Thin-film composite polyester nanofiltration membrane with high flux and efficient dye/salts separation fabricated from precise molecular sieving structure of β-cyclodextrin

Unraveling Anomalies in Preferential Liquid Transport through the Intrinsic Pores of Cyclodextrin in Polyester Nanofilms

The precise manipulation of the porous structure of the nanofiltration membrane is critical for unlocking enhanced separation efficiencies across various liquids and solutes. Ultrathin films of crosslinked macrocycles, specifically cyclodextrins (CDs), have drawn considerable attention in this area owing to their ability to facilitate precise molecular separation with high liquid permeance for both polar and non-polar liquids, resembling Janus membranes. However, the functional role of the intrinsic cavity of CD in liquid transport remains inadequately understood, demanding immediate attention in designing nanofiltration membranes. Here, the synthesis of polyester nanofilms derived from crosslinked β-CD, demonstrating remarkable Na2SO4 rejection (≈92 - 99.5%), high water permeance (≈4.4 - 37.4 Lm-2h-1bar-1), extremely low hexane permeance (<1 Lm-2h-1bar-1), and extremely high ratio (α > 500) of permeances for polar and non-polar liquids, is reported. Molecular simulations support the findings, indicating that neither the polar nor the non-polar liquids flow through the β-CD cavity in the nanofilm. Instead, liquid transport predominantly occurs through the 2.2 nm hydrophilic aggregate pores. This challenges the presumed functional role of macrocyclic cavities in liquid transport and raises questions about the existence of the Janus structure in nanofiltration membranes produced from the macrocyclic monomers.

Preparation of a CPVC composite loose nanofiltration membrane based on plant polyphenols for effective dye wastewater treatment

The textile industry's high-salinity wastewater presents a significant difficulty for fractioning salts and dyes. To fractionate the dyes and salts, a high-performance CPVC composite loose nanofiltration membrane (LNM) was fabricated by interfacial polymerization. The organic phase was obtained by crosslinking polyethylenimine (PEI) with tannic acid (TA) and gallic acid (GA) using TMC. The resultant composite LNM performance was enhanced by adjusting the coating parameters, which included TA and GA concentrations as well as coating time. The study examined the effects of the total content of TA/PEI and GA/PEI concentrations on the chemical structure, surface roughness, and microstructure of the selective layer of LNM using SEM, AFM, FTIR, and water contact angle measurements. It also investigated the filtration performance of the membrane's selective layer, including pure water flux, PEG800 rejection rate, and membrane fouling analysis. However, the resultant membrane treated simulated reactive black 5 (RB5) dye wastewater. When the total content of TA/PEI is 4 kg L-1, the permeability of pure water flux is high at 7.5 L per m2 per h per bar when the total content of GA/PEI is 14 kg L-1 and the pure water flux is high at 8.8 L per m2 per h per bar. The overall PEG800 rejection rates were 97-98.98%. The optimal TA : PEI ratios reached a good pure water permeability up to 6.4 L per (m2 per h per bar) with a high rejection rate of 99.69% for a ratio 1/3 to dye, and GA : PEI ratios reached a good water permeability at 5.5 and 6.5 L per (m2 per h per bar) with rejection rates of 99.21% and 98.88% for ratio 1/3 and 3.5/10.5 for simulated RB5 dye, and the NaCl retention rate gradually decreased from 4% to 3%. The resultant LNM demonstrated promising applications in dye and salt fractionation.

β-cyclodextrin polymer composites for the removal of pharmaceutical substances, endocrine disruptor chemicals, and dyes from aqueous solution- A review of recent trends

Cyclodextrin (CD) and its derivatives are receiving attention as a new-generation adsorbent for water pollution treatment due to their external hydrophilic and internal hydrophobic properties. Among types of CD, β-Cyclodextrin (βCD) has been a material of choice with a proven track record for a range of utilities in distinct domains, owing to its unique cage-like structural conformations and inclusion complex-forming ability, especially to mitigate emerging contaminants (ECs). This article outlines βCD composites in developing approaches of their melds and composites for purposes such as membranes for removal of the ECs in aqueous setups have been explored with emphasis on recent trends. Electrospinning has bestowed an entirely different viewpoint on polymeric materials, comprising βCD, in the framework of diverse functions across a multitude of niches. Besides, this article especially discusses βCD polymer composite membrane-based removal of contaminants such as pharmaceutical substances, endocrine disruptors chemicals, and dyes. Finally, in this article, the challenges and future directions of βCD-based adsorbents are discussed, which may shed light on pragmatic commercial applications of βCD polymer composite membranes.

Tailoring the performance of composite PEI nanofiltration membranes via incorporating activated cyclodextrins

Cyclodextrins (CDs) with unique cavity structures have been used as materials for nanofiltration membrane fabrications. In the present work, the activated CD (O-CD), oxidated by NaIO4, and polyethyleneimine (PEI) were co-deposited on a hydrolyzed polyacrylonitrile support, post-treated by glycerol protection and heating treatment, to prepare nanofiltration membranes with low molecular weight cut-off (MWCO). As the cavities in CD present and the aldehyde groups introduced after oxidation, the O-CDs were expected to crosslink the PEI layer and provide extra permeating channels. The filtration experiments showed that the incorporation of O-CDs improved the permeances of the O-CD-PEI/HPAN nanofiltration membranes. The performance can be tailored by the control of the loading or the oxidation degree of the O-CD. At optimal conditions, the permeance increment was nearly double (from 9.2 to 21.1 Lm-2·h-1·bar-1). While the selectivity was without significant sacrifice, the rejection of PEG 200 remained around 90%. Meanwhile, the membrane stability was demonstrated by pro-longed filtratiing a PEG 200 aqueous solution. The constant permeance and rejection confirmed the O-CD-PEI/HPAN membranes were stable. The incorporation of activated CD in PEI offers a facile strategy to promote the permeance of PEI-based membranes.

Low-pressure thin-film composite nanofiltration membranes with enhanced selectivity and antifouling property for effective dye/salt separation

For better sustainable resource recovery and elevating the separation efficiency of dye/salt mixture, it is essential to develop an appropriate nanofiltration membrane for the treatment of textile dyeing wastewater containing relatively smaller molecule dyes. In this work, a novel composite polyamide-polyester nanofiltration membrane was fabricated by tailoring amino functionalized quantum dots (NGQDs) and β-cyclodextrin (CD). An in-situ interfacial polymerization occurred between the synthesized NGQDs-CD and trimesoyl chloride (TMC) on the modified multi-carbon nanotubes (MWCNTs) substrate. The incorporation of NGQDs significantly elevated the rejection (increased by ∼ 45.08%) of the resultant membrane for small molecular dye (Methyl orange, MO) compared to the pristine CD membrane at low pressure (1.5 bar). The newly developed NGQDs-CD-MWCNTs membrane exhibited enhanced water permeability without compromising the dye rejection compared to the pure NGQDs membrane. The improved performance of the membrane was primarily attributed to the synergistic effect of functionalized NGQDs and the special hollow-bowl structure of CD. The optimal NGQDs-CD-MWCNTs-5 membrane expressed pure water permeability of 12.35 L m^-2h^-1 bar^-1 at the pressure of 1.5 bar. Noteworthily, the NGQDs-CD-MWCNTs-5 membrane not only showed high rejection for the larger molecular dye of Congo Red (CR, 99.50%) but also for the smaller molecular dye of MO (96.01%) and Brilliant Green (BG, 95.60%) with the permeability of 8.81, 11.40, and 6.37 L m^-2h^-1 bar^-1, respectively at low pressure (1.5 bar). The rejection of inorganic salts by the NGQDs-CD-MWCNTs-5 membrane was 17.20% for sodium chloride (NaCl), 14.30% for magnesium chloride (MgCl₂), 24.63% for magnesium sulfate (MgSO₄), and 54.58% for sodium sulfate (Na₂SO₄), respectively. The great rejection of dyes remained in the dye/salt binary mixed system (higher than 99% for BG and CR, <21% for NaCl). Importantly, the NGQDs-CD-MWCNTs-5 membrane exhibited favorable antifouling performance and potential good operation stability performance. Consequently, the fabricated NGQDs-CD-MWCNTs-5 membrane suggested a prospective application for the reuse of salts and water in textile wastewater treatment owing to the effective selective separation performance.

A review on polyester and polyester-amide thin film composite nanofiltration membranes: Synthesis, characteristics and applications

Nanofiltration (NF) membranes have been widely used in various fields including water treatment and other separation processes, while conventional thin film composite (TFC) membranes with polyamide (PA) selective layers suffer the problems of fouling and chlorine intolerance. Due to the abundant hydrophilic hydroxyl groups and ester bonds free from chlorine attack, the TFC membranes composed of polyester (PE) or polyester-amide (PEA) selective layers have been proven to possess enhanced anti-fouling properties and superior chlorine resistance. In this review, the research progress of PE and PEA nanofiltration membranes is systematically summarized according to the variety of hydroxyl-containing monomers for membrane fabrication by the interfacial polymerization (IP) reaction. The synthesis strategies as well as the mechanisms for tailoring properties and performance of PE and PEA membranes are analyzed, and the membrane application advantages are demonstrated. Moreover, current challenges and future perspectives of the development of PE and PEA nanofiltration membranes are proposed. This review can offer guidance for designing high-performance PE and PEA membranes, thereby further promoting the efficacy of nanofiltration.

Loosely Sandwich-Structured Membranes Decorated with UiO-66-NH2 for Efficient Antibiotic Separation and Organic Solvent Resistance

Thin-film nanocomposite (TFN) membranes with efficient molecular separation and organic solvent resistance are active in demand in wastewater treatment and resource reclamation, meeting the goal of emission peaks and carbon neutrality. In this work, a simple and rational design strategy has been employed to construct a sandwich-structured membrane for removing fluoroquinolone antibiotics and recycling organic solvents. The sandwich-structured membrane is composed of a porous substrate, a hydrophilic tannic acid-polyethyleneimine (TA-PEI) interlayer, and a polyamide (PA) selective layer decorated with metal-organic framework (PA-MOF). Results manifest that the hydrophilic TA-PEI interlayer played a bridging and gutter effect to achieve effective control in amide storage, amine diffusion, and nanomaterial downward leakage at the immiscible interface. The PA-MOF selective layer has been changed to a loosely crumpled surface, endowing functionalities on the sandwich-structured membrane that included limited pores, strengthened electronegativity, and stronger hydrophilicity. Thus, an enhanced water flux of 87.23 ± 7.43 LMH was achieved by the TFN-2 membrane (0.04 mg·mL^-1 UiO-66-NH₂), which is more than five times that of the thin-film composite membrane (17.46 ± 3.88 LMH). The rejection against norfloxacin, ciprofloxacin, and levofloxacin is 92.94 ± 1.60%, 94.62 ± 1.29%, and 96.92 ± 1.05%, respectively, effectively breaking through the "trade-off" effect between membrane permeability and rejection efficiency. Further antifouling results showed that the sandwich-structured membrane had lower flux decay ratios (3.36∼7.07%) and higher flux recovery ratios (93.40∼98.40%), as well as superior long-term stability after 30 days of filtration. Moreover, organic solvent resistance testing confirms that the sandwich-structured membrane maintained stable solvent flux and better recovery rates in ethanol, acetone, isopropanol, and N,N-dimethylformamide. Detailed nanofiltration mechanism studies revealed that these outstanding performances are based on the joint effect of the TA-PEI interlayer and PA-MOF selective layer, proposing a new perspective to break through the bottleneck of nanofiltration application in a complex environment.