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- ItemMicrogravity Removes Reaction Limits from Nonpolar Nanoparticle Agglomeration(Weinheim : Wiley-VCH, 2022) Pyttlik, Andrea; Kuttich, Björn; Kraus, TobiasGravity can affect the agglomeration of nanoparticles by changing convection and sedimentation. The temperature-induced agglomeration of hexadecanethiol-capped gold nanoparticles in microgravity (µ g) is studied at the ZARM (Center of Applied Space Technology and Microgravity) drop tower and compared to their agglomeration on the ground (1 g). Nonpolar nanoparticles with a hydrodynamic diameter of 13 nm are dispersed in tetradecane, rapidly cooled from 70 to 10 °C to induce agglomeration, and observed by dynamic light scattering at a time resolution of 1 s. The mean hydrodynamic diameters of the agglomerates formed after 8 s in microgravity are 3 times (for low initial concentrations) to 5 times (at high initial concentrations) larger than on the ground. The observations are consistent with an agglomeration process that is closer to the reaction limit on thground and closer to the diffusion limit in microgravity.
- ItemAmbient Hydrogenation and Deuteration of Alkenes Using a Nanostructured Ni-Core-Shell Catalyst(Weinheim : Wiley-VCH, 2021) Gao, Jie; Ma, Rui; Feng, Lu; Liu, Yuefeng; Jackstell, Ralf; Jagadeesh, Rajenahally V.; Beller, MatthiasA general protocol for the selective hydrogenation and deuteration of a variety of alkenes is presented. Key to success for these reactions is the use of a specific nickel-graphitic shell-based core–shell-structured catalyst, which is conveniently prepared by impregnation and subsequent calcination of nickel nitrate on carbon at 450 °C under argon. Applying this nanostructured catalyst, both terminal and internal alkenes, which are of industrial and commercial importance, were selectively hydrogenated and deuterated at ambient conditions (room temperature, using 1 bar hydrogen or 1 bar deuterium), giving access to the corresponding alkanes and deuterium-labeled alkanes in good to excellent yields. The synthetic utility and practicability of this Ni-based hydrogenation protocol is demonstrated by gram-scale reactions as well as efficient catalyst recycling experiments. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH
- ItemCobalt Single-Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid(Weinheim : Wiley-VCH, 2020) Li, Xiang; Surkus, Annette-Enrica; Rabeah, Jabor; Anwar, Muhammad; Dastigir, Sarim; Junge, Henrik; Brückner, Angelika; Beller, MatthiasMetal–organic framework (MOF)-derived Co-N-C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co-N-C catalyst achieves superior activity, better acid resistance, and improved long-term stability compared with nanoparticles synthesized by a similar route. High-angle annular dark-field–scanning transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and X-ray absorption fine structure characterizations reveal the formation of CoIINx centers as active sites. The optimal low-cost catalyst is a promising candidate for liquid H2 generation. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
- ItemFour-Dimensional Deoxyribonucleic Acid–Gold Nanoparticle Assemblies(Weinheim : Wiley-VCH, 2020) Luo, Ming; Xuan, Mingjun; Huo, Shuaidong; Fan, Jilin; Chakraborty, Gurudas; Wang, Yixi; Zhao, Hui; Herrmann, Andreas; Zheng, LifeiOrganization of gold nanoobjects by oligonucleotides has resulted in many three-dimensional colloidal assemblies with diverse size, shape, and complexity; nonetheless, autonomous and temporal control during formation remains challenging. In contrast, living systems temporally and spatially self-regulate formation of functional structures by internally orchestrating assembly and disassembly kinetics of dissipative biomacromolecular networks. We present a novel approach for fabricating four-dimensional gold nanostructures by adding an additional dimension: time. The dissipative character of our system is achieved using exonuclease III digestion of deoxyribonucleic acid (DNA) fuel as an energy-dissipating pathway. Temporal control over amorphous clusters composed of spherical gold nanoparticles (AuNPs) and well-defined core–satellite structures from gold nanorods (AuNRs) and AuNPs is demonstrated. Furthermore, the high specificity of DNA hybridization allowed us to demonstrate selective activation of the evolution of multiple architectures of higher complexity in a single mixture containing small and larger spherical AuNPs and AuNRs. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA
- ItemA Tunable Polymer–Metal Based Anti-Reflective Metasurface(Weinheim : Wiley-VCH, 2020) Brasse, Yannic; Ng, Charlene; Magnozzi, Michele; Zhang, Heyou; Mulvaney, Paul; Fery, Andreas; Gómez, Daniel E.Anti-reflective surfaces are of great interest for optical devices, sensing, photovoltaics, and photocatalysis. However, most of the anti-reflective surfaces lack in situ tunability of the extinction with respect to wavelength. This communication demonstrates a tunable anti-reflective surface based on colloidal particles comprising a metal core with an electrochromic polymer shell. Random deposition of these particles on a reflective surface results in a decrease in the reflectance of up to 99.8% at the localized surface plasmon resonance frequency. This narrow band feature can be tuned by varying the pH or by application of an electric potential, resulting in wavelength shifts of up to 30 nm. Electrophoretic particle deposition is shown to be an efficient method for controlling the interparticle distance and thereby further optimizing the overall efficiency of the anti-reflective metasurface. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemTailoring Plasmonics of Au@Ag Nanoparticles by Silica Encapsulation(Weinheim : Wiley-VCH, 2021) Schultz, Johannes; Kirner, Felizitas; Potapov, Pavel; Büchner, Bernd; Lubk, Axel; Sturm, Elena V.Hybrid metallic nanoparticles (NPs) encapsulated in oxide shells are currently intensely studied for plasmonic applications in sensing, medicine, catalysis, and photovoltaics. Here, a method for the synthesis of Au@Ag@SiO2 cubes with a uniform silica shell of variable and adjustable thickness in the nanometer range is introduced and their excellent, highly reproducible, and tunable optical response is demonstrated. Varying the silica shell thickness, the excitation energies of the single NP plasmon modes can be tuned in a broad spectral range between 2.55 and 3.25 eV. Most importantly, a strong coherent coupling of the surface plasmons is revealed at the silver–silica interface with Mie resonances at the silica–vacuum interface leading to a significant field enhancement at the encapsulated NP surface in the range of 100% at shell thicknesses t ≃ 20 nm. Consequently, the synthesis method and the field enhancement open pathways to a widespread use of silver NPs in plasmonic applications including photonic crystals and may be transferred to other non-precious metals. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
- ItemInfluence of Nanoparticle Processing on the Thermoelectric Properties of (BixSb1−X)2Te3 Ternary Alloys(Weinheim : Wiley-VCH, 2021) Salloum, Sarah; Bendt, Georg; Heidelmann, Markus; Loza, Kateryna; Bayesteh, Samaneh; Izadi, M. Sepideh; Patrick, Kawulok; He, Ran; Schlörb, Heike; Perez, Nicolas; Reith, Heiko; Nielsch, Kornelius; Schierning, Gabi; Schulz, StephanThe synthesis of phase‐pure ternary solutions of tetradymite‐type materials (BixSb1−x)2Te3 (x=0.25; 0.50; 0.75) in an ionic liquid approach has been carried out. The nanoparticles are characterized by means of energy‐dispersive X‐ray spectroscopy (EDX), powder X‐ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy. In addition, the role of different processing approaches on the thermoelectric properties ‐ Seebeck coefficient as well as electrical and thermal conductivity ‐ is demonstrated.
- ItemSelective Hydrogenation and Hydrodeoxygenation of Aromatic Ketones to Cyclohexane Derivatives Using a Rh@SILP Catalyst(Weinheim : Wiley-VCH, 2020) Moos, Gilles; Emondts, Meike; Bordet, Alexis; Leitner, WalterRhodium nanoparticles immobilized on an acid-free triphenylphosphonium-based supported ionic liquid phase (Rh@SILP(Ph3-P-NTf2)) enabled the selective hydrogenation and hydrodeoxygenation of aromatic ketones. The flexible molecular approach used to assemble the individual catalyst components (SiO2, ionic liquid, nanoparticles) led to outstanding catalytic properties. In particular, intimate contact between the nanoparticles and the phosphonium ionic liquid is required for the deoxygenation reactivity. The Rh@SILP(Ph3-P-NTf2) catalyst was active for the hydrodeoxygenation of benzylic ketones under mild conditions, and the product distribution for non-benzylic ketones was controlled with high selectivity between the hydrogenated (alcohol) and hydrodeoxygenated (alkane) products by adjusting the reaction temperature. The versatile Rh@SILP(Ph3-P-NTf2) catalyst opens the way to the production of a wide range of high-value cyclohexane derivatives by the hydrogenation and/or hydrodeoxygenation of Friedel–Crafts acylation products and lignin-derived aromatic ketones. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.