Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating.

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37 dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14 µm and thermal conductivity (0.19 W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

Cuproptosis-immunotherapy using PD-1 overexpressing T cell membrane-coated nanosheets efficiently treats tumor.

The cuproptosis cell death pathway brings fresh opportunities for tumor therapy. However, efficient and targeted cuproptosis induction in tumors is still a challenge. Unfortunately, the well-known cuproptosis initiator, disulfiram and copper complex (DSF/Cu2+), also increases PD-L1 level in tumors, which may diminish the final therapeutic outcome. In this study, DSF/Cu2+-loading MXene nanosheets are coated with PD-1 overexpressing T cell membrane to generate CuX-P system. CuX-P could recognize and stick to PD-L1 on tumor cells like a patch, which promotes the endocytosis of both CuX-P and PD-L1 by tumor cells. Following internalization and release of DSF/Cu2+ in the cytoplasm, PD-L1 expression is upregulated. However, due to the presence of CuX-P in the tumor microenvironment, the then supplemented PD-L1 on tumor surface again binds CuX-P for internalization. This feedback loop keeps blocking and consuming the PD-L1 on tumor surface and promotes the enrichment of CuX-P in tumors to induce cuproptosis. After CuX-P treatment with laser irradiation, strong anti-tumor immune responses are stimulated in a mouse model with triple-negative breast cancer. Thus, this study develops a tumor-targeted biomimetic system that offers simultaneous cuproptosis killing, photothermal therapy (PTT) and immunotherapy in mice.

Sustainable Starch/Lignin Nanoparticle Composites Biofilms for Food Packaging Applications.

Construction of sustainable composite biofilms from natural biopolymers are greatly promising for advanced packaging applications due to their biodegradable, biocompatible, and renewable properties. In this work, sustainable advanced food packaging films are developed by incorporating lignin nanoparticles (LNPs) as green nanofillers to starch films. This seamless combination of bio-nanofiller with biopolymer matrix is enabled by the uniform size of nanofillers and the strong interfacial hydrogen bonding. As a result, the as-prepared biocomposites exhibit enhanced mechanical properties, thermal stability, and antioxidant activity. Moreover, they also present outstanding ultraviolet (UV) irradiation shielding performance. As a proof of concept in the application of food packaging, we evaluate the effect of composite films on delaying oxidative deterioration of soybean oil. The results indicate our composite film could significantly decrease peroxide value (POV), saponification value (SV), and acid value (AV) to delay oxidation of soybean oil during storage. Overall, this work provides a simple and effective method for the preparation of starch-based films with enhanced antioxidant and barrier properties for advanced food packaging applications.

Acidic deep eutectic solvent assisted mechanochemical delignification of lignocellulosic biomass at room temperature.

Lignocellulosic biomass is the most abundant natural polymer on Earth, but the efficient fractionation and refinery of all its components remain challenging. Acidic deep eutectic solvents refining is a promising method, while it is likely to cause lignin condensation and carbohydrates degradation, especially at server operation conditions. Here we propose the use of acidic deep eutectic solvent (DES), choline chloride/p-toluenesulfonic acid assisted mechanochemical pretreatment (DM) for efficient lignocellulose fractionation at mild condition. Four representative lignocellulose, wheat straw, moso bamboo, poplar wood and pine wood were selected at varied milling time (3, 6 h) to assess the fractionation ability of this strategy. This DM pretreatment demonstrated a rather high cellulose retentions (∼90 %) and extent of delignification for wheat straw and bamboo biomass, which corresponds to a high extent of enzymatic hydrolysis (∼75.5 %) for sugar platform pursuing. The extracted lignin showed rather high content of ß-O-4' leakages due to the swelling effect of deep eutectic solvent and mild operation conditions. This work provided a promising strategy to fractionate lignocellulose using deep eutectic solvents with the goal of simultaneous cellulose hydrolysis and reactive lignin obtaining that is usually difficult to realize using traditional chemical fractionation approach.

Rheology-Guided Assembly of a Highly Aligned MXene/Cellulose Nanofiber Composite Film for High-Performance Electromagnetic Interference Shielding and Infrared Stealth.

Delicately aligned structures of two-dimensional (2D) MXene nanosheets have demonstrated positive effects on applications, especially in electromagnetic interference (EMI) shielding and infrared (IR) stealth. However, precise regulation of structural assembly by theory-guided solution processing is still a great challenge. Herein, one-dimensional (1D) cellulose nanofibers (CNFs) with a high aspect ratio are applied as a reinforcing agent and a rheological modifier for MXene/CNF colloids to fabricate aligned MXene-based materials for EMI shielding and IR stealth. Notably, a systematical rheological study of the MXene/CNF colloids is proposed to determine the optimal solution-processing conditions for finely oriented component arrangement requirements and provides in-depth information on the interactions between the components. The delicately regulated orientation structure assembled by shear inducement is convincingly demonstrated through micro-CT and wide-angle X-ray diffraction/small-angle X-ray scattering (WAXD/SAXS), which endows the MXene/CNF film with a significantly enhanced electrical conductivity of 46 685 S m-1, a tensile strength of 281.7 MPa, and Young's modulus of 14.8 GPa. Furthermore, the highly aligned structure of the ultrathin film possesses a great enhancement in EMI shielding effectiveness (50.2 dB) and IR stealth (0.562 emissivity). These findings provide a fruitful understanding of the optimized fabrication in solution processing of high-performance MXene-based functional composite films and open up a great opportunity for the development of multifunctional stealth materials.

Facile Fabrication of Densely Packed Ti3C2 MXene/Nanocellulose Composite Films for Enhancing Electromagnetic Interference Shielding and Electro-/Photothermal Performance.

The development of modern electronics has raised great demand for multifunctional materials to protect electronic instruments against electromagnetic interference (EMI) radiation and ice accretion in cold weather. However, it is still a great challenge to prepare high-performance multifunctional films with excellent flexibilty, mechanical strength, and durability. Here, we propose a layer-by-layer assembly of cellulose nanofiber (CNF)/Ti3C2Tx nanocomposites (TM) on a bacterial cellulose (BC) substrate via repeated spray coating. CNFs are hybridized with Ti3C2Tx nanoflakes to improve the mechanical properties of the functional coating layer and its adhesion with the BC substrate. The densely packed hierarchical structure and strong interfacial interactions endows the TM/BC films with good flexibility, ultrahigh mechanical strength (>250 MPa), and desirable toughness (>20 MJ cm-3). Furthermore, benefiting from the densely packed hierarchical structure, the resultant TM/BC films present outstanding EMI shielding effictiveness of 60 dB and efficient electro-/photothermal heating performance. Silicone encapsulation further imparts high hydrophobicity and exceptional durability against solutions and deformations to the multifunctional films. Impressively, the silicone-coated TM/BC film (Si-TM/BC) exhibits desirable low voltage-driven Joule heating and excellent photoresponsive heating performance, which demonstrates great feasibility for efficient thermal deicing under actual conditions. Therefore, we believe that the Si-TM/BC film with excellent mechanical properties and durability holds great promise for the practical applications of EMI shielding and ice accretion elimination.

Ultrarobust Ti3C2Tx MXene-Based Soft Actuators via Bamboo-Inspired Mesoscale Assembly of Hybrid Nanostructures.

Soft actuation materials are highly desirable in flexible electronics, soft robotics, etc. However, traditional bilayered actuators usually suffer from poor mechanical properties as well as deteriorated performance reliability. Here, inspired by the delicate architecture of natural bamboo, we present a hierarchical gradient structured soft actuator via mesoscale assembly of micro-nano-scaled two-dimentional MXenes and one-dimentional cellulose nanofibers with molecular-scaled strong hydrogen bonding. The resultant actuator integrates high tensile strength (237.1 MPa), high Young's modulus (8.5 GPa), superior toughness (10.9 MJ/m3), and direct and fast hygroscopic actuation within a single body, which is difficult to achieve by traditional bilayered actuators. The proof-of-concept prototype robot is demonstrated to emphasize its high mechanical robustness even after bending 100 000 times, kneading, or being trampled by an adult (7 500 000 times heavier than a crawling robot). This bioinspired mesoscale assembly strategy provides an approach for soft materials to the application of next-generation robust robotics.

Protein-Inspired Self-Healable Ti3C2 MXenes/Rubber-Based Supramolecular Elastomer for Intelligent Sensing.

Progress toward the integration of electronic sensors with a signal processing system is important for artificial intelligent and smart robotics. It demands mechanically robust, highly sensitive, and self-healable sensing materials which could generate discernible electric variations responding to external stimuli. Here, inspired by the supramolecular interactions of amino acid residues in proteins, we report a self-healable nanostructured Ti3C2MXenes/rubber-based supramolecular elastomer (NMSE) for intelligent sensing. MXene nanoflakes modified with serine through an esterification reaction assemble with an elastomer matrix, constructing delicate dynamic supramolecular hydrogen bonding interfaces. NMSE features desirable recovered toughness (12.34 MJ/m3) and excellent self-healing performance (∼100%) at room temperature. The NMSE-based sensor with high gauge factor (107.43), low strain detection limit (0.1%), and fast responding time (50 ms) can precisely detect subtle human motions (including speech, facial expression, pulse, and heartbeat) and moisture variations even after cut/healing processes. Moreover, NMSE-based sensors integrated with a complete signal process system show great feasibility for speech-controlled motions, which demonstrates promising potential in future wearable electronics and soft intelligent robotics.

Arbitrarily 3D Configurable Hygroscopic Robots with a Covalent-Noncovalent Interpenetrating Network and Self-Healing Ability.

Soft materials that can reversibly transform shape in response to moisture have applications in diverse areas such as soft robotics and biomedicine. However, the design of a structurally transformable or mechanically self-healing version of such a humidity-responsive material, which can arbitrarily change shape and reconfigure its 3D structures remains challenging. Here, by drawing inspiration from a covalent-noncovalent network, an elaborately designed biopolyester is developed that features a simple hygroscopic actuation mechanism, straightforward manufacturability at low ambient temperature (≤35 °C), fast and stable response, robust mechanical properties, and excellent self-healing ability. Diverse functions derived from various 3D shapes that can grasp, swing, close-open, lift, or transport an object are further demonstrated. This strategy of easy-to-process 3D structured self-healing actuators is expected to combine with other actuation mechanisms to extend new possibilities in diverse practical applications.

Thickness-independent capacitance of vertically aligned liquid-crystalline MXenes.

The scalable and sustainable manufacture of thick electrode films with high energy and power densities is critical for the large-scale storage of electrochemical energy for application in transportation and stationary electric grids. Two-dimensional nanomaterials have become the predominant choice of electrode material in the pursuit of high energy and power densities owing to their large surface-area-to-volume ratios and lack of solid-state diffusion1,2. However, traditional electrode fabrication methods often lead to restacking of two-dimensional nanomaterials, which limits ion transport in thick films and results in systems in which the electrochemical performance is highly dependent on the thickness of the film1-4. Strategies for facilitating ion transport-such as increasing the interlayer spacing by intercalation5-8 or introducing film porosity by designing nanoarchitectures9,10-result in materials with low volumetric energy storage as well as complex and lengthy ion transport paths that impede performance at high charge-discharge rates. Vertical alignment of two-dimensional flakes enables directional ion transport that can lead to thickness-independent electrochemical performances in thick films11-13. However, so far only limited success11,12 has been reported, and the mitigation of performance losses remains a major challenge when working with films of two-dimensional nanomaterials with thicknesses that are near to or exceed the industrial standard of 100 micrometres. Here we demonstrate electrochemical energy storage that is independent of film thickness for vertically aligned two-dimensional titanium carbide (Ti3C2T x ), a material from the MXene family (two-dimensional carbides and nitrides of transition metals (M), where X stands for carbon or nitrogen). The vertical alignment was achieved by mechanical shearing of a discotic lamellar liquid-crystal phase of Ti3C2T x . The resulting electrode films show excellent performance that is nearly independent of film thickness up to 200 micrometres, which makes them highly attractive for energy storage applications. Furthermore, the self-assembly approach presented here is scalable and can be extended to other systems that involve directional transport, such as catalysis and filtration.

Layer-by-layer assembly of MXene and carbon nanotubes on electrospun polymer films for flexible energy storage.

Free-standing, highly flexible and foldable supercapacitor electrodes were fabricated through the spray-coating assisted layer-by-layer assembly of Ti3C2Tx (MXene) nanoflakes together with multi-walled carbon nanotubes (MWCNTs) on electrospun polycaprolactone (PCL) fiber networks. The open structure of the PCL network and the use of MWCNTs as spacers not only limit the restacking of Ti3C2Tx flakes but also increase the accessible surface of the active materials, facilitating fast diffusion of electrolyte ions within the electrode. Composite electrodes have areal capacitance (30-50 mF cm-2) comparable to other templated electrodes reported in the literature, but showed significantly improved rate performance (14-16% capacitance retention at a scan rate of 100 V s-1). Furthermore, the composite electrodes are flexible and foldable, demonstrating good tolerance against repeated mechanical deformation, including twisting and folding. Therefore, these tens of micron thick fiber electrodes will be attractive for applications in energy storage, electroanalytical chemistry, brain electrodes, electrocatalysis and other fields, where flexible freestanding electrodes with an open and accessible surface are highly desired.

In situ doping enables the multifunctionalization of templately synthesized polyaniline@cellulose nanocomposites.

Cellulose aerogels have been widely studied as promising environmentally friendly materials due to their low density, biocompatibility and degradability. However, their applications are limited due to their highly combustible nature. In this study, polyaniline (PANI) decorated bacterial cellulose (BC) composite aerogel has been synthesized with in situ polymerization of aniline monomer on the surface of BC scaffold. The PANI decorated BC composite aerogel has a very high specific area of 124.0m2/g and well-preserved nanoporous structure, while its conductivity drastically increased to 10.44S/m. Interestingly, phosphate groups were incorporated onto PANI backbones due to its unique doping/dedoping structure. The resultant composite aerogel presented excellent flame retardancy, which can be self-extinguished within 1s. Moreover, PANI@BC composite hydrogel exhibited self-motion behavior under low voltage electric field, illustrating potential electromechanical actuator application. This simple and sustainable in situ doping method opens up new opportunities for cost-efficient fabrication of multifunctional cellulose-based electronics.

New Scalable Approach toward Shape Memory Polymer Composites via "Spring-Buckle" Microstructure Design.

Shape memory polymers (SMPs) have attracted tremendous research interest since their discovery. However, most advances in research of SMPs are based on molecular designs, i.e., "bottom-up" strategies. Due to the viscoelasticity of polymers, slow and incomplete shape variations are inevitable for most existing SMPs. Here, we propose a simple and scalable approach to design and fabricate SMP composites (SMPCs) based on a "spring-buckle" microstructure design. Specifically, a highly elastic "spring" is employed as a basic skeleton for the SMPCs, onto which self-adhesive and stimuli-responsive "buckles" are installed as reversible switch units. The resultant SMPCs with such "spring-buckle" microstructure enable quick programming at ambient temperature and ultrafast (2-3 s) and nearly complete (∼100%) shape recovery triggered by organic solvents, benefiting from a unique capillary effect. This structural approach provides a novel design philosophy for shape memory materials and opens up new opportunities for their applications in sensor, actuator, aerospace, and other applications.

Water-soluble cellulose acetate from waste cotton fabrics and the aqueous processing of all-cellulose composites.

The objective of this study is to explore the possibility of using waste cotton fabrics (WCFs) as low cost feedstock for the production of value-added products. Our previous study (Tian et al., 2014) demonstrated that acidic ionic liquids (ILs) can be highly efficient catalysts for controllable synthesis of cellulose acetate (CA) due to their dual function of swelling and catalyzing. In this study, an optimized "quasi-homogeneous" process which required a small amount of acidic ILs as catalyst was developed to synthesize water-soluble CA from WCFs. The process was optimized by varying the amounts of ILs and the reaction time. The highest conversion of water-soluble CA from WCFs reached 90.8%. The structure of the obtained water-soluble CA was characterized and compared with the original WCFs. Moreover, we demonstrate for the first time that fully bio-based and transparent all-cellulose composites can be fabricated by simple aqueous blending of the obtained water-soluble CA and two kinds of nanocelluloses (cellulose nanocrystals and cellulose nanofibrils), which is attractive for the applications in disposable packaging materials, sheet coating and binders, etc.

Biotemplate synthesis of polyaniline@cellulose nanowhiskers/natural rubber nanocomposites with 3D hierarchical multiscale structure and improved electrical conductivity.

Development of novel and versatile strategies to construct conductive polymer composites with low percolation thresholds and high mechanical properties is of great importance. In this work, we report a facile and effective strategy to prepare polyaniline@cellulose nanowhiskers (PANI@CNs)/natural rubber (NR) nanocomposites with 3D hierarchical multiscale structure. Specifically, PANI was synthesized in situ on the surface of CNs biotemplate to form PANI@CNs nanohybrids with high aspect ratio and good dispersity. Then NR latex was introduced into PANI@CNs nanohybrids suspension to enable the self-assembly of PANI@CNs nanohybrids onto NR latex microspheres. During cocoagulation process, PANI@CNs nanohybrids selectively located in the interstitial space between NR microspheres and organized into a 3D hierarchical multiscale conductive network structure in NR matrix. The combination of the biotemplate synthesis of PANI and latex cocoagulation method significantly enhanced the electrical conductivity and mechanical properties of the NR-based nanocomposites simultaneously. The electrical conductivity of PANI@CNs/NR nanocomposites containing 5 phr PANI showed 11 orders of magnitude higher than that of the PANI/NR composites at the same loading fraction,; meanwhile, the percolation threshold was drastically decreased from 8.0 to 3.6 vol %.

Facile synthesis of tunable silver nanostructures for antibacterial application using cellulose nanocrystals.

In this study, we report a facile and environmentally friendly strategy for synthesis of well dispersed and stable silver nanostructures using cellulose nanocrystals in aqueous solution without employing any other reductants, capping or dispersing agents. Importantly, it is feasible to adjust the morphology of the silver nanostructures by varying the precursor AgNO3 concentration. Silver nanospheres were formed when the AgNO3 concentration was 0.4 mM, while the dendritic nanostructures predominated when the AgNO3 concentration was increased to 250 mM. The antibacterial activity of the two different silver nanostructures against Escherichia coli and Staphylococcus aureus was characterized. Dendritic nanostructure showed a better antibacterial activity than that of silver nanosphere. The approach presented in this paper offers a very promising route to noble metal nanoparticles using renewable reducing agents.