A nanofluidic ion regulation membrane with aligned cellulose nanofibers

Superstrong, sustainable, origami wood paper enabled by dual-phase nanostructure regulation in cell walls

Constructing a crystalline-amorphous hybrid structure is an effective strategy to overcome the conflict between the strength and toughness of materials. However, achieving such a material structure often involves complex, energy-intensive processing. Here, we leverage the natural wood featuring coexisting crystalline and amorphous regions to achieve superstrong and ultratough wood paper (W-paper) via a dual-phase nanostructure regulation strategy. After partially removing amorphous hemicellulose and eliminating most lignin, the treated wood can self-densify through an energy-efficient air drying, resulting in a W-paper with high tensile strength, toughness, and folding endurance. Coarse-grained molecular dynamics simulations reveal the underlying deformation mechanism of the crystalline and amorphous regions inside cell walls and the failure mechanism of the W-paper under tension. Life cycle assessment reveals that W-paper shows a lower environmental impact than commercial paper and common plastics. This dual-phase nanostructure regulation based on natural wood may provide valuable insights for developing high-performance and sustainable film materials.

Wood Ion Pumps Enabled by Light-Responsive MoS2-Decorated Nanocellulosic Channels

Light-driven active ion transport discovered in nanomaterials (e.g., graphene, metal-organic framework, and MXene) implicates crucial applications in membrane-based technology and energy conversion systems. However, it remains a challenge to achieve bulk assembly. Herein, we employ the scalable wood as a framework for in situ growth of MoS2 nanosheets to facilitate light-responsive ion transport. Owing to the aligned and negatively charged wood nanochannels, the MoS2-decorated wood exhibits an excellent nanofluidic conductivity of 8.3 × 10-5 S cm-1 in 1 × 10-6 M KCl. Asymmetric light illumination creates the separation of electrons and holes in MoS2 nanosheets, enabling ions to move uphill against a wide range of concentration gradients. As a result, the MoS2-decorated wood can pump ions uphill against a 20-fold concentration gradient at a light intensity of 300 mW cm-2. When the illumination is applied to the opposite side, the osmotic current along the 20-fold concentration gradient can be enhanced to 75.1 nA, and the corresponding osmotic energy conversion power density increases to more than 12.6 times that of the nonilluminated state. Based on the light-responsive behaviors, we are extending the use of MoS2-decorated wood as the ionic elements for nanofluidic circuits, such as ion switches, ion diodes, and ion transistors. This work provides a facile and scalable strategy for fabricating light-controlled nanofluidic devices from biomass materials.

Emerging approaches of utilizing trees to produce advanced structural and functional materials

The global number of trees is approximately 3 trillion, covering 31% of the land area. Trees are considered a cheap, abundant, renewable, and environmentally friendly feedstock for producing advanced structural and functional materials toward a widespread application in sustainable energy and environment. In this highlight, we reveal the structure and composition of wood, leaves, and tree extracts, and then highlight the strategies to control their hierarchical structures and properties. Moreover, we provide an up-to-date overview of their emerging applications in sustainable buildings, ionic nanofluidics, batteries, capacitors, solar cells, environmental remediation, biodegradable packaging, and nanomaterial synthesis. Finally, we outline the challenges and opportunities in valorizing trees for creating a sustainable future.

All-Cellulose Nanofiber-Based Sustainable Triboelectric Nanogenerators for Enhanced Energy Harvesting

Triboelectric nanogenerators (TENGs) show promising potential in energy harvesting and sensing for various electronic devices in multiple fields. However, the majority of materials currently utilized in TENGs are unrenewable, undegradable, and necessitate complex preparation processes, resulting in restricted performance and durability for practical applications. Here, we propose a strategy that combines straightforward chemical modification and electrospinning techniques to construct all-cellulose nanofiber-based TENGs with substantial power output. By using cellulose acetate (CA) as the raw material, the prepared cellulose membranes (CMs) and fluorinated cellulose membranes (FCMs) with different functional groups and hydrophobic properties are applied as the tribopositive and tribonegative friction layers of FCM/CM-based triboelectric nanogenerators (FC-TENGs), respectively. This approach modulates the microstructure and triboelectric polarity of the friction materials in FC-TENGs, thus enhancing their triboelectric charge densities and contact areas. As a result, the assembled FC-TENGs demonstrate enhanced output performance (94 V, 8.5 µA, and 0.15 W/m2) and exceptional durability in 15,000 cycles. The prepared FC-TENGs with efficient energy harvesting capabilities can be implemented in practical applications to power various electronic devices. Our work strengthens the viability of cellulose-based TENGs for sustainable development and provides novel perspectives on the cost-effective and valuable utilization of cellulose in the future.

Visible Microfluidic Deprotonation for Aramid Nanofibers as Building Blocks of Cascade-Microfluidic-Processed Colloidal Aerogels

 Microfluidic deprotonation approach is proposed to realize continuous, scalable, efficient, and uniform production of aramid nanofibers (ANFs) by virtue of large specific surface area, high mixing efficiency, strong heat transfer capacity, narrow residence time distribution, mild laminar-flow process, and amplification-free effect of the microchannel reactor. By means of monitoring capabilities endowed by the high transparency of the microchannel, the kinetic exfoliation process of original aramid particles is in situ observed and the corresponding exfoliation mechanism is established quantificationally. The deprotonated time can be reduced from the traditional several days to 7 min for the final colloidal dispersion due to the synergistic effect between enhanced local shearing/mixing and the rotational motion of aramid particles in microchannel revealed by numerical simulations. Furthermore, the cascade microfluidic processing approach is used to make various ANF colloidal aerogels including aerogel fibers, aerogel films, and 3D-printed aerogel articles. Comprehensive characterizations show that these cascade-microfluidic-processed colloidal aerogels have identical features as those prepared in batch-style mode, revealing the versatile use value of these ANFs. This work achieves significant progress toward continuous and efficient production of ANFs, bringing about appreciable prospects for the practical application of ANF-based materials and providing inspiration for exfoliating any other nano-building blocks.

Pore-Forming Toxin-Driven Recovery of Peroxidase-Mimicking Activity in Biomass Channels for Label-Free Electrochemical Bacteria Sensing

The development of sensitive, selective, and rapid methods to detect bacteria in complex media is essential to ensuring human health. Virulence factors, particularly pore-forming toxins (PFTs) secreted by pathogenic bacteria, play a crucial role in bacterial diseases and serve as indicators of disease severity. In this study, a nanochannel-based label-free electrochemical sensing platform was developed for the detection of specific pathogenic bacteria based on their secreted PFTs. In this design, wood substrate channels were functionalized with a Fe-based metal-organic framework (FeMOF) and then protected with a layer of phosphatidylcholine (PC)-based phospholipid membrane (PM) that serves as a peroxidase mimetic and a channel gatekeeper, respectively. Using Staphylococcus aureus (S. aureus) as the model bacteria, the PC-specific PFTs secreted by S. aureus perforate the PM layer. Now exposed to the FeMOF, uncharged 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) molecules in the electrolyte undergo oxidation to cationic products (ABTS•+). The measured transmembrane ionic current indicates the presence of S. aureus and methicillin-resistant S. aureus (MRSA) with a low detection limit of 3 cfu mL-1. Besides excellent specificity, this sensing approach exhibits satisfactory performance for the detection of target bacteria in the complex media of food.

New Emerging Fast Charging Microscale Electrode Materials

Fast charging lithium (Li)-ion batteries are intensively pursued for next-generation energy storage devices, whose electrochemical performance is largely determined by their constituent electrode materials. While nanosizing of electrode materials enhances high-rate capability in academic research, it presents practical limitations like volumetric packing density and high synthetic cost. As an alternative to nanosizing, microscale electrode materials cannot only effectively overcome the limitations of the nanosizing strategy but also satisfy the requirement of fast-charging batteries. Therefore, this review summarizes the new emerging microscale electrode materials for fast charging from the commercialization perspective. First, the fundamental theory of electronic/ionic motion in both individual active particles and the whole electrode is proposed. Then, based on these theories, the corresponding optimization strategies are summarized toward fast-charging microscale electrode materials. In addition, advanced functional design to tackle the mechanical degradation problems related to next generation high capacity alloy- and conversion-type electrode materials (Li, S, Si et al.) for achieving fast charging and stable cycling batteries. Finally, general conclusions and the future perspective on the potential research directions of microscale electrode materials are proposed. It is anticipated that this review will provide the basic guidelines for both fundamental research and practical applications of fast-charging batteries.

Ion transport in nanofluidics under external fields

Nanofluidic channels with tailored ion transport dynamics are usually used as channels for ion transport, to enable high-performance ion regulation behaviors. The rational construction of nanofluidics and the introduction of external fields are of vital significance to the advancement and development of these ion transport properties. Focusing on the recent advances of nanofluidics, in this review, various dimensional nanomaterials and their derived homogeneous/heterogeneous nanofluidics are first briefly introduced. Then we discuss the basic principles and properties of ion transport in nanofluidics. As the major part of this review, we focus on recent progress in ion transport in nanofluidics regulated by external physical fields (electric field, light, heat, pressure, etc.) and chemical fields (pH, concentration gradient, chemical reaction, etc.), and reveal the advantages and ion regulation mechanisms of each type. Moreover, the representative applications of these nanofluidic channels in sensing, ionic devices, energy conversion, and other areas are summarized. Finally, the major challenges that need to be addressed in this research field and the future perspective of nanofluidics development and practical applications are briefly illustrated.

Micro "Hyper-Channels" on Laser-Refined Cellulose Structures

Controlled liquid transportation is widely applied in both academia and industry. However, liquid transport applications are limited by parameters such as driving forces, precision, and velocity. Herein, a simple laser-refining technology is presented to produce micro "hyper-channels". A cellulose substrate is rendered hydrophobic through silanization and refined with a laser to produce both hierarchical nanostructures and a wettability contrast simultaneously. Such a method enables faster ("hyper"-channel) aqueous liquid transportation (≈25X, 50 mm s-1 ) compared to conventional methods. Complex patterns can be readily produced at different scales with spatial resolution as low as 50 µm. This technique also controls the refining depth on the thin paper substrate. Shallow channels can be fabricated on thin paper substrates that enable fluidic channel-crossover without liquid mixing. With certain parameters, the technique creates "portals" through the substrate, allowing trans-dimensional liquid transportation between two layers of a single sheet of substrate. The fluid throughput can be increased, while also permitting fluidic channel crossover without liquid mixing. By introducing multiple portals, the controlled fluid can transfer trans-dimensionally several times, enabling further fluidic complexity. The real-life utility of the method is demonstrated by creating a trans-dimensional microfluidic device for colorimetric detection.

Ionic Transistors

Biological voltage-gated ion channels, which behave as life's transistors, regulate ion transport precisely and selectively through atomic-scale selectivity filters to sustain important life activities. By this inspiration, voltage-adaptable ionic transistors that use ions as signal carriers may provide an alternative information processing unit beyond solid-state electronic devices. This review provides a comprehensive overview of the first generation of biomimetic ionic transistors, including their operating mechanisms, device architecture development, and property characterizations. Despite its infancy, significant progress has been made in the applications of ionic transistors in fields such as DNA detection, drug delivery, and ionic circuits. Challenges and prospects of full exploitation of ionic transistors for a broad spectrum of practical applications are also discussed.

Damage-Tolerant Wood Layers for Corrosion Protection of Metal Structures

Mechanically strong and damage-tolerant corrosion protection layers are of great technological importance. However, corrosion protection layers with high modulus (>1.5 GPa) and tensile strength (>100 MPa) are rare. Here, we report that a 130 μm thick densified wood veneer with a Young's modulus of 34.49 GPa and tensile strength of 693 MPa exhibits both low diffusivity for metal ions and the ability of self-recovery from mechanical damage. Densified wood veneer is employed as an intermediate layer to render a mechanically strong corrosion protection structure, referred to as "wood corrosion protection structure", or WCPS. The corrosion rate of low-carbon steel protected by WCPS is reduced by 2 orders of magnitude than state-of-the-art corrosion protection layers during a salt spray test. The introduction of engineered wood veneer as a thin and mechanically strong material points to new directions of sustainable corrosion protection design.

Engineered cellulose nanofibers membranes with oppositely charge characteristics for high-performance salinity gradient power generation by reverse electrodialysis

Reverse electrodialysis (RED) using nanofluidic ion-selective membrane may convert the salinity difference between seawater and river water into electricity. However, heterogeneous modification reactions of cellulose commonly leads to the inhomogeneous distribution of surface charges, thereby hampering the improvement of cellulose-based nanofluidic membranes for energy conversion. Herein, RED devices based on cellulose nanofibers (CNF) membranes with opposite charge characteristics were developed for the generation of salinity gradient power. Anion-CNF membrane (A-CNF) with varying negative charge densities was synthesized using 2,2,6,6-Tetramethylpiperidine 1-oxy radical (TEMPO) oxidation modification, whereas cation-CNF membrane (C-CNF) was prepared through etherification. By mixing artificial seawater and river water, the output power density of CNF RED device is up to 2.87 W m-2. The output voltage of 30 RED units connected in series may reach up to 3.11 V, which can be used to directly power tiny electronic devices viz. LED lamp, calculator, etc. The results of this work provide a feasible possibility for widespread application of ion exchange membranes for salinity gradient energy harvesting.

Farming on the Ocean via Desalination (FOOD)

Today, agricultural irrigation consumes the largest amount of freshwater globally, while humans are threatened by water scarcity. To eliminate the trade-off between hunger and thirst, here, we show off-grid maritime agriculture based on a floating solar-driven agro-desalination wooden dome. In this dome, part of the visible light is transmitted for photosynthesis, and the remaining solar energy drives solar desalination, providing enough water (>4 mm day-1) for irrigation. Based on this water-food synergy, the stages of germination and growth are demonstrated. This technology can, to a large extent, support food security and sustainable agriculture and, in principle, be used to create self-circulation systems at sea to help humans survive weather extremes such as floods and droughts.

The Critical Roles of Water in the Processing, Structure, and Properties of Nanocellulose

The cellulose industry depends heavily on water owing to the hydrophilic nature of cellulose fibrils and its potential for sustainable and innovative production methods. The emergence of nanocellulose, with its excellent properties, and the incorporation of nanomaterials have garnered significant attention. At the nanoscale level, nanocellulose offers a higher exposure of hydroxyl groups, making it more intimate with water than micro- and macroscale cellulose fibers. Gaining a deeper understanding of the interaction between nanocellulose and water holds the potential to reduce production costs and provide valuable insights into designing functional nanocellulose-based materials. In this review, water molecules interacting with nanocellulose are classified into free water (FW) and bound water (BW), based on their interaction forces with surface hydroxyls and their mobility in different states. In addition, the water-holding capacity of cellulosic materials and various water detection methods are also discussed. The review also examines water-utilization and water-removal methods in the fabrication, dispersion, and transport of nanocellulose, aiming to elucidate the challenges and tradeoffs in these processes while minimizing energy and time costs. Furthermore, the influence of water on nanocellulose properties, including mechanical properties, ion conductivity, and biodegradability, are discussed. Finally, we provide our perspective on the challenges and opportunities in developing nanocellulose and its interplay with water.

Cellulose-Based Conductive Materials for Energy and Sensing Applications

Cellulose-based conductive materials (CCMs) have emerged as a promising class of materials with various applications in energy and sensing. This review provides a comprehensive overview of the synthesis methods and properties of CCMs and their applications in batteries, supercapacitors, chemical sensors, biosensors, and mechanical sensors. Derived from renewable resources, cellulose serves as a scaffold for integrating conductive additives such as carbon nanotubes (CNTs), graphene, metal particles, metal-organic frameworks (MOFs), carbides and nitrides of transition metals (MXene), and conductive polymers. This combination results in materials with excellent electrical conductivity while retaining the eco-friendliness and biocompatibility of cellulose. In the field of energy storage, CCMs show great potential for batteries and supercapacitors due to their high surface area, excellent mechanical strength, tunable chemistry, and high porosity. Their flexibility makes them ideal for wearable and flexible electronics, contributing to advances in portable energy storage and electronic integration into various substrates. In addition, CCMs play a key role in sensing applications. Their biocompatibility allows for the development of implantable biosensors and biodegradable environmental sensors to meet the growing demand for health and environmental monitoring. Looking to the future, this review emphasizes the need for scalable synthetic methods, improved mechanical and thermal properties, and exploration of novel cellulose sources and modifications. Continued innovation in CCMs promises to revolutionize sustainable energy storage and sensing technologies, providing environmentally friendly solutions to pressing global challenges.

Plant-inspired multifunctional fluorescent cellulose nanocrystals intelligent nanocomposite hydrogel

Intelligent hydrogel has great application potentials in flexible sensing and artificial intelligence devices due to its intrinsic characteristics. However, developing an intelligent hydrogel with favorable properties including high strength, superior toughness, excellent conductivity and ionic sensing via a facile route is still a challenge. Herein, inspired by biologically chelating interactions of phytic acid (PA) in plants, a plant-inspired versatile intelligent nanocomposite hydrogel was readily fabricated by incorporating PA into the interface of fluorescent cellulose nanocrystals (F-CNC). Under PA "molecular bridge", the hydrogel simultaneously realized superflexibility (1000 %), high strength, superb self-healing ability, remarkable fluorescence and chloride ion sensibility as well as good ionic conductivity (2.4 S/m). The hydrogel could be assembled as a flexible sensor for real-time monitoring of human motion with excellent sensitivity and stability since high sensitivity toward both strain and pressure. F-CNC acted as a functional trigger could confer the hydrogel good fluorescence and high sensitivity toward chloride ion. This design confirms the synergy of F-CNC in boosting strength, ionic sensing, and ionic conductivity, addressing a long-standing dilemma among strength, stretchability, and sensitivity for intelligent hydrogel. The one-step incorporating tactic under mild ambient conditions may open an innovative avenue for the construction of intelligent hydrogel with novel properties.

Ultra-mechanosensitive Chloride Ion Transport through Bioinspired High-Density Elastomeric Nanochannels

Mechanosensitive ion channels play crucial roles in physiological activities, where small mechanical stimuli induce the membrane tension, trigger the ion channels' deformation, and are further transformed into significant electrochemical signals. Artificial ion channels with stiff moduli have been developed to mimic mechanosensory behaviors, exhibiting an electrochemical response by the high-pressure-induced flow. However, fabricating flexible mechanosensitive channels capable of regulating specific ion transporting upon dramatic deformation has remained a challenge. Here, we demonstrate bioinspired high-density elastomeric channels self-assembled by polyisoprene-b-poly4-vinylpyridine, which exhibit ultra-mechanosensitive chloride ion transport resulting from nanochannel deformation. The PI-formed continuous elastic matrix can transmit external forces into internal tensions, while P4VP forms transmembrane chloride channels that undergo dramatic deformation and respond to mechanical stimuli. The integrated and flexible chloride channels present a dramatic and stable electrochemical signal toward a low pressure of 0.2 mbar. This research first demonstrates the artificial mechanosensory chloride channels, which could provide a promising avenue for designing flexible and responsive channel systems.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

A recyclable biomass electrolyte towards green zinc-ion batteries

The operation of traditional aqueous-electrolyte zinc-ion batteries is adversely affected by the uncontrollable growth of zinc dendrites and the occurrence of side reactions. These problems can be avoided by the development of functional hydrogel electrolytes as replacements for aqueous electrolytes. However, the mechanism by which most hydrogel electrolytes inhibit the growth of zinc dendrites on a zinc anode has not been investigated in detail, and there is a lack of a large-scale recovery method for mainstream hydrogel electrolytes. In this paper, we describe the development of a recyclable and biodegradable hydrogel electrolyte based on natural biomaterials, namely chitosan and polyaspartic acid. The distinctive adsorptivity and inducibility of chitosan and polyaspartic acid in the hydrogel electrolyte triggers a double coupling network and an associated synergistic inhibition mechanism, thereby effectively inhibiting the side reactions on the zinc anode. In addition, this hydrogel electrolyte played a crucial role in an aqueous acid-based Zinc/MnO₂ battery, by maintaining its interior two-electron redox reaction and inhibiting the formation of zinc dendrites. Furthermore, the sustainable biomass-based hydrogel electrolyte is biodegradable, and could be recovered from the Zinc/MnO₂ battery for subsequent recycling.

Dopamine modified layered double hydroxide membranes based on nanofibril architectures: Toward superior tellurium separation properties for water treatment

Two-dimensional (2D) membrane materials are widely employed for the accurate sieving of ionic contaminants and are of great importance for water reuse. However, 2D membrane materials often suffer from uneven thickness and surface defects, which severely limit their application prospects. Herein, a continuous 2D membrane (LCUM/D) was prepared using cellulose nanofibrils (CNFs) as the support backbone for the assembled layered double hydroxides (LDHs) and dopamine (DA) as the adhesive. The results demonstrated that LDHs could be uniformly distributed in the network structure of CNFs, and the defects on the membrane surface could be effectively compensated by DA. Simultaneously, the continuous LCUM/D showed excellent rejection (97.18%) and selectivity of ionic contaminants tellurium. Dopamine not only compensated for the surface defects of the 2D membrane and enhanced the rejection of tellurium, but also caused no significant loss of water permeance. Moreover, the LCUM/D exhibited stability, which facilitated its long-term application. In addition, the improved hydrophilicity allowed LCUM/D satisfactory anti-fouling properties. This study provides new dimensional insights into the fabrication of continuous 2D membranes for the removal of ionic contaminant and enhances their application prospects in wastewater treatment.

Zirconium Component Modified Porous Nanowood for Efficient Removal of Phosphate from Aqueous Solutions

Rapid urban industrialization and agricultural production have led to the discharge of excessive phosphate into aquatic systems, resulting in a rise in water pollution. Therefore, there is an urgent need to explore efficient phosphate removal technologies. Herein, a novel phosphate capture nanocomposite (PEI-PW@Zr) with mild preparation conditions, environmental friendliness, recyclability, and high efficiency has been developed by modifying aminated nanowood with a zirconium (Zr) component. The Zr component imparts the ability to capture phosphate to the PEI-PW@Zr, while the porous structure provides a mass transfer channel, resulting in excellent adsorption efficiency. Additionally, the nanocomposite maintains more than 80% phosphate adsorption efficiency even after ten adsorption-desorption cycles, indicating its recyclability and potential for repeated use. This compressible nanocomposite provides novel insights into the design of efficient phosphate removal cleaners and offers potential approaches for the functionalization of biomass-based composites.

Rational Design of Cellulosic Triboelectric Materials for Self-Powered Wearable Electronics

With the rapid development of the Internet of Things and flexible electronic technologies, there is a growing demand for wireless, sustainable, multifunctional, and independently operating self-powered wearable devices. Nevertheless, structural flexibility, long operating time, and wearing comfort have become key requirements for the widespread adoption of wearable electronics. Triboelectric nanogenerators as a distributed energy harvesting technology have great potential for application development in wearable sensing. Compared with rigid electronics, cellulosic self-powered wearable electronics have significant advantages in terms of flexibility, breathability, and functionality. In this paper, the research progress of advanced cellulosic triboelectric materials for self-powered wearable electronics is reviewed. The interfacial characteristics of cellulose are introduced from the top-down, bottom-up, and interfacial characteristics of the composite material preparation process. Meanwhile, the modulation strategies of triboelectric properties of cellulosic triboelectric materials are presented. Furthermore, the design strategies of triboelectric materials such as surface functionalization, interfacial structure design, and vacuum-assisted self-assembly are systematically discussed. In particular, cellulosic self-powered wearable electronics in the fields of human energy harvesting, tactile sensing, health monitoring, human-machine interaction, and intelligent fire warning are outlined in detail. Finally, the current challenges and future development directions of cellulosic triboelectric materials for self-powered wearable electronics are discussed.

Inspired by Wood: Thick Electrodes for Supercapacitors

The emergence and development of thick electrodes provide an efficient way for the high-energy-density supercapacitor design. Wood is a kind of biomass material with porous hierarchical structure, which has the characteristics of a straight channel, uniform pore structure, good mechanical strength, and easy processing. The wood-inspired low-tortuosity and vertically aligned channel architecture are highly suitable for the construction of thick electrochemical supcapacitor electrodes with high energy densities. This review summarizes the design concepts and processing parameters of thick electrode supercapacitors inspired by natural woods, including wood-based pore structural design regulation, electric double layer capacitances (EDLCs)/pseudocapacitance construction, and electrical conductivity optimization. In addition, the optimization strategies for preparing thick electrodes with wood-like structures (e.g., 3D printing, freeze-drying, and aligned-low tortuosity channels) are also discussed in detail. Further, this review presents current challenges and future trends in the design of thick electrodes for supercapacitors with wood-inspired pore structures. As a guideline, the brilliant blueprint optimization will promote sustainable development of wood-inspired structure design for thick electrodes and broaden the application scopes.

Host-Guest Recognition Boosts Biomimetic Mono/Multivalent Cation Separation

Biomimetic ion permselective membranes with ultrahigh ion permeability and selectivity represent a research frontier in ion separation, yet the successful fabrication of such membranes remains a formidable challenge. Here, we demonstrate a 4-sulfocalix[4]arene (4-SCA)-modified graphene oxide (GO) membrane that shows extraordinary performance in separating mono-from multivalent cations, as well as having reversible pH-responsiveness. The resulting 4-SCA-modified GO (SCA-GO) membrane preferentially transports potassium ions (K⁺) over radionuclide cations (Co²⁺, UO₂²⁺, La³⁺, Eu³⁺, and Th⁴⁺). The ion selectivities are an order of magnitude higher than that of the unmodified GO membrane. Theoretical calculations and experimental investigations demonstrate that the much-improved ion selectivity arises from the specific recognition between 4-SCA and radionuclide cations. The transport of multivalent radionuclides is impeded by a binding-obstructing mechanism from the host-guest interactions. Interestingly, the host-guest interactions are responsive to the protonation/deprotonation transformation of the 4-SCA. Therefore, the SCA-GO membrane mimics pH-regulated ion selective behavior found in biological ion channels. Our strategy of designing a biomimetic permselective GO membrane may allow efficient nuclear wastewater treatment and, more importantly, deepen our understanding of biomimetic ion transport mechanisms.

Dual-network polyvinyl alcohol/polyacrylamide/xanthan gum ionic conductive hydrogels for flexible electronic devices

Ionic conductive hydrogels (ICHs) have received widespread attention as an ideal candidate for flexible electronic devices. However, conventional ICHs failed in widespread applications due to their inability to simultaneously possess high toughness, high ionic conductivity, and anti-freezing properties. Here, polyvinyl alcohol (PVA) and polyacrylamide (PAAm) were first dissolved in the zinc chloride solution, in which zinc ions (Zn²⁺) act as ionic cross-linkers and conducting ions, followed by the introduction of xanthan gum (XG) with a unique structure of trisaccharide side chains into the PVA/PAAm semi-interpenetrating network to prepare a dual-network ICHs (refers as PPXZ). Enabled by the synergistic effect of intermolecular chemical covalent cross-linking and physical cross-linking, PPXZ hydrogels exhibit significantly improved mechanical properties without sacrificing electrical conductivity. Furthermore, PPXZ hydrogels are successfully applied to flexible electronic devices, such as strain sensors and zinc ion hybrid supercapacitors, exhibiting satisfactory sensing sensitivity and cycling stability at a wide temperature range, respectively. Even at a high current density (10 A g^-1), the capacity of the supercapacitor retains 88.24 % after 10,000 cycles. This strategy provides new insight for ICHs in wide temperature-applied flexible electronic devices.

Sorption-Deformation-Percolation Model for Diffusion in Nanoporous Media

Diffusion of molecules in porous media is a critical process that is fundamental to numerous chemical, physical, and biological applications. The prevailing theoretical frameworks are challenged when explaining the complex dynamics resulting from the highly tortuous host structure and strong guest-host interactions, especially when the pore size approximates the size of diffusing molecule. This study, using molecular dynamics, formulates a semiempirical model based on theoretical considerations and factorization that offer an alternative view of diffusion and its link with the structure and behavior (sorption and deformation) of material. By analyzing the intermittent dynamics of water, microscopic self-diffusion coefficients are predicted. The apparent tortuosity, defined as the ratio of the bulk to the confined self-diffusion coefficients, is found to depend quantitatively on a limited set of material parameters: heat of adsorption, elastic modulus, and percolation probability, all of which are experimentally accessible. The proposed sorption-deformation-percolation model provides guidance on the understanding and fine-tuning of diffusion.

Lignin-Based Materials for Additive Manufacturing: Chemistry, Processing, Structures, Properties, and Applications

The utilization of lignin, the most abundant aromatic biomass component, is at the forefront of sustainable engineering, energy, and environment research, where its abundance and low-cost features enable widespread application. Constructing lignin into material parts with controlled and desired macro- and microstructures and properties via additive manufacturing has been recognized as a promising technology and paves the way to the practical application of lignin. Considering the rapid development and significant progress recently achieved in this field, a comprehensive and critical review and outlook on three-dimensional (3D) printing of lignin is highly desirable. This article fulfils this demand with an overview on the structure of lignin and presents the state-of-the-art of 3D printing of pristine lignin and lignin-based composites, and highlights the key challenges. It is attempted to deliver better fundamental understanding of the impacts of morphology, microstructure, physical, chemical, and biological modifications, and composition/hybrids on the rheological behavior of lignin/polymer blends, as well as, on the mechanical, physical, and chemical performance of the 3D printed lignin-based materials. The main points toward future developments involve hybrid manufacturing, in situ polymerization, and surface tension or energy driven molecular segregation are also elaborated and discussed to promote the high-value utilization of lignin.

Photosensitive ion channels in layered MXene membranes modified with plasmonic gold nanostars and cellulose nanofibers

Ion channels transduce external stimuli into ion-transport-mediated signaling, which has received considerable attention in diverse fields such as sensors, energy harvesting devices, and desalination membrane. In this work, we present a photosensitive ion channel based on plasmonic gold nanostars (AuNSs) and cellulose nanofibers (CNFs) embedded in layered MXene nanosheets. The MXene/AuNS/CNF (MAC) membrane provides subnanometer-sized ionic pathways for light-sensitive cationic flow. When the MAC nanochannel is exposed to NIR light, a photothermal gradient is formed, which induces directional photothermo-osmotic flow of nanoconfined electrolyte against the thermal gradient and produces a net ionic current. MAC membrane exhibits enhanced photothermal current compared with pristine MXene, which is attributed to the combined photothermal effects of plasmonic AuNSs and MXene and the widened interspacing of the MAC composite via the hydrophilic nanofibrils. The MAC composite membranes are envisioned to be applied in flexible ionic channels with ionogels and light-controlled ionic circuits.

Bioresource Upgrade for Sustainable Energy, Environment, and Biomedicine

We conceptualize bioresource upgrade for sustainable energy, environment, and biomedicine with a focus on circular economy, sustainability, and carbon neutrality using high availability and low utilization biomass (HALUB). We acme energy-efficient technologies for sustainable energy and material recovery and applications. The technologies of thermochemical conversion (TC), biochemical conversion (BC), electrochemical conversion (EC), and photochemical conversion (PTC) are summarized for HALUB. Microalgal biomass could contribute to a biofuel HHV of 35.72 MJ Kg-1 and total benefit of 749 $/ton biomass via TC. Specific surface area of biochar reached 3000 m2 g-1 via pyrolytic carbonization of waste bean dregs. Lignocellulosic biomass can be effectively converted into bio-stimulants and biofertilizers via BC with a high conversion efficiency of more than 90%. Besides, lignocellulosic biomass can contribute to a current density of 672 mA m-2 via EC. Bioresource can be 100% selectively synthesized via electrocatalysis through EC and PTC. Machine learning, techno-economic analysis, and life cycle analysis are essential to various upgrading approaches of HALUB. Sustainable biomaterials, sustainable living materials and technologies for biomedical and multifunctional applications like nano-catalysis, microfluidic and micro/nanomotors beyond are also highlighted. New techniques and systems for the complete conversion and utilization of HALUB for new energy and materials are further discussed.

Two-Dimensional Nanofluidic Membranes with Intercalated In-Plane Shortcuts for High-Performance Blue Energy Harvesting

Two-dimensional nanofluidic membranes offer great opportunities for developing efficient and robust devices for ionic/water-nexus energy harvesting. However, low counterion concentration and long pathway through limited ionic flux restrict their output performance. Herein, it is demonstrated that rapid diffusion kinetics can be realized in two-dimensional nanofluidic membranes by introducing in-plane holes across nanosheets, which not only increase counterion concentration but also shorten pathway length through the membranes. Thus, the holey membranes exhibited an enhanced performance relative to the pristine ones in terms of osmotic energy conversion. In particular, a biomimetic multilayered membrane sequentially assembled from pristine and holey sections offers an optimized combination of selectivity and permeability, therefore generating a power density up to 6.78 W m^-2 by mixing seawater and river water, superior to the majority of the state-of-the-art lamellar nanofluidic membranes. This work highlights the importance of channel morphologies and presents a general strategy for effectively improving ion transport through lamellar membranes for high-performance nanofluidic devices.

Specific Ion and Electric Field Controlled Diverse Ion Distribution and Electroosmotic Transport in a Polyelectrolyte Brush Grafted Nanochannel

Controlling ion distribution inside a charged nanochannel is central to using such channels in diverse applications. Here, we show the possibility of using a charged polyelectrolyte (PE) brush-grafted nanochannel for triggering diverse nanoscopic ion distribution and nanofluidic electroosmotic transport by controlling the valence and size of the counterions (that screen the charges of the PE brushes) and the strength of an externally applied axial electric field. We atomistically simulate separate cases of fully charged polyacrylic acid (PAA) brush functionalized nanochannels with Na⁺, Cs⁺, Ca²⁺, Ba²⁺, and Y³⁺ counterions screening the PE charges. Four key findings emerge from our simulations. First, we find that the counterions with a greater valence and a smaller size prefer to remain localized inside the brush layer. Second, for the case where there is an added chloride salt with the same cation (as the screening counterions), there are more coions (Cl^- ions) in the brush-free bulk than counterions (for counterions Na⁺, Ca²⁺, Ba²⁺, Y³⁺): this is a manifestation of the overscreening (OS) of the PE brush layer. Contrastingly, the number of Cs⁺ ions remain higher than the Cl^- ions inside the brush-free bulk, ensuring that there is no OS effect for this case. Third, large applied electric field enables a few Na⁺, Cs⁺, and Ba²⁺ counterions to leave the brush layer and to go to the bulk: this makes the OS of the PE brush layer disappear for the cases of PE brushes being screened by the Na⁺ and Ba²⁺ ions. On the other hand, no such electric-field-mediated disappearance of OS is observed for the cases of Ca²⁺ and Y³⁺ screening counterions; we attribute this to the firm attachment of these counterions to the negatively charged monomers. Free energy associated with a counterion binding to a PE chain corroborates this diversity in the counterion-specific response to the applied electric field. Finally, we demonstrate that such diverse ion distributions, along with specific electric-field-strength-dependent ion properties, lead to (1) electroosmotic (EOS) transport in nanochannels grafted with PAA brushes screened with Cs⁺ ions to be always counterion dominated, (2) EOS transport in nanochannels grafted with PAA brushes screened with Ca²⁺ and Y³⁺ ions to be always coion-dominated, and (3) EOS transport in nanochannels grafted with PAA brushes screened with Na⁺ and Ba²⁺ ions to be coion dominated for smaller electric fields and counterion dominated for larger electric fields.

Engineering Polymeric Nanofluidic Membranes for Efficient Ionic Transport: Biomimetic Design, Material Construction, and Advanced Functionalities

Design elements extracted from biological ion channels guide the engineering of artificial nanofluidic membranes for efficient ionic transport and spawn biomimetic devices with great potential in many cutting-edge areas. In this context, polymeric nanofluidic membranes can be especially attractive because of their inherent flexibility and benign processability, which facilitate massive fabrication and facile device integration for large-scale applications. Herein, the state-of-the-art achievements of polymeric nanofluidic membranes are systematically summarized. Theoretical fundamentals underlying both biological and synthetic ion channels are introduced. The advances of engineering polymeric nanofluidic membranes are then detailed from aspects of structural design, material construction, and chemical functionalization, emphasizing their broad chemical and reticular/topological variety as well as considerable property tunability. After that, this Review expands on examples of evolving these polymeric membranes into macroscopic devices and their potentials in addressing compelling issues in energy conversion and storage systems where efficient ion transport is highly desirable. Finally, a brief outlook on possible future developments in this field is provided.

Advanced Bacterial Cellulose Ionic Conductors with Gigantic Thermopower for Low-Grade Heat Harvesting

Ionic conductors such as polymer electrolytes and ionic liquids have high thermoelectric voltages several orders of magnitude higher than electronic thermoelectric materials, while their conductivity is much lower than the latter. This work reports a novel approach to achieve high-performance ionic conductors using calcium ion (Ca²⁺) coordinated bacterial cellulose (CaBC) through molecular channel engineering. Through the coordination of Ca²⁺ with cellulose molecular chain, the distance between the cellulose molecular chains is widened, so that ions can transport along the cellulose molecular chain. Therefore, we reported ionic thermoelectric (i-TE) material based on CaBC/NaCl with a relatively high ionic Seebeck coefficient of -27.2 mV K^-1 and high ionic conductivity of 204.2 mS cm^-1. This ionic hydrogel is promising in the design of high-thermopower i-TE materials for low-grade heat energy harvesting.

Functionalized Wood Veneers as Vibration Sensors: Exploring Wood Piezoelectricity and Hierarchical Structure Effects

Functional wood materials often rely on active additives due to the weak piezoelectric response of wood itself. Here, we chemically modify wood to form functionalized, eco-friendly wood veneer for self-powered vibration sensors. Only the piezoelectricity of the cellulose microfibrils is used, where the drastic improvement comes only from molecular and nanoscale wood structure tuning. Sequential wood modifications (delignification, oxidation, and model fluorination) are performed, and effects on vibration sensing abilities are investigated. Wood veneer piezoelectricity is characterized by the piezoresponse force microscopy mode in atomic force microscopy. Delignification, oxidation, and model fluorination of wood-based sensors provide output voltages of 11.4, 23.2, and 60 mV by facilitating cellulose microfibril deformation. The vibration sensing ability correlates with improved piezoelectricity and increased cellulose deformation, most likely by large, local cell wall bending. This shows that nanostructural wood materials design can tailor the functional properties of wood devices with potential in sustainable nanotechnology.

Bilayer Wood Membrane with Aligned Ion Nanochannels for Spontaneous Moist-Electric Generation

Water-enabled electricity generation (WEG) technologies are considered to be an attractive and renewable approach to meet energy crisis and environmental pollution globally. However, the existing WEG technologies still face tremendous challenges including high material cost, harmful components, and specific environmental requirements. Herein, a high-performance wood-based moisture-enabled electric generator (WMEG) is fabricated. Natural wood is cut perpendicular to the tree growth direction and engineered by simple chemical modification. The obtained bilayer wood membrane has robust mechanical framework with aligned ion nanochannels, abundant dissociated functional groups, and spontaneous water adsorption in the air. At the relative humidity of 85%, one WMEG can generate a voltage of 0.57 V. The device can also effectively sense biological water information as a self-powered sensor. The biophile design contributes a practical moist-electric generation strategy that offers clean energy, especially for undeveloped and disaster-relief regions where electricity is limited by high cost or crippled power facilities.

Flexible iontronics based on 2D nanofluidic material

Iontronics focuses on the interactions between electrons and ions, playing essential roles in most processes across physics, chemistry and life science. Osmotic power source as an example of iontronics, could transform ion gradient into electrical energy, however, it generates low power, sensitive to humidity and can’t operate under freezing point. Herein, based on 2D nanofluidic graphene oxide material, we demonstrate an ultrathin (∼10 µm) osmotic power source with voltage of 1.5 V, volumetric specific energy density of 6 mWh cm⁻³ and power density of 28 mW cm⁻³, achieving the highest values so far. Coupled with triboelectric nanogenerator, it could form a self-charged conformable triboiontronic device. Furthermore, the 3D aerogel scales up areal power density up to 1.3 mW cm⁻² purely from ion gradient based on nanoconfined enhancement from graphene oxide that can operate under −40 °C and overcome humidity limitations, enabling to power the future implantable electronics in human-machine interface.

Osmotic power source based on 2D nanofluidic graphene oxide could overcome humidity and temperature limitations due to high areal power density purely from ion gradient. Here, authors couple it with triboelectric nanogenerator, and demonstrate a self-chargeable conformable tribo-iontronic device.

Progress, Challenge and Perspective of Fabricating Cellulose

Cellulose as the most abundant biopolymers on Earth, presents appealing performance in mechanical properties, thermal management, and versatile functionalization. The development of fabrication methods closely relates to enrich its functionality and reduce manufacture cost. However, cellulose is hard to be dissolved by most common solvents or melt due to its recalcitrant property. Herein, the recent progress of fabricating cellulose is summarized. First, the unique hierarchical structure of cellulose is fully investigated and the resulted processability is highlighted in directions of down to nanocellulose, dissolution, and thermoplastic processing. Then, the reported fabrication methods are summarized in three aspects: (1) self-assembly from nano/micro cellulose suspensions, especially the self-assembly of cellulose nanocrystals; (2) dissolution-regeneration-drying, covering spinning and solvent infusion processing; and (3) thermoplastic processing, focusing on analysis of the setup and the morphology changes of the prepared products. In each aspect, the flowchart of the fabrication process, the behind mechanism, fabricated products, and effects of processing parameters are explored. Finally, this review provides a perspective on the further direction of fabricating cellulose, especially the challenges toward mass production of cellulose. This article is protected by copyright. All rights reserved.

Giant Osmotic Energy Conversion through Vertical-Aligned Ion-Permselective Nanochannels in Covalent Organic Framework Membranes

Nanofluidic membranes have been demonstrated as promising candidates for osmotic energy harvesting. However, it remains a long-standing challenge to fabricate high-efficiency ion-permselective membranes with well-defined channel architectures. Here, we demonstrate high-performance osmotic energy conversion membranes based on oriented two-dimensional covalent organic frameworks (COFs) with ultrashort vertically aligned nanofluidic channels that enabled efficient and selective ion transport. Experiments combined with molecular dynamics simulations revealed that exquisite control over channel orientation, charge polarity, and charge density contributed to high ion selectivity and permeability. When applied to osmotic energy conversion, a pair of 100 nm thick oppositely charged COF membranes achieved an ultrahigh output power density of 43.2 W m^-2 at a 50-fold salinity gradient and up to 228.9 W m^-2 for the Dead Sea and river water system. The achieved power density outperforms the state-of-the-art nanofluidic membranes, suggesting the great potential of oriented COF membranes in the fields of advanced membrane technology and energy conversion.

Environment tolerant, adaptable and stretchable organohydrogels: preparation, optimization, and applications

Multiple stretchable materials have been successively developed and applied to wearable devices, soft robotics, and tissue engineering. Organohydrogels are currently being widely studied and formed by dispersing immiscible hydrophilic/hydrophobic polymer networks or only hydrophilic polymer networks in an organic/water solvent system. In particular, they can not only inherit and carry forward the merits of hydrogels, but also have some unique advantageous features, such as anti-freezing and water retention abilities, solvent resistance, adjustable surface wettability, and shape memory effect, which are conducive to the wide environmental adaptability and intelligent applications. This review first summarizes the structure, preparation strategy, and unique advantages of the reported organohydrogels. Furthermore, organohydrogels can be optimized for electro-mechanical properties or endowed with various functionalities by adding or modifying various functional components owing to their modifiability. Correspondingly, different optimization strategies, mechanisms, and advanced developments are described in detail, mainly involving the mechanical properties, conductivity, adhesion, self-healing properties, and antibacterial properties of organohydrogels. Moreover, the applications of organohydrogels in flexible sensors, energy storage devices, nanogenerators, and biomedicine have been summarized, confirming their unlimited potential in future development. Finally, the existing challenges and future prospects of organohydrogels are provided.

Exploring the TEMPO-Oxidized Nanofibrillar Cellulose and Short Ionic-Complementary Peptide Composite Hydrogel as Biofunctional Cellular Scaffolds

Multicomponent self-assembly is an emerging approach in peptide nanotechnology to develop nanomaterials with superior physical and biological properties. Inspired by the multicomponent nature of the native extracellular matrix (ECM) and the well-established advantages of co-assembly in the field of nanotechnology, we have attempted to explore the noncovalent interactions among the sugar and peptide-based biomolecular building blocks as an approach to design and develop advanced tissue scaffolds. We utilized TEMPO-oxidized nanofibrillar cellulose (TO-NFC) and a short ionic complementary peptide, Nap-FEFK, to fabricate highly tunable supramolecular hydrogels. The differential doping of the peptide into the TO-NFC hydrogel was observed to tune the surface hydrophobicity, microporosity, and mechanical stiffness of the scaffold. Interestingly, a differential cellular response was observed toward composite scaffolds with a variable ratio of TO-NFC versus Nap-FEFK. Composite scaffolds having a 10:1 (w/w) ratio of TO-NFC and the Nap-FEFK peptide showed enhanced cellular survival and proliferation under two-dimensional cell culture conditions. More interestingly, the cellular proliferation on the 10:1 matrix was found to be similar to that of Matrigel in three-dimensional culture conditions, which clearly indicated the potential of these hydrogels in advanced tissue engineering applications. Additionally, these composite hydrogels did not elicit any significant inflammatory response in Raw cells and supported their survival and proliferation, which further emphasized their ability to form versatile scaffolds for tissue regeneration. This multicomponent assembly approach to construct biomolecular composite hydrogels to access superior physical and biological properties within the scaffold is expected to improve the scope for designing novel ECM-mimicking biomaterials for regenerative medicine.

Natural wood-derived free-standing films as efficient and stable separators for high-performance lithium ion batteries

A sustainable and low-cost separator is highly required for electrochemical energy storage systems. Herein, a type of modified natural wood film with excellent mechanical properties, ion conductivity and thermal stability is fabricated for high-performance lithium ion batteries. Using the modified natural wood film as a separator, the fabricated symmetric cell exhibits a more stable and lower plating/stripping voltage for Li than that of the cell with a commercialized polypropylene (PP) separator. The LiFePO₄/Li half-cell with the modified wood film separator shows a small polarization voltage and high discharge capacity because of the multi-level nanostructure and abundant functional groups of the modified wood films. The results suggest that the modified wood films are a promising candidate for use as separators in lithium ion batteries. As desired, the LiFePO₄/Li half-cells with the modified wood film separator deliver much higher discharge capacities and more stable Coulomb efficiency over two hundred charge/discharge cycles than the cell based on the PP separator. The present work systematically investigate the feasibility of abundant and cheap natural wood-derived materials for use as efficient separators instead of synthetic polymers for high-performance lithium ion batteries with long cycle life.

Increased ion transport and high-efficient osmotic energy conversion through aqueous stable graphitic carbon nitride/cellulose nanofiber composite membrane

Increased attention has evoked on the utilization of renewable energy, particularly osmotic power as a potential solution to the energy crisis and environmental pollution. Herein, we fabricate graphitic carbon nitride (g-C₃N₄)/cellulose nanofiber (CNF) composite membranes with tailored lamellar nanochannels for capturing osmotic energy from salinity gradients. Composite membranes exhibiting charge-governed ion conductivity were prepared via co-homogenization of g-C₃N₄ with CNF and vacuum filtration. Ion conductivity was efficiently modulated by fine-tuning the charge density through controlling the weight content of CNF in the composite membranes. Higher ion conductivity of 0.014 S cm^-1 at low concentrations (<10^-2 M KCl) was achieved due to the increased charge density of the lamellar nanochannels and the excellent aqueous stability of the membranes. We demonstrate the potential of the composite membranes in nanofluidic osmotic energy conversion, displaying thermo-enhanced power output performance. This work could inspire new designs of cellulose-based nanofluidic devices for improved osmotic energy conversion.

Highly Conductive and Mechanically Robust Cellulose Nanocomposite Hydrogels with Antifreezing and Antidehydration Performances for Flexible Humidity Sensors

Conductive hydrogels are emerging as an appealing material platform for flexible electronic devices owing to their attractive mechanical flexibility and conductive properties. However, the conventional water-based conductive hydrogels tend to inevitably freeze at subzero temperature and suffer from continuous water evaporation under ambient conditions, leading to a decrease in their electrical conductivities and mechanical properties. Thus, it is extremely necessary, but generally challenging, to create an antifreezing and antidehydration conductive gel for maintaining high and stable performances in terms of electrical conductivity and mechanical properties. Herein, we fabricated a cellulose nanofibril (CNF)-reinforced and highly ion-conductive organogel featuring excellent antifreezing and antidehydration performances by immersing it in the CaCl₂/sorbitol solution for solvent displacement. The incorporation of a rigid CNF serving as a dynamic connected bridge provided a hierarchical honeycomb-like cellular structure for the obtained CS-nanocomposite (NC) organogel networks, facilitating significant mechanical reinforcement. The synergy effects of sorbitol and CaCl₂ allowed high-performance integration with excellent antifreezing tolerance, antidehydration ability, and ionic conductivity. Strong hydrogen bonds were formed between water molecules and sorbitol molecules to impede the formation of ice crystals and water evaporation, thereby imparting the CS-NC organogels with extreme-temperature tolerance as low as -50 °C and pre-eminent antidehydration performance with over 90% weight retention. Furthermore, this CS-NC organogel exhibited high humidity sensitivity in a wide humidity detection range (23∼97% relative humidity) because of the ready formation of hydrogen bonds between water molecules and numerous hydrophilic groups in the binary solvent and elaborated polymer chains, which can be assembled as a stretchable humidity sensor to monitor human respiration with a fast response. This work provides a new prospect for fabricating intrinsically stretchable and high-performance humidity sensors using cellulose-based humidity-responsive materials for the emerging wearable applications.

Heat- and freeze-tolerant organohydrogel with enhanced ionic conductivity over a wide temperature range for highly mechanoresponsive smart paint

Binary solvent-based fabrication permits the conductive organohydrogel to function well at low-temperature environments. However, the deep cryogenic and high temperatures are still threatening the performance of conductive organohydrogels in the application of stretchable electronics, biosensors, and intelligent coatings. Here, a radically new method is developed to introduce propylene and carbonate cellulose nanofibrils into freeze tolerance polymer matrix, and fabricate an antifreezing/antiheating organohydrogel integrated a high mechanical strength (1.6 MPa) and high level of ionic conductivity (4.2 S cm^-1) over a wide temperature range (-40 to 100 °C). In this designed system, the propylene carbonate with low freezing point and high boiling point was shown to enhance antifreezing (-40 °C) and antiheating (100 °C) performance of organohydrogel. Furthermore, negative charge-rich cellulose nanofibrils (CNFs) were served as an ion transport channel and nanoreinforcements to boost the conductive and mechanical properties of the organohydrogel. In particular, Molecular Dynamics (MD) simulations reveal that propylene carbonate with high dielectric constant is capable of generating ion migration-facilitated effects, enabling the high ionic conductivity of organohydrogel. Tapping into these attributes, potential applications in mechanoresponsive smart coating have been demonstrated utilizing the appealing organohydrogel as a paint, rendering unprecedented protection and monitoring performance.

The effect of crosslinking on ion transport in nanocellulose-based membranes

Ion selective membranes are at the heart of energy conversion and harvesting, water treatment, and biotechnologies. The currently available membranes are mostly based on expensive and non-biodegradable polymers. Here, we report a cation-selective and low-cost membrane prepared from renewable nanocellulose and 1,2,3,4-butanetetracarboxylic acid which simultaneously serves as crosslinker and source of anionic surface groups. Charge density and structure of the membranes are studied. By using different degrees of crosslinking, simultaneous control over both the nanochannel structure and surface charge concentration is achieved, which in turn determines the resulting ion transport properties. Increasing negative charge concentration via higher crosslinker content, the obtained ion conductivity reaches up to 8 mS/cm (0.1 M KCl). Optimal ion selectivity, also influenced by the solution pH, is achieved at 20 wt% crosslinker addition (with ion conductivity of 1.6 mS/cm). As regular ~1.4 nm nanochannels were formed at this composition, nanofluidic contribution to ion transport is likely.

A Printed Flexible Humidity Sensor with High Sensitivity and Fast Response Using a Cellulose Nanofiber/Carbon Black Composite

In the emerging Internet of Things (IoT) society, there is a significant need for low-cost, high-performance flexible humidity sensors in wearable devices. However, commercially available humidity sensors lack flexibility or require expensive and complex fabrication methods, limiting their application and widespread use. We report a high-performance printed flexible humidity sensor using a cellulose nanofiber/carbon black (CNF/CB) composite. The cellulose nanofiber enables excellent dispersion of carbon black, which facilitates the ink preparation and printing process. At the same time, its hydrophilic and porous nature provides high sensitivity and fast response to humidity. Significant resistance changes of 120% were observed in the sensor at humidity ranging from 30% RH to 90% RH, with a fast response time of 10 s and a recovery time of 6 s. Furthermore, the developed sensor also exhibited high-performance uniformity, response stability, and flexibility. A simple humidity detection device was fabricated and successfully applied to monitor human respiration and noncontact fingertip moisture as a proof-of-concept.

Polydimethylsiloxane-decorated magnetic cellulose nanofiber composite for highly efficient oil-water separation

Developing three-dimensional porous hydrophobic and oleophilic materials (3D-PHOMs) for efficient and selective oil-water separation is important to clean up oil spills and organic pollutants. However, 3D-PHOMs are still confined to lab-scale research due to several crucial drawbacks. Herein, a hydrophobic oil-water separation composite, containing cellulose nanofiber (delignificated porous wood, PW) substrate, magnetic nickel (Ni) layer and hydrophobic polydimethylsiloxane (PDMS) coating, is prepared using electroless deposition (ELD) and surface modification techniques. Owing to the porosity, hydrophobicity (>130° of water contact angle), lipophilicity, convenient magnetic collection and high cycle compressibility, the as-fabricated PDMS-Ni-PW exhibits excellent oil adsorption capacity (>60% of the volumetric absorption capacity) and outstanding cyclic stability (>80% of the adsorption capacity after 200 cycles). Thanks to the low surface energy and rough surface structure, the adsorbent demonstrates superior oil-retention ability (>80% at 200 rpm). Also, the oil-collecting apparatus is successfully designed to continuously separate various oils, e.g., n-hexane and dichloromethane, from water due to the unidirectional liquid transport of the adsorbent. These excellent properties make PDMS-modified cellulose nanofiber a promising candidate for oil-water separation.

Nanocellulose-enhanced organohydrogel with high-strength, conductivity, and anti-freezing properties for wearable strain sensors

The use of ion-conductive hydrogels in strain sensors with high mechanical properties, conductivity, and anti-freezing properties is challenging. Here, high-strength, transparent, conductive, and anti-freezing organohydrogels were fabricated through the radical polymerization of polyacrylamide (PAM)/sodium alginate (SA)/TEMPO-oxidized cellulose nanofibrils (TOCNs) in a dimethyl sulfoxide (DMSO)/water solution, followed by soaking in a CaCl₂ solution. The resulting organohydrogels demonstrated a high strength (tensile strength of 1.04 MPa), stretchability (681%), transparency (>84% transmittance), and ionic conductivity (1.25 S m^-1). The organohydrogel-based strain sensor showed a high strain sensitivity (GF = 2.1). In addition, due to a synergistic effect between the DMSO/H₂O binary solvent and CaCl₂, the organohydrogel remained flexible (could bend 180°) and conductive (1.01 S m^-1) at -20 °C. Interestingly, the TOCNs exerted a reinforcing effect on both the mechanical properties and ionic conductivity. This research provides a novel strategy to prepare ion-conductive organohydrogels with good mechanical properties, conductivity, and anti-freezing properties for use as flexible electronic materials.