Solventless nanoparticles synthesis under low pressure

In the present study, metal nanocrystals were obtained by the very easy, economical, and nontoxic thermal decomposition method and stabilized by coating oleate without any solvent. These nanocrystals have a highly crystalline structure due to a high decomposition temperature (~563-573 K) at low pressure and very narrow distribution. The prepared Fe3O4 nanocrystals were controlled by the annealing time and vacuum pressure. A TEM image of monodispersed Fe3O4 nanocrystals showed the 2D assembly of nanocrystals, demonstrating their uniformity. The particle size is 10.6 +/- 1.2 nm. TEM images of silver nanocrystals a showed 2D assembly with 9.5 +/- 0.7 nm. An electron diffraction image and X-ray diffraction of the nanocrystals showed the highly crystalline nature of metal nanocrystals.     

Optical properties of ZnO nanocrystals doped with Cd, Mg, Mn, and Fe ions

ZnO nanocrystals doped with Cd, Mg, Mn, and Fe ions were obtained by thermolysis of a family of metal cupferrates. The nanocrystals were characterized by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, UV-visible, luminescence, and excitation spectroscopy. The band gap of the nanocrystals can be tuned in the range of 2.9-3.8 eV by the use of the dopants. In most cases, the nanocrystals are sufficiently defect-free to exhibit band edge luminescence.     

Size-dependent dissociation pH of thiolate ligands from cadmium chalcogenide nanocrystals

A method, pseudo steady-state titration, is introduced for determining the precipitation pH of nanocrystals coated by electron-donating ligands. CdSe nanocrystals coated with hydrophilic deprotonated thiol (thiolate) ligands were studied systematically. For comparison, CdTe and CdS nanocrystals coated with the same types of ligands were also examined. The results show that the precipitation of the nanocrystals is caused by the dissociation of the nanocrystal-ligand coordinating bonds from the nanocrystal surface. The ligands are removed from the surface due to protonation in a relatively low pH range, between 2 and 7 depending on the size, approximately within the quantum confinement size regime, and chemical composition (band gap) of the nanocrystals. In contrast, the redispersion of the nanocrystals was found to be solely determined by the deprotonation of the ligands. The size-dependent dissociation pH of the ligands was tentatively used as a means for determining the size-dependent free energy associated with the formation of a nanocrystal-ligand coordinating bond.     

One-step facile surface engineering of hydrophobic nanocrystals with designer molecular recognition

High quality nanocrystals have demonstrated substantial potential for biomedical applications. However, being generally hydrophobic, their use has been greatly limited by complicated and inefficient surface engineering that often fails to yield biocompatible nanocrystals with minimal aggregation in biological fluids and active targeting toward specific biomolecules. Using chimeric DNA molecules, we developed a one-step facile surface engineering method for hydrophobic nanocrystals. The procedure is simple and versatile, generating individual nanocrystals with multiple ligands. In addition, the resulting nanocrystals can actively and specifically target various molecular addresses, varying from nucleic acids to cancer cells. Together, the strategy developed here holds great promise in generating critical technologies needed for biomedical applications of nanocrystals.     

Synthesis and characterization of single-crystalline In2O3 nanocrystals via solution dispersion

In this paper, In2O3 nanocrystals were prepared by solution dispersion from bulk indium. In2O3 nanocrystals with an average diameter of 30 nm have a single-crystalline phase and appear as a square or rhombohedral shape, and little spherical particles are also present. In addition, these nanocrystals show strong ultraviolet-blue emission.     

AC electric field‐assisted assembly and alignment of cellulose nanocrystals

In this article, we describe an efficient physical electric‐field‐assisted method to study self‐assembly and orientation of cellulose nanocrystals. When applying an alternating voltage to a cellulose nanocrystals suspension deposited onto a thin gap of coplanar lithographically patterned metallic electrodes, a highly homogeneous orientation of cellulose nanocrystals is obtained. Parameters such as strength and frequency of the applied electric field and cellulose nanocrystals aspect ratios were studied to determine how they affect cellulose nanocrystals assembly and orientation. The prepared films were analyzed by atomic force microscopy, and the results suggest that the alignment of cellulose nanocrystals generated films is greatly influenced by the frequency and the strength of the applied electric field. The orientation of cellulose nanocrystals becomes more homogeneous with increasing electric field higher than 2000 V/cm with a frequency ranging between 10⁴ and 10⁶ Hz. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1430–1436, 2008     

Large-scale cubic InN nanocrystals by a combined solution- and vapor-phase method under silica confinement

Large-scale cubic InN nanocrystals were synthesized by a combined solution- and vapor-phase method under silica confinement. Nearly monodisperse cubic InN nanocrystals with uniform spherical shape were dispersed stably in various organic solvents after removal of the silica shells. The average size of InN nanocrystals is 5.7 ± 0.6 nm. Powder X-ray diffraction results indicate that the InN nanocrystals are of high crystallinity with a cubic phase. X-ray photoelectron spectroscopy and energy-dispersive spectroscopy confirm that the nanocrystals are composed of In and N elements. The InN nanocrystals exhibit infrared photoluminescence at room temperature, with a peak energy of ~0.62 eV, which is smaller than that of high-quality wurtzite InN (~0.65-0.7 eV) and is in agreement with theoretical calculations. The small emission peak energy of InN nanocrystals, as compared to other low-cost solution or vapor methods, reveals the superior crystalline quality of our samples, with low or negligible defect density. This work will significantly promote InN-based applications in IR optoelectronic device and biology.     

An alternative of CdSe nanocrystal emitters: pure and tunable impurity emissions in ZnSe nanocrystals

The concept, decoupling doping from nucleation and/or growth, allows us to dope nearly all nanocrystals in a given sample which is indicated by complete quenching of the host emission and bright emission from the dopants at characteristic wavelengths tunable in most parts of the visible window using a ZnSe host. In an extreme case, ZnSe coated MnSe nanocrystals (MnSe:ZnSe) emit similarly as commonly known doped nanocrystals. In comparison with CdSe nanocrystals, these alternative emitters not only are intrinsically less toxic but also show some unexpected and expected advantages: stable against thermal and environmental changes, zero reabsorption, and no Forster energy transfer. In addition to their applications to replace CdSe based nanocrystal emitters, the unique structure and properties of the doped nanocrystals are of interest for studying fundamental issues in the field.     

Growth kinetics of platinum nanocrystals prepared by two different methods: role of the surface

In order to examine the applicability of the diffusion-limited Ostwald ripening model to the growth kinetics of nanocrystals, platinum nanocrystals prepared by two different methods have been investigated by a combined use of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). One of the methods of synthesis involved the reduction of chloroplatinic acid by sodium citrate while in the other method reduction was carried out in the presence of polyvinylpyrrolidone (PVP) as a capping agent. The growth of platinum nanocrystals prepared by citrate reduction in the absence of any capping agent follows a Ostwald ripening growth with a D(3) dependence. In the presence of PVP, the growth of platinum nanocrystals does not completely follow the Ostwald ripening model, making it necessary to include a surface reaction term in the growth equation. Thus, the growth of platinum nanocrystals in the presence of PVP has contributions both from diffusion and surface reaction, exhibiting a D(3)+D(2) type behavior.     

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.     

Synthesis of beltlike CdS nanocrystals via solvothermal route

CdS nanocrystals with a beltlike morphology were prepared via a low-temperature solvothermal route in ethylenediamine. The obtained nanocrystals were characterized by X-ray powder diffraction, transmission electron microscopic, ultraviolet-visible and fluorescence spectroscopy. In the mixed solvents of ethylenediamine and distilled water, CdS nanocrystals with various morphologies were obtained with the change of the volume ratio of the two constituents.     

Nanocrystals Assembled by the Chemical Reaction of the Dispersion Solvent

The development of methods to pattern nanocrystals with different sizes and shapes remains a challenge. In this study, we demonstrate a unique class of bottom‐up approaches to assemble nanocrystals into patterns. Our approach for patterning nanocrystals focuses on the utilization and control of the chemical reaction of solvents surrounding nanocrystals. The photopolymerization of solvent molecules through a photomask creates time‐dependent concentration gradients of the solvents. Dispersed nanocrystals such as silver nanowires (AgNWs) migrate and are gradually organized and integrated into the polymerizing films based on the concentration gradients. The AgNW‐embedded film properties are determined by the organized AgNW structures and include light transmission and electrical conductivity. Overall, the demonstrated method is very simple, widely applicable to various nanocrystals and solvents, and can thus contribute to the development of a new class of nanocrystal patterning methods.     

Carbon monoxide-assisted synthesis of single-crystalline Pd tetrapod nanocrystals through hydride formation

Carbon monoxide can adsorb specifically on Pd(111) to induce the formation of unique Pd nanostructures. In the copresence of CO and H(2), single-crystalline Pd tetrapod nanocrystals have now been successfully prepared. The Pd tetrapods are enclosed by (111) surfaces and are yielded through hydride formation. Density functional theory calculations revealed that the formation of PdH(x) in the presence of H(2) reduces the binding energy of CO on Pd and thus helps to decrease the CO coverage during the synthesis, which is essential to the formation of the PdH(x) tetrapod nanocrystals. In addition to tetrapod nanocrystals, tetrahedral nanocrystals were also produced in the copresence of CO and H(2) when the reaction temperature was ramped to further lower the CO coverage. Upon aging in air, the as-prepared PdH(x) nanocrystals exhibited a shape-dependent hydrogen releasing behavior. The conversion rate of PdH(x) tetrapod nanocrystals into metallic Pd was faster than that of tetrahedral nanocrystals.     

Study of quasi-monodisperse In2O3 nanocrystals: synthesis and optical determination

In this communication, we report a successful synthesis of quasi-monodisperse In2O3 nanocrystals with high crystallinity in a high-temperature organic solution. The average size of nanocrystals can be tuned using a dynamic injection technique. TEM and XRD investigations indicate that each nanocrystal is a single crystal. The optical determination implies that the photoluminescence behavior of these In2O3 nanocrystals is different from that of the bulk, probably due to the combination of weak quantum-confinement-effects and the nature of high crystallinity in nanocrystals.     

Microwave-assisted aqueous synthesis: a rapid approach to prepare highly luminescent ZnSe(S) alloyed quantum dots

In this paper, we present a new procedure for the rapid synthesis of luminescent ZnSe nanocrystals in aqueous phase by microwave irradiation with controllable temperature. The effects of microwave irradiation and experimental conditions on the synthesis of nanocrystals were investigated systematically. It was found that there were significant effects of pH value of reaction solutions, molar ratio of precursors, and heating time of microwave irradiation on the optical properties of the ZnSe nanocrystals. A series of nanocrystals with different size was prepared in 1 h, and the photoluminescence quantum yield reached up to 17% at the optimal reaction condition. The results of HRTEM and XRD showed that the as-prepared nanocrystals had high crystallinity. The characterizations of EDS spectra and elemental analysis showed that the sulfur content of nanocrystals increased with the growth of nanocrystals. We speculated that the structure of nanocrystals was an alloy ZnSe(S) shell on the surface of the ZnSe particles core. Furthermore, we found that the oxygen from air in the reaction vessel played an important role in the decomposition of the thiol group under microwave irradiation.     

Synthesis and photocatalytic activity of single-crystalline hollow rh-In2O3 nanocrystals

We report here for the first time the hollow, metastable, single-crystal, rhombohedral In(2)O(3) (rh-In(2)O(3)) nanocrystals synthesized by annealing solvothermally prepared InOOH solid nanocrystals under ambient pressure at 400 °C, through a mechanism of the Kirkendall effect, in which pore formation is attributed to the difference in diffusion rates of anions (OH(-) and O(2-)) in a diffusion couple. The InOOH solid nanocrystals were prepared via a controlled hydrolysis solvothermal route by using In(NO(3))(3)·4.5H(2)O as a starting material and glycerol-ethanol as a mixed solvent. The glycerol-ethanol mixed solvent plays a key role on the formation of the intermediate InOOH, thus the final product of rh-In(2)O(3). The as-synthesized In(2)O(3) nanocrystals present excellent photocatalytic degradation of rhodamine B (RhB) and methylene blue (MB) dyes, which present ～92% degradation of RhB or MB after 4 or 3 h reaction in the presence of the as-synthesized In(2)O(3) nanocrystals, respectively.     

单源前体合成水溶性的CdS和ZnS纳米晶

0引言量子点(QuantumDots)一般指半径小于或接近玻尔激子半径的半导体纳米晶颗粒。和有机染料分子相比,无机半导体纳米晶的带隙宽度可通过简单     

Redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification with an inorganic barium hydroxide

The present paper describes the synthesis of the redispersible rutile TiO2 nanocrystals in organic media by surface chemical modification reaction in an aqueous barium hydroxide solution. In our facile surface modification reactions, the surfaces of the TiO2 nanocrystals are coated by bimetallic TiOBa spices and saturated with BaOH terminal groups. The inherent characteristics such as morphology, size, crystallinity, and color of the nanocrystals remained almost unchanged after surface-treatment, but their dispersibility in organic media such as methanol and DMF were remarkably enhanced. It is ascribed that BaOH groups in the surface of the TiO2 nanocrystals prevented the formation of covalently bound agglomerates through Ti-O-Ti condensation reaction among the nanocrystals during the purification and water-elimination procedures.     

铒镱共掺磷酸镧纳晶的合成和近红外荧光性质

以磷酸三丁酯作为配体,使用高温溶液法合成了掺铒磷酸镧纳米晶体,高分辨电镜和XRD结果表明产物尺寸均一,直径4nm左右,具有高度的结晶性,在甲苯等有机溶剂中分散性良好.近红外发光光谱表明,产物在1535 nm处有发光峰,半高全宽为50 nm,高于目前掺铒光纤放大器(EDFA)的增益带宽.通过IR、元素分析研究发现,使用真空干燥等方法不能有效去除纳晶表面的羟基.为了进一步消除表面缺陷和猝灭基团对纳晶发光性质的影响,我们尝试在其外围生长一层LaPO₄壳做成核壳粒子以消除表面缺陷和隔离猝灭基团,结果表明,新的纳晶的发光强度得到了显著提高.     

Homogeneous and disordered assembly of densely packed titanium oxide nanocrystals: an approach to coupled synthesis and assembly in aqueous solution

A homogeneous and disordered assembly of densely packed nanocrystals 2-3 nm in size was synthesized at room temperature in an aqueous solution without the assistance of any organic molecules. The assembled nanocrystals of titanium oxides, such as anatase titanium dioxide, sodium titanate, and a solid solution with rutile tin dioxide, formed macroscopic transparent objects 2-5 mm in size. In general, it is not easy to obtain homogeneous and disordered assembly of nanocrystals without assistance of any organic molecules for the inhibition of inhomogeneous and disordered aggregation. In the present work, the formation of the hydrated layer on the surface of nanocrystals facilitated the homogeneous and disordered assembly. The crystal phases and the compositions of the nanocrystals were controlled by the tuning of the synthetic conditions, such as the initial pH and metal source concentration. Based on the formation processes and mechanisms, this approach for the coupled synthesis and assembly can be applied to a variety of nanomaterials for preparation of homogeneous but disordered assembly.