Cellulose nanofiber intermediary to fabricate highly-permeable ultrathin nanofiltration membranes for fast water purification

Nonlinear rheology and nanostructural features of twin-chain polymer networks with controlled porosity

HYPOTHESIS

Twin-Chain Networks (TCNs) are polyvinyl alcohol (PVA)-based cryogels with enhanced porosity. They include two PVAs undergoing a polymer-polymer phase separation in pre-gel solution, granting the formation of sponge-like networks after gelation. Gel structural and transport properties, affecting networks' tortuosity, can be optimized for specific applications, such as the cleaning of Modern and Contemporary Art, by selecting polymer pairs with specific micro-segregation behavior in the pre-gel solution.

EXPERIMENTS

In this work, TCNs were obtained by using PVAs of increasing molecular weight as porogens. Pre-gel solutions and gels morphology were observed through Confocal Laser Scanning Microscopy (CLSM), while properties like elasticity, crystallinity and characteristic dimensions at the nanoscale were explored through rheology, Differential Scanning Calorimetry (DSC) and Small Angle X-ray Scattering (SAXS). The gels' yielding behavior in the non-linear viscoelastic region was related to the crosslinks size/local concentration and the tortuosity at the nanoscale (obtained through Fluorescence Correlation Spectroscopy, FCS, measurements).

FINDINGS

TCNs pores size increases with the porogen molecular weight. Despite a clear difference in the gels porosity at the micron-scale, only minor structural differences emerged through SAXS, DSC and linear rheology analysis. Gels deformation in the non-linear regime, analyzed through the Sequence of Physical Processes (SPP) approach, unraveled, for the first time, the hidden nanoscale features determining gels behavior at yielding, clarifying the role of the different porogens during cryostructuration. The nature of gels' physical junctions was found to be intertwined with the gels' tortuosity at the nanoscale, eventually affecting the cleaning ability of this new class of materials.

Ultrasound-Assisted sequential processing of barley straw using binary acidic and hydrated ternary deep eutectic solvents for nanocellulose production

This study aimed to valorise barley straw by using a binary acidic deep eutectic solvent (DES) made from choline chloride and lactic acid for biomass pretreatment, and a hydrated ternary DES (HDES) composed of betaine, oxalic acid, and water (BOW HDES) for downstream processing to produce nanocellulose. The ultrasound-assisted DES pretreatment significantly enhanced lignin and hemicellulose solubilisation, achieving an average lignin removal of 70.54 % and hemicellulose solubilisation of 69.58 % under optimal conditions. Purification of US-DES-treated solid residue resulted in a cellulose yield of 39.81 ± 1.47 % with a purity of 91.31 ± 0.93 %, comparable to or exceeding conventional fractionation methods. The yield of lignin-rich material was 9.40 ± 0.89 % with a lignin purity of 83.29 ± 1.57 %. Further, nanocellulose was produced using a sequential process comprising low-viscosity HDES treatment, which improved fibre swelling and solubilisation, followed by high-intensity ultrasound (HIUS) treatment for nanoscale defibrillation. DLS analysis of the optimal nanocellulose sample revealed that 77.8 % of nanoparticles had a diameter below 100 nm, demonstrating a high yield of nanoscale material. XRD analysis confirmed the preservation of the cellulose I crystalline structure throughout processing, ensuring structural integrity. These findings demonstrate an efficient and sustainable biorefinery approach for lignin, cellulose, and nanocellulose extraction from agricultural residues, offering potential for scalable nanocellulose production.

Highly Permeable Nanofibrous Composite Nanofiltration Membranes by Controllable Interfacial Copolymerization

An ultrathin nanofibrous composite nanofiltration (NF) membrane was developed through controlled interfacial copolymerization where an electrospun sulfonated poly(ether sulfone) (SPES) nanofibrous membrane serves as the substrate and 2,5-diaminobenzenesulfonic acid (2,5-DABSA) and piperazine (PIP) serve as aqueous phase monomers. The integration of the electrostatic interaction and hydrogen bonding between SPES nanofibers and PIP/2,5-DABSA triggered the controlled diffusion rate of monomers into the organic phase, resulting in the fabrication of an ultrathin polyamide barrier layer (∼56 nm). Additionally, a polyamide structure was created through the ternary interfacial copolymerization of PIP/2,5-DABSA and trimesoyl chloride (TMC), which offers high permeability to the composite NF membrane. Meanwhile, the -SO3H groups on 2,5-DABSA issued highly negative charges to the polyamide barrier layer, leading to a significant improvement in the rejection ratio against SO42- and fouling resistance against bovine serum albumin. The impact of 2,5-DABSA monomer on the cross-linking degree and pore size distribution of the polyamide barrier layer was investigated by optimizing the proportion of PIP and 2,5-DABSA monomers in the interfacial polymerization (IP) process. The ion selectivity and robustness of the composite NF membrane was determined and compared with conventional and commercial NF membranes comprehensively. Molecular dynamics simulations were conducted to demonstrate the mechanism of the controlled diffusion of monomers; the cross-linking degree and fractional free volume of the polyamide barrier layer were also evaluated. The NF-M(1:1) composite membrane exhibited a significant enhancement in the permeation flux as 137.4 L/m2·h at 0.5 MPa, which was 4 times higher than that of conventional NF membranes, while maintaining excellent divalent salt rejection against Na2SO4 at 99.4%, compared with 98.0% of the conventional NF membrane, effectively breaking through the trade-off effect in the long-term filtration performance.

Regulating Zn2+/H+ selectivity through functional group design of separators for long-lifespan aqueous zinc batteries

Zn anodes in aqueous rechargeable zinc batteries (AZBs) are plagued by irreversibility issues stemming from dendrite growth, hydrogen evolution, and corrosion. The design of separator offers a promising approach to enhance the reversibility of Zn anodes, but a universal strategy for rational separator design remains elusive. In this study, we propose a comprehensive design principle that takes into account the selective binding with Zn2+, H+ and H2O, and further suggest that separators should ideally exhibit strong binding strength with H+ and H2O but weak with Zn2+. We explore four typical scenarios based on varying binding strengths and identify polyethersulfone (PES) as a highly promising separator through screening of various commercial separators. Both experiment and theoretical calculations reveal that PES effectively regulates the transfer of Zn2+, H+ and H2O, thereby concurrently suppressing dendrite growth, hydrogen evolution, and corrosion. As a result, the Zn‖Zn symmetric battery can operate for over 4000 h at 1 mA cm-2 and 1 mA h cm-2. Furthermore, the full battery can deliver an impressive lifespan of over 6400 cycles at 3 A g-1. This work not only introduces a new separator for high-performance AZBs but also provides guiding principles for functional separator design.

Nanocellulose-based functional materials towards water treatment

Water resources are important ecological resources for human survival. To date, advanced water purification technology has become one of the focus of global attention due to the continuous deterioration of the environment and the serious shortage of freshwater resources. Recently, nanocellulose, as a kind of sustainable and carbon-neutral biopolymer, has not only the properties of cellulose, but also the important nature of nanomaterials, including large specific surface area, tailorable surface chemistry, excellent mechanical flexibility, biodegradability, and environmental compatibility. Herein, this review covers several methods of extraction and preparation of nanocellulose and the functional modification strategies. Subsequently, we systematically review the application and latest research progress of nanocellulose-based functional material towards water treatment, from micro/nanoparticles filtration, dyes/organics adsorption/degradation, heavy metal ions adsorption/detection and oil-water separation to seawater desalination. Furthermore, scalable and low-cost nanocellulose synthesis strategies are discussed. Finally, the challenges and opportunities of nanocellulose water purification substrate in industrial application and emerging directions are briefly discussed. This review is expected to provide new insights for the application of advanced functional materials based on nanocellulose in water treatment and environmental remediation, and promote rapid cross-disciplinary development.

Reconstructing Electrically Conductive Nanofiltration Membranes with an Aniline-Functionalized Carbon Nanotubes Interlayer for Highly Effective Toxic Organic Treatment

Conductive nanofiltration (CNF) membranes hold great promise for removing small organic pollutants from water through enhanced Donnan exclusion and electrocatalytic degradation. However, current CNF membranes face limitations in conductivity, structural stability, and nanochannel control strategies. This work addresses these challenges by introducing aniline-functionalized carbon nanotubes (NH2-CNTs) as an interlayer. NH2-CNTs enhance the dispersibility and adhesion of pristine carbon nanotubes, leading to a more conductive and stable composite nanofiltration membrane. The redesigned NH2-CNTs interlayered conductive nanofiltration (NICNF) membrane exhibits a 10-fold increase in conductivity and a high response degree (80%) with excellent cyclic stability, surpassing existing CNF membranes. The synergistic effects of enhanced Donnan exclusion, voltage switching, and electrocatalysis enable the NICNF membrane to achieve selective recovery of mixed dyes, 98.97% removal of residual wastewater toxicity, and a 5.2-fold increase in permeance compared to the commercial NF270 membrane. This research paves the way for next-generation multifunctional membranes capable of the efficient recovery and degradation of toxic organic pollutants in wastewater.

A review on the potential of cellulose nanomaterials for the development of thin film composite polyamide membranes for water treatment

Membrane-based separation technologies have drawn significant interest because of their compactness, low energy consumption, and ability to be easily integrated with existing processes. There has been significant interest in the utilization of natural materials derived from sustainable and renewable resources for membrane fabrication. Cellulose is one of the promising polymers which has been extensively studied in membrane fabrication and modification due to its abundant availability, non-toxicity and biodegradability. While there have been several reviews in recent years separately on TFC membranes and cellulose-based materials for different applications, reviews exclusively focusing on cellulosic nanomaterials-based TFC membranes are still lacking. This review provides an overview of the types of cellulose nanomaterials exploited for the development and modification of TFC membranes, particularly those used for desalination and wastewater treatment. We have presented a brief description of cellulose-based nanomaterials followed by a detailed discussion of different studies addressing each cellulose nanomaterial separately. In addition, we have summarized the performance of different studies in the literature, paying particular attention to the enhancement achieved by the incorporation of cellulose nanomaterial in the membrane.

Cellulose Membranes: Synthesis and Applications for Water and Gas Separation and Purification

Membranes are a selective barrier that allows certain species (molecules and ions) to pass through while blocking others. Some rely on size exclusion, where larger molecules get stuck while smaller ones permeate through. Others use differences in charge or polarity to attract and repel specific species. Membranes can purify air and water by allowing only air and water molecules to pass through, while preventing contaminants such as microorganisms and particles, or to separate a target gas or vapor, such as H2 and CO2, from other gases. The higher the flux and selectivity, the better a material is for membranes. The desirable performance can be tuned through material type (polymers, ceramics, and biobased materials), microstructure (porosity and tortuosity), and surface chemistry. Most membranes are made from plastic from petroleum-based resources, contributing to global climate change and plastic pollution. Cellulose can be an alternative sustainable resource for making renewable membranes. Cellulose exists in plant cell walls as natural fibers, which can be broken down into smaller components such as cellulose fibrils, nanofibrils, nanocrystals, and cellulose macromolecules through mechanical and chemical processing. Membranes made from reassembling these particles and molecules have variable pore architecture, porosity, and separation properties and, therefore, have a wide range of applications in nano-, micro-, and ultrafiltration and forward osmosis. Despite their advantages, cellulose membranes face some challenges. Improving the selectivity of membranes for specific molecules often comes at the expense of permeability. The stability of cellulose membranes in harsh environments or under continuous operation needs further improvement. Research is ongoing to address these challenges and develop advanced cellulose membranes with enhanced performance. This article reviews the microstructures, fabrication methods, and potential applications of cellulose membranes, providing some critical insights into processing-structure-property relationships for current state-of-the-art cellulosic membranes that could be used to improve their performance.

Biotechnological innovations in nanocellulose production from waste biomass with a focus on pineapple waste

New materials' synthesis and utilization have shown many critical challenges in healthcare and other industrial sectors as most of these materials are directly or indirectly developed from fossil fuel resources. Environmental regulations and sustainability concepts have promoted the use of natural compounds with unique structures and properties that can be biodegradable, biocompatible, and eco-friendly. In this context, nanocellulose (NC) utility in different sectors and industries is reported due to their unique properties including biocompatibility and antimicrobial characteristics. The bacterial nanocellulose (BNC)-based materials have been synthesized by bacterial cells and extracted from plant waste materials including pineapple plant waste biomass. These materials have been utilized in the form of nanofibers and nanocrystals. These materials are found to have excellent surface properties, low density, and good transparency, and are rich in hydroxyl groups for their modifications to other useful products. These materials are well utilized in different sectors including biomedical or health care centres, nanocomposite materials, supercapacitors, and polymer matrix production. This review explores different approaches for NC production from pineapple waste residues using biotechnological interventions, approaches for their modification, and wider applications in different sectors. Recent technological developments in NC production by enzymatic treatment are critically discussed. The utilization of pineapple waste-derived NC from a bioeconomic perspective is summarized in the paper. The chemical composition and properties of nanocellulose extracted from pineapple waste may have unique characteristics compared to other sources. Pineapple waste for nanocellulose production aligns with the principles of sustainability, waste reduction, and innovation, making it a promising and novel approach in the field of nanocellulose materials.

Electrochemical quantification of atrazine-fulvic acid and removal through bismuth tungstate photocatalytic hybrid membranes

Herbicides such as atrazine and humus substances such as fulvic acid are widely used in agricultural sector. They can be traced in surface and groundwater around the agriculture field at concentrations beyond the approved limit due to their mobility and persistence. Bismuth-based photocatalysts activated by visible light are potential materials for removing various organic pollutants from water bodies. These photocatalysts can also be suitable candidates for developing a hybrid membrane with anti-fouling properties. In this study, Bi2WO6 nanoparticles were synthesized via the hydrothermal method and integrated into the cellulose acetate (CA), polyetherimide (PEI), polysulfone (PSF) and polyvinylidene fluoride (PVDF) polymers via physical blending approach. The hybrid membranes were then characterized by FTIR, XPS and FESEM to confirm the chemical bonding, chemical composition and surface morphology of Bi2WO6. Thus, the pure water flux of CA (35.6 L m-2 h-1), PEI (46.56 L m-2 h-1), PSF (6.84 L m-2 h-1), and PVDF (68.47 L m-2 h-1) hybrid membranes has significantly enhanced than the pristine CA, PEI, PSF and PVDF membranes. The significant rejection of atrazine-fulvic acid was observed with hybrid membranes in the order of CA (84.1%) > PVDF (72.7%) > PEI (47.8%) > PSF (37.2%), and these membranes have shown an excellent flux recovery ratio than pristine membranes. Further, electrochemical quantification studies were performed to analyze the removal efficiency of atrazine-fulvic acid from water. In this present work, GO-modified SPE was employed for electrochemical sensing studies. The resultant CA hybrid membrane achieved removal efficiency of 84.08% for atrazine. It was observed that the Bi2WO6 established strong bonding with CA, and PVDF membranes, thus showing a significant removal efficiency and FRR than other hybrid and pristine membranes.

Wastewater treatment with nanomaterials for the future: A state-of-the-art review

Aquatic and terrestrial ecosystems are both threatened by toxic wastewater. The unique properties of nanomaterials are currently being studied thoroughly for treating sewage. Nanomaterials also have the advantage of being capable of removing organic matter, fungi, and viruses from wastewater. Advanced oxidation processes are used in nanomaterials to treat wastewater. Additionally, nanomaterials have a large effective area of contact due to their tiny dimensions. The adsorption and reactivity of nanomaterials are strong. Wastewater treatment would benefit from the development of nanomaterial technology. Second, the paper provides a comprehensive analysis of the unique characteristics of nanomaterials in wastewater treatment, their proper use, and their prospects. In addition to focusing on their economic feasibility, since limited forms of nanomaterials have been manufactured, it is also necessary to consider their feasibility in terms of their technical results. According to this study, the significant adsorption area, excellent chemical reaction, and electrical conductivity of nanoparticles (NPs) contribute to the successful treatment of wastewater.

Biomimetic Microadhesion Guided Instant Spinning

Animals create high-performance fibers at natural ambient conditions via a unique spinning process. In contrast, the spinning technologies developed by human beings are usually clumsy and require sophisticated skills. Here, inspired by adhesion-based silkworm spinning, we report a microadhesion guided (MAG) spinning technology for instant and on-demand fabrication of micro/nanofibers. Enabled by the adhesion between the spinning fluids and the microneedles, the MAG spinning can generate micro/nanofibers with programmable morphology. By further mimicking the head movement of the silkworm spinning, the MAG technology is extended with three different modes: straight, vibratory, and twisted spinning, which generate oriented fibers, hierarchical cross-linked fibers, and all-in-one fibers, respectively. Due to the prevalence of microadhesion and its unprecedented flexibility in operation, equipment-free MAG spinning is finally realized for instant fiber fabrication by only polymeric foams. Finally, the MAG spinning is demonstrated as a promising instant technology for emergent applications, such as wound dressing.

High Flux Nanofiltration Membranes with Double-Walled Carbon Nanotube (DWCNT) as the Interlayer

Nanofiltration (NF) membranes with a high permeability and rejection are of great interest in desalination, separation and purification. However, how to improve the permeation and separation performance still poses a great challenge in the preparation of NF membranes. Herein, the novel composite NF membrane was prepared through the interfacial polymerization of M-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a double-walled carbon nanotube (DWCNT) interlayer supported by PES substrate. The DWCNT interlayer had a great impact on the polyamide layer formation. With the increase of the DWCNT dosage, the XPS results revealed an increase in the number of carboxyl groups, which decreased the crosslinking degree of the polyamide layer. Additionally, the AFM results showed that the surface roughness and specific surface area increased gradually. The water flux of the prepared membrane increased from 25.4 L/(m²·h) and 26.6 L/(m²·h) to 109 L/(m²·h) and 104.3 L/(m²·h) with 2000 ppm Na₂SO₄ and NaCl solution, respectively, under 0.5 MPa. Meanwhile, the rejection of Na₂SO₄ and NaCl decreased from 99.88% and 99.38% to 96.48% and 60.47%. The proposed method provides a novel insight into the rational design of the multifunctional interlayer, which shows great potential in the preparation of high-performance membranes.

Fabrication of Thin Film Composite Membranes on Nanozeolite Modified Support Layer for Tailored Nanofiltration Performance

Thin-film composite (TFC) structure has been widely employed in polymeric membrane fabrication to achieve superior performance for desalination and water treatment. In particular, TFC membranes with a thin active polyamide (PA) selective layer are proven to offer improved permeability without compromising salt rejection. Several modifications to TFCs have been proposed over the years to enhance their performance by altering the selective, intermediate, or support layer. This study proposes the modification of the membrane support using nanozeolites prepared by a unique ball milling technique for tailoring the nanofiltration performance. TFC membranes were fabricated by the interfacial polymerization of Piperazine (PIP) and 1,3,5-Benzenetricarbonyl trichloride (TMC) on Polysulfone (PSf) supports modified with nanozeolites. The nanozeolite concentration in the casting solution varied from 0 to 0.2%. Supports prepared with different nanozeolite concentrations resulted in varied hydrophilicity, porosity, and permeability. Results showed that optimum membrane performance was obtained for supports modified with 0.1% nanozeolites where pure water permeance of 17.1 ± 2.1 Lm^-2 h^-1 bar^-1 was observed with a salt rejection of 11.47%, 33.84%, 94%, and 95.1% for NaCl, MgCl₂, MgSO_4, and Na₂SO₄ respectively.

Encapsulating Amidoximated Nanofibrous Aerogels within Wood Cell Tracheids for Efficient Cascading Adsorption of Uranium Ions

Continuous filtering adsorption has drawn growing interest in the exploration of uranium resources in seawater and reduction in the environmental risks of uraniferous wastewater from nuclear industries. For most filtering adsorbents, repeated filtration, high membrane thickness, and high pressure are normally essential to achieve both a high rejection ratio and high filtration flux. Herein cellulose fibrils were preferentially exfoliated from the lignin-poor layer of secondary cell walls of balsa wood during an in situ amidoximation process. By maintaining honeycomb-like cellular microstructures and cellulose aerogel stuffing in their cell tracheids, the resultant nanowoods showed superior mechanical properties (e.g., compressive strength ∼1.3 MPa in transverse direction) with large surface areas (∼80 m² g^-1). When their cell tracheids were aligned perpendicular to the flow and the edges sealed with a thermoset polymer, they could serve as efficient and high-pressure filtration membranes to capture aquatic uranium ions. In analogy to a typical cascading filtration system, the filtrate passed successively the layered-organized cell tracheids through abundant micropores on their cell walls, enabling a high rejection ratio of >99% and flux of ∼920 L m^-2 h^-1 under pressure up to 6 bar (membrane thickness of 2 mm). Thus, this study not only provides an in situ approach to producing robust woods with functional nanocellulose encapsulated into their cell tracheids but also offers a sustainable route for high-efficiency extraction of aqueous uranium.

Progress and Prospects of Nanocellulose-Based Membranes for Desalination and Water Treatment

Membrane-based desalination has proved to be the best solution for solving the water shortage issues globally. Membranes are extremely beneficial in the effective recovery of clean water from contaminated water sources, however, the durability as well as the separation efficiency of the membranes are restricted by the type of membrane materials/additives used in the preparation processes. Nanocellulose is one of the most promising green materials for nanocomposite preparation due to its biodegradability, renewability, abundance, easy modification, and exceptional mechanical properties. This nanocellulose has been used in membrane development for desalination application in the recent past. The study discusses the application of membranes based on different nanocellulose forms such as cellulose nanocrystals, cellulose nanofibrils, and bacterial nanocellulose for water desalination applications such as nanofiltration, reverse osmosis, pervaporation, forward osmosis, and membrane distillation. From the analysis of studies, it was confirmed that the nanocellulose-based membranes are effective in the desalination application. The chemical modification of nanocellulose can definitely improve the surface affinity as well as the reactivity of membranes for the efficient separation of specific contaminants/ions.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Fabrication of Poly(amide-co-ester) Solvent Resistant Nanofiltration Membrane from P-nitrophenol and Trimethyl Chloride via Interfacial Polymerization

P-nitrophenol (PNP), a refractory hazardous substance, has not been efficiently utilized so far. In this paper, PNP is used as a membrane modification material for preparing poly(amide-co-ester) composite nanofiltration membrane. An organic solvent nanofiltration (OSN) membrane was prepared via interfacial polymerization reactionby using PNP and trimethyl chloride (TMC) on a ethylenediamine (EDA) crosslinked polyetherimide substrate. The results of ATR-FTIR and XPS show that interfacial polymerization occurs among with PNP and TMC and the terminal amine groups on the ethylenediamine crosslinked -PEI support forming a poly(amide-co-ester) toplayer. The NF-1PNP membrane maintained stable DMF performance permeance of 2.2 L m−2 h−1 bar−1 and rejection of 98% for Rose Bengal red (RB 1017.64 g mol−1) in 36 h continuous separation process. Furthermore, the average pore diameter of the two membranes including NF-1PNP and NF-1.25PNP, which is 0.40 and 0.36nm, respectively. This study not only provides a good way for the preparation of OSN membrane, but also provides a good demonstration for the comprehensive utilization of PNP and other toxic and harmful pollutants.

Pore-size control of chitin nanofibrous composite membrane using metal-organic frameworks

Herein, environmentally benign chitin nanofiber (ChNF) membranes were fabricated by regulating suspension behavior. The introduction of zeolitic imidazole frameworks (ZIF-8) into the composite membranes led to the domain formation of ChNF derived by coordinative interaction, resulting in pore size-tunable membranes. Based on the rheological, morphological, and structural characterizations, the driving force of pore-size control was studied in the aqueous suspension of ChNF and ZIF-8 according to the relative concentration. At critical concentration, the 30-ChNF membrane presents superior water permeance (40 LMH h^-1) while maintaining a high rejection rate (>80% for all organic dyes). Moreover, the molecular size cut-off of the composite membranes for dyes can be controlled in the range of less than 1 nm to 2 nm. The experimental results provide a simple strategy for the preparation of pore tunable ChNF membranes using MOF with high mechanical strength, good durability, high flux, dye rejection, and antifouling ability.

Tailored design of nanofiltration membranes for water treatment based on synthesis-property-performance relationships

Tailored design of high-performance nanofiltration (NF) membranes is desirable because the requirements for membrane performance, particularly ion/salt rejection and selectivity, differ among the various applications of NF technology ranging from drinking water production to resource mining. However, this customization greatly relies on a comprehensive understanding of the influence of membrane fabrication methods and conditions on membrane properties and the relationships between the membrane structural and physicochemical properties and membrane performance. Since the inception of NF, much progress has been made in forming the foundation of tailored design of NF membranes and the underlying governing principles. This progress includes theories regarding NF mass transfer and solute rejection, further exploitation of the classical interfacial polymerization technique, and development of novel materials and membrane fabrication methods. In this critical review, we first summarize the progress made in controllable design of NF membrane properties in recent years from the perspective of optimizing interfacial polymerization techniques and adopting new manufacturing processes and materials. We then discuss the property-performance relationships based on solvent/solute mass transfer theories and mathematical models, and draw conclusions on membrane structural and physicochemical parameter regulation by modifying the fabrication process to improve membrane separation performance. Next, existing and potential applications of these NF membranes in water treatment processes are systematically discussed according to the different separation requirements. Finally, we point out the prospects and challenges of tailored design of NF membranes for water treatment applications. This review bridges the long-existing gaps between the pressing demand for suitable NF membranes from the industrial community and the surge of publications by the scientific community in recent years.

Nano-Interlayers Fabricated via Interfacial Azo-Coupling Polymerization: Effect of Pore Properties of Interlayers on Overall Performance of Thin-Film Composite for Nanofiltration

The supporting layer of nanofiltration membranes is critical to the overall nanofiltration performance. However, conventional supports lack efficient surface porosity, which leads to the limited utilization rate of the polyamide (PA) layer. Herein a double-skin-layer nanofiltration membrane with porous organic polymer nanointerlayers prepared via a two-step interfacial polymerization technique is presented to investigate the effect of the interlayers' pore properties on the performance of the thin-film composite. Nanometer interlayers with different pore sizes are fabricated via interfacial azo-coupling polymerization. The pore properties of the nanointerlayer extremely influence the permeance, where a suitable pore size of 4.22 nm promotes pure water permeance of up to 32.2 L m^-2 h^-1 bar^-1, which is ∼3.8-fold greater than the membrane without an interlayer. However, an interlayer with 0.54 nm pores limits the performance (4.7 L m^-2 h^-1 bar^-1), which is even lower than the unmodified membrane (7.5 L m^-2 h^-1 bar^-1), because of the narrow pores and confined transport mode. However, the confined diffusion rate of amino monomers from the support to interface leads to a thinner PA layer of ∼45 nm and results in high flux. This work provides a facial route for the fabrication of interlayers and facilitate the design of high-performance membrane materials with interlayers.

Confined assembly of ultrathin nanoporous nitrogen-doped graphene nanofilms with dual metal coordination chemistry

Graphene oxide (GO) nanosheets with unique structure have received much attention in providing opportunity for high-performance membranes in separation. However, the rational design of ultrathin graphene membranes with controlled structures remains a big challenge. Here, we report a methodology to synthesize dual metal-coordinated ultrathin nanoporous graphene nanofilms by tailoring well-aligned nanocrystals as building blocks on heteroatom-doped GO nanosheets with tunable architectures. Manipulation of metal nitrate as bifunctional dopants realizes N-doping of graphene oxide and preferential growth of α-Mn₂O₃ nanocrystals. Generation of Mn-O-C bond during cross-linking greatly strengthens the stability of membranes for long-term steady operation. Meanwhile, because of spatial confinement effects and high binding energy, N-doped reduced GO nanosheets are desirable supports to construct numerous Mn-N-C bonds, thus generating artificial nanopores to significantly increase nanochannels for ultrafast mass transport. Moreover, the size-selective permeability of ultrathin nanoporous GO-based nanofilms can be optimized by managing the types of metal source for target coordination.

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Dual metal-coordinated GO-based nanofilms are achieved by a general and facile method

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Mn-N-C bonds are constructed in rGO nanosheets with N-containing coordinated links

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Artificial nanopores are used to increase nanochannels for ultrafast mass transport

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Generation of Mn-O-C bond greatly strengthens the stability of nanofilms in separation

Fabrication of Antiswelling Loose Nanofiltration Membranes via a "Selective-Etching-Induced Reinforcing" Strategy for Bioseparation

With diverse selectivity, higher permeance, and good antifouling property, loose polyamide nanofiltration (NF) membranes can be potentially deployed in various bioseparation applications. However, the loose NF membrane with a low crosslinking degree generally suffers from the alkali-induced pore swelling during chemical cleaning, resulting in degradation of separation performance with time. In this work, we conceive a novel strategy to tailor the separating layer through alkaline post-etching following the interfacial polymerization process, where piperazine and tannic acid (TA) were used as water-phase monomers, and trimesoyl chloride (TMC) and ferric acetylacetonate were employed as organic monomers in n-hexane. Thereinto, the polyester network formed by TA and TMC was selectively etched by alkaline treatment, thus obtaining a loose NF membrane, whose structure and performance could be facilely tailored by controlling the TA ratio and the etching pH. As a result, the well-designed loose NF membrane exhibited higher flux, better selectivity, and more stable separation performance in a long-term filtration of diluted cane molasses. Interestingly, the obtained loose NF membrane showed excellent antiswelling ability during alkaline cleaning because of network locking induced by Fe³⁺ chelation, decrease in the carboxyl proportion (more hydroxyl generation due to the ester bond hydrolysis), and enhanced interface interaction between the separation layer and the sublayer attributed to catechol adhesion effect. Therefore, such a "selective-etching-induced reinforcing" strategy could endow the polyamide NF membrane with both loose and antiswelling separation layer in a reliable and scalable way, which provides a new perspective for preparing highly selective and stable NF membrane for resource recovery.

High-Throughput Zwitterion-Modified MoS2 Membranes: Preparation and Application in Dye Desalination

Although loose nanofiltration membranes have been extensively studied for dye desalination, high-throughput membranes with antifouling and antibacterial properties are still highly needed. In this study, a zwitterion-modified molybdenum disulfide (MoS₂) dual-layer loose nanofiltration membrane was prepared with the integration of antibacterial, antifouling, and high-flux properties. To be specific, MoS₂ nanosheets were loaded on a polyacrylonitrile ultrafiltration membrane through pressure-assisted self-assembly. Then, poly (sulfobetaine methacrylate) (PSBMA) was coated on the surface of the MoS₂ membrane via a simple polydopamine (PDA)-assisted one-step codeposition to prepare PSBMA/PDA/MoS₂ nanofiltration membranes. Elemental and morphological analyses confirmed the formation of the MoS₂ layer and PSBMA/PDA coating. In addition, the effect of the PSBMA amount and codeposition time on surface properties and membrane performances was investigated. Under optimum conditions, the as-prepared membrane showed excellent water permeance of 262 LMH/bar with good dye rejection (99.8% for methylene blue) and salt permeability, as well as excellent antifouling and antibacterial properties benefiting from the synergy of PSBMA/PDA coating layers and MoS₂ layers.

Bacterial nanocellulose papers with high porosity for optimized permeance and rejection of nm-sized pollutants

Access to clean potable water is increasingly becoming a struggle for whole humankind, thus water treatment to remediate wastewater and fresh water sources is an important task. Pollutants in the nanoscale, such as viruses and macromolecules, are usually removed by means of membrane filtration processes, predominantly nanofiltration or ultrafiltration. Cellulose nanopapers, prepared from renewable resources and manufactured by papermaking, have recently been demonstrated to be versatile alternatives to polymer membranes in this domain. Unfortunately, so far nanopaper filters suffer from limited permeance and thus efficiency. We here present nanopapers made from bacterial cellulose dispersed in water or different types of low surface tension organic liquids (alcohol, ketone, ether) through a simple papermaking process. Nanopapers prepared from organic liquids (BC-org) exhibited 40 times higher permeance, caused by a lower paper density hence increased porosity, compared to conventional nanopapers produced from aqueous dispersions, ultimately enhancing the efficiency of bacterial cellulose nanopaper membranes. Despite their higher porosity, BC-org nanopapers still have pore sizes of 15-20 nm similar to BC nanopapers made from aqueous dispersions, thus enabling removal of contaminants the size of viruses by a size-exclusion mechanism at high permeance.

A. M. N, Halim AS, Kumar USU, Bairwan R, Suriani AB. A Review on Micro- to Nanocellulose Biopolymer Scaffold Forming for Tissue Engineering Applications

Biopolymers have been used as a replacement material for synthetic polymers in scaffold forming due to its biocompatibility and nontoxic properties. Production of scaffold for tissue repair is a major part of tissue engineering. Tissue engineering techniques for scaffold forming with cellulose-based material is at the forefront of present-day research. Micro- and nanocellulose-based materials are at the forefront of scientific development in the areas of biomedical engineering. Cellulose in scaffold forming has attracted a lot of attention because of its availability and toxicity properties. The discovery of nanocellulose has further improved the usability of cellulose as a reinforcement in biopolymers intended for scaffold fabrication. Its unique physical, chemical, mechanical, and biological properties offer some important advantages over synthetic polymer materials. This review presents a critical overview of micro- and nanoscale cellulose-based materials used for scaffold preparation. It also analyses the relationship between the method of fabrication and properties of the fabricated scaffold. The review concludes with future potential research on cellulose micro- and nano-based scaffolds. The review provides an up-to-date summary of the status and future prospective applications of micro- and nanocellulose-based scaffolds for tissue engineering.

Ultrafast Ion Sieving from Honeycomb-like Polyamide Membranes Formed Using Porous Protein Assemblies

Despite the commercial success of thin film composite polyamide membranes, further improvements to the water permeation of polyamide membranes without degradation in product water quality remain a great challenge. Herein, we report the fabrication of an interfacially polymerized polyamide nanofiltration membrane with a novel 3D honeycomb-like spatial structure, which is formed from a tobacco mosaic virus (TMV) porous protein nanosheet-coated microfiltration membrane support. TMV nanosheets with uniform pores and appropriate hydrophilicity deposited inside the support membrane pores facilitate the construction of a localized water-oil reaction interface with evenly distributed monomers and guide the formation of a defect-free polyamide layer with a spatial structure that copies the geometry of the membrane cavities. Such a 3D morphology possesses ultrahigh specific surface area, leading to unprecedented membrane water permeance as high as 84 L m^-2 h^-1 bar^-1, high MgSO₄ rejection of 98%, and monovalent/divalent ion sieving selectivity up to 89.

Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly(vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance

Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES-PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m^-2 h^-1 bar^-1 and a 99.4% Na₂SO₄ rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

Ultrathin Nanofiltration Membrane from Confined Polymerization within the Nanowire Network for High Efficiency Divalent Cation Removal

Membranes with high permeance and high rejection for di- and multivalent cation removal are highly desired for efficient brackish water and industrial water treatment. In this work, we report a facile strategy for constructing ultrathin nanofiltration (NF) membranes by in situ cross-linking of amine which is confined in a network film. The network made of single-walled carbon nanotubes (SWCNTs) serves as a framework for poly(ethylene imine) (PEI) to attach and stay, facilitating the formation of a polyamine (PA) layer with high quality and controlled thickness. Benefiting from the ultrathin thickness of the SWCNT network (∼31 nm), an active layer (∼34 nm thick) comes with a high permeance of 27 L m^-2 h^-1 bar^-1 along with a high rejection of 97% to MgCl₂, 2-5 times higher than the NF membranes with the same high rejection for MgCl₂ reported so far. In addition, the SWCNT-interpenetrated PA structure endows the ultrathin NF membrane with good operational stability. This work demonstrates the capability to control the position, thickness, and even quality of the PA layer by using a confined framework and provides a feasible strategy for the fabrication of highly permeable ultrathin NF membranes with a reinforced active layer.

Nanofiltration Membranes with Metal Cation-Immobilized Aminophosphonate Networks for Efficient Heavy Metal Ion Removal and Organic Dye Degradation

Modifications to the surface of polymeric membranes to integrate supplemental properties like surface charge or catalytic activity are the cornerstone of the membrane process advancement to effectuate improvements in functionality and selectivity. Herein, a new approach is demonstrated to construct nanofiltration membranes with a metal-organic coordinated selective layer. Polyethylenimine (PEI) was integrated with phosphite linkages to form a characteristic aminophosphonate ester polymer based on the Kabachnik-Fields reaction, and a thin polymer layer was deposited on an ultrafiltration (UF) membrane to form the aminophosphonate networks surface-modified membranes. The aminophosphonate polymer interlayer facilitated the immobilization of metal cation moieties through the strong coordinative chemical bonding with the amino groups and phosphite moieties. Typically, the incorporated Fe³⁺ strengthened the membranes' electropositivity leading to excellent heavy metal ion removal (>98%) and efficient organic dye separation (>99.8%). Meanwhile, the strategy also enabled the embedment of a photocatalytic layer comprising nanoneedle-like α-FeOOH that endowed the membrane with high photo-Fenton activity for organic dye mineralization. Subsequently, the α-FeOOH-embedded membrane afforded the photocatalytic self-cleaning potentiality for organic fouling mitigation. This contribution underscores the prospect of advancing the integration of metal-specific functionalities and the membrane process for advanced membrane technologies in water treatment.