T. Yong-Jin Han

Highly compressible 3D periodic graphene aerogel microlattices

Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Youngs moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.

Supercapacitors Based on Three-Dimensional Hierarchical Graphene Aerogels with Periodic Macropores

Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g(-1)) and power densities (>4 kW·kg(-1)) that equal or exceed those of reported devices made with electrodes 10-100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications.

Synthesis of ZnO coated activated carbon aerogel by simple sol-gel route†

We demonstrated the synthesis of high surface area ZnO–ACA composites with well-crystallized ZnO nanoparticles by simple sol–gel process. The coverage of ZnO nanoparticles on the carbon framework of ACA is very uniform, with no exposed carbon framework. Thermal removal of carbon produces ZnO replica structure mimicking the original ACA framework.

Route to high surface area TiO2/C and TiCN/C composites

In this study, the synthesis and characterization of high surface area carbon-supported titania and titanium carbonitride aerogels is presented. An activated carbon aerogel with surface area greater than 2000 m2 g−1 was used as a support for the sol–gel deposition of titania. The resulting titania-coated carbon aerogel retained a surface area greater than 2000 m2 g−1 even after conversion to the anatase crystalline phase. The carbon-supported titanium carbonitride aerogel was made by the carbothermal reduction of the titania-coated carbon aerogel under flowing nitrogen at 1400 °C. The resulting monolith consisted of nitrogen-rich titanium carbonitride (TiC1−xNx, x = 0.90) nanocrystals and exhibited a surface area of 1838 m2 g−1.

Shape control synthesis of fluorapatite structures based on supersaturation: prismatic nanowires, ellipsoids, star, and aggregate formation

Fluorapatite nanostructures of various shapes (prismatic, ellipsoidal, star, and aggregate) were synthesized and their structures correlated with the supersaturation of the system. Reagent concentration and pH were adjusted and the change in supersaturation was simulated by the Geochemists Workbench® software and the MINTEQ database. A higher pH caused changes to the FAP surface charge and was shown to be the dominant force behind aggregate formation. This led to nanorod aggregates and when combined with an increase in reagent concentration, FAP stars were generated. Increasing reaction temperature (room temperature to 100 °C) allowed release of calcium by the chelating agent, EDTA, which steadily increased the supersaturation as demonstrated by simulation. This condition led to ellipsoidal nanorods. As the crystal growth continued with an increasing reaction temperature of up to 150 °C, ellipsoidal nanorods transformed to prismatic nanowires. This transformation was explained by the decreasing supersaturation of the system as the growth nutrients were consumed. Microwave irradiation, the role of fluorite, and control of monodispersity for the FAP synthesis are also discussed.

The solubility and recrystallization of 1,3,5-triamino-2,4,6-trinitrobenzene in a 3-ethyl-1-methylimidazolium acetate–DMSO co-solvent system

Ionic liquids have previously been shown to dissolve strong inter- and intramolecular hydrogen-bonded solids, including natural fibers. Much of this solubility is attributed to the anions in ionic liquids, which can disrupt hydrogen bonding. We have studied the solubility and recrystallization of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a very strong inter- and intramolecular hydrogen-bonded solid, in various ionic liquid solvent systems. We discovered that acetate-based ionic liquids were the best solvents for dissolving TATB, while other anions, such as Cl−, HSO4− and NO3− showed moderate improvements in the solubility compared to conventional organic solvents. Ionic liquid–DMSO co-solvent systems were also investigated for dissolving and recrystallizing TATB.

Multiphase separation of copper nanowires

This communication reports a new method to purify copper nanowires with nearly 100% yield from undesired copper nanoparticle side-products formed during batch processes of copper nanowire synthesis. This simple separation method can yield large quantities of long, uniform, high-purity copper nanowires to meet the requirements of nanoelectronics applications as well as provide an avenue for purifying copper nanowires in the industrial scale synthesis of copper nanowires, a key step for commercialization and application of nanowires.

Synthesis and Characterization of Nanocarbon-Supported Titanium Dioxide

In this report, we describe recent efforts in fabricating new nanocarbon-supported titanium dioxide structures that exhibit high surface area and improved electrical conductivity. Nanocarbons consisting of single-walled carbon nanotubes and carbon aerogel nanoparticles were used to support titanium dioxide particles and produce monoliths with densities as low as 80 mg/cm 3 . The electrical conductivity of the nanocarbon-supported titanium dioxide was dictated by the conductivity of the nanocarbon support while the pore structure was dominated by the titanium dioxide aerogel particles. The conductivity of the monoliths presented here was 72 S/m and the surface area was 203 m 2 /g.