Time-resolved control of nanoparticle integration in titanium-organic frameworks for enhanced catalytic performance.

Among the multiple applications of metal-organic frameworks (MOFs), their use as a porous platform for the support of metallic nanoparticles stands out for the possibility of integrating a good anchorage, that improves the stability of the catalyst, with the presence of a porous network that allows the diffusion of substrates and products. Here we introduce an alternative way to control the injection of Au nanoparticles at variable stages of nucleation of a titanium(iv) MOF crystal (MUV-10). This allows the analysis of the different modes of nanoparticle integration into the porous matrix as a function of the crystal formation stage and their correlation with the catalytic performance of the resulting composite. Our results reveal a direct effect of the stage at which the Au nanoparticles are integrated into MUV-10 crystals not only on their catalytic activity for the cyclotrimerization of propargyl esters and the hydrochlorination of alkynes, but also on the selectivity and recyclability of the final solid catalyst, which are far superior than those reported for the same reactions with TiO2 supports.

Gold-nanoparticles ingestion disrupts reproduction and development in the German cockroach.

The present work shows the effects of gold nanoparticles (AuNPs) orally administered on reproduction and development of the insect Blattella germanica. Newly emerged females were provided with food containing AuNPs (87.44µg/g) of a size between 15 and 30nm (mean 21.8nm), and were allowed to mate with males. Food ingestion, mortality, reproductive parameters (time to ootheca formation and eclosion, ootheca viability and fertility) as well as postembryonic developmental parameters of the first ootheca (nymphal survival and life span) were recorded throughout the experiment. Gold from AuNPs was accumulated by adults of B. germanica with a bioaccumulation factor of 0.1. Ingestion of AuNPs did not disturb the time for ootheca formation nor ootheca eclosion. However, ootheca viability was decreased almost by 25% in AuNPs treated females in comparison to controls. At the same time the number of hatched nymphs was decreased by 32.8% (p<0.001) in AuNP group respect to control one. The postembryonic developmental parameters were also affected by AuNPs treatment, with a 35.8% of decrease (p<0.01) in number of nymphs that moulted to second and third instars and a reduction of their life span. Ingestion of AuNPs causes sublethal effects in B. germanica that compromises life-traits involved in population dynamics. B. germanica is proposed as a model species in nanotoxicological studies for urban environments.

Hybrid Materials Based on Magnetic Layered Double Hydroxides: A Molecular Perspective.

Design of functional hybrids lies at the very core of synthetic chemistry as it has enabled the development of an unlimited number of solids displaying unprecedented or even improved properties built upon the association at the molecular level of quite disparate components by chemical design. Multifunctional hybrids are a particularly appealing case among hybrid organic/inorganic materials. Here, chemical knowledge is used to deploy molecular components bearing different functionalities within a single solid so that these properties can coexist or event interact leading to unprecedented phenomena. From a molecular perspective, this can be done either by controlled assembly of organic/inorganic molecular tectons into an extended architecture of hybrid nature or by intercalation of organic moieties within the empty channels or interlamellar space offered by inorganic solids with three-dimensional (MOFs, zeolites, and mesoporous hosts) or layered structures (phosphates, silicates, metal dichalcogenides, or anionic clays). This Account specifically illustrates the use of layered double hydroxides (LDHs) in the preparation of magnetic hybrids, in line with the development of soft inorganic chemistry processes (also called "Chimie Douce"), which has significantly contributed to boost the preparation hybrid materials based on solid-state hosts and subsequent development of applications. Several features sustain the importance of LDHs in this context. Their magnetism can be manipulated at a molecular level by adequate choice of constituting metals and interlayer separation for tuning the nature and extent of magnetic interactions across and between planes. They display unparalleled versatility in accommodating a broad range of anionic species in their interlamellar space that encompasses not only simple anions but chemical systems of increasing dimensionality and functionalities. Their swelling characteristics allow for their exfoliation in organic solvents with high dielectric strength, to produce two-dimensional nanosheets with atomic thickness that can be used as macromolecular building blocks in the assembly of nanocomposites. We describe how these advantageous properties turn LDHs into excellent vehicles for the preparation of multifunctional materials with increasing levels of complexity. For clarity, the reader will first find a succinct description of the most relevant aspects controlling the magnetism of LDHs followed by their use in the preparation of magnetic hybrids from a molecular perspective. This includes the intercalation anionic species of increasing nuclearity like paramagnetic mononuclear complexes, stimulus-responsive molecular guests, one- and two-dimensional coordination polymers, or even preassembled 2D networks. This approach allows us to evolve from "dual-function" materials with coexistence, for example, of magnetism and superconductivity, to smart materials in which the magnetic or structural properties of the LDH layers can be tuned by applying an external stimulus like light or temperature. We will conclude with a brief look into the promising features offered by magnetic nanocomposites based on LDHs and our views on the most promising directions to be pursued in this context.

Stimuli-responsive hybrid materials: breathing in magnetic layered double hydroxides induced by a thermoresponsive molecule.

A hybrid magnetic multilayer material of micrometric size, with highly crystalline hexagonal crystals consisting of CoAl-LDH ferromagnetic layers intercalated with thermoresponsive 4-(4-anilinophenylazo)benzenesulfonate (AO5) molecules diluted (ratio 9 : 1) with a flexible sodium dodecylsulphate (SDS) surfactant has been obtained. The resulting material exhibits thermochromism attributable to the isomerization between the azo (prevalent at room temperature) and the hydrazone (favoured at higher temperatures) tautomers, leading to a thermomechanical response. In fact, these crystals exhibited thermally induced motion triggering remarkable changes in the crystal morphology and volume. In situ variable temperature XRD of these thin hybrids shows that the reversible change into the two tautomers is reflected in a shift of the position of the diffraction peaks at high temperatures towards lower interlayer spacing for the hydrazone form, as well as a broadening of the peaks reflecting lower crystallinity and ordering due to non-uniform spacing between the layers. These structural variations between room temperature (basal spacing (BS) = 25.91 Å) and 100 °C (BS = 25.05 Å) are also reflected in the magnetic properties of the layered double hydroxide (LDH) due to the variation of the magnetic coupling between the layers. Overall, our study constitutes one of the few examples showing fully reversible thermo-responsive breathing in a 2D hybrid material. In addition, the magnetic response of the hybrid can be modulated due to the thermotropism of the organic component that, by influencing the distance and in-plane correlation of the inorganic LDH, modulates the magnetism of the CoAl-LDH sheets in a certain range.

Self-Assembly of 1D/2D Hybrid Nanostructures Consisting of a Cd(II) Coordination Polymer and NiAl-Layered Double Hydroxides.

The preparation and characterization of a novel hybrid material based on the combination of a 2D-layered double hydroxide (LDH) nanosheets and a 1D-coordination polymer (1D-CP) has been achieved through a simple mixture of suspensions of both building blocks via an exfoliation/restacking approach. The hybrid material has been thoroughly characterized demonstrating that the 1D-CP moieties are intercalated as well as adsorbed on the surface of the LDH, giving rise to a layered assembly with the coexistence of the functionalities of their initial constituents. This hybrid represents the first example of the assembly of 1D/2D nanomaterials combining LDH with CP and opens the door for a plethora of different functional hybrid systems.

Photo-switching in a hybrid material made of magnetic layered double hydroxides intercalated with azobenzene molecules.

A magnetic photoresponsive hybrid material is prepared by intercalation of a switchable trans-azobenzene-4,4'-dicarboxylate guest in the interlamellar space offered by a ferromagnetic Co(2+)Al(3+)-layered double hydroxide (LDH) host. Magnetic switching is triggered by compression/modification of the in-plane structure coupled the guest's isomerization causing a change in the magnetization of 27%.

Silica supported Fe(3)O(4) magnetic nanoparticles for magnetic solid-phase extraction and magnetic in-tube solid-phase microextraction: application to organophosphorous compounds.

This work demonstrates the application of silica supported Fe3O4 nanoparticles as sorbent phase for magnetic solid-phase extraction (MSPE) and magnetic on-line in-tube solid-phase microextraction (Magnetic-IT-SPME) combined with capillary liquid chromatography-diode array detection (CapLC-DAD) to determine organophosphorous compounds (OPs) at trace level. In MSPE, magnetism is used as separation tool while in Magnetic-IT-SPME, the application of an external magnetic field gave rise to a significant improvement of the adsorption of OPs on the sorbent phase. Extraction efficiency, analysis time, reproducibility and sensitivity have been compared. This work showed that Magnetic-IT-SPME can be extended to OPs with successful results in terms of simplicity, speed, extraction efficiency and limit of detection. Finally, wastewater samples were analysed to determine OPs at nanograms per litre.

Evaluation of Superparamagnetic Silica Nanoparticles for Extraction of Triazines in Magnetic in-Tube Solid Phase Microextraction Coupled to Capillary Liquid Chromatography.

The use of magnetic nanomaterials for analytical applications has increased in the recent years. In particular, magnetic nanomaterials have shown great potential as adsorbent phase in several extraction procedures due to the significant advantages over the conventional methods. In the present work, the influence of magnetic forces over the extraction efficiency of triazines using superparamagnetic silica nanoparticles (NPs) in magnetic in tube solid phase microextraction (Magnetic-IT-SPME) coupled to CapLC has been evaluated. Atrazine, terbutylazine and simazine has been selected as target analytes. The superparamagnetic silica nanomaterial (SiO2-Fe3O4) deposited onto the surface of a capillary column gave rise to a magnetic extraction phase for IT-SPME that provided a enhancemment of the extraction efficiency for triazines. This improvement is based on two phenomena, the superparamegnetic behavior of Fe3O4 NPs and the diamagnetic repulsions that take place in a microfluidic device such a capillary column. A systematic study of analytes adsorption and desorption was conducted as function of the magnetic field and the relationship with triazines magnetic susceptibility. The positive influence of magnetism on the extraction procedure was demonstrated. The analytical characteristics of the optimized procedure were established and the method was applied to the determination of the target analytes in water samples with satisfactory results. When coupling Magnetic-IT-SPME with CapLC, improved adsorption efficiencies (60%-63%) were achieved compared with conventional adsorption materials (0.8%-3%).

Interplay between chemical composition and cation ordering in the magnetism of Ni/Fe layered double hydroxides.

We report the synthesis of a family of ferrimagnetic NiFe layered double hydroxides (LDHs) with a variable Ni(2+)/Fe(3+) in-plane composition of [Ni(1-x)Fe(x)(OH)2](CO3)(x/2)·yH2O (x = 0.20, 0.25, and 0.33) by following a modified homogeneous precipitation. These layered magnets display high crystallinity, homogeneous hexagonal morphologies, and micrometric size that enable their quantitative exfoliation into single layers by sonomechanical treatment of the solids in polar solvents. This was confirmed by dynamic light scattering, UV-vis spectroscopy, high-resolution transmission electron miscroscopy, and atomic force microscopy methodologies to study the resulting steady suspensions. Our magnetic study reflects that the iron content in the LDH layers controls the overall magnetism of these lamellae. Hence, the gradual replacement of Ni(2+) with Fe(3+) centers introduces a larger amount of antiferromagnetically coupled Fe-OH-Fe pairs across the layers, provoking that the compound with the highest Fe/Ni ratio displays spontaneous magnetization at higher temperatures (T(irr) = 15.1 K) and the hardest coercive field (3.6 kG). Mössbauer spectroscopy confirms that the cation distribution in the layers is not random and reflects the occurrence of Fe clustering due to the higher affinity of Fe(3+) ions to accommodate other homometallic centers in their surroundings. In our opinion, this clarifies the origin of the glassy behavior, also reported for other magnetic LDHs, and points out spin frustration as the most likely cause.

Graphene as a carbon source effects the nanometallurgy of nickel in Ni,Mn layered double hydroxide-graphene oxide composites.

Thermal treatment of the hybrid material formed by the spontaneous precipitation of graphene oxide and Ni,Mn layered double hydroxide leads to the segregation of nickel metal nanoparticles (Ni NPs) and the decomposition of graphene to CO(2). Increasing the temperature increases the Ni NP size and results in the complete disappearance of graphene.

Magnetic in-tube solid phase microextraction.

We report a new in-tube solid phase microextraction approach named magnetic in-tube solid phase microextraction, magnetic-IT-SPME. Magnetic-IT-SPME has been developed, taking advantage of magnetic microfluidic principles with the aim to improve extraction efficiency of IT-SPME systems. First, a magnetic hybrid material formed by Fe(3)O(4) nanoparticles supported on SiO(2) was synthesized and immobilized in the surface of a bared fused silica capillary column to obtain a magnetic adsorbent extraction phase. The capillary column was placed inside a magnetic coil that allowed the application of a variable magnetic field. Acetylsalicylic acid, acetaminophen, atenolol, diclofenac, and ibuprofen were tested as target analytes. The application of a controlled magnetic field resulted in quantitative extraction efficiencies of the target analytes between 70 and 100%. These results demonstrated that magnetic forces solve the low extraction efficiency (10-30%) of IT-SPME systems, which is one of their main drawbacks.

Preconcentration of emerging contaminants in environmental water samples by using silica supported Fe3O4 magnetic nanoparticles for improving mass detection in capillary liquid chromatography.

A magnetic material based on Fe(3)O(4) magnetic nanoparticles incorporated in a silica matrix by using a sol-gel procedure has been used to extract and preconcentrate emerging contaminants such as acetylsalicylic acid, acetaminophen, diclofenac and ibuprofen from environmental water samples prior to the analysis with Capillary LC-MS. The use of the proposed silica supported Fe(3)O(4) magnetic nanoparticles enables surfactant free extracts for the analysis with MS detection without interferences in the ionisation step. Under the optimum conditions, we demonstrated the reusability of the magnetic sorbent material during 20 uses without loss in the extraction efficiency. In addition, no cleanup was necessary. The preconcentration factor was 100 and the detection limits were between 50 and 150 ng/L. The proposed procedure has been applied to the analysis of water samples obtaining recoveries between 80 and 110% and RSD values lower than 12%. Concentrations of the target analytes over the range 1.7 and 0.1 µg/L have been found in different water samples.

Coexistence of superconductivity and magnetism by chemical design.

Although the coexistence of superconductivity and ferromagnetism in one compound is rare, some examples of such materials are known to exist. Methods to physically prepare hybrid structures with both competing phases are also known, which rely on the nanofabrication of alternating conducting layers. Chemical methods of building up hybrid materials with organic molecules (superconducting layers) and metal complexes (magnetic layers) have provided examples of superconductivity with some magnetic properties, but not fully ordered. Now, we report a chemical design strategy that uses the self assembly in solution of macromolecular nanosheet building blocks to engineer the coexistence of superconductivity and magnetism in [Ni(0.66)Al(0.33)(OH)(2)][TaS(2)] at ∼4 K. The method is further demonstrated in the isostructural [Ni(0.66)Fe(0.33)(OH)(2)][TaS(2)], in which the magnetic ordering is shifted from 4 K to 16 K.

Confined growth of cyanide-based magnets in two dimensions.

Herein we report the first hybrid magnetic material resulting from the intercalation of a cyanide-based molecular magnet into a solid-state layered host. More specifically, the use of a diamagnetic cationic Zn(II)-Al(lII) layered double hydroxide host allows for the formation of an anionic two-dimensional ferromagnetic Ni(II)-Cr(III) Prussian Blue analogue, from the templated assembly of its ionic molecular components in the confined interlamellar space offered by the inorganic host.

Spontaneous magnetization in Ni-Al and Ni-Fe layered double hydroxides.

Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses.