Grain boundaries are Brownian ratchets.

We demonstrate that grain boundaries (GBs) behave as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under oscillatory driving forces or cyclic thermal annealing. We observed these phenomena for nearly all nonsymmetric GBs but not for symmetric ones. Our observations build on molecular dynamics and phase-field crystal simulations for a wide range of GB types and driving forces in both bicrystal and polycrystalline microstructures. We corroborate these simulation results through in situ experimental observations. We analyze these results with a Markov chain model and explore the implications of GB ratchet behavior for materials processing and microstructure tailoring.

In situ synthesis of BiOCl nanosheets on three-dimensional hierarchical structures for efficient photocatalysis under visible light.

Assembling two-dimensional (2D) nanomaterials into three-dimensional (3D) hierarchical structures with novel functions is challenging and has attracted considerable attention. However, it is quite difficult to obtain complex 3D architectures of 2D materials with a uniform and intact structure using traditional methods, such as hydrothermal/solvothermal methods and direct precipitation methods. Here, we use butterfly wing scales as bio-templates to prepare 3D hierarchical BiOCl/Au wing scales for plasmonic photocatalysis. The as-prepared materials exhibit excellent photodegradation of rhodamine B (RhB) under visible light. The degradation rates of BiOCl microspheres and BiOCl and BiOCl/Au butterfly wing scales are 48.8%, 72.6%, and 93.8%, respectively, within 20-min illumination at the same loading capacities. This excellent performance of BiOCl/Au is attributed to the coupling of enhanced carrier separation efficiency and the effect of localized surface plasmon resonance (LSPR) aroused by 3D metallic structures. This study provides a relatively facile method to obtain complex 3D constructure of 2D materials. It also demonstrates a nature-led route to prepare highly efficient plasmonic photocatalysts.

Large-Area 3D Hierarchical Superstructures Assembled from Colloidal Nanoparticles.

Assembling nanosized building blocks into macroscopic 3D complex structures is challenging. Here, nanosized metal and semiconductor building blocks with a variety of sizes and shapes (spheres, stars, and rods) are successfully assembled into a broad range of hierarchical (nanometer to micrometer) assemblies of functional materials in centimeter size using butterfly wings as templates. This is achieved by the introduction of steric hindrance to the assembly process, which compensates for attraction from the environmentally sensitive hydrogen bonds and prevents the aggregation of nanosized building blocks. Of these materials, Au nanostar assemblies show a superior enhancement in surface-enhanced Raman scattering (SERS) performance (rhodamine 6G, 1506 cm-1 ) under 532, 633, and 780 nm excitation-this is 3.1-4.4, 3.6-3.9, and 2.9-47.3 folds surpassing Au nanosphere assemblies and commercial SERS substrates (Q-SERS), respectively. This method provides a versatile route for the assembly of various nanosized building blocks into different 3D superstructures and for the construction of hybrid nanomaterials and nanocomposites.

Regain Strain-Hardening in High-Strength Metals by Nanofiller Incorporation at Grain Boundaries.

Grain refinement to the nano/ultrafine-grained regime can make metals several times stronger, but this process is usually accompanied by a dramatic loss of ductility. Such strength-ductility trade-off originates from a lack of strain-hardening capacity in tiny grains. Here, we present a strategy to regain the strain-hardening ability of high-strength metals by incorporation of extrinsic nanofillers at grain boundaries. We demonstrate that the dislocation storage ability in Cu grains can be considerably improved through this novel grain-boundary engineering approach, leading to a remarkably enhanced strain-hardening capacity and tensile ductility (uniform elongation). Experiments and large-scale atomistic simulations reveal that a key benefit of incorporated nanofillers is a reduction in the grain-boundary energy, enabling concurrent dislocation storage near the boundaries and in the Cu grain interior during straining. The strategy of grain-boundary engineering through nanofillers is easily controllable, generally applicable, and may open new avenues for producing nanostructured metals with extraordinary mechanical properties.

Resistance-breaking population of Meloidogyne incognita utilizes plant peroxidase to scavenge reactive oxygen species, thereby promoting parasitism on tomato carrying Mi-1 gene.

Resistance conferred by the Mi-1 gene from Solanum peruvianum is effective and widely used for controlling root-knot nematodes (RKNs, Meloidogyne spp.). However, breakdown of resistance by RKNs seriously threatens the durable application of the resistance resource. Here, a resistance-breaking population of M. incognita was selected from an avirulent population by continuously inoculating on Mi-1-carrying tomato. Histological observations showed the resistance-breaking population would not induce hypersensitive response (HR) when infecting Mi-1-carrying tomato, while avirulent population did. A total of 308 differentially expressed genes (DEGs) were identified from Mi-1-carrying tomato upon infection with resistance-breaking versus avirulent populations by RNA-seq. The expression patterns of 23 selected DEGs were validated by quantitative real-time PCR (qRT-PCR). Subsequently, seven out of nine highly up-regulated DEGs were successfully knocked down in Mi-1-carrying tomato by tobacco rattle virus (TRV) mediated RNAi. The TRV line targeting a peroxidase gene showed a much higher magnitude of reactive oxygen species (ROS) and distinct reduction of pathogenicity upon infection of the resistance-breaking population compared with that of TRV::gfp line. Our results suggested that plant peroxidase might be exploited by resistance-breaking population of M. incognita to scavenge ROS, so as to overcome Mi-1-mediated resistance.

Tumor marker detection using surface enhanced Raman spectroscopy on 3D Au butterfly wings.

Tumor markers are usually over-expressed in human body fluids during the development of cancers. Monitoring tumor markers' level is thus important for early diagnosis and screening of cancers. One way to achieve this is based on the surface enhanced Raman scattering (SERS) technique that can drastically amplify Raman signals of analytes on a plasmonic metal (e.g., Au, Ag, and Cu) surface. However, this promising method suffers from aggregation of plasmonic nanoparticles. Here we report a stable, reproducible, and facile SERS-based readout method to detect an important tumor marker, carcinoembryonic antigen (CEA). This route utilizes Au butterfly wings with natural three dimensional (3D) hierarchical sub-micrometer structures rather than relying on the aggregates of metal nanoparticles. The Au butterfly wings show excellent SERS property and are temperature (80 °C) and time (6 months) stable on a sub-micrometer scale. Thus, the detecting antibodies and enzyme-linked secondary antibodies that are usually applied in conventional enzyme-linked immunosorbent assay (ELISA) can be replaced by chemically synthesized CEA aptamers, significantly simplifying the whole detection process. We demonstrate the feasibility of this method via quantitative detection of clinical CEA level in human body fluids. This work thus demonstrates a promising tumor marker detection technique based on a hierarchical sub-micrometer SERS structure, which could be useful for the mass screening of early stage cancers.

Light-Driven Overall Water Splitting Enabled by a Photo-Dember Effect Realized on 3D Plasmonic Structures.

Photoelectric conversion driven by sunlight has a broad range of energy/environmental applications (e.g., in solar cells and water splitting). However, difficulties are encountered in the separation of photoexcited charges. Here, we realize a long-range (∼1.5 µm period) electric polarization via asymmetric localization of surface plasmons on a three-dimensional silver structure (3D-Ag). This visible-light-responsive effect-the photo-Dember effect, can be analogous to the thermoelectric effect, in which hot carriers are thermally generated instead of being photogenerated. The induced electric field can efficiently separate photogenerated charges, enabling sunlight-driven overall water splitting on a series of dopant-free commercial semiconductor particles (i.e., ZnO, CeO2, TiO2, and WO3) once they are combined with the 3D-Ag substrate. These photocatalytic processes can last over 30 h on 3D-Ag+ZnO, 3D-Ag+CeO2, and 3D-Ag+TiO2, thus demonstrating good catalytic stability for these systems. Using commercial WO3 powder as a reference, the amount of O2 generated with 3D-Ag+CeO2 surpasses even its recently reported counterpart in which sacrificial reagents had to be involved to run half-reactions. This plasmon-mediated charge separation strategy provides an effective way to improve the efficiency of photoelectric energy conversion, which can be useful in photovoltaics and photocatalysis.

Enhanced Mechanical Properties of Graphene (Reduced Graphene Oxide)/Aluminum Composites with a Bioinspired Nanolaminated Structure.

Bulk graphene (reduced graphene oxide)-reinforced Al matrix composites with a bioinspired nanolaminated microstructure were fabricated via a composite powder assembly approach. Compared with the unreinforced Al matrix, these composites were shown to possess significantly improved stiffness and tensile strength, and a similar or even slightly higher total elongation. These observations were interpreted by the facilitated load transfer between graphene and the Al matrix, and the extrinsic toughening effect as a result of the nanolaminated microstructure.

"Egg-Box"-Assisted Fabrication of Porous Carbon with Small Mesopores for High-Rate Electric Double Layer Capacitors.

Here we report a method to fabricate porous carbon with small mesopores around 2-4 nm by simple activation of charcoals derived from carbonization of seaweed consisting of microcrystalline domains formed by the "egg-box" model. The existence of mesopores in charcoals leads to a high specific surface area up to 3270 m(2) g(-1), with 95% surface area provided by small mesopores. This special pore structure shows high adaptability when used as electrode materials for an electric double layer capacitor, especially at high charge-discharge rate. The gravimetric capacitance values of the porous carbon are 425 and 210 F g(-1) and volumetric capacitance values are 242 and 120 F cm(-3) in 1 M H2SO4 and 1 M TEA BF4/AN, respectively. The capacitances even remain at 280 F g(-1) (160 F cm(-3)) at 100 A g(-1) and 156 F g(-1) (90 F cm(-3)) at 50 A g(-1) in the aqueous and organic electrolytes, demonstrating excellent high-rate capacitive performance.

Uniform dispersion of graphene oxide in aluminum powder by direct electrostatic adsorption for fabrication of graphene/aluminum composites.

The excellent properties of graphene promote it as an ideal reinforcement in composites. However, dispersing graphene homogenously into metals is a key challenge that limits the development of high-performance graphene-reinforced metal matrix composites. Here, via simple electrostatic interaction between graphene oxide (GO) and Al flakes, uniform distribution of reduced graphene oxide (RGO) in an Al matrix is achieved. The adsorption process of GO on Al flakes is efficient, as it can be completed in minutes and proceeds spontaneously without any chemical agents. GO can be partially reduced by the electron interchange during the adsorption process and could be thoroughly reduced after subsequent thermal annealing. A densified RGO/Al composite can be obtained by hot pressing the RGO/Al composite powders. By employing the preceding fabrication process, a composite reinforced with only 0.3 wt.% of RGO shows an 18 and 17% increase in elastic modulus and hardness, respectively, over unreinforced Al, demonstrating RGO is a better reinforcement than most other reinforcements.

Metal-organic frameworks reactivate deceased diatoms to be efficient CO(2) absorbents.

Diatomite combined with certain metal-organic frameworks (MOFs) is shown to be an effective CO2 absorbent, although diatomite alone is regarded as inert with respect to CO2 absorption. This finding opens the prospect of reactivating millions of tons of diatomite for CO2 absorption. It also shows for the first time that diatom frustules can act as CO2 buffers, an important link in a successive biological CO2 concentration mechanism chain that impacts on global warming.