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The building sector, including building operations and materials, was responsible for the emission of ∼11.9 gigatons of global energy-related CO

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.

Cellulose, the abundantly available and sustainable biopolymer, exhibits intrinsic mechanical properties superior to many high-performance structural materials. The exceptional mechanical properties of cellulose-based materials inherently hinge upon their bottom-up hierarchical material structure starting from cellulose molecular chains to large scale fibers. However, fully atomistic simulation of such materials at experimental sample dimension becomes computationally prohibitive for the exploration of mechanics involving length scale effects. To address this challenge, here we develop a bottom-up, scalable coarse-grained (CG) modeling scheme of cellulose materials to study the deformation and failure mechanism of cellulose-based materials with insight of the interplay among cellulose building blocks at different length scales, starting from molecular chain, to nanofiber, and finally to microfiber scales. After studying the response of cellulose fibers under different loadings such as shearing and opening, this CG scheme is applied to study the deformation process of a cellulose nanopaper under tension, thus revealing the nanoscale failure mechanism otherwise impossible by atomistic simulations. In addition, the CG model also predicts the strength and stiffness of the nanopaper with respect to varying fiber lengths. Given its scalable nature, such a CG modeling scheme can be readily adapted to study the mechanical behaviors of other cellulose-based materials with mechanistic insight from molecular scale, and thus holds promise to foster the design of cellulose-based high-performance materials.

In nature, cellulose nanofibers form hierarchical structures across multiple length scales to achieve high-performance properties and different functionalities. Cellulose nanofibers, which are separated from plants or synthesized biologically, are being extensively investigated and processed into different materials owing to their good properties. The alignment of cellulose nanofibers is reported to significantly influence the performance of cellulose nanofiber-based materials. The alignment of cellulose nanofibers can bridge the nanoscale and macroscale, bringing enhanced nanoscale properties to high-performance macroscale materials. However, compared with extensive reviews on the alignment of cellulose nanocrystals, reviews focusing on cellulose nanofibers are seldom reported, possibly because of the challenge of aligning cellulose nanofibers. In this review, the alignment of cellulose nanofibers, including cellulose nanofibrils and bacterial cellulose, is extensively discussed from different aspects of the driving force, evaluation, strategies, properties, and applications. Future perspectives on challenges and opportunities in cellulose nanofiber alignment are also briefly highlighted.

Conventional strategies for materials design have long been used by leveraging primary bonding, such as covalent, ionic, and metallic bonds, between constituent atoms. However, bond energy required to break primary bonds is high. Therefore, high temperatures and enormous energy consumption are often required in processing and manufacturing such materials. On the contrary, intermolecular bonds (hydrogen bonds, van der Waals forces, electrostatic interactions, imine bonds, etc.) formed between different molecules and functional groups are relatively weaker than primary bonds. They, thus, require less energy to break and reform. Moreover, intermolecular bonds can form at considerably longer bond lengths between two groups with no constraint on a specific bond angle between them, a feature that primary bonds lack. These features motivate unconventional strategies for the material design by tuning the intermolecular bonding between constituent atoms or groups to achieve superior physical properties. This paper reviews recent development in such strategies that utilize intermolecular bonding and analyzes how such design strategies lead to enhanced thermal stability and mechanical properties of the resulting materials. The applications of the materials designed and fabricated by tuning the intermolecular bonding are also summarized, along with major challenges that remain and future perspectives that call for further attention to maximize the potential of programming material properties by tuning intermolecular bonding.

The stability of single-atom catalysts is critical for their practical applications. Although a high temperature can promote the bond formation between metal atoms and the substrate with an enhanced stability, it often causes atom agglomeration and is incompatible with many temperature-sensitive substrates. Here, we report using controllable high-temperature shockwaves to synthesize and stabilize single atoms at very high temperatures (1,500–2,000 K), achieved by a periodic on–off heating that features a short on state (55 ms) and a ten-times longer off state. The high temperature provides the activation energy for atom dispersion by forming thermodynamically favourable metal–defect bonds and the off-state critically ensures the overall stability, especially for the substrate. The resultant high-temperature single atoms exhibit a superior thermal stability as durable catalysts. The reported shockwave method is facile, ultrafast and universal (for example, Pt, Ru and Co single atoms, and carbon, C3N4 and TiO2 substrates), which opens a general route for single-atom manufacturing that is conventionally challenging. A repeated on–off high-temperature shockwave is shown to be a generalizable way of efficiently synthesizing and stabilizing single atoms at high temperatures.

Pristine graphene depositing on metallic substrates often wrinkles when the film-substrate system undergoes a temperature drop from the chemical vapor deposition (CVD) chamber to ambient environment. The pattern of wrinkles is governed by the crystallographic planes of the substrates and the defects in the film. In this paper, we report how commonly seen Stone-Wales defects and grain boundaries (GBs) influence the morphology of graphene on different planes of single crystalline copper substrate. Stone-Wales defects weaken the bending stiffness in graphene, and result in wrinkling along the defect direction. In the presence of GBs, primary wrinkles are always parallel to the GB direction, and there are also secondary wrinkles perpendicular to the GB. In combination with planes of the substrate and the orientation of defects, we demonstrate that we may manipulate wrinkling patterns for possible engineering applications.

The huge consumption of single-use plastic straws has brought a long-lasting environmental problem. Paper straws, the current replacement for plastic straws, suffer from drawbacks, such as a high cost of the water-proof wax layer and poor water stability due to the easy delamination of the wax layer. It is therefore crucial to find a high-performing alternative to mitigate the environmental problems brought by plastic straws. In this paper, all natural, degradable, cellulose-lignin reinforced composite straws, inspired by the reinforcement principle of cellulose and lignin in natural wood are developed. The cellulose-lignin reinforced composite straw is fabricated by rolling up a wet film made of homogeneously mixed cellulose microfibers, cellulose nanofibers, and lignin powders, which is then baked in oven at 150 °C. When baked, lignin melts and infiltrates the micro-nanocellulose network, acting as a polyphenolic binder to improve the mechanical strength and hydrophobicity performance of the resulting straw. The obtained straws demonstrate several advantageous properties over paper straws, including 1) excellent mechanical performance, 2) high hydrostability, and 3) low cost. Moreover, the natural degradability of the cellulose-lignin reinforced composite straws makes them promising candidates to replace plastic straws and suggests possible substitutes for other petroleum-based plastics.

Anisotropic cellular materials with direction-dependent structure and durable mechanical properties enable various applications (e.g., nanofluidics, biomedical devices, tissue engineering, and wate...

The abundance of cellulose found in natural resources such as wood, and the wide spectrum of structural diversity of cellulose nanomaterials in the form of micro-nano-sized particles and fibers, have sparked a tremendous interest to utilize cellulose's intriguing mechanical properties in designing high-performance functional materials, where cellulose's structure-mechanics relationships are pivotal. In this progress report, multiscale mechanics understanding of cellulose, including the key role of hydrogen bonding, the dependence of structural interfaces on the spatial hydrogen bond density, the effect of nanofiber size and orientation on the fracture toughness, are discussed along with recent development on enabling experimental design techniques such as structural alteration, manipulation of anisotropy, interface and topology engineering. Progress in these fronts renders cellulose a prospect of being effectuated in an array of emerging sustainable applications and being fabricated into high-performance structural materials that are both strong and tough.

Conformal polymer coating leads to damage-tolerant architected ceramic structures with high strength and toughness., Ceramic materials, despite their high strength and modulus, are limited in many structural applications due to inherent brittleness and low toughness. Nevertheless, ceramic-based structures, in nature, overcome this limitation using bottom-up complex hierarchical assembly of hard ceramic and soft polymer, where ceramics are packaged with tiny fraction of polymers in an internalized fashion. Here, we propose a far simpler approach of entirely externalizing the soft phase via conformal polymer coating over architected ceramic structures, leading to damage tolerance. Architected structures are printed using silica-filled preceramic polymer, pyrolyzed to stabilize the ceramic scaffolds, and then dip-coated conformally with a thin, flexible epoxy polymer. The polymer-coated architected structures show multifold improvement in compressive strength and toughness while resisting catastrophic failure through a considerable delay of the damage propagation. This surface modification approach allows a simple strategy to build complex ceramic parts that are far more damage-tolerant than their traditional counterparts.

We study the roles of graphene acting as a buffer layer for growth of an AlN film on a sapphire substrate. Graphene can reduce the density of AlN nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in AlN and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AlN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry.

In this article, we present the electronic properties of various carbon honeycombs (C-honeycombs) with different cell sizes and junction types based on ab initio calculations. Among the three typical C-honeycombs with junctions connected via the zigzag edge, the armchair edge, or the hybrid edges of graphene nanoribbons, it is found that the zigzag C-honeycombs and the hybrid ones exhibit metallic properties. However, the armchair C-honeycombs are metallic only if the number of atomic planes N of the graphene nanoribbon in the C-honeycomb sidewall follows N = 3p+1, with p as an integer and are semiconducting for other N. For those semiconducting ones, the bandgap of the C-honeycomb is about 1.19 eV with the narrowest sidewall (5.2 A) and monotonically decreases to about 0.15 eV when the width is increased to 34.8 A. The semiconducting nature of such C-honeycombs with nanometer size pores may be used for lightweight semiconductor in electronic devices or supercapacitor energy storage. As a comparison, we show that all boron honeycombs are metallic, and their electronic properties are independent of sidewall widths.

High-mobility semiconductive ultrathin films of bismuth oxyselenide (Bi2O2Se) have attracted great interest due to their potential applications in advanced electronic and photoelectronic devices. Enthusiasm aside, future success of such applications hinges upon the fundamental understanding of two dimensional (2D) Bi2O2Se, which is far from mature. In particular, unlike many other 2D materials with a van der Waals gap, 2D Bi2O2Se features a weak electrostatic stacking interaction, which gives rise to a significantly different mechanical response. The unique mechanical response of 2D Bi2O2Se has a strong influence on its band gap, a critical property toward its device applications. Here, using ab initio calculations, we investigate the mechanical and electronic responses of both bulk and monolayer Bi2O2Se under uniaxial and biaxial tension as well as those of monolayer Bi2O2Se under in-plane shearing. The distinct mechanical responses of bulk and monolayer Bi2O2Se under different mechanical deformation are explained by the associated study of the evolution of electron localization function and charge density analysis. We reveal that the band gap of both bulk and monolayer Bi2O2Se decreases as the applied tensile strain increases. The critical uniaxial and biaxial tensile strains, above which bulk and monolayer Bi2O2Se transform from being semiconductive to being metallic, are determined. These findings suggest fertile yet largely unexplored opportunities of strain engineering of 2D Bi2O2Se toward new device applications.

Carbon honeycomb is a 3-dimensional carbon allotrope experimentally discovered recently but its lattice structure has not been well identified. In this paper we perform density-functional theory (DFT) calculations to examine the stability of carbon honeycombs with different configurations (chirality and sidewall width). We find that graphene nanoribbons with both zigzag edges and armchair edges can form stable carbon honeycombs if sp(3) carbon-carbon bonding is formed in the junction. We further study the mechanical properties and the thermal conductivity of carbon honeycombs with different chirality and the sidewall widths using both DFT calculations and molecular dynamics simulations. All these stable carbon honeycombs exhibit superior mechanical properties (large strength and ductility) and high thermal conductivity (larger than 100 W/m K) with a density as low as 0.5 g/cm(3). Light-weight carbon honeycombs could be promising functional materials for many engineering applications. (C) 2017 Elsevier Ltd. All rights reserved.

Low-dimensional carbon allotropes, from fullerenes, carbon nanotubes, to graphene, have been broadly explored due to their outstanding and special properties. However, there exist significant challenges in retaining such properties of basic building blocks when scaling them up to three-dimensional materials and structures for many technological applications. Here we show theoretically the atomistic structure of a stable three-dimensional carbon honeycomb (C-honeycomb) structure with superb mechanical and thermal properties. A combination of sp2 bonding in the wall and sp3 bonding in the triple junction of C-honeycomb is the key to retain the stability of C-honeycomb. The specific strength could be the best in structural carbon materials, and this strength remains at a high level but tunable with different cell sizes. C-honeycomb is also found to have a very high thermal conductivity, for example, >100 W/mK along the axis of the hexagonal cell with a density only ∼0.4 g/cm3. Because of the low density and ...

While the speculation that graphene may owe double or even higher capacity of lithium adsorption than graphite does remains speculative, there is growing evidence that defects and edges may promote lithium adsorption on graphene and other nanostructured carbon. Here we report a first-principles study on how grain boundary defects in graphene may influence the adsorption of lithium. The adsorption energy for Li atoms trapping in 5-, 7-, and 8-rings is much lower than the counter-part of Li atoms and pristine graphene. Such defective graphene could adsorb more Li atoms, and may reach the speculated ratio of 1:1 for C-Li adsorption. In a contrast study of lithium on fullerenes of different size, we find that the adsorption energy decreases with increasing size of fullerenes, but does not approach the energy when Li atoms adsorb on flat graphene. The energy in carbon nanotubes, however, converges to the adsorption energy between Li atoms and flat graphene if the radius of carbon nanotubes is sufficiently large. It hence indicates that while curvature plays a role in the enhanced adsorption in fullerenes, the twelve 5 rings in a fullerene ball is the primary factor accounting for the enhanced lithium adsorption.

Direct formation of ultra-small nanoparticles on carbon supports by rapid high temperature synthesis method offers new opportunities for scalable nanomanufacturing and the synthesis of stable multi-elemental nanoparticles. However, the underlying mechanisms affecting the dispersion and stability of nanoparticles on the supports during high temperature processing remain enigmatic. In this work, we report the observation of metallic nanoparticles formation and stabilization on carbon supports through in situ Joule heating method. We find that the formation of metallic nanoparticles is associated with the simultaneous phase transition of amorphous carbon to a highly defective turbostratic graphite (T-graphite). Molecular dynamic (MD) simulations suggest that the defective T-graphite provide numerous nucleation sites for the nanoparticles to form. Furthermore, the nanoparticles partially intercalate and take root on edge planes, leading to high binding energy on support. This interaction between nanoparticles and T-graphite substrate strengthens the anchoring and provides excellent thermal stability to the nanoparticles. These findings provide mechanistic understanding of rapid high temperature synthesis of metal nanoparticles on carbon supports and the origin of their stability., Metal nanoparticle-decorated carbon supports are vital for many applications, ranging from energy storage and catalysis to filtration and environmental remedies. Here, using real-time electron microscopy of a single carbon nanofiber during Joule heating, the authors report atomistic mechanisms responsible for nucleation and stabilization of nanoparticles on amorphous carbon supports.

Two dimensional (2D) materials have attracted great interest due to their unique structures and properties. However, the loss of the exceptional properties of 2D constituents in their 3D counterparts poses a grand challenge to the widespread use of 2D materials. How to achieve comparable superior properties in 3D materials made of 2D constituents still remains elusive. Here we demonstrate an effective approach to tailoring the mechanical properties of 3D materials, made of 2D constituents via ion intercalation. We show that, by intercalating Li ions into graphite, the inter-graphene-layer friction can be drastically increased up to 7 times of that in natural graphite. We attribute the drastic increase of inter-graphene-layer friction to the electrostatic interaction of graphene layers with the intercalants. The layered structure of 2D materials and the weak inter-layer interactions allow for facile intercalation of various foreign species into the vdW gap of 2D materials. Therefore, fertile opportunities exist to leverage ion intercalation to fine tune the interlayer interaction between 2D constituents, paving a promising way to programmable mechanical properties of their 3D counterpart materials.

Wrinkles are ubiquitous for graphene films grown on various substrates by chemical vapor deposition at high temperature due to the strain induced by thermal mismatch between the graphene and substrates, which greatly degrades the extraordinary properties of graphene. Here we show that the wrinkle formation of graphene grown on Cu substrates is strongly dependent on the crystallographic orientations. Wrinkle-free single-crystal graphene was grown on a wafer-scale twin-boundary-free single-crystal Cu(111) thin film fabricated on sapphire substrate through strain engineering. The wrinkle-free feature of graphene originated from the relatively small thermal expansion of the Cu(111) thin film substrate and the relatively strong interfacial coupling between Cu(111) and graphene, based on the strain analyses as well as molecular dynamics simulations. Moreover, we demonstrated the transfer of an ultraflat graphene film onto target substrates from the reusable single-crystal Cu(111)/sapphire growth substrate. The wrinkle-free graphene shows enhanced electrical mobility compared to graphene with wrinkles.

Environmental isotopes and chemical compositions are useful tools for the study of groundwater flow systems. Groundwater of the Chaobai River catchment, Beijing was sampled for chemical and stable isotopes analyses in 2005. Geochemical signatures evolve progressively from CaMg-HCO 3 to NaK-HCO 3 , and then to Na-HCO 3 compositions as groundwater flows from the mountain to discharge areas. Groundwater can be divided into two groups on the basis of stable isotope compositions: ancient groundwater and modern groundwater. Modern groundwater (-9.9% 0 to -6.6% 0 for δ 18 O) plots along a line with a slope of 4.0 on a δ 2 H versus δ 18 O diagram, reflecting evaporation during the process of recharge, whereas ancient groundwater samples (30 to 12 Ka.) are different in isotopic composition (-11.0% 0 and -68.2% 0 for δ 18 O and δ 2 H, respectively), reflecting the cold and arid climate in the last glacial period. The results have important implications for groundwater management in Beijing City.

Recent success in the synthesis of the two-dimensional borophene on silver substrates has attracted strong interest in exploring its extraordinary properties for potential technological applications. The single-layer borophene has a buckled structure with atomic ridges. By using the first-principles density functional theory calculations, we show that the two-dimensional borophene is highly stretchable with strong anisotropy The strain-to-failure in the direction along the atomic ridges is nearly twice as large as that across the atomic ridges. The straining-induced flattening and the subsequent stretch of the flat borophene are accounted for the large strain-to-failure for tension along the atomic ridges. We also investigated the mechanics of monolayer borophene under biaxial tension and we found that the biaxial tension increases the strength across the atomic ridges but decreases the failure strain along the atomic ridges. Furthermore, when the bilayer borophene is stretched along the cross-plane direction, the strength and failure strain of the bilalyer borophene are much higher than those of the bilayer graphene due to the very strong inter-layer chemical bonding.