Room-Temperature Interconversion Between Ultrathin CdTe Magic-Size Nanowires Induced by Ligand Shell Dynamics

The formation mechanisms of colloidal magic-size semiconductor nanostructures have remained obscure. Herein, we report the room temperature synthesis of three species of ultrathin CdTe magic-size nanowires (MSNWs) with diameters of 0.7 ± 0.1 nm, 0.9 ± 0.2 nm, and 1.1 ± 0.2 nm, and lowest energy exciton transitions at 373, 418, and 450 nm, respectively. The MSNWs are obtained from Cd(oleate) 2 and TOP-Te, provided diphenylphosphine and a primary alkylamine (RNH 2) are present at sufficiently high concentrations, and exhibit sequential, discontinuous growth. The population of each MSNW species is entirely determined by the RNH 2 concentration [RNH 2] so that single species are only obtained at specific concentrations, while mixtures are obtained at concentrations intermediate between the specific ones. Moreover, the MSNWs remain responsive to [RNH 2], interconverting from thinner to thicker upon [RNH 2] decrease and from thicker to thinner upon [RNH 2] increase. Our results allow us to propose a mechanism for the formation and interconversion of CdTe MSNWs and demonstrate that primary alkylamines play crucial roles in all four elementary kinetic steps (viz., monomer formation, nucleation, growth in length, and interconversion between species), thus being the decisive element in the creation of a reaction pathway that leads exclusively to CdTe MSNWs. The insights provided by our work thus contribute toward unravelling the mechanisms behind the formation of shape-controlled and atomically precise magic-size semiconductor nanostructures

Correction to "Luminescent Gold Nanocluster-Decorated Polymeric Hybrid Particles with Assembly-Induced Emission"

Correction to “Luminescent Gold Nanocluster-Decorated Polymeric Hybrid Particles with Assembly-Induced Emission

Cation Exchange and Spontaneous Crystal Repair Resulting in Ultrathin, Planar CdS Nanosheets

Cation exchange has become a major postsynthetic tool to obtain nanocrystals with a combination of stoichiometry, size, and shape that is challenging to achieve by direct wet-chemical synthesis. Here, we report on the transformation of highly anisotropic, ultrathin, and planar PbS nanosheets into CdS nanosheets of the same dimensions. We monitor the evolution of the Cd-for-Pb exchange by ex-situ TEM, HAADF-STEM, and EDX. We observe that in the early stages of the exchange the sheets show large in-sheet voids that repair spontaneously upon further exchange and annealing, resulting in ultrathin, planar, and crystalline CdS nanosheets. After cation exchange, the nanosheets show broad sub-band gap luminescence, as often observed in CdS nanocrystals. The photoluminescence excitation spectrum reveals the heavy- and light-hole exciton features, with very strong quantum confinement and large electron–hole Coulomb energy, typical for 2D ultrathin Cd-chalcogenide nanosheets

Influence of carbon support surface modification on the performance of nickel catalysts in carbon dioxide hydrogenation

The interaction between metal nanoparticles and a support is of key importance in catalysis. In this study, we demonstrate that the introduction of oxygen- or nitrogen-containing surface groups on a graphite nanoplatelet support influences the performance of nickel supported catalysts during CO2 hydrogenation. By careful design of the synthesis conditions, the Ni nanoparticle size of the fresh catalysts was not affected by the type of support surface groups. A combination of H2 chemisorption and high resolution TEM demonstrates that the available metal surface depends on the interaction with the carbon support. The amination treatment to introduce nitrogen-containing groups results in the weakest interaction between the Ni and the support, showing the highest initial Ni weight-based activity, although at the expense of nanoparticle stability. Hence initial enhancement in activity is not always optimal for long term catalysis. The use of carbon with a higher density of oxygen functional groups that are stable above 350 °C, is beneficial for preventing deactivation due to particle growth. Furthermore, small amounts of contaminants can have a substantial influence on the CH4 selectivity at low conversions

Influence of carbon support surface modification on the performance of nickel catalysts in carbon dioxide hydrogenation

The interaction between metal nanoparticles and a support is of key importance in catalysis. In this study, we demonstrate that the introduction of oxygen- or nitrogen-containing support surface groups on a graphite nanoplatelet support influence the performance of nickel supported catalysts during CO2 hydrogenation. By careful design of the synthesis conditions, the Ni nanoparticle size of the fresh catalysts was not affected by the type of support surface groups. A combination of H2 chemisorption and high resolution TEM demonstrates that the available metal surface depends on the interaction with the carbon support. The amination treatment results in the weakest interaction between the Ni and the support, showing the highest initial Ni weight-based activity, although at the expense of nanoparticle stability. Hence initial enhancement in activity is not always optimal for long term catalysis. The use of carbon with a higher density of oxygen functional groups that are stable above 350 °C, is beneficial for preventing deactivation due to particle growth. Furthermore, small amounts of contaminants can have a substantial influence on the CH4 selectivity at low conversions

Silica as support and binder in bifunctional catalysts with ultralow Pt loadings for the hydroconversion of n-alkanes

Hydroconversion is a key step in the production of ultraclean fuels from renewable sources. This reaction is carried out using a bifunctional catalyst consisting of a base metal sulfide or a noble metal and a solid acid. Recently, we have shown that for Pt/Al2O3/ZSM-22 catalysts with low Pt loadings (≤0.01 wt%) it is advantageous – to both the activity as well as the isomer selectivity - to emplace the Pt on the zeolite crystallites instead of on the Al2O3 binder. When these low loadings of Pt were on the alumina binder, small clusters or even single atoms were present which were hard to reduce leading to inactivity of the catalysts. Herein, we explore the replacement of alumina by silica, and the performance of catalysts with ultralow Pt loadings on the conversion of longer-chain hydrocarbons. A series of Pt/SiO2/ZSM-22 catalysts with varying Pt weight loadings (0.001, 0.005, 0.01, 0.05, 0.1 and 0.5 wt%) and location (on silica or on ZSM-22) was prepared and characterized using ICP, NH3-TPD, HAADF-STEM and XAS. Their hydroconversion performance was evaluated using n-heptane and n-hexadecane as model feedstocks. As for the Pt/Al2O3/ZSM-22 catalysts systems, for Pt/SiO2/ZSM-22 catalysts with low Pt loadings (≤0.01 wt% for n-heptane conversion) it was beneficial to have the Pt nanoparticles on the ZSM-22 crystals. Hydroconversion of n-hexadecane over Pt/SiO2/ZSM-22 and Pt/Al2O3/ZSM-22 catalysts showed that for feedstocks with a higher molecular weight, higher Pt loadings (≥0.05 wt%) are required for sufficient catalytic performance. For the conversion of n-hexadecane it was beneficial to locate these higher amounts of Pt on the binder

Intra- and Interparticle Heterogeneities in Solid Activators for Single-Site Olefin Polymerization Catalysis as Revealed by Micro-Spectroscopy

Transition metal–zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal–zeolite catalysts

Magnetic Petrology of Equatorial Atlantic Sediments: Electron Microscopic Results and their Environmental Magnetic Implications

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