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.
One plausible approach to endow aerogels with specific properties while preserving their other attributes is to fine‐tune the building blocks. However, the preparation of metallic aerogels with ...designated properties, for example catalytically beneficial morphologies and transition‐metal doping, still remains a challenge. Here, we report on the first aerogel electrocatalyst composed entirely of alloyed PdNi hollow nanospheres (HNSs) with controllable chemical composition and shell thickness. The combination of transition‐metal doping, hollow building blocks, and the three‐dimensional network structure make the PdNi HNS aerogels promising electrocatalysts for ethanol oxidation. The mass activity of the Pd83Ni17 HNS aerogel is 5.6‐fold higher than that of the commercial Pd/C catalyst. This work expands the exploitation of the electrocatalysis properties of aerogels through the morphology and composition control of its building blocks.
Function follows form: Aerogel electrocatalysts consisting of alloyed PdNi hollow nanospheres (HNS) were prepared. Their chemical composition and shell thickness can be controlled based on the ratio of the Ni/Pd precursors. The mass activity of the Pd83Ni17 HNS aerogel is 5.6 times higher than that of the commercial Pd/C catalyst.
We report an efficient approach to assemble a variety of electrostatically stabilized all‐inorganic semiconductor nanocrystals (NCs) by their linking with appropriate ions into multibranched gel ...networks. These all‐inorganic non‐ordered 3D assemblies benefit from strong interparticle coupling, which facilitates charge transport between the NCs with diverse morphologies, compositions, sizes, and functional capping ligands. Moreover, the resulting dry gels (aerogels) are highly porous monolithic structures, which preserve the quantum confinement of their building blocks. The inorganic semiconductor aerogel made of 4.5 nm CdSe colloidal NCs capped with I− ions and bridged with Cd2+ ions had a large surface area of 146 m2 g−1.
An assembly approach for a variety of electrostatically stabilized all‐inorganic semiconductor nanocrystals is based on their linking with appropriate ions into multibranched gel networks. The resulting aerogels are highly porous monolithic structures, which preserve the quantum confinement of their building blocks.
In this study we report on mechanical properties of molded, single component Al2O3, Ga2O3, Fe2O3, and ZrO2 as well as mixed aerogels, made from yttrium stabilized zirconia, yttrium aluminum garnet, ...and zinc aluminum spinel. Initially all aerogels were produced equally in molded bodies by a facile epoxy method and were annealed afterward at 300 °C. Then we performed uniaxial pressure tests on cylindrical aerogel monoliths to gain Young’s modulus which depends on composition, density, and post-treatment. Already pure aerogels like ZrO2 show well-promising Young’s modulus of 10.7 MPa, whereas most popular SiO2 materials display a modulus between 2 and 3 MPa at comparable densities. Moreover we focused on Al2O3 aerogels which exhibit high stability and interesting densification behavior depending on the annealing temperature. On the basis of this observation, we combined the toughness of the Al2O3 scaffold with the extraordinary hardness of ZrO2, by adding up to 20 atom % Zr, to increase the specific Young’s modulus. For the mixed material with a Zr content of 20 atom %, we reach a record value for compressible aerogels of 125 MPa mL g–1.
Solar radiation is a versatile source of energy, convertible to different forms of power. A direct path to exploit it is the generation of heat, for applications including passive building heating, ...but it can also drive secondary energy‐conversion steps. We present a novel concept for a hybrid material which is both strongly photo‐absorbing and with superior characteristics for the insulation of heat. The combination of that two properties is rather unique, and make this material an optical superheater. To realize such a material, we are combining plasmonic nanoheaters with alumina aerogel. The aerogel has the double function of providing structural support for plasmonic nanocrystals, which serve as nanoheaters, and reducing the diffusion rate of the heat generated by them, resulting in large local temperature increases under a relatively low radiation intensity. This work includes theoretical discussion on the physical mechanisms impacting the system's balanced thermal equilibrium.
White light, white heat: Gold nanorods (AuNRs) embedded into highly insulating alumina aerogel pellets give a hybrid system that has a tremendous light to heat conversion performance. The AuNRs withstand the high local temperatures (175 °C) with little to no melting. The system allows the design and modelling of novel concepts for photoheaters.
In order to enable future use of aerogels in heterogeneous solid or fluidized bed catalysis a method of production of millimeter sized monolithic Au/Al
2
O
3
aerogel spheres by a continuous flow ...reactor is developed. Flow velocities and synthesis parameters are optimized to produce aerogel spheres in three different sizes. The resulting aerogel spheres exhibit a porous aluminium oxide aerogel matrix with a large specific surface area of 400 m
2
g
−1
on which gold nanoparticles are evenly distributed. The aerogel spheres are compared to xerogels of the same material in contrast to their surface area, pore size distribution, morphology, crystal structure and thermal properties. The presented method allows a broad access to various mixed aerogel systems of oxidic carrier material and noble metal nanoparticles and is therefore relevant for the shaping of different aerogel catalyst systems.
In order to enable future use of aerogels in heterogeneous solid or fluidized bed catalysis a method of production of millimeter sized monolithic Au/Al
2
O
3
aerogel spheres by a continuous flow reactor is developed.
The n‐type semiconductor system Bi2Te3Bi2Se3 is known as a low‐temperature thermoelectric material with a potentially high efficiency. Herein, a facile approach is reported to synthesize core/shell ...heterostructured Bi2Te2Se/Bi2Te3 nanosheets (NSs) with lateral dimensions of 1–3 μm and thickness of about 50 nm. Bi2Te3 and Bi2Se3, as well as heterostructured Bi2Te2Se/Bi2Te3 NSs are obtained via colloidal synthesis. Heterostructured NSs show an inhomogeneous distribution of the chalcogen atoms forming selenium and tellurium‐rich layers across the NS thickness, resulting in a core/shell structure. Detailed morphological studies reveal that these structures contain nanosized pores. These features contribute to the overall thermoelectric properties of the material, inducing strong phonon scattering at grain boundaries in compacted solids. NSs are processed into nanostructured bulks through spark plasma sintering of dry powders to form a thermoelectric material with high power factor. Electrical characterization of our materials reveals a strong anisotropic behavior in consolidated pellets. It is further demonstrated that by simple thermal annealing, core/shell structure can be controllably transformed into alloyed one. Using this approach pellets with Bi2Te2.55Se0.45 composition are obtained, which exhibit low thermal conductivity and high power factor for in‐plane direction with zT of 1.34 at 400 K.
Bi2Te3, Bi2Se3, and core/shell Bi2Te2Se/Bi2Te3 nanosheets with lateral dimensions of 1–3 μm and thickness of about 50 nm are obtained via colloidal synthesis. Heterostructured nanosheets show an inhomogeneous distribution of the chalcogen atoms and nanosized pores. They are processed into nanostructured bulks with Bi2Te2.55Se0.45 composition, exhibiting low thermal conductivity and high power factor with zT of 1.34 at 400 K.
Solar radiation is a versatile source of energy, convertible to different forms of power. A direct path to exploit it is the generation of heat, for applications including passive building heating, ...but it can also drive secondary energy‐conversion steps. We present a novel concept for a hybrid material which is both strongly photo‐absorbing and with superior characteristics for the insulation of heat. The combination of that two properties is rather unique, and make this material an optical superheater. To realize such a material, we are combining plasmonic nanoheaters with alumina aerogel. The aerogel has the double function of providing structural support for plasmonic nanocrystals, which serve as nanoheaters, and reducing the diffusion rate of the heat generated by them, resulting in large local temperature increases under a relatively low radiation intensity. This work includes theoretical discussion on the physical mechanisms impacting the system's balanced thermal equilibrium.
Mit Weißlicht zur Weißglut: Gold‐Nanostäbchen (AuNRs), die in stark isolierende Aluminiumoxid‐Aerogel‐Tabletten eingebettet werden, ergeben ein Hybridsystem mit enormer Licht‐zu‐Hitze‐Umwandlungsleistung. Die AuNRs überstehen die hohen lokalen Temperaturen (175 °C) mit wenig oder ohne Schmelzen. Das System ermöglicht die Entwicklung und Modellierung neuartiger Konzepte für Photoerhitzer.
Nanostructured tin oxide materials with a high specific surface area and porosity are promising for applications such as electrocatalysis, lithium ion batteries or sensors. Here, we present a facile ...strategy for the synthesis of tin oxide aerogels using inexpensive hexahydroxostannate as a tin precursor. This easy and scalable method yields tin oxide aerogels with a high specific surface area and a wide pore size distribution. The method can be modified by adding hexahydroxoantimonate to obtain antimony-doped tin oxide aerogels that exhibit electrical conductivity after annealing. Cogelation with other preformed nanoparticles (
e.g.
Au, Pt) leads to mixed gels. Both modifications do not have a large impact on the porous properties of the obtained aerogels. Tin oxide materials prepared
via
this route can be tailored to a specific application by versatile modification possibilities.
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