Recent Advances and Challenges in Anion Exchange Membranes Development/Application for Water Electrolysis: A Review

In recent years, anion exchange membranes (AEMs) have aroused widespread interest in hydrogen production via water electrolysis using renewable energy sources. The two current commercial low-temperature water electrolysis technologies used are alkaline water electrolysis (AWE) and proton exchange membrane (PEM) water electrolysis. The AWE technology exhibited the advantages of high stability and increased cost-effectiveness with low hydrogen production efficiency. In contrast, PEM water electrolysis exhibited high hydrogen efficiency with low stability and cost-effectiveness, respectively. Unfortunately, the major challenges that AEMs, as well as the corresponding ion transportation membranes, including alkaline hydrogen separator and proton exchange membranes, still face are hydrogen production efficiency, long-term stability, and cost-effectiveness under working conditions, which exhibited critical issues that need to be addressed as a top priority. This review comprehensively presented research progress on AEMs in recent years, providing a thorough understanding of academic studies and industrial applications. It focused on analyzing the chemical structure of polymers and the performance of AEMs and established the relationship between the structure and efficiency of the membranes. This review aimed to identify approaches for improving AEM ion conductivity and alkaline stability. Additionally, future research directions for the commercialization of anion exchange membranes were discussed based on the analysis and assessment of the current applications of AEMs in patents.

Highly Efficient Cationic/Anionic Cellulose Membranes for Removal of Cr(VI) and Pb(II) Ions

To achieve high throughput, low-pressure drops, and high adsorption capacity of Cr(VI) and Pb(II) in industrial wastewater treatment, cellulose membranes containing cationic and anionic groups were fabricated, respectively. In this process, cost-effective cotton fabrics were oxidized using sodium periodate, followed by quaternary ammonium or sulfonation modifications. The chemical composition, surface morphology, and thermal and mechanical properties of the cellulose membranes were investigated by ATR-FTIR, solid-state NMR, SEM, TGA, and tensile experiments. Quaternary ammonium, aldehyde, and sulfonate groups were distributed on the cationic/anionic cellulose fibers as adsorption sites, which issue remarkable adsorption capability to the cellulose membranes. The highly toxic Cr(VI) and Pb(II) ions were used to challenge the adsorption capacity of the cationic and anionic cellulose membranes, respectively. The maximum adsorption capacities of Cr(VI) and Pb(II) ions were 61.7 and 63.7 mg/g, respectively, suggested by Langmuir isotherms, kinetics, and thermodynamics in the static experiments. The dynamic adsorption capability of cationic cellulose membranes against Cr(VI) ions was determined and compared with that of commercially available anionic-exchange membranes. Spiral wound filtration cartridges were fabricated by cationic and anionic cellulose membranes, respectively, and were used to adsorb Cr(VI) and Pb(II) from lab-made wastewater, respectively. The cationic cellulose cartridge can purify 4.4 L of wastewater containing 1.0 mg/L of Cr(VI) ions with a 100% removal ratio, while the pressure drop was retained at 246 Pa. Similarly, the anionic cellulose cartridge exhibited even more impressive adsorption capability; the removal ratio against Pb(II) was 99% when 8.6 L of 1.0 mg/L of Pb(II) ions containing wastewater was treated, and the pressure drop was retained at 234 Pa. A composite cartridge fabricated by the integration of cationic and anionic cellulose membranes was successfully employed to purify the wastewater containing Cr(VI) and Pb(II) simultaneously. The possible adsorption mechanism was proposed, and the recycling ability of the cellulose membranes was also discussed.

Exploring nanofibrous networks with x-ray photon correlation spectroscopy through a digital twin

We demonstrate a framework of interpreting data from x-ray photon correlation spectroscopy experiments with the aid of numerical simulations to describe nanoscale dynamics in soft matter. This is exemplified with the transport of passive tracer gold nanoparticles in networks of charge-stabilized cellulose nanofibers. The main structure of dynamic modes in reciprocal space could be replicated with a simulated system of confined Brownian motion, a digital twin, allowing for a direct measurement of important effective material properties describing the local environment of the tracers.

High-Flux Nanofibrous Composite Reverse Osmosis Membrane Containing Interfacial Water Channels for Desalination

A nanofibrous composite reverse osmosis (RO) membrane with a polyamide barrier layer containing interfacial water channels was fabricated on an electrospun nanofibrous substrate via an interfacial polymerization process. The RO membrane was employed for desalination of brackish water and exhibited enhanced permeation flux as well as rejection ratio. Nanocellulose was prepared by sequential oxidations of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and sodium periodate systems and surface grafting with different alkyl groups including octyl, decanyl, dodecanyl, tetradecanyl, cetyl, and octadecanyl groups. The chemical structure of the modified nanocellulose was verified subsequently by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), and solid NMR measurements. Two monomers, trimesoyl chloride (TMC) and m-phenylenediamine (MPD), were employed to prepare a cross-linked polyamide matrix, i.e., the barrier layer of the RO membrane, which integrated with the alkyl groups-grafted nanocellulose to build up interfacial water channels via interfacial polymerization. The top and cross-sectional morphologies of the composite barrier layer were observed by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) to verify the integration structure of the nanofibrous composite containing water channels. The aggregation and distribution of water molecules in the nanofibrous composite RO membrane verified the existence of water channels, demonstrated by molecular dynamics (MD) simulations. The desalination performance of the nanofibrous composite RO membrane was conducted and compared with that of commercially available RO membranes in the processing of brackish water, where 3 times higher permeation flux and 99.1% rejection ratio against NaCl were accomplished. This indicated that the engineering of interfacial water channels in the barrier layer could substantially increase the permeation flux of the nanofibrous composite membrane while retaining the high rejection ratio as well, i.e., to break through the trade-off between permeation flux and rejection ratio. Antifouling properties, chlorine resistance, and long-term desalination performance were also demonstrated to evaluate the potential applications of the nanofibrous composite RO membrane; remarkable durability and robustness were achieved in addition to 3 times higher permeation flux and a higher rejection ratio against commercial RO membranes in brackish water desalination.

Sodium Alginate-Aldehyde Cellulose Nanocrystal Composite Hydrogel for Doxycycline and Other Tetracycline Removal

A novel composite hydrogel bead composed of sodium alginate (SA) and aldehyde cellulose nanocrystal (DCNC) was developed for antibiotic remediation through a one-step cross-linking process in a calcium chloride bath. Structural and physical properties of the hydrogel bead, with varying composition ratios, were analyzed using techniques such as BET analysis, SEM imaging, tensile testing, and rheology measurement. The optimal composition ratio was found to be 40% (SA) and 60% (DCNC) by weight. The performance of the SA-DCNC hydrogel bead for antibiotic remediation was evaluated using doxycycline (DOXY) and three other tetracyclines in both single- and multidrug systems, yielding a maximum adsorption capacity of 421.5 mg g^-1 at pH 7 and 649.9 mg g^-1 at pH 11 for DOXY. The adsorption mechanisms were investigated through adsorption studies focusing on the effects of contact time, pH, concentration, and competitive contaminants, along with X-ray photoelectron spectroscopy analysis of samples. The adsorption of DOXY was confirmed to be the synergetic effects of chemical reaction, electrostatic interaction, hydrogen bonding, and pore diffusion/surface deposition. The SA-DCNC composite hydrogel demonstrated high reusability, with more than 80% of its adsorption efficiency remaining after five cycles of the adsorption-desorption test. The SA-DCNC composite hydrogel bead could be a promising biomaterial for future antibiotic remediation applications in both pilot and industrial scales because of its high adsorption efficiency and ease of recycling.

A Comparative Study of Mechanism and Performance of Anionic and Cationic Dialdehyde Nanocelluloses for Dye Adsorption and Separation

In this study, anionic dialdehyde cellulose (DAC) and cationic dialdehyde cellulose (c-DAC) nanofibrous adsorbents were prepared via a two-step reaction from bamboo pulp, using sodium periodate and Girard's reagent T as oxidizing and cationizing agents, respectively. The performance of DAC and c-DAC for selective dye adsorption and separation was evaluated by six different organic dyes (with varying charge properties) and certain binary mixtures. Both adsorbents could remove the dyes but with different capability, where DAC exhibited high adsorption efficiency against cationic dyes (e.g., the maximum adsorption capacity for Bismarck brown Y was 552.1 mg/g) and c-DAC exhibited high adsorption efficiency against anionic dyes (e.g., the maximum adsorption capacity for Congo red was 540.3 mg/g). To investigate the adsorption mechanism for these adsorbents, effects of contact time, initial pH value, initial dye concentration, and ionic strength on the adsorption activity against Congo red were investigated. The adsorption equilibrium data of DAC were found to fit best with the Langmuir isotherm model, whereas that of c-DAC were found to fit best with the Freundlich model. Both DAC and c-DAC adsorption kinetic data could be described by the pseudo-second-order kinetic model, and these adsorbents possessed stable adsorption efficiency in the pH range of 4-10. Furthermore, their dye adsorption capabilities were found to increase with increasing ionic strength (salt concentration). The distinctive complementary features of DAC and c-DAC will allow them to remove a wide range of organic dyes from industrial wastewater.

Bioactive polymer-enabled conformal neural interface and its application strategies

Neural interface is a powerful tool to control the varying neuron activities in the brain, where the performance can directly affect the quality of recording neural signals and the reliability of in vivo connection between the brain and external equipment. Recent advances in bioelectronic innovation have provided promising pathways to fabricate flexible electrodes by integrating electrodes on bioactive polymer substrates. These bioactive polymer-based electrodes can enable the conformal contact with irregular tissue and result in low inflammation when compared to conventional rigid inorganic electrodes. In this review, we focus on the use of silk fibroin and cellulose biopolymers as well as certain synthetic polymers to offer the desired flexibility for constructing electrode substrates for a conformal neural interface. First, the development of a neural interface is reviewed, and the signal recording methods and tissue response features of the implanted electrodes are discussed in terms of biocompatibility and flexibility of corresponding neural interfaces. Following this, the material selection, structure design and integration of conformal neural interfaces accompanied by their effective applications are described. Finally, we offer our perspectives on the evolution of desired bioactive polymer-enabled neural interfaces, regarding the biocompatibility, electrical properties and mechanical softness.

Low Fouling Nanostructured Cellulose Membranes for Ultrafiltration in Wastewater Treatment

Ultrafiltration (UF) is a common technique used in wastewater treatments. However, the issue of membrane fouling in UF can greatly hinder the effectiveness of the treatments. This study demonstrated a low-fouling composite cellulose membrane system based on microfibrillated cellulose (MFC) and silica nanoparticle additives. The incorporation of 'non-spherical' silica nanoparticles was found to exhibit better structural integration in the membrane (i.e., minimal aggregation of silica nanoparticles in the membrane scaffold) as compared to spherical silica. The resulting composite membranes were tested for UF using local wastewater, where the best-performing membrane exhibited higher permeation flux than commercial polyvinylidene difluoride (PVDF) and polyether sulfone (PES) membranes while maintaining a high separation efficiency (~99.6%) and good flux recovery ratio (>90%). The analysis of the fouling behavior using different models suggested that the processes of cake layer formation and pore-constriction were probably two dominant fouling mechanisms, likely due to the presence of humic substances in wastewater. The demonstrated cellulose composite membrane system showed low-fouling and high restoration capability by a simple hydraulic cleaning method due to the super hydrophilic nature of the cellulose scaffold containing silica nanoparticles.

Effective Thallium(I) Removal by Nanocellulose Bioadsorbent Prepared by Nitro-Oxidation of Sorghum Stalks

Thallium(I) (Tl(I)) pollution has become a pressing environmental issue due to its harmful effect on human health and aquatic life. Effective technology to remove Tl(I) ions from drinking water can offer immediate societal benefits especially in the developing countries. In this study, a bio-adsorbent system based on nitro-oxidized nanocellulose (NOCNF) extracted from sorghum stalks was shown to be a highly effective Tl(I) removal medium. The nitro-oxidation process (NOP) is an energy-efficient, zero-waste approach that can extract nanocellulose from any lignocellulosic feedstock, where the effluent can be neutralized directly into a fertilizer without the need for post-treatment. The demonstrated NOCNF adsorbent exhibited high Tl(I) removal efficiency (>90% at concentration < 500 ppm) and high maximum removal capacity (Qm = 1898 mg/g using the Langmuir model). The Tl(I) adsorption mechanism by NOCNF was investigated by thorough characterization of NOCNF-Tl floc samples using spectroscopic (FTIR), diffraction (WAXD), microscopic (SEM, TEM, and AFM) and zeta-potential techniques. The results indicate that adsorption occurs mainly due to electrostatic attraction between cationic Tl(I) ions and anionic carboxylate groups on NOCNF, where the adsorbed Tl(I) sites become nuclei for the growth of thallium oxide nanocrystals at high Tl(I) concentrations. The mineralization process enhances the Tl(I) removal efficiency, and the mechanism is consistent with the isotherm data analysis using the Freundlich model.

Ionic Liquid-Mediated Interfacial Polymerization for Fabrication of Reverse Osmosis Membranes

This study revealed the effects of incorporating ionic liquid (IL) molecules: 1-ethyl, 1-butyl, and 1-octyl-3-methyl-imidazolium chlorides with different alkyl chain lengths, in interfacial polymerization (IP) on the structure and property (i.e., permeate-flux and salt rejection ratio) relationships of resulting RO membranes. The IL additive was added in the aqueous meta-phenylene diamine (MPD; 0.1% w/v) phase, which was subsequently reacted with trimesoyl chloride (TMC; 0.004% w/v) in the hexane phase to produce polyamide (PA) barrier layer. The structure of resulting free-standing PA thin films was characterized by grazing incidence wide-angle X-rays scattering (GIWAXS), which results were correlated with the performance of thin-film composite RO membranes having PA barrier layers prepared under the same IP conditions. Additionally, the membrane surface properties were characterized by zeta potential and water contact angle measurements. It was found that the membrane prepared by the longer chain IL molecule generally showed lower salt rejection ratio and higher permeation flux, possibly due to the inclusion of IL molecules in the PA scaffold. This hypothesis was supported by the GIWAXS results, where a self-assembled surfactant-like structure formed by IL with the longest aliphatic chain length was detected.

Nano-Filamented Textile Sensor Platform with High Structure Sensitivity

A key challenge to the creation of chemically responsive electro-functionality of nonconductive, hydrophobic, and free-contacted textile or fibrous network materials is how to impart the 3D structure with functional filaments to enable responsive structure sensitivity, which is critical in establishing the fibrous platform technology for sensor applications. We demonstrate this capability using an electrospun polymeric fibrous substrate embedded with nano-filaments defined by size-tunable gold nanoparticles and structurally sensitive dendrons as crosslinkers. The resulting interparticle properties strongly depend on the assembly of the nano-filaments, enabling an interface with high structure sensitivity to molecular interactions. This is demonstrated with chemiresistive responses to vaporous alcohol molecules with different chain lengths and isomers, which is critical in breath and sweat sensing involving a high-moisture or -humidity background. The sensitivity scales with the chain length and varies with their isomers. This approach harnesses the multifunctional tunability of the nano-filaments in a sensor array format, showing high structure sensitivity to the alcohol molecules with different chain lengths and isomers. The high structure sensitivity and its implications for a paradigm shift in the design of textile sensor arrays for multiplexing human performance monitoring via breath or sweat sensing and environmental monitoring of air quality are also discussed.

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.

Lamellar crystal-dominated surfaces of polymer films achieved via melt stretching-induced free surface crystallization

Lamellar crystal-dominated (LCD) surfaces hold great superiority and broad prospects in polymer surface engineering. The key to this is avoiding the formation of an amorphous phase in the interlamellar region. Here we give a first report of achieving LCD surfaces of polyethylene films via melt stretching-induced free surface crystallization. We demonstrate that the resultant surface is constructed directly by orientated and edge-on lamellae within a surface depth of tens to hundreds of nanometers, while the normally existing amorphous phase is avoided. The crystallization-driven formation of the LCD surface has been ascribed to the heterogeneous chain dynamics of a melt free surface, that is, high chain mobility, low viscosity and loose chain entanglement, which facilitates the complete chain disentanglement during crystallization. In addition, we confirm that the surface morphology is controllable with respect to lamellar orientation, spacing and depth by changing the melt stretching strain or quenching the deformed melt. Meanwhile, owing to a possible kinetics competition between crystallization and chain disentanglement, the structural spacing of surface lamellae holds a positive correlation with the lamellar depth. Since free surface effects are immanent in polymer materials, the currently proposed melt processing strategy is demonstrated to be transferable to other semicrystalline polymers.

Understanding ion-induced assembly of cellulose nanofibrillar gels through shear-free mixing and in situ scanning-SAXS

During the past decade, cellulose nanofibrils (CNFs) have shown tremendous potential as a building block to fabricate new advanced materials that are both biocompatible and biodegradable. The excellent mechanical properties of the individual CNF can be transferred to macroscale fibers through careful control in hydrodynamic alignment and assembly processes. The optimization of such processes relies on the understanding of nanofibril dynamics during the process, which in turn requires in situ characterization. Here, we use a shear-free mixing experiment combined with scanning small-angle X-ray scattering (scanning-SAXS) to provide time-resolved nanoscale kinetics during the in situ assembly of dispersed cellulose nanofibrils (CNFs) upon mixing with a sodium chloride solution. The addition of monovalent ions led to the transition to a volume-spanning arrested (gel) state. The transition of CNFs is associated with segmental aggregation of the particles, leading to a connected network and reduced Brownian motion, whereby an aligned structure can be preserved. Furthermore, we find that the extensional flow seems to enhance the formation of these segmental aggregates, which in turn provides a comprehensible explanation for the superior material properties obtained in shear-free processes used for spinning filaments from CNFs. This observation clearly highlights the need for different assembly strategies depending on morphology and interactions of the dispersed nanoparticles, where this work can be used as a guide for improved nanomaterial processes.

Elucidating the Opportunities and Challenges for Nanocellulose Spinning

Man-made continuous fibers play an essential role in society today. With the increase in global sustainability challenges, there is a broad spectrum of societal needs where the development of advanced biobased fibers could provide means to address the challenges. Biobased regenerated fibers, produced from dissolved cellulose are widely used today for clothes, upholstery, and linens. With new developments in the area of advanced biobased fibers, it would be possible to compete with high-performance synthetic fibers such as glass fibers and carbon fibers as well as to provide unique functionalities. One possible development is to fabricate fibers by spinning filaments from nanocellulose, Nature's nanoscale high-performance building block, which will require detailed insights into nanoscale assembly mechanisms during spinning, as well as knowledge regarding possible functionalization. If successful, this could result in a new class of man-made biobased fibers. This work aims to identify the progress made in the field of spinning of nanocellulose filaments, as well as outline necessary steps for efficient fabrication of such nanocellulose-based filaments with controlled and predictable properties.

Shear-free mixing to achieve accurate temporospatial nanoscale kinetics through scanning-SAXS: ion-induced phase transition of dispersed cellulose nanocrystals

Time-resolved in situ characterization of well-defined mixing processes using small-angle X-ray scattering (SAXS) is usually challenging, especially if the process involves changes of material viscoelasticity. In specific, it can be difficult to create a continuous mixing experiment without shearing the material of interest; a desirable situation since shear flow both affects nanoscale structures and flow stability as well as resulting in unreliable time-resolved data. Here, we demonstrate a flow-focusing mixing device for in situ nanostructural characterization using scanning-SAXS. Given the interfacial tension and viscosity ratio between core and sheath fluids, the core material confined by sheath flows is completely detached from the walls and forms a zero-shear plug flow at the channel center, allowing for a trivial conversion of spatial coordinates to mixing times. With this technique, the time-resolved gel formation of dispersed cellulose nanocrystals (CNCs) was studied by mixing with a sodium chloride solution. It is observed how locally ordered regions, so called tactoids, are disrupted when the added monovalent ions affect the electrostatic interactions, which in turn leads to a loss of CNC alignment through enhanced rotary diffusion. The demonstrated flow-focusing scanning-SAXS technique can be used to unveil important kinetics during structural formation of nanocellulosic materials. However, the same technique is also applicable in many soft matter systems to provide new insights into the nanoscale dynamics during mixing.

Cross-Sections of Nanocellulose from Wood Analyzed by Quantized Polydispersity of Elementary Microfibrils

Bio-based nanocellulose has been shown to possess impressive mechanical properties and simplicity for chemical modifications. The chemical properties are largely influenced by the surface area and functionality of the nanoscale materials. However, finding the typical cross-sections of nanocellulose, such as cellulose nanofibers (CNFs), has been a long-standing puzzle, where subtle changes in extraction methods seem to yield different shapes and dimensions. Here, we extracted CNFs from wood with two different oxidation methods and variations in degree of oxidation and high-pressure homogenization. The cross-sections of CNFs were characterized by small-angle X-ray scattering and wide-angle X-ray diffraction in dispersed and freeze-dried states, respectively, where the results were analyzed by assuming that the cross-sectional distribution was quantized with an 18-chain elementary microfibril, the building block of the cell wall. We find that the results agree well with a pseudosquare unit having a size of about 2.4 nm regardless of sample, while the aggregate level strongly depends on the extraction conditions. Furthermore, we find that aggregates have a preferred cohesion of phase boundaries parallel to the (110)-plane of the cellulose fibril, leading to a ribbon shape on average.

Sustainable carboxylated cellulose filters for efficient removal and recovery of lanthanum

Carboxylated cellulose filters were fabricated by oxidation of a cellulose fibrous mat via TEMPO-mediated oxidation. These carboxylated cellulose filters were employed as sustainable filters for removal and recovery of lanthanum ions (La (III)) with high adsorption capability. The surface chemistry of the carboxylated cellulose fibers before and after adsorption of La (III) was investigated systematically. The distribution of La (III) on carboxylated cellulose fibers were explored by EDX mapping approach, which revealed that the adsorption occurred on both the surface and the internal structure of the cellulose fibers. The kinetics and isotherms of the adsorption were conducted to understand the adsorption mechanism of the carboxylated cellulose filter and to learn the maximum adsorption capacity for La (III) which was as high as 33.7 mg/g. The adsorption selectivity of the carboxylated cellulose filter for La (III) was determined when interfering ions including mono- and di-covalent ions were involved. The carboxylated cellulose filter exhibited high adsorption capability and high permeation flux evidenced by the breakthrough curves of the dynamic adsorption of La (III) under an extremely low pressure of 0.07 kPa. A variety of desorption reagents were selected to recover lanthanum from the carboxylated cellulose filter, where the optimized conditions for recovery were explored. Finally, a spiral wound cartridge of the carboxylated cellulose fibrous mat was fabricated and the removal and the recovery of La (III, 2.5 ppm) from massive lanthanum-containing water were demonstrated. It was very impressive that the high rejection ratio of 94.3% was achieved under the low pressure drop of 3.0 kPa remaining throughout the separation process, and the treated solution volume was high up to 21.4 L, which was about six-times higher than that of commercially available nanofibrous adsorption membranes, indicating that the carboxylated cellulose filter could be used as a highly efficient adsorption medium for industrial recovery of rare earth metals.

Surface-Mediated Interconnections of Nanoparticles in Cellulosic Fibrous Materials toward 3D Sensors

Fibrous materials serve as an intriguing class of 3D materials to meet the growing demands for flexible, foldable, biocompatible, biodegradable, disposable, inexpensive, and wearable sensors and the rising desires for higher sensitivity, greater miniaturization, lower cost, and better wearability. The use of such materials for the creation of a fibrous sensor substrate that interfaces with a sensing film in 3D with the transducing electronics is however difficult by conventional photolithographic methods. Here, a highly effective pathway featuring surface-mediated interconnection (SMI) of metal nanoclusters (NCs) and nanoparticles (NPs) in fibrous materials at ambient conditions is demonstrated for fabricating fibrous sensor substrates or platforms. Bimodally distributed gold-copper alloy NCs and NPs are used as a model system to demonstrate the semiconductive-to-metallic conductivity transition, quantized capacitive charging, and anisotropic conductivity characteristics. Upon coupling SMI of NCs/NPs as electrically conductive microelectrodes and surface-mediated assembly (SMA) of the NCs/NPs as chemically sensitive interfaces, the resulting fibrous chemiresistors function as sensitive and selective sensors for gaseous and vaporous analytes. This new SMI-SMA strategy has significant implications for manufacturing high-performance fibrous platforms to meet the growing demands of the advanced multifunctional sensors and biosensors.

Integrated dynamic wet spinning of core-sheath hydrogel fibers for optical-to-brain/tissue communications

Hydrogel optical light-guides have received substantial interest for applications such as deep-tissue biosensors, optogenetic stimulation and photomedicine due to their biocompatibility, (micro)structure control and tissue-like Young's modulus. However, despite recent developments, large-scale fabrication with a continuous synthetic methodology, which could produce core-sheath hydrogel fibers with the desired optical and mechanical properties suitable for deep-tissue applications, has yet to be achieved. In this study, we report a versatile concept of integrated light-triggered dynamic wet spinning capable of continuously producing core-sheath hydrogel optical fibers with tunable fiber diameters, and mechanical and optical propagation properties. Furthermore, this concept also exhibited versatility for various kinds of core-sheath functional fibers. The wet spinning synthetic procedure and fabrication process were optimized with the rational design of the core/sheath material interface compatibility [core = poly(ethylene glycol diacrylate-co-acrylamide); sheath = Ca-alginate], optical transparency, refractive index and spinning solution viscosity. The resulting hydrogel optical fibers exhibited desirable low optical attenuation (0.18 ± 0.01 dB cm⁻¹ with 650 nm laser light), excellent biocompatibility and tissue-like Young's modulus (<2.60 MPa). The optical waveguide hydrogel fibers were successfully employed for deep-tissue cancer therapy and brain optogenetic stimulation, confirming that they could serve as an efficient versatile tool for diverse deep-tissue therapy and brain optogenetic applications.

Hierarchical Assembly of Nanocellulose into Filaments by Flow-Assisted Alignment and Interfacial Complexation: Conquering the Conflicts between Strength and Toughness

Filaments comprising solely cellulose nanofibrils (CNFs) have been fabricated by flow-assisted assembling, where the strength can be improved greatly with the sacrifice of toughness. Inspired by the architecture of natural nacre and plant cell wall, the combined technique of convergent microfluidic spinning and in situ interfacial complexation between CNF and chitosan molecules was used to construct the filaments with hierarchical assembly of highly oriented CNFs locked by chitosan complexes, showing simultaneous enhancements of strength and toughness. In specific, the best performing filament exhibited a toughness of 88.9 kJ/m³ and a tensile strength of 1289 MPa because of the strong interfacial complexation interactions between CNFs and chitosan molecules. The tensile strength was further raised to 1627 MPa when the filaments were cross-linked synergistically by using Ca²⁺, surpassing the reported values in the literature. Molecular dynamics simulations revealed the possible fracture mechanism of the filaments under tension. With excellent mechanical performance and biocompatibility, the resulting CNF/chitosan filament system showed a promising application potential as nonabsorbable surgical sutures. The demonstrated spinning technology also offered a new avenue for the fabrication of high-performance filaments.

Cellulose nanofibrils and nanocrystals in confined flow: Single-particle dynamics to collective alignment revealed through scanning small-angle x-ray scattering and numerical simulations

Nanostructured materials made through flow-assisted assembly of proteinaceous or polymeric nanosized fibrillar building blocks are promising contenders for a family of high-performance biocompatible materials in a wide variety of applications. Optimization of these processes relies on improving our knowledge of the physical mechanisms from nano- to macroscale and especially understanding the alignment of elongated nanoparticles in flows. Here, we study the full projected orientation distributions of cellulose nanocrystals (CNCs) and nanofibrils (CNFs) in confined flow using scanning microbeam SAXS. For CNCs, we further compare with a simulated system of dilute Brownian ellipsoids, which agrees well at dilute concentrations. However, increasing CNC concentration to a semidilute regime results in locally arranged domains called tactoids, which aid in aligning the CNC at low shear rates, but limit alignment at higher rates. Similarly, shear alignment of CNF at semidilute conditions is also limited owing to probable bundle or flock formation of the highly entangled nanofibrils. This work provides a quantitative comparison of full projected orientation distributions of elongated nanoparticles in confined flow and provides an important stepping stone towards predicting and controlling processes to create nanostructured materials on an industrial scale.

Arsenic(III) Removal by Nanostructured Dialdehyde Cellulose-Cysteine Microscale and Nanoscale Fibers

Arsenite (As(III)) contamination in drinking water has become a worldwide problem in recent years, which leads to development of various As(III) remediation approaches. In this study, two biomass-based nanostructured materials, microscale dialdehyde cellulose-cysteine (MDAC-cys) and nanoscale dialdehyde cellulose-cysteine (NDAC-cys) fibers, have been prepared from wood pulp. Their As(III) removal efficiencies and mechanism were determined by combined adsorption, atomic fluorescence spectrometry, microscopy (scanning electron microscopy, transmission electron microscopy, and atomic force microscopy), and spectroscopy (Fourier transform infrared, 13C CPMAS NMR) methods. The adsorption results of these materials could be well described by the Freundlich isotherm model, where the maximum adsorption capacities estimated by the Langmuir isotherm model were 344.82 mg/g for MDAC-cys and 357.14 mg/g for NDAC-cys, respectively. Both MDAC-cys and NDAC-cys materials were further characterized by X-ray diffraction and thermogravimetric analysis, where the results indicated that the thiol groups (the S content in MDAC-cys was 12.70 and NDAC-cys was 17.15%) on cysteine were primarily responsible for the adsorption process. The nanostructured MDAC-cys system appeared to be more suitable for practical applications because of its high cost-effectiveness.

A study of TiO2 nanocrystal growth and environmental remediation capability of TiO2/CNC nanocomposites

Nanocellulose, which can be derived from any cellulosic biomass, has emerged as an appealing nanoscale scaffold to develop inorganic-organic nanocomposites for a wide range of applications. In this study, titanium dioxide (TiO₂) nanocrystals were synthesized in the cellulose nanocrystal (CNC) scaffold using a simple approach, i.e., hydrolysis of a titanium oxysulfate precursor in a CNC suspension at low temperature. The resulting TiO₂ nanoparticles exhibited a narrow size range between 3 and 5 nm, uniformly distributed on and strongly adhered to the CNC surface. The structure of the resulting nanocomposite was evaluated by transmission electron microscopy (TEM) and X-ray diffraction (XRD) methods. The growth mechanism of TiO₂ nanocrystals in the CNC scaffold was also investigated by solution small-angle X-ray scattering (SAXS), where the results suggested the mineralization process could be described by the Lifshitz-Slyozov-Wagner theory for Ostwald ripening. The demonstrated TiO₂/CNC nanocomposite system exhibited excellent performance in dye degradation and antibacterial activity, suitable for a wide range of environmental remediation applications.

Molecular Structure of Aromatic Reverse Osmosis Polyamide Barrier Layers

The molecular structures of polyamide barrier layers in reverse osmosis membranes, made by interfacial polymerization of m-phenylenediamine and trimesoyl chloride under different reaction and post-treatment conditions, were characterized by grazing incidence wide-angle X-ray scattering (GIWAXS). The molecular backbone packing is consistent with two different aromatic molecular packing motifs (parallel and perpendicular) with preferential surface-induced orientation. The results suggest that the perpendicular, T-shaped, packing motif (5 Å spacing) might be associated with optimal membrane permeance, compared with the parallel packings (3.5-4.0 Å spacings).

Single Molecular Layer of Silk Nanoribbon as Potential Basic Building Block of Silk Materials

In this study, nascent silk nanoribbons (SNRs) with an average thickness of 0.4 nm were extracted from natural silkworm silk by partially dissolving degummed silk (DS) in sodium hydroxide (NaOH)/urea solution at -12 °C. In this gentle treatment, the solvent could not destroy the nanofibrillar structure completely, but the chosen conditions would influence the dimensions of resulting SNRs. Molecular dynamics simulations of silk models indicated that the potential of mean force required to break hydrogen bonds between silk fibroin chains was 40% larger than that of van der Waals interactions between β-sheet layers, allowing the exfoliating treatment. It was found that the resulting SNRs contained a single β-sheet layer and amorphous silk fibroin molecules, which could be considered as the basic building block of DS consisting of hierarchical structures. The demonstrated technique for extracting ultrathin SNRs having the height of a single β-sheet layer may provide a useful pathway for creating stronger and tougher silk-based materials and/or adding functionality and durability in materials for various applications. The hierarchical structure model based on SNRs may afford more insight into the structure and property relationship of fabricating silk-based materials.

Anionic Surfactant-Triggered Steiner Geometrical Poly(vinylidene fluoride) Nanofiber/Nanonet Air Filter for Efficient Particulate Matter Removal

The emergence of Steiner minimal tree is of fundamental importance, and designing such geometric structure and developing its application have practical effect in material engineering and biomedicine. We used a cutting-edge nanotechnology, electrospinning/netting, to generate a Steiner geometrical poly(vinylidene fluoride) (PVDF) nanofiber/nanonet filter for removing airborne particulate matter (PM). Manipulation of surface morphologies by precise control of charged situation enabled the creation of two-dimensional nanonets with Steiner geometry. A significant crystalline phase transition of PVDF from α-phase to β-phase was triggered by the dipole orientation and the intermolecular interactions derived from the electrostatic potential analysis. Particularly, the synergy of electrical interaction (ion-dipole and dipole-dipole) and hydrophobic interaction facilitated the formation of Steiner geometric structure during the evolution process of nanonets. The resultant PVDF nanofiber/nanonet air filter exhibited high filtration efficiency of 99.985% and low pressure drop of 66.7 Pa under the airflow velocity of 32 L/min for PM_0.26 removal by the safest physical sieving mechanism. Furthermore, such filter possessed robust structure integrity for reusability, comparable optical transmittance, superior thermal stability, and prominent purification capacity for smoke PM_2.5. The successful construction of such fascinating Steiner geometrical PVDF nanonets will provide new insights into the design and exploitation of novel filter media for air cleaning and haze treatment.

Nanocomposite Film Containing Fibrous Cellulose Scaffold and Ag/TiO₂ Nanoparticles and Its Antibacterial Activity

Cellulose is a natural polymer that is widely used in daily life, but it is susceptible to microorganism growth. In this study, a simple sol⁻gel technique was utilized to incorporate the cellulose scaffold with Ag/TiO₂ nanoparticles. The morphology and crystal structure of the as-prepared Ag/TiO₂/cellulose composite film were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. Antibacterial tests involving the use of Escherichia coli (E. coli) were carried out under dark and UV-light conditions to evaluate the efficiency of the Ag/TiO₂/cellulose composite film in comparison with pristine cellulose paper and TiO₂/cellulose composite film. The results indicated that the antibacterial activity of the Ag/TiO₂/cellulose composite film outperformed all other samples, where the Ag content of 0.030 wt% could inhibit more than 99% of E. coli. This study suggests that finely dispersed nanocale Ag/TiO₂ particles in the cellulose scaffold were effective at slowing down bacterial growth, and the mechanisms of this are also discussed.