628 research outputs found
Great Location: About Effects of Surface Bound Neighboring Groups for Passive and Active Fine-Tuning of CO2 Adsorption Properties in Model Carbon Capture Materials
Improved carbon capture materials are crucial for managing the CO2 level in the atmosphere. The past focus was on increasing adsorption capacities. It is widely known that controlling the heat of adsorption (ÎHads) is equally important. If it is too low, CO2 uptake takes place at unfavorable conditions and with insufficient selectivity. If it is too high, chemisorption occurs, and the materials can hardly be regenerated. The conventional approach for influencing ÎHads is the modification of the adsorbing center. This paper proposes an alternative strategy. The hypothesis is that fine-tuning of the molecular environment around the adsorbing center is a powerful tool for the adjustment of CO2-binding properties. Via click chemistry, any desired neighboring group (NG) can be incorporated on the surfaces of the nanoporous organosilica model materials. Passive NGs induce a change in the polarity of the surface, whereas active NGs are capable of direct interaction with the active center/CO2 pair. The effects on ÎHads and on the selectivity are studied. A situation can be realized which resembles frustrated Lewis acidâbase pairs, and the investigation of the binding-species by solid-state NMR indicates that the pushâpull effects could play an essential role not only in CO2 adsorption but also in its activation. © 2021 The Authors. Advanced Materials published by Wiley-VCH Gmb
Copolymerization of Mesoporous Styrene-Bridged Organosilica Nanoparticles with Functional Monomers for the Stimuli-Responsive Remediation of Water
For every mass product, there are problems associated with the resulting waste. Residues of hormones in urine cannot be removed sufficiently from wastewater, and this has undesired consequences. An ideal adsorbent would take up the impurity, enable a simple separation and recyclability. Polymer colloids with high affinity towards the drug, accessible porosity, high surface area, and stimuli-responsive properties would be candidates, but such a complex system does not exist. Here, porous vinyl-functionalized organosilica nanoparticles prepared from a styrene bridged sol-gel precursor act as monomers. Initiation of the polymerization at the pore walls and addition of functional monomers result in a special copolymer, which is covalently linked to the surface and covers it. An orthogonal modification of external surface was done by click attachment of a thermoresponsive polymer. The final core-shell system is able to remove quantitatively hydrophobic molecules such as the hormone progesterone from water. A change of temperature closes the pores and induces the aggregation of the particles. After separation one can reopen the particles and recycle them. © 2020 The Authors. Published by Wiley-VCH Gmb
Tunable high-index photonic glasses
Materials with extreme photonic properties such as maximum diffuse
reflectance, high albedo, or tunable band gaps are essential in many current
and future photonic devices and coatings. While photonic crystals, periodic
anisotropic structures, are well established, their disordered counterparts,
photonic glasses (PGs), are less understood despite their most interesting
isotropic photonic properties. Here, we introduce a controlled high index model
PG system. It is made of monodisperse spherical TiO colloids to exploit
strongly resonant Mie scattering for optimal turbidity. We report spectrally
resolved combined measurements of turbidity and light energy velocity from
large monolithic crack-free samples. This material class reveals pronounced
resonances enabled by the possibility to tune both the refractive index of the
extremely low polydisperse constituents and their radius. All our results are
rationalized by a model based on the energy coherent potential approximation,
which is free of any fitting parameter. Surprisingly good quantitative
agreement is found even at high index and elevated packing fraction. This class
of PGs may be the key to optimized tunable photonic materials and also central
to understand fundamental questions such as isotropic structural colors, random
lasing or strong light localization in 3D.Comment: Main text: 8 pages, 4 figures; Supporting Information: 5 pages, 5
figure
CHEMIE und sauberes Wasser : Einfach ein gutes Match
Die VerfĂŒgbarmachung von sauberem Wasser stellt eine der gröĂten, globalen Herausforderungen dar. FĂŒr den Mangel an sauberem Wasser ist die Chemie selbst eine der Ursachen und sollte daher auch Lösungen fĂŒr diese Probleme anbieten und kann dies auch leisten. Am Institut fĂŒr Anorganische Chemie (ACI) forschen Wissenschaftler*innen an zahlreichen Innovationen. Eine sehr kleine Auswahl wird in den folgenden Abschnitten anhand von Beispielen angesprochen
Lithium related deep and shallow acceptors in Li-doped ZnO nanocrystals
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 107, 024311 (2010) and may be found at https://doi.org/10.1063/1.3275889.We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep Li acceptor with an acceptor energy of 800 meV could be identified in both EPR and PL measurements and is responsible for the yellow luminescence at 2.2 eV. Additionally, a shallow acceptor state at 150 meV above the valence band maximum is made responsible for the observed donor-acceptor pair and free electron-acceptor transitions at 3.235 and 3.301 eV, possibly stemming from the formation of Li-related defect complexes acting as acceptors.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement
Redox-active organic-inorganic hybrid polyoxometalate micelles
A redox-active hybrid organic-inorganic polyoxometalate surfactant showed solvent-dependent self-assembly to form nano-scale architectures. The supramolecular assemblies exhibited contrasting electronic structure and redox activity to their molecular building units, and were found to be stable under electrochemical reduction and re-oxidation
Non-Classical Self-Assembly of Anisotropic Magneto-Organosilica Janus Particles Possessing Surfactant Properties and the Field-Triggered Breakdown of Surface Activity and Amphiphilic Properties
Using colloidal particles as models to understand processes on a smaller scale is a precious approach. Compared to molecules, particles are less defined, but their architecture can be more complex and so is their long-range interaction. One can observe phenomena that are unknown or much more difficult to realize on the molecular level. The current paper focuses on particle-based surfactants and reports on numerous unexpected properties. The main goal is creating an amphiphilic system with responsiveness in surface activity and associated self-organization phenomena depending on applying an external trigger, preferably a physical field. A key step is the creation of a Janus-type particle characterized by two types of dipoles (electric and magnetic) which geometrically stand orthogonal to each other. In a field, one can control which contribution and direction dominate the interparticle interactions. As a result, one can drastically change the system's properties. The features of ferrite-core organosilica-shell particles with grain-like morphology modified by click chemistry are studied in response to spatially isotropic and anisotropic triggers. A highly unusual aggregationâdissolutionâreaggregation sequence w as discovered. Using a magnetic field, one can even switch off the amphiphilic properties and use this for the field-triggered breaking of multiphase systems such as emulsions
Li-doped ZnO nanorods with single-crystal quality - non-classical crystallization and self-assembly into mesoporous materials
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugÀnglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.The benefits and promise of nanoscale dimensions for the properties of (ceramic) semiconductors are widely known. 1-D nanostructures in particular have proven to be of extraordinary relevance due to their applicability in future electronic and optoelectronic devices. Key to successful technological implementation of semiconductor nanostructures is the control of their electronic properties via doping. Despite its tremendous importance, precise chemical doping of defined nano-objects has been addressed rarely so far. Frequent problems are the creation of secondary defects and related undesired property changes by incorporation of hetero-elements, and the difficulty in ensuring a uniform and precise positioning of the dopant in the nanocrystal lattice. Here, we present the synthesis of Li-doped zinc oxide nanorods, which possess excellent (single-crystal) quality. The method is based on a novel non-classical crystallization mechanism, comprising an unusually oriented disassembly step. Afterwards, the nanorods are incorporated into mesoporous layers using colloidal self-assembly. Proof-of-principle gas sensing measurements with these novel materials demonstrate the beneficial role of Li-doping, indicating not only better conductivity but also the occurrence of catalytic effects
Cooperative Functionalities in Porous Nanoparticles for Seeking Extracellular DNA and Targeting Pathogenic Biofilms via Photodynamic Therapy
Many pathogenic bacteria are getting more and more resistant against antibiotic treatment and even become up to 1.000à times more resilient in the form of a mature biofilm. Thus, one is currently prospecting for alternative methods for treating microbial infections, and photodynamic therapy is a highly promising approach by creating so-called reactive oxygen species (ROS) produced by a photosensitizer (PS) upon irradiation with light. Unfortunately, the unspecific activity of ROS is also problematic as they are harmful to healthy tissue as well. Notably, one knows that uncontrolled existence of ROS in the body plays a major role in the development of cancer. These arguments create need for advanced theranostic materials which are capable of autonomous targeting and detecting the existence of a biofilm, followed by specific activation to combat the infection. The focus of this contribution is on mesoporous organosilica colloids functionalized by orthogonal and localized click-chemistry methods. The external zone of the particles is modified by a dye of the Hoechst family. The particles readily enter a mature biofilm where adduct formation with extracellular DNA and a resulting change in the fluorescence signal occurs, but they cannot cross cellular membranes such as in healthy tissue. A different dye suitable for photochemical ROS generation, Acridine Orange, is covalently linked to the surfaces of the internal mesopores. The spectral overlap between the emission of Hoechst with the absorption band of Acridine Orange facilitates energy transfer by Förster resonance with up to 88% efficiency. The theranostic properties of the materials including viability studies were investigated in vitro on mature biofilms formed by Pseudomonas fluorescens and prove the high efficacy
Design of Active Defects in Semiconductors: 3D Electron Diffraction Revealed Novel Organometallic Lead Bromide Phases Containing Ferrocene as Redox Switches
Once the optical, electronic, or photocatalytic properties of a semiconductor are set by adjusting composition, crystal phase, and morphology, one cannot change them anymore, respectively, on demand. Materials enabling postsynthetic and reversible switching of features such as absorption coefficient, bandgap, or charge carrier dynamics are highly desired. Hybrid perovskites facilitate exceptional possibilities for progress in the field of smart semiconductors because active organic molecules become an integral constituent of the crystalline structure. This paper reports the integration of ferrocene ligands into semiconducting 2D phases based on lead bromide. The complex crystal structures of the resulting, novel ferrovskite (â ferrocene perovskite) phases are determined by 3D electron diffraction. The ferrocene ligands exhibit strong structure-directing effects on the 2D hybrid phases, which is why the formation of exotic types of face- and edge-sharing lead bromide octahedra is observed. The bandgap of the materials ranges from 3.06 up to 3.51 eV, depending on the connectivity of the octahedra. By deploying the redox features of ferrocene, one can create defect states or even a defect band leading to control over the direction of exciton migration and energy transport in the semiconductor, enabling fluorescence via indirect to direct gap transition. © 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
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