David Kisailus

Hierarchically Ordered Macro−Mesoporous TiO2−Graphene Composite Films: Improved Mass Transfer, Reduced Charge Recombination, and Their Enhanced Photocatalytic Activities

Hierarchically ordered macro-mesoporous titania films have been produced through a confinement self-assembly method within the regular voids of a colloidal crystal with three-dimensional periodicity. Furthermore, graphene as an excellent electron-accepting and electron-transporting material has been incorporated into the hierarchically ordered macro-mesoporous titania frameworks by in situ reduction of graphene oxide added in the self-assembly system. Incorporation of interconnected macropores in mesoporous films improves the mass transport through the film, reduces the length of the mesopore channel, and increases the accessible surface area of the thin film, whereas the introduction of graphene effectively suppresses the charge recombination. Therefore, the significant enhancement of photocatalytic activity for degrading the methyl blue has been achieved. The apparent rate constants for macro-mesoporous titania films without and with graphene are up to 0.045 and 0.071 min(-1), respectively, almost 11 and 17 times higher than that for pure mesoporous titania films (0.0041 min(-1)).

Accurate Control of Multishelled Co3O4 Hollow Microspheres as High-Performance Anode Materials in Lithium-Ion Batteries

More than just an empty shell: Multishelled Co3O4 microspheres were synthesized as anode materials for lithium-ion batteries in high yield and purity. As their porous hollow multishell structure guarantees a shorter Li+ diffusion length and sufficient void space to buffer the volume expansion, their rate capacity, cycling performance, and specific capacity were excellent (1615.8 mA?h?g-1 in the 30th cycle for triple-shelled Co3O4; see graph).

Multishelled TiO2 hollow microspheres as anodes with superior reversible capacity for lithium ion batteries

Herein, uniform multishelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, intershell spacing, and number of internal multishells, which are achieved by controlling the size, charge, and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multishelled TiO2 hollow microspheres show excellent rate capacity, good cycling performance, and high specific capacity. A superior capacity, up to 237 mAh/g with minimal irreversible capacity after 100 cycles is achieved at a current rate of 1 C (167.5 mA/g), and a capacity of 119 mAh/g is achieved at a current rate of 10 C even after 1200 cycles.

The stomatopod dactyl club: a formidable damage-tolerant biological hammer.

Hammering Home the Lesson Stomatopods are marine crustaceans that use hammerlike claws for defense and to attack their prey. The claws undergo repeated high-velocity and high-force impacts. Weaver et al. (p. 1275; see the Perspective by Tanner) used a variety of techniques to examine the structure, mechanical behavior, and toughening mechanisms of the claw of the Peacock Mantis shrimp. The claws composite structure is optimized for toughness, which helps to prevent the complete failure that might arise from the claws repetitive hammering. The structure of mantis clubs is optimized to prevent complete failure caused by repetitive impacts. Nature has evolved efficient strategies to synthesize complex mineralized structures that exhibit exceptional damage tolerance. One such example is found in the hypermineralized hammer-like dactyl clubs of the stomatopods, a group of highly aggressive marine crustaceans. The dactyl clubs from one species, Odontodactylus scyllarus, exhibit an impressive set of characteristics adapted for surviving high-velocity impacts on the heavily mineralized prey on which they feed. Consisting of a multiphase composite of oriented crystalline hydroxyapatite and amorphous calcium phosphate and carbonate, in conjunction with a highly expanded helicoidal organization of the fibrillar chitinous organic matrix, these structures display several effective lines of defense against catastrophic failure during repetitive high-energy loading events.

Analysis of an ultra hard magnetic biomineral in chiton radular teeth

Recent analyses of the ultrastructural and mechanical properties of mineralized biological materials have demonstrated some common architectural features that can help explain their observed damage tolerance. Nature has accomplished this feat through the precise control of anisotropic crystal nucleation and growth processes in conjunction with nanoscale control over the self-assembly of spatially distinct organic and inorganic phases, resulting in effective inhibition of crack propagation through these materials. One such example is found in the hyper-mineralized and abrasion resistant radular teeth of the chitons, a group of herbivorous marine mollusks who have the surprising capacity to erode away the rocky substrates on which they graze 1-4 . Through the use of modern microscopy and nanomechanical characterization techniques, we describe the architectural and mechanical properties of the radular teeth from Cryptochiton stelleri. Chiton teeth are shown to exhibit the largest hardness and stiffness of any biominerals reported to date, being notably as much as three-fold harder than human enamel and the calcium carbonate-based shells of mollusks. We explain how the unique multi-phasic design of these materials contributes not only to their functionality, but also highlights some interesting design principles that might be applied to the fabrication of synthetic composites.

Bio-inspired impact-resistant composites

Through evolutionary processes, biological composites have been optimized to fulfil specific functions. This optimization is exemplified in the mineralized dactyl club of the smashing predator stomatopod (specifically, Odontodactylus scyllarus). This crustaceans club has been designed to withstand the thousands of high-velocity blows that it delivers to its prey. The endocuticle of this multiregional structure is characterized by a helicoidal arrangement of mineralized fiber layers, an architecture which results in impact resistance and energy absorbance. Here, we apply the helicoidal design strategy observed in the stomatopod club to the fabrication of high-performance carbon fiber-epoxy composites. Through experimental and computational methods, a helicoidal architecture is shown to reduce through-thickness damage propagation in a composite panel during an impact event and result in an increase in toughness. These findings have implications in the design of composite parts for aerospace, automotive and armor applications.

Crustacean-derived biomimetic components and nanostructured composites.

Over millions of years, the crustacean exoskeleton has evolved into a rigid, tough, and complex cuticle that is used for structural support, mobility, protection of vital organs, and defense against predation. The crustacean cuticle is characterized by a hierarchically arranged chitin fiber scaffold, mineralized predominately by calcium carbonate and/or calcium phosphate. The structural organization of the mineral and organic within the cuticle occurs over multiple length scales, resulting in a strong and tough biological composite. Here, the ultrastructural details observed in three species of crustacean are reviewed: the American lobster (Homarus americanus), the edible crab (Cancer pagurus), and the peacock mantis shrimp (Odontodactylus scyllarus). The Review concludes with a discussion of recent advances in the development of biomimetics with controlled organic scaffolding, mineralization, and the construction of nanoscale composites, inspired by the organization and formation of the crustacean cuticle.

Silica coating on barium titanate particles

Abstract Barium titanate (BaTiO 3 ) fine particles were coated with silica via the sol-gel reactions of tetraethyl orthosilicate. The solgel silica coating significantly stabilizes the BaTiO 3 particles in acidic solutions and changes the zeta potential of the particles to that similar to pure silica.

Urease-Mediated Room-Temperature Synthesis of Nanocrystalline Titanium Dioxide

Enzymes are an important class of biological molecules whose specific functionalities can be exploited to perform tasks beyond the reach of conventional chemistry. Because they are operational under environmentally friendly, ambient conditions, the adaptation of these biomacromolecules can potentially be used to replace current energy-intensive and environmentally harsh synthesis methods for materials. Here we used a hydrolytic enzyme, urease, to modify the solution environment around a water-soluble and stable TiO(2) precursor to synthesize nanocrystalline titanium dioxide under environmentally benign conditions. This urease-mediated synthesis yields nearly monodisperse TiO(2) nanostructures with high surface area that can be utilized for numerous energy-based applications such as low-cost photovoltaics and photocatalysts.

Analysis of the mechanical response of biomimetic materials with highly oriented microstructures through 3D printing, mechanical testing and modeling.

Many biomineralized organisms have evolved highly oriented nanostructures to perform specific functions. One key example is the abrasion-resistant rod-like microstructure found in the radular teeth of Chitons (Cryptochiton stelleri), a large mollusk. The teeth consist of a soft core and a hard shell that is abrasion resistant under extreme mechanical loads with which they are subjected during the scraping process. Such remarkable mechanical properties are achieved through a hierarchical arrangement of nanostructured magnetite rods surrounded with α-chitin. We present a combined biomimetic approach in which designs were analyzed with additive manufacturing, experiments, analytical and computational models to gain insights into the abrasion resistance and toughness of rod-like microstructures. Staggered configurations of hard hexagonal rods surrounded by thin weak interfacial material were printed, and mechanically characterized with a cube-corner indenter. Experimental results demonstrate a higher contact resistance and stiffness for the staggered alignments compared to randomly distributed fibrous materials. Moreover, we reveal an optimal rod aspect ratio that lead to an increase in the site-specific properties measured by indentation. Anisotropy has a significant effect (up to 50%) on the Youngs modulus in directions parallel and perpendicular to the longitudinal axis of the rods, and 30% on hardness and fracture toughness. Optical microscopy suggests that energy is dissipated in the form of median cracks when the load is parallel to the rods and lateral cracks when the load is perpendicular to the rods. Computational models suggest that inelastic deformation of the rods at early stages of indentation can vary the resistance to penetration. As such, we found that the mechanical behavior of the system is influenced by interfacial shear strain which influences the lateral load transfer and therefore the spread of damage. This new methodology can help to elucidate the evolutionary designs of biomineralized microstructures and understand the tolerance to fracture and damage of chiton radular teeth.