A novel positively charged composite nanofiltration membrane based on polyethyleneimine with a tunable active layer structure developed via interfacial polymerization

Development of novel ionic covalent organic frameworks composite nanofiltration membranes for dye/salt separation

Covalent organic frameworks (COF) have desirable properties such as high porosity, low mass density, excellent heat resistance and regulatable structure, making them an ideal candidate for membrane material. Traditional methods for preparing covalent organic framework composite membranes, such as interfacial polymerization, vacuum filtration, and covalent organic framework abrasive coating. Stand-alone COF membranes produced by the above methods usually suffer from problems such as poor mechanical properties. Here, we fabricated high performance COF composite membranes by modified casting-precipitation-evaporation method. The designed composite membranes consisted of the ionic COF (iCOF) selective layer and the support layer are applied in dye/salt separation. The high permeability (∼ 68 L h-1 m-2 bar-1), high dyes rejection (97% for Rose Bengal), and low salts rejection (∼ 2.86% for NaCl) are achieved by the iCOF functional layer. The as-prepared composite membranes have a hydrophilic and highly smooth surface, making them have good anti-fouling performance. In addition, the rigid pore structure of iCOF selective layer endows the composite membranes with excellent stability, the composite membranes maintain original structure under high pressure (6 bar) and ultrasonic treatment (16 kHz for 60 min). This work may open up a novel path to fabricate iCOF composite membranes, which exhibit great potential in dye/salt separation.

Incorporation of an Intermediate Polyelectrolyte Layer for Improved Interfacial Polymerization on PAI Hollow Fiber Membranes

In a single-step spinning process, we create a thin-walled, robust hollow fiber support made of Torlon® polyamide-imide featuring an intermediate polyethyleneimine (PEI) lumen layer to facilitate the integration and covalent attachment of a dense selective layer. Subsequently, interfacial polymerization of m-phenylenediamine and trimesoyl chloride forms a dense selective polyamide (PA) layer on the inside of the hollow fiber. The resulting thin-film composite hollow fiber membranes show high NaCl rejections of around 96% with a pure water permeability of 1.2 LMH/bar. The high success rate of fabricating the thin-film composite hollow fiber membrane proves our hypothesis of a supporting effect of the intermediate PEI layer on separation layer formation. This work marks a step towards the development of a robust method for the large-scale manufacturing of thin-film composite hollow fiber membranes for reverse osmosis and nanofiltration.

Guided Bone Regeneration with a Nitric-Oxide Releasing Polymer Inducing Angiogenesis and Osteogenesis in Critical-Sized Bone Defects

Synthetic scaffolds, as bone grafts, provide a favorable environment for the repair and growth of new bone tissue at defect sites. However, the lack of angio- and osteo-induction limits the usefulness of artificial scaffolds for bone regeneration. Nitric oxide (NO) performs essential roles in healing processes, such as regulating inflammation and addressing incomplete revascularization. In this study, we developed a polymer capable of controlled NO release to promote the osteogenic capacity in artificial scaffolds. The biological efficiency of the NO compound was assessed by its effect on pre-osteoblasts and macrophages in vitro and the extent of vascularization and bone formation in the calvaria defect model in vivo. The compound did not inhibit cell adhesion or proliferation. NO treatment significantly increased both alkaline phosphatase activity and mineralization in pre-osteoblasts. Macrophages treated with NO secreted high levels of anti-inflammatory factors and adopted the pro-regenerative M2 phenotype. In the critical-sized defect model, the collagen scaffold containing the NO compound enhanced neovascularization and bone formation. The developed NO-releasing system promoted osteogenesis and regeneration of damaged bone tissue. As the multiple functions of NO involve macrophage modulation and angiogenesis, such release systems may be valuable for guiding bone regeneration in critical-sized defects. This article is protected by copyright. All rights reserved.

Fabrication of High-Performance Nanofiltration Membrane Using Polydopamine and Carbon Nitride as the Interlayer

In order to recover lithium from brine with a high Mg2+/Li+ ratio, a positively charged nanofiltration (NF) membrane was prepared by depositing polydopamine (PDA)-coated graphitic carbon nitride (g-C3N4) as the interlayer (PDA-g-C3N4) and the interfacial polymerization (IP) of polyethyleneimine (PEI) and trimesoyl chloride (TMC) was carried out. Under optimal conditions, the water contact angle of the composite membrane is only 55.5° and the isoelectric point (IEP) is 6.01. The final positively charged NF membrane (M5) exhibits high permeance (10.19 L·m−2·h−1·bar−1) and high rejection of Mg2+ (98.20%) but low rejection of Li+ (13.33%). The separation factor (SF) is up to 48.08, and the Mg2+/Li+ ratio of the permeate is 0.036 in the simulated brine. In conclusion, the M5 membrane shows a good separation performance for salt lake brine (SF = 12.79 and Mg2+/Li+ ratio of the permeate = 1.43) and good fouling resistance. Therefore, the positively charged M5 membrane with PDA-g-C3N4 as the interlayer has the potential to be used for the recovery of lithium from brine.

Impact of nano-ZnO consolidated poly (ether ether sulfone) nano filtration membrane for evacuation of hazardous metal particles

Industrial wastewater contains heavy metals, colors, dyes, cyanides, and natural manufactured compounds are expanding around the world. It prompts extreme water shortage just as water quality issues. With enhancing worldwide interest for clean and reestablish water for human utilization. Wastewater treatment with membrane innovation is arising as a main cycle to address the issues. In this current work, we have found the expulsion of dangerous metal particles utilizing a nano-ZnO (0.5 wt%) incorporated poly (ether ether sulfone) (PEES) nanofiltration membrane. The created membranes were reviewed by ATR-FTIR, AFM, SEM investigations, XRD, contact angle estimation, mechanical properties, pure water flux, porosity and molecular weight cut-off, arsenic, fluoride, and nitrate rejection studies were illustrated. Because of the hydrophilic nature of ZnO, the resultant membranes had better hydrophilicity than PEES membranes based on porosity, water content, surface chemistry, membrane morphology, and contact angle data. The Nano-ZnO incorporated membrane demonstrated a superior quality execution contrasted with neat PEES membrane. We discovered that the rejection of As(III) and As (V) were > 85% and > 98% separately, and an expanded permeability of 559.28 ± 2 Lm^-2 h^-1 and 297.95 ± 2 Lm^-2 h^-1 individually was seen at pH 10. Fluoride and nitrate particles additionally indicated the most extreme expulsion efficiencies were > 89% and > 75% separately. The prepared membrane samples were incubated in water (40 °C) and sodium hypochlorite solution (active chlorine concentration 400 mg/L) for up to 10 days to determine the stability of polymer membrane matrix. The general outcomes inferred that the nano-ZnO incorporated PEES membrane gave remarkable result to eliminate dangerous metal ions with moderate permeability.

Highly antifouling polymer-nanoparticle-nanoparticle/polymer hybrid membranes

We introduce highly antifouling Polymer-Nanoparticle-Nanoparticle/Polymer (PNNP) hybrid membranes as multi-functional materials for versatile purification of wastewater. Nitrogen-rich polyethylenimine (PEI)-functionalized halloysite nanotube (HNT-SiO2-PEI) nanoparticles were developed and embedded in polyvinyl chloride (PVC) membranes for protein and dye filtration. Bulk and surface characteristics of the resulting HNT-SiO2-PEI nanocomposites were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Moreover, microstructure and physicochemical properties of HNT-SiO2-PEI/PVC membranes were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflectance (ATR)-FTIR. Results of these analyses indicated that the overall porosity and mean pore size of nanocomposite membranes were enhanced, but the surface roughness was reduced. Additionally, surface hydrophilicity and flexibility of the original PVC membranes were significantly improved by incorporating HNT-SiO2-PEI nanoparticles. Based on pure water permeability and bovine serum albumin (BSA)/dye rejection tests, the highest nanoparticle-embedded membrane performance was observed at 2 weight percent (wt%) of HNT-SiO2-PEI. The nanocomposite incorporation in the PVC membranes further improved its antifouling performance and flux recovery ratio (96.8%). Notably, dye separation performance increased up to 99.97%. Overall, hydrophobic PVC membranes were successfully modified by incorporating HNT-SiO2-PEI nanomaterial and better-quality wastewater treatment performance was obtained.

Highly Robust Interfacially Polymerized PA Layer on Thermally Responsive Semi-IPN Hydrogel: Toward On-Demand Tuning of Porosity and Surface Charge

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel-liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc.

Carbodiimide-assisted zwitterionic modification of poly(piperazine amide) thin-film composite membrane for enhanced separation and anti-depositing performances to cationic/anionic dye aqueous solutions

In this work, a novel method of carbodiimide-assisted zwitterionic modification was proposed and implemented to incorporate zwitterionic moieties onto poly(piperazine amide) membrane for improved water permeability and anti-depositing property, which are crucial for highly efficient nanofiltration of dye-contained effluents. Carboxyl groups of polyamide layer were firstly transferred into N-acylurea using excess l-ethyl-3-(3-(dimethylamino)propyl)-carbodiimide. Zwitterions were then incorporated through ring-opening reaction between tertiary amine groups of N-acylurea and 1, 4-butanesultone. Carbodiimide-assisted zwitterionic modification was verified by ATR-IR and XPS analyses and was found to not affect membrane pore size but significantly enhance membrane's permeation and anti-dye-deposition performances. Compared with those of virgin membrane, water permeabilities of the desired zwitterionic membrane to pure water, Congo red aqueous solution and Victoria blue B aqueous solution were higher by 42.9, 62.3 and 95.2 %, respectively, hydraulic resistances from irreversible deposition of Congo red and Victoria blue B molecules were dramatically lowered by 68.4 and 91.8 %, respectively. Furthermore, the perm-selectivity performance of the desired zwitterionic membrane in terms of molecular weight cut-off and pure water permeability was better than most of the reported zwitterionic membranes, and the separation and anti-depositing performances to both anionic and cationic dye aqueous solutions were better than commercial membrane NF270.

A pH-stable positively charged composite nanofiltration membrane with excellent rejection performance

A novel kind of pH-stable positively charged composite nanofiltration (NF) membrane with excellent rejection performance was developed via interfacial polymerization on the surface of a polysulfone (PSF) ultrafiltration (UF) membrane, using a mixture of polyethyleneimine (PEI) and piperazine (PIP) as the monomers of the aqueous phase, and cyanuric chloride (CC) as the monomer of the organic phase. The strong electron withdrawing and steric hindrance effects of the chloride group in the molecules of CC could protect the amido bond from the attack of hydrogen ions (H⁺) or hydroxyl ions (OH⁻) under acidic or alkaline conditions, thus the resultant polyamide composite membranes could be stable in acidic or alkali aqueous solution. A more compact PA active layer could be developed via mixing PIP into the PEI aqueous solution, where the PIP molecules could fill the pores of the polymer networks. There was no obvious change in the surface morphologies, the chemical structures, and the rejection performances after immersing the resultant polyamine composite NF membranes in the strong acidic solution (pH 1) and the strong alkaline solution (pH 13) for 30 days, respectively. The rejection performances of this kind of polyamine composite NF membranes could be adjusted through adjusting the mass ratio of PEI to PIP in the aqueous phase.

A pH-stable positively charged composite nanofiltration (NF) membrane was developed via the interfacial polymerization (IP) between polyethyleneimine (PEI), piperazine (PIP), and cyanuric chloride (CC).