A de novo sacrificial-MOF strategy to construct enhanced-flux nanofiltration membranes for efficient dye removal

Microplastics and dye removal from textile wastewater using MIL-53 (Fe) metal-organic framework-based ultrafiltration membranes

Microplastics (MPs) and other organic matters in textile wastewater have posed a formidable challenge for treatment processes, particularly in the primary stages such as ultrafiltration (UF). UF plays a crucial role in preventing the entry of pollutants into subsequent treatment steps. However, the performance efficiency of UF membranes is compromised by the potential fouling of membrane pores by MPs, dyes and other organic pollutants such as bovine serum albumin (BSA). This study focuses on enhancing UF membrane performance, specifically its antifouling properties, through the development of high-performance membranes using MIL-53(Fe) metal-organic framework (MOF) particles (noted as MIL-53 here). Various concentrations of the MIL-53 (0.05, 0.1, 0.2, and 0.5 wt%) were integrated into the membrane structure through phase inversion process. Streaming zeta potential results confirmed the negatively charged surface of the membranes and their high hydrophilicity was validated through contact angle analysis. FTIR, SEM, EDS, and XRD confirmed the presence of MIL-53 particles on the surface of membranes. The developed membranes were tested for 24 h to assess their antifouling properties, with a subsequent 30-min hydraulic flush to measure their flux recovery ratios. Methylene Blue (MB) dye was used as a cationic dye present in textile wastewater to evaluate the efficiency of the developed membranes in dye removal and the synergistic effects of dye rejection in the presence of organic matters (i.e., MPs and BSA). Since previous studies have not fully addressed the combination of dyes and organic matter, this study thoroughly investigated the effect of particle-type foulants (MPs) and their interactions with dye (MB), as well as water soluble protein-type foulants (BSA) and their interaction with MB. The results indicated that the developed membranes exhibited higher MB rejection when the dye was present with either MP or BSA, along with improved antifouling properties. The optimised UF membrane integrated with 0.1 wt% MIL-53 demonstrated nearly 96% BSA rejection and around 86% MB rejection in the mixed foulant case (BSA-MB). The modified membrane exhibited a substantial increase in water flux from 176 L m-2.h-1 to 327 L m-2.h-1. The findings of this research show the potential of iron-based MOFs in improving the performance of UF membranes and provide a platform for future studies on significant areas such as long-term stability studies and testing with other pollutants found in textile wastewater.

pH-triggered polydopamine-decorated nanocellulose membranes for continuously selective separation of organic dyes

Membrane separation technology has emerged as a powerful tool to separate organic dyes from industrial wastewater. However, continuously selective separation of organic dyes with similar molecular weight remains challenging. Herein, we presented a pH-triggered membrane composed of polydopamine-decorated tunicate-derived cellulose nanofibers (PDA@TCNFs) for selective separation of organic dyes. Such self-supporting membranes with nanoporous structure were fabricated by facile vacuum-assisted filtration of PDA@TCNF suspension. The incorporation of polydopamine not only enhanced the stability of the membranes, but also endowed membranes with excellent pH sensitivity, facilitating the continuously selective separation of organic dyes. These pH-triggered PDA@TCNF membranes could selectively separate Methyl Orange (MO) and Rhodamine B (RB) from the MO/RB mixed solution by switching the pH values. The continuously selective separation of the MO/RB mixed solution was demonstrated, where both MO and RB recovery ratios maintained at ∼99 % during 50 repeated cycles. This work provides a new strategy to develop a pH-triggered sustainable nanocellulose-based membrane for continuously selective separation of mixed dyes.

Recent Advances in Metal-Organic Framework (MOF)-Based Composites for Organic Effluent Remediation

Environmental pollution caused by organic effluents emitted by industry has become a worldwide issue and poses a serious threat to the public and the ecosystem. Metal-organic frameworks (MOFs), comprising metal-containing clusters and organic bridging ligands, are porous and crystalline materials, possessing fascinating shape and size-dependent properties such as high surface area, abundant active sites, well-defined crystal morphologies, and huge potential for surface functionalization. To date, numerous well designated MOFs have emerged as critical functional materials to solve the growing challenges associated with water environmental issues. Here we present the recent progress of MOF-based materials and their applications in the treatment of organic effluents. Firstly, several traditional and emerging synthesis strategies for MOF composites are introduced. Then, the structural and functional regulations of MOF composites are presented and analyzed. Finally, typical applications of MOF-based materials in treating organic effluents, including chemical, pharmaceutical, textile, and agricultural wastewaters are summarized. Overall, this review is anticipated to tailor design and regulation of MOF-based functional materials for boosting the performance of organic effluent remediation.

Optimization of Y and T-shaped microchannels for liquid-liquid extraction

Solvent extraction on a micro-scale has received much attention due to its advantages in recent years. The purpose of this research is to compare the inlet geometry of T and Y-shaped microchannels. In this research, solvent extraction of Crystal Violet (CV) was investigated using Di-(2-ethylhexyl) phosphoric acid (D2EHPA) extractor and hexane solvent in Y and T-shaped microchannels with lengths of 4, 6, and 8 cm. The effect of parameters such as inlet geometry, length of microchannels (4-8 cm), dye solution pH (3-11), flow rate (1-1.5 mL/h) and the concentration of CV (25-75 ppm) was investigated. The Results showed that under the same conditions, Y-shaped microchannel performance is better than T-shaped microchannel. pH of dye solution phase, flow rate, inlet CV concentration, and microchannel length were obtained as optimal conditions for extraction, 10.9, 1.1 mL/h, 46.4 ppm, and 7.6 cm, respectively, and the amount of extraction, in this case, was % 97/96 was obtained.

Review of Synthesis and Separation Application of Metal-Organic Framework-Based Mixed-Matrix Membranes

Metal-organic frameworks (MOFs) are porous crystalline materials assembled from organic ligands and metallic secondary building blocks. Their special structural composition gives them the advantages of high porosity, high specific surface area, adjustable pore size, and good stability. MOF membranes and MOF-based mixed-matrix membranes prepared from MOF crystals have ultra-high porosity, uniform pore size, excellent adsorption properties, high selectivity, and high throughput, which contribute to their being widely used in separation fields. This review summarizes the synthesis methods of MOF membranes, including in situ growth, secondary growth, and electrochemical methods. Mixed-matrix membranes composed of Zeolite Imidazolate Frameworks (ZIF), University of Oslo (UIO), and Materials of Institute Lavoisier (MIL) frameworks are introduced. In addition, the main applications of MOF membranes in lithium-sulfur battery separators, wastewater purification, seawater desalination, and gas separation are reviewed. Finally, we review the development prospects of MOF membranes for the large-scale application of MOF membranes in factories.

Constructing Mechanical Shuttles in a Three-dimensional (3D) Porous Architecture for Selective Transport of Lithium Ions

Lithium (Li) extraction from brines is a major barrier to the sustainable development of batteries and alloys; however, current separation technology suffers from a trade-off between ion selectivity and permeability. Herein, a crown ether mechanically interlocked 3D porous organic framework (Crown-POF) was prepared as the porous filler of thin-film nanocomposite membranes. Crown-POF with penta-coordinated (four O_crown atoms and one N_tert-amine atom) adsorption sites enables a special recognition for Li⁺ ion. Moreover, the four N_tert-amine atoms on each POF branch facilitate the flipping motion of Li⁺ ion along the skeletal thread, while retaining the specified binding pattern. Accordingly, the crown ether interlocked POF network displays an ultrafast ion transfer rate, over 10 times that of the conventional porous materials. Notably, the nanocomposite membrane gives high speed and selectivity for Li⁺ ion transport as compared with other porous solid-based mixed-matrix membranes.

Coenzyme self-sufficiency system-recent advances in microbial production of high-value chemical phenyllactic acid

Phenyllactic acid (PLA), a natural antimicrobial substance, has many potential applications in the food, animal feed, pharmaceutical and cosmetic industries. However, its production is limited by the complex reaction steps involved in its chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, enzymatic or whole-cell catalysis was developed as an alternative method for PLA production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value PLA. Specially, the advantages and disadvantages of the using of the three kinds of substrates, which includes phenylpyruvate, phenylalanine and glucose as starting materials by natural or engineered microbes is summarized. Notably, the bio-conversion of PLA often requires the consumption of expensive coenzyme NADH. To overcome the issues of NADH regeneration, efficiently internal cofactor regeneration systems constructed by co-expressing different enzyme combinations composed of lactate dehydrogenase with others for enhancing the PLA production, as well as their possible improvements, are discussed. In particular, the construction of fusion proteins with different linkers can achieve higher PLA yield and more efficient cofactor regeneration than that of multi-enzyme co-expression. Overall, this review provides a comprehensive overview of PLA biosynthesis pathways and strategies for increasing PLA yield through biotechnology, providing future directions for the large-scale commercial production of PLA and the expansion of downstream applications.

Interaction of Direct Blue 86 with cationic surfactant micelles: spectroscopic, conductometric and thermodynamic aspects

Due to the amphiphilic structure of surfactants, aqueous surfactant solutions can behave like very good solvents and dissolve both polar and non-polar solutes. This study reports on the solubilisation of a direct dye (Direct Blue 86) in a micellar medium using the cationic surfactant cetyltrimethylammonium bromide (CTAB). Solubilisation of dyes is important for their subsequent removal from aqueous media. UV spectroscopy and conductometry, among others, were used to quantitatively evaluate this process. The extent of solubilisation, the interaction between the molecules and the stability of the processes were checked using the partition coefficient (K x), the binding constant (K b) and the corresponding thermodynamic parameters. From the results, it could be concluded that the solubilisation of Direct Blue 86 is a spontaneous process supported by an increase in entropy. It was also found that the micellar medium CTAB is efficient for solubilisation and binding of the dye and can be used economically.

Recent trends and challenges with the synthesis of membranes: Industrial opportunities towards environmental remediation

The industrial and agricultural revolution has posed a serious and potential threat to environment. The industrial and agricultural pollutants are directly released into the environment. This issue has clinched the scientists to work on different materials in order to decontaminate the environment. Among all other techniques, the membrane filtration technology has fascinated researchers to overcome the pollution by its promising features. This review elaborated various membrane synthesis approaches along with their mechanism of filtration, their applications towards environmental remediation such as removal of heavy metals, degradation of dyes, pharma waste, organic pollutants, as well as gas sensing applications. The membrane synthesis using different sort of materials in which inorganic, carbon materials, polymers and metal organic framework (MOFs) are highlighted. These materials have been involved in synthesis of membrane to make it more cost effective and productive to remove such hazardous materials from wastewater. Based on the reported literature, it has been found that inorganic and polymer membranes are facing issues of brittleness and swelling prior to the industrial scale applications related to the high temperature and pressure which needs to be addressed to enhance the permeation performance.

Ni-MOF composite polypyrrole applied to supercapacitor energy storage

Electrodes for supercapacitors made from metal-organic frameworks (MOFs) are still hindered by electron transfer properties. Therefore, an electrode composite material Ni-MOF@PPy was synthesized from a Ni-based metal-organic framework (Ni-MOF) doped with poly-pyrrole (PPy) using a simple chemical oxidation method to improve its electron transfer property. After introducing the electrochemically active substance K₄Fe(CN)₆ into the electrolyte, the composite material had a specific capacitance of 1815.4 F g^-1 at a current density of 1 A g^-1. Ni-MOF@PPy and active carbon (AC) as the positive and negative electrodes have been used, respectively, to assemble asymmetric supercapacitors (ASCs) in the KOH and K₄Fe(CN)₆ mixed electrolyte. This novel Ni-MOF@PPy//AC ASC energy storage device can provide 38.5 W h kg^-1 energy density, 7001 W kg^-1 power density, and 90.2% capacitance retention after 3000 cycles. Therefore, Ni-MOF@PPy//AC ASC is an excellent energy storage device with practical and economic value. The synergistic effect strategy proposed in this work can be easily applied to develop other MOFs with unique crystal structures as well as other redox active additives, providing new avenues and research ideas for exploring novel energy storage devices.

Recent progress in nanomaterial-functionalized membranes for removal of pollutants

Membrane technology has gained tremendous attention for removing pollutants from wastewater, mainly due to their affordable capital cost, miniature equipment size, low energy consumption, and high efficiency even for the pollutants present in lower concentrations. In this paper, we review the literature to summarize the progress of nanomaterial-modified membranes for wastewater treatment applications. Introduction of nanomaterial in the polymeric matrix influences membrane properties such as surface roughness, hydrophobicity, porosity, and fouling resistance. This review also covers the importance of functionalization strategies to prepare thin-film nanocomposite hybrid membranes and their effect on eliminating pollutants. Systematic discussion regarding the impact of the nanomaterials incorporated within membrane, toward the recovery of various pollutants such as metal ions, organic compounds, dyes, and microbes. Successful examples are provided to show the potential of nanomaterial-functionalized membranes for regeneration of wastewater. In the end, future prospects are discussed to develop nanomaterial-based membrane technology.

Zero Discharge of Dyes and Regeneration of a Washing Solution in Membrane-Based Dye Removal by Cold Plasma Treatment

Although dye removal from wastewater streams has been investigated via several approaches using adsorbents, resins, or membranes, it is still hard to avoid the fact that dyes are persistently left in the adsorption materials or washing solutions used to regenerate the used adsorbents. In particular, given that cleaning agents are composed of acid/base, organic solvents, or electrolytes, dye adsorption and adsorbent regeneration processes leave behind more hard-to-manage wastewater containing dyes. In this study, we demonstrated that cold plasma (CP) treatment, which is one of the advanced oxidation processes (AOPs), can be used for zero discharge of dyes and regeneration of a washing solution in a membrane-based dye removal process. Specifically, CP treatment was found to successfully remove dyes released from a washing process to regenerate a used membrane, thereby effectively recycling a cleaning solution. As a result, the regenerated washing solution was more favorable for the adsorbed dyes’ elution, leading to the successful regeneration of a used membrane without a significant loss of dye removal efficiency. This fact was evidenced by a comparative study on the effect of CP treatment on the reusability of membranes and washing solutions and the kinetic analysis of the AOP of the desorbed dyes. We hope that this study contributes to opening a new door for environmentally friendly and sustainable dye removal.

Mussel-inspired tannic acid/polyethyleneimine assembling positively-charged membranes with excellent cation permselectivity

The extraction of valuable target ions through monovalent cation exchange membranes (MCEMs) has been increasingly attracting in modern energy and environmental fields. However, the separation performance of MCEMs in terms of the permselectivity and cation fluxes, is typically restricted by membrane architecture and applied materials. Recently, mussel-inspired surface modification methods have been deployed in new membrane fabrications with special surface characteristics and functions. Herein, a facile layer-by-layer assembly method was designed to construct a series of de novo positively-charged tannic acid/polyethyleneimine (TA/PEI) membranes containing a negatively-charged support membrane and a TA/PEI selective layer. Notably, the peculiar support membrane with a much dense structure and abundant cation exchange groups can enable our TA/PEI membranes to possess high total cation fluxes. The selective layer with vast positive charges ensures mussel-inspired TA/PEI assembled positively-charged membranes to have a high permselectivity. Most importantly, compared with the separation performance of the state-of-the-art MCEMs, the superior separation performance of our developed new MCEMs at 5 mA·cm^-2 and 10 mA·cm^-2 is beyond the current "Upper Bound" plot between Na⁺ flux and the permselectivity (Na⁺/Mg²⁺), which opens new avenues for the construction of MCEMs. Furthermore, high purity of Li⁺ (95.37%) can be obtained through deploying mussel-inspired TA/PEI assembled positively-charged membranes with high permselectivity of Li⁺/Mg²⁺ (13.72), proving its great potentials in the field of resource recovery towards sustainability.

Collagen Fibril-Assembled Skin-Simulated Membrane for Continuous Molecular Separation

A skin-simulated thin-film-composite membrane was fabricated using a vacuum-assisted interfacial polymerization method. A negatively charged surface-selective layer on a polyacrylonitrile (PAN) substrate was cross-linked using trimesoyl chloride to form polyamide and polyester with a three-layer structure that was similar to skin. The loading of collagen fibrils assembled on the membrane surface was varied, and a selective layer was obtained, of which the thickness, morphology, and hydrophilicity can be manipulated. The optimal membrane decorated with 0.5 mg of collagen fibril had a selective layer thickness of around 130 nm with pure water permeability up to 84.7 LMH bar^-1. Furthermore, the membrane exhibited impressive rejections toward dyes (Congo red with a molecular weight of 696.68 Da: 99.6%, reactive blue 19 with a molecular weight of 626.54 Da: 99.8%, and Coomassie blueG-250 with a molecular weight of 854.02 Da: 98.6%) while high permeations of Na₂SO₄ and NaCl were achieved. This facile strategy provides a useful guideline for constructing bionic membranes through biomaterials.

Covalent Organic Framework-Mediated Thin-Film Composite Polyamide Membranes toward Precise Ion Sieving

Covalent organic frameworks (COFs) have evinced a potential solution that promises for fast and efficient molecular separation due to the presence of orderly arranged pores and regulable pore apertures. Herein, the synthesized COF (TPB-DMTP-COF) with the pore aperture matching the pore size of the nanofiltration (NF) membrane was utilized to modulate the physicochemical characters of the polyamide (PA) membranes. It is demonstrated that COFs with superior polymer affinity and hydrophilicity not only circumvent the nonselective interfacial cavities but also improve the hydrophilicity of the resultant thin-film nanocomposite (TFN) membranes. Furthermore, the predeposited COF layer is able to slow down the diffusion rate toward the reaction boundary through hydrogen bonding, which is consistent with the results of molecular dynamic (MD) and dissipative particle dynamic (DPD) simulations. In this context, COF-modulated TFN membranes show a roughened and thickened surface with bubble-shaped structures in contrast to the nodular structure of original polyamide membranes. Combined with the introduced in-plane pores of COFs, the resultant TFN membranes display a significantly elevated water permeance of 35.7 L m² h^-1 bar^-1, almost 4-fold that of unmodified polyamide membranes. Furthermore, the selectivity coefficient of Cl^-/SO₄^2- for COF-modulated TFN membranes achieves a high value of 84 mainly related to the enhanced charge density, far exceeding the traditional NF membranes. This work is considered to provide a guideline of exploring hydrophilic COFs as an interlayer for constructing highly permeable membranes with precise ion-sieving ability.

Dye contaminated wastewater treatment through metal–organic framework (MOF) based materials

A complete discussion of MOFs and MOF composites such as MOF-based membranes, magnetic MOFs, and metal–organic gels (MOGs) used for dye removal along with their adsorption efficiency has been done.

TEA driven C, N co-doped superfine Fe3O4 nanoparticles for efficient trifunctional electrode materials

Poor conductivity is an obstacle that restricts the development of the electrochemistry performance of Fe₃O₄. In this work, a novel carbon and nitrogen co-doped ultrafine Fe₃O₄ nanoparticles (CN-Fe₃O₄) have been synthesized by triethylamine (TEA) induction and subsequent calcination. The addition of TEA could not only regulate the size of Fe₃O₄ nanoparticles, but also promote the formation of amorphous carbon layer. Well-designed CN-Fe₃O₄ heterostructures provide a highly interconnected porous conductive network, large heterogeneous interface area, large specific surface area and a large number of active sites, which greatly improve conductivity and promote electron transfer and electrolyte diffusion. The prepared CN-Fe₃O₄ electrode exhibits a high specific capacitance of 399.3 mF cm^-2 and good cycling stability. Meanwhile, CN-Fe₃O₄ catalyst exhibits excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities, with overpotentials of 136 and 281 mV at the current density of 10 mA cm^-2, respectively. This work provides a promising approach for the design of high-performance anode materials for supercapacitors and provides profound implications for the development of catalysts with bifunctional catalytic activity.

Preparation of a rice straw-based green separation layer for efficient and persistent oil-in-water emulsion separation

Inefficiency, high cost, and complex operation have emerged as shackles for large-scale separate oil-in-water emulsion. Herein, a low-cost and eco-friendly separation layer with a rough structure and rich anionic groups was fabricated from rice straw (RS) via a simple acid-base treatment and slight squeeze process. The separation layer's morphology, composition, and wettability were investigated. It was then employed to separate oil-in-water emulsion. The RS after acid and alkali treatment (A₁A₂-RS) exhibited a clear fiber structure and abundant humps, which made the separation layer superwettable and highly electronegative (-26.55 mV). The overlapped and intertwined A₁A₂-RS layer structure owned a superior performance for hexadecyl-trimethyl-ammonium-bromide (CTAB) adsorption and tiny oil interception. As a result, the separation layer had stable fluxes (>500 LMH) for multiple CTAB-stabilized emulsions and the obtained filtrates performed low total organic carbon (TOC) contents (<30 mg/L). In addition, the A₁A₂-RS layer had excellent renewability (10 cycles/ 200 mL) and the flux could be substantially recovered merely by aqueous wash. Moreover, filtrate analysis showed that the A₁A₂-RS layer had a good effect on actual emulsion treatment with a TOC removal rate of 89.56%.

Aqueous One-Step Modulation for Synthesizing Monodispersed ZIF-8 Nanocrystals for Mixed-Matrix Membrane

Enhancing the monodispersity and surface properties of nanoporous zeolitic imidazolate frameworks (ZIFs) are crucial for maximizing their performance in advanced nanocomposites for separations. Herein, we developed an in situ method to synthesize monodispersed ZIF-8 nanocrystals with unique dopamine (DA) surface decoration layer (ZIF-8-DA) in an aqueous solution at room temperature. Interestingly, the in situ formation of the monodispersed ZIF-8-DA nanocrystals experiences a triple-stage crystallization process, resulting in a rhombic dodecahedron architecture, which is greatly different from the synthesis of conventional ZIF-8. The crystallinity and abundant microporosity of ZIF-8-DA nanocrystals is well maintained even with the DA surface decoration. Owing to the advanced surface compatibility and pore properties of ZIF-8-DA, ZIF-8-DA/Matrimid mixed-matrix membranes exhibit both higher gas permeability and selectivity than the pristine Matrimid polyimide membrane, which breaks out the traditional "trade-off" phenomena between permeability and selectivity.