Synthesis of Extremely Small CdSe and Bright Blue Luminescent CdSe/ZnS Nanoparticles by a Prefocused Hot-Injection Approach

Although cadmium selenide is a well-explored material in aqueous and hot-injection synthesis of semiconductor quantum dots, only a few syntheses are reported for the preparation of extremely small cadmium selenide nanocrystallites. We present a hot-injection approach based on the enhancement of the nucleation rate to make cadmium selenide quantum dots with a diameter tunable between 1.5 and 2.2 nm. Furthermore, we present a procedure on how to coat these particles with zinc sulfide, leading to highly efficient fluorophors in the blue region of the visible spectrum. The work was performed without the use of highly reactive (pyrophoric) precursors and represents a basic concept for the preparation of small nanoparticles in general

Fe^II Spin Transition Materials Including an Amino–Ester 1,2,4-Triazole Derivative, Operating at, below, and above Room Temperature

A new family of one-dimensional Fe^II 1,2,4-triazole spin transition coordination polymers for which a modification of anion and crystallization solvent can tune the switching temperature over a wide range, including the room temperature region, is reported. This series of materials was prepared as powders after reaction of ethyl-4<i>H</i>-1,2,4-triazol-4-yl-acetate (αEtGlytrz) with an iron salt from a MeOH/H₂O medium affording: [Fe­(αEtGlytrz)₃]­(ClO₄)₂ (<b>1</b>); [Fe­(αEtGlytrz)₃]­(ClO₄)₂·CH₃OH (<b>2</b>); [Fe­(αEtGlytrz)₃]­(NO₃)₂·H₂O (<b>3</b>); [Fe­(αEtGlytrz)₃]­(NO₃)₂ (<b>4</b>); [Fe­(αEtGlytrz)₃]­(BF₄)₂·0.5H₂O (<b>5</b>); [Fe­(αEtGlytrz)₃]­(BF₄)₂ (<b>6</b>); and [Fe­(αEtGlytrz)₃]­(CF₃SO₃)₂·2H₂O (<b>7</b>). Their spin transition properties were investigated by ⁵⁷Fe Mossbauer spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and differential scanning calorimetry (DSC). The temperature dependence of the high-spin molar fraction derived from ⁵⁷Fe Mössbauer spectroscopy in <b>1</b> reveals an abrupt single step transition between low-spin and high-spin states with a hysteresis loop of width 5 K (<i>T</i>_c^↑ = 296 K and <i>T</i>_c^↓ = 291 K). The properties drastically change with modification of anion and/or lattice solvent. The transition temperatures, deduced by SQUID magnetometry, shift to <i>T</i>_c^↑ = 273 K and <i>T</i>_c^↓ = 263 K for (<b>2</b>), <i>T</i>_c^↑ = 353 K and <i>T</i>_c^↓ = 333 K for (<b>3</b>), <i>T</i>_c^↑ = 338 K and <i>T</i>_c^↓ = 278 K for (<b>4</b>), <i>T</i>^↑ = 320 K and <i>T</i>^↓ = 305 K for (<b>5</b>), <i>T</i>_c^↑ = 106 K and <i>T</i>_c^↓ = 92 K for (<b>6</b>), and <i>T</i>^↑ = 325 K and <i>T</i>^↓ = 322 K for (<b>7</b>). Annealing experiments of <b>3</b> lead to a change of the morphology, texture, and magnetic properties of the sample. A dehydration/rehydration process associated with a spin state change was analyzed by a mean-field macroscopic master equation using a two-level Hamiltonian Ising-like model for <b>3</b>. A new structural-property relationship was also identified for this series of materials [Fe­(αEtGlytrz)₃]­(anion)₂·<i>n</i>Solvent based on Mössbauer and DSC measurements. The entropy gap associated with the spin transition and the volume of the inserted counteranion shows a linear trend, with decrease in entropy with increasing the size of the counteranion. The first materials of this substance class to display a complete spin transition in both spin states are also presented

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Computational Fluid Dynamics Simulation of a High-Throughput Catalytic Fixed-Bed Reactor for Total Oxidation of Methane

This paper presents a two-dimensional computational fluid dynamics (CFD) study to investigate the performance of our high-throughput fixed-bed reactor used for the total oxidation of diluted volatile organic compounds (VOCs) in a continuous gas stream. The CFD model, based on a porous medium and a power-law kinetic model, is validated by comparing the calculated and experimentally determined conversion of methane, the selected VOC, over the β-cyclodextrin-Cu/hydroxyapatite catalyst for different operating conditions. The CFD model captures the effect of varying partial pressures of methane and oxygen on the methane conversion at various space times and temperatures. Overall, the simulation results qualitatively agree with experimental data within an average deviation of 17%. Analysis of the flow field, calculated using CFD, suggests that the reactor behavior resembles that of an ideal plug-flow reactor. The findings set out the lines for creating a simplified one-dimensional model of the high-throughput reactor in future research

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Synthesis, Crystal Structures, and Properties of Novel Heterometallic La/Pr−Cu−K and Sm/Eu/Tb−Cu Coordination Polymers

Five new heterometallic coordination polymers, {[LnCu2K(pydc)4(H2O)9]·H2O}n [Ln = La (1), Ln = Pr (2), H2pydc = pyridine-2,5-dicarboxylic acid], {[Ln2Cu(pydc)4(H2O)8]·H2O}n [Ln = Sm (3), Ln = Eu (4), Ln = Tb (5)], have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, thermogravimetric analysis, and single-crystal X-ray diffraction. X-ray structural analysis revealed that complexes 1 and 2 are the first Ln/Cu/K structures containing Cu(II) sandwiched in the interlayer regions of the two La/K planes alternately arranged along the b-axis. In complexes 3−5, two distinct types of building blocks, Ln(pydc)(H2O)4 and Cu(pydc)2, are linked together by pydc ligands to form a two-dimensional net structure. The magnetic properties of 1 and 2 and the luminescence properties of 3−5 have been investigated

Composition and Size-Dependent Extinction Coefficient of Colloidal PbSe Quantum Dots

Inductively coupled plasma mass spectrometry (ICP-MS) was combined with UV–vis−NIR spectrophotometry and transmission electron microscopy to determine the nanocrystal composition and molar extinction coefficient ϵ of colloidal PbSe quantum dot (Q-PbSe) suspensions. The ICP-MS results show a nonstoichiometric Pb/Se ratio, with a systematic excess of lead for all samples studied. The observed ratio is consistent with a faceted spherical Q-PbSe model, composed of a quasi stoichiometric Q-PbSe core terminated by a Pb surface shell. At high photon energies, we find that ϵ scales with the nanocrystal volume, irrespective of the Q-PbSe size. From ϵ, we calculated a size-independent absorption coefficient. Its value is in good agreement with the theoretical value for bulk PbSe. At the band gap, ϵ is size-dependent. The resulting absorption coefficient increases quadratically with decreasing Q-PbSe size. Calculations of the oscillator strength of the first optical transition are in good agreement with theoretical tight binding calculations, showing that the oscillator strength increases linearly with Q-PbSe size