Thin-film Nanofibrous Composite Research Articles

Structure design and performance optimization of PVDF-CTFE nanofibrous composite nanofiltration membrane modified by C–Cl active site grafting

The substrate membrane plays a crucial role in determining the performance of composite nanofiltration membranes prepared by interfacial polymerization (IP). In this study, persistent hydrophilic modification of polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-CTFE) was achieved by incorporating N-methylglucamine (N-MG) without altering the membrane's morphology or pore size. Moreover, thin-film nanofibrous composite (TFNC) nanofiltration membranes were prepared using the surfactant assembly regulated interfacial polymerization (SARIP) method with the modified PVDF-CTFE@N-MG nanofibrous membrane as the substrate. The effect of N-MG addition on the substrate membrane's hydrophilicity and the structure and performance of the polyamide (PA) separation layer was investigated. The results showed that the addition of N-MG significantly improved the hydrophilicity of the PVDF-CTFE nanofibrous membrane. The TFNC-5 membrane, prepared with the modified PVDF-CTFE@N-MG nanofibrous membrane as the substrate, exhibited permeability exceeding 13.5 L m−2 h−1·bar−1 for various dye solutions at 3 bar pressure, with rejection rates above 98 %. It also demonstrated excellent selective separation performance (separation factor for NaCl/Orange G reaching 97.38) and long-term operational stability. This work provides a method for the preparation of low-pressure, high-flux nanofiltration membranes, which is applicable to seawater desalination and dye wastewater treatment.

Low temperature regulated reverse interfacial polymerization for fabricating thin film composite membranes based on nanofibrous substrates

In this study, a novel thin film nanofibrous composite (TFNC) nanofiltration (NF) membranes comprised of polyacrylonitrile (PAN) nanofibrous supporting layer and polyamide (PA) compact separating layer was constructed by low-temperature-controlled reverse interfacial polymerization (LTIP-R) at − 5 °C. The strategy for lowering the temperature of organic phase solution played a crucial role in forming a dense and thin PA layer on the PAN nanofibrous substrate with submicron pores. The results revealed that the reduced evaporation rate of organic phase at low temperature was contributed to maintaining a complete and uniform interface for the following reverse IP process, effectively overcoming shortcomings of surface incompleteness and easy infiltration of PA barrier layer. Owing to the reduced thickness and the enhanced wholeness of the PA separating layer via LTIP-R, the optimized TFNC membranes exhibited NF performance with great rejection of divalent salt ions (98.2%) and an improved permeation (13.3 L‧m−2‧h−1‧bar−1). This work would provide an efficient and facile method to fabricate high performance NF membranes for practical applications.

Composite nanofiltration membrane prepared by depositing barium alginate interlayer on electrospun polyacrylonitrile substrate

Interlayer-regulated thin-film nanofibrous composite (TFNC) membranes were fabricated extensively for seawater purification, but the mechanical and stability performance of the composite membranes continually existed a tremendous challenge. In this work, a composite nanofiltration (NF) membrane was prepared by interfacial polymerization (IP) method of piperazine (PIP) and trimesoyl chloride (TMC) combined through coating barium alginate (BaAlg) on the polyacrylonitrile substrate obtained by the electrospun technology. With the deposition of the BaAlg hydrogel interlayer, the diffusion rate of PIP depressed and a homogeneous polyamide (PA) selective layer could be realized. The TFNC membranes of BaAlg interlayer modified via cross-linking sodium alginate (SA) with barium ions had higher stability, hydrophilicity and separation performance. The impact of SA content, operating pressure and time on the NF membrane desalination performance was explored. The mechanical properties of composite NF membranes were greatly improved and the tensile strength could be as high as 8.17 MPa. The preferred TFNC membranes could display a permeation flux of 112.5 ± 1.8 L·m−2·h−1, and the Na2SO4 retention rate was up to 98.7 ± 0.5 %. The prepared NF membranes are of great importance in seawater purification, which is conducive to obtaining high performance with excellent development potential.

Coordination of thin-film nanofibrous composite dialysis membrane and reduced graphene oxide aerogel adsorbents for elimination of indoxyl sulfate

• A novel combination of PVA/PAN TNFC dialysis membrane with rGO aerogel was proposed. • The rGO aerogel exhibited good adsorption performance for indoxyl sulfate. • The coordination of TFNC membrane and rGO lightened conventional hemodialysis. The protein-bound uremic toxins, represented by indoxyl sulfate (IS), have been associated with the progression of chronic kidney disease and the development of cardiovascular disease in the presence of impaired renal function. Herein, we proposed a novel strategy of thin-film nanofibrous composite (TNFC) dialysis membrane combined with reduced graphene oxide (rGO) aerogel adsorbents for clinical removal of IS as well as high retention of proteins. The TFNC membrane was prepared by electrospinning in conjunction with coating-reaction method and proved to have good selectivity and permeability. To further improve the removal rate of toxins, we used a medium hydrothermal method following by freeze-drying treatment to obtain the rGO aerogel adsorbents. It exhibited excellent adsorption for IS with a maximum adsorption capacity of 69.40 mg∙g −1 through π−π interaction and hydrogen bonding interaction based on Langmuir isotherm models. Time-dependent absorption experiments showed that it reached adsorption equilibrium within 4 h, which was matched with the hemodialysis time. The coordination was significantly exhibited by introducing rGO aerogel blocks into the dialysate for absorbing the diffused free IS during hemodialysis. Taking the advantages of the TFNC dialysis membrane and the rGO aerogel, the volume of dialysate for hemodialysis was only one-tenth of that without adsorbent blocks but with very comparable dialysis performance (the clearance of IS at 51.8% and the retention of HSA over 98%), which could lighten conventional hemodialysis effectively and be benefit to realize the miniaturization of the hemodialysis equipment. Therefore, the coordination of the TFNC dialysis membrane and rGO aerogel adsorbents would open a new path for the development of portable artificial kidney.

Acid mine drainage treatment by fertilizer drawn forward osmosis for irrigation

This work utilized fertilizer driven forward osmosis (FDFO) to extract fresh water from acid mine drainage (AMD) wastewater for irrigation, and investigated the effects of draw solutes on membrane fouling behaviours. The carbon nanotubes (CNTs) and polydopamine (PDA) were coated on the thin film nanofibrous composite (TFNC) membrane #FO-0 as anti-fouling modification. When 1 M NH4H2PO4 (MAP) and 500 mg/L copper AMD wastewater (pH=3.0) used as draw and feed solutions, #FO-0 and PDA-coated TFNC membrane (#FO-PDA) exhibited rapid declines of water fluxes due to the dense fouling layer. In contrast, the CNT-coated membrane #FO-CNT exhibited the lowest flux decline of 26.0% attributed to better hydrophilicity, the lowest roughness and neutral surface charge. All the TFNC membranes exhibited insignificant membrane fouling when (NH4)2SO4 (SOA) was used as draw solute. Additionally, the osmotic backwashing could effectively recover water flux. The discharged draw solution promoted plant growth without posed potential health threat.

Highly permeable composite nanofiltration membrane via γ-cyclodextrin modulation for multiple applications

The treatment of pharmaceutical wastewater has become a worldwide problem. Highly efficient treatment for wastewater is extremely critical for ecological environment. Herein, a thin-film nanofibrous composite (TFNC) nanofiltration (NF) membrane modulated by γ-cyclodextrin (γ-CD) was prepared via interfacial polymerization. The γ-CD and piperazine (PIP) were adopted and acting as the mixed reaction monomers in aqueous phase for the fabrication of the separation layer. Not only PIP, γ-CD units would also react with organic phase trimesoyl chloride (TMC) at the interface and participate into the polymerization network. Compared with pure polyamide TFNC membranes, the γ-CD modulated TFNC membranes demonstrated thinner skin thickness. Owing to the 3D hollow structure of γ-CD, the self-contained through cavities would provide additional direct nanochannels to facilitate the water transport. Under 0.5 MPa, the optimized PIP0.5γCD0.5 and PIP0.5γCD1.5 TFNC membranes showed much higher permeate flux of 23.27 and 26.34 L m-2h−1 bar−1, respectively, than that of pure polyamide membranes (9.13 and 9.85 L m-2h−1 bar−1) and the Na2SO4 rejection remained high (>98.7%). Moreover, both TFNC membranes exhibited extremely high rejection (>99%) for several pharmaceuticals (doxycycline hydrochloride, tetracycline, and amoxicillin), and the PIP0.5γCD0.5 TFNC membrane exhibited a good separation factor (31.8) for NaCl/tetracycline solution. In addition, both optimized TFNC membranes showed good pressure resistance and long-term operating stability. This research revealed a facile modulation strategy for the fabrication of high-performance NF membrane and indicated the great promise for desalination, pharmaceuticals wastewater treatment and antibiotics concentration.

Development of high‐flux aciduric ultra‐thin nanofibrous pervaporation composite membrane for acetic acid dehydration

AbstractAcetic acid is an essential intermediate chemical in industry. Traditional inorganic membrane cannot meet the demand of high‐efficient dehydration and polymeric membrane is restricted by its low organic solution resistance. In this work, a novel aciduric pervaporation composite membrane was successfully generated by fabricating an ultrathin polysulfonamide (PSA) layer on the polyacrylonitrile (PAN) nanofibrous substrate via interfacial polymerization (IP) method. Through the optimization of fabrication process including selecting the suitable structure of diamine (taking three types aliphatic amines as candidates), optimizing the concentration of two phase solutions, the resultant thin‐film nanofibrous composite (TFNC) membrane was fabricated by using aliphatic amine triethylenetetramine (TETA: 3.0 wt%) and 1, 3‐benzenedisulfonyl chloride (BDSC: 1.0 wt%) as IP monomers and the network structure with suitable sieving size was constructed. The ultrathin aciduric PSA selective layer (thickness: 104 ± 15 nm) endowed the TFNC membrane with excellent separation efficiency. For dehydrating 70 wt% acetic acid aqueous solution at 60°C, PSA‐3.0‐1.0/PAN TFNC membrane exhibited competitive separation efficiency and great acid stability. It possessed extremely high permeate flux (15,321 g/m2 h) with stable separation factor (109). For long‐term acid dehydration evaluation, PSA/PAN membrane showed great stability during 7 days pervaporation. This work took advantage of traditional IP method for designing a novel pervaporation membrane with aciduric chemical structure, suggested an effective and facile approach to develop novel pervaporation membranes for harsh environment separation.

High-performance TFNC membrane with adsorption assisted for removal of Pb(II) and other contaminants

Rapid and thorough removal of heavy metal ions in wastewater is critical for the urgent need of clean water. Herein, we prepared a high-performance thin film nanofibrous composite (TFNC) membrane consisting of a polyacrylonitrile (PAN)-UiO-66-(COOH)2 composite nanofibrous substrate (CPAN) and a calcium alginate (CaAlg) skin layer. Owing to abundant adsorption sites of UiO-66-(COOH)2 MOF, the optimal CPAN-2 nanofibrous substrate showed excellent adsorption capacity for lead ions. The maximum Pb2+ adsorption capacity of CPAN-2 substrate calculated by Langmuir isotherm model was 254.5 mg/g. Meanwhile, due to the relatively loose structure of CaAlg skin layer, this TFNC membrane showed high water permeate flux about 50 L m−2h−1 at 0.1 MPa, and the rejection for dyes was higher than 95%. Therefore, CaAlg/CPAN TFNC membranes were appropriate for dynamic adsorption/filtration to remove Pb2+. Compared with original CaAlg/PAN membrane, the optimal CaAlg/CPAN TFNC membrane showed much better ability to treat Pb(II)-containing wastewater and had good recyclability. Most importantly, the CaAlg/CPAN TFNC membrane could treat 7659 L m−2 wastewater containing single lead ions under WHO drinking water standard, and effectively deal with more simulated lead-containing wastewater. This work could provide a substitutable solution for effective removal of heavy metal ions and other various contaminants in wastewater.

Dialysis/adsorption bifunctional thin-film nanofibrous composite membrane for creatinine clearance in portable artificial kidney

In this study, we proposed a facile strategy for the lightweight design for portable artificial kidney by using a novel dialysis/adsorption bifunctional thin-film nanofibrous composite (TFNC) membrane, which consisting of polyvinyl alcohol (PVA) hydrogel as a separation layer and polyacrylonitrile (PAN) nanofibrous membrane with UiO-66-(COOH)2 nanoparticles as a porous affinity substrate were developed to effectively remove creatinine and substantially reduce the volume of dialysate in dialysis process simultaneously. Here, as-synthesized UiO-66-(COOH)2 nanoparticles were strung through PAN nanofibers using colloid-electrospinning technique to prepare necklace-like nanofibrous affinity membrane for creatinine adsorption. The obtained PAN/UiO-66-(COOH)2 nanofibrous membrane (PAN-U) with optimum UiO-66-(COOH)2 loading (60 wt%) exhibited encouraging maximum adsorption capacities (54 mg/g) based on Langmuir isotherm models and pseudo-second-order kinetic models. In addition, the simulated dialysis results demonstrated that 62.8% of creatinine were eliminated and over 98% of bovine serum albumin (BSA) were rejected. Furthermore, the PVA/PAN-U TFNC membrane not only improved the clearance of creatinine in simulated blood, but also efficiently maintained the concentration of creatinine in simulated dialysate at a very low level compared to the pure PVA/PAN TFNC membrane. More importantly, the usage of dialysate in volume for PVA/PAN-U TFNC membranes in dialysis was only one tenth of that for PVA/PAN TFNC membranes but with very comparable dialysis performance. Therefore, the introduction of adsorption function in TFNC hemodialysis membrane may facilitate the development of the lightweight of portable artificial kidney.

High permeability composite nanofiltration membrane assisted by introducing TpPa covalent organic frameworks interlayer with nanorods for desalination and NaCl/dye separation

• A TpPa layer with nanorods was prepared as an auxiliary interlayer. • TpPa interlayer played a decisive role for the formation of PA skin layer. • The PA/TpPa-12/PAN membrane showed excellent nanofiltration performance and NaCl/dyes selectivity. Nanofiltration (NF) membrane with high permeability and selectivity is extremely crucial for water purification. Herein, we prepared a high permeability thin-film nanofibrous composite (TFNC) membrane via interfacial polymerization (IP) technique assisted by introducing TpPa covalent organic frameworks (COFs) interlayer with nanorods on the polyacrylonitrile (PAN) nanofibrous substrate for NF. TpPa COFs interlayer with nanorods played a decisive role in adjusting the structure and performance of polyamide (PA) skin layer. On the one hand, TpPa COFs interlayer could regulate the diffusion and transfer rate of piperazine in the aqueous phase solution during IP process, which would modulate the mophology and reduce the thickness of the PA skin layer. Meanwhile, the TpPa COFs nanorods could create massive voids under PA layer to enhance the flux of TFNC membrane. Additionally, the TpPa COFs with nanoporous structure themselves also provided additional nanochannels for water transport. The structure of COFs interlayer could be tuned by altering the Pa contents of aqueous phase solution, which further optimized the overall performance. The permeation water flux of optimal TFNC membrane could reach to 104.8 L m −2 h −1 with a relatively high rejection of 98.4% for Na 2 SO 4 under 0.5 MPa, which was about 2.3 times than that of the unmodified PA membrane prepared without TpPa COFs interlayer. Besides, the optimal membrane exhibited good selectivity to NaCl/dye solution (NaCl/Acid Fuchsin was 402.5 and NaCl/Congo Red was 398.0) and long-term test stability. This work showed a new avenue to prepare high-performance NF membrane for the potential applications in water desalination and dye wastewater recovery.

Highly solvent-durable thin-film molecular sieve membranes with insoluble polyimide nanofibrous substrate

Permselective thin-film composite membranes are gaining a significant role in solvent-based molecular sieving applications. Nevertheless, the lack of desirable substrate materials, which combines high flux, solvent resistance as well as a straightforward fabrication process, is still the biggest bottleneck for large-scale commercial implementation. For the first time, we propose to fabricate an insoluble polyimide nanofibrous substrate by a sequential strategy involving electrospinning polyamic acid followed by a thermal imidization. The water-absent electrospinning process leads to 1-fold enhanced mechanical strength and higher solvent-resistance of substrate compared to the conventional phase inversion process. The resultant thin-film nanofibrous composite (TFNC) membranes exhibit exceptional potential for nanofiltration by showing high permeability, rejection, and stability in water as well as polar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran compared to state-of-art membranes. The strategy of using electrospun insoluble polyimide as the substrate establishes a scalable approach to design high-performance TFNC membranes for a wide range of challenging molecular sieving applications.

Electrospun transition layer that enhances the structure and performance of thin-film nanofibrous composite membranes

Electrospun nanofibers with completely interconnected pore structures are increasingly considered as substrates for fabricating thin-film nanofibrous composite (TFNC) nanofiltration (NF) membranes. The poor adhesion between the large-pore substrate and dense selective layer has been considered as the bottleneck for wide application. This work presents the role of a transition layer on membrane structure as well as performance enhancement. Specifically, both polyethyleneimine (PEI)/polyacrylonitrile (PAN) transition layer and PAN substrate layer are formed by electrospinning. Interfacial polymerization (IP) is subsequently performed with trimesoyl chloride and piperazine. The introduction of the PEI modified transition layer improves the hydrophilicity, provides additional reaction sites for IP, and avoids the polymerization in the pores of nanofibers. The resultant composite NF membranes exhibit a compact and defect-free selective layer. Such an optimal structure leads to an excellent separation performance of 95.6% for orange ΙΙ dye (MW = 350.32 g/mol) rejection and 38.5 L m−2h−1 bar-1 for the pure water permeability. It exhibits stable long-term performance during low pressure (0.2 MPa) nanofiltration, which will afford significant directions for the actual application of the TFNC membranes in water purification and other fields.

High-performance polyamide composite membranes via double-interfacial polymerizations on a nanofibrous substrate for pervaporation dehydration

A novel double-interfacial polymerizations (double-IP) strategy was demonstrated for the maneuverable fabrication of high-performance polyamide (PA) composite membranes based on nanofibrous substrates for efficient isopropanol dehydration by pervaporation. Firstly, an ultra-thin auxiliary polyamide layer (A-PA) was synthesized on a highly porous polyacrylonitrile (PAN) nanofibrous substrate by using low concentration ethylenediamine (EDA) and trimesoyl chloride (TMC) solution, which decreased the reaction rate and prolonged polymerization time to achieve a smooth, relatively loose but intact A-PA layer. Secondly, a more compact PA selective layer (S-PA) was fabricated with relatively high concentration EDA and TMC solution on A-PA surface. Benefiting from the A-PA layer, the amount and diffusion rate of adsorbed EDA solution through the layer to contact TMC solution were effectively controlled in second IP process. S-PA layers tended to be more uniform, and there was no marked void or detachment observed between two PA layers. Significantly, the pervaporation performance of as-prepared membranes were tuned by changing the structure of S-PA layers with the assistant of different A-PA layers. The optimized two-tier polyamide (Bi-PA) thin-film nanofibrous composite (TFNC) pervaporation membranes exhibited high permeate flux (6075 g/(m2 h)) and enhanced separation factor (1314) for dehydrating 90 wt% aqueous isopropanol solution at 70 °C. This work may suggest an efficient and facile approach to fabricate high performance pervaporation membranes.

Physical Studies of Forward Osmosis Membranes Prepared by Cross-linking Polyvinyl Alcohol on Electrospun Nanofibers

The conventional nanofiber-supported forward osmosis (FO) membrane possessed some issues, for example, easy deformation and weak interfacial strength between the substrate and selective layer. A dual-layered composite membrane consists of electrospun nanofibrous membranes (ENMs) as the support layer and cross-linked polyvinyl alcohol (PVA) top coating as the active layer is fabricated. Hence, the objective of this work is to study the physical properties of the prepared PVA/ polyvinylidene fluoride (PVDF) composite membranes. The novelty of this work relies on the new exploitation of the prepared dual-layered thin film nanofibrous composite (TFNC) membranes via the cross-linked technique in the FO process. The experiment works include the fabrication of nanofibrous substrates and selective layer via electrospinning, followed by the PVA cross-linking process prior to the characterisation studies and FO evaluation. FO performance test revealed a comparable water flux with the conventional dual-layered composite membrane, besides exhibited a significantly low Js /Jw ratio. This study indicated that dual-layered cross-linked PVA on electrospun PVDF nanofibers is a promising approach to overcome the drawback of the existing issues in the conventional method of preparing surface coated composite membranes which is a viable option to manufacture high-performance TFNC-FO membranes.

Antifouling nanocellulose membranes: How subtle adjustment of surface charge lead to self-cleaning property

Membrane fouling is a major issue in wastewater treatment. In this study, a unique class of low fouling nanocellulose-enabled thin film nanofibrous composite (TFNC) ultrafiltration (UF) membranes was fabricated by coating of negatively charged TEMPO-oxidized cellulose nanofibers (CNF) on the porous electrospun polyacrylonitrile (ePAN) substrate. The surface charge density of the nanocellulose barrier layer was controlled by using CNF with different degree of oxidation (DO) and coating area density (AD, g/m2). The morphology, pore size distribution, hydrophilicity and zeta potential of these CNF-TFNC membranes were characterized, all of which exhibited excellent permeation flux (15-61 L m−2h−1 at 0.5 psi), high rejection ratio (>98%), and good antifouling tendency against bovine serum albumin (BSA). The practical antifouling and self-cleaning characteristics of CNF-TFNC membranes were further evaluated using biotreated municipal wastewater. The best performing membrane (CNF with 0.40 AD and 1.80 DO) achieved a near total flux recovery ratio (98 ± 2%) using simple hydraulic flushing. This could be attributed to the strong electrostatic repulsions between the CNF layer and foulants, both of which were negatively charged. Conversely, the commercial polyvinylidene difluoride (PVDF) UF membrane suffered severe fouling decay and very low flux recovery ratio (33 ± 3%). The results indicated the practicality of using charged CNF as a barrier layer for antifouling ultrafiltration membranes in wastewater treatment.

Customizing versatile polyamide nanofiltration membrane by the incorporation of a novel glycolic acid inhibitor

Novel thin film nanofibrous composite (TFNC) nanofiltration (NF) membranes comprised of polyacrlonitrile (PAN) supporting layer and polyamide (PA) separating skin layer were constructed by interfacial polymerization (IP) of trimesoyl chloride (TMC) with piperazine/glycolic acid (PIP/GLA) onto a PAN nanofibrous substrate. GLA in aqueous phase played a significant part in tuning the structures of PA skin layer. GLA molecules acted as an inhibitor to compete with PIP to react with TMC, tuning the pore size of the PA selective layer for versatile nanofiltration applications, such as desalination and dye separation. Especially, the optimized composite membranes NF3 (28.5 L m−2 h−1 bar−1, 96.4% Na2SO4 rejection) and NF6 (79.7 L m−2 h−1 bar−1, 99.2% Direct Red 80 rejection) exhibited high separation performance. In addition, the existence of the co-reactant GLA improved the anti-fouling performance of the composite membranes due to hydrophilic carboxyl groups of GLA itself. This work provided a simple and efficient method to finely tune the structural properties of PA skin layer for versatile nanofiltration applications.

Novel gelatin/polyacrylonitrile thin film nanofibrous composite membranes with high filtration performance

High performance thin film nanofibrous composite (TFNC) membrane consisting of a thin gelatin (GE) selective skin layer and a polyacrylonitrile (PAN) nanofibrous substrate was fabricated in this work. Ultrathin GE nanofibers were electrospun and deposited onto the PAN nanofibrous supporting membranes and followed by moistening treatment and hot-pressing treatment. The moistened electrospun GE nanofibers would be melted and pressed into an integrated selective skin layer on the porous PAN nanofibrous membranes. The treated GE/PAN double-layer membranes were then chemically cross-linked by glutaraldehyde (GA). The depositing time of GE nanofibers was optimized to achieve a thin and integrated GE separating layer. The optimized GE/PAN TFNC membrane exhibited high flux (182.1 L m−2 h−1) and rejection (98.3%) in BSA test at 0.3 MPa. In addition, the GE/PAN composite membrane possessed great mechanical stabilities.

Salt-tuned fabrication of novel polyamide composite nanofiltration membranes with three-dimensional turing structures for effective desalination

High performance thin-film nanofibrous composite (TFNC) membranes with Turing structures were constructed by interfacial polymerization (IP) of trimesoyl chloride (TMC) and piperazine (PIP) tuned with high content salt (NaCl) in aqueous phase onto a polyacrylonitrile (PAN) nanofibrous mat for nanofiltration (NF). The concentration of salt in aqueous phase played a key role in the structural transition of polyamide (PA) membrane surfaces with two type Turing structures from the crossed ridge networks to crowed nodular arrays. The introduction of NaCl induced the uneven distribution of the IP reaction and could fine-tune the hydrophilicity and compactness of the formed ultrathin PA layer. The skillful manipulation of IP by regulating the NaCl content in aqueous phase enabled a great improvement in NF performance. Under 0.5 MPa, the flux of the optimized TFNC membrane (20.0 wt% NaCl in aqueous phase) reached 129.0 L m-2 h-1 (Na2SO4 rejection was 99.1%) which was approximately 2.5 times greater than that of the original membrane fabricated without salt addition. Moreover, the resultant membrane exhibited excellent stability and anti-fouling properties for long-term use. This approach is easy to be connected with commercialized IP technology to prepare high-performance NF membranes.

Engineering a superwetting thin film nanofibrous composite membrane with excellent antifouling and self-cleaning properties to separate surfactant-stabilized oil-in-water emulsions

In recent years, novel superwetting membranes have gained popularity for oily wastewater treatments via synergy between surface chemistry and topography. However, the water fluxes of the superwetting membranes normally decrease rapidly due to pore clogging and surface fouling, especially when treating surfactant-stabilized oil-in-water emulsions. Herein, a facile strategy is proposed to develop a superwetting thin film nanofibrous composite (TFNC) membrane with remarkable antifouling and self-cleaning properties to effectively separate surfactant-stabilized oil-in-water emulsions. The membrane is composed of an ultrathin carbon nanotubes (CNTs)-polyvinyl alcohol (PVA) composite skin layer, and a highly porous electrospun nanofibrous substrate as well as a non-woven mechanical support. The robust three-dimensional (3D) CNTs composite skin layer were immobilized on the nanofibrous substrate surface by crosslinking the CNTs with PVA. This skin layer serves as a functional barrier to reject oil droplets, which exhibited excellent performance in treating surfactant-stabilized oil-in-water emulsions with a rejection of 95% and a competitive flux of ~60 Lm−2h−1 under an ultra-low pressure (20 kPa) in a cross-flow filtration process. Moreover, the CNTs composite layer also protects the membrane surface from fouling. The TFNC membrane possesses outstanding reusability, as the water flux could be recovered by 100% in a continuous cyclic operation without cleaning, which should be attributed to the underwater oil repellence of its superhydrophilic surface and self-cleaning property based on the capillary pumping effect occurred in the micron/nano-channels of the membrane surface.

Biomimetic sulfated silk nanofibrils for constructing rapid mid-molecule toxins removal nanochannels

Biomacromolecules and their assemblies exhibit the great potential for biomimetic construction of novel and functional nanomaterials. In this work, sulfated silk nanofibrils (SSNFs) were firstly prepared with special designed sulfated silk fibroin molecule by a facile self-assembly technique, which were incorporated into the poly (vinyl alcohol) (PVA) hydrogel. Then they were together coated on the electrospun polyacrlonitrile (PAN) nanofibrous scaffold to fabricate a novel PVA/SSNFs/PAN thin film nanofibrous composite (TFNC) membranes for hemodiafiltration. Combining the results from filtration and hemodiafiltration tests, it could be deduced that the formation of nanogaps between PVA matrix and SSNFs provided more nanochannels for water and uremic toxins to transport rapidly through the functional layer. Especially the incorporation of SSNFs into PVA hydrogel layer endowed PVA/SSNFs TFNC hemodiafiltration membranes with rapid mid-molecule toxins removal channels. PVA/SSNFs-5 could clear 65.7% of lysozyme, also maintaining 85.0% clearance of urea and 94.7% interception of BSA after 4 h of dialysis. In addition, the blood compatibility of PVA/SSNFs TFNC membranes was also enhanced after the introduction of biomimetic SSNFs due to the heparin-like structure of sulfated silk fibroin (SSF). The biomimetic assembly route demonstrated here represents a green and efficient way for designing various functional nanomaterials in bio-nanotechnologies.