Facile synthesis of silver chalcogenide (Ag2E; E=Se, S, Te) semiconductor nanocrystals

A general, one-pot, single-step method for producing colloidal silver chalcogenide (Ag(2)E; E = Se, S, Te) nanocrystals is presented, with an emphasis on Ag(2)Se. The method avoids exotic chemicals, high temperatures, and high pressures and requires only a few minutes of reaction time. While Ag(2)S and Ag(2)Te are formed in their low-temperature monoclinic phases, Ag(2)Se is obtained in a metastable tetragonal phase not observed in the bulk.     

Controlled synthesis and self-assembly of highly monodisperse Ag and Ag(2)S nanocrystals

A facile method to control the synthesis and self‐assembly of monodisperse Ag and Ag₂S nanocrystals with a narrow‐size distribution is described. Uniform Ag nanoparticles of less than 4 nm were obtained by thermolysis of Ag–oleate complexes in the presence of oleic acid and dodecylamine, and monodisperse Ag nanoparticles of less than 10 nm were also prepared in one step by using dodecylamine and oleic acid as capping agents. Moreover, the surface‐enhanced Raman scattering (SERS) properties of the Ag substrates have also been investigated. It is worth mentioning that these Ag nanoparticles and assemblies show great differences in the SERS activities of Rhodamine B dye. In addition, the superlattices of Ag₂S nanocrystals were synthesized with Ag–oleate complexes, alkanethiol, and sulfur as the reactants. The resulting highly monodisperse nanocrystals can easily self‐assemble into interesting superstructures in the solution phase without any additional assembly steps. This method may be extended to the size‐controlled preparation and assembly of many other noble‐metal and transition‐metal chalcogenide nanoparticles. These results will aid the study of the physicochemical properties of the superlattice assemblies and construction of functional macroscopic architectures or devices.     

Syringe pump-assisted synthesis of water-soluble cubic structure Ag2Se nanocrystals by a cation-exchange reaction

Water-soluble cubic structure Ag(2)Se (alpha-Ag(2)Se) nanocrystals smaller than 5 nm can be obtained by cation-exchange reaction at room temperature, using water-dispersed ZnSe nanocrystals as precursors, which is achieved by controlling the injection speed of AgNO(3) solutions via a syringe pump in the presence of the stabilizer of trisodium citrate. Meanwhile, the thermal stability of the product Ag(2)Se nanocrystals is studied. The results show that the mean sizes and shapes of the precursor ZnSe and product Ag(2)Se nanocrystals are similar, and Se anion sublattices between them are topotaxial. In addition, no phase transition is observed for the product Ag(2)Se (cubic structure) nanocrystals below 180 degrees C. The present synthetic method based on cation-exchange reactions can also be applied to the syntheses of PbSe and CuSe nanocrystals.     

Controllable synthesis of Cu2S nanocrystals and their assembly into a superlattice

Highly uniform Cu2S nanocrystals with controllable sizes and shapes (circular and elongated) have been synthesized through a novel water-oil interface confined reaction. They can self-assemble into highly ordered multilayer superlattices. By controlling the size and shape of building block nanocrystals, the packing symmetry of the superlattice can be engineered. For circular nanocrystals, both fcc and hcp multilayer superlattices are found in the sample. For elongated nanocrystals, they can also generate a close-packed layer and further stack into a multilayer superlattice. The dipole moment of the inner nanocrystals is useful for their stacking. This work provides a simple bottom-up approach to integrate nanocrystals, as well as to adjust the packing symmetry of the final superlattice, which may have potential applications for nanomaterials and nanodevices in the future.     

Monodisperse nanocrystals: general synthesis, assembly, and their applications

This article summarizes the recent advances in the synthesis, assembly and applications of monodisperse nanocrystals, which may be suggestive for the designed synthesis and assemblies of target nanocrystals according to practical requirements.     

Ag/ZnO heterostructure nanocrystals: synthesis, characterization, and photocatalysis

A high yield of the dimer-type heterostructure of Ag/ZnO nanocrystals with different Ag contents is successfully prepared through a simple solvothermal method in the absence of surfactants. The samples are characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and IR spectroscopy. The results show that all samples are composed of metallic Ag and ZnO; Ag nanoparticles locate on the surface of ZnO nanorods; the binding energy of Ag 3d(5/2) for the Ag/ZnO sample with a Ag content of 5.0 atom % shifts remarkably to the lower binding energy compared with the corresponding value of pure metallic Ag because of the interaction between Ag and ZnO nanocrystals; the concentration of oxygen vacancy for the as-synthesized samples varies with the increasing Ag content, and the Ag/ZnO sample with a Ag content of 5.0 atom % has the largest density of oxygen vacancy. In addition, the relationship between their structure and photocatalytic property is investigated in detail. It is found that the photocatalytic property is closely related to its structure, such as heterostructure, oxygen defect, and crystallinity. The presence of metallic Ag nanoparticles and oxygen vacancy on the surface of ZnO nanorods promotes the separation of photogenerated electron-hole pairs and thus enhances the photocatalytic activity.     

Untersuchung der Zustandsdiagramme der Systeme Ag2Se0,5Te0,5?Ag2S und Ag2S0,5Te0,5 −Ag2Se

Investigation of the State Diagrams of the Systems Ag₂Se_0.5Te_0.5? Ag₂S and Ag₂S_0.5Te_0.5? Ag₂Se The Systems Ag₂Se_0.5Te_0.5? Ag₂S and Ag₂S_0.5Te_0.5? Ag₂Se were investigated by the methods of DTA, X-ray and microstructure analysis and measuring of the conductivity. It was found, that the systems are polythermic sections of the ternary diagram Ag₂Te? Ag₂Se? Ag₂S. In all regions from 0 till 100 Mol.-% Ag₂S, resp. Ag₂Se, except the phases with composition Ag₂Se_0.5Te_0.5 and Ag₂S_0.5Te_0.5 mixed crystals are formed. The structure of the observed interphases was not investigated. The state diagrams of the systems Ag₂Se_0.5Te_0.5 ?Ag₂S and Ag₂S_0.5Te_0.5? Ag₂Se are characterized with peritectical destruction at 140°C for the first and eutectical destructions at 70°C for both systems. In the systems Ag₂Se_0.5Te_0.5? Ag₂S a peritectical reaction at 780°C is observed.     

Synthesis of faceted and cubic Ag2S nanocrystals in aqueous solutions

With thiourea (Tu) as sulfur source and the assistance of CTAB, faceted and cubic Ag2S nanocrystals have been synthesized successfully via a simple hydrothermal route by modulating the ratio of Tu and AgNO3, respectively. It is the first report that the fabrication of faceted and cubic Ag2S nanocrystals takes place in aqueous medium, which makes the synthesis environmentally benign, user-friendly, economical and practicable to industry production. It is also found that the cooperation effect of CTAB and Tu should be responsible for the formation of the as-obtained Ag2S nanocrystals. The UV-vis absorption spectrum of the products shows obvious blue shift.     

Synthesis of highly luminescent Cd(Se,S) nanocrystals

Highly luminescent semiconductor nanocrystals with graded band gap were synthesized using a hot injection method. The band gap of nanocrystals were controlled by gradual incorporation of sulfur to CdSe nanocrystals by applying severely asymmetric composition of reactants [(Cd)/(Se,S) ? 1]. The maximum emission wavelength of the grown nanocrystals was varied by controlling the concentration ratio of VI group element, i.e. Se and S. A green light was emitted from Cd(Se,S) nanocrystals with [Se]:[S] = 1:3 in the reactant mixture and the maximum quantum yield measured by comparing with Rhodamine 6G was larger than 80%.

     

Formation of Ag2Se nanotubes and dendrite-like structures from UV irradiation of a CSe2/Ag colloidal solution

Ag2Se nanotubes have been successfully synthesized by UV photodissociation of adsorbed CSe2 on the surface of Ag nanowires under ambient conditions. Transmission electron microscopy was used to trace the growth of hollow interiors, allowing a detail study of the Kirkendall effect in 1-dimensional nanosystems. Voids were observed to grow from both ends of the nanowires along the longitudinal axis and ultimately merged to form hollow nanotubes. This phenomenon is attributed to the crystallographic selective adsorption of poly(vinylpyrolidone) on Ag nanowire templates. In addition, we observed the formation of dendrites on aging of the reaction mixture and explained its growth based on a diffusion-limited aggregation model.     

Colloidal synthesis of magnetic CuCr2S4 nanocrystals and nanoclusters

Nanocrystals and nanoclusters of the room-temperature magnetic spinel CuCr(2)S(4) have been synthesized using a facile solution-based method. The synthesis involves hot injection of an excess of 1-dodecanethiol (1-DDT) into a boiling coordinating solvent containing CuCl(2) and CrCl(3)·6H(2)O. Using octadecylamine (ODA) as a solvent yields cube-shaped nanocrystals with an average size of 20 ± 2 nm, while with oleylamine (OLA), nanoclusters with an average size of 31 ± 2.5 nm are obtained. In both cases, powder X-ray diffraction patterns confirmed the formation of the pure spinel phase without any impurities. While the synthesized powders are superparamagnetic near room temperature, they exhibit ferromagnetic behavior at lower temperatures, with magnetization (M(S)) values of 30 emu/g (1.63 μ(B)/f.u.) and 33 emu/g (1.79 μ(B)/f.u.) for the ODA- and OLA-capped nanocrystals and nanoclusters, respectively, at 5 K.     

Silver Halide and Silver Chalcogenide Systems. IV. Excess enthalpies of the liquid mixtures of AgCl + Ag2Se,Agl + Ag2Se,AgCl + Ag2Te,AgBr + Ag2Te,and Agl + Ag2Te

The integral enthalpies of mixing of the liquid mixtures AgCl + Ag₂Se, AgI + Ag₂Se, AgCl + Ag₂Te, AgBr + Ag₂Te and AgI + Ag₂Te were determined in an isoperibolic calorimeter. The systems have endothermic effects which can be explained by a misfit energy, due to the substitution of ions of different size in the polymeric network of these melts.     

Supramolecular assembly of three Ag(I) coordination polymers derived from flexible N-containing ligands and polycarboxylates: synthesis,structures, and catalytic properties

Three Ag(I) coordination polymers [Ag(L1)]·(H₃bptc)·H₂O (1), [Ag₂(L2)(oba)]·H₂O (2), and [Ag₂(L2)₂]·(H₂bptc) (3) [L1 = 1,4-bis(3,5-dimethylpyrazole)butane, L2 = 1,4-bis(2-methylbenzimidazole)butane, H₄bptc = 3,3′,4,4′-biphenyltetracarboxylic acid, H₂oba = 4,4′-oxybis(benzoic acid)] constructed from N-containing ligands with different flexibilities and organic carboxylates as co-ligands have been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis. All three complexes display 1D chain structures, which are further extended into 2D supramolecular networks via non-classical C–H···O hydrogen bonding interactions. The fluorescence and catalytic properties of the complexes 1–3 have been investigated in detail. Complexes 2 and 3 reveal promising catalytic activities for the degradation of methyl orange in a Fenton-like process.     

2D assembly of gold-PNIPAM core-shell nanocrystals

2D arrays of Au-PNIPAM core-shell nanocrystals were fabricated using convective deposition and spin-coating. The particle density and ordering were studied by AFM. Annealing at 700 °C removes the polymer shell, while retaining a monolayer of well-separated gold nanoparticles. The surface plasmon modes of the colloid monolayers could be measured by spectroscopic ellipsometry.     

Selective degradation of chemical bonds: from single-source molecular precursors to metallic Ag and semiconducting Ag2S nanocrystals via instant thermal activation

Selective formation of metallic Ag and semiconducting Ag(2)S nanocrystals has been achieved via a modified hot-injection process from a single-source precursor molecule, Ag(SCOPh), which can potentially generate both [Ag] and [AgS] fragments simultaneously. When the precursor molecules are injected into a preheated reaction system at 160 degrees C, spherical Ag(2)S nanocrystals are directly obtained even without a molecular activator, such as alkylamines. Mixtures of Ag and Ag(2)S or pure metallic Ag nanocrystals are obtained if the precursor molecules are injected at lower than 160 degrees C or room temperature. These results are attributed to the direct transfer of thermal energies to precursor molecules, which are enough to dissociate S-C as well as Ag-S bonds simultaneously. Detailed characterizations about the produced nanocrystals have been performed using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), as well as energy-dispersive X-ray (EDX) spectrum.