Machine intelligence-accelerated discovery of all-natural plastic substitutes.

One possible solution against the accumulation of petrochemical plastics in natural environments is to develop biodegradable plastic substitutes using natural components. However, discovering all-natural alternatives that meet specific properties, such as optical transparency, fire retardancy and mechanical resilience, which have made petrochemical plastics successful, remains challenging. Current approaches still rely on iterative optimization experiments. Here we show an integrated workflow that combines robotics and machine learning to accelerate the discovery of all-natural plastic substitutes with programmable optical, thermal and mechanical properties. First, an automated pipetting robot is commanded to prepare 286 nanocomposite films with various properties to train a support-vector machine classifier. Next, through 14 active learning loops with data augmentation, 135 all-natural nanocomposites are fabricated stagewise, establishing an artificial neural network prediction model. We demonstrate that the prediction model can conduct a two-way design task: (1) predicting the physicochemical properties of an all-natural nanocomposite from its composition and (2) automating the inverse design of biodegradable plastic substitutes that fulfils various user-specific requirements. By harnessing the model's prediction capabilities, we prepare several all-natural substitutes, that could replace non-biodegradable counterparts as exhibiting analogous properties. Our methodology integrates robot-assisted experiments, machine intelligence and simulation tools to accelerate the discovery and design of eco-friendly plastic substitutes starting from building blocks taken from the generally-recognized-as-safe database.

Advances in green materials derived from wood for detecting and removing mercury ions in water.

The issue of mercury pollution in environmental remediation has garnered significant attention due to its severe health hazards to humans. Various strategies have been devised to mitigate the impact of toxic mercury ions, including coagulation, ion exchange, adsorption, membrane technology, and electrochemical treatment. Among these approaches, adsorption has emerged as an efficient and widely employed method for the uptake of low concentrations of mercury ions. It offers convenient operation, high removal efficiency, and facile regeneration of the adsorbent. Wood, being the most abundant renewable and sustainable bioresource, has garnered attention as a promising material for treating heavy metal wastewater. This is attributed to its unique physical and chemical characteristics, encompassing hierarchical pores, aligned channels, active functional groups, biodegradability, and cost-effectiveness. However, a comprehensive examination of the cutting-edge applications of wood and wood-derived biopolymers in the detection and removal of mercury ions from wastewater has yet to be undertaken. Consequently, this article presents a chronological overview of recent advancements in materials and structures derived from bulk wood and its constituents, including cellulose, lignin, hemicellulose, and tannin, with a specific focus on their utility in detecting and eliminating mercury from water sources. Subsequently, the most promising techniques and strategies involving wood and wood-derived biopolymers in addressing the predicament of mercury pollution are explored. Furthermore, this piece offers insights into the existing challenges and future prospects concerning environmentally friendly materials derived from wood, aiming to foster the development of cost-effective mercury adsorbents and detection devices.

A cellulose-derived supramolecule for fast ion transport.

Supramolecular frameworks have been widely synthesized for ion transport applications. However, conventional approaches of constructing ion transport pathways in supramolecular frameworks typically require complex processes and display poor scalability, high cost, and limited sustainability. Here, we report the scalable and cost-effective synthesis of an ion-conducting (e.g., Na+) cellulose-derived supramolecule (Na-CS) that features a three-dimensional, hierarchical, and crystalline structure composed of massively aligned, one-dimensional, and ångström-scale open channels. Using wood-based Na-CS as a model material, we achieve high ionic conductivities (e.g., 0.23 S/cm in 20 wt% NaOH at 25 °C) even with a highly dense microstructure, in stark contrast to conventional membranes that typically rely on large pores (e.g., submicrometers to a few micrometers) to obtain comparable ionic conductivities. This synthesis approach can be universally applied to a variety of cellulose materials beyond wood, including cotton textiles, fibers, paper, and ink, which suggests excellent potential for a number of applications such as ion-conductive membranes, ionic cables, and ionotronic devices.

Conductive Hydrogels Based on Industrial Lignin: Opportunities and Challenges.

The development of green materials, especially the preparation of high-performance conductive hydrogels from biodegradable biomass materials, is of great importance and has received worldwide attention. As an aromatic polymer found in many natural biomass resources, lignin has the advantage of being renewable, biodegradable, non-toxic, widely available, and inexpensive. The unique physicochemical properties of lignin, such as the presence of hydroxyl, carboxyl, and sulfonate groups, make it promising for use in composite conductive hydrogels. In this review, the source, structure, and reaction characteristics of industrial lignin are provided. Description of the preparation method (physical and chemical strategies) of lignin-based conductive hydrogel is elaborated along with their several important properties, such as electrical conductivity, mechanical properties, and porous structure. Furthermore, we provide insights into the latest research advances in industrial lignin conductive hydrogels, including biosensors, strain sensors, flexible energy storage devices, and other emerging applications. Finally, the prospects and challenges for the development of lignin-conductive hydrogels are presented.

Fabrication of Cellulose-Graphite Foam via Ion Cross-linking and Ambient-Drying.

Conventional plastic foams are usually produced by fossil-fuel-derived polymers, which are difficult to degrade in nature. As an alternative, cellulose is a promising biodegradable polymer that can be used to fabricate greener foams, yet such a process typically relies on methods (e.g., freeze-drying and supercritical-drying) that are hardly scalable and time-consuming. Here, we develop a fast and scalable approach to prepare cellulose-graphite foams via rapidly cross-linking the cellulose fibrils in metal ions-containing solution followed by ambient drying. The prepared foams exhibit low density, high compressive strength, and excellent water stability. Moreover, the cross-linking of the cellulose fibrils can be triggered by various metal ions, indicating good universality. We further use density functional theory to reveal the cross-linking effect of different ions, which shows good agreement with our experimental observation. Our approach presents a sustainable route toward low-cost, environmentally friendly, and scalable foam production for a range of applications.

Highly Flexible and Broad-Range Mechanically Tunable All-Wood Hydrogels with Nanoscale Channels via the Hofmeister Effect for Human Motion Monitoring.

Wood-based hydrogel with a unique anisotropic structure is an attractive soft material, but the presence of rigid crystalline cellulose in natural wood makes the hydrogel less flexible. In this study, an all-wood hydrogel was constructed by cross-linking cellulose fibers, polyvinyl alcohol (PVA) chains, and lignin molecules through the Hofmeister effect. The all-wood hydrogel shows a high tensile strength of 36.5 MPa and a strain up to ~ 438% in the longitudinal direction, which is much higher than its tensile strength (~ 2.6 MPa) and strain (~ 198%) in the radial direction, respectively. The high mechanical strength of all-wood hydrogels is mainly attributed to the strong hydrogen bonding, physical entanglement, and van der Waals forces between lignin molecules, cellulose nanofibers, and PVA chains. Thanks to its excellent flexibility, good conductivity, and sensitivity, the all-wood hydrogel can accurately distinguish diverse macroscale or subtle human movements, including finger flexion, pulse, and swallowing behavior. In particular, when "An Qi" was called four times within 15 s, two variations of the pronunciation could be identified. With recyclable, biodegradable, and adjustable mechanical properties, the all-wood hydrogel is a multifunctional soft material with promising applications, such as human motion monitoring, tissue engineering, and robotics materials.

Rapid Pressureless Sintering of Glasses.

Silica glasses have wide applications in industrial fields due to their extraordinary properties, such as high transparency, low thermal expansion coefficient, and high hardness. However, current methods of fabricating silica glass generally require long thermal treatment time (up to hours) and complex setups, leading to high cost and slow manufacturing speed. Herein, to obtain high-quality glasses using a facile and rapid method, an ultrafast high-temperature sintering (UHS) technique is reported that requires no additional pressure. Using UHS, silica precursors can be densified in seconds due to the large heating rate (up to 102 K s-1 ) of closely placed carbon heaters. The typical sintering time is as short as ≈10 s, ≈1-3 orders of magnitude faster than other methods. The sintered glasses exhibit relative densities of > 98% and high visible transmittances of ≈90%. The powder-based sintering process also allows rapid doping of metal ions to fabricate colored glasses. The UHS is further extended to sinter other functional glasses such as indium tin oxide (ITO)-doped silica glass, and other transparent ceramics such as Gd-doped yttrium aluminum garnet. This study demonstrates an UHS proof-of-concept for the rapid fabrication of high-quality glass and opens an avenue toward rapid discovery of transparent materials.

Anisotropic, strong, self-adhesive and strain-sensitive hydrogels enabled by magnetically-oriented cellulose/polydopamine nanocomposites.

Recently, great efforts have been devoted to developing conductive adhesive hydrogels to meet the needs of various applications. However, grand challenges remain in achieving anisotropic hydrogels simultaneously featuring multiple properties using natural polymers and renewable resources. Here, a cellulose-based conductive hydrogel with strong, ultrastretchable, and adhesive properties is prepared via a simple magnetic field-induced strategy. This strategy involves the formation of a suspension mixture with well-oriented cellulose-polydopamine nanocomposites under magnetic fields, followed by rapid orientation via covalent crosslinking. The tensile strength of the oriented hydrogel in longitudinal direction is ~0.22 MPa, which is ~1.4 times higher than that in radial direction. Moreover, the hydrogel shows good cyclic loading-unloading ability, high conductivity (6.9 ± 0.6 S m-1), and strong adhesion (71 kPa). The hydrogel also shows significant anisotropic properties and made it a versatile platform for wearable sensors to monitor large and subtle human motion in the foreseeable future.

3D-Printed, High-Porosity, High-Strength Graphite Aerogel.

The global demand for plastic foam materials is enormous (annual worth of ≈$341.3 billion) and still surging with an annual growth rate of 4.8%, driven by increasing modern societal needs. The majority of existing foam materials are made of plastics, which take hundreds of years to degrade, leading to severe global pollution issues. Here, a degradable, recyclable, and cost-effective solution to foam materials based on 3D graphite-cellulose nanofibers (G-CNF) foam fabricated from resource-abundant graphite and cellulose via advanced 3D printing is reported. The CNFs can directly disperse the graphite under physical sonication without the need for any chemical reactions. The interaction of the CNFs with graphite through the function of hydrophilic and hydrophobic faces in CNFs renders the dispersion polymer-like rheological properties and good processability with tunable viscosity for 3D printing. A robust, degradable, and recyclable G-CNF foam with designed shapes can be printed in a large scale, demonstrating higher mechanical strength (3.72 MPa versus 0.28 MPa in tensile strength and 2.34 MPa versus 1.11 MPa in compressive stiffness), better fire resistance, degradability, and recyclability than commercial polystyrene foam material. The demonstrated G-CNF foam can potentially replace the commercial plastic foam materials, representing a sustainable solution toward white pollution.

Copper-coordinated cellulose ion conductors for solid-state batteries.

Although solid-state lithium (Li)-metal batteries promise both high energy density and safety, existing solid ion conductors fail to satisfy the rigorous requirements of battery operations. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact with electrodes. Conversely, polymer ion conductors that are Li-metal-stable usually provide better interfacial compatibility and mechanical tolerance, but typically suffer from inferior ionic conductivity owing to the coupling of the ion transport with the motion of the polymer chains1-3. Here we report a general strategy for achieving high-performance solid polymer ion conductors by engineering of molecular channels. Through the coordination of copper ions (Cu2+) with one-dimensional cellulose nanofibrils, we show that the opening of molecular channels within the normally ion-insulating cellulose enables rapid transport of Li+ ions along the polymer chains. In addition to high Li+ conductivity (1.5 × 10-3 siemens per centimetre at room temperature along the molecular chain direction), the Cu2+-coordinated cellulose ion conductor also exhibits a high transference number (0.78, compared with 0.2-0.5 in other polymers2) and a wide window of electrochemical stability (0-4.5 volts) that can accommodate both the Li-metal anode and high-voltage cathodes. This one-dimensional ion conductor also allows ion percolation in thick LiFePO4 solid-state cathodes for application in batteries with a high energy density. Furthermore, we have verified the universality of this molecular-channel engineering approach with other polymers and cations, achieving similarly high conductivities, with implications that could go beyond safe, high-performance solid-state batteries.

Scalable Wood Hydrogel Membrane with Nanoscale Channels.

Many efforts have been dedicated to exploring nanofluidic systems for various applications including water purification and energy generation. However, creating robust nanofluidic materials with tunable channel orientations and numerous nanochannels or nanopores on a large scale remains challenging. Here, we demonstrate a scalable and cost-effective method to fabricate a robust and highly conductive nanofluidic wood hydrogel membrane in which ions can transport across the membrane. The ionically conductive balsa wood hydrogel membrane is fabricated by infiltrating poly(vinyl alcohol) (PVA)/acrylic acid (AA) hydrogel into the inherent bimodal porous wood structure. The balsa wood hydrogel membrane demonstrates a 3 times higher strength (52.7 MPa) and 2 orders of magnitude higher ionic conductivity compared to those of natural balsa both in the radial direction (coded as R direction) and along the longitudinal direction (coded as L direction). The ionic conductivity of the balsa wood hydrogel membrane is 1.29 mS cm-1 along the L direction and nearly 1 mS cm-1 along the R direction at low salt concentrations (up to 10 mM). In addition, the surface-charge-governed ion transport also renders the balsa wood hydrogel membrane able to harvest electrical energy from salinity gradients. A current density of up to 17.65 µA m-2 and an output power density of 0.56 mW m-2 are obtained under a 1000-fold salt concentration gradient, which can be further improved to 2.7 mW m-2 by increasing the AA content from 25 wt % to 50 wt %. These findings make contributions to develop energy-harvesting systems and other nanofluidic devices from sustainable wood materials.

High-Temperature Ultrafast Sintering: Exploiting a New Kinetic Region to Fabricate Porous Solid-State Electrolyte Scaffolds.

Solid-state batteries (SSBs) promise better safety and potentially higher energy density than the conventional liquid- or gel-based ones. In practice, the implementation of SSBs often necessitates 3D porous scaffolds made by ceramic solid-state electrolytes (SSEs). Herein, a general and facile method to sinter 3D porous scaffolds with a range of ceramic SSEs on various substrates at high temperature in seconds is reported. The high temperature enables rapid reactive sintering toward the desired crystalline phase and expedites the surface diffusion of grains for neck growth; meanwhile, the short sintering duration limits the coarsening, thus accurately controlling the degree of densification to preserve desired porous structures, as well as reducing the loss of volatile elements. As a proof-of-concept, a composite SSE with a good ionic conductivity (i.e., ≈1.9 × 10-4 S cm-1 at room temperature) is demonstrated by integrating poly(ethylene oxide) with the 3D porous Li6.5 La3 Zr1.5 Ta0.5 O12 scaffold sintered by this method. This method opens a new door toward sintering a variety of ceramic-SSE-based 3D scaffolds for all-solid-state battery applications.

Solar-assisted fabrication of large-scale, patternable transparent wood.

Transparent wood is considered a promising structural and light management material for energy-efficient engineering applications. However, the solution-based delignification process that is used to fabricate transparent wood generally consumes large amounts of chemicals and energy. Here, we report a method to produce optically transparent wood by modifying the wood's lignin structure using a solar-assisted chemical brushing approach. This method preserves most of the lignin to act as a binder, providing a robust wood scaffold for polymer infiltration while greatly reducing the chemical and energy consumption as well as processing time. The obtained transparent wood (~1 mm in thickness) demonstrates a high transmittance (>90%), high haze (>60%), and excellent light-guiding effect over visible wavelength. Furthermore, we can achieve diverse patterns directly on wood surfaces using this approach, which endows transparent wood with excellent patternability. Combining its efficient, patternable, and scalable production, this transparent wood is a promising candidate for applications in energy-efficient buildings.

In Situ Lignin Modification toward Photonic Wood.

Lignin serves as a binder that forms strong matrices of the cell walls of wood. However, it has many photolabile chromophore groups that create a monotonic brownish color and make wood susceptible to photodegradation. Herein, a new strategy is reported for modifying lignin using an in situ, rapid, and scalable process that involves the photocatalytic oxidation of native lignin in wood by H2 O2 and UV light. The reaction selectively eliminates lignin's chromophores while leaving the aromatic skeleton intact, thus modulating the optical properties of wood. The resulting "photonic wood" retains ≈80% of its original lignin content, which continues to serve as a strong binder and water-proofing agent. As a result, photonic wood features a much higher mechanical strength in a wet environment (20-times higher tensile strength and 12-times greater compression resistance), significant scalability (≈2 m long sample), and largely reduced processing times (1-6.5 h vs 4-14 h) compared with delignification methods. Additionally, this in situ lignin-modified wood structure is easily patterned through a photocatalytic oxidation process. This photocatalytic production of photonic wood paves the way for the large-scale manufacturing of sustainable biosourced functional materials for a range of applications, including energy-efficient buildings, optical management, and fluidic, ionic, electronic, and optical devices.

Advanced Nanowood Materials for the Water-Energy Nexus.

Wood materials are being reinvented to carry superior properties for a variety of new applications. Cutting-edge nanomanufacturing transforms traditional bulky and low-value woods into advanced materials that have desired structures, durability, and functions to replace nonrenewable plastics, polymers, and metals. Here, a first prospect report on how novel nanowood materials have been developed and applied in water and associated industries is provided, wherein their unique features and promises are discussed. First, the unique hierarchical structure and associated properties of the material are introduced, and then how such features can be harnessed and modified by either bottom-up or top-down manufacturing to enable different functions for water filtration, chemical adsorption and catalysis, energy and resource recovery, as well as energy-efficient desalination and environmental cleanup are discussed. The study recognizes that this is a nascent but very promising field; therefore, insights are offered to encourage more research and development. Trees harness solar energy and CO2 and provide abundant carbon-negative materials. Once harvested and utilized, it is believed that advanced wood materials will play a vital role in enabling a circular water economy.

Residual lignin in cellulose nanofibrils enhances the interfacial stabilization of Pickering emulsions.

Lignocellulose nanofibrils (LCNF) were used to prepare oil-in-water Pickering emulsions and to assess the role residual lignin in interfacial stabilization. Two LCNF fractions of similar morphology (length ∼700 nm and width ∼8 nm) and structure (polymorphism and crystallinity) were obtained by microfluidization of fibers obtained by hydrothermal treatment of wood with a recyclable organic acid. The LCNF with higher residual lignin was less hydrophilic and, correspondingly, performed better as Pickering stabilizer, producing emulsions of smaller droplet size and higher resistance to creaming. Long-term emulsion stabilization (over 40 days) was achieved with LCNF at concentrations as low as 0.24 (w/v)% based on emulsion volume. We conclude that LCNF-stabilized Pickering emulsions can be finely tuned by varying the residual lignin content, providing a rationale for LCNF selection according to lignin type and concentration as variables affecting stabilization. Complementary considerations include the possible benefits of the residual lignin in LCNF, including antioxidant and UV absorption properties.

Scalable aesthetic transparent wood for energy efficient buildings.

Nowadays, energy-saving building materials are important for reducing indoor energy consumption by enabling better thermal insulation, promoting effective sunlight harvesting and offering comfortable indoor lighting. Here, we demonstrate a novel scalable aesthetic transparent wood (called aesthetic wood hereafter) with combined aesthetic features (e.g. intact wood patterns), excellent optical properties (an average transmittance of ~ 80% and a haze of ~ 93%), good UV-blocking ability, and low thermal conductivity (0.24 W m-1K-1) based on a process of spatially selective delignification and epoxy infiltration. Moreover, the rapid fabrication process and mechanical robustness (a high longitudinal tensile strength of 91.95 MPa and toughness of 2.73 MJ m-3) of the aesthetic wood facilitate good scale-up capability (320 mm × 170 mm × 0.6 mm) while saving large amounts of time and energy. The aesthetic wood holds great potential in energy-efficient building applications, such as glass ceilings, rooftops, transparent decorations, and indoor panels.

Single-digit-micrometer thickness wood speaker.

Thin films of several microns in thickness are ubiquitously used in packaging, electronics, and acoustic sensors. Here we demonstrate that natural wood can be directly converted into an ultrathin film with a record-small thickness of less than 10 µm through partial delignification followed by densification. Benefiting from this aligned and laminated structure, the ultrathin wood film exhibits excellent mechanical properties with a high tensile strength of 342 MPa and a Young's modulus of 43.6 GPa, respectively. The material's ultrathin thickness and exceptional mechanical strength enable excellent acoustic properties with a 1.83-times higher resonance frequency and a 1.25-times greater displacement amplitude than a commercial polypropylene diaphragm found in an audio speaker. As a proof-of-concept, we directly use the ultrathin wood film as a diaphragm in a real speaker that can output music. The ultrathin wood film with excellent mechanical property and acoustic performance is a promising candidate for next-generation acoustic speakers.

Antibacterial Performance of a Mussel-Inspired Polydopamine-Treated Ag/Graphene Nanocomposite Material.

Graphene-based nanocomposites have attracted tremendous attention in recent years. In this study, a facile yet effective approach was developed to synthesize reduced graphene oxide and an Ag-graphene nanocomposite. The basic strategy involved in the preparation of reduced graphene oxide includes reducing graphene oxide with dopamine, followed by in situ syntheses of the Ag-PDA-reducing graphene oxide (RGO) nanocomposite through adding AgNO3 solution and a small amount of dopamine. The nanocomposite was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), FTIR spectra, Raman spectra, ultraviolet-visible (UV-vis), and X-ray photoelectron spectroscopy (XPS), results indicated that a uniform PDA film is formed on the surface of the GO and GO is successfully reduced. Besides, the in situ synthesized Ag nanoparticles (AgNPs) were evenly distributed on the RGO surface. To investigate antibacterial properties Ag-PDA-RGO, different dosages were selected for evaluating the antibacterial activity against Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli. The Ag-PDA-RGO nanocomposites displayed excellent antibacterial property. The antibacterial ratio reached 99.9% against S. aureus and 90.9% against E. coli when the dosage of 100 mg/L Ag-PDA-RGO nanocomposites was 100 µL. The novel Ag-PDA-RGO nanocomposite prepared by a facile yet effective, environmentally friendly, and low-cost method holds great promise in a wide range of modern biomedical applications.