No abstract

Exceptional magnetic properties of magnetite, Fe3O4, nanoparticles make them one of the most intensively studied inorganic nanomaterials for biomedical applications. We report successful gram-scale syntheses, via hydrothermal route or controlled coprecipitation in an automated reactor, of colloidal Fe3O4 nanoparticles with sizes of 12.9 ± 5.9, 17.9 ± 4.4, and 19.8 ± 3.2 nm. To investigate structure–property relationships as a function of the synthetic procedure, we used multiple techniques to characterize the structure, phase composition, and magnetic behavior of these nanoparticles. For the iron oxide cores of these nanoparticles, powder X-ray diffraction and electron microscopy both confirm single-phase Fe3O4 composition. In addition to the core composition, the magnetic performance of nanoparticles in the 13–20 nm size range can be strongly influenced by the surface properties, which we analyzed by three complementary techniques. Raman scattering and X-ray photoelectron spectroscopy (XPS) measurements indicate overoxidation of nanoparticle surfaces, while transmission electron microscopy (TEM) shows no distinct core–shell structure. Considered together, Raman, XPS, and TEM observations suggest that our nanoparticles have a gradually varying nonstoichiometric Fe3O4+δ composition, which could be attributed to the formation of Fe3O4–γ-Fe2O3 solid solutions at their outermost surface. Detailed analyses by TEM reveal that the hydrothermally produced samples include single-domain nanocrystals coexisting with defective twinned and dimer nanoparticles, which form as a result of oriented-attachment crystal growth. All our nanoparticles exhibit superparamagnetic-like behavior with a characteristic blocking temperature above room temperature. We attribute the estimated saturation magnetization values up to 84.01 ± 0.25 emu/g at 300 K to the relatively large size of the nanoparticles (13–20 nm) coupled with the syntheses under elevated temperature; alternative explanations, such as surface-mediated effects, are not supported by our spectroscopy or microscopy measurements. For these colloids, the heating efficiency in magnetic hyperthermia correlates with their saturation magnetization, making them appealing for therapeutic and other biomedical applications that rely on high-performance nanoparticle-mediated hyperthermia.

Co-self-assembly of mesostructured silica films from solutions of tetrahydrofuran (THF) and water, silica precursor species, and structure-directing Pluronic P123 block-copolymer molecules is reported with and without conjugated polymer guest species. The solution-phase behavior of the ternary THF-water-P123 system guided the selection of nonequilibrium synthesis conditions that allowed highly ordered 2D hexagonal or lamellar mesostructured silica to be prepared. Dilute water molecules produced in situ by silica condensation were necessary and sufficient to promote P123 self-aggregation into micelles and ultimately liquid crystal-like inorganic-organic mesophases as the THF evaporated. Solid-state twodimensional 13 C{ 1 H} and 29 Si{ 1 H} NMR characterization of the product film materials revealed highly mobile block copolymer components at room temperature and preferential interactions of poly(ethylene oxide) moieties with the silica framework at 260 K. Solution processing in THF permitted highly hydrophobic, high molecular weight, conjugated polymers to be directly coassembled within the mesostructured inorganic-organic host matrices during their formation. The incorporated conjugated polymers exhibited semiconducting properties and enhanced environmental photo-stability that may be exploited in electronic and optoelectronic devices.

A series of colloidal M x Fe 3−x O 4 (M = Mn, Co, Ni; x = 0−1) nanoparticles with diameters ranging from 6.8 to 11.6 nm was synthesized by hydrothermal reaction in aqueous medium at low temperature (200 °C). Energy-dispersive X-ray microanalysis and inductively coupled plasma spectrometry confirm that the actual elemental compositions agree well with the nominal ones. The structural properties of the obtained nanoparticles were investigated by powder X-ray diffraction, Raman spectroscopy, Mossbauer spectroscopy, X-ray and neutron pair distribution function analysis, and electron microscopy. The results demonstrate that our synthesis technique leads to the formation of chemically uniform single-phase solid solution nanoparticles with cubic spinel structure, confirming intrinsic doping. The local structure of the Fe 3 O 4 NPs is distorted with respect to the cubic inverse-spinel structure, while chemical substitution of Fe by Mn or Ni partially eliminates the local distortions. Magnetic studies showed that, in comparison to nondoped Fe 3 O 4 , the saturation magnetization (M s ) of M x Fe 3−x O 4 (M = Mn, Ni) decreases with increasing dopant concentration, while Co-doped samples showed similar M s . On the other hand, whereas Mn-and Ni-doped nanoparticles exhibit superparamagnetic behavior at room temperature, ferrimagnetism emerges for Co x Fe 3−x O 4 nanoparticles, which can be tuned by the level of Co doping.

We report on the self-aggregation of the cationic dye pinacyanol acetate and its use for the preparation of nanostructured silica via templated sol-gel reaction. The dye forms nematic and hexagonal chromonic liquid crystals at low concentrations in water (i.e., from 0.75 wt %); the type of counterion appears to play an important role in liquid crystal formation. From analysis of small X-ray scattering (SAXS) curves, it is inferred that dye aggregates have the morphology of hollow long tubes with one-molecule-thick walls; the diameter of the tubes does not to change much with concentration. The dye aggregates can be aligned by shear or by a magnetic field. The high-resolution (1)H NMR spectra show that aggregation takes place over a range of concentrations rather than having a sharp "critical" aggregation. Within the aggregates the conjugated moiety, including the three-carbon link, is in close proximity to the aromatic groups of stack neighbors. On the other hand, dye aggregates direct the formation of silica nanofibers synthesized via sol-gel reaction, mimicking the elongated structures found in aqueous media. The nanofibers show a hierarchical organization; i.e., they contain hexagonal arrays of 3 nm cylindrical mesopores left after calcination of the templating molecules, and the pore walls are 2.7 nm thick. As the nanofibers form entangled networks, the obtained materials also show interparticle porosity. The present findings open new possibilities for the use of commercial cationic dyes in the synthesis of nanostructured materials.

Island clusters: By using kinetic control, stable Agn clusters (n≤10) are synthesized in microemulsions. Nanoislands composed of the subnanosized clusters can be deposited onto a substrate (see picture). The clusters are characterized by a variety of methods, including scanning tunneling microscopy (STM), mass spectrometry, UV/Vis spectroscopy, and differential pulse voltammetry.

Magnetic macroporous polymers have been successfully prepared using Pickering high internal phase ratio emulsions (HIPEs) as templates. To stabilize the HIPEs, two types of oleic acid-modified iron oxide nanoparticles (NPs) were used as emulsifiers. The results revealed that partially hydrophobic NPs could stabilize W/O HIPEs with an internal phase above 90%. Depending upon the oleic acid content, the nanoparticles showed either an arrangement at the oil-water interface or a partial dispersion into the oil phase. Such different abilities to migrate to the interface had significant effects on the maximum internal phase fraction achievable and the droplet size distribution of the emulsions. Highly macroporous composite polymers were obtained by polymerization in the external phase of these emulsions. The density, porosity, pore morphology and magnetic properties were characterized as a function of the oleic acid content, concentration of NPs, and internal phase volume of the initial HIPEs. SEM imaging indicated that a close-cell structure was obtained. Furthermore, the composite materials showed superparamagnetic behavior and a relatively high magnetic moment.

An effective method to boost electrocatalytic activity of nickel phosphides in H 2 evolution reaction is reported. The method took advantage of density functional theory calculations that allowed design of highly active material based on combination of d-metal with p-metal within a phosphide structure. Furthermore, principle is proven experimentally through successful synthesis of self-supported ternary Al−Ni−P foam electrocatalyst by alloying of Ni and Al followed by gas transport phosphorization reaction. As a cathode for H 2 evolution reaction in acidic electrolyte, Al−Ni−P significantly outperforms pure Ni−P, and it has an exchange current density of 0.6 mA/cm 2 and Tafel slope of 65 mV/decade.