Fabrication of high-performance composite nanofiltration membranes for dye wastewater treatment: mussel-inspired layer-by-layer self-assembly

High-Performance Polyurea Improved by Reactive Nanocluster for Antibiofouling

Polyurea has found applications in protective coatings. Yet, the too fast polymerization and lack of functions limit its application. Herein, we report a high-performance polyurea via the stepwise polymerization of an isocyanate (NCO)-terminated prepolymer consisting of poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPG-b-PEG-b-PPG) with a nanocluster synthesized via the hydrolysis of N-phenylaminomethyltriethoxysilane. Such a nanocluster contains low-reactivity secondary amines, so the polymerization of polyurea can be slowed down (over 1 h), which improves its wetting and adhesion to a substrate. The residual silanol groups on the nanocluster further increase the adhesion. Such polyurea exhibits high adhesion on various substrates, including glass, ceramic, steel, copper, titanium, wood, and natural rubber (∼2.35-14.64 MPa). Besides, the nanoclusters can cross-link the prepolymer into a tough network, endowing the polyurea with a high mechanical strength of ∼25 MPa, much higher than the traditional polyaspartic ester polyurea. On the other hand, the PEG segments enable the polyurea to have good fouling resistance against proteins (fibrinogen absorption was reduced by over 90%), bacteria (RBA of S. aureusE. coli and Pseudomonas sp. was less than 10%), as well as diatom (diatom density was less than 100 cells/mm2). The polyurea is expected to find applications in biomedical engineering and marine antifouling.

Improving antifouling performance of FO membrane by surface immobilization of silver nanoparticles based on a tannic acid: diethylenetriamine precursor layer for municipal wastewater treatment

In this study, a facile method for multifunctional surface modification on forward osmosis (FO) membrane was constructed by surface immobilization of AgNPs based on tannic acid (TA)/diethylenetriamine (DETA) precursor layer. The cellulose triacetate (CTA) FO membranes modified by TA and DETA with different co-deposition time (6 h, 12 h, 24 h) were investigated. Results indicated that the TA/DETA (24)-Ag CTA membrane with a TA/DETA co-deposition time of 24 h was identified to be optimal, which attained more hydrophilic. And it had the bacterial mortality of Escherichia coli and Staphylococcus aureus reaching 98.23% and 99.83% respectively and possessed excellent physical and chemical binding stability. Meanwhile, the coating layer resulted in the antifouling ability without damaging the membrane intrinsic transport characteristics. As for synthetic municipal wastewater treatment, the water flux of CTA FO membrane decreased approximately 49% of the initial flux after running for 14 days. In contrast, the flux decline rate of TA/DETA (24)-Ag CTA membrane was about 37%. Furthermore, less foulant deposition and higher recovery rate of water flux was observed for TA/DETA (24)-Ag CTA membrane, implying that the modified membrane effectively alleviated membrane fouling and processed a lower flux decline during municipal wastewater treatment. It was attributed to the enhanced surface hydrophilicity and antibacterial property of the coating layer, which improved antifouling property.

Tannic Acid-Modified Decellularized Tendon Scaffold with Antioxidant and Anti-Inflammatory Activities for Tendon Regeneration

Tendon regeneration is greatly influenced by the oxidant and the inflammatory microenvironment. Persistent inflammation during the tendon repair can cause matrix degradation, tendon adhesion, and excessive accumulation of reactive oxygen species (ROS), while excessive ROS affect extracellular matrix remodeling and tendon integration. Herein, we used tannic acid (TA) to modify a decellularized tendon slice (DTS) to fabricate a functional scaffold (DTS-TA) with antioxidant and anti-inflammatory properties for tendon repair. The characterizations and cytocompatibility of the scaffolds were examined in vitro. The antioxidant and anti-inflammatory activities of the scaffold were evaluated in vitro and further studied in vivo using a subcutaneous implantation model. It was found that the modified DTS combined with TA via hydrogen bonds and covalent bonds, and the hydrophilicity, thermal stability, biodegradability, and mechanical characteristics of the scaffold were significantly improved. Afterward, the results demonstrated that DTS-TA could effectively reduce inflammation by increasing the M2/M1 macrophage ratio and interleukin-4 (IL-4) expression, decreasing the secretion of interleukin-6 (IL-6) and interleukin-1β (IL-1β), as well as scavenging excessive ROS in vitro and in vivo. In summary, DTS modified with TA provides a potential versatile scaffold for tendon regeneration.

Reliable lateral Zn deposition along (002) plane by oxidized PAN separator for zinc-ion batteries

Aqueous zinc ion batteries (AZIBs) are the promising candidate for energy storage where safety and low cost are the major concerns. However, the uneven and random electrodeposition of Zn has become a serious impediment to the deep recharging of AZIBs. Conventional modifications on zinc substrate can promote homogenous zinc deposition initially, but not sustainably. Here, an oxidized polyacrylonitrile (OPAN) membrane with a conjugated planar structure is proposed as a zinc ion battery separator. This separator can continuously regulate the growth of Zn with (002) texture to inhibit dendrites. In addition, the separator has a fast Zn2+ ion transfer, which can spontaneously repel SO42- and relieve side reactions. As a result, the Zn-symmetric batteries show cycle lifetime of more than 1300 hours at 1 mA cm-2 and 1 mA h cm-2, and kept stable for more than 160 hours even at 65% high discharge of depth (DOD). The MnO2//Zn full celled assembled with an OPAN separator had very little decay for 5000 cycles at 2 A g-1. This work provides a new method for realizing the continuous and uniform deposition of Zn metals, which also provides a new route for batteries with metallic anodes.

Influence of Temperature-Guided SAM Growth on Wetting and Its Mass Transfer Models

The formation and growth of self-assembled monolayers (SAMs) composed of amphiphiles have garnered significant attention due to their diverse technical applications. This article reports the findings of molecular dynamics simulations aimed at elucidating the intricate relationship between the wetting behavior of amphiphiles, specifically n-alkanols, and the growth of their SAMs on a mica surface under varying temperature conditions. The investigation quantifies the structural characteristics of the formed SAMs, including density profiles, in-plane radial distribution functions, order parameters, and end-to-end length distributions of n-alkanol molecules within the SAM. Thermodynamic properties, such as the second virial coefficient and excess entropy, are examined in relation to temperature and time. The growth of the SAM is assessed by analyzing characteristic time scales at different temperatures and in-plane diffusion of n-alkanol molecules and utilizing classical theories of mass transfer to quantify the growth rate as a function of temperature. These results are then correlated with changes in the contact angle and spreading coefficient of n-alkanol droplets on the mica surface over time, providing insights into the impact of SAM growth on the wetting behavior and the mass transfer model of such systems.

Rapid Construction of Caffeic Acid/p-Phenylenediamine Antifouling Hydrophilic Coating on a PVDF Membrane for Emulsion Separation

The current methods of constructing modification strategies for hydrophilic membranes are time-consuming, complex in operation, and poor in universality, which limit their application on membranes. In this work, inspired by the adhesion properties and versatility of caffeic acid (CA) and p-phenylenediamine (PPDA), a simple, rapid, and universal method was designed for the separation of oil-in-water emulsion by preparing a stable hydrophilic coating separation membrane. The preparation time of the membrane was shortened to 40 min. The developed PVDF-PCA/PPDA membrane showed superhydrophilic and underwater superoleophobic properties. When applied to petroleum ether-in-water emulsion, isooctane-in-water emulsion, and dodecane-in-water emulsion separation, the oil rejection was more than 99.0%. In the circulating separation of 10 g/L soybean oil-in-water emulsion, the oil rejection was more than 99.3%, and the highest flux was 1036 L·m-2·h-1. The prepared PVDF-PCA/PPDA membrane performed well in the separation test of oily wastewater. The proposed strategy is simple and rapid; it may become a universal method for preparing membranes with super strong antifouling properties against viscous oil and accelerate the research progress of membrane separation of oil-in-water emulsions.

Resource recovery from RO concentrate using nanofiltration: Impact of active layer thickness on performance

Modelling the removal of monovalent and divalent ions from seawater via nanofiltration is crucial for pre-treatment in seawater reverse osmosis systems. Effective separation of divalent ions through nanofiltration and allowing the permeate containing only monovalent ions to pass through the reverse osmosis system produces pure NaCl salt from the concentrate. However, the Donnan steric pore model and dielectric exclusion assume a uniformly distributed cylinder pore morphology, which is not representative of the actual membrane structure. This study analyzed the impact of membrane thickness on neutral solute removal and investigated the effect of two different methods for calculating the Peclet number on rejection rates of monovalent and divalent salts. Results show that membrane thickness has a significant effect on rejection rates, particularly for uncharged solutes in the range of 0.5-0.7 solute radius to membrane pore size ratio. Operating pressures above 10 bar favour the use of effective active layer thickness over the membrane pore size to calculate the Peclet number. At low pressures, using the effective active layer can lead to overestimation of monovalent salt rejection and underestimation of divalent salt rejection. This study highlights the importance of appropriate Peclet number calculation methods based on applied pressure when modelling membrane separation performance.

High-Flux lamellar MoSe2 membranes for efficient dye/salt separation

Membrane-based technology is emerging as an efficient technique for wastewater treatment in recent years. Membranes made up of two-dimensional materials provide high selectivity and water flux compared to conventional polymeric membranes. Herein, we report the synthesis and use of MoSe₂ membrane for dye and drug separation in wastewater, mainly from textile and pharmaceutical industries. The as-prepared MoSe₂ membrane shows ∼ 100% rejection for organic dyes and ciprofloxacin drug with a water flux reaching up to ∼ 900 Lm^-2h^-1bar^-1. Further, the MoSe₂ membrane shows lower NaCl rejection of ∼ 1.9% for the dye/salt mixture. The interlayer spacing in the MoSe₂ membrane allows the water molecules and ions from the salt to pass through freely but restricts the movement of large contaminants. The membrane is stable against the bovine albumin serum fouling with a flux recovery rate of 96%. It also shows good performance even in harsh environments (pH 3-10). To the best of our knowledge, the MoSe₂ membranes were fabricated for the first time for wastewater treatment application. The dye/salt separation performance of the MoSe₂ membrane is significantly better than several other membranes. This work highlights the promising potential for using two-dimensional materials for textile and pharmaceutical wastewater treatment.

Evolution, Stability, and Applicability of Surfactant Aggregates in Targeted Delivery

Self-assembly/self-aggregation of surfactant molecules in bulk and the vicinity of a surface has been a topic of interest for decades because of its utilization in numerous modern technical applications. In this article, the results of molecular dynamics simulations are reported to investigate the self-aggregation of sodium dodecyl sulfate (SDS) at an interface of mica and water. SDS molecules starting from lower to higher surface concentrations tend to create distinct aggregated structures in the vicinity of a mica surface. The structural properties, such as density profiles, radial distribution functions, and thermodynamic properties like excess entropy and second virial coefficient, are calculated to address the bits and pieces of the self-aggregation. The change in the free energy for aggregates of varied sizes approaching the surface from the bulk aqueous solution, along with the change in their shapes during the process in terms of change in the radius of gyration and its components, is reported respectively to model a generic pathway for a surfactant-based targeted delivery system.

Efficient removal of dyes from aqueous solutions using short-length bimodal mesoporous carbon adsorbents

Ordered mesoporous carbons (OMCs) with controlled mesopore lengths and volumes were synthesized and investigated to remove the model dye methylene blue (MB) from aqueous solutions. The pore size, specific surface area, pore volume, and pore length of OMCs (CMK-3, sCMK-3, and sCMK-5) were analyzed and benchmarked against commercial activated carbon (AC). CMK-3 and sCMK-3 had narrow pore size distributions (PSDs) centered at ∼4.4 nm, whereas the PSD of sCMK-5 was bimodal, derived from the same pores as CMK-3 (∼4.4 nm) and the inner diameter of the carbon nanotubes (∼5.8 nm). The pore length decreased from 743 nm for CMK-3 to 173 nm for sCMK-3 and 169 nm for sCMK-5, facilitating the MB accessibility and efficient utilization of internal mesopores. The MB adsorption on the prepared adsorbents was well described by a pseudo-second-order kinetic model (R² > 0.999), and the initial adsorption rate (h) on sCMK-5 was 34.07-fold faster than that on commercial AC. The Langmuir model adequately explained the equilibrium adsorption data, and the increase in the Langmuir maximal adsorption capacity (q_m) of the OMCs was proportional to the specific surface area. The MB adsorption on sCMK-5 was endothermic and spontaneous, and proceeded primarily through physical adsorption as well as chemisorption reacting with oxygen atoms in hydroxyl groups. The prepared adsorbents were also suitable for polishing textile wastewater containing color-causing substances along with the background organic matter. These OMCs are promising for treating wastewater as efficient adsorbents for large molecular pollutants such as dyes.

Exploring MOF-199 composites as redox-active materials for hybrid battery-supercapacitor devices

Metal-organic frameworks (MOFs) have emerged as intriguing porous materials with diverse potential applications. Herein, we synthesized a copper-based MOF (MOF-199) and investigated its use in energy storage applications. Methods were adapted to intensify the electrochemical characteristics of MOF-199 by preparing composites with graphene and polyaniline (PANI). The specific capacity of the synthesized MOF in a three-electrode assembly was significantly enhanced from 88 C g^-1 to 475 C g^-1 and 766 C g^-1 with the addition of graphene and polyaniline (PANI), respectively. Due to the superior performance of (MOF-199)/PANI, a hybrid supercapacitor was fabricated with the structure of (MOF-199)/PANI//activated carbon, which displayed an excellent maximum energy and power density of 64 W h kg^-1 and 7200 W kg^-1, respectively. The hybrid device exhibited an appreciable capacity retention of 92% after 1000 charge-discharge cycles. Moreover, using Dunn's model, the capacitive and diffusive contributions as well as the k ₁ and k ₂ currents of the fabricated device were calculated, validating the hybrid nature of the supercapattery device. The current studies showed that MOF-199 exhibits promising electrochemical features and can be considered as potential electrode material for hybrid energy storage devices.

Design of a new polyethersulfone nanofiltration membrane with anti-fouling properties using supported protic ionic liquid modification for dye/salt removal

Facile techniques to fabricate the nanofiltration membranes with ideal molecular sieving is one of the most interesting subjects in membrane separation technology. In this study, the application of modified graphene oxide (GO) with triethylenetetramine (TETA), CuFe₂ O₄ , and acetic acid (AC) (supported GO-TETA-CuFe₂ O₄ @AC) as a supported protic ionic liquid (PIL) modifier for polyethersulfone (PES) membrane was evaluated to approve the improvement of anti-fouling properties and wastewater rejection of the fabricated membranes. To enhance the key properties of graphene oxide, it was modified by hydrophilic nanomaterials (TETA-CuFe₂ O₄ ). High flux and promising flux recovery ratio (up to 95% compared to the unmodified membrane) can be observed in the modified membranes. The modified membranes by GO-TETA-CuFe₂ O₄ @AC were studied at optimum concentrations (0.5 wt.%) for salt rejection and different dyes. The obtained data indicated that the modified membranes by GO-TETA-CuFe₂ O₄ @AC indicated higher salt removal (up to 97% for BaCl₂ than the unmodified membrane), which was related to the efficient modification. The obtained pure water flux (PWF) for bare and optimal modified membrane from 13.11 to 27.87 kg/m² ·h, respectively. To exact evaluate the effect of membrane modification on performance examination, the modified membranes were evaluated for chlorine resistance testing. This study aimed to develop cost-effective nanofiltration (NF) membranes with high anti-fouling properties and to determine the maximum filtration capacity of in-time dyes and salts in effluents. PRACTITIONER POINTS: A GO-TETA-CuFe2O4 mixed matrix membrane was prepared for removal of salts and dyes. The effect of GO-TETA-CuFe2O4 enhanced the hydrophilicity and porosity. The membrane exhibited superior antifouling properties and ions rejection.

Plant Polyphenol Pyrogallol and Polyamine-Based Co-Deposition for High-Efficiency Nanofiltration Membrane Preparation towards Inorganic Salt Removal

The co-deposition between polyphenols and amines has been demonstrated in order to prepare positively charged nanofiltration (NF) membranes for multivalent cation rejection in recent years; however, the low reactivities of the involved polyphenols usually cause a long co-deposition time and unsatisfactory rejection. Herein, a novel plant polyphenol (PG) was co-deposited with tetraethylenepentamine (TEPA) in a much shorter time period to prepare positively charged NF with high multivalent cation rejection membranes. The performance of the co-deposition membranes can be easily controlled by adjusting the mass ratio of PG and TEPA, reaction time, and pH value of the buffer solution. The optimal membrane, prepared under a polyphenol and polyamine mass ratio of 1:1, coating time of 2 h, and pH value of 8.0, shows a decent pure water permeability of 8.43 L m^-2 h^-1 bar^-1 while maintaining a superior 96.24% MgCl₂ rejection. More importantly, the universality of this method was corroborated by employing other amines with different molecular weights in the co-deposition. This work provides new insights for the preparation of high-performance positively charged NF membranes.

Metal-Polyphenol Coordination at the Aqueous Contra-diffusion "Interface": A Green Way to High-Performance Iron(III)/Tannic Acid Thin-Film-Composite Nanofiltration Membranes

Thin-film-composite (TFC) nanofiltration membranes have found wide uses in environment remediation and industrial separation. There is a growing trend to avoid the use of organic solvents and toxic chemicals during membrane fabrication. Therefore, the aqueous fabrication of TFC membranes receives considerable interest as a green and sustainable process. However, it remains challenging to construct a defect-free and ultrathin film in a homogeneous aqueous phase without the assistance of an interface. The contra-diffusion process provides a special "interface" to confine the film formation within a narrow space by regulating the competition between precursor diffusion and interfacial reactions. Herein, Fe³⁺/tannic acid (TA) TFC membranes were fabricated by a contra-diffusion process. The effects of fabrication parameters on the Fe³⁺/TA TFC membrane microstructure and performance were also investigated. The negatively charged membrane performs a competitive Na₂SO₄ rejection of 95.6% with a permeation flux of 44.3 L m^-2 h^-1 under 0.6 MPa as well as more than 99.5% rejection to several anionic dyes. The as-prepared membranes perform superior nanofiltration performance compared to other reported Fe³⁺/TA-based membranes, owing to the thin and defect-free selective layers by self-regulation. Moreover, the membranes exhibit stable rejection during a long-term nanofiltration test.

Strategies to improve membrane performance in wastewater treatment

Membrane technology has rapidly gained popularity in wastewater treatment due to its cost-effectiveness, environmentally friendly tools, and elevated productivity. Although membrane performance in wastewater treatment has been reviewed in several past studies, the key techniques for improving membrane performance, as well as their challenges, and solutions associated with the membrane process, were not sufficiently highlighted in those studies. Also, very few studies have addressed hybrid techniques to improve membrane performance. The present review aims to fill those gaps and achieve public health benefits through safe water processing. Despite its higher cost, membrane performance can result in a 36% reduction in flux degradation. The issue with fouling has been identified as one of the key challenges of membrane technology. Chemical cleaning is quite effective in removing accumulated foulant. Fouling mitigation techniques have also been shown to have a positive effect on membrane photobioreactors that handle wastewater effluent, resulting in a 50% and 60% reduction in fouling rates for backwash and nitrogen bubble scouring techniques. Membrane hybrid approaches such as hybrid forward-reverse osmosis show promise in removing high concentrations of phosphorus, ammonium, and salt from wastewater. The incorporation of the forward osmosis process can reject 99% of phosphorus and 97% of ammonium, and the reverse osmosis approach can achieve a 99% salt rejection rate. The control strategies for membrane fouling have not been successfully optimized yet and more research is needed to achieve a realistic, long-term direct membrane filtering operation.

A novel synergistic effect of TiO2 and ZnO incorporation in PES-based thin-film nanocomposite nanofiltration membrane for treatment of textile wastewater

A novel synergistic effect of TiO₂ and ZnO incorporation in the PES-based thin-film nanocomposite nanofiltration membranes was developed for the treatment of common effluent treatment plant (CETP) textile wastewater. PES@TiO₂ membranes were developed by phase inversion via the immersion precipitation method followed by the addition of zinc oxide nanoparticles prepared by the rapid microwave-assisted hydrothermal process via interfacial polymerization. p-Phenylenediamine was used as a monomer for the IP process that was coated on the PES@TiO₂ support layer. Various techniques have been applied to characterize the developed thin-film nanocomposite membranes such as Fourier transform infrared (FTIR) microscopy, field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), and contact angle measurement to examine the presence of vibrational modes, surface morphology, the crystal structure of nanoparticles, and hydrophilicity of the membrane, respectively. Membrane properties include porosity, salt rejection, mean pore radius, pure water flux, and industrial effluent rejection efficiency that were studied. The thin-film nanocomposite membrane T5-PES@TiO₂(2%)-ZnO(0.3%) was prepared with a combination of 17 wt% PES, 78 wt% DMF, 3 wt% PVP K30, 2% TiO₂, 2.5 wt% PPD, 0.3 wt% ZnO, and 1.0 wt% TMC that exhibited high water permeability, porosity, higher industrial effluent rejection, and salt rejection efficiency compared to the neat PES membrane.

Structural and mechanistic insights into starch microgel/anthocyanin complex assembly and controlled release performance

We report a self-assembly method for the fabrication of multilayer-starch-based microgels used for anthocyanin encapsulation. Alcohol-heating treatment and ionization reactions were employed to reduce the crystallinity of starch and introduce ionic groups on the molecule to further cross-link it with sodium trimetaphosphate and produce a starch microgel. The molecular interactions between the starch and the anthocyanins facilitated the anthocyanin encapsulation and the starch-microgel/anthocyanin complexes with one, two, and three self-assembled layers were obtained. The Lay-1 microgel exhibited an encapsulation efficiency of 50.1% when the anthocyanin concentration, cross-linking starch concentration, contact time, and temperature were 0.25 mg/mL, 1.5 mg/mL, 3 h, and 40 °C, respectively. An increase in the number of layers resulted in a more compact microgel structure with the zeta potential presenting variations upon structural changes. Furthermore, the encapsulated anthocyanins presented a slow release from Lay-1, while the multilayered microgels (Lay-2 and Lay-3) displayed outstanding encapsulation stability. This study gives an insight on the encapsulation and release of anthocyanins by starch microgels, and provides a novel strategy for the design of starch-based encapsulation materials presenting great stability.

Polyhedral Oligomeric Silsesquioxane Encountering Tannic Acid: A Mild and Efficient Strategy for Interface Modification on Carbon Fiber Composites

Designing and controlling the interfacial chemistry and microstructure of the carbon fiber is an important step in the surface modification and preparation of high-performance composites. To address this issue, a tannic acid (TA)/polyhedral oligomeric silsesquioxane (POSS) hybrid microstructure, similar to the topological structure, is designed on the fiber surface by one-pot synthesis under mild conditions. Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) show that the functionality and surface roughness of the fiber are significantly broadened. Correspondingly, the tensile strength (TS) of CF-TA/POSS₁₀₀ and interlaminar shear strength (ILSS) of CF-TA/POSS₁₀₀-based composites increased by 18 and 34%, respectively. Following that, a failure mechanism study is conducted to demonstrate the interphase structure containing TA/POSS, which is quite critical in optimizing the mechanical performance of the multiscale composites. Moreover, the strategy for the use of TA for constructing a robust coating to replace the traditional modification without affecting the fiber intrinsic strength is an improved design and provides a new idea for the development of high-performance composites.

Mussel-inspired polyethylene glycol coating for constructing antifouling membrane for water purification

HYPOTHESIS

Polyethylene glycol (PEG) holds considerable potential in the fabrication of antifouling surfaces due to its strong hydration property. However, anchoring PEG polymer as a stable surface coating is still challenging because of its weak surface bonding property. Inspired by the mussel adhesion strategy, it is hypothesized that PEG polymer can be robustly attached onto substrates with the assistance of a "bio-glue" layer.

EXPERIMENTS

The "bio-glue" layer composited of Levodopa/polyethyleneimine (LP) is firstly deposited onto substrates, followed by covalently anchoring the poly(ethylene glycol) diglycidyl ether (PEGDE) layer via ring-opening reaction. The antifouling property of as-prepared coating was characterized using several techniques including quartz crystal microbalance (QCM) and surface forces apparatus (SFA). Furthermore, the PEGDE/LP coating was applied in membrane functionalization for oil-in-water (O/W) emulsion separation.

FINDINGS

PEGDE/LP coating shows outstanding stability and superior antifouling properties towards various potential foulants. In the O/W emulsion separation process, the PEGDE/LP-coated membrane maintains its super-hydrophilic property under harsh solution conditions and achieves high water flux (∼3000 L m^-2 h^-1 bar^-1) and 90% water flux recovery ratio for separation of O/W emulsions containing different bio-foulants. This coating strategy provides a promising approach for fabricating stable coating with outstanding antifouling properties in various environmental engineering applications.

Antibacterial polyvinyl alcohol nanofiltration membrane incorporated with Cu(OH)2 nanowires for dye/salt wastewater treatment

In many important industries, such as the textile printing industry, a large amount of dye/salt wastewater is often discharged, which can destroy the ecological environment of the water body. Membrane technology has a great potential in the treatment of environmental problems caused by dye/salt wastewater. Polyvinyl alcohol (PVA) nanofiltration (NF) membrane has a bright future in dye/salt wastewater treatment, however, works on this are rare. Herein, antibacterial PVA NF membrane incorporated with Cu(OH)₂ nanowires for the dye/salt wastewater treatment is reported. The membrane was prepared via coating the solutions containing PVA, glutaraldehyde and Cu(OH)₂ nanowires on the polyethersulfone ultrafiltration membrane. Cu(OH)₂ nanowires has a diameter of 60 nm and was successfully introduced into the membrane. The introduction of nanowires improved the membrane hydrophilicity and roughness, which is conducive to the improvement of membrane flux. Membrane separation performance for one component solution and dye/salt solution were investigated. The introduction of Cu(OH)₂ increases the flux of the membrane obviously (the highest increase is 178.78% (from 21.49 to 38.42 L·m^-2·h^-1·bar^-1, for NaCl solution as the feed). Besides, the membrane doped with nanowires also possessed a high dye/salt selectivity. For one component solution, the dye removal rate was over 97.00% while the salt rejection was low (the lowest was 13.18% (NaCl)). For the dye/salt solution, the dye (Congo Red) rejection kept at a high level (98.91%) and the salt (NaCl) rejection was still low (13.71%), while the flux was also high (37.56 L·m^-2·h^-1·bar^-1). The performance is superior to that of many membranes reported in previous works. Moreover, the Cu(OH)₂ nanowires endowed the membrane with an improved and high antibacterial property. The sterilization rate of Escherichia coli and Staphylococcus aureus reached more than 99.99%.

Waste-to-Resource: New application of modified mine silicate waste to remove Pb2+ ion and methylene blue dye, adsorption properties, mechanism of action and recycling

Currently, heavy metals and dyes are some of the most critical pollutants in the aquatic environment. So, in this paper "waste-to-resource conversion", as a new application of modified mine silicate waste to remove Pb²⁺ ion and methylene blue (MB) dye, adsorption properties, mechanism of action and recycling were studied. Silicate wastes are located in the alteration zone and the margin of molybdenum ore, these wastes are under the influence of hydrothermal solutions which are impregnated with iron and manganese ions. Hence, acid and base modifications have been commonly used. So, in this study, a highly porous nanostructure of modified silicate waste was used to remove MB and Pb²⁺ ion, in subsequent to our previous study on the application of the raw material of the same in the removal of malachite green. Acid, base, and acid/base treatments were used to activate and modify the adsorbent. Results show a significantly higher potential of modified adsorbent in the removal of MB and Pb²⁺ compared to the raw material. According to the isotherm and kinetic studies for MB and Pb²⁺ the Langmuir and Temkin and pseudo-second-order models were investigated with experimental data. Modified nanomaterial was used for several adsorption and desorption processes, without a significant decrease in the capability of the adsorbent in the removal of MB and Pb²⁺ pollutants. Leached iron and manganese ions (as production of modification) are deposited in the form of sludge using a simple pH adjustment and precipitation process and can be used to recover iron and manganese metals in the long run. The comparison of monolayer adsorption capacity using for Pb²⁺ ion and MB dye are as ((untreated SW: 29.41, 1.05); (NaOH treated: 21.74, 100); (Nitric Acid treated: 16.67, 142.86); (Citric Acid treated: 40, 125); (Nitric/Citric Acids treated: 15.63, 111.11) and (Nitric/Citric Acids/NaOH treated: 15.15, 83.33)), respectively. Higher adsorption capacity and re-generable properties of this adsorbent suggest the usage of this natural and abundant mine waste to treat wastewater containing toxic elements and dyes.

Metal-Coordinated Nanofiltration Membranes Constructed on Metal Ions Blended Support toward Enhanced Dye/Salt Separation and Antifouling Performances

Metal-phenol coordination is a widely used method to prepare nanofiltration membrane. However, the facile, controllable and scaled fabrication remains a great challenge. Herein, a novel strategy was developed to fabricate a loose nanofiltration membrane via integrating blending and interfacial coordination strategy. Specifically, iron acetylacetonate was firstly blended in Polyether sulfone (PES) substrate via non-solvent induced phase separation (NIPS), and then the loose selective layer was formed on the membrane surface with tannic acid (TA) crosslinking reaction with Fe3+. The surface properties, morphologies, permeability and selectivity of the membranes were carefully investigated. The introduction of TA improved the surface hydrophilicity and negative charge. Moreover, the thickness of top layer increased about from ~30 nm to 119 nm with the increase of TA assembly time. Under the optimum preparation condition, the membrane with assembly 3 h (PES/Fe-TA3h) showed pure water flux of 175.8 L·m−2·h−1, dye rejections of 97.7%, 97.1% and 95.0% for Congo red (CR), Methyl blue (MB) and Eriochrome Black T (EBT), along with a salt penetration rate of 93.8%, 95.1%, 97.4% and 98.1% for Na2SO4, MgSO4, NaCl and MgCl2 at 0.2 MPa, respectively. Both static adhesion tests and dynamic fouling experiments implied that the TA modified membranes showed significantly reduced adsorption and high FRR for the dye solutions separation. The PES/Fe-TA3h membrane exhibited high FRR of 90.3%, 87.5% and 81.6% for CR, EBT and MB in the fouling test, stable CR rejection (>97.2%) and NaCl permeation (>94.6%) in 24 h continuous filtration test. The combination of blending and interfacial coordination assembly method could be expected to be a universal way to fabricate the loose nanofiltration membrane for effective fractionation of dyes and salts in the saline textile wastewater.

Heparinized anticoagulant coatings based on polyphenol-amine inspired chemistry for blood-contacting catheters

Blood-contacting catheters occupy a vital position in modern clinical treatment including but not limited to cardiovascular diseases, but catheter-related thrombosis associated with high morbidity and mortality remains a major health concern. Hence, there is an urgent need for functionalized catheter surfaces with superior hemocompatibility that prevent protein adsorption and thrombus formation. In this work, we developed a strategy for constructing a kind of polyphenol-amine coating on the TPU surface (TLA) with tannic acid and lysine via simple dip-coating, inspired by dopamine adhesion. Based on the long-term stability and modifiable properties of TLA coatings, heparin was introduced by an amide reaction to provide anticoagulant activity (TLH). X-ray photoelectron spectroscopy and surface zeta potential measurements fully indicated the successful immobilization of heparin. Water contact angle measurements demonstrated good hydrophilicity and stability for 15 days of TLH coatings. Furthermore, the TLH coatings exhibited significant hemocompatibility and no cytotoxicity. The good antithrombotic properties of the functionalized surfaces were confirmed by an ex vivo blood circulation model. The present work is supposed to find potential clinical applications for preventing surface-induced thrombosis of blood-contacting catheters.

Study on the cross-flow ultrafiltration of mixtures of macromolecular organic and inorganic salts

Ultrafiltration (UF) has been widely applied to water treatment in the past few decades, but severe membrane fouling is one of the most significant obstacles for its further development. In reality, the constituents of feed water are complex, and the fouling behavior could be different from that induced by a single foulant. In this study, the membrane fouling induced by mixed organic foulant (sodium alginate, SA) and inorganic ions under various conditions were investigated. The effects of ion concentration and valence on the combined fouling as well as the rejection performance were examined. The results showed that compared to SA alone, the presence of inorganic ions could aggravate the organic fouling of UF membranes significantly. The fouling became more severe as the ion concentration increased. Also, ions with higher valence tended to exacerbate the fouling compared with monovalent ions. It was also found that the existence of inorganic ions had negligible effects on the rejection of organic molecules, however, the rejection of salts can be improved because of the organic matter. In addition, the analysis of the classic fouling models showed that the complete blocking model is the main fouling mechanism of the mixed SA and inorganic salts.

Conformationally tunable calix[4]pyrrole-based nanofilms for efficient molecular separation

Preparation of nanofilms which are able to reject water-soluble low molecular weight organic compounds in nanofiltration remains to be a challenge. Herein, we report a new kind of self-standing, defect-free, robust, centimeter-sized and thickness controllable calix[4]pyrrole (C[4]P)-based nanofilms with excellent molecular sieving performance in nanofiltration. The nanofilms were prepared via confined dynamic condensation of the tetra-benzoyl-hydrazine derivative of calix[4]pyrrole (CPTBH) with 1,3,5-benzenetricarboxaldehyde (BTC) at the air/dimethyl sulfoxide (DMSO) interface. Nanofiltration tests under 2 bar pressure with porous polyethylene terephthalate (PET) as the support and a CsF treated CPTBH-BTC nanofilm (∼100 nm) as the selective layer depicted a water permeance of 15 L m^-2h^-1 bar^-1 and a methanol permeance of 45 L m^-2h^-1 bar^-1. High rejection rates (>95%) were found in aqueous solution for most of the tested dyes and pharmaceuticals. Remarkably, the composite membrane also demonstrated good separation performance in aqueous phase to some amino acids and organic dyes with molecular weights around 200 g/mol. High-performance nanofiltration in methanol was also realized. In this case, the molecular weight cutoff value is ∼ 800 g/mol. These findings showed that introduction of macrocyclic hosts is an effective way to develop nanofilms with high solvent permeance but low molecular weight cutoff value.

Natural polysaccharides based self-assembled nanoparticles for biomedical applications - A review

In recent years, nanoparticles (NPs) derived from the self-assembly of natural polysaccharides have shown great potential in the biomedical field. Here, we described several self-assembly modes of natural polysaccharides in detail, summarized the natural polysaccharides mostly used for self-assembly, and provided insights into the current applications and achievements of these self-assembled NPs. As one of the most widespread substances in nature, most natural polysaccharides exhibit advantages of biodegradability, low immunogenicity, low toxicity, and degradable properties. Therefore, they have been fully explored, and the application of chitosan, hyaluronic acid, alginate, starch, and their derivatives has been extensively studied, especially in the fields of biomedical. Polysaccharides based NPs were proved to improve the solubility of insoluble drugs, enhance tissue target ability and realize the controlled and sustained release of drugs. When modified by hydrophobic groups, the amphiphilic polysaccharides can self-assemble into NPs. Other driven forces of self-assembly include electrostatic interaction and hydrogen bonds. Up to the present, polysaccharides-based nanoparticles have been widely applied for tumor treatment, antibacterial application, gene therapy, photodynamic therapy and transporting insulin.

Tetracycline removal from aqueous solution by biochar derived from algae and modified with MnMoO4: effects of operating parameters, isotherm, kinetic, and thermodynamic study

The aim of the present study is to improve the adsorption of tetracycline (TC) onto biochar of microalgae modified by nanocomposite of MnMoO₄ (MM40BC60). The synthesized nanocomposite was characterized by Scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, Fourier transforms infrared (FTIR) spectroscopy to investigate the morphology, surface area, pores and the functional groups of MM40BC60, respectively. The effect of various parameters including initial pH, TC concentration, and temperature on the adsorption performance of TC to the adsorbent was evaluated with considering kinetics, isotherms, and thermodynamics models. The adsorption of TC on MM40BC60 shows good agreement with the pseudo-second-order kinetic and the Langmuir isotherm models. Results of the thermodynamic study showed that the adsorption process was a spontaneous and endothermic reaction in nature.

A New Polyvinylidene Fluoride Membrane Synthesized by Integrating of Powdered Activated Carbon for Treatment of Stabilized Leachate

Stabilized landfill leachate contains a wide variety of highly concentrated non-biodegradable organics, which are extremely toxic to the environment. Though numerous techniques have been developed for leachate treatment, advanced membrane filtration is one of the most environmentally friendly methods to purify wastewater effectively. In the current study, a novel polymeric membrane was produced by integrating powdered activated carbon (PAC) on polyvinylidene fluoride (PVDF) to synthesize a thin membrane using the phase inversion method. The membrane design was optimized using response surface methodology (RSM). The fabricated membrane was effectively applied for the filtration of stabilized leachate using a cross-flow ring (CFR) test. The findings suggested that the filtration properties of fabricated membrane were effectively enhanced through the incorporation of PAC. The optimum removal efficiencies by the fabricated membrane (14.9 wt.% PVDF, 1.0 wt.% PAC) were 35.34, 48.71, and 22.00% for COD, colour and NH3-N, respectively. Water flux and transmembrane pressure were also enhanced by the incorporated PAC and recorded 61.0 L/m2·h and 0.67 bar, respectively, under the conditions of the optimum removal efficiency. Moreover, the performance of fabricated membranes in terms of pollutant removal, pure water permeation, and different morphological characteristics were systematically analyzed. Despite the limited achievement, which might be improved by the addition of a hydrophilic additive, the study offers an efficient way to fabricate PVDF-PAC membrane and to optimize its treatability through the RSM tool.