Switching Plasmons: Gold Nanorod–Copper Chalcogenide Core–Shell Nanoparticle Clusters with Selectable Metal/Semiconductor NIR Plasmon Resonances

Exerting control over the near-infrared (NIR) plasmonic response of nanosized metals and semiconductors can facilitate access to unexplored phenomena and applications. Here we combine electrostatic self-assembly and Cd²⁺/Cu⁺ cation exchange to obtain an anisotropic core–shell nanoparticle cluster (NPC) whose optical properties stem from two dissimilar plasmonic materials: a gold nanorod (AuNR) core and a copper selenide (Cu_2–<i>x</i>Se, <i>x</i> ≥ 0) supraparticle shell. The spectral response of the AuNR@Cu₂Se NPCs is governed by the transverse and longitudinal plasmon bands (LPB) of the anisotropic metallic core, since the Cu₂Se shell is nonplasmonic. Under aerobic conditions the shell undergoes vacancy doping (<i>x</i> > 0), leading to the plasmon-rich NIR spectrum of the AuNR@Cu_2–<i>x</i>Se NPCs. For low vacancy doping levels the NIR optical properties of the dually plasmonic NPCs are determined by the LPBs of the semiconductor shell (along its major longitudinal axis) and of the metal core. Conversely, for high vacancy doping levels their NIR optical response is dominated by the two most intense plasmon modes from the shell: the transverse (along the shortest transversal axis) and longitudinal (along the major longitudinal axis) modes. The optical properties of the NPCs can be reversibly switched back to a purely metallic plasmonic character upon reversible conversion of AuNR@Cu_2–<i>x</i>Se into AuNR@Cu₂Se. Such well-defined nanosized colloidal assemblies feature the unique ability of holding an all-metallic, a metallic/semiconductor, or an all-semiconductor plasmonic response in the NIR. Therefore, they can serve as an ideal platform to evaluate the crosstalk between plasmonic metals and plasmonic semiconductors at the nanoscale. Furthermore, their versatility to display plasmon modes in the first, second, or both NIR windows is particularly advantageous for bioapplications, especially considering their strong absorbing and near-field enhancing properties

Quantification of Nanoscale Silver Particles Removal and Release from Municipal Wastewater Treatment Plants in Germany

The majority of pure silver nanoparticles in consumer products are likely released into sewer systems and usually end up in wastewater treatment plants (WWTPs). Research investigating the reduction in nanoscale silver particles (n-Ag-Ps) has focused on the biological treatment process, generally in controlled laboratory experiments. This study, analyzing the field-collected samples from nine municipal WWTPs in Germany, is the first to evaluate the reduction in n-Ag-Ps by mechanical and biological treatments in sequence in WWTPs. Additionally, the concentration of n-Ag-Ps in effluent was determined through two different methods that are presented here: novel ionic exchange resin (IER) and cloud point extraction (CPE) methods. The n-Ag-Ps concentrations in influent were all low (<1.5 μg/L) and decreased (average removal efficiency of ∼35%) significantly after mechanical treatment, indicating that the mechanical treatment contributes to the n-Ag-Ps removal. Afterward, more than 72% of the remaining n-Ag-Ps in the semi-treated wastewater (i.e., wastewater after mechanical treatment) were reduced by biological treatment. Together, these processes reduced 95% of the n-Ag-Ps that entered WWTPs, which resulted in low concentration of n-Ag-Ps in the effluents (<12 ng/L). For a WWTP with 520000 t/d treatment capacity, we estimated that the daily n-Ag-Ps load in effluent discharge equated to about 4.4 g/d. Obviously, WWTPs are not potential point sources for n-Ag-Ps in the aquatic environment

Bulk Synthesis and Structure of a Microcrystalline Allotrope of Germanium (<i>m-allo</i>-Ge)

An easy to reproduce and scale-up method for the preparation of a microcrystalline allotrope of germanium is presented. Based on the report of the oxidation of a single crystal of Li₇Ge₁₂ the synthesis and structure determination of a powdered sample of Li₇Ge₁₂ is investigated. Besides the known oxidation of Li₇Ge₁₂ with benzophenone a variety of protic solvents such as alcohols and water were used as oxidants. Electron energy loss spectroscopy (EELS) proves that the reaction products do not contain Li. The structure determination of the powder samples based on selected area electron diffraction (SAED), powder X-ray diffraction, quantum chemical calculations (DFT-B3LYP level of theory), and simulated powder X-ray diffraction diagrams obtained using the DIFFaX and FAULTS software packages show that the microcrystalline powders do not match any of the existing structures of germanium including the rough model of so-called <i>allo</i>-Ge. It is shown that the structural motif of layered Ge slabs of the precursor Li₇Ge₁₂ that contain five-membered rings is retained in <i>m</i>icrocrystalline <i>allo</i>-Ge (<i>m-allo</i>-Ge). The covalent connectivity between the slabs and the statistic of the layer sequence is determined. According to B3LYP-DFT calculations of a periodic approximate model a direct band gap is expected for <i>m-allo-</i>Ge

Puzzling Intergrowth in Cerium Nitridophosphate Unraveled by Joint Venture of Aberration-Corrected Scanning Transmission Electron Microscopy and Synchrotron Diffraction

Thorough investigation of nitridophosphates has rapidly accelerated through development of new synthesis strategies. Here we used the recently developed high-pressure metathesis to prepare the first rare-earth metal nitridophosphate, Ce₄Li₃P₁₈N₃₅, with a high degree of condensation >1/2. Ce₄Li₃P₁₈N₃₅ consists of an unprecedented hexagonal framework of PN₄ tetrahedra and exhibits blue luminescence peaking at 455 nm. Transmission electron microscopy (TEM) revealed two intergrown domains with slight structural and compositional variations. One domain type shows extremely weak superstructure phenomena revealed by atomic-resolution scanning TEM (STEM) and single-crystal diffraction using synchrotron radiation. The corresponding superstructure involves a modulated displacement of Ce atoms in channels of tetrahedra 6-rings. The displacement model was refined in a supercell as well as in an equivalent commensurate (3 + 2)-dimensional description in superspace group <i>P</i>6₃(α, β, 0)­0­(−α – β, α, 0)­0. In the second domain type, STEM revealed disordered vacancies of the same Ce atoms that were modulated in the first domain type, leading to sum formula Ce_{4–0.5<i>x</i>}Li₃P₁₈N_{35–1.5<i>x</i>}O_1.5<i>x</i> (<i>x</i> ≈ 0.72) of the average structure. The examination of these structural intricacies may indicate the detection limit of synchrotron diffraction and TEM. We discuss the occurrence of either Ce displacements or Ce vacancies that induce the incorporation of O as necessary stabilization of the crystal structure

Fast Characterization of Polyplexes by Taylor Dispersion Analysis

In a single procedure, Taylor dispersion analysis (TDA) was used for the size characterization of polyplexes and the quantification of free polycation contained in excess within the polyplex sample. TDA analysis was carried out in frontal mode for a better sensitivity of detection. The proof of concept was established using a model polyplex generated from the mixture of linear polylysine (DP 20) and DNA from salmon testes at nitrogen to phosphate (N/P) ratio of 12. Polyplex hydrodynamic radius was compared to the values obtained by dynamic light scattering measurements. TDA was found to give access to the weight-average hydrodynamic radius, while DLS basically gives an intensity-average (harmonic <i>z</i>-average) value. The method was next applied to the study of various polyplexes issued from polylysines of various DP (50, 100) and different topologies (dendrigraft polylysines of generation 2 and 3). This new methodology should greatly contribute to the physicochemical characterization of polyplexes used for gene transfection

Bending Gold Nanorods with Light

V-shaped gold nanoantennas are the functional components of plasmonic metasurfaces, which are capable of manipulating light in unprecedented ways. Designing a metasurface requires the custom arrangement of individual antennas with controlled shape and orientation. Here, we show how highly crystalline gold nanorods in solution can be bent, one-by-one, into a V-shaped geometry and printed to the surface of a solid support through a combination of plasmonic heating and optical force. Significantly, we demonstrate that both the bending angle and the orientation of each rod-antenna can be adjusted independent from each other by tuning the laser intensity and polarization. This approach is applicable for the patterning of V-shaped plasmonic antennas on almost any substrate, which holds great potential for the fabrication of ultrathin optical components and devices

<i>In Situ</i> SAXS Study on a New Mechanism for Mesostructure Formation of Ordered Mesoporous Carbons: Thermally Induced Self-Assembly

A new mechanism for mesostructure formation of ordered mesoporous carbons (OMCs) was investigated with in situ small-angle X-ray scattering (SAXS) measurements: thermally induced self-assembly. Unlike the well-established evaporation-induced self-assembly (EISA), the structure formation for organic–organic self-assembly of an oligomeric resol precursor and the block-copolymer templates Pluronic P123 and F127 does not occur during evaporation but only by following a thermopolymerization step at temperatures above 100 °C. The systems investigated here were cubic (<i>Im</i>3̅<i>m</i>), orthorhombic <i>Fmmm</i>) and 2D-hexagonal (plane group <i>p</i>6<i>mm</i>) mesoporous carbon phases in confined environments, as thin films and within the pores of anodic alumina membranes (AAMs), respectively. The thin films were prepared by spin-coating mixtures of the resol precursor and the surfactants in ethanol followed by thermopolymerization of the precursor oligomers. The carbon phases within the pores of AAMs were made by imbibition of the latter solutions followed by solvent evaporation and thermopolymerization within the solid template. This thermopolymerization step was investigated in detail with in situ grazing incidence small-angle X-ray scattering (GISAXS, for films) and in situ SAXS (for AAMs). It was found that the structural evolution strongly depends on the chosen temperature, which controls both the rate of the mesostructure formation and the spatial dimensions of the resulting mesophase. Therefore the process of structure formation differs significantly from the known EISA process and may rather be viewed as thermally induced self-assembly. The complete process of structure formation, template removal, and shrinkage during carbonization up to 1100 °C was monitored in this in situ SAXS study

Nanocellulose-Assisted Formation of Porous Hematite Nanostructures

We report the formation of porous iron oxide (hematite) nanostructures via sol–gel transformations of molecular precursors in the confined space of self-organized nanocrystalline cellulose (NCC) used as a shape-persistent template. The obtained structures are highly porous α-Fe₂O₃ (hematite) morphologies with a well-defined anisotropic porosity. The character of the porous nanostructure depends on the iron salt used as the precursor and the heat treatment. Moreover, a postsynthetic hydrothermal treatment of the NCC/iron salt composites strongly affects the crystal growth as well as the porous nanomorphology of the obtained hematite scaffolds. We demonstrate that the hydrothermal treatment alters the crystallization mechanism of the molecular iron precursors, which proceeds via the formation of anisotropic iron oxyhydroxide species. The nanocellulose templating technique established here enables the straightforward fabrication of a variety of mesoporous crystalline iron oxide scaffolds with defined porous structure and is particularly attractive for the processing of porous hematite films on different substrates

Connecting Composition-Driven Faceting with Facet-Driven Composition Modulation in GaAs–AlGaAs Core–Shell Nanowires

Ternary III–V alloys of tunable bandgap are a foundation for engineering advanced optoelectronic devices based on quantum-confined structures including quantum wells, nanowires, and dots. In this context, core–shell nanowires provide useful geometric degrees of freedom in heterostructure design, but alloy segregation is frequently observed in epitaxial shells even in the absence of interface strain. High-resolution scanning transmission electron microscopy and laser-assisted atom probe tomography were used to investigate the driving forces of segregation in nonplanar GaAs–AlGaAs core–shell nanowires. Growth-temperature-dependent studies of Al-rich regions growing on radial {112} nanofacets suggest that facet-dependent bonding preferences drive the enrichment, rather than kinetically limited diffusion. Observations of the distinct interface faceting when pure AlAs is grown on GaAs confirm the preferential bonding of Al on {112} facets over {110} facets, explaining the decomposition behavior. Furthermore, three-dimensional composition profiles generated by atom probe tomography reveal the presence of Al-rich nanorings perpendicular to the growth direction; correlated electron microscopy shows that short zincblende insertions in a nanowire segment with predominantly wurtzite structure are enriched in Al, demonstrating that crystal phase engineering can be used to modulate composition. The findings suggest strategies to limit alloy decomposition and promote new geometries of quantum confined structures