Magnetically Induced CO2 Methanation Using Exchange-Coupled Spinel Ferrites in Cuboctahedron-Shaped Nanocrystals.

Magnetically induced catalysis can be promoted taking advantage of optimal heating properties from the magnetic nanoparticles to be employed. However, when unprotected, these heating agents that are usually air-sensitive, get sintered under the harsh catalytic conditions. In this context, we present, to the best of our knowledge, the first example of air-stable magnetic nanoparticles that: 1) show excellent performance as heating agents in the CO2 methanation catalyzed by Ni/SiRAlOx, with CH4 yields above 95 %, and 2) do not sinter under reaction conditions. To attain both characteristics we demonstrate, first the exchange-coupled magnetic approach as an alternative and effective way to tune the magnetic response and heating efficiency, and second, the chemical stability of cuboctahedron-shaped core-shell hard CoFe2 O4 -soft Fe3 O4 nanoparticles.

Engineered Nanostructured Materials for Ofloxacin Delivery.

Antibiotic resistance is emerging as a growing worldwide problem and finding solutions to this issue is becoming a new challenge for scientists. As the development of new drugs slowed down, advances in nanotechnology offer great opportunities, with the possibility of designing new systems for carrying, delivery and administration of drugs already in use. Engineered combinations of the synthetic, broad-spectrum antibiotic ofloxacin, rarely studied in this field, with different types of silver, mesoporous silica-based and Pluronic/silica-based nanoparticles have been explored. The nanocarriers as silver core@silica mesoporous (AgMSNPs) and dye-doped silica nanoparticles functionalized with ofloxacin were synthesized and their antibacterial properties studied against S. aureus and E. coli. The best antibacterial results were obtained for the AgMSNPs nanosystem@ofloxacin for the strain S. aureus ATCC 25923, with MIC and MBC values of 5 and 25 µg/mL, proving the efficacy and synergetic effect of the antibiotic and the Ag core of the nanoparticles.

Shaping iron oxide nanocrystals for magnetic separation applications.

Iron oxide nanostructures are attractive for a variety of bio-related applications given their wide range of magnetic properties. Here, we report on the study of the magnetophoretic mobility of octapod-shaped nanocrystals, which we relate to stoichiometry, quality and elongation in the 111 direction of these cubic structures. This special morphology combines magnetocrystalline anisotropies, increases shape anisotropy and hinders the formation of an epitaxial wüstite-magnetite interface. As a result, one obtains nanocrystals with large magnetic susceptibility and small coercivity, that is, with optimum characteristics for magnetic guidance, separation, and drug delivery, due to the increased magnetophoretic mobility displayed.

Toxicological Evaluation of Luminescent Silica Nanoparticles as New Drug Nanocarriers in Different Cancer Cell Lines.

Luminescent mesoporous silica nanoparticles, CdTeQDs@MNs@PEG1, SiQDs@Isoc@MNs and SiQDs@Isoc@MNs@PEG2, were successfully synthetized and characterized by SEM, TEM, XRD, N2 nitrogen isotherms, ¹H NMR, IR, absorption, and emission spectroscopy. Cytotoxic evaluation of these nanoparticles was performed in relevant in vitro cell models, such as human hepatoma HepG2, human brain endothelial (hCMEC/D3), and human epithelial colorectal adenocarcinoma (Caco-2) cell lines. None of the tested nanoparticles showed significant cytotoxicity in any of the three performed assays (MTT/NR/ LDH) compared with the respective solvent and/or coating controls, excepting for CdTeQDs@MNs@PEG1 nanoparticles, where significant toxicity was noticed in hCMEC/D3 cells. The results presented reveal that SiQDs-based mesoporous silica nanoparticles are promising nanoplatforms for cancer treatment, with a pH-responsive drug release profile and the ability to load 80% of doxorubicin.

Plasmonic Retrofitting of Membrane Materials: Shifting from Self-Regulation to On-Command Control of Fluid Flow.

This work calls for a paradigm shift in order to change the operational patterns of self-regulated membranes in response to chemical signals. To this end, the fabrication of a retrofitting material is introduced aimed at developing an innovative generation of porous substrates endowed with symbiotic but fully independent sensing and actuating capabilities. This is accomplished by transferring carefully engineered plasmonic architectures onto commercial microfiltration membranes lacking of such features. The integration of these materials leads to the formation of a coating surface proficient for ultrasensitive detection and "on-command" gating. Both functionalities can be synergistically modulated by the spatial and temporal distribution of an impinging light beam offering an unprecedented control over the membrane performance in terms of permeability. The implementation of these hybrid nanocomposites in conventional polymeric porous materials holds great potential in applications ranging from intelligent fluid management to advanced filtration technologies and controlled release.

Synthesis and Characterization of PtTe2 Multi-Crystallite Nanoparticles using Organotellurium Nanocomposites.

Herein, we report the synthesis of new PtTe2 multi-crystallite nanoparticles (NPs) in different sizes through an annealing process using new nanostructured Pt-Te organometallic NPs as a single source precursor. This precursor was obtained in a single reaction step using Ph2Te2 and H2PtCl6 and could be successfully size controlled in the nanoscale range. The resulting organometallic composite precursor could be thermally decomposed in 1,5 pentanediol to yield the new PtTe2 multi-crystallite NPs. The final size of the multi-crystallite spheres was successfully controlled by selecting the nanoprecursor size. The sizes of the PtTe2 crystallites formed using the large spheres were estimated to be in the range of 2.5-6.5 nm. The results provide information relevant to understanding specific mechanistic aspects related to the synthesis of organometallic nanomaterials and nanocrystals based on platinum and tellurium.

Redispersion and Self-Assembly of C60 Fullerene in Water and Toluene.

This work aims at assessing the influence of two different solvents, bidistilled water and toluene, on dispersions of carbon-based engineered nanomaterials, namely, fullerenes, and their self-assembly behavior. The obtained self-assembled carbon-based materials were characterized using UV-vis spectrophotometry and transmission electron microscopy techniques. The results obtained were unexpected when toluene was used for dispersing fullerene C60, with the formation of two different types of self-assembled structures: fullerene C60 nanowhiskers (FNWs) and a type of quasispherical nanostructure. The FNWs ranged between 1 and 6 µm in length, whereas the quasispherical fullerene C60 nanoaggregates ranged between 10 and 50 nm in diameter. Aggregates obtained in toluene showed a well-formed crystal structure. When using water, the obtained aggregates were amorphous and showed a no well-defined shape. Their sizes ranged between 20 and 40 nm for nanosized structures and between 0.4 and 4.8 µm for micron-sized self-aggregates.

Unraveling the Organotellurium Chemistry Applied to the Synthesis of Gold Nanomaterials.

Long-term preservation of the properties of gold nanoparticles in both solution and the dry powder form can be difficult. We have overcome this challenge by using organotellurium derivatives as both reducing agents and stabilizers in the synthesis of gold nanoparticles. This new synthetic protocol takes advantage of the photochemical and oxidative properties of diphenyl ditelluride (Ph2Te2), which, so far, have never been exploited in the synthesis of gold nanoparticles. The Au/Te core/shell (inorganic/organic) hybrid nanomaterial can be obtained in a one-step reaction, using only Ph2Te2 and HAuCl4. By modifying the reaction conditions, different resonance conditions of the gold core are achieved due to the formation of external shells with different thicknesses. The organotellurium shell can be easily removed by resuspension of the nanoparticles in environmentally friendly solvents, such as water or ethanol, making the Au core available for subsequent applications. A mechanism for the formation of core/shell nanoparticles has also been discussed.

Room-temperature ferromagnetism in thin films of LaMnO3 deposited by a chemical method over large areas.

Hole-doping into the Mott insulator LaMnO3 results in a very rich magneto-electric phase diagram, including colossal magnetoresistance and different types of charge and orbital ordering. On the other hand, LaMnO3 presents an important catalytic activity for oxygen reduction, which is fundamental for increasing the efficiency of solid-oxide fuel cells and other energy-conversion devices. In this work, we report the chemical solution (water-based) synthesis of high-quality epitaxial thin films of LaMnO3, free of defects at square-centimeter scales, and compatible with standard microfabrication techniques. The films show a robust ferromagnetic moment and large magnetoresistance at room temperature. Through a comparison with films grown by pulsed laser deposition, we show that the quasi-equilibrium growth conditions characteristic of this chemical process can be exploited to tune new functionalities of the material.

Unveiling nanometer scale extinction and scattering phenomena through combined electron energy loss spectroscopy and cathodoluminescence measurements.

Plasmon modes of the exact same individual gold nanoprisms are investigated through combined nanometer-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) measurements. We show that CL only probes the radiative modes, in contrast to EELS, which additionally reveals dark modes. The combination of both techniques on the same particles thus provides complementary information and also demonstrates that although the radiative modes give rise to very similar spatial distributions when probed by EELS or CL, their resonant energies appear to be different. We trace this phenomenon back to plasmon dissipation, which affects in different ways the plasmon signatures probed by these techniques. Our experiments are in agreement with electromagnetic numerical simulations and can be further interpreted within the framework of a quasistatic analytical model. We therefore demonstrate that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution.

Room-temperature ferromagnetism in antiferromagnetic cobalt oxide nanooctahedra.

Cobalt oxide octahedra were synthesized by thermal decomposition. Each octahedron-shaped nanoparticle consists of an antiferromagnetic CoO core enclosed by eight {111} facets interfaced to a thin (∼ 4 nm) surface layer of strained Co3O4. The nearly perfectly octahedral shaped particles with 20, 40, and 85 nm edge length show a weak room-temperature ferromagnetism that can be attributed to ferromagnetic correlations appearing due to strained lattice configurations at the CoO/Co3O4 interface.

Synthesis of functionalized fluorescent silver nanoparticles and their toxicological effect in aquatic environments (Goldfish) and HEPG2 cells.

Silver nanoparticles, AgNPs, are widely used in our daily life, mostly due to their antibacterial, antiviral, and antifungal properties. However, their potential toxicity remains unclear. In order to unravel this issue, emissive AgNPs were first synthetized using an inexpensive photochemical method, and then their permeation was assessed in vivo in goldfish and in vitro in human hepatoma cells (HepG2). In addition, the oxidative stress caused by AgNPs was assessed in enzymes such as glutathione-S-transferase (GST), catalase (CAT), and in lipid peroxidation (LPO). This study demonstrates that the smallest sized AgNPs@3 promote the largest changes in gold fish livers, whereas AgNPs@1 were found to be toxic in HEPG2 cells depending on both the size and functionalized/stabilizer ligand.

Multiwalled carbon nanotubes drive the activity of metal@oxide core-shell catalysts in modular nanocomposites.

Rational nanostructure manipulation has been used to prepare nanocomposites in which multiwalled carbon nanotubes (MWCNTs) were embedded inside mesoporous layers of oxides (TiO(2), ZrO(2), or CeO(2)), which in turn contained dispersed metal nanoparticles (Pd or Pt). We show that the MWCNTs induce the crystallization of the oxide layer at room temperature and that the mesoporous oxide shell allows the particles to be accessible for catalytic reactions. In contrast to samples prepared in the absence of MWCNTs, both the activity and the stability of core-shell catalysts is largely enhanced, resulting in nanocomposites with remarkable performance for the water-gas-shift reaction, photocatalytic reforming of methanol, and Suzuki coupling. The modular approach shown here demonstrates that high-performance catalytic materials can be obtained through the precise organization of nanoscale building blocks.

Surface plasmon mapping of dumbbell-shaped gold nanorods: the effect of silver coating.

We report on the identification of surface plasmons in individual gold dumbbell-shaped nanoparticles (AuDBs), as well as AuDBs coated with silver. We use spatially resolved electron energy-loss spectroscopy in a scanning electron microscope, which allows us to map plasmon-energy and intensity spatial distributions. Two dominant plasmon resonances are experimentally resolved in both AuDBs and silver-coated AuDBs. The intensity of these features is peaked either at the tips or at the sides of the nanoparticles. We present boundary element method simulations in good agreement with the experiment, allowing us to elucidate the nature of such modes. While the lower-energy, tip-focused plasmon is of longitudinal character for all dumbbells under consideration, the second side-bound plasmon has a more involved symmetry, starting as a longitudinal quadrupole in homogeneous AuDBs and picking up transversal components when silver coating is added. The longitudinal dipolar mode energy is found to blue-shift upon coating with silver. We find that the substrate produces sizable shifts in the plasmons of silver-coated AuDBs. Our analysis portraits a complex plasmonic scenario in metal nanoparticles coated with silver, including a transition from the original homogeneous gold dumbbell plasmons to the modes of homogeneous silver rods. We believe that these findings can have potential application to plasmon engineering.

Highly active nanoreactors: nanomaterial encapsulation based on confined catalysis.

It happens inside: highly active nanoreactors are prepared by encapsulating dendritic Pt nanoparticles (NPs) grown on a polystyrene template inside hollow porous silica capsules. The catalytic activity of these Pt NPs is preserved after encapsulation and template removal. Different metals, such as Ni, can thus be reduced inside the capsules, thereby leading to the formation of composites with tunable magnetic properties.

Growth and branching of gold nanoparticles through mesoporous silica thin films.

Composite materials made of mesoporous oxide thin films containing metallic nanoparticles are of high interest in various fields, including catalysis, biosensing and non-linear optics. We demonstrate in this work the fabrication of such composite materials containing a sub-monolayer of gold nanoparticles (GNPs) of various shapes covered with mesoporous silica thin films. Additionally, the shape of the GNPs (and thus their optical properties) can be modified in situ through seeded growth and branching. Such growth proceeds upon wetting with HAuCl(4) solution, a surfactant (cetyltrimethylammonium bromide, CTAB) and a mild reducing agent (ascorbic acid, AA). The effect of varying several reaction parameters (time and CTAB and AA concentrations) was evaluated, showing that more anisotropic particles are obtained at longer reaction times, lower CTAB concentration and higher AA concentration. The final shape of the GNPs was also found to depend on their initial shape and size, as well as the pore size of the mesoporous film covering them. Because the growth proceeds through the pores of the film, it may lead to shapes that are not easily obtained in solution, such as particles with branches on one side only. Finally, we have confirmed that no damage was induced to the mesoporous silica structure during the growth process and thus the final particles remain well covered by the thin film, which can eventually be used as a filter between the GNPs and the outer medium.

Acoustic Vibrations in Bimetallic Au@Pd Core-Shell Nanorods.

The acoustic vibrations of gold nanorods coated with palladium were investigated as a function of Pd amount using ultrafast pump-probe spectroscopy. Both the extensional and breathing vibrational modes of the nanorods were coherently excited and detected. This permits precise determination of their periods, which were found to decrease and increase with Pd deposition, for the extensional and vibrational modes, respectively. These opposite behaviors reflect changes of the nanoparticle size and mechanical properties, in agreement with numerical simulations. Comparison of experimental and computed periods yields information on the amount of deposited Pd, providing a novel tool to characterize bicomponent nano-objects for small fractions of one of the components (Pd/Au atomic fraction down to 5%).

Novel small stable gold nanoparticles bearing fluorescent cysteine-coumarin probes as new metal-modulated chemosensors.

Emissive molecular probes based on amino acid moieties are very appealing because of their application as new building blocks in peptide synthesis. Two new bioinspired coumarin probes (L1 and L2) were synthesized and fully characterized by elemental analysis, infrared, (1)H NMR, (13)C NMR, UV-vis absorption and emission spectroscopy, matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF-MS), lifetime measurements, and X-ray crystal diffraction. Their sensing ability toward alkaline earth, transition, and post-transition metal ions (Ca(2+), Zn(2+), Cd(2+), Cu(2+), Ni(2+), Hg(2+), Ag(+), and Al(3+)) and their acid-base behavior (H(+), OH(-)) were explored in absolute ethanol by absorption and fluorescence spectroscopy. Compound L1 shows a strong complexation constant with the soft metal ions Zn(2+), Cd(2+), and Ag(+). Compound L2 shows a high fluorescence quantum yield, and it could be used as a non-pH-dependent fluorescent biological probe. Very small gold nanoparticles (AuNPs) using compounds L1 and L2 as stabilizers were obtained by using a reductive method and were characterized by UV-vis, light scattering, and transmission electron microscopy (TEM). Dynamic light scattering and TEM studies show that the formation of small nanoparticles is around 4.27 ± 0.64 nm for L1 and around 2.69 ± 0.96 nm for L2. The new stable Cou@AuNPs behaved as supramolecular chemosensors, which have been selective for the heavy element Hg(2+), with a concomitant change of color from pink to dark red/brown and an increase of size up to 100-fold.

Growth of pentatwinned gold nanorods into truncated decahedra.

The growth mechanism from pentatwinned (PTW) gold nanorods into truncated quasi-decahedral particles when a gold salt (HAuCl4) is reduced by N, N-dimethylformamide (DMF) in the presence of poly(vinylpyrrolidone), was elucidated through a combination of different techniques, including transmission and scanning electron microscopy, high resolution TEM and selected area electron diffraction. Particles with intermediate shapes between the original pentatwinned Au nanorods, used as seeds, and the final quasi-decahedral particles were obtained by simply tuning the [HAuCl4] to [seeds] ratio. From the thorough structural analysis of all the intermediate morphologies obtained, it was concluded that gradual morphology changes are related to the preferential growth of higher energy crystallographic facets. As a result of the particle growth and concomitant decreased anisotropy, a progressive blue-shift of the surface plasmon resonance bands of the nanoparticles was registered by vis-NIR extinction spectroscopy.