Room temperature synthesis of HgTe nanocrystals

We report a new method to synthesize monodisperse zinc blende HgTe nanocrystals at room temperature in noncoordinating solvent-octadecene. Thiol was needed to control the reaction at a suitable nucleation and growth speed. In the early stage of the reaction, HgTe nanocrystals formed aggregates, and then the aggregates were dispersed and individual dot-shaped nanocrystals were formed with stronger photoluminescence emitting. UV-vis, photoluminescence, and TEM have been used to study the properties of as-prepared HgTe nanocrystals.     

Room temperature synthesis of upconversion fluorescent nanocrystals

Synthesis of nanocrystals that exhibit strong upconversion (UC) luminescence upon infrared excitation has been challenging due to the stringent control needed over experimental variables. Herein, we report a method to synthesize nanocrystals demonstrating high UC at room temperature in aqueous solution on graphene.     

Dispersions of alkyl-capped silicon nanocrystals in aqueous media: photoluminescence and ageing

Alkyl-capped silicon nanocrystals can be dispersed in aqueous media by shaking or stirring their solutions in organic solvents (DMSO, ether, THF) with excess water. THF is the most straightforward choice with which to prepare stable aqueous dispersions, because the nanocrystals are very soluble in THF and it is also miscible with water. As little as 0.01% v/v tetrahydrofuran is sufficient. DMSO and ether were the preferred choices for subsequent staining of live cells because THF shows some acute toxicity even when very dilute. The luminescence intensity of the aqueous dispersions is linear in particle concentration and independent of pH over the range 5-9. The sols retain their photoluminescence and are stable against flocculation for at least 6 months.     

Solid-state synthesis of luminescent silicon nitride nanocrystals

Silicon nitride nanocrystals (NCs) have been prepared via in situ nitridation of magnesium followed by a metathesis reaction with sol-gel derived silica particles. Highly luminescent, freestanding β-Si(3)N(4) NCs with complex surface chemistry dominated by Si-H and N-H moieties were isolated upon etching with hydrofluoric acid.     

Growth of tetrahedral silver nanocrystals in aqueous solution and their SERS enhancement

Silver nanocrystals with tetrahedral shapes and {111} faces have been synthesized by the light-driven growth method in an aqueous solution. The nanocrystals of T(d) symmetry were formed under the effect of tartrate and citrate as the structural-directing reagents at the appropriate stages of reaction. Further, the nanocrystals may be assembled through electrostatic interaction to develop large-scale particle surfaces with sharp vertexes, which can generate strong localized electromagnetic field for surface-enhanced Raman scattering (SERS) studies. Benzenethiol was used as the probe to evaluate their SERS enhancement, and enhancement factors of up to 10(6) are reached. As a kind of promising material, these novel nanocrystals will be applied in surface enhanced spectroscopy and plasmonics field.     

Nonhydrolytic synthesis of high-quality anisotropically shaped brookite TiO2 nanocrystals

A surfactant-assisted nonaqueous strategy, relying on high-temperature aminolysis of titanium carboxylate complexes, has been developed to access anisotropically shaped TiO2 nanocrystals selectively trapped in the metastable brookite phase. Judicious temporal manipulation of precursor supply to the reaction mixture enables systematic tuning of the nanostructure geometric features over an exceptionally wide dimensional range (30-200 nm). Such degree of control is rationalized within the frame of a self-regulated phase-changing seed-catalyzed mechanism, in which homogeneous nucleation, on one side, and heterogeneous nucleation/growth processes, on the other side, are properly balanced while switching from the anatase to the brookite structures, respectively, in a continuous unidirectional crystal development regime. The time variation of the chemical potential for the monomer species in the solution, the size dependence of thermodynamic structural stability of the involved titania polymorphs, and the reduced activation barrier for brookite nucleation onto initially formed anatase seeds play decisive roles in the crystal-phase- and shape-tailored growth of titania nanostructures by the present approach.     

Micro-emulsion synthesis of monodisperse surface stabilized silicon nanocrystals

Silicon nanocrystals with a uniform size distribution were synthesized in inverse micelles using powerful hydride reducing agents. The silicon nanocrystals surfaces were then stabilized with 1-heptene to produce particles with strong blue photoluminescence.     

Room temperature solution synthesis of monodispersed single-crystalline ZnO nanorods and derived hierarchical nanostructures

In this work, we report a room temperature wet-chemical approach to synthesize highly regulated, monodispersed ZnO nanorods and derived hierarchical nanostructures. In particular, ZnO has been prepared into single-crystalline conical or prismatic nanorods, and various hierarchical structures such as hexagonally branched, reversed umbrella-type, and cactus-like ZnO nanostructures comprising individual c-oriented nanorods. Depending on the synthetic conditions used, the diameter of nanorods can be controlled with a size down to 10-30 nm, while the aspect ratio can be controlled up to 50-100. Various preparative parameters, such as initial reactant concentrations, solvents, ligands, surfactants, precursor salts, and reaction time, have been systematically examined. Due to slow reactions at room temperature, excellent crystallinity and high morphological yield (100% in most cases) have been achieved via tuning the synthetic parameters. Our photoluminescence and UV measurements also confirm the attained crystal perfection and size uniformity.     

Low temperature induced synthesis of TiN nanocrystals

TiN nanocrystals were successfully prepared through the direct reaction between TiCl(4) and NaNH(2) induced at 300 degrees C. The yield based on Ti is approximately 80%. X-ray powder diffraction indicated that the product was cubic TiN with a lattice constant of a = 4.243 A. Transmission electron microscopy revealed that nanocrystalline TiN with a diameter of 10 nm or so and extremely long straight rods were synthesized. The possible formation mechanism was also proposed.     

Efficient one-pot synthesis of highly photoluminescent alkyl-functionalised silicon nanocrystals

The chemical reduction of micelles formed by mixing silicon tetrachloride and hexyltrichlorosilane in apolar solvent, where hexyltrichlorosilane serves as both reactant and surfactant, yields brightly luminescent silicon nanocrystals, and enables efficient synthesis of alkyl-functionalised silicon quantum dots (SiQDs) in a single step.     

Room temperature, high-yield synthesis of multiple shapes of gold nanoparticles in aqueous solution

A seed-mediated growth method was used to control the morphology and dimensions of Au nanocrystals by the manipulation of the experimental parameters in aqueous solution at room temperature. This chemical route produces various structural architectures with rod-, rectangle-, hexagon-, cube-, triangle-, and starlike profiles and branched (such as bi-, tri-, tetra-, and multipod) Au nanocrystals of various dimensions in high yield in the presence of a single surfactant, cetyltrimethylammonium bromide.     

Room temperature synthesis of protonated layered titanate sheets using peroxo titanium carbonate complex solution

We report the synthesis of peroxo titanium carbonate complex solution as a novel water-soluble precursor for the direct synthesis of layered protonated titanate at room temperature. The synthesized titanates showed excellent removal capacity for Pb(2+) and methylene blue. Based on experimental observations, a probable mechanism for the formation of protonated layered dititanate sheets is also discussed.     

Molecular hydrogen-induced nucleation of hydrogenated silicon nanocrystals at low temperature

Highly crystallized hydrogenated silicon layers were obtained via the treatment of hydrogenated polymorphous silicon films in a molecular hydrogen ambient. This contrasts other postdeposition studies that obtained nanocrystalline silicon films but necessitated either a plasma activation or high-temperature annealing. The structure of the samples was analyzed by Raman spectroscopy to determine the crystallite volume fraction, which was found to increase up to 80% within 1 hour of treatment. Atomic force microscopy (AFM) showed that the roughness of the surfaces was found to increase after the H₂ treatment. Optical transmission and spectroscopic ellipsometry revealed the pronounced porosity of the films characterized by a static refractive index that is below three, which is a low value for hydrogenated silicon films and a void fraction that is around 15% in the bulk of the films. The effect of the hydrogen molecules on the structure of the films was discussed in terms of the compressive stress exerted by the molecules, trapped in structural inhomogeneities, on the amorphous tissue. It is suggested that for this process to take effect, the films need to be porous and that the amorphous network needs to be in a “relaxed” state.     

Room temperature synthesis of surface-functionalised boron nanoparticles

Capped boron nanoparticles have been synthesized at room temperature by a simple route that does not involve the use of flammable boranes.     

Controlling synthesis of BiIn dendritic nanocrystals by solution dispersion

In this study, we report a novel and simple solution-phase route for one-dimensional metal nanocrystals. BiIn nanocrystals were prepared by directly dispersing melting BiIn alloy at an appropriate solvent. The as-obtained BiIn nanocrystals with a dendritic shape possess a good crystalline phase. The morphology of the nanocrystals can be greatly modified by changing the reaction parameters. This strong UV emission might arise from the quantum-confined In2O3 particles.     

Shape‐controlled synthesis of Pt nanocrystals: an evolution of the tetrahedral shape

Platinum nanocrystals with sizes smaller than 10 nm are obtained by H₂‐reduction of aqueous K₂PtCl₆ in the presence of different concentrations of poly (N‐vinyl‐2‐pyrrolidone; PVP:M_w ≈ 360 000) at pH = 2.5–7.0. Tetrahedral Pt nanocrystals (3–10 nm) are produced with high selectivity (73–83% by number) at moderate PVP:K₂PtCl₆ ratios. The co‐existing round/spheroidal crystallites are found to be smaller than the tetrahedrally shaped ones in the systems of varying K₂PtCl₆:PVP ratios. Careful examinations of the particle size and shape evolution of the crystallites at different stages of the crystal growth with transmission electron microscopy (TEM) and ultraviolet–visible absorption spectroscopy (UV–vis) suggest that the tetradedrally shaped Pt crystallites share the same type of nuclei with the round ones at the early stage of the crystal formation. Evolution of the tetrahedral shape happens in the later slow crystal growth. Copyright © 2006 John Wiley & Sons, Ltd.     

Room temperature synthesis of hollow CdMoO(4) microspheres by a surfactant-free aqueous solution route

Hollow cadmium molybdate microspheres have been successfully prepared via a template-free aqueous solution method with the assistance of NaCl at room temperature. The structure and morphology of the CdMoO(4) hollow microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The microspheres have diameters of 3-6 microm and hollow interiors of 2-3 microm. The shell is composed of numerous single-crystalline nanorods with diameters of 30-120 nm and lengths of 1-2 microm which are radially oriented to the center. A certain concentration of NaCl plays a key important role in the formation process of hollow microspheres, which might provide a suitable chemical environment to favor the formation of hollow CdMoO(4) microspheres. A possible NaCl-induced Ostwald ripening process is proposed for the formation of hollow CdMoO(4) microspheres on the basis of scanning electron microscopy observation of intermediate products at different precipitation stages.     

Anionic microemulsion-mediated low temperature synthesis of anisotropic silicalite-1 nanocrystals

The low-temperature (368 K) synthesis of silicalite-1 nanocrystals in anionic microemulsions is reported. In the presence of AOT/isooctane mixtures silicalite-1 nanocrystals can be formed that are coffin-shaped and approximately 100 x 40 x 200 nm in size. This is in contrast to samples made without the microemulsion under the same conditions where irregular spherical particles approximately 100 nm in diameter are formed. The current work shows that, in contrast to previous work in this area, the anionic microemulsions cannot stabilize colloidal silica due to the strong repulsive electrostatic forces between the anionic silicate species and the surfactant headgroup. The crystal morphology of the silicalite-1 obtained is also shown to be sensitive to the surfactant identity as syntheses using SDS/heptane/butanol mixtures lead to different morphologies. It is also possible to uncouple zeolite nucleation from growth in these systems. This was demonstrated by adding a solution containing 25 nm silicalite-1 nanocrystals to the AOT/isooctane mixture, which leads to large micron-sized spheres of silicalite-1 containing large mesopores. This report demonstrates that anionic microemulsions lead to fundamentally different crystal habits than the nonionic or cationic microemulsions investigated previously. The future outlook for the use of microemulsion-mediated zeolite growth is also discussed.     

Photochemical synthesis of bismuth selenide nanocrystals in an aqueous micellar solution

The photolytic decomposition of triphenylbismuth and di-tert-butyl diselenide under aqueous micellar conditions yields 5-nm bismuth selenide nanocrystals of the BiSe stoichiometry. This is the first example of the bismuth-rich BiSe phase being prepared in a well-dispersed colloidal nanocrystal form.     

Microreactor with integrated temperature control for the synthesis of CdSe nanocrystals

The recent needs in the nanosciences field have promoted the interest towards the development of miniaturized and highly integrated devices able to improve and automate the current processes associated with efficient nanomaterials production. Herein, a green tape based microfluidic system to perform high temperature controlled synthetic reactions of nanocrystals is presented. The device, which integrates both the microfluidics and a thermally controlled platform, was applied to the automated and continuous synthesis of CdSe quantum dots. Since temperature can be accurately regulated as required, size-controlled and reproducible quantum dots could be obtained by regulating this parameter and the molar ratio of precursors. The obtained nanocrystals were characterized by UV-vis and fluorescence spectrophotometry. The band width of the emission peaks obtained indicates a narrow size distribution of the nanocrystals, which confirms the uniform temperature profile applied for each synthetic process, being the optimum temperature at 270 °C (full width at half maximum = 40 nm). This approach allows a temperature controlled, easy, low cost and automated method to produce quantum dots in organic media, enhancing its application from laboratory-scale to pilot-line scale processes.