Flow of Multicomponent Electrolyte Solutions through Narrow Pores of Nanofiltration Membranes

The slow flow of a multicomponent electrolyte solution in a narrow pore of a nanofiltration membrane is considered. The well-known semiempirical method of subdivision of electrical potential into quasi-equilibrium and streaming parts and the definition of streaming concentrations and pressure are discussed. The usefulness of this tool for solving the electrohydrodynamic equations is shown and justified: the use of a small parameter enables a system of electrohydrodynamic partial differential equations to be reduced to a system of ordinary differential equations for streaming functions. Boundary conditions for streaming functions at both the capillary inlet and outlet are derived. The proposed model is developed for the flow of a multicomponent electrolyte solution with an arbitrary number of ions. This is coupled with (i) the introduction of specific interactions between all ions and the pore wall and (ii) the inclusion of the dissociation of water in both conservation and transport equations. Effective distribution coefficients of ions are introduced that are functions of both the specific interaction potentials and the surface potential of the nanofiltration membrane material. The axial dependency of surface potential is expressed by the use of a charge regulation model from which the discontinuity in electric potential and ion pore concentrations at the pore inlet and outlet can be described.A relation between the frequently used capillary and homogeneous models of nanofiltration membranes is developed. An example of application of the homogeneous model for interpretation of experimental data on nanofiltration separation of electrolyte solutions is presented, which shows a reasonable predictive ability for the homogeneous model.     

Fabrication of the polyethersulfone/functionalized mesoporous carbon nanocomposite nanofiltration membrane for dyes and heavy metal ions removal: Experimental and quantum mechanical simulation method

The presence of industrial pollutants, especially salts, heavy metals ions, and dyes in water and wastewater is considered a serious environmental issue. To eliminate these pollutants, a high-performing nanofiltration (NF) membrane was prepared by blending the functionalized mesoporous carbon CMK-5 (F-CMK-5) nanofiller. This membrane was synthesized by introducing the active groups of sulfonyl and amide to the surface of mesoporous carbon CMK-5 through covalent functionalization. Characterizations were conducted to study the membranes' physical properties and separation performance in terms of antifouling properties and rejection of salts, heavy metal ions, and dyes. The interactions between the active sites of the nanocomposite membrane and the studied solutes, including dyes and heavy metal ions in aqueous solutions, were studied by the density functional based tight binding method and structural optimization was carried out. Insertion of the F-CMK-5 nanofiller was eventuated in a remarkable increase in surface hydrophilicity, pure water flux, and antifouling properties. For all membranes, the lowest and the highest salt rejection was obtained for NaCl and Na₂SO₄, respectively, exhibiting the characteristics of NF membranes. Moreover, M_0.3 with 0.3 wt% nanofiller showed the highest rejection for heavy metal ions (Fe²⁺ = 99.9%, Zn²⁺ = 99.9%, Cu²⁺ = 99.7%, and Pb²⁺ = 99.2%) and dyes (RB5 = 99.21, DR16 = 98.87, and MB = 98.12%), as well as high separation performance for filtration of multipollutant solutions. The reusability and 144 h uninterrupted filtration experiments for M_0.3 confirmed the stability of the membrane. The findings suggest that the PES/F-CMK-5 nanocomposite NF membrane is a promising candidate for water and wastewater treatment.     

Ultra-Fast Preparation of Large-Area Graphdiyne-Based Membranes via Alkynylated Surface-Modification for Nanofiltration

Graphdiynes (GDYs), two-dimensional graphene-like carbon systems, are considered as potential advanced membrane material due to their unique physicochemical features. Nevertheless, the scale-up of integrated GDY membranes is technologically challenging, and most studies remain at the theoretical stage. Herein, we report a simple and efficient alkynylated surface-mediated strategy to prepare hydrogen-substituted graphdiyne (HsGDY) membranes on commercial alumina tubes. Surface alkynylation initiates an accelerated surface-confined coupling reaction in the presence of a copper catalyst and facilitates the nanoscale epitaxial lateral growth of HsGDY. A continuous and ultra-thin HsGDY membrane (∼100 nm) can be produced within 15 min. The resulting membranes exhibit outstanding molecular sieving together with excellent water permeances (ca. 1100 L m⁻² h⁻¹ MPa⁻¹), and show a long-term durability in cross-flow nanofiltration, owing to the superhydrophilic surface and hydrophobic pore walls.     

Crosslinked Polyvinylnorbornene‐Based Membranes as a New Class of Solvent‐Resistant Nanofiltration Membranes

Solvent resistant nanofiltration (SRNF) has received increasing attention since the turn of the century within energy‐ and waste‐efficient unit processes. This work explores the synthesis and characterization of crosslinked polynorbornenes for SRNF. A series of polyvinylnorbornene thin‐film composite membranes with increasing degree of crosslinking were prepared and tested for their SRNF performance in heptane, chloroform, and toluene. Sudan Black B (457 g mol^?1) was used as the solute. Then, 99% retention was achieved in heptane, 86% in chloroform, and 75% in toluene. It was further shown that the permeance and retention can be fine‐tuned in these solvents by controlling the extent of crosslinking. This work thus introduces the crosslinking of polynorbornenes as a promising material route for SRNF. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1593–1600     

Composite nanofiltration membrane comprising one-dimensional erdite,two-dimensional reduced graphene oxide,and silkworm pupae binder

Composite nanofiltration membranes offer advantages because of synergetic effects among the constituent materials’ properties. However, the sustainability of both the membrane fabrication and the raw materials has been a drawback of this energy-efficient separation technology. We report the facile fabrication of a nanocomposite membrane composed of a two-dimensional (2D) material of reduced graphene oxide (rGO) combined with a one-dimensional (1D) material of a ternary metal-based chalcogenide (NaFeS₂ or NFS) using silkworm pupae protein as a natural binder. All the source materials can be derived from either nature or waste, ensuring the sustainability of the membrane and its production method. The structural characteristics of the synthesized membranes were analyzed, and the morphology of the composite membranes was studied thoroughly. Thermogravimetric analysis, differential scanning calorimetry, and nanoindentation characterizations indicated that the composite membranes were mechanically and thermally stable. The water and acetone fluxes; salt, dye, and pollutant rejections; and long-term membrane performance were evaluated using a cross-flow filtration system. Solute rejection was observed to increase (up to 98%, 94%, 95%, and 78% for Rhodamine B, 2,4-dichlorophenol, MgCl₂, and NaCl, respectively) with increasing concentration of the nanomaterials in the membrane. The fine-tuning of the molecular weight cutoff from 794 to 600 g mol^?1 was achieved by varying the concentration of the nanomaterials from 1 to 3 mg mL^?1. Our research findings demonstrate the synergetic effects of combining 1D and 2D materials using silkworm pupae binder. The composite membrane was stable in different classes of organic solvents, including hydrocarbons, alcohols, esters, ethers, polar aprotic solvents, halogenated solvents, and ketones. This first use of natural pupae binder in constructing membrane materials paves the way toward the development of more sustainable membranes.     

A comparative study on the monovalent and divalent cation separation of polymeric films and membranes from salt solutions under diffusion-dialysis

This study deals with selective separation of mono- and divalent cations from aqueous salt solutions using polymeric films based on polyethylene (PE) and polyamide6 (PA6), and two different commercial nanofiltration (NF) membranes. The diffusion rates (D) of ions (Na⁺ and Ca²⁺), separation factors (α) and ion rejections (R) of the films and NF membranes are examined comparatively as well as their surface morphology and hydrophilicity. It is observed that the diffusion rates of Na⁺ are in the range of 0.7–1.8 × 10⁻⁸cm² .s⁻¹ in the decreasing order of PE > NF90 > NF270 > PA6 while Ca²⁺ shows diffusion rates of 7.4–18.4 × 10⁻⁸ cm² .s⁻¹ in the increasing order of NF270 > NF90 ≈ PA6 > PE. Rejection values of the polymeric films and NF membranes against to Na⁺ and Ca²⁺ vary between 90% and 99.6%.The highest α(Ca²⁺/Na⁺) is found to be 20 for PA6 film. D, α, and R value of both polymeric films and NF membranes are strongly affected by the existence of osmosis during diffusion-dialysis and the sizes of hydrated sodiu and calcium ions. In conclusion, the film based on PA6 may be a good alternative for selective separation of mono- an divalent cations.     

Solvent‐Resistant Nanofiltration for Product Purification and Catalyst Recovery in Click Chemistry Reactions

The quickly developing field of “click” chemistry would undoubtedly benefit from the availability of an easy and efficient technology for product purification to reduce the potential health risks associated with the presence of copper in the final product. Therefore, solvent‐resistant nanofiltration (SRNF) membranes have been developed to selectively separate “clicked” polymers from the copper catalyst and solvent. By using these solvent‐stable cross‐linked polyimide membranes in diafiltration, up to 98 % of the initially present copper could be removed through the membrane together with the DMF solvent, the polymer product being almost completely retained. This paper also presents the first SRNF application in which the catalyst permeates through the membrane and the reaction product is retained.     

壳聚糖-聚丙烯腈复合纳滤膜的氨气等离子改性

利用氨气低温等离子体对壳聚糖聚丙烯腈复合膜进行表面改性,制成了在低压、弱酸条件下,带正电荷的壳聚糖一聚丙烯腈复合纳滤膜。探讨了等离子处理时间、放电功率对膜亲水性改善效果的影响,采用单因素实验确定了最佳等离子体处理条件。通过扫描探针显微镜、接触角测试、表面光电子能谱检测等手段对膜表面进行了表征。经过等离体改性后,复合膜的亲水性及纳滤性能均大幅提高。改性后,在0．05MPa、pH≈6．7条件下,壳聚糖一聚丙烯腈复合膜对0．1mol／L的）,一氨基丁酸溶液的通量为3．19L／（m^2·h）,截留率为78％。     

Formation of appropriate sites on nanofiltration membrane surface for binding TiO2 photo-catalyst: Performance, characterization and fouling-resistant capability

Titanium dioxide (TiO₂) nanoparticles were assembled on the surface of nanofiltration blend membrane. For settling TiO₂ on the membrane surface, two membrane categories were used: (i) unmodified polyethersulfone (PES)/polyimide (PI) blend membrane, and (ii) –OH functionalized PES/PI blend membrane with different concentrations of diethanolamine (DEA). These membranes were radiated by UV light after TiO₂ depositing with different concentrations. 15 min immersion in colloidal suspension and 15 min UV irradiation with 160 W lamps were used for modification. The modification resulted in the formation of a photo-catalytic property with enhanced membrane hydrophilicity. The self-assembly of TiO₂ nanoparticles was established through coordinance bonds with –OH functional groups on the membrane surface. A comparison between the UV irradiated TiO₂ deposited blend membrane and deposited-functionalized blend membranes showed that –OH groups originate excellent adhesion of TiO₂ nanoparticles on the membrane surface, increase reversible deposition, and diminish irreversible fouling. The membranes were characterized using SEM, FTIR, EDX, contact angle, cross flow filtration, and antifouling measurements. SEM images show that the presence of –OH groups on the DEA-modified membrane surface is the main parameter for extra uniformly settlement of TiO₂ nanoparticles on the membrane surface. This procedure is a superior technique for modification of PES/PI nanofiltration membranes to enhance water flux and minimization membrane fouling.     

荷正电聚乙烯亚胺纳滤膜的制备与应用

纳滤是介于超滤与反渗透之间的膜分离技术,具有操作压力低,无相变,分离效率高及运行成本低等优点,广泛地应用于饮用水制备、污水处理、化工、制药和食品等领域.近年来,随着分离体系复杂程度的增加及对膜分离性能要求的提高,荷正电纳滤膜越来越受到研究者的关注.聚乙烯亚胺(PEI)是一类重要的多胺类荷正电纳滤膜材料,具有优异的亲水性、高荷电密度及反应活性.开发具有高分离性、高稳定性、耐酸碱性、耐溶剂性、抗菌性和耐污染性的荷正电PEI纳滤膜(P-PEI-NFM)日益成为研究的热点.本文对近年来P-PEI-NFM的制备方法进行归纳,总结了P-PEI-NFM在水软化、重金属脱除、碱性染料的分离及浓缩、抗生素分离和耐溶剂纳滤的应用.探讨了P-PEI-NFM存在的主要问题,并对未来的研究方向进行了展望.