Cathodic corrosion as a facile and effective method to prepare clean metal alloy nanoparticles

The cathodic corrosion method described here is a simple, clean, and fast way of synthesizing nanoalloys with high catalytic performance. Using a series of Pt-Rh alloys as an example, we show that this one-step method can convert a bulk alloy electrode into an aqueous suspension of nanoparticles, retaining the composition and crystal lattice structure of the starting alloy. Compared to pure metals, these alloy nanocatalysts are more active toward CO and methanol oxidation and nitrate reduction reactions. Nanoparticles made of PtRu, PtIr, PtNi, AuCo, AuCu, and FeCo bulk alloys demonstrate the universality of this synthesis method.     

A novel route to obtain metal and oxide nanoparticles co-existing on a substrate

In this work we present a novel route to cover large surfaces with metal and oxide nanoparticles (NPs) by growing and annealing of metallic bilayers. We have used this method to fabricate ensembles of Au and α-Fe₂O₃ NPs on silica substrates from Fe/Au bilayers. The morphology of the hybrid nanostructures and the presence of defects and disorder can be tuned through the processing parameters as the initial film thickness and the annealing conditions. The proximity effects between both types of NPs alter their physical properties. In particular, we observe that the presence of α-Fe₂O₃ NPs modifies the surface plasmon resonance of Au NPs.     

Nanorods of transition metal oxalates: A versatile route to the oxide nanoparticles

A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ～55 nm in diameter. Oxides with different morphology, Fe₃O₄ nanoparticles faceted (cuboidal) and Fe₂O₃ nanoparticles (spherical) could be obtained.     

A facile route to synthesize silver nanoparticles in polyelectrolyte capsules

We are reporting a novel green approach to incorporate silver nanoparticles (NPs) selectively in the polyelectrolyte capsule shell for remote opening of polyelectrolyte capsules. This approach involves in situ reduction of silver nitrate to silver NPs using PEG as a reducing agent (polyol reduction method). These nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica template followed by the synthesis of silver NPs and subsequently the dissolution of the silica core. The size of silver nanoparticles synthesized was 60±20 nm which increased to 100±20 nm when the concentration of AgNO(3) increased from 25 mM to 50 mM. The incorporated silver NPs induced rupture and deformation of the capsules under laser irradiation. This method has advantages over other conventional methods involving chemical agents that are associated with cytotoxicity in biological applications such as drug delivery and catalysis.     

Synthesis and characterization of ultrafine CeF3 nanoparticles modified by catanionic surfactant via a reverse micelles route

In this article, we firstly reported on the synthesis and characterization of ultrafine CeF3 nanoparticles (NPs) modified by catanionic surfactant via a reverse micelles-based route. The catanionic surfactant PN was prepared by mixing the di(2-ethylhexyl) phosphoric acid (DEHPA) and primary amine (N1923) with 1:1 molar ratio. It exhibited a high surface activity and formed much small reverse micelles in comparison with its individual component (DEHPA or N1923). The PN reverse micelles were then used as templates to prepare ultrafine CeF3 NPs. The narrow distributed nanoparticles have an average diameter 1.8 nm. FTIR spectra indicated that there existed strong chemical interactions between nanoparticles and the adsorbed surfactants. The modification resulted in the FTIR peak position of PO shifting to lower energy. Due to the effect of modification and small size, the CeF3 NPs showed a remarkable red shift of 54 nm in the fluorescence emission in comparison with that of bulk material and a red shift of 18 nm in contrast with that of the normal CeF3 NPs with an average diameter of 16 nm.     

A facile route to design pH-responsive viscoelastic wormlike micelles: Smart use of hydrotropes

A simple and effective route to design pH-responsive viscoelastic wormlike micelles based on commercial compounds is reported. According to this route, pH-sensitive viscoelastic fluids can be easily obtained by introducing a pH-responsive hydrotrope into a surfactant solution. In this paper, the mixed system of cetyltrimethylammonium bromide (CTAB) and potassium phthalic acid (PPA) was studied in detail. This pH-sensitive fluid can be switched between a gellike state and a waterlike state within a narrow pH change. Rheology and DLS results revealed that the pH-sensitive flowing behavior was attributed to the microstructure transition between wormlike micelles and short cylindrical micelles. Combined with fluorescence anisotropy, NMR, and UV–vis, it was demonstrated that the pH response of viscoelastic fluid originated from the different binding abilities of hydrotrope to surfactant as pH varies. Furthermore, different kinds of hydrotropes can be utilized to prepare pH-responsive viscoelastic fluids in the desired pH areas.     

A facile chemical route to semiconductor metal sulfide nanocrystal superlattices

We report a facile chemical route for the synthesis of monodisperse nanocrystals of various metal sulfides (PbS, Cu(2)S, and Ag(2)S) and their assemblies into nanocrystal superlattices (NCSs); the sulfides NCSs were precipitated by adding ethanol to nanocrystal colloids, which were obtained directly by a reaction between metal thiolate and thioacetamide in a pure dodecanethiol solvent.     

A facile "dispersion-decomposition" route to metal sulfide nanocrystals

In this paper, we demonstrate a simple and general "dispersion-decomposition" approach to the synthesis of metal sulfide nanocrystals with the assistance of alkylthiol. This is a direct heating process without precursor injection. By using inorganic metal salts and alkylthiol as the raw materials, high-quality Ag(2)S, Cu(2)S, PbS, Ni(3)S(4), CdS, and ZnS nanocrystals were successfully synthesized. The mechanism study shows that the reaction undergoes two steps. A key intermediate compound, metal thiolate, is generated first. It melts and disperses into the solvent at a relatively low temperature, and then it decomposes into metal sulfide as a single precursor upon heating. This method avoids using toxic phosphine agent and injection during the reaction process. The size and shape of the nanocrystal can be also controlled by the concentration of the reactant and ligands. Furthermore, the optical properties and assembly of the nanocrystals have also been studied. This report provides a facile, direct-heating "dispersion-decomposition" approach to synthesize metal sulfides nanocrystals that has potential for future large-scale synthesis.     

Metal exchange in organomercury complexes; a facile route to cyclometallated transition metal complexes

Cyclometallated derivatives of 2-phenylpyridine (HL) are readily obtained by transmetallation reactions of 2-(2′-pyridyl)phenylmercury(II) chloride, [Hg(L)Cl], with labile transition metal compounds. The products of these reactions are cyclometallated, containing metalcarbon bonds. The yields are high, and comparable with or better than those obtained from direct reactions with 2-phenylpyridine. The products are easily isolated, and are unequivocally metallated. The metal exchange reaction may be used to prepare cyclometallated complexes which are not available by direct reaction with 2-phenylpyridine. The use of the mercury(II) complex enables the use of kinetically inert chloro complexes in the transmetallation.     

Energy transfer from C-phycocyanin to phthalocyanine metal complex in reverse micelles

A new mimic system of photosynthetic apparatus was constructed from C-phycocyanin and phthalocyanine zinc. C-PC was solubilized in the reverse micelles of non ionic surfactant Tween-80, cosurfactant pentanol, and solvent cyclohexane, in which the overall concentration of surfactant was 20% (w/v) and the mass ratio of Tween-80 to pentanol was 4:1. When the molar ratio of water to Tween-80 (R_w)≥9.0, the characteristic properties of C-PC were maintained. When it was excited, the energy transfer from C-PC to phthalocyanine zinc took place. The energy transfer efficiency was only related with the concentration of phthalocyanine, but not that of C-PC. Furthermore, the energy transfer was roughly in keeping with Perrin formulation, which indicated that the energy transfer took place approximately through dipole-dipole interaction in rigid system. The radii of the quenching sphere were calculated from the experimental results. For example, when the concentration of phthalocyanine zinc was 2.10 × 10~(-4) mol/     

Generalized route to metal nanoparticles with liquid behavior

We report the generalized synthesis of metal nanoparticles with liquid-like behavior. We introduce a thiol-containing ionic liquid, N,N-dioctyl-N-(3-mercaptopropyl)-N-methylammonium bromide, which serves as a ligand for platinum, gold, palladium, and rhodium nanoparticles. A rapid reduction using THF-soluble metal salts in the presence of the thiol generates nanoparticles with tunable sizes and size distributions. The as-synthesized nanoparticles are a solid and decompose before melting. Upon exchange of the halide anion for an amphiphilic sulfonate anion, however, the nanoparticles exhibit liquid-like properties at room temperature. The liquids have high metal loadings; for example, the 2.7 nm platinum nanoparticle liquid is 36% platinum by mass.     

Biochemical synthesis of gold and zinc nanoparticles in reverse micelles

Gold and zinc nanoparticles were obtained in AOT reverse micelles in isooctane by reduction of the corresponding metal ions by the natural pigment quercetin (the biochemical synthesis technique). Gold and zinc ions were introduced into the micellar solution of quercetin in the form of aqueous solutions, HAuCl₄ and [Zn(NH₃)₄]SO₄, to the water to AOT molar ratios 1–3 and 3–4, respectively. The process of nanoparticle formation was investigated by spectrophotometry. Nanoparticle size and shape were determined by transmission electron microscopy. The data obtained allow to conclude that there are two steps in metal ion-quercetin interaction: (1) complex formation, and (2) complex dissociation with subsequent formation of nanoparticles and a second product, presumably oxidized quercetin. Gold nanoparticles were found to be of various shapes (spheres, hexahedrons, triangles, and cylinders) and sizes, mainly in the 10–20 nm range; zinc nanoparticles are chiefly spherical and ～5 nm in size. In both cases, the nanoparticles are stable in the air in micellar solution over long periods of time (from a several months to a several years).     

Tuning the properties of CdSe nanoparticles in reverse micelles

A new and simple approach of synthesizing size-quantized CdSe colloids in reverse micellar suspension is described. The room temperature reaction between Cd²⁺ and selenosulfate is carried out within the water pool of di-octyl sulphosuccinate (Aerosol-OT) reverse micelles. The size dependent absorption and emission properties of these small CdSe particles (3—5 nm) are described. The Q-sized CdSe nanoparticles exhibit an emission yield of 0.13. Up to a factor of two enhancement in the emission efficiency can be achieved following the surface functionalization of CdSe colloids with triethyl amine.     

Modulation of dynamics and reactivity of water in reverse micelles of mixed surfactants

In this contribution, we attempt to correlate the change in water dynamics in a reverse micellar (RM) core caused by the modification of the interface by mixing an anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and a nonionic surfactant, tetraethylene glycol monododecyl ether (Brij-30), at different proportions, and its consequent effect on the reactivity of water, measured by monitoring the solvolysis reaction of benzoyl chloride (BzCl). The dimension of the RM droplets at different mixing ratios of AOT and Brij-30 (X(Brij-30)) has been measured using dynamic light scattering (DLS) technique. The physical properties of the RM water have been determined using Fourier transform infrared spectroscopy (FTIR) and compressibility studies, which show that with increasing X(Brij-30), the water properties tend toward that of bulk-like water. The solvation dynamics, probed by coumarin 500 dye, gets faster with X(Brij-30). The rotational anisotropy studies along with a wobbling-in-cone analysis show that the probe experiences less restriction at higher X(Brij-30). The kinetics of the water-mediated solvolysis also gets faster with X(Brij-30). The increased rate of solvolysis has been correlated with the accelerated solvation dynamics, which is another consequence of surfactant headgroup-water interaction.     

A simple urea-based route to ternary metal oxynitride nanoparticles

Ternary metal oxynitrides are generally prepared by heating the corresponding metal oxides with ammonia for long durations at high temperatures. In order to find a simple route that avoids use of gaseous ammonia, we have employed urea as the nitriding agent. In this method, ternary metal oxynitrides are obtained by heating the corresponding metal carbonates and transition metal oxides with excess urea. By this route, ternary metal oxynitrides of the formulae MTaO₂N (M=Ca, Sr or Ba), MNbO₂N (M=Sr or Ba), LaTiO₂N and SrMoO_3−xN_x have been prepared successfully. The oxynitrides so obtained were generally in the form of nanoparticles, and were characterized by various physical techniques.     

AHOT/异辛烷反胶束体系制备铁酸钴纳米粒子

分别以阴离子表面活性剂二(2-乙基己基)丁二酸酯磺酸钠(AOT)和新型表面活性剂二(2-乙基己基)羟基丁二酸酯磺酸钠(AHOT)与异辛烷/水构建的反胶束体系为微反应器,合成了CoFe2O4纳米粒子;利用TGA,XRD,TEM等手段对产物进行了表征;讨论了两种表面活性剂构建的反胶束体系对产物合成过程及纳米粒子形貌和尺寸的影响.