Reticular chemistry has boosted the design of thousands of metal and covalent organic frameworks for unlimited chemical compositions, structures, and sizable porosities. The ability to generate ...porous materials at will on the basis of geometrical design concepts is responsible for the rapid growth of the field and the increasing number of applications derived. Despite their promising features, the synthesis of targeted homo- and heterometallic titanium–organic frameworks amenable to these principles is relentlessly limited by the high reactivity of this metal in solution that impedes the controlled assembly of titanium molecular clusters. We describe an unprecedented methodology for the synthesis of heterometallic titanium frameworks by metal-exchange reactions of MOF crystals at temperatures below those conventionally used in solvothermal synthesis. The combination of hard (titanium) and soft (calcium) metals in the heterometallic nodes of MUV-10(Ca) enables controlled metal exchange in soft positions for the generation of heterometallic secondary building units (SBUs) with variable nuclearity, controlled by the metal incorporated. The structural information encoded in the newly formed SBUs drives an MOF-to-MOF conversion into bipartite nets compatible with the connectivity of the organic linker originally present in the crystal. Our simulations show that this transformation has a thermodynamic origin and is controlled by the terminations of the (111) surfaces of the crystal. The reaction of MUV-10(Ca) with first-row transition metals permits the production of crystals of MUV-101(Fe,Co,Ni,Zn) and MUV-102(Cu), heterometallic titanium MOFs isostructural with archetypical solids such as MIL-100 and HKUST. In comparison to de novo synthesis, this metal-induced topological transformation provides control over the formation of hierarchical micro-/mesopore structures at different reaction times and enables the formation of heterometallic titanium MOFs not accessible under solvothermal conditions at high temperature, thus opening the door for the isolation of additional titanium heterometallic phases not linked exclusively to trimesate linkers.
Shape-memory alloys capable of a superelastic stress-induced phase transformation and a high displacement actuation have promise for applications in micro-electromechanical systems for wearable ...healthcare and flexible electronic technologies. However, some of the fundamental aspects of their nanoscale behaviour remain unclear, including the question of whether the critical stress for the stress-induced martensitic transformation exhibits a size effect similar to that observed in confined plasticity. Here we provide evidence of a strong size effect on the critical stress that induces such a transformation with a threefold increase in the trigger stress in pillars milled on 001 L2
single crystals from a Cu-Al-Ni shape-memory alloy from 2 μm to 260 nm in diameter. A power-law size dependence of n = -2 is observed for the nanoscale superelasticity. Our observation is supported by the atomic lattice shearing and an elastic model for homogeneous martensite nucleation.
A series of nanocomposites containing gold nanoparticles (AuNPs) are prepared by stereolithography (SL) by simply adding a precursor (KAuCl4) to a photoresist. A thermal treatment is performed after ...manufacturing the nanocomposites, triggering the reduction of KAuCl4 into AuNPs in solid state. In this approach, the photopolymerization of the resin and the formation of the AuNPs occur independently, allowing the optimization of these two processes separately. Advanced electron microscopy analyses reveal the distribution, size and morphology of the AuNPs synthesized within the resin, showing the influence of the gold precursor concentration and different thermal treatments. The localized surface plasmon resonance (LSPR) of the AuNPs modifies the optical properties of the 3D-printed nanocomposites, yielding transparent yet colored materials even for concentrations as low as 0.1 wt% KAuCl4. This behavior can be modelled by the Mie theory, correlating the macroscopic properties of the nanocomposites with the individual AuNPs embedded in the resin. The possibility of tuning the LSPR of the AuNPs together with the ability of manufacturing 3D-structures with sub-millimeter precision by SL, paves the way for the design of advanced platforms for plasmonics, such as sensors for surface enhanced Raman spectroscopy (SERS).
•Development of gold nanocomposites with optical activity for additive manufacturing.•The gold nanoparticles are formed in situ via thermal treatment in solid state after the manufacturing of the object.•This approach allows to control independently the manufacturing of the object and the synthesis of the gold nanoparticles.•Correlation of the macroscopic optical properties with the micro/nanostructure of the material.
Hydrogen is the next energy vector for a decarbonization society but industrial production is still methane-based. The Steam Iron Process (SIP) could provide a carbon-free production and safety ...storage option. Here, we show that a Fe2O3-3 wt% of Al2O3 foams created by freeze-casting withstand 10 redox cycles at different temperatures with no reduction in performance or pore shrinking. The use of stearic acid as a dispersant agent/binder produces the porous structure enhancement of the foam and promotes the early reduction of the hematite phase during foam sintering. The Al2O3 incorporation was detected as a solid solution in the Fe2O3 phase at the particle surface. This result is relevant as correlated the positive values of the zeta potential observed. Freeze-casted foams could improve long-term redox performances combining a unique tailored interconnected pore structure with a specific chemical composition.
In the past decade, profuse research efforts explored the uses of iron oxide particles in nanomedicine. To a great extent, the efficiency and fate of those magnetic nanoparticles depend on how their ...surfaces interface with the proteins in a physiological environment. It is well reported how an ungoverned protein corona can be detrimental to cellular uptake and targeting efficiency and how it can modify the nanoparticles biodistribution. Novel strategies are emerging to achieve enhanced and more reproducible performances of engineered nanoparticles with a custom-built protein corona. Here we report on a generalized protocol to preform a monolayer of human serum albumin (HSA) on superparamagnetic iron oxide nanoparticles (SPIONs) of different sizes. The resulting molecular structures are described by molecular dynamics simulations of the hybrid nanoconjugates. The simulations outcomes regarding the number of proteins in the corona and their monolayer arrangement on the particle surface are in agreement with the results obtained from dynamic light scattering and electronic microscopy analysis. Using tryptophan fluorescence quenching, we revealed the existence of a strong interaction between the SPIONs and the HSA which endorses the robustness of the protein−nanoparticle conjugates in this system. Moreover, we evaluated the effect of the HSA corona on the SPIONs efficiency as magnetic resonance imaging (MRI) contrast agents in water, human serum, and saline media. The protein corona did not affect the efficiency of the SPIONs as T 2 contrast agents but reduce their T 1 efficiency. In addition, we observed a greater stability for HSA-SPIONs nanoconjugates in saline and in acid media, preventing nanoparticle dissolution in extreme gastric conditions.
Polymer nanocomposites (PNCs) attract the attention of researchers and industry because of their potential properties in widespread fields. Specifically, electrically conductive and semiconductor ...PNCs are gaining interest as promising materials for biomedical, optoelectronic and sensing applications, among others. Here, metallic nanoparticles (NPs) are extensively used as nanoadditives to increase the electrical conductivity of mere acrylic resin. As the in situ formation of metallic NPs within the acrylic matrix is hindered by the solubility of the NP precursors, we propose a method to increase the density of Ag NPs by using different intermediate solvents, allowing preparation of Ag/acrylic resin nanocomposites with improved electrical behaviour. We fabricated 3D structures using stereolithography (SLA) by dissolving different quantities of metal precursor (AgClO
) in methanol and in
,
-dimethylformamide (DMF) and adding these solutions to the acrylic resin. The high density of Ag NPs obtained notably increases the electrical conductivity of the nanocomposites, reaching the semiconductor regime. We analysed the effect of the auxiliary solvents during the printing process and the implications on the mechanical properties and the degree of cure of the fabricated nanocomposites. The good quality of the materials prepared by this method turn these nanocomposites into promising candidates for electronic applications.
SiO2 and TiO2 thin films with gold nanoparticles (NPs) are of particular interest as photovoltaic materials. A novel method for the preparation of spin‐coated SiO2–Au and TiO2–Au nanocomposites is ...presented. This fast and inexpensive method, which includes three separate stages, is based on the in situ synthesis of both the metal‐oxide matrix and the Au NPs during a baking process at relatively low temperature. It allows the formation of nanocomposite thin films with a higher concentration of Au NPs than other methods. High‐resolution transmission electron microscopy studies revealed a homogeneous distribution of NPs over the film volume along with their narrow size distribution. The optical manifestation of localized surface plasmon resonance was studied in more detail for TiO2‐based Au‐doped nanocomposite films deposited on glass (in absorption and transmittance) and silicon (in specular reflectance). Maxwell–Garnett effective‐medium theory applied to such metal‐doped nanocomposite films describes the peculiarities of the experimental spectra, including modification of the antireflective properties of bare TiO2 films deposited on silicon by varying the concentration of metal NPs. The antireflective capabilities of the film are increased after a wet etching process.
TiO2 and SiO2 thin films doped with Au nanoparticles in a dielectric layer are produced by a novel method of fabrication. A posterior HF etching step leaves a significant proportion of the Au nanoparticles uncovered and lying on the film surface to give a strongly enhanced antireflective effect. Additional light trapping in the Si substrate is expected due to preferential light scattering into Si as a material with higher permittivity.
Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of ...alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of interest for quantum information applications of single emitters on the basis of perovskite nanocrystals with high photon emission rates.
Tools for numerical simulation of transmission electron microscopy (TEM) images are frequently used to provide insight about the origin of contrast features, hence, to understand and to measure ...correctly the properties of a material. We describe in this work a methodology for simulating the compositional-strain contrast of TEM images of large nanocrystalline heterostructures. The methodology combines finite element calculations and a generalized form of the single slice approach that takes into account also the imaging conditions. It is simple and computationally efficient and as an example of its reliability we compare experimental and simulated images of a sample of self-assembled In(Ga)As/GaAs QDs.
•A theoretical and computational method for simulating BF/DF TEM images.•Simulation of compositional-strain contrast of complex heterostructures.•The method is applied to images of a single quantum dot (QD) and arrays of QDs.
Chemical looping water splitting systems operate at relatively high temperatures (450–800 °C) to produce, purify, or store hydrogen by the cyclic reduction and oxidation (redox) of a solid oxygen ...carrier. Therefore, to improve long-term operation, it is necessary to develop highly stable oxygen carriers with large specific surface areas. In this work, highly interconnected doped Fe2O3 foams are fabricated through the freeze-casting technique of a submicrometric camphene-based suspension to prevent Fe sintering and pore clogging during redox operation. The influence of the dopant elements (Al and Ce) over the pore morphology evolution, and redox performances are examined. The use of an Fe2O3 porous structure with initial pore size above 100 microns shows a significant reduction of the sample densification, and the addition of Al2O3 by the citrate method prevent the rapid formation of an Fe3O4 layer at the foams struts that diminish the reoxidation rate step in the redox processing.
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