Nitrogen adsorption data, FIB-SEM tomography and TEM micrographs of neutron-irradiated superfine grain graphite.

This manuscript provides raw nitrogen gas adsorption data, images and videos obtained from a technique that combines Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) known as FIB-SEM tomography and Transmission Electron Microscopy (TEM) micrographs. This collection of data is useful for characterization of the effects of high fluence neutron irradiation in nuclear graphite as described in the associated manuscript, "Mesopores development in superfine grain graphite neutron-irradiated at high fluence" (Contescu et al., 2019). Nitrogen adsorption isotherms at 77 K are provided for graphite samples before and after neutron irradiation at 300, 450, and 750 °C at fluences before and after turnaround. FIB-SEM tomography reveals porosity of unirradiated and irradiated samples. Using this technique, four data sets were obtained, of which the first three are presented in video format, whereas the fourth one is a series of images provided in raw format unique to this manuscript. All microscopy data document the microstructure, surface area and porosity of superfine grain graphite G347A (Tokai Carbon, Japan) before irradiation and irradiated after turnaround at 400 °C. TEM micrographs provide unique information on irradiation damage at high neutron fluence (>27. 8 displacements per atom, dpa) in the microstructure and crystal lattice of graphite. Additional TEM micrographs are provided here, which do not duplicate the research paper published elsewhere (Contescu et al., 2019). These data sets are unique, as samples at high irradiation doses have never been measured or imaged before with the aforementioned techniques.

Crown ethers in graphene.

Crown ethers are at their most basic level rings constructed of oxygen atoms linked by two- or three-carbon chains. They have attracted attention for their ability to selectively incorporate various atoms or molecules within the cavity formed by the ring. However, crown ethers are typically highly flexible, frustrating efforts to rigidify them for many uses that demand higher binding affinity and selectivity. Here we present atomic-resolution images of the same basic structures of the original crown ethers embedded in graphene. This arrangement constrains the crown ethers to be rigid and planar. First-principles calculations show that the close similarity of the structures should also extend to their selectivity towards specific metal cations. Crown ethers in graphene offer a simple environment that can be systematically tested and modelled. Thus, we expect that our finding will introduce a new wave of investigations and applications of chemically functionalized graphene.

Lab-in-a-shell: encapsulating metal clusters for size sieving catalysis.

Here we describe a lab-in-a-shell strategy for the preparation of multifunctional core-shell nanospheres consisting of a core of metal clusters and an outer microporous silica shell. Various metal clusters (e.g., Pd and Pt) were encapsulated and confined in the void space mediated by the entrapped polymer dots inside hollow silica nanospheres acting first as complexing agent for metal ions and additionally as encapsulator for clusters, limiting growth and suppressing the sintering. The Pd clusters encapsulated in hybrid core-shell structures exhibit exceptional size-selective catalysis in allylic oxidations of substrates with the same reactive site but different molecular size (cyclohexene ∼0.5 nm, cholesteryl acetate ∼1.91 nm). The solvent-free aerobic oxidation of diverse hydrocarbons and alcohols was further carried out to illustrate the benefits of such an architecture in catalysis. High activity, outstanding thermal stability and good recyclability were observed over the core-shell nanocatalyst.

Microstructure-Dependent Gas Adsorption: Accurate Predictions of Methane Uptake in Nanoporous Carbons.

We present a framework for rapidly predicting gas adsorption properties based on van der Waals density functional calculations and thermodynamic modeling. Utilizing this model and experimentally determined pore size distributions, we are able to accurately predict uptakes in five activated carbon materials without empirical potentials or lengthy simulations. Our results demonstrate that materials with smaller pores and higher heats of adsorption can still have poor adsorption characteristics due to relatively low densities of highly adsorbent pores.

Isotope effect on adsorbed quantum phases: diffusion of H2 and D2 in nanoporous carbon.

Quasielastic neutron scattering of H(2) and D(2) in the same nanoporous carbon at 10-40 K demonstrates extreme quantum sieving, with D(2) diffusing up to 76 times faster. D(2) also shows liquidlike diffusion while H(2) exhibits Chudley-Elliott jump diffusion, evidence of their different relationships with the local lattice of adsorption sites due to quantum effects on intermolecular interactions. The onset of diffusion occurs at 22-25 K for H(2) and 10-13 K for D(2). At these temperatures, H(2) and D(2) have identical thermal de Broglie wavelengths that correlate with the dominant pore size.

Topological defects: origin of nanopores and enhanced adsorption performance in nanoporous carbon.

A scanning transmission electron microscopy investigation of two nanoporous carbon materials, wood-based ultramicroporous carbon and poly(furfuryl alcohol)-derived carbon, is reported. Atomic-resolution images demonstrate they comprise isotropic, three-dimensional networks of wrinkled one-atom-thick graphene sheets. In each graphene plane, nonhexagonal defects are frequently observed as connected five- and seven-atom rings. Atomic-level modeling shows that these topological defects induce localized rippling of graphene sheets, which interferes with their graphitic stacking and induces nanopores that lead to enhanced adsorption of H(2) molecules. The poly(furfuryl alcohol)-derived carbon contains larger regions of stacked layers, and shows significantly smaller surface area and pore volume than the ultramicroporous carbon.

Thermal treatment effects on charge storage performance of graphene-based materials for supercapacitors.

Graphene materials were synthesized by reduction of exfoliated graphite oxide and then thermally treated in nitrogen to improve the surface area and their electrochemical performance as electrical double-layer capacitor electrodes. The structural and surface properties of the prepared reduced graphite oxide (RGO) were investigated using atomic force microscopy, scanning electron microscopy, Raman spectra, X-ray diffraction pattern analysis, and nitrogen adsorption/desorption studies. RGO forms a continuous network of crumpled sheets, which consist of large amounts of few-layer and single-layer graphenes. Electrochemical studies were conducted by cyclic voltammetry, impedance spectroscopy, and galvanostatic charge-discharge measurements. The modified RGO materials showed enhanced electrochemical performance, with maximum specific capacitance of 96 F/g, energy density of 12.8 Wh/kg, and power density of 160 kW/kg. These results demonstrate that thermal treatment of RGO at selected conditions is a convenient and efficient method for improving its specific capacitance, energy, and power density.

Tetrahydrofuran-induced K and Li doping onto poly(furfuryl alcohol)-derived activated carbon (PFAC): influence on microstructure and H2 sorption properties.

We have doped poly(furfuryl alcohol)-derived activated carbon (PFAC) with two alkali metals, potassium (K) and lithium (Li), by previously reacting the metals with naphthalene in the presence of tetrahydrofuran (THF), followed by introducing them to pristine PFAC. The THF molecule causes a minor alteration of the microstructure of PFAC as confirmed by Raman spectra, X-ray diffraction, and pore textural analysis. Raman spectra and X-ray diffraction indicated a slight localized ordering toward the stacking defects of disordered carbon, as in PFAC, which can be attributed to the movement of THF molecules within the internal planes of graphene sheets. Pore textural analysis confirmed the lowering of the specific surface area and pore volume of both K- and Li-doped PFACs (BET SSA, 1378 m(2)/g (PFAC); 1252 m(2)/g (K-PFAC), 1081 m(2)/g (Li-PFAC)). Volumetric hydrogen adsorption measurements at temperatures of 298, 288, 273, and 77 K and pressures of up to 1 bar indicated the enhanced adsorption potential imposed by the presence of alkali metals, which can be reconfirmed by the elevated heats of adsorption of metal-doped PFACs (Li-PFAC, -(10-11) kJ/mol; K-PFAC, -(16-19) kJ/mol) compared to that of pristine PFAC (-9.6 kJ/mol).

Hydrogen confinement in carbon nanopores: extreme densification at ambient temperature.

In-situ small-angle neutron scattering studies of H(2) confined in small pores of polyfurfuryl alcohol-derived activated carbon at room temperature have provided for the first time its phase behavior in equilibrium with external H(2) at pressures up to 200 bar. The data were used to evaluate the density of the adsorbed fluid, which appears to be a function of both pore size and pressure and is comparable to the density of liquid H(2) in narrow nanopores at ∼200 bar. The surface-molecule interactions responsible for densification of H(2) within the pores create internal pressures that exceed the external gas pressure by a factor of up to ∼50, confirming the benefits of adsorptive storage over compressive storage. These results can be used to guide the development of new carbon adsorbents tailored for maximum H(2) storage capacities at near-ambient temperatures.