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Polysulfone (PSF) is extensively used for the production of ultrafiltration (UF) membranes thanks to its high strength, chemical stability, and good processibility. However, PSF is intrinsically hydrophobic, and hydrophilic modification is always required to PSF-based membranes if they are intended to be used in aqueous systems. Facile strategies to prepare hydrophilic PSF membranes are thus highly demanded. Herein we spray coat a PSF-based amphiphilic block polymer onto macroporous substrates followed by selective swelling to prepare flat-sheet PSF UF membranes. The polymer is a triblock polymer containing PSF as the majority middle block tethered with shorter block of polyethylene glycol (PEG) on both ends, that is, PEG-b-PSF-b-PEG. We use the technique of spray coating to homogeneously dispense diluted triblock polymer solutions on the top of macroporous supports, instantly resulting in uniform, defect-free polymer coating layers with the thickness down to ~ 1.2 μm. The bi-layered composite structures are then immerged in ethanol/acetone mixture to generate mesoscale pores in the coating layers following the mechanism of selective swelling-induced pore generation, thus producing composite membranes with the mesoporous triblock polymer coating as the selective layers. This facile strategy is free from additional hydrophilic modification and much smaller dosages of polymers are used compared to conventional casting methods. The pore sizes, porosities, hydrophilicity, and consequently the separation properties of the membranes can be flexibly tuned by changing the swelling duration and the composition of the swelling bath. This strategy combining spray coating and selective swelling is upscalable for the production of high-performance PSF UF membranes.

The compact finite difference scheme is designed to numerically solve the nonlinear Schrodinger equation and coupled nonlinear Schrodinger equations on an unbounded domain in this paper. The original problem on an unbounded domain is reduced to an initial boundary value problem defined on a bounded computational domain by applying the artificial boundary method. Then, the reduced problem on the bounded computational domain is solved by an efficient semi-implicit compact finite difference scheme, which is a fourth-order scheme with respect to spatial variable. The scheme efficiently avoids the time-consuming iteration procedure necessary for the nonlinear scheme and thus is relatively time-saving. Finally, the stability of the proposed scheme is rigorously analyzed. Numerical examples are given to illustrate the accuracy and effectiveness of the proposed method.

Multilayer indium selenide (InSe) is a good candidate for high performance electronic and optoelectronic devices. The electrical performance of InSe is effectively regulated by dielectric layers, contact electrodes and surface doping. However, as a powerful tool to tune properties of materials, alloy engineering is absent for multilayer InSe. In this letter, for the first time, we investigate the electrical property of InSe1-xTex alloys and optoelectronic property of InSe-InSe0.82Te0.18p-n heterojunction. The electrical transport properties of InSe1-xTex alloys strongly depend on the content of Te composition. With the ratio of Te/Se increasing, the n-type electron transport behavior of InSe gradually transfers to the p-type hole transport behavior of InSe0.82Te0.18. The p-n InSe-InSe0.82Te0.18 heterojunction shows a rectification effect and a self-powered photodetection. The self-powered photodetector (SPPD) has a broad photodetection range from visible light (400 nm) to near-infrared (NIR) light (1000 nm). The responsivity (R) of SPPD is 14.1 mA/W under illuminated by NIR light (900 nm) at zero bias, which is comparable to some of the 2D heterojunctions NIR photodetectors measured with an external bias. The SPPD also shows a stable and fast response to NIR light (900 nm). This work demonstrates that the electrical transport properties of InSe1-xTex alloys significantly rely on the ratio of Te/Se and suggests that InSe-InSe1-xTex p-n heterojunction has a excellent potential for application in the self-powered optoelectronic device.

A hierarchical tree-like nanofiber membrane (TLNM) with high hydrophobicity was prepared via electrospinning polyvinylidene fluoride (PVDF) blended with tetrabutylammonium chloride (TBAC) and fluorinated acrylate copolymer (FA). Then, the hydrophobicity of PVDF/TBAC/FA TLNMs was further enhanced after ultrasonic treatment. The introduction of TBAC and FA promoted the formation of tree-like structures and the as-prepared PVDF/TBAC/FA TLNMs showed strong hydrophobicity with a water contact angle of 137 ± 3°, extremely small pore size of 0.21–0.26 μm, outstanding mechanical strength of 7.90 MPa and high liquid entry pressure of 0.23 MPa, making the membrane possess excellent performance in the direct contact membrane distillation (DCMD) process. The PVDF/TBAC/3% FA TLNMs with a thickness of 60 ± 3 μm showed a superior permeate flux of 54.39 L/m2 h and the salt rejection rate kept above 99.5% after 9 h using a 3.5 wt% NaCl as the feed solution while with the feed and permeate temperatures were set as 60 °C and 20 °C, respectively. This work highlights the promising application of this TLNMs in the field of membrane distillation.

The concentration of pomegranate juice and the corresponding effect of membrane wetting was studied through the non-thermal Osmotic Distillation technique using flat sheet PVDF and PTFE membranes. Analytical techniques like contact angle analysis, FTIR, SEM, AFM and pore geometry analysis revealed that the PVDF membrane was much prone to wetting as compared to PTFE membrane. In a total operational time of 24 h, the water flux and juice concentration attained values of 0.208 kg m−2 hr−1 and 18 oBrix, respectively in PVDF membrane and 0.935 kg m−2 hr−1 and 41 oBrix, respectively in PTFE membrane. After 24 h of continuous operation, the hydrophobicity declined by 29% in PVDF membrane as opposed to 6% in PTFE membrane, which was a clear sign of membrane wetting in the former case. Similarly, the normalized flux decline was 83% in PVDF membrane which was much higher as compared to the 55% decline in PTFE membrane. The FTIR, SEM and pore geometry analysis further confirmed the sensitivity of PVDF membrane to wetting. The major reasons for this response were higher surface energy of the PVDF membrane and the non-woven polyester fibers present as a support layer in the membrane.

Reverse osmosis (RO) has been widely used as a dominant desalination technology to produce fresh water from seawater (SW), but still consumes huge energy. To reduce the energy consumption of RO, pressure retarded osmosis (PRO) has been developed to extract osmotic energy from RO brine. In this study, the PRO process is optimized for efficient energy recovery from RO brine via one system/module-level mathematic model in RO-PRO hybrid system. The system-level model illustrates that the specific energy consumption (SEC) of the hybrid system can be significantly reduced when achieving a high permeate flow under high operating pressure in PRO. However, the specific PRO membrane configuration has to sacrifice a high permeate flow under high operating pressure. The module-level model finds that the increase of PRO operating temperature facilitates to achieve a high permeate flow under a high optimal operating pressure. Furthermore, results present that the SEC at a kiloton-scale SWRO desalination capacity can be reduced by 14.41% (0.6 M NaCl as a draw solution) and 17.93% (1.2 M NaCl as a draw solution) when the PRO operating temperature increases from 25 °C to 50 °C, confirming the great potential of temperature-enhanced PRO to further reduce the SEC of seawater desalination.

In this study, a new type of polyimide (PI) composite material was synthesized by a two-step method using 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPDA), 4,4′-methylenedianiline (MDA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA). The PI material was then used to prepare an ultrafiltration (UF) membrane by phase inversion method. The membrane showed a dense surface layer, a porous sublayer, and fully developed finger-like macrovoids at the bottom, which had excellent hydrophilicity and antifouling property. In the recovery experiments with a protein solution, the PI membrane displayed a satisfactory water flux recovery ratio of 90.03%. The PI membrane can operate stably in 1 mol L−1 hydrochloric acid solution, and the retention rate of BSA remains at 93%. In addition, the flux of the membrane is 325.60 L m−2 h−1 and the BSA retention rate the retention rate is still higher than 95% after soaking in various solvents for 7 days.

The numerical solution of the logarithmic Schrodinger equation on unbounded domains is considered in this paper. It is difficult to develop numerical methods for the logarithmic Schrodinger equation on unbounded domains, due to the blow up of the logarithmic nonlinearity and the unboundedness of the physical domain. Thus, a regularized version of the logarithmic Schrodinger equation on unbounded domains with a small regularization parameter is developed. Then, the local artificial boundary conditions for the regularized logarithmic Schrodinger equation are designed by applying the unified approach, which based on the idea of well-known operator splitting method. The regularized logarithmic Schrodinger equation defined on unbounded domains is reduced to an initial boundary value problem on the bounded computational domain, which can be solved by the finite difference method. The convergence and the stability of the reduced problem are analyzed by introducing some auxiliary variables. In order to choose the optimal absorb parameter in the local artificial boundary conditions, an adaptive algorithm is presented. Numerical results are reported to verify the accuracy and effectiveness of our proposed method.

The anti-biofouling performance of silver nanoparticles (Ag NPs) modified polyethersulfone (PES) membrane was evaluated during the concentration of fermentation broth. The Ag NPs containing membrane did not exhibit biofouling mitigation performance during the first filtration cycle, but could help to recover water flux upon physical cleaning. After three filtration-clean cycles, the Ag NPs containing membranes presented higher water flux and slower flux decline than the control membranes without Ag NPs. Ag NPs on the membrane surface facilitated the effective removal of cake layer. Moreover, the Ag NPs-containing membrane had no negative effects on the activities of bacteria in fermentation broth.

A green and sustainable technique is desired for juice concentration to increase its shelf life and save the transportation cost. In this study, we investigated an integrated forward osmosis-membrane distillation (FO-MD) process for juice concentration and developed a food preservative potassium sorbate as a renewable draw solute. The upstream FO process was used to concentrate apple juice in ambient operation conditions for preserving juice nutrition and flavor. Potassium sorbate preservative was developed as draw solute to minimize the accumulation of a draw solute in the concentrated juice without interfering juice flavor, and the slow diffusion of potassium sorbate preservative across the FO membrane to the feed juice concentrate can also prevent the bacterial growth during the concentration process by taking advantage of reverse salt flux. The downstream MD process was used to recover potassium sorbate draw solutes from the FO effluent and maintain the constant draw solute concentration for achieving stable water flux of FO membranes. Thin-film composite (TFC) polyamide membranes and poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrospun nanofibrous membranes were fabricated and employed in the FO and MD processes, respectively. Results illustrate that the integrated FO–MD process presents a synergistic flux balancing behavior and achieves a constant water flux for both FO and MD membranes. The FO–MD process was able to continuously concentrate apple juice over long-term bench-scale operation. Importantly, the concentrated apple juice has almost no loss in nutrition and also has very low amount of potassium sorbate (0.45 g/L) far below the required maximum level in food industry (1.00 g/L). Our work provides a food preservative potassium sorbate draw solute facilitated FO-MD process for juice concentration, which may have practical application potentials in the food processing.

Water/energy sustainability has initiated strong academic interests in the development of forward osmosis (FO) to produce clean water. High water flux is critical to operate FO efficiently in industrial applications. Operation parameters including draw solution (DS) concentration and temperature highly affect water flux. As such, we investigated impacts of DS concentration and temperature on water fluxes of one commercial thin-film composite FO membrane via theoretical analysis and experimental measurement. Solution-diffusion model was revised by incorporating all concentration/temperature-related parameters. Results demonstrated the validity of revised SD model by comparing experimental and theoretical water fluxes at a wide DS concentration/temperature range. Concentration/temperature-induced water flux increment efficiencies (CIE and TIE) were introduced to quantify utilization efficiencies of high-salinity water and heat. Results revealed that water fluxes were increased with the increase of both DS concentration (0.5–5.0 M) and temperature (18–50 °C). However, the CIE decreased with the increase of DS concentration, but increased with the increase of temperature. Furthermore, the TIE increased with the increase of both DS concentration and temperature from 25 to 47 °C. Correlation coefficient of CIE and TIE was defined and calculated to optimize the FO process efficiency through identifying favorable zones of DS concentration and temperature.

Sludge thickening from sewage treatment plants is an essential step in reducing the sludge volume and processing cost of the subsequent treatment. Forward osmosis (FO) technology is one of the research endeavors used in the field of membrane separation and feed solution concentration. However, the traditional used single-skinned FO membranes encounter the problems of serious internal concentration polarization (ICP) and fouling phenomenon within porous substrates. A novel double-skinned FO membrane was proposed in this study in order to enhance the anti-fouling performance and mitigate the ICP phenomenon. Single-skinned FO membrane using the same substrate was also fabricated. Results demonstrated that the double-skinned FO membrane significantly reduced ICP and exhibited higher flux when using draw solutions with high concentrations as compared to the single-skinned FO membrane. Furthermore, the double-skinned FO membrane demonstrated reasonably high-water flux (11.6 LMH), whereas zero flux was recorded from the single-skinned FO membrane when using the feed solution that contained 15.0 g/L organic foulants in the fouling tests. At last, the double-skinned FO membrane exhibited superior anti-fouling properties and much higher flux than that of single-skinned FO membrane operated under both modes during the long-term sludge thickening process, indicating the great potential of the double-skinned FO membrane to deal with the high-water-content sewage sludge in the water treatment process.

Membrane fouling and degradation caused by free chlorine oxidation seriously hinder the long-term operation of aromatic polyamide (PA) thin-film-composite (TFC) membranes. In this study, sulfonamide monomers 4-aminobenzene sulfonamide (4-ABSA) and 2-aminoethanesulfonamide (2-AESA)) were facilely grafted onto the PA RO membranes surface via layer-by-layer interfacial polymerization (LbL-IP) method, endowing with much improved water flux, antifouling, and chlorine-resistance properties. The chemical compositions and surface properties of the RO membranes were systematically investigated by various techniques, as FTIR and XPS results clearly showed that sulfonamide groups were successfully grafted onto RO membranes’ surface. Compared to the pristine membrane, the water flux of the two modified membranes increased by 50.8% and 59.1%, reached 3.65 ± 0.15 L m−2 h−1 bar−1 and 3.85 ± 0.05 L m−2 h−1 bar−1, respectively, meanwhile their NaCl rejection remained above 99.25 ± 0.08%. Due to the improvement of surface hydrophilicity and decrease of surface roughness, the antifouling performance of the modified membranes was greatly improved. Moreover, the N–H moieties on sulfonamide can act as sacrificial units for free chloride attack to significantly improve the chlorine-resistance performances of the modified RO membranes compared to the pristine one, with NaCl rejection remain above 98.95 ± 0.09% after chlorination intensity of 8000 ppm⋅h under acidic condition of pH 4. This simple and efficient surface grafting strategy and modifying materials make it have great application potential in the field of water treatment.

The increasing accumulation of pharmaceuticals in aquatic ecosystems could impair freshwater quality and threaten human health. Despite the adsorption of pharmaceuticals on biochars is one of the most cost-effective and eco-friendly removal methods, the wide variation of experimental designs and research aims among previous studies pose significant challenge in selecting biochar for optimal removal. In this work, literature data of 1033 sets with 21 variables collected from 267 papers over ten years (2010–2020) covering 19 pharmaceuticals onto 88 biochars were assessed by different machine learning (ML) algorithms i.e., Linear regression model (LM), Feed-forward neural networks (NNET), Deep neutral networks (DNN), Cubist, K-nearest neighbor (KNN), and Random forest (RF), to predict equilibrium adsorption capacity (Qe) and explore adsorption mechanisms. LM showed the best performance on ranking importance of input variables. Except for initial concentration of pharmaceuticals, Qe was strongly governed by biochars' properties including specific surface area (BET), pore volume (PV), and pore structure (PS) rather than pharmaceuticals’ properties and experimental conditions. The most accurate model for estimating Qe was achieved by Cubist, followed by KNN, RF, KNN, NNET and LM. The generalization ability was observed by the tuned Cubist with 26 rules for the prediction of the unseen data. This study not only provides an insightful evidence for data-based adsorption mechanisms of pharmaceuticals on biochars, but also offers a potential method to accurately predict the biochar adsorption performance without conducting any experiments, which will be of high interests in practice in terms of water/wastewater treatment using biochars.

Membrane biofouling remains a major limiting factor for the membrane-based water purification technology. The development of antibacterial membrane surfaces is very important for membrane biofouling mitigation. In this study, we developed a one-pot method of synthesizing silver nanoparticles (Ag NPs) and immobilizing them onto membranes via simply soaking the membranes in a mixture solution of silver nitrate, poly (ethylene glycol) methyl ether thiol (mPEG-SH) and dopamine. Results illustrate that mPEG-SH works as a ligand to slow down the reduction process of silver ions by dopamine for the synthesis of Ag NPs in a controllable manner and also the prevention of Ag NPs aggregation in solution. Moreover, the Ag NPs could be in situ immobilized onto polysulfone ultrafiltration membrane, glass fiber membrane and stainless steel, regardless of their surface properties, but the size of Ag NPs was affected by the substrates. In addition, the Ag NPs immobilization on the polysulfone ultrafiltration membranes increased the bovine serum albumin rejection rate of membrane by 16%, but decreased membrane permeability by 14% compared to that of the pristine membranes. The Ag NPs containing membranes exhibited outstanding antibacterial properties with more than 90% antibacterial efficiency against both Gram-negative bacteria Escherichia coli and Gram-positive bacteria Staphylococcus aureus. During the filtration test, the silver release from the Ag NPs containing polysulfone ultrafiltration membranes was very slow and the total accumulation of silver ions released from the membranes was only 7% of its initial Ag NPs loading after 24 h filtration operation. The silver ion concentration in the permeate water was 0.35 ± 0.16 ppb, far below the maximal contaminant limit of silver ions in drinking water with no risk for the application of Ag NPs incorporated membranes to treat water. Our work provides a facile and universal approach of synthetizing and simultaneously immobilizing Ag NPs onto diverse membranes for antibacterial properties.

In the present work, a dual signals electrochemiluminescence (ECL) ratiometric strategy was designed based on the synergic effect of the catalysis effect and ECL resonance energy transfer. It was found that CdSe quantum dots (CdSe QDs) can catalyze the oxidation of luminol to promote the signal intensity of luminol at 0.45 V. At the same time, a stronger cathodic ECL peak at −0.75 V from CdSe QDs was observed, which could be attributed to the resonance energy transfer between luminol as a donor and CdSe QDs as an acceptor. Moreover both signals from two different potentials increased with the increase hydrogen peroxide concentration. On the basis of the above results, an enzyme-free ECL sensor was fabricated by immobilization of coating CdSe QDs on Au-graphite oxide (GO-Au) composites modified glassy carbon electrode (GCE), and luminol solution as probe solution, which was used to detect rapidly and sensitively hydrogen peroxide in the range of 0.5–500 μM with a detection limit of 0.5 μM based on the ration of two signals. The sensor exhibited good reproducibility and sensitivity, suggesting that the simple method will be promising in the detection of active oxygen in environmental samples.

Membrane distillation (MD) works as a promising alternative of RO to desalinate hypersaline water owing to its unique advantages including high concentration brine tolerance, 100% theoretical solute rejection, and low operating pressure. Hydrophobic MD membranes face critical challenge to treat industrial wastewaters containing low surface tension substances because these substances led to membrane wetting with loss of membrane permeability and rejection. In this study, we report a simple and facile approach to fabricate amphiphobic polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun nanofibrous membranes with anti-wetting property. 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS) was used to fluorinate PVDF-HFP fibers and was then crosslinked to form a network upon dealcoholization under thermal treatment. The FAS-coated PVDF-HFP nanofibrous membranes exhibited great stable amphiphobicity with high contact angles against both water and oil, even challenged under critical conditions including boiling water, and strong base and acid etchings. Surface fluorination of PVDF-HFP nanofibrous membrane with the FAS coating did not sacrifice its permeate flux and salt rejection much. The fabricated amphiphobic nanofibrous membrane exhibited robust MD performance in the long-term operation and also in the presence of surfactant sodium dodecyl sulfate in the feed saline solution.

Forward osmosis (FO) has increasingly penetrated into traditional process, i.e. microalgae dewatering, to become one of the new energy saving technologies. However, FO membranes can be fouled by soluble algal products (SAP) and fouling behavior of the membrane is not clear due to the variety of SAP composition. In this work, two types of membranes including a self-made TFC and a commercial CTA, and three kinds of draw solutions including NaCl, MgCl2 and CaCl2 were adopted to investigate the dewatering of SAP from microalgae of Chlorella vulgaris. The dependence of permeate flux and foulants composition on the membranes, membrane orientation and reverse salt diffusion were then compared for membrane fouling behavior. The results showed that TFC membrane exhibited higher water permeability but more loss of water flux in comparison with CTA. The SAP was inclined to be adsorbed by TFC membrane while adsorbate was easier to be removed by physical cleaning. By contrast, the pollutants accumulated on the membrane surface of CTA were much more irreversible. The interaction between SAP from feed solution and calcium cations from draw solution induced the formation of cake layer on the surface of TFC membrane while irreversible granular deposits of SAP were found accumulated on CTA membrane surface. Possible membrane fouling mechanism was finally discussed for better fabrication of anti-fouling forward osmosis membranes, thus to propel the integration of forward osmosis with traditional field of microalgae dewatering.

Osmotic microbial fuel cell (OsMFC) integrating forward osmosis into microbial fuel cell (MFC) favors the merits of organic removal, bioenergy generation, and high-quality water extraction from wastewater. This study demonstrated an 18.7% power density enhancement over a conventional MFC due to the water-flux-facilitated proton advection and net positive charge (NPC)-flux-promoted countercurrent proton exchange. Among the three examined membrane cleaning methods, chemical cleaning using 0.2% NaClO was found to be especially effective in removing organic foulants composed of proteins and polysaccharides, resulting in a water flux recovery of up to 91.6% with minimal impact on average maximum power density and internal resistance. The effects of operating parameters including anode HRT and draw solution concentration were studied. Shortening HRT from 6.0 to 3.0 h increased power density by 78.0% due to a high organic loading rate and a slightly reduced polarization concentration. Increasing draw solution concentration from 0.2 to 1.0 M NaCl enhanced power density by approximately 2.7-fold due to enhanced proton advection. Water-flux-facilitated proton advection played a more important role in determining the electricity generation performance of OsMFC than the NPC-flux-promoted countercurrent proton exchange under varied operating conditions.

Water contamination by organic dyes has become a serious environmental pollution. Here, a facile, green and cost-effective synthesis approach was developed to in situ grow silver nanoparticles (Ag NPs) on the eco-friendly and low cost natural material montmorillonite (Mt) through dopamine chemistry. The loading amount of silver on the montmorillonite reached 20 mass %. The Ag NPs supported montmorillonite (Ag NPs@Mt) exhibited excellent catalytic performances to reduce a model organic dye methylene blue in the presence of NaBH 4 with catalytic efficiency higher than 98% and apparent reduction rate constant k app higher than 1.70 min − 1 . More importantly, the Ag NPs@Mt was proven to show excellent recyclability for at least 20 cycles and long-term stability for one month soaking in water. This low-cost and recyclable Ag NPs@Mt shows great potential in large scale application to treat dye containing wastewater.

Polymeric membranes are more practicable to the cost-effective and energy-efficient solvent recovery and molecular separation in solvent mixtures, but the construction of structure-defined chemically stable as well as high permeance polymer membranes for organic solvent nanofiltration (OSN) applications is an important challenge. Herein, we designed and constructed crosslinked block copolystyrene membranes containing flexible alkylcarboxylated and alkylsufonated side chains for high-separation performance in organic media. The flexible side chains anchored on the all-carbon network render the membranes with good dimensional flexibility due to the rational manipulation of the intermolecular and intramolecular bonding interactions within the crosslinked structured polymer chains. Depending on the crosslinking degree, the resultant membranes exhibited outstanding stability in polar protic solvents, mild polar aprotic solvents (THF, acetonitrile and acetone) and nonpolar solvents. Specifically, the CPS-24% membrane with a cutoff of 380 g mol−1 showed good ethanol permeance of 4.16 L m−2 h−1 bar−1 and a high-efficient molecular separation (>96%) of a broad range of small molecular weight solutes (organic dye molecules, organic building blocks and antibiotics). The membrane also achieved molecular level selectivity of two molecules with a mass difference down to 141 g mol−1, which is attractive for molecular separation in the chemical and pharmaceutical industry. This work provides a promising strategy to improve selective solvent permeation and separation of organic molecules in OSN membranes by introducing flexible hydrophilic/hydrophobic side chain domains into the main backbone of rigid polymer structures.

Forward osmosis (FO) technology has drawn increasingly research interests in juice concentration due to its great advantages in producing high-quality concentrated juice. However, the lack of suitable draw solutes is a significant obstacle hindering the practical application of FO for juice concentration. In this work, a series of food preservatives were systematically investigated as draw solutes in the FO system. By careful evaluation of these preservatives, we selected 4 M sodium diacetate (SDA) as one model of draw solution to concentrate grape juice in a 72-h continuous FO test. The concentrated grape juice with 5.14 folds was obtained with no loss of the titratable acidity and the vitamin C content. Moreover, the SDA accumulation in the concentrated product was only 2.0 ± 0.1 g/kg, after being diluted to regenerate juice, the preservative concentration in juice is 0.39 g/kg, which is lower than the safety limit of SDA (0.5 g/kg, FAO). Our findings demonstrate the application potential of the preservative draw solutions for juice concentration in the FO.

It has been well recognized that there are a number of indoor contaminants including particulate matter, gaseous pollutants and microbials. The removal of indoor contaminants often requires multiple layers of various air filters. Herein, we report on a multifunctional air purifying filter produced by the hydrothermal growth of ZnO nanorod-wrapped PTFE nanofibers, constructed of nanostructured Ag deposited on the ZnO nanorods with a hierarchical structure for gas contaminant removal. Atomic layer deposition (ALD) was used to seed a layer of ZnO nanoseeds onto the PTFE fibrils which were then subjected to a hydrothermal reaction to form ZnO nanorods. Ag nanoparticels were subsequently assembled on the surface of the ZnO nanorods via a silver electroless deposition reaction. The resulting composite membrane exhibited an excellent dynamic antibacterial property of ~100% and a formaldehyde degradation rate of 60%. Compared with the pristine membrane, the gas permeation of the composite membrane increased from 227.26 m3 m−2 h−1 kPa−1 to 275.36 m3 m−2 h−1 kPa−1. The successful fabrication of this composite membrane with remarkable antibacterial and excellent formaldehyde degradation performance may provide a new route for the preparation of indoor air purification filters.

The commonly used commercial hydrophobic membranes are facing great challenges in wetting and low permeation when used in membrane distillation (MD) because of the limited materials and structures. To address these problems, we herein fabricated a kind of carbon nanotubes (CNTs) enhanced membrane with high flux and stable performance in membrane distillation, where a porous hydrophobic network of multi-walled carbon nanotubes (MWCNTs) was spray-coated onto the commercial flat-sheet hydrophobic membrane surface. Then, we systematically investigated the impact of the CNTs loading on the substrate surface properties, membrane structures and MD performance (flux and rejection), and experimentally illustrated the role of CNTs towards improving MD performance. Results illustrate that there is an optimal match of the CNTs spray amount with the substrate pore size and the substrate materials to achieve the maximum specific surface area of membrane, and thus the maximum flux and salt rejection of the resultant CNTs-enhanced membrane, which is governed by the interfacial energy of the CNTs and the substrate, and thus the CNTs packing density. Results find that the CNTs packing density decreases with the decrease of the substrate free surface energy, and the loosest CNTs packing is formed on the polytetrafluoroethylene (PTFE) membrane with the lowest free surface energy. Under the optimized conditions, the CNTs enhanced PTFE membrane exhibited salt rejection of >99.9% and water flux of 33.2 LMH in MD, which was three times as high as that of the pristine PTFE membrane under the temperature difference of 40 °C between hot and cold streams when operated in direct contact membrane distillation. Our research here provides an efficient method to enhance the permeation and stability of commercial membranes by spray-coating CNTs and also supplies some insights on the design of next-generation MD membranes.

Hydraulic fracturing flowback and produced water is a highly impaired wastewater containing dissolved salts polar and non-polar organic compounds, oil and surfactants. Here a combined electrocoagulation - microfiltration – membrane distillation process has been used to treat this wastewater. Electrocoagulation followed by microfiltration was used to pretreat the wastewater prior membrane distillation. The initial total dissolved solids (TDS) concentration was extremely high being 245,300 mg L−1. After electrocoagulation, the total organic carbon (TOC) was reduced from 120 mg L−1 to 64 mg L−1. Tangential flow microfiltration using a 0.1 μm pore size polyethersulfone membrane was used to separate the particulate matter after electrocoagulation and to further reduce the TOC to 44 mg L−1. Membrane distillation was used to desalinate the pretreated produced water resulting in a high quality treated water (TDS of 56 mg L−1 and TOC 1 mg L−1). Three membranes with very different surface morphology were used: commercially available polyvinylidene fluoride, electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers and multiwalled carbon nanotube coated polytetrafluoroethylene. The TDS in the retentate increased to over 350,000 mg L−1. During membrane distillation, the temperature of the feed tank was maintained at 36 °C while the feed entered the module at 60 °C in order to minimize scaling on the membrane. The surface properties of an ideal membrane that is resistant to wetting and provides high flux is likely to depend on the TDS and properties of the wastewater.

Forward osmosis (FO) has increasingly been an energy saving technology in microalgae dewatering, whereas membrane fouling is still a major obstacle for FO application. To explore the fouling mechanism of algal cells and their organic matters during microalgal FO dewatering process, Chlorella vulgaris and Scenedesmus obliquus were adopted as algae species, and the algae-derived foulants including algae cells, soluble algal products (SAP) and algal broth were used as feed solutions. The water fluxes behaviors of algal foulants had been investigated, and the dissolved organic carbon (DOC), protein and carbohydrates proportions of the feed solutions were then characterized, followed by the scanning electronic microscopy (SEM) and the analysis of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory for the FO membrane foulants. The results indicated that algal broth resulted in the fastest flux decline due to the combined fouling between SAP and algae cells. The competitive adsorption phenomenon between cells and SAP was found in C. vulgaris broth but not in S. obliquus, resulting in a high protein content loss in the feed solution of C. vulgaris. The fouling potential of those individual and combined feed solutions could be well predicated using the XDLVO theory, and the higher the interfacial energy, the faster the flux decline was found for both adhesion and cohesion stages. The findings improve the understanding of FO membrane fouling mechanism by microalgae, indicating the selection of algae species for FO processes.

Polyethersulfone (PES)/sulfonated polysulfone (SPSf)/TiO2 mixed matrix membranes (MMMs) were fabricated using non-solvent induced phase inversion (NIPS) technique for oil-in-water emulsion separation. The performance of the membrane was tailored by tuning the morphology through the addition of TiO2 nanoparticles (NPs) (0.05–0.15 wt %) and by varying the polymer concentrations (18–28 wt). The optimum concentration of TiO2 was found to be 0.075 wt %), where the water permeability and solute rejection trade-off neutralised. In this membrane the polymer concentration was 22 wt %. In terms of performance, the membrane had pure water permeance of 555.2 LMH bar-1, 90% oil rejection and 89.5% permeance recovery rate (PRR) at an initial concentration of 900 ppm. The surface porosity was 13.1%. Molecular dynamic (MD) simulations and spectroscopic analyses proved that the NPs formed hydrogen bonds with the polymer chains. This resulted in two effects with ripple impacts: a) slowed movement of polymer chains or slow solid-liquid phase separation, leading to the MMMs with the thicker top layer and high surface porosity, and b) stable and even distribution of NPs within the framework as observed with elemental mapping. Accordingly, the MMMs obtained desired asymmetric features corresponded to their overall superior performance. In conclusion, small concentrations of TiO2 NPs can be used to successfully modify morphology and separation performance of membranes used for oil-in-water emulsion filtration.

In this work, antifouling thin-film composite (TFC) nanofiltration (NF) membrane having zwitterionic PEI moieties was fabricated through the layer-by-layer interfacial polymerization (LbL-IP) via grafting hyperbranched polyethyleneimine (PEI) onto the polyamide surface, followed by in-situ N-methylation of PEI and then quaternization using 3-bromopropionic acid to form zwitterionic PEI. The successful surface modifications of TFC NF membrane with PEI and zwitterionic PEI were confirmed by XPS and ATR-FTIR results. Benefitting from the strong hydrophilicity and hyperbranched steric structure, the zwitterionic PEI-grafted TFC membrane (NF-ZPEI) exhibited a stronger hydration capacity and a thicker hydration layer than the PEI-grafted TFC membrane (NF-PEI) and the control sample (NF-PA). Meantime, the water permeability of NF-ZPEI membrane was enhanced by 11.6% higher than the control sample. The NF-ZPEI membrane also exhibited the improved ion selectivity of having a decreased rejection towards NaCl and maintaining a high rejection towards divalent ions. Dynamic fouling experiments were performed to demonstrate the impact of surface hydrophilicity and surface charge on the membrane fouling performances. Results illustrate that the zwitterionic PEI grafted on the TFC NF membrane mitigated the electrostatic attraction between the membrane surface and protein foulants, and exhibited the improved antifouling properties of having a low flux decline and a high flux recovery. Our work provides some insights on the zwitterionic surface modification of the TFC NF membrane with both the enhanced water permeability and the antifouling properties towards charged foulants.

We report a novel high-flux nanofiltration (NF) membrane for the precise separation of dyes and salts, which was fabricated using polysulfone-block-polyethylene glycol (PSf-b-PEG) block copolymer through the non-solvent induced phase separation (NIPS) method. The PSf-b-PEG membrane exhibited a very dense sponge-like porous structure with rich interconnected pores, contributing to its superior mechanical strength of 22.4 ± 0.9 MPa. The pore size of PSf-b-PEG membrane was mostly distributed around 1.3 nm in diameter with the mean effective pore size of 3.8 nm in diameter, while the membrane molecular weight cut off (MWCO) towards dyes was about 655 Da. The PSf-b-PEG membrane exhibited a very high water permeance of 49.3 ± 0.9 L m−2 h−1 bar−1 and a precise separation of salts and dyes with high above 98% Congo Red dye rejection and nearly 100% Na2SO4 passage, succeeding the separation performances of current NF membranes used for the separation of dyes and salts. Long-term NF tests prove the highly stable and outstanding separation performances of PSf-b-PEG membrane with the top dense skin layer as the effective selective layer. Our work suggests that the PSf-b-PEG membrane has a great potential to be further optimized and used for practical applications.

A dual-layered hierarchical fibrous composite (HFC) membrane with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a thin active layer and poly(ethylene terephthalate) (PET) as a thick support layer was fabricated through electrospinning process. The membrane was tested for the concentration of clarified pomegranate juice through the osmotic membrane distillation (OMD) process. Experimental data showed that the transmembrane water flux until 8.621 ± 0.235 kg.m−2. h−1 was achieved at 25 ± 1 °C, which is about 4-fold higher than most of the reported work. The juice was successfully concentrated to 51.3 ± 0.052°Bx in a total time of 25.5 h. Membrane hydrophobicity analysis showed that the contact angle of the membrane dropped from 143.7°±3° to 120.1°±3°, while the liquid entry pressure decreased from 28.0 ± 1.8–25.0 ± 1.7 kPa, after the completion of the OMD process. Detailed morphology analysis depicted that pore blockage occurred due to the gel layer formation when the juice viscosity increased exponentially during the final stages of OMD process. Gel layer formation along with random fouling spots were found to be the main cause of drop in water vapor flux. However, simple washing of the membrane with deionized water effectively cleaned the fouling areas and removed the gel layer from the pores of the membrane. The first-ever application of dual-layered electrospun HFC membrane in the OMD concentration of pomegranate juice thus displayed a satisfactory performance, benefiting from the unique structures of the HFC membrane having the minimized mass transfer resistance and durable antifouling performance.