Showing papers by "Kwang S. Kim published in 2013"
TL;DR: This review deals with wide-ranging environmental studies of graphene-based materials on the adsorption of hazardous materials and photocatalytic degradation of pollutants for water remediation and the physisorption, chemisor adaptation, reactive adsorptive, and separation for gas storage.
Abstract: This review deals with wide-ranging environmental studies of graphene-based materials on the adsorption of hazardous materials and photocatalytic degradation of pollutants for water remediation and the physisorption, chemisorption, reactive adsorption, and separation for gas storage. The environmental and biological toxicity of graphene, which is an important issue if graphene composites are to be applied in environmental remediation, is also addressed.
453 citations
TL;DR: In this paper, the authors provide a comprehensive review of the experimental work that is devoted to understanding the fundamental problems and recent progress in the development of anode and cathode catalysts for DMFCs.
399 citations
TL;DR: In this paper, a 3D reduced graphene oxide (RGO)-based hydrogels were synthesized by the reduction of graphene oxide using sodium ascorbate and showed a large surface area, and a uniform pore size distribution.
398 citations
TL;DR: The synthesis of platinum clusters (diameter ≤1.4 nm) deposited on genomic double-stranded DNA–graphene oxide composites and their high-performance electrocatalysis of the oxygen reduction reaction are reported.
Abstract: Platinum nanoclusters are well-known catalysts for the oxygen reduction reaction, although the performance of clusters smaller than 2 nm is poorly studied. Here, the authors report 1.4 nm platinum clusters supported on DNA–graphene oxide composites and demonstrate promising electrochemical activity and stability.
173 citations
TL;DR: In this article, a solid-state complex utilizing non-covalent interactions between two aromatic cations is synthesized and characterized, and the X-ray study of the structure shows that the anion templated π+−π+ interactions are the major driving force in the crystal packing.
Abstract: A solid-state complex utilizing non-covalent interactions between two aromatic cations is synthesized and characterized. The X-ray study of the structure shows that the anion templated π+–π+ interactions are the major driving force in the crystal packing, while π+–π, π–π, π–anion and π+–anion interactions assist the overall stabilization of self-assembly. In addition, we also identify the cation-mediated non-covalent interaction between two π anions (π−–π− interaction). The interaction energies of the important driving forces (π+–π+, π+–π, π–anion, π+–anion, and π−–π− interactions) observed in the crystal structure are calculated using dispersion-corrected density functional theory (DFT-D).
126 citations
TL;DR: The effective methods to induce weak ferromagnetism in pristine MoS2 persisting up to room temperature with the improved transport property, which would lead to new spintronics devices.
Abstract: We report the effective methods to induce weak ferromagnetism in pristine ${\mathrm{MoS}}_{2}$ persisting up to room temperature with the improved transport property, which would lead to new spintronics devices. The hydrogenation of ${\mathrm{MoS}}_{2}$ by heating at $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ for 1 h leads to the easy axis out of plane, while the irradiation of proton with a dose of $1\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }\text{ }\mathrm{P}/{\mathrm{cm}}^{2}$ leads to the easy axis in plane. The theoretical modeling supports such magnetic easy axes.
115 citations
TL;DR: The quadruply/quintuply charged imidazole-based homo-calix compounds, calix[4/5]imidazolium, are reported, which recognize neutral fullerenes through π+–π interactions and makes them soluble in water, which could be useful in fullerene chemistry.
Abstract: Only two types of neutral homo-calix compounds, including analogues, have been reported Chun et al now describe a new class of positively charged calix[n]imidazolium, which is synthesized in one pot and is able to recognize anions and fullerenes in aqueous media
86 citations
TL;DR: Fluorescence image detection of RNA in living cells such as onion cells, HeLa cells, and animal model cells was successfully demonstrated which displays a chelation-enhanced fluorescence effect.
Abstract: A water-soluble imidazolium-based fluorescent chemosensor senses RNA selectively through fluorescence enhancement over other biologically relevant biomolecules in aqueous solution at physiological pH 7.4. Fluorescence image detection of RNA in living cells such as onion cells, HeLa cells, and animal model cells was successfully demonstrated which displays a chelation-enhanced fluorescence effect. These affinities can be attributed to the strong electrostatic (C–H)+···A– ionic H-bonding and the aromatic moiety driven π-stacking of imidazolium-based cyclophane with the size-complementary major groove of RNA.
84 citations
TL;DR: The as formed material shows that graphene can be uniformly N-doped using the presented synthetic method and displays selectivity towards CO2 adsorption compared to H2, N2, Ar or CH4.
Abstract: For effective adsorption of carbon dioxide (CO2), we investigate a porous N functionalized graphene adsorbent produced by the chemical activation of a reduced graphene oxide/polyaniline composite. The N-doped graphene composite is microporous with a maximum BET surface area of 1336 m2 g−1. It shows a highly reversible maximum CO2 storage capacity of 2.7 mmol g−1 at 298 K and 1 atm (5.8 mmol g−1 at 273 K and 1 atm). The N-doped graphene shows good stability during recycling with only an initial decrease of 10% (3–2.7 mmol g−1) in adsorption capacity before attaining a cycling equilibrium. The adsorbance capacity is correlated with N content × pore volume or N content × surface area. Given that there is no proper correlation parameter, these factors can be used to increase the CO2 adsorption capacity of N-doped graphene materials for practical utility. The as synthesized material also displays selectivity towards CO2 adsorption compared to H2, N2, Ar or CH4. The as formed material shows that graphene can be uniformly N-doped using the presented synthetic method.
82 citations
TL;DR: The synthesis of PtDs on genomic-double-stranded-DNA/reduced-graphene-oxide (gdsDNA/rGO) by the NaBH4 reduction of H(2)PtCl(6) in the presence of plant gdsDNA is reported, which exhibits a highly stable mass activity for the ORR over a wide pH range of 1-13.
Abstract: Controlling the morphology and size of platinum nanodendrites (PtDs) is a key factor in improving their catalytic activity and stability. Here, we report the synthesis of PtDs on genomic-double-stranded-DNA/reduced-graphene-oxide (gdsDNA/rGO) by the NaBH4 reduction of H2PtCl6 in the presence of plant gdsDNA. Compared to industrially adopted catalysts (i.e., state-of-the-art Pt/C catalyst, Pt/rGO, Pt3Co, etc.), the as-synthesized PtDs/gdsDNA/rGO hybrid displays very high oxygen reduction reaction (ORR) catalytic activities (much higher than the 2015 U.S. Department of Energy (DOE) target values), which are the rate-determining steps in electrochemical energy devices, in terms of onset-potential, half-wave potential, specific-activity, mass-activity, stability, and durability. Moreover, the hybrid exhibits a highly stable mass activity for the ORR over a wide pH range of 1–13. These exceptional properties would make the hybrid applicable in next-generation electrochemical energy devices.
79 citations
TL;DR: Microporous carbon materials used for CO₂ capture were synthesized by the chemical activation of polyindole nanofibers at temperatures from 500 to 800 °C using KOH, which resulted in nitrogen (N)-doped carbon materials, which remained remarkably stable even after 10 cycles.
Abstract: Adsorption with solid sorbents is considered to be one of the most promising methods for the capture of carbon dioxide (CO2) from power plant flue gases. In this study, microporous carbon materials used for CO2 capture were synthesized by the chemical activation of polyindole nanofibers (PIF) at temperatures from 500 to 800 °C using KOH, which resulted in nitrogen (N)-doped carbon materials. The N-doped carbon materials were found to be microporous with an optimal adsorption pore size for CO2 of 0.6 nm and a maximum (Brunauer–Emmett–Teller) BET surface area of 1185 m2 g–1. The PIF activated at 600 °C (PIF6) has a surface area of 527 m2 g–1 and a maximum CO2 storage capacity of 3.2 mmol g–1 at 25 °C and 1 bar. This high CO2 uptake is attributed to its highly microporous character and optimum N content. Additionally, PIF6 material displays a high CO2 uptake at low pressure (1.81 mmol g–1 at 0.2 bar and 25 °C), which is the best low pressure CO2 uptake reported for carbon-based materials. The adsorption capa...
TL;DR: First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.
Abstract: Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.
TL;DR: The complexes of a DNA base bound to graphitic systems are studied and the optB86b nonlocal functional and the Tkatchenko-Scheffler functional are used to study the binding energies of nucleobases on graphene.
Abstract: The complexes of a DNA base bound to graphitic systems are studied. Considering naphthalene as the simplest graphitic system, DNA base−naphthalene complexes are scrutinized at high levels of ab initio theory including coupled cluster theory with singles, doubles, and perturbative triples excitations (CCSD(T)) at the complete basis set (CBS) limit. The stacked configurations are the most stable, where the CCSD(T)/CBS binding energies of guanine, adenine, thymine, and cytosine are 9.31, 8.48, 8.53, 7.30 kcal/mol, respectively. The energy components are investigated using symmetry-adapted perturbation theory based on density functional theory including the dispersion energy. We compared the CCSD(T)/CBS results with several density functional methods applicable to periodic systems. Considering accuracy and availability, the optB86b nonlocal functional and the Tkatchenko−Scheffler functional are used to study the binding energies of nucleobases on graphene. The predicted values are 18−24 kcal/mol, though many-body effects on screening and energy need to be further considered.
TL;DR: PIG6, a polyindole-reduced graphene oxide (PIG) hybrid, shows high adsorption selectivity ratios for CO2 over N2, CH4 and H2 of 23, 4 and 85 at 25 °C, respectively.
Abstract: A polyindole-reduced graphene oxide (PIG) hybrid was synthesized by reducing graphene oxide sheets in the presence of polyindole. We have shown PIG as a material for capturing carbon dioxide (CO2). The PIG hybrid was chemically activated at temperatures of 400–800 ° C, which resulted in nitrogen (N)-doped graphene sheets. The N-doped graphene sheets are microporous with an adsorption pore size of 0.6 nm for CO2 and show a maximum (Brunauer, Emmet and Teller) surface area of 936 m2 g−1. The hybrid activated at 600 ° C (PIG6) possesses a surface area of 534 m2 g−1 and a micropore volume of 0.29 cm3 g−1. PIG6 shows a maximum CO2 adsorption capacity of 3.0 mmol g−1 at 25 ° C and 1 atm. This high CO2 uptake is due to the highly microporous character of the material and its N content. The material retains its original adsorption capacity on recycling even after 10 cycles (within experimental error). PIG6 also shows high adsorption selectivity ratios for CO2 over N2, CH4 and H2 of 23, 4 and 85 at 25 ° C, respectively.
TL;DR: The thermal response of the conductance could be utilized to maintain a certain degree of p-doping of monolayer graphene, which provides the facile, sustainable, and controllable large-area doping method of graphene for future generation of printed flexible electronics.
Abstract: Here, we report a substrate-induced intercalation phenomenon of an organic solvent at the interface between monolayer graphene and a target substrate. A simple dipping of the transferred chemical vapor deposition (CVD)-grown graphene on the SiO2 substrate into chloroform (CHCl3, CF), a common organic solvent, induces a spontaneous formation of CF clusters beneath the basal plane of the graphene as well as inside the wrinkles. The microscopic and spectroscopic observations showed the doping behavior of monolayer graphene, which indicates the adsorption of CF to monolayer graphene. Interestingly, the intercalated organic solvent showed remarkable stability for over 40 days under ambient conditions. To reveal the underlying mechanism of the stable solvent intercalation, desorption energy of CF molecules at the graphene/substrate interface was measured using Arrhenius plots of the conductance change upon time and temperature. Two stages of solvent intercalations with high desorption energies (70 and 370 meV) ...
TL;DR: It is found that nearly parallel stacked forms are the minimum energy structure for benzene to pyrene excimers and the equilibrium layer-to-layer distance for bilayer-long arenes in the first singlet excited state, which is predicted to be bound.
Abstract: Excited dimers (excimers) formed by aromatic molecules are important in biological systems as well as in chemical sensing. The structure of many biological systems is governed by excimer formation. Since theoretical studies of such systems provide important information about mutual arrangement of aromatic molecules in structural biology, we carried out extensive calculations on the benzene excimer using EOM-CCSD, RI-CC2, CASPT2, and TD-DFT approaches. For the benzene excimer, we evaluate the reliability of the TD-DFT method based on the B3LYP, PBE, PBE0, and ωPBEh functionals. We extended the calculations to naphthalene, anthracene, and pyrene excimers. We find that nearly parallel stacked forms are the minimum energy structure. On the basis of the benzene to pyrene excimers, we might roughly estimate the equilibrium layer-to-layer distance for bilayer-long arenes in the first singlet excited state, which is predicted to be bound.
TL;DR: To understand the ionization process of water clusters, DFT‐ and MP2‐based Born‐Oppenheimer MD (BOMD) simulations are performed on ionization, and some functionals are found to be reliable, in reasonable agreement with high‐level ab initio results.
Abstract: Despite utmost importance in understanding water ionization process, reliable theoretical results of structural changes and molecular dynamics (MD) of water clusters on ionization have hardly been reported yet. Here, we investigate the water cations [(H2O)n = 2–6+] with density functional theory (DFT), Moller–Plesset second-order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The complete basis set limits of interaction energies at the CCSD(T) level are reported, and the geometrical structures, electronic properties, and infrared spectra are investigated. The characteristics of structures and spectra of the water cluster cations reflect the formation of the hydronium cation moiety (H3O+) and the hydroxyl radical. Although most density functionals fail to predict reasonable energetics of the water cations, some functionals are found to be reliable, in reasonable agreement with high-level ab initio results. To understand the ionization process of water clusters, DFT- and MP2-based Born-Oppenheimer MD (BOMD) simulations are performed on ionization. On ionization, the water clusters tend to have an Eigen-like form with the hydronium cation instead of a Zundel-like form, based on reliable BOMD simulations. For the vertically ionized water hexamer, the relatively stable (H2O)5+ (5sL4A) cluster tends to form with a detached water molecule (H2O). © 2013 Wiley Periodicals, Inc.
TL;DR: A Monte Carlo integration of the second-order many-body perturbation (MP2) corrections to energies and self-energies eliminates the usual computational bottleneck of the MP2 algorithm, thereby achieving near-linear size dependence of its operation cost, a negligible core and disk memory cost, and a naturally parallel computational kernel.
Abstract: A Monte Carlo (MC) integration of the second-order many-body perturbation (MP2) corrections to energies and self-energies eliminates the usual computational bottleneck of the MP2 algorithm (i.e., the basis transformation of two-electron integrals), thereby achieving near-linear size dependence of its operation cost, a negligible core and disk memory cost, and a naturally parallel computational kernel. In this method, the correlation correction expressions are recast into high-dimensional integrals, which are approximated as the sums of integrands evaluated at coordinates of four electron random walkers guided by a Metropolis algorithm for importance sampling. The gravest drawback of this method, however, is the inevitable statistical uncertainties in its results, which decay slowly as the inverse square-root of the number of MC steps. We propose an algorithm that can increase the number of MC sampling points in each MC step by many orders of magnitude by having 2m electron walkers (m > 2) and then using m(m - 1)/2 permutations of their coordinates in evaluating the integrands. Hence, this algorithm brings an O(m(2))-fold increase in the number of MC sampling points at a mere O(m) additional cost of propagating redundant walkers, which is a net O(m)-fold enhancement in sampling efficiency. We have demonstrated a large performance increase in the Monte Carlo MP2 calculations for the correlation energies of benzene and benzene dimer as well as for the correlation corrections to the energy, ionization potential, and electron affinity of C60. The calculation for C60 has been performed with a parallel implementation of this method running on up to 400 processors of a supercomputer, yielding an accurate prediction of its large electron affinity, which makes its derivative useful as an electron acceptor in bulk heterojunction organic solar cells.
TL;DR: New fluorescent benzimidazolium-based receptors selectively display the effective fluorescence quenching effect for biologically important anions, GTP and I(-), in aqueous solution of physiological pH 7.4.
Abstract: New fluorescent benzimidazolium-based receptors selectively display the effective fluorescence quenching effect for biologically important anions, GTP and I−, in aqueous solution of physiological pH 7.4. These affinities can be attributed to the strong ionic H-bonding along with additional interactions of fluorophore moieties with the nucleic base of GTP and I−.
TL;DR: The quasiparticle energies of small molecules have been reproduced within a few mEh of the correct values with 10(8) Monte Carlo steps, and Linear-to-quadratic scaling of the size dependence of computational cost is demonstrated even for these small molecules.
Abstract: A stochastic method is proposed that evaluates the second-order perturbation corrections to the Dyson self-energies of a molecule (i.e., quasiparticle energies or correlated ionization potentials and electron affinities) directly and not as small differences between two large, noisy quantities. With the aid of a Laplace transform, the usual sum-of-integral expressions of the second-order self-energy in many-body Green's function theory are rewritten into a sum of just four 13-dimensional integrals, 12-dimensional parts of which are evaluated by Monte Carlo integration. Efficient importance sampling is achieved with the Metropolis algorithm and a 12-dimensional weight function that is analytically integrable, is positive everywhere, and cancels all the singularities in the integrands exactly and analytically. The quasiparticle energies of small molecules have been reproduced within a few mEh of the correct values with 108 Monte Carlo steps. Linear-to-quadratic scaling of the size dependence of computationa...
TL;DR: In this paper, angle-resolved photo-emission spectroscopy was used to study the interaction between graphene and Cu substrates and showed that the electron transfer was limited to that between the Shockley surface state of Cu(111) and the π band of graphene.
Abstract: Copper is considered to be the most promising substrate for the growth of high-quality and large area graphene by chemical vapor deposition (CVD), in particular, on the (111) facet. Because the interactions between graphene and Cu substrates influence the orientation, quality, and properties of the synthesized graphene, we studied the interactions using angle-resolved photoemission spectroscopy. The evolution of both the Shockley surface state of the Cu(111) and the π band of the graphene was measured from the initial stage of CVD growth to the formation of a monolayer. Graphene growth was initiated along the Cu(111) lattice, where the Dirac band crossed the Fermi energy (EF) at the K point without hybridization with the d-band of Cu. Then two rotated domains were additionally grown as the area covered with graphene became wider. The Dirac energy was about −0.4 eV and the energy of the Shockley surface state of Cu(111) shifted toward the EF by ∼0.15 eV upon graphene formation. These results indicate weak interactions between graphene and Cu, and that the electron transfer is limited to that between the Shockley surface state of Cu(111) and the π band of graphene. This weak interaction and slight lattice mismatch between graphene and Cu resulted in the growth of rotated graphene domains (9.6° and 8.4°), which showed no significant differences in the Dirac band with respect to different orientations. These rotated graphene domains resulted in grain boundaries which would hinder a large-sized single monolayer growth on Cu substrates.
TL;DR: The resulting TES-ADT FETs using cleaned graphene source/drain electrodes exhibited a superior device performance compared to devices using as-transferred graphene electrodes, with mobilities as high as 1.38 cm(2) V(-1) s(-1).
Abstract: Graphene has shown great potential as an electrode material for organic electronic devices such as organic field-effect transistors (FETs) because of its high conductivity, thinness, and good compatibility with organic semiconductor materials. To achieve high performance in graphene-based organic FETs, favorable molecular orientation and good crystallinity of organic semiconductors on graphene are desired. This strongly depends on the surface properties of graphene. Here, we investigate the effects of polymer residues that remain on graphene source/drain electrodes after the transfer/patterning processes on the self-organizing properties and field-effect characteristics of the overlying solution-processed triethylsilylethynyl-anthradithiophene (TES-ADT). A solvent-assisted polymer residue removal process was introduced to effectively remove residues or impurities on the graphene surface. Unlike vacuum-deposited small molecules, TES-ADT displayed a standing-up molecular assembly, which facilitates lateral charge transport, on both the residue-removed clean graphene and as-transferred graphene with polymer residues. However, TES-ADT films grown on the cleaned graphene showed a higher crystallinity and larger grain size than those on the as-transferred graphene. The resulting TES-ADT FETs using cleaned graphene source/drain electrodes therefore exhibited a superior device performance compared to devices using as-transferred graphene electrodes, with mobilities as high as 1.38 cm2 V−1 s−1.
TL;DR: Highly adhesive properties of graphene grain boundaries to permanganate lead to a very quick, easy and convenient method to visualize the grain boundaries simply using an optical microscope, which would be vital to improve specific propertiesof graphene.
TL;DR: Using macroscopic hydrogels of water-intercalated metal-oxide/graphene platelets is a novel approach to produce microscopic hydrogel with extraordinary surface accessibility and electronic properties as discussed by the authors.
Abstract: Preventing the π–π restacking of graphene-based platelets is essential to advance their fundamental attributes in a wide range of scalable chemical processes. Using macroscopic hydrogels of water-intercalated metal-oxide/graphene platelets is a novel approach to produce microscopic hydrogels with extraordinary surface accessibility and electronic properties. Nanoparticle decoration and surface hydration prevent irreversible π–π stacking, paving the way for reversible self-assembly and aqueous-phase exfoliation. The hydrophilic nanoparticle coating facilitates the colloidal stability of hybrid microgels in aqueous and organic media without the assistance of surfactants. This allows these materials to versatilely function as basic building blocks as well as applied nanomaterials in wet-chemistry applications. The preservation of unique properties of SnO2-decorated graphene platelets leads to significantly enhanced adsorptive and photocatalytic activities. By exploiting the fluorescence quenching effect, a dye–hydrogel complex can be utilized as a supramolecular sensor for sensitive DNA detection. This study also initiates an innovative synthetic strategy to synthesize high-quality graphene-based nanomaterials.
TL;DR: In this article, the van der Waals interactions between semiconducting and metallic single-walled carbon nanotubes (SWNTs) were investigated and it was shown that a K atom binds the SWNTs more strongly than a K+ ion.
Abstract: Despite intense studies of carbon nanotubes for decades, the separation of semiconducting and metallic single-walled carbon nanotubes (SWNTs) remains to be one of the most important tasks to be resolved. Here we demonstrate that a K atom binds the semiconducting SWNTs more strongly than the metallic SWNTs, while this binding strength hierarchy is reversed for a K+ ion, consistent with experimental reports. This was shown by first-principles calculations, which properly describe the van der Waals interactions, and the origin of such results is explained. These results could be exploited as useful guidance toward separating semiconducting and metallic SWNTs via noncovalent functionalization.
TL;DR: A simple but efficient method to fabricate versatile graphene nanonet (GNN)-devices which were comprised of continuous networks of graphene nanoribbons (GNRs) with chemical functional groups on their edges with high mobility and low noise.
Abstract: We report a simple but efficient method to fabricate versatile graphene nanonet (GNN)-devices. In this method, networks of V2O5 nanowires (NWs) were prepared in specific regions of single-layer graphene, and the graphene layer was selectively etched via a reactive ion etching method using the V2O5 NWs as a shadow mask. The process allowed us to prepare large scale patterns of GNN structures which were comprised of continuous networks of graphene nanoribbons (GNRs) with chemical functional groups on their edges. The GNN can be easily functionalized with biomolecules for fluorescent biochip applications. Furthermore, electrical channels based on GNN exhibited a rather high mobility and low noise compared with other network structures based on nanostructures such as carbon nanotubes, which was attributed to the continuous connection of nanoribbons in GNN structures. As a proof of concept, we built DNA sensors based on GNN channels and demonstrated the selective detection of DNA. Since our method allows us to prepare high-performance networks of GNRs over a large surface area, it should open up various practical biosensing applications.
TL;DR: In this article, Hanji fiber-filter sheets using replacement liquid in water-swollen fiber with non-polar solvent such as ethanol, methanol and pentane were used.
Abstract: : The purposes of this study are to prepare Hanji fiber-filter sheets using replacement liquid in water-swollen fiber with non-polar solvent such as ethanol, methanol and pentane. The experiments were studied on the selection of optimal non-polar solvent and the optimal drying method for wetted fiber and then were to know physicochemical characteristics of prepared Hanji fiber-filter sheet. The Ethanol as liquid changer in water-swollen fiber was excellent solvent and the optimal drying method for them was freeze drying served with vacuum pump. The bulk density and porosity of prepared fiber sheet from freeze dryer were 0.11-0.13 g/mL, half of natural dried fiber sheet, and 90%, respectively. The results of SEM observation for the fiber sheet prepared with natural drying or heating drying were shown very close structure of fiber wall in dry state. However, the freeze drying sheet were shown the open structure. So, the head loss of freeze drying sheet was very lower than natural drying and heating drying sheets. From the results of BTEX removal experiments, the sheets dried at water wetted condition was shown more higher efficiency than the fiber sheets dried at solvent wetted condition.
01 Aug 2013
TL;DR: Results indicate weak interactions between graphene and Cu, and that the electron transfer is limited to that between the Shockley surface state of Cu(111) and the π band of graphene.
Abstract: Copper is considered to be the most promising substrate for the growth of high-quality and large area graphene by chemical vapor deposition (CVD), in particular, on the (111) facet. Because the interactions between graphene and Cu substrates influence the orientation, quality, and properties of the synthesized graphene, we studied the interactions using angle-resolved photoemission spectroscopy. The evolution of both the Shockley surface state of the Cu(111) and the π band of the graphene was measured from the initial stage of CVD growth to the formation of a monolayer. Graphene growth was initiated along the Cu(111) lattice, where the Dirac band crossed the Fermi energy (EF) at the K point without hybridization with the d-band of Cu. Then two rotated domains were additionally grown as the area covered with graphene became wider. The Dirac energy was about -0.4 eV and the energy of the Shockley surface state of Cu(111) shifted toward the EF by ~0.15 eV upon graphene formation. These results indicate weak interactions between graphene and Cu, and that the electron transfer is limited to that between the Shockley surface state of Cu(111) and the π band of graphene. This weak interaction and slight lattice mismatch between graphene and Cu resulted in the growth of rotated graphene domains (9.6° and 8.4°), which showed no significant differences in the Dirac band with respect to different orientations. These rotated graphene domains resulted in grain boundaries which would hinder a large-sized single monolayer growth on Cu substrates.
TL;DR: The growth mechanism of CHQ nanostructures is proposed based on thermodynamic and kinetic model studies and theoretical simulations and provides a route to shape-engineering of new nanomaterials.
Abstract: Harnessing the self-assembly of organic molecules for the synthesis of arbitrarily structured nanomaterials with diverse physical and chemical properties is undoubtedly one of the most important goals of nanotechnology research. Although performed with ease in Nature, our ability to artificially shape-engineer self-assembled materials in the laboratory remains limited to a known set of precursor molecules that assemble to a few well-known topologies. Currently lacking are materials from which a diverse range of structural topologies can be chosen and extracted from the synthesis process by careful control of the external parameters of the growth conditions. Self-assembly of organic molecules is largely guided by the interplay of intermolecular noncovalent interactions. The strength of these interactions is comparable across both the solution and solid phase. This results in a dynamic equilibrium that may enable the shapes of self-assembled structures to be controlled and optimized into their thermodynamically or kinetically favored morphologies. Here we show the shape control of electroand photochemically active calix[4]hydroquinone (CHQ) into nanoplates, -polygons and -tubes and their dynamic conversion into nanospheres and -hemispheres through a subsequent anisotropic growth phase to form thermodynamically more stable structures. We propose the growth mechanism of CHQ nanostructures based on thermodynamic and kinetic model studies and theoretical simulations. This understanding provides a route to shape-engineering of new nanomaterials. These CHQ nanostructures can be implemented as nanolenses for high-resolution optical imaging or form dielectric templates for a diverse range of metal-coated highly tunable plasmonic materials without the need for additional reducing agents. The self-assembly of CHQ molecules shows the structural versatility of calixarene motifs capable of forming various intermolecular structures when combined with solvent and guest molecules. CHQ consists of four hydroquinone subunits where there are four inner OH groups to stabilize the cone shape of CHQ through the circular proton-tunneling resonance; the other OH groups and aromatic rings contribute to intermolecular interactions (see the Supporting Information). Thus, a CHQ molecule has eight hydrogen bond donors, eight receptors, and four p–p stacking pairs leading to the formation of self-assembled supramolecular structures. Figure 1 shows the CHQ nanostructures with