBTC-filled PEG membrane showed a good stability in the long-term desulfurization under a high operating temperature of 75 &deg, C for five days.

In this study, a reduced graphene oxide (rGO)@sodium lignosulfonate (NaLS) composite material was fabtricated using a one-step method and then mixed with natural polysaccharide calcium alginate (CaAlg) to prepare the rGO@NaLS/CaAlg pervaporation membrane. The appearance and physical properties of the rGO@NaLS/CaAlg membrane were characterized by scanning electron microscopy and water contact angle. The swelling performance of the membrane and its dehydration performance to organic solvents were evaluated. The results indicate that the addition of rGO@NaLS can increase the hydrophilicity of the rGO@NaLS/CaAlg membrane and reduce its degree of swelling in the ethanol solution. The membrane incorporated with 6 wt% rGO@NaLS exhibits the best pervaporation performance, and ethanol can be purified to 99.8%.

A novel aromatic poly (m-phenylene isophthalamide) (PMIA) hollow fiber substrate was first introduced to poly(piperazine-amide) (PA) composite membrane for nanofiltration. Chemical composition, morphological structure and top surface property were comprehensively characterized. Analyses indicated that a negative charged polyamide selective layer was successfully synthesized on PMIA substrate via interfacial polymerization. For nanofiltration tests, the as-prepared PA/PMIA hollow fiber membrane exhibited not only a superior permeation (104.13 ± 0.70 L·m−2·h−1, 0.6 MPa), but also an excellent salt rejection in the order as: R N a 2 S O 4 (98.45%) > R MgS O 4 (97.98%) > R CaC l 2 (96.02%) > R MgC l 2 (95.74%) > RNaCl(54.07%). Additionally, nanofiltration performance was evaluated with three kinds of anionic dyes (Chromotrope FB, Reactive Yellow 3, Direct Fast Blue B2RL) in varied conditions, including operating pressure, dye content, pH environment and salty co-exist. Evidence supported that an outstanding dye-removal ability was achieved using the developed PA/PMIA membrane, which was specifically higher than 97%. Integrate all the findings, this work provided a new PMIA based hollow fiber nanofiltration membrane, which should be promising in application of dye wastewater treatment.

Due to the importance of food safety, natural edible pigments attract more and more attention. Because of the application of adsorption technology in the extraction and purification of natural edible pigments, it is necessary to develop a highly efficient adsorbent. In this paper, we prepared a series of core shell spherical adsorbents (CSS-ZIFs) having different types of zeolitic imidazolate frameworks (ZIF-67, ZIF-7, ZIF-8 and ZIF-9) nanoparticles as the shell on the resin microsphere as the core. The XRD、BET and SEM characterizations proved the core-shell structure of the CSS-ZIFs, and the adsorption performance of the CSS-ZIFs were further studied for removing a natural edible pigment (Roselle red) from water. The CSS-7 (ZIF-7 as the shell) showed the best removal rates of 95.3–97.7% mainly due to the strong π-π attraction and weak cation-cation repulsion between ZIFs and Roselle red molecules. This study demonstrates that novel CSS-ZIFs can be used as a kind of feasible adsorbents for Roselle red extraction and separation, and further applied to the adsorption separation of other natural active substances.

Bio-ethanol recovery via pervaporation process has drawn growing attention in the past few decades, however, its large-scale industry application remains limited due to the relatively low separation efficiency, especially in flux. In view of this, surface patterned nonporous PDMS (Polydimethylsiloxane) composite membranes with enhanced ethanol recovery efficiency were fabricated in this work. Line and space pattern was first printed on two-layer PVDF (Polyvinylidene fluoride) substrate using phase separation micromolding followed by modified immersion precipitation. And then PDMS solution prepared with three kinds of crosslinking agents (TEOS, Tetraethyl orthosilicate; VTES, Triethoxyvinylsilane; p-TTES, p-tolyltriethoxysilane) were cast atop the as-prepared patterned substrate as selective layer. Morphology, topography and surface chemistry were thoroughly characterized and results indicated that PDMS cross linked with TEOS showed the largest pattern size, while for membranes prepared with VTES and p-TTES, pattern size appeared to be smoothed. This can be mainly ascribed to the higher steric effect introduced by vinyl and phenmethyl groups, which increased the rigidity of polymer and thereby reduced the pattern size. Pervaporation performance for both patterned and non-patterned composite membranes under varied feed concentration and temperature were also evaluated. Evidence supported that permeate flux of patterned membranes cross linked with TEOS reached 977.73 g m−2 h−1 (45 °C, 2 wt% ethanol concentration) and are generally 2.11 times as high as that of non-patterned one. In addition, although increased the permeate flux, surface patterning exerted no adverse effect on membrane selectivity. The overall findings of this work provide a promising platform for nonporous composite membrane preparation to achieve high permeate flux without losing selectivity.

Membrane gas separation offers high energy efficiency, easy operation, and reduced environmental impacts for vast hydrocarbon recovery in the petrochemical industry. However, the recovery of real light hydrocarbon mixtures (e.g., olefin/nitrogen) remains challenging for lack of high-performance membranes with sufficient reverse selectivity (large molecules permeate faster) and permeability. Here, we report the incorporation of fine-tuned, giant-pore featured MIL-101 nanocrystals into rubbery polymers to fabricate hybrid membranes, which successfully exploited the giant-pore channels and large sorption volume of the MIL-101 pore system. The synthesized MIL-101/poly(dimethylsiloxane) (PDMS) hybrid membranes demonstrated remarkably simultaneous improvement of gas permeance and separation factor for the model gas mixture propylene/nitrogen. Compared with the pristine PDMS, the propylene permeance and separation factor could be improved by more than 50% by adjusting MIL-101 loading and operating conditions. By consulting molecular simulations and gas sorption analysis, we verified that the giant-pore system of MIL-101 and the elastic PDMS chains exhibited a synergistic effect on improving both hydrocarbon solution and diffusion. Pore properties of MIL-101 contributed favorably to accelerated propylene diffusion in MIL-101 that is 236% faster than that in PDMS. In the meantime, MIL-101 reinforced the hydrocarbon solution additionally to PDMS, which further facilitated hydrocarbon transport.

Cu(OH)2 nanowires were prepared and incorporated into poly(vinylidene fluoride) (PVDF) to fabricate Cu(OH)2-PVDF ultrafiltration (UF) membrane via immersion precipitation phase inversion process. The effect of Cu(OH)2 nanowires on the morphology of membranes was investigated by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements. The results showed that all the Cu(OH)2-PVDF membranes had wider fingerlike pore structure and better hydrophilicity, smoother surface than pristine PVDF membrane due to the incorporation of Cu(OH)2 nanowires. In addition, water flux and bovine serum albumin (BSA) rejection were also measured to investigate the filtration performance of membranes. The results indicated that all the Cu(OH)2-PVDF membranes had high water flux, outstanding BSA rejection and excellent antifouling properties. It is worth mentioning that the optimized performance could be obtained when the Cu(OH)2 nanowires content reached 1.2 wt%. Furthermore, the membrane with 1.2 wt% Cu(OH)2 nanowires showed outstanding oil-water emulsion separation capability.

Lignosulfonates are a by-product of the agricultural and forestry waste and paper industries. Strengthening the sustainable use of lignosulfonates is a problem to be solved. In this study, hydrophilic agricultural and forestry waste calcium lignosulfonate (CaLS) was combined with single/double-layered MXene, and added to the natural polysaccharide sodium alginate (SA) to prepare a pervaporation me, membrane with a three-component hybrid structure. Characterization experiments such as scanning electron microscopy and contact angle demonstrated that CaLS increased the hydrophilicity and reduced swelling of the membrane, and MXene formed a layered cross-sectional morphology that further reduced swelling. A 90% ethanol aqueous solution was used to evaluate the dehydration performance of the membrane. The results showed that the permeation flux and separation factor of the membrane increased by 74% and 160%, respectively. Compared to the pure SA membrane after CaLS was incorporated. MXene further improved the pervaporation performance of the MXene@CaLS/SA membrane, with the permeation flux of about 938 g·m−2·h−1, and the separation factor of 4612 (two and four times higher than the pure SA membrane, respectively). This study provides a theoretical and technical basis for the development of new separation materials, and will help expand the high-value utilization of lignosulfonates.

Chitosan-functionalized graphene oxide (CS–GO) was synthesized and incorporated into PVDF ultrafiltration membrane. The effect of CS–GO addition on the morphology and membrane performance was studied with water contact angle (CA), scanning electron microscopy (SEM), atomic force microscopy (AFM), porosity and pore size, permeation measurements, rejection tests and antifouling experiments. We found that the water flux of CS–GO/PVDF composite membrane increased by 44% after incorporating 0.6 wt% of CS-GO into the PVDF matrix versus pristine PVDF membrane. In addition, the CS-GO/PVDF membrane exhibited higher water flux, BSA rejection rate, water flux recovery ratio and lower BSA solution flux attenuation rate than unfilled PVDF membranes, CS/PVDF, and GO/PVDF membranes. The excellent water permeability and antifouling performance can be attributed to the high hydrophilicity and good dispersion of CS–GO in the matrix.

There is a lack of stable and hydrophobic organic solvent nanofiltration (OSN) membranes meaning that their implementation in non-polar solvent nanofiltration remains a challenge, typically in solvent (e.g. hexane) recovery during vegetable oil production (e.g. soybean oil/hexane). Considering this, novel trifluoropropylmethylsiloxane dimethylsiloxane (PDMS–PTFPMS)/polyvinylidene fluoride (PVDF) membranes, with both high hexane permeability of PDMS and excellent hexane stability of PTFPMS, were successfully developed to recover hexane via OSN. Their microstructure and surface properties were characterized by SEM, FTIR, DSC, TGA, XPS and contact angle measurements. We explored the effects of the ratio of the PTFPMS segment in polymer chain and polymer viscosity on membrane performance. With regards to the F50-M membrane, we also conducted a comprehensive study on the OSN performance of the F50-M membrane under different operational conditions. The oil rejection was above 95% with stable hexane permeability of 3.06 kg−1 μm m−2 h−1 bar−1 over a 32-day period. Experimental results confirmed its ability to recover hexane under various operational conditions, showing high oil rejection and excellent long-term operational stability. We attributed its outstanding performance to its unique microstructure and surface properties due to the fluorine-containing PTFPMS segment. This study indicates that fluoropolymer membranes are promising candidates in OSN processes, offering a wider choice of membrane materials and application fields.

The air sparging method, which involves the introduction of air bubbles, is widely used in membrane separation to enhance performance. However, in flat sheet modules with distributors, the bubble behavior is complicated, which can have a critical impact on the air sparging efficiency. In this work, industrial-scale transparent modules were fabricated to visualize the two-phase flow with a distributor in different air sparging methods. Initially, the pressure drop in the channels induced by the inclusion of a distributor and spacer was evaluated, and the flow regime of the fluid was determined in visualization test. As for two-phase flows, five different solutions were investigated, categorized into two groups according to the coalescence behavior, namely the coalescence group and the non-coalescence group. Then, the bubble behaviors in a tubular flow module with different air sparging devices were studied for the two coalescence groups. In the pre-mixing method, the anti-coalescence phenomenon of bubbles clearly occurred at a high gas flow rate in the non-coalescence system. When an aerator head was used, smaller air bubbles were obtained, especially for the non-coalescence system, where the bubbles were small enough to ignore the resistance of the orifice. The flow patterns were subsequently investigated with empty flat sheet modules with different air sparging devices. Three flow regions were depicted for different solutions and air sparging devices. In the pre-mixing method, the coalescence effect led to a higher liquid flow rate being required to reach region (III) for water. The introduction of an aerator nozzle had the advantage of uniformly distributing the bubbles, while a higher gas flow rate was required to achieve a bubbly flow. With the incorporation of a spacer, the liquid flow rates needed to be higher than 0.32 m s−1 and 0.29 m s−1 to eliminate stagnant bubbles in the pre-mixing and air nozzle methods, respectively, in the coalescence system, and it was found the phenomenon was similar as for ethanol solution. According to our results, optimal operating conditions of air sparging devices for two-phase flow are proposed.

In this contribution, zeolitic imidazolate framework (ZIF-7)/polydimethylsiloxane (PDMS) mixed matrix membranes (MMMs) with uniformly dispersed ZIF-7 were fabricated. The homogeneous dispersion of ZIF-7 nanoparticles in PDMS matrix and better interface compatibility were characterized by SEM and EDS. PV performance reveals that the MMMs display increased total flux and the highest separation factor occurs at 20 wt% ZIF-7 loading, which were 1689 g m −2 h −1 and 66 respectively as compared to 1080 g m −2 h −1 and 51 for pure PDMS membrane when separating 1 wt% butanol aqueous solution at 60 °C. The total flux reaches 3496 g m −2 h −1 with 80 wt% butanol in permeate for the enrichment of 5 wt% butanol solution at 60 °C. The enhanced flux may result from enlarged free volume in the polymer matrix caused by the incorporation of ZIF-7 nanoparticles. Moreover, the super-hydrophobic ZIF-7 pore channels and butanol preferential permeation may contribute to the improvement of separation factor. The result also shows that there is a 21.1% reduction of energy barrier for penetrant transportation for 20 wt% ZIF-7 filled PDMS membrane as compared to pristine PDMS membrane. A long period of pervaporation experiment was also carried out to investigate the structure stability of the ZIF-7/PDMS membrane, and the MMM remains intact during the 240 h continuous operation, which is the key to industrial application for membrane-based separation process. All above indicated that ZIF-7 is a good filler to fabricate butanol permselective pervaporation membranes for butanol separation and enrichment.

TS-1 molecular sieves were synthesized and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and UV–Vis spectroscopy. Results showed that the morphology, crystallinity, and purity of TS-1 were closely related to the Ti/Si ratio, crystallization time, crystallization temperature, and calcination time. The TS-1 particles were incorporated into polydimethylsiloxane to form mixed matrix membranes (MMMs), and these MMMs were first used to separate ethanol/water mixtures via pervaporation. The MMMs with 50 wt% TS-1 (Ti/Si ratio of 0.02) loading showed the highest separation factor of 14.1 for 5 wt% ethanol feed concentration at 50°C. POLYM. ENG. SCI., 56:583–589, 2016. © 2016 Society of Plastics Engineers

Bio-inspired polydopamine has been established as a facile and versatile surface modification agent in recent years, many applications have been found such as tailoring the wettability of membrane surfaces, constructing antifouling or antimicrobial surface and serving as a platform for further modifications. To our knowledge, these applications were almost all aimed at liquid systems. For gas separations, however, polydopamine (PDA) was rarely investigated and exploited in literature. In this work, we report a facile method to fabricate ultrathin reverse-selective gas separation membranes (bigger molecules permeate more) via self-polymerization and adhesion of polydopamine onto a thin PDMS interlayer (spin-coated on a porous substrate). The as-prepared hierarchical structured membranes (PDA@PDMS) were used to selectively collect hydrocarbons from nitrogen (propylene/nitrogen as a model gas pair) with considerably enhanced separation selectivity and high gas permeance. Evidence supported that in two ways polydopamine skin layer favorably promoted the overall separation performance. Firstly, polydopamine exhibits much better affinity with propylene than that with nitrogen as indicated by gas sorption test. Secondly, owing to the excellent adhesion property and the dense structure of polydopamine, the in-situ polymerized polydopamine contributes to reducing the overall membrane thickness as well as minimizing the possible microstructural defects. Furthermore, polydopamine provides abundant functional groups for further design of membrane surface chemistry, which we believe would have good potential in other possible gas applications (e.g., carbon capture, olefin/paraffin). (C) 2015 Elsevier B.V. All rights reserved.

The surface modification of support membranes is an important approach for the preparation of polyamide (PA) thin-film nanocomposite membranes with nanoporous materials embedded in PA. A surface modification route is reported to fabricate novel PA nanocomposite membranes incorporating amino-functionalized MIL type metal–organic framework materials (NH2_MIL-88B). The support membrane was modified to grow an interlayer of NH2_MIL-88B nanoparticles on the support surface, and then a PA layer was coated on the NH2_MIL-88B interlayer, affording PA@NH2_MIL-88B nanocomposite membranes. The prepared PA and PA@NH2_MIL-88B membranes were characterized to investigate the physicochemical properties of the membrane structures and their separation performance for removing phenol from water. The surface modification route resulted in selective layers of the PA@NH2_MIL-88B membranes that were less cross-linked, thinner and more hydrophilic than pure PA membranes. The membrane performance is improved by the water-preferential pathways of NH2_MIL-88B, the defect-free nanocomposite layer of PA@NH2_MIL-88, and decreases in the cross-linking degree and membrane thickness. The PA@NH2_MIL-88B membranes showed significantly enhanced fluxes with high rejections (about 91 to 92%) and exhibited good durability. The reported approach can be further applied in the preparation of other polymer nanocomposite membranes with high performance.

In this study, a facile polypiperazine-amide (PPA) composite nanofiltration (NF) membrane with nanomaterial graphene oxide (GO) incorporated into a polyamide (PA) layer for high water flux and anti-fouling was fabricated by interfacial polymerization (IP). The chemical composition, structure and surface properties of the fabricated PPA/GO and PPA composite NF membranes were characterized by FTIR, XPS, FE-SEM, AFM, zeta-potential and contact angle measurements. The separation properties and anti-fouling ability of the PPA/GO NF membrane were investigated and discussed. The experimental results indicated that the water flux of the PPA/GO (300 mg L−1 GO) membrane increased from 66 (L m−2 h−1) to 87.6 (L m−2 h−1) under the operating pressure of 0.6 MPa, almost 1.4 times that of the PPA (without GO) membrane. However, the high salt rejection was still retained in the order of Na2SO4 (98.2%) > MgSO4 (96.5%) > NaCl (56.8%) > MgCl2 (50.5%). An anti-fouling test revealed that the PPA/GO membrane had excellent anti-fouling properties due to the enhanced hydrophilicity and decreased roughness induced by the GO nanosheets. Thus, the PPA/GO membrane can be efficiently and endurably applied in water purification.

The UNIFAC model and its various modified models on behalf of the group contribution methods offer reliable knowledge of phase equilibrium data, which are making great contributions for separation processes. The application of the UNIFAC-ZM model for the silicone polymer system is not only restricted by the poor accuracy under a large temperature range, but also limited by the lack of SiO group related group interaction parameters. In this work, first, modification of the model was made with consideration of the temperature effect on group interactions. Then inverse gas chromatography (IGC), a simple method to determine the infinite dilution activity coefficient, was applied to determine the interaction parameters between the common groups CH3, OH, H2O, CH3CO and SiO contained in polydimethylsiloxane (PDMS) based on the equilibrium chromatography theory. The achieved model was further proved to agree with the experimental results well. The new model was also applied in the calculation of the partition equilibrium between acetone/butanol/ethanol water solutions of different concentrations and PDMS of different polymerization degrees and side chain length. All these results would not only help the improvement of UNIFAC model, but also instruct the separation processes of silicone polymer compounds.

Inverse gas chromatography is a versatile and effective method for the characterization of the solubility thermodynamics and diffusion kinetic of solvent–polymer system with the advantages of fast, low dosage of samples and large range of temperature. Polydimethylsiloxane (PDMS) is well known as an excellent polymer membrane material for its high permeability to gases and liquids and widely used in the separation and purification of bio-fermentation broth which was mainly consisted by acetone, butanol, ethanol and water. In this paper, the inverse gas chromatography method was applied to measure solubility thermodynamics parameters like the infinite dilution activity coefficient and Flory–Huggins interaction parameter between those small molecules and PDMS. The infinite dilution diffusion coefficients were calculated by Van Deemter model over a temperature range of 373.2–413.2 K. The diffusion coefficient was fitted with the temperature according to the Arrhenius correlation. The data could help the selection of membrane material in pervaporation or gas separation and the analysis of mass transfer process.

The removal of perfluorooctane sulphonate (PFOS) with coexisting substances is very important. Inorganic ions and humic acid (HA) commonly coexist and may influence PFOS removal performance. However, there is little information on the capacity for systematic PFOS removal in the presence of inorganic ions and HA during nanofiltration (NF) process. In this paper, the impact of the coexistence of anions, cations, and HA on PFOS removal were investigated by NF. More specifically, the effect and interaction of anions, cations, and HA on PFOS removal performance and mechanism were examined. The PFOS removal rejection increased from 92% to 99% when HA was present together with both cations and anions. The higher the valence of the inorganic ion was, the greater the PFOS rejection was. The sieving effect was dominant in the improvement of PFOS removal by the presence of cations. The electrostatic repulsion played an important role in the improvement of PFOS removal by the presence of anions. Furthermore, density functional theory (DFT) was applied to calculate the interaction between PFOS molecules, cations, and HA. Corresponding DFT structures and thermodynamics parameters were obtained. It showed that the Ca2+ ions could more easily bridge two PFOS than one PFOS, HA could more easily coordinate with both Ca2+ and PFOS molecules. The increase of PFOS size after the coordination reaction results in the improvement of the sieving effect. Additionally, other analyses including X-ray photoelectron spectroscopy, atomic force microscopy, and the surface zeta potential also demonstrated the sieving effect mainly governed PFOS removal in coexistence with HA and cations. The electrostatic repulsion was dominant in PFOS separation performance in coexistence with HA and anions.

Graphene oxide (GO) has potential application in membrane separation owing to its extraordinary permeance. In this paper, the reduced graphene oxide (rGO) was synthesized by a green hydrothermal reduction method, and the rGO membranes was prepared on polyvinylidene fluoride (PVDF) supporting membranes by vacuum filtration. The interlayer structure of GO and the permeability of rGO membranes can be controlled by adjusting the reduction degree of GO through changing the hydrothermal reaction time. The disorder and defects of rGO nanosheets, the less oxygen-containing functional group and the enhanced hydrophobicity facilitate transport of water molecular in relatively smaller interlayer space owing to hydrothermal reduction. Compared with the GO membranes, the hydrothermally reduced rGO membranes showed a more excellent permeability without sacrificing rejection. The rejection of the prepared rGO membrane for Methyl blue, Congo red and Crystal violet all exceed 99%.

Bio-ethanol, clean and renewable, has proved to be a promising alternative energy resource to replace conventional fossil fuels. In its continuous production via the fermentation–pervaporation process, hydrophobic polymer membranes such as polydimethylsiloxane (PDMS) have been developed to enrich ethanol from dilute fermentation broth. However, the efficiency of current ethanol recovery via pervaporation is not high enough for large-scale bioethanol production. To address this issue, we separately fabricated two types of lotus-inspired PDMS composite membranes to combine the beneficial properties (low surface energy and super-hydrophobicity) of superhydrophobic lotus leaves with the pervaporation process and optimized the separation performance. First, we prepared lotus leaf powder/PDMS mixed matrix membranes (MMMs) to exploit the intrinsic properties of lotus leaf’s material. In addition, polydivinylbenzene (PDVB)-coated PDMS composite membranes were fabricated to mimic and make use of the properties coming from the lotus leaf’s hierarchical structure. The morphology, surface chemistry, and pervaporation performance were systematically investigated for all the membranes. And results showed that MMMs at 1.5 wt% lotus powder loading displayed the ideal dispersion condition and increased the total flux of pervaporation process by 22% (750 g∙m−2∙h−1, 6 wt%, 37 °C). For the PDVB-coated PDMS membrane, the hierarchical roughness was successfully established on the PDMS surface, which resulted in a super-hydrophobic surface with water contact angle higher than 150°. As PDVB also has preferential adsorption for ethanol, the PDVB-coated PDMS membrane showed a higher ethanol recovery performance with the separation factor and total flux increased by 13% and 30%, respectively. Therefore, it was demonstrated that PDVB coating is an effective method to fabricate superhydrophobic membranes and both the two lotus-inspired strategies are feasible in optimizing pervaporation performance for ethanol recovery.

Incorporating nanofillers into polymer matrix to construct mixed matrix membranes (MMMs) is an effective approach to improve either sorption selectivity or diffusion selectivity or both. In this contribution, octa-vinyl polyhedral oligomeric silsesquioxanes (V-POSS) particles were chemically incorporated into polydimethylsiloxane (PDMS) matrix to fabricate POSS-g-PDMS MMMs. POSS-g-PDMS MMMs exhibited a homogeneous phase and achieved good integration between V-POSS and PDMS. Compared with pure PDMS membrane, POSS-g-PDMS MMMs possessed higher crosslinking density and gel content as well as enhanced ethanol affinity and hydrophobicity, which contributed to the significant improvement of ethanol sorption selectivity with a little sacrifice of diffusion selectivity. The chemical incorporation of V-POSS into PDMS matrix significantly enhanced both separation factor and permeation flux, which showed reversal trade-off effect. The best pervaporation performance of POSS-g-PDMS MMMs was achieved at 5 wt% POSS loading, with separation factor of 17.7 and permeation flux of 536 g/(m2 h), increased by 130% and 260% compared with pure PDMS membrane, respectively. An excessive POSS loading sharply depressed the fast transport of small molecules and finally led to the decline of diffusion selectivity and separation factor. The sorption and diffusion selectivity results suggested selective sorption was a major contributor to the high separation factor of MMMs at 5 wt% POSS loading, and diffusion was a rate-controlling process. The effect of variation of external driving forces and intrinsic membrane properties induced by increasing feed temperature and ethanol concentration on pervaporation performance was also investigated in detail. This work may provide useful insights of PDMS based mixed matrix membranes, especially those with covalent bonding between organic and inorganic phases for pervaporation recovery applications.

The single/double-layered MXene nanosheets with two-dimensional intergaps and good hydrophilicity have been known as promising porous fillers for preparing high-performance mixed matrix membranes for pervaporation dehydration. However, the single/double-layered MXene nanosheets must be exfoliated from multi-layered MXene (mMXene) through long-time ultrasonication and then be collected through high-speed centrifugation, which limits the facile and large-scale application of single/double-layered MXene nanosheets in membrane fabrication. In this study, mMXene particles with intergaps were directly obtained under mild conditions and then used to fabricate the sodium alginate (SA) mixed matrix membranes. The effects of mMXene content on membrane structure properties and pervaporation dehydration performance were studied. Compared with the pure SA membrane, the SA/mMXene mixed matrix membrane hydrophilicity increases but the degree of swelling decreases with increasing the mMXene content, and the mixed matrix membrane containing 0.12 wt% mMXene in SA shows the 10 times higher separation factor of 9946 and the 24.5% lower permeate flux of 505 g m−2 h−1 for dehydration of ethanol/water (90 wt%) solution. The hydrophilic mMXene fillers attribute to the enhancement in the preferential sorption of water and the constraint in the selective diffusion of ethanol, giving the significant improvement in membrane selectivity.

The lack of fresh water in the world makes the search for an effective method to decontaminate water an urgent priority. An important step is to remove different multivalent ions in salt treatment. Nanofiltration (NF) has been used for treating water containing different kinds of salts. In this work, sulfonate group-modified graphene oxide (SGO) was prepared, and added during the interfacial polymerization (IP) reaction to prepare SGO-modifiedNF membranes (PA-SGO). The chemical composition, structure and surface properties of PA and PA-SGO membranes were characterized by FT-IR, XPS, SEM, AFM, contact angle and zeta potential measurements. Their water flux, salt rejection and anti-fouling abilities were investigated systematically. The testing results showed that the water flux of PA-SGO (0.03% SGO) was 45.85 LMH under a pressure of 0.2 MPa, and the salt rejection varied in the order of Na