ABSTRACT
We report on a comparative study of 5.5 nm (embedded in an ordered mesoporous silica matrix) and 100 nm (free) (photo)magnetic CoFe Prussian blue analogue (PBA) particles. Co and Fe K-edge X-ray absorption spectroscopy, X-ray diffraction, infrared spectroscopy, and magnetic measurements point out a core-shell structure of the particles in their ground states. In the 5.5 nm particles, the 11.5 Å thick shell is made of Fe(CN)6 entities and CoII-NC-FeIII linkages departing from the geometry usually encountered in PBA, whatever the oxidation state (CoIIFeIII or CoIIIFeII) of the CoFe pairs in the core. In the photomagnetic particles, the photomagnetic effect in the core of the particles is due to the same photoinduced CoIII(LS)FeII â CoII(HS)FeIII electron transfer whatever the size of the particles. The shell of the nanoparticles exhibits a peculiar photoinduced structural rearrangement, and the nanoparticles in their photoexcited state exhibit a superparamagnetic behavior.
ABSTRACT
When using the bottom-up approach with anisotropic building-blocks, an important goal is to find simple methods to elaborate nanocomposite materials with a truly macroscopic anisotropy. Here, micrometer size colloidal mesoporous particles with a highly anisotropic rod-like shape (aspect ratio ≈ 10) have been fabricated from silica (SiO2 ) and iron oxide (Fe2 O3 ). When dispersed in a solvent, these particles can be easily oriented using a magnetic field (≈200 mT). A macroscopic orientation of the particles is achieved, with their long axis parallel to the field, due to the shape anisotropy of the magnetic component of the particles. The iron oxide nanocrystals are confined inside the porosity and they form columns in the nanochannels. Two different polymorphs of Fe2 O3 iron oxide have been stabilized, the superparamagnetic γ-phase and the rarest multiferroic ε-phase. The phase transformation between these two polymorphs occurs around 900 °C. Because growth occurs under confinement, a preferred crystallographic orientation of iron oxide is obtained, and structural relationships between the two polymorphs are revealed. These findings open completely new possibilities for the design of macroscopically oriented mesoporous nanocomposites, using such strongly anisotropic Fe2 O3 /silica particles. Moreover, in the case of the ε-phase, nanocomposites with original anisotropic magnetic properties are in view.
ABSTRACT
Mesoporous silica monoliths with various ordered nanostructures containing transition metal M(2+) cations in variable amounts were elaborated and studied. A phase diagram depicting the different phases as a function of the M(2+) salt/tetramethyl orthosilicate (TMOS) and surfactant P123/TMOS ratios was established. Thermal treatment resulted in mesoporous monoliths containing isolated, accessible M(2+) species or condensed metal oxides, hydroxides, and salts, depending on the strength of the interactions between the metal species and the ethylene oxide units of P123. The ordered mesoporosity of the monoliths containing accessible M(2+) ions was used as a nanoreactor for the elaboration of various transition metal compounds (Prussian blue analogues, Hofmann compounds, metal-organic frameworks), and this opens the way to the elaboration of a large range of nanoparticles of multifunctional materials.
ABSTRACT
Recently we conceived of an original strategy that allows the precipitation of Prussian blue analogues (PBAs) in the ordered pores of silica monoliths to lead to photomagnetic CoFe PBA-silica nanocomposites. To determine the critical parameters and fully control the synthesis of the photoactive CoFe PBA in the pores of the silica matrix, X-ray absorption spectroscopy was performed at the cobalt K-edge. This study showed that cobalt cation chemistry is the keystone of the entire process. The local environment and the electronic structure of the cobalt cation undergo several modifications during the formation process: first the incorporation of the cation as an octahedral complex into the ordered block copolymer phase, then the deprotonation by thermohydrolysis to give a fourfold-coordinated deprotonated lowly condensed species and finally the formation of the 3D coordination network of CoFe PBA in acidic conditions through a rapid reprotonation followed by nucleophilic substitution accompanied by the electronic transfer, thus leading to the photomagnetic Co(III)(LS)-Fe(II)(LS) (LS=low spin) pairs.
ABSTRACT
The research of new molecular materials able to replace classical solid materials in electronics has attracted growing attention over the past decade. Among these compounds photoswitchable Prussian blue analogues (PBA) are particularly interesting for the elaboration of new optical memories. However these coordination polymers are generally synthesised as insoluble powders that cannot be integrated into a real device. Hence their successful integration into real applications depends on an additional processing step. Nanostructured oxides elaborated by sol-gel chemistry combined with surfactant micelle templating can be used as nanoreactors to confine PBA precipitation and organize the functional nano-objects in the three dimensions of space. In this work we present the elaboration of different CoFe PBA/silica nanocomposites. Our synthetic procedure fully controls the synthesis of PBA in the porosity of the silica matrix from the insertion of the precursors up to the formation of the photomagnetic compound. We present results on systems from the simplest to the most elaborate: from disordered xerogels to ordered nanostructured films passing through mesoporous monoliths.
ABSTRACT
The porosity of ordered mesoporous silica monoliths has been successfully used as nanoreactor for the elaboration of CoFe Prussian blue analogue nanoparticles. The nanocomposite exhibits a reversible photomagnetic effect different from that of typical powdered compounds due to particle size reduction.
ABSTRACT
New hybrid nanocomposites based on a methacrylate functionalized titanium-oxo cluster as nano-cross-linker show improved mechanical properties, optical transparency and photochromic activity.
Subject(s)
Nanostructures/chemistry , Organometallic Compounds/chemistry , Titanium/chemistry , Crystallography, X-Ray , Models, Molecular , Molecular Structure , TemperatureABSTRACT
Oxo alcoxo metallic clusters can be employed as inorganic nanobuilding blocks to obtain well-defined organic-inorganic hybrid materials. A better understanding of the surface reactivity of the clusters should allow optimization of the elaboration of hybrid materials through a better control of the hybrid interface. The oxo alcoxo cluster Ti(16)O(16)(OEt)32 presents a shell of labile ethoxy groups that can be selectively transalcoholyzed with preservation of the titanium oxo core, leading to new oxo alcoxo clusters Ti(16)O(16)(OEt)32-x(OR)x (R: alkyl, phenyl, styrenic, etc. groups). The reactivity of the Ti(16)O(16)(OEt)32 cluster toward aliphatic and aromatic alcohols is investigated to determine both the kinetics and the number of substituted titanium atoms, which are strongly dependent on the nature of the alcohol. Characterization of the organic modification of the cluster is performed in situ by liquid (13)C NMR measurements, using the molecular structures of two new clusters, Ti(16)O(16)(OEt)28(OnPr)4 and Ti(16)O(16)(OEt)(24)(OnPr)(8) (OnPr = propoxy groups), as references. The structures of these clusters have been established using single-crystal X-ray diffraction. Moreover, a complete spectroscopic assignment of each ethoxy group is proposed after combining crystallographic data, (13)C NMR T(1) relaxation measurements, and (1)H-(1)H, (1)H-(13)C 2D NMR experiments. Finally, the cluster is functionalized with polymerizable ligands via transalcoholysis and transesterification reactions using hydroxystyrene and acetoxystyrene.
