Mülheim (Ruhr), Germany
Mülheim (Ruhr), Germany

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Gu D.,Fudan University | Bongard H.,MPI fur Kohlenforschung | Meng Y.,MPI fur Kohlenforschung | Miyasaka K.,KAIST | And 10 more authors.
Chemistry of Materials | Year: 2010

Highly ordered mesoporous carbon FDU-16 rhombic dodecahedral single crystals with body-centered cubic structure (space group Im3̄m) have been successfully synthesized by employing an organic-organic assembly of triblock copolymer Pluronic F127 (EO106PO70EO106) and phenol/formaldehyde resol in basic aqueous solution. Synthetic factors (including reaction time, temperature, and stirring rate) are explored for controlling the formation of rhombic dodecahedral single crystals. The optimal stirring rate and the reaction temperature are 300 ± 10 rpm and ∼66 °C, respectively. High-resolution scanning electron microscopy (HRSEM), scanning transmission electron microscopy (STEM), and ultramicrotomy are applied to study the fine structures of the carbon single crystals. The mesopores are arranged in body-centered cubic symmetry throughout the entire particle. Surface steps are clearly observed in the {110} surface, which suggests a layer-by-layer growth of the mesoporous carbon FDU-16 single crystals. Cryo-SEM results from the reactant solution confirm the formation of resol/F127 unit micelles, further supporting the layer-by-layer growth process. The mesoporous carbon FDU-16 single crystals grow up to the final size of 2-4 μm within 2 days. These findings may have consequences for the growth mechanism of other carbon materials in aqueous solution; moreover, the high-quality single crystals also have potential applications in nanodevice technologies. © 2010 American Chemical Society.

Marlow F.,MPI fur Kohlenforschung | Marlow F.,University of Duisburg - Essen | Muldarisnur M.,Andalas University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

Self-assembly of colloidal particles is a promising approach for fabrication of three-dimensional periodic structures which are especially interesting for photonic crystals. This approach is simple and cheap, but it still suffers under the existence of many intrinsic defects. The efforts to improve the self-assembly process have led to many deposition methods with a different degree of controllability. One of the best fabrication techniques is the capillary deposition method leading to non-scattered photon propagation in the order of 80 μm. To improve understanding of the selfassembly process we investigate the stages of the process separately. The most important stage is likely the deposition of suspended particles into a dense arrangement forming a crystal. This is studied spectroscopically. Another crucial stage is the drying of colloidal crystal which is connected with a continuous shrinkage process. Several minutes after starting the drying, a surprise occurs: The system expands shortly before it shrinks monotonously until reaching its final state after about one day. We called this "v"-event because of the characteristic shape of the curve for the Bragg peak. The event is assigned to the start of a nano-dewetting process occurring at the colloidal particles. © 2016 SPIE.

Metzelthin A.,Ruhr University Bochum | Sanchez-Garcia E.,MPI fur Kohlenforschung | Sanchez-Garcia E.,Koç University | Birer A.O.,Ruhr University Bochum | And 4 more authors.
ChemPhysChem | Year: 2011

We have studied the aggregation process of (C 2H 2)⋯furan trimers at ultracold temperatures (0.37 K) in helium nanodroplets. Computational sampling of the potential energy surface using the multiple-minima-hypersurface (MMH) approach yielded seven possible minimum structures, optimized at the MP2 level of theory with the cc-pVTZ and 6-311++G(d,p) basis sets. Experimentally, we could assign five transitions in the IR spectrum of acetylene-furan aggregates in the acetylene C-H asym stretch region between 3240 and 3300 cm -1 to vibrational bands of the 2:1 acetylene-furan trimer. The transitions were assigned to three ring structures that all contain the T-shaped acetylene dimer as structural sub-motif. Two of the structures form a nonplanar ring involving a C-H Ac⋯π Fu bond, the third is a nearly planar ring containing a C-H Ac⋯O Fu bond. This assignment was corroborated by quantum mechanical/molecular dynamics (QM/MD) simulations mimicking in detail the aggregation process of precooled monomers. The simulations provided evidence for a transition from a higher level local minimum to the global minimum state over a small barrier during the aggregation process. The experimentally observed structures can be explained by a step-by-step aggregation of moieties pre-cooled to 0.37 K that are steered by intermediate and short-range electrostatic interactions. Thus, we are able to unravel a special aggregation mechanism which differs from aggregation of molecules with large dipole moments where this aggregation process is dominated by long range 1/r 3 dipole-dipole interaction ("electrostatic steering"). This mechanism is expected to be a general mechanism in ultracold chemistry. Brrrr-cold! The aggregation process of (C 2H 2)⋯furan trimers at ultracold temperatures (0.37 K) in helium nanodroplets is studied by a combination of computational and spectroscopic techniques. The results unravel a special aggregation mechanism for non- and weakly polar molecules, which is expected to be generally applicable in ultracold chemistry. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gu D.,Fudan University | Bongard H.,MPI fur Kohlenforschung | Deng Y.,Fudan University | Feng D.,Fudan University | And 6 more authors.
Advanced Materials | Year: 2010

Onionlike mesoporous carbon and carbonsilica nanocomposites with multilayer vesicle structures can be synthesized by an organic-inorganic co-assembly method under hydrothermal conditions in an aqueous emulsion solution (see figure). The nanocomposite vesicles have ordered lamellar mesostructures with about 3-9 layers and carbon pillars are located between the neighboring shells. (Chemical Equation Persentation). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

Schuth F.,MPI fur Kohlenforschung
Angewandte Chemie - International Edition | Year: 2014

Down to the last detail: Nanostructured solid catalysts were already known in the early 20th century, but their exact structure was unclear. Nowadays, the arrangement of atoms and particles in solids can be manipulated and analyzed down to the atomic scale (see image). The use of specific highly active catalysts enables industrially relevant reactions to be performed at room temperature. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schuth F.,MPI fur Kohlenforschung
Physica Status Solidi (B) Basic Research | Year: 2013

The strong influence of the support properties on the activity of gold catalysts has been observed in many publications. The most studied reaction in this respect seems to be CO-oxidation, for which gold catalysts have outstanding activity. However, since in most studies the support properties are also important in influencing the nature of the gold particles deposited on them by co-precipitation or deposition-precipitation, it is difficult to study the support effect alone. We have in a series of studies used colloidal impregnation of preformed gold particles approximately 3nm in size on different supports in order to decouple the gold particle formation from the deposition process, in order to isolate the support effect. Even for such similarly prepared catalysts very strong differences between different supports were observed. The analysis of the data, also in the light of literature data, suggests that there is no unique factor explaining the high activity of gold catalysts, but rather a combination of effects, which act in different proportion for different catalysts. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Galeano C.,MPI fur Kohlenforschung | Baldizzone C.,MPI fur Eisenforschung | Bongard H.,MPI fur Kohlenforschung | Spliethoff B.,MPI fur Kohlenforschung | And 4 more authors.
Advanced Functional Materials | Year: 2014

The synthesis of yolk-shell catalysts, consisting of platinum or gold-platinum cores and graphitic carbon shells, and their electrocatalytic stabilities are described. Different encapsulation pathways for the metal nanoparticles are explored and optimized. Electrochemical studies of the optimized AuPt, @C catalyst revealed a high stability of the encapsulated metal particles. However, in order to reach full activity, several thousand potential cycles are required. After the electrochemical surface area is fully developed, the catalysts show exceptionally high stability, with almost no degradation over approximately 30 000 potential cycles between 0.4 and 1.4 VRHE. Encapsulation of noble metals in graphitic hollow shells by hard templating is explored as a means for stabilizing fuel cell catalysts. Small platinum particles can be encapsulated, but the achievable loading is too small. Encapsulation of Au-Pt yolk-shell particles allows higher loading, and with such cores, stable catalysts could be produced. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Schuth F.,MPI fur Kohlenforschung | Palkovits R.,MPI fur Kohlenforschung | Schlogl R.,Fritz Haber Institute | Su D.S.,Fritz Haber Institute
Energy and Environmental Science | Year: 2012

The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered. This journal is © 2012 The Royal Society of Chemistry.

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