A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660?nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.     

A mild phosphine-free synthesis of alkylamine-capped CdSe nanocrystals

A new phosphine-free approach has been developed to synthesize high-quality cadmium selenide (CdSe) nanocrystals with cubic zinc-blende structure, by using the highly reactive selenium (Se) precursor at milder temperature than that used in the traditional phosphine route. This Se precursor was obtained from the reduction of Se powder by sodium borohydride in N,N-dimetbylformamide, in the absence of phosphine. Without the addition of other long-chain coordinating substances in this approach, the alkylamines such as dodecylamine (DDA) and octylamine (OA) were used as reaction solvents, and they also acted as surface capping reagents to produce DDA-capped and OA-capped CdSe NCs, respectively. The rapid nucleation and slow growth were observed by ultraviolet-visible absorption spectrum. The resulting OA-capped CdSe NCs grew faster compared with DDA-capped CdSe NCs under the same other conditions. These as-synthesized CdSe nanocrystals showed relatively narrow size distribution and high photoluminescence quantum efficiency (up to 9.4% for OA-capped CdSe NCs). This mild approach is low cost, relatively low danger and high production yield (approximately 80%), indicating that it is very effective for the phosphine-free synthesis of alkylamine-capped CdSe nanocrystals.     

Cluster synthesis of branched CdTe nanocrystals for use in light-emitting diodes

Highly luminescent cadmium telluride (CdTe) nanocrystals were synthesized using Li(2)[Cd(4)(SPh)(10)] as a reactive Cd cluster compound at relatively low temperature, making it a safe precursor for the large scale synthesis of CdTe nanocrystals. Transmission electron microscopy (TEM) showed that the shape of the CdTe nanocrystals changes from nanorods to branched structures with increasing reaction time. The nanocrystals show high luminescent quantum yields up to 37% for CdTe branched nanostructures, and as high as 52% for CdTe/CdS core-shell heterostructures. CdTe/CdS nanocrystals were used to make light-emitting diodes in combination with organic layers for electron and hole injection. The devices show a maximum luminance efficiency of 0.35?cd?A(-1).     

A facile soft template synthesis and characterization of PbHAsO4 nanocrystals

Monoclinic lead hydrogen arsenate (LHA) nanocrystals with different crystallization morphologies and crystallite sizes were prepared successfully by a soft template synthesis method in the presence of sodium dodecylbenzenesulfonate (SDBS) or polyvinylpyrrolidone (PVP). The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The possible mechanism of SDBS and PVP in the experiment was briefly illustrated.     

A facile hydrothermal synthesis route to single-crystalline lead iodide nanobelts and nanobelt bundles

Single-crystalline PbI2 nanobelt bundles have been prepared using lead monoxide powder and hydroiodic acid as reagents at the assistance of dodecylamine. The assembled PbI2 nanobelt bundles can be spilt into nanobelts through long-playing sonication. The prepared nanobelt bundles consist of several nanobelts and the nanobelts have lengths of tens of microns, widths of 50-150 nanometers, and thicknesses ca. 20 nanometers. X-Ray diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM) transmission electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission microscopy (HRTEM) was used to characterize the as-prepared product. The possible formation mechanism of PbI2 nanobelt bundles was tentatively proposed.     

Morphology-controlled synthesis and growth mechanisms of branched α-MnO2 nanorods via facile microwave-assisted hydrothermal method

Multiple branched manganese oxide nanorods were obtained through the rapid one-step microwave-assisted hydrothermal synthesis by the reduction of potassium permanganate in hydrochloric acid solution without using any catalysts or surfactants. The formation mechanism of the branched α-MnO₂ was studied by systematically varying the reaction time, which were “oriented attachment” and rolling-cum-phase process. The electrochemical performance of the samples was examined by cyclic voltammetry. The specific surface area of the branched α-MnO₂ and the electrolyte in the solution were found to remarkably affect the specific capacitance. This microwave-assisted technique enables the quick and simple preparation of branched MnO₂ nanorods under mild conditions and maybe readily extended to the preparation of many other branched nanoparticles.     

One-step hydrothermal synthesis of CdTe nanowires with amorphous carbon sheaths

CdTe nanowires with carbon sheaths were synthesized via a one-step hydrothermal process using ascorbic acid as a reducing agent and carbonization source. The average diameter of CdTe core nanowires and thickness of amorphous carbon sheaths are about 20 nm and 10 nm, respectively. During this process, carbon-coated Te nanowires were formed and then reacted with Cd²⁺ ions, resulting in the formation of carbon-coated CdTe nanowires. Additionally, the size and shape of the CdTe nanowires were determined during the initial stage of Te formation.     

Direct fabrication of TiO2 nanoparticles deposited on hydroxyapatite crystals under mild hydrothermal conditions

TiO2 nanoparticles-deposited on hydroxyapatite (HAp) have been successfully synthesized by direct (single step) hydrothermal treatments of a CaCO3 suspension in a H3PO4 solution with 10 vol% TAS-FINE (titanium amine complex) at 150 degrees C for 6 h or 120 degrees C for 12-24 h under nearly neutral pH conditions. The obtained products were characterized by XRD, SEM-EDX, visible, Raman, and TEM. The XRD and Raman results showed the formation of HAp and TiO2 anatase phases under these hydrothermal conditions. SEM and TEM observations revealed that anatase TiO2 nanoparticles with the size of about 10 nm were deposited on the surfaces of the HAp crystals.     

Shape evolution of lead telluride and selenide nanostructures under different hydrothermal synthesis conditions

Face-open nanoboxes of lead telluride and selenide have been synthesized by a simple hydrothermal method. Nano- and microcrystals of various morphologies, including microflowers, semi-microflowers, cubic nanoparticles, etc., have also been observed at different synthesis conditions. Temperature, time, and concentrations of various reactants play a major role in controlling the morphology and shape evolution of the product. This simple synthesis technique for the growth of various nano- and microstructures opens a new route to prepare hierarchical structures of a variety of binary semiconducting materials in a large quantity. A possible growth mechanism of such nano- and microstructures has been proposed.     

Sequential synthesis of type II colloidal CdTe/CdSe core-shell nanocrystals

Colloidal type II CdTe/CdSe nanocrystals were synthesized by sequential addition of a tri-n-octylphosphine telluride (TOPTe)/TOP solution and several shell-precursor solutions to a CdO/TOP solution; the shell-precursor solutions consisted of CdO and TOPSe in TOP. For the growth of the CdTe core, the TOPTe/TOP solution was swiftly added to the CdO/TOP solution at a higher temperature (300 degrees C) than the growth temperature (250 degrees C). For the growth of the CdSe shell, in contrast, the CdO/TOPSe/TOP solution was slowly added to the CdTe/TOP solution at a lower temperature than the growth temperature (200-240 degrees C). The temporal evolution of the optical properties of the growing core-shell nanocrystals was monitored in detail. During the growth of the CdSe shell, the core-shell nanocrystals exhibited interesting changes in photoluminescence (PL) properties. The highest PL efficiency (approximately 38 %) was detected from core-shell nanocrystals with a CdSe shell thickness of 0.4-0.5 nm (indicated by TEM); the formation of the first monolayer is proposed. Our synthetic approach is well suited to a practical realization of engineering materials with bandgaps in the near-IR and IR spectral ranges.     

Controllable synthesis of hydroxyapatite nanocrystals via a dendrimer-assisted hydrothermal process

The morphology and size of hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (denoted HAP) can be controlled under hydrothermal treatment assisted with different dendrimers, such as carboxylic terminated poly(amidoamine) (PAMAM) and polyhydroxy terminated PAMAM. The structure and morphology were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR) and transmission electron microscopy (TEM). IR spectra were also used to investigate the complexation of Ca²⁺ with PAMAM. The results revealed that the inner cores of the PAMAM dendrimers are hydrophilic and potentially open to calcium ions, since interior nitrogen moieties serve as complexation sites, especially in case of the polyhydroxy terminated PAMAM. And the reasonable mechanism of crystallization was proposed that it can be attributed to the localization of nucleation site: external or interior PAMAM. Additionally, the PAMAM dendrimer with carboxylic and polyhydroxy groups has an effective influence on the size and shape of hydroxyapatite (HAP) nanostructures. Different crystal morphology was accomplished by adsorption of different dendrimers onto specific faces of growing crystals, altering the relative growth rates of the different crystallographic faces and leading to different crystal habits.     

Fabrication of protein-coated CdS nanocrystals via microwave-assisted hydrothermal method

CdS nanocrystals coated with protein were synthesised in the aqueous solution of bovine serum albumin protein by a rapid microwave-assisted hydrothermal method. Transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA) and cell cytotoxicity were used to characterise the morphology, composition and properties of the nanocrystals. The results indicate that the as-prepared CdS nanocrystals were wrapped up with the protein. The cytotoxicity profile on the human cervical cancer cell line HeLa shows that the potential cellular toxicity of the nanocrystals is efficiently prevented due to the presence of protein coating, which may offer the possibility of applications in biomedical research.     

Characterization and synthesis of KTa0.1Nb0.9O3 particles via high temperature mixing method under hydrothermal conditions

KTa_0.1Nb_0.9O₃ (KTN) particles with an orthorhombic perovskite structure have been synthesized via a high temperature mixing method (HTMM) under hydrothermal conditions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influence of alkaline concentration and solvent composition on the phase structure and morphology of the obtained powders was investigated. The results show that the well-crystallized KTN powders with sizes of 200–500 nm are successfully prepared at temperatures as low as 240 °C when the KOH concentration is 2.0 M and the isopropanol/water (I/W) volume ratio equals to 100/0.     

Aqueous synthesis of Au:CdTe nanocrystals for noninvasive fluorescence imaging in living cells

The gold-doped cadmium telluride (Au:CdTe) nanocrystals were synthesized by aqueous solution route using L-glutathione and L-cysteine as stabilizers. As-prepared Au:CdTe nanocrystals have good monodispersity and a zinc-blende structure. Compared with undoped CdTe nanocrystals, the Au:CdTe nanocrystals exhibited improved photostability, higher cellular affinity, and lower cytotoxicity. The Au:CdTe nanocrystals were used as probes for long-term noninvasive fluorescence imaging in living cells (The human lung epithelial carcinoma A549 cells). They could be endocytic uptaken by A549 cells and stably labeled the cytoplasm for over a week. By transmission electron microscopy (TEM) analysis, the Au:CdTe NCs could be observed in vesicles after being uptaken by A549 cells. Doping semiconductor nanocrystals with gold has the potential to engineer the photostability and biocompatibility for extensive biomedical applications. This work developed a facile aqueous solution route to synthesize gold-doped semiconductor nanocrystals and may assist in the design of doped nanobiomaterials.     

A facile and general approach to polynary semiconductor nanocrystals via a modified two-phase method

Cu(2)ZnSnS(4) nanocrystals were synthesized through a modified two-phase method and characterized with transmission electron microscopy (TEM), powder x-ray diffraction (XRD) and UV-vis spectroscopy. Inorganic metal salts were dissolved in the polar solvent triethylene glycol (TEG) and then transferred into the non-polar solvent 1-octadecene (ODE) by forming metal complexes between metal ions and octadecylamine (ODA). Since nucleation and growth occur in the single phase of the ODE solution, nanocrystals could be produced with qualities similar to those obtained through the hot-injection route. Balancing the reactivity of the metal precursors is a key factor in producing nanocrystals of a single crystalline phase. We found that increasing the reaction temperature increases the reactivity of each of the metal precursors by differing amounts, thus providing the necessary flexibility for obtaining a balanced reactivity that produces the desired product. The versatility of this synthesis strategy was demonstrated by extending it to the production of other polynary nanocrystals such as binary (CuS), ternary (CuInS(2)) and pentanary (Cu(2 - x)Ag(x)ZnSnS(4)) nanocrystals. This method is considered as a green synthesis route due to the use of inorganic metal salts as precursors, smaller amounts of coordinating solvent, shorter reaction time and simpler post-reaction treatment.