Herein, we report on a room-temperature anion exchange reaction of highly emitting, all-inorganic CsPbBr3 nanocrystals (NCs) taking place entirely in the solid state. A fast exchange from Br to I and ...Br to mixed Br/Cl without exertion of additional energy is observed within minutes to hours, taking place by immobilization of the perovskite NCs on pure potassium halide salts (KCl, KBr, and KI). Via adjustment of the halide ratios of the embedding salt matrix, the bright fluorescence of the CsPbX3 (X = Cl, Br, or I) NCs can be tuned over a wide spectral range (400–700 nm) while maintaining the initial photoluminescence quantum yields of ∼80% and narrow full widths at half-maximum. We found that combinations of different initial CsPbX3 NCs and KX matrices result in different final halogen contents of the NCs. This is explained with a host-lattice limiting exchange mechanism. The anion exchange rate can be accelerated by pressing the soft, NC-loaded salts under pressure of 2.2 GPa. Because of the “cold flow” behavior of the potassium salts during the pressing, a complete embedding of the NCs into transparent salt pellets is achieved. This strategy allows for an easy adjustment of the NC loading as well as the form and thickness of the resulting composite. An encapsulation of the NC−salt pellets with silicone yields robustness and stability of the embedded NCs under ambient conditions. The ease of handling and the superior stability make the resulting perovskite composite materials attractive for various photonic and optoelectronic applications as demonstrated in a proof-of-concept color-converting layer for a light−emitting diode.
The abundance of accessible colloidally prepared nanoparticles forms the basis for nanoparticle-based aerogels. Synthetic methods have been developed to destabilize colloidal nanoparticle solutions ...in a controlled manner, resulting first in wet gels and then in aerogels. In addition to other ways to make aerogels, efforts have been made, in particular, to transfer particles of different sizes, shapes, natures, and compositions together into aerogels. All this happens in the context of the phenomenon of self-organization at the nanoscale, which is due to Brownian motion and complex potentials between particles. Some of these ways are traced, recent developments are compiled as examples and some ideas for the further development of this fruitful research field are collected.
In this work, we present a simple seeded growth approach to obtain gold nanoparticles over a large range of sizes. The method produces particles with uniform spherical shape and narrow size ...distributions. Using ascorbic acid as a reductant and sodium citrate as stabilizer we utilize biocompatible and easy to exchange substances. The investigation of the growth process via TEM measurements revealed the formation of small gold clusters on the surface of the seeds, which subsequently grow and result in a “blackberry-like” intermediate shape of the gold nanoparticles. Applying heat caused an intraparticle ripening process, which finally lead to a smooth spherical particle shape. Furthermore, the optical properties of the resulting gold sols are discussed in the light of Mie theory and an influence of the polydispersity was found for large particles.
Modern Inorganic Aerogels Ziegler, Christoph; Wolf, André; Liu, Wei ...
Angewandte Chemie International Edition,
October 16, 2017, Letnik:
56, Številka:
43
Journal Article
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Essentially, the term aerogel describes a special geometric structure of matter. It is neither limited to any material nor to any synthesis procedure. Hence, the possible variety of materials and ...therefore the multitude of their applications are almost unbounded. In fact, the same applies for nanoparticles. These are also just defined by their geometrical properties. In the past few decades nano‐sized materials have been intensively studied and possible applications appeared in nearly all areas of natural sciences. To date a large variety of metal, semiconductor, oxide, and other nanoparticles are available from colloidal synthesis. However, for many applications of these materials an assembly into macroscopic structures is needed. Here we present a comprehensive picture of the developments that enabled the fusion of the colloidal nanoparticle and the aerogel world. This became possible by the controlled destabilization of pre‐formed nanoparticles, which leads to their assembly into three‐dimensional macroscopic networks. This revolutionary approach makes it possible to use precisely controlled nanoparticles as building blocks for macroscopic porous structures with programmable properties.
Make something big! The controlled destabilization of colloidal nanoparticles and the resulting assembly into macroscopic 3D structures enables the fusion of the nano and the macro worlds. Nanoparticles can be used like a toolbox to create materials with designed properties. This Review summarizes this exciting area of modern nanotechnology.
Amongst various porous materials, noble metal aerogels attract wide attention due to their concurrently featured catalytic properties and large surface areas. However, insufficient understanding and ...investigation of key factors (e.g. reductants and ligands) in the fabrication process limits on-target design, impeding material diversity and available applications. Herein, unveiling multiple roles of reductants, we develop an efficient method, i.e. the excessive-reductant-directed gelation strategy. It enables to integrate ligand chemistry for creating gold aerogels with a record-high specific surface area (59.8 m
g
), and to expand the composition to all common noble metals. Moreover, we demonstrate impressive electrocatalytic performance of these aerogels for the ethanol oxidation and oxygen evolution reaction, and discover an unconventional organic-ligand-enhancing effect. The present work not only enriches the composition and structural diversity of noble metal aerogels, but also opens up new dimensions for devising efficient electrocatalysts for broad material systems.
We simulated irreversible aggregation of non-interacting particles and of particles interacting via repulsive and attractive potentials explicitly implementing the rotational diffusion of aggregating ...clusters. Our study confirms that the attraction between particles influences neither the aggregation mechanism nor the structure of the aggregates, which are identical to those of non-interacting particles. In contrast, repulsive particles form more compact aggregates and their fractal dimension and aggregation times increase with the decrease of the temperature. A comparison of the fractal dimensions obtained for non-rotating clusters of non-interacting particles and for rotating clusters of repulsive particles provides an explanation for the conformity of the respective values obtained earlier in the well established model of diffusion-limited cluster aggregation neglecting rotational diffusion and in experiments on colloidal particles.
All inorganic lead halide perovskite nanocrystals (PNCs) typically suffer from poor stability against moisture and UV radiation as well as degradation during thermal treatment. The stability of PNCs ...can be significantly enhanced through polymer encapsulation, often accompanied by a decrease of photoluminescence quantum yield (PLQY) due to the loss of highly dynamic oleylamine/oleic acid (OLA/OA) ligands. Herein, we propose a solution for this problem by utilizing partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and highly branched poly(ethylenimine) (b-PEI) as double ligands stabilizing the PNCs already during the mechanochemical synthesis (grinding). The hydrophobic polymer of h-PMMA imparts excellent film-forming properties and water stability to the resulting NC–polymer composite. In its own turn, the b-PEI forms an amino-rich, strongly binding ligand layer on the surface of the PNCs being responsible for the significant improvement of the PLQY and the stability of the resulting material. Moreover, the introduction of b-PEI promotes a partial phase conversion from CsPbBr3 to CsPb2Br5 to obtain CsPbBr3/CsPb2Br5 nanocrystals with a core–shell-like structure. As-prepared PNCs solutions are directly processable as inks, while their PLQY drops only slightly from 75% in colloidal solution to 65% in films. Moreover, the final PNC–polymer film exhibits excellent stability against water, heat, and ultraviolet light irradiation. These superior properties allowed us to fabricate a proof of concept thin film OLED with h-PMMA/b-PEI-stabilized PNCs as an easily processable, narrowly emitting color conversion composite material.
Despite the increasing use of semiconductor nanocrystals (quantum dots, QDs) with unique size-controlled optical and chemical properties in (bio)analytical detection, biosensing and fluorescence ...imaging and the obvious relevance of reliable values of fluorescence quantum yields for these applications, evaluated procedures for the determination of the fluorescence quantum yields (Φf) of these materials are still missing. This limits the value of literature data of QDs in comparison to common organic dyes and hampers the comparability of the performance of QDs from different sources or manufacturers. This encouraged us to investigate achievable uncertainties for the determination of Φf values of these chromophores and to illustrate common pitfalls exemplarily for differently sized water-soluble CdTe QDs. Special attention is dedicated to the colloidal nature and complicated surface chemistry of QDs thereby deriving procedures to minimize uncertainties related to these features.
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