Superelastic and superflexible cellulose aerogels for thermal insulation and oil/water separation.

Aerogels with low thermal conductivity and high adsorption capacity present a promising solution to curb water pollution caused by organic reagents as well as mitigate heat loss. Although aerogels exhibiting good adsorption capacity and thermal insulation have been reported, materials with mechanical integrity, high flexibility and shear resistance still pose a formidable task. Here, we produced bacterial cellulose-based ultralight multifunctional hybrid aerogels by using freeze-drying followed by chemical vapor deposition silylation method. The hybrid aerogels displayed a low density of 10-15 mg/cm3, high porosity exceeding 99.1 %, low thermal conductivity (27.3-29.2 mW/m.K) and superior hydrophobicity (water contact angle>120o). They also exhibited excellent mechanical properties including superelasticity, high flexibility and shear resistance. The hybrid aerogels demonstrated high heat shielding efficiency when used as an insulating material. As a selective oil absorbent, the hybrid aerogels exhibit a maximum adsorption capacity of up to approximately 156 times its own weight and excellent recoverability. Especially, the aerogel's highly accessible porous microstructure results in an impressive flux rate of up to 162 L/h.g when used as a filter in a continuous oil-water separator to isolate n-hexane-water mixtures. This work presents a novel endeavor to create high-performance, sustainable, reusable, and adaptable multifunctional aerogels.

Biobased Composites with High Lignin Content and Excellent Mechanical Properties toward the Ingenious Photoresponsive Actuator.

The fabrication of biobased smart materials from renewable biomasses is of great importance for sustainable development. Although lignin possesses photothermal conversion potential, the development of lignin-based actuators with large contraction and fast photoresponse has various hurdles. Herein, simply by blending with castor oil-derived polyamide elastomers, a lignin-based photoresponsive actuator can be obtained, which accomplishes up to 18% light-driven contraction under loading within 3 s. The crystals in polymer matrix serve as switch segments, firmly locking the stress-induced strain energy, which is swiftly released due to photothermal processes and induced a huge contraction. The composite, LP4-50, can contract and induce dynamic bending in multiple directions when irradiated locally with a near-infrared 808 nm laser. Furthermore, at standard 1 sun irradiation (100 mW/cm2), LP4-50 was successfully employed to power a thermoelectric generator. This strategy establishes the groundwork for further research into the photothermal characteristics of lignin and encourages new applications in stimulus-responsive actuators.

Ultralight and robust aerogels based on nanochitin towards water-resistant thermal insulators.

The development of lightweight, strong and high-performance thermal insulators from renewable biomass are highly desired for sustainable development. Here, ultralight aerogels based on renewable nanochitin with outstanding mechanical properties, excellent water-resistant, and promising thermal insulation properties are fabricated. The pristine nanochitin aerogels (PNCAs) assembled from mechanically strong carboxylated chitin nanorods are firstly prepared through acid-induced gelation and supercritical drying. The resultant PNCAs present tunable density (10-50 mg/cm3) and strong mechanical stiffness (the specific compression modulus of 30.2 MPa cm3/g) combining with low thermal conductivity (27.2 mW/m K). After a facile silylation modification, the silylated nanochitin aerogels (SNCAs) exhibit hydrophobic behavior (contact angle >130°), improved compression performance (the specific compression modulus of 65 MPa cm3/g), and promising thermal insulation property (30.5-35.8 mW/m K). Moreover, the silylated aerogel shows a negligible loss of mechanical performance when exposed to water for 12 h at 35 °C.

Synthetic nacre by predesigned matrix-directed mineralization.

Although biomimetic designs are expected to play a key role in exploring future structural materials, facile fabrication of bulk biomimetic materials under ambient conditions remains a major challenge. Here, we describe a mesoscale "assembly-and-mineralization" approach inspired by the natural process in mollusks to fabricate bulk synthetic nacre that highly resembles both the chemical composition and the hierarchical structure of natural nacre. The millimeter-thick synthetic nacre consists of alternating organic layers and aragonite platelet layers (91 weight percent) and exhibits good ultimate strength and fracture toughness. This predesigned matrix-directed mineralization method represents a rational strategy for the preparation of robust composite materials with hierarchically ordered structures, where various constituents are adaptable, including brittle and heat-labile materials.

Micrometer-Thick Graphene Oxide-Layered Double Hydroxide Nacre-Inspired Coatings and Their Properties.

Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire-retardant micrometer-thick hybrid coatings are reported, which can be constructed via an enhanced layer-by-layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young's modulus of ≈ 18 GPa and hardness of ≈ 0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined 2D microstructures. This kind of nacre-inspired GO-LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities.

Ultrathin hybrid films of polyoxohydroxy clusters and proteins: layer-by-layer assembly and their optical and mechanical properties.

The hierarchical assembly of inorganic and organic building blocks is an efficient strategy to produce high-performance materials which has been demonstrated in various biomaterials. Here, we report a layer-by-layer (LBL) assembly method to fabricate ultrathin hybrid films from nanometer-scale ionic clusters and proteins. Two types of cationic clusters (hydrolyzed aluminum clusters and zirconium-glycine clusters) were assembled with negatively charged bovine serum albumin (BSA) protein to form high-quality hybrid films, due to their strong electrostatic interactions and hydrogen bonding. The obtained hybrid films were characterized by scanning electron microscope (SEM), UV-vis, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The results demonstrated that the cluster-protein hybrid films exhibited structural homogeneity, relative transparency, and bright blue fluorescence. More importantly, these hybrid films displayed up to a 70% increase in hardness and up to a 100% increase in reduced Young's modulus compared to the pure BSA film. These hybrid cluster-protein films could be potentially used as biomedical coatings in the future because of their good transparency and excellent mechanical properties.

25th anniversary article: Artificial carbonate nanocrystals and layered structural nanocomposites inspired by nacre: synthesis, fabrication and applications.

Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of next generation advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. Among these rigid biomaterials, nacre, as the main constituent of the armor system of seashells, exhibiting a well-defined 'brick-and-mortar' architecture, excellent mechanical properties, and interesting iridescence, has become one of the most attractive models for novel artificial materials design. In this review, recent advances in nacre-inspired artificial carbonate nanocrystals and layered structural nanocomposites are presented. To clearly illustrate the inspiration of nacre, the basic principles relating to plate-like aragonite single-crystal growth and the contribution of hierarchical structure to outstanding properties in nacre are discussed. The inspiration of nacre for the synthesis of carbonate nanocrystals and the fabrication of layered structural nanocomposites is also discussed. Furthermore, the broad applications of these nacre inspired materials are emphasized. Finally, a brief summary of present nacre-inspired materials and challenges for the next generation of nacre-inspired materials is given.

Bio-inspired in situ growth of monolayer silver nanoparticles on graphene oxide paper as multifunctional substrate.

In this study, we report a facile bio-inspired method for large-scale preparation of highly dispersed Ag nanoparticles (NPs) on the surface of flexible reduced graphene oxide (rGO) paper with using dopamine (DA) both as a reductant and a surface modifier. Through the self-polymerization of dopamine, free-standing GO paper can be simultaneously reduced and modified with following in situ growth of monolayer Ag NPs on such a substrate. The spherical Ag NPs with an average diameter of 80 nm have a narrow size distribution and tunable cover density. Such a flexible rGO/Ag hybrid paper presents enhanced antibacterial activity against E. coli and a high active and sensitive SERS response toward Rhodamine 6G (R6G) molecules. The detection signals can be obtained while the R6G concentration is as low as to 10(-8) M. This work provides a simple strategy for large-scale fabrication of monolayer Ag NPs on flexible rGO paper as a portable antibacterial substrate and a potential SERS substrate for molecular detection applications.

Gold nanoparticle functionalized artificial nacre: facile in situ growth of nanoparticles on montmorillonite nanosheets, self-assembly, and their multiple properties.

Artificial nacre based on clay nanosheets have been emerging as a new generation of bioinspired materials due to their super mechanical, fire-retardant, heat-shield, and gas barrier properties. Functional design in artificial nacre is highly demanded to further broaden the applications of these promising bioinspired materials. However, there is rarely a report on the functionalization of artificial nacre at present possibly due to the lack of a feasible strategy to introduce functional components in nacre-like materials without weakening other properties. In this study, we report a feasible method to fabricate artificial nacre-like functional hybrid films by using Au nanoparticle (NP) modified natural clay montmorillonite (MTM) nanosheets as efficient two-dimensional building blocks. First, Au NPs-chitosan-MTM hybrid nanosheets were prepared and homogeneously dispersed in deionized water by the facile in situ growth of Au NPs on chitosan-MTM nanosheets. Then, the obtained Au NPs-chitosan-MTM hybrid nanosheet suspension can be sprayed or vacuum filtrated to form nacre-like layered hybrid nanocoatings or free-standing hybrid films, respectively. Finally, as-fabricated artificial nacre nanocoatings or hybrid films have been demonstrated to behave with surface enhanced Raman scattering (SERS), catalytic, and photothermal conversion properties indicating the successful functionalization of artificial nacre by introducing Au NPs.