Size-controlled synthesis of orderly organized cube-shaped lead sulfide nanocrystals via a solvothermal single-source precursor method

Monodisperse cube-shaped lead sulfide (PbS) nanocrystals were successfully synthesized by virtue of a solvothermal single-source precursor method at mild reaction conditions. These resulted PbS nanocrystals have the average size in a range of 10 nm and a uniform cubic shape, shown by TEM and HRTEM, respectively. Due to their narrow size distribution, orderly self-organized arrays on a large scale can be easily obtained. Experimental results indicate that several factors, such as coordinating ability of the solvent, carbon number of the substitute alkyls (n), reaction temperature, and concentration of the precursor, play key roles in the final size and size distribution of PbS nanocrystals. This finding will enhance our understanding for the formation mechanism of nanostructured materials with special shapes.     

Synthesis and magnetic properties of Gd doped EuS nanocrystals with enhanced Curie temperatures

EuS nanocrystals (NCs) were doped with Gd resulting in an enhancement of their magnetic properties. New EuS and GdS single source precursors (SSPs) were synthesized, characterized, and employed to synthesize Eu(1-x)Gd(x)S NCs by decomposition in oleylamine and trioctylphosphine at 290 °C. The doped NCs were characterized using X-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy, which support the uniform distribution of Gd dopants through electron energy loss spectroscopy (EELS) mapping. X-ray absorption spectroscopy (XAS) revealed the dopant ions in Eu(1-x)Gd(x)S NCs to be predominantly Gd(3+). NCs with a variety of doping ratios of Gd (0 ≤ x < 1) were systematically studied using vibrating sample magnetometry and the observed magnetic properties were correlated with the Gd doping levels (x) as quantified with ICP-AES. Enhancement of the Curie temperature (T(C)) was observed for samples with low Gd concentrations (x ≤ 10%) with a maximum T(C) of 29.4 K observed for NCs containing 5.3% Gd. Overall, the observed T(C), Weiss temperature (θ), and hysteretic behavior correspond directly to the doping level in Eu(1-x)Gd(x)S NCs and the trends qualitatively follow those previously reported for bulk and thin film samples.     

Size-controlled synthesis of highly water-soluble silver nanocrystals

We describe a modified polyol process for the synthesis of silver nanocrystals with uniform sizes ranging from several nanometers to 20 nm. The use of polyacrylic acid, in place of polyvinylpyrrolidone in the conventional polyol process, significantly limits the growth of silver nanocrystals, prevents the interparticle aggregation and fusion, and leads to a uniform population of samples with high water solubility. The size of nanocrystals can be conveniently tuned by controlling the reaction time, the concentration and chain length of the polymeric surfactants, and the reaction temperature. Uniform silver nanocrystals within sizes below 20 nm are preferred candidates over larger particles for applications where high density of optical absorption is required, for example, for photothermal conversion in cancer therapy.     

Size-controlled synthesis of quantum-sized EuS nanoparticles and tuning of their Faraday rotation peak

Size-controlled EuS nanoparticles were synthesized by the reaction of europium metal with thiourea as a sulfur source in liq. NH3, whose surface was confirmed to be modified with thiourea by FT-IR measurement, and the opto-magnetic properties (Faraday effect) of the EuS nanoparticles were investigated by using PMMA films containing the nanoparticles, showing that their Faraday rotation peaks were adjustable by control of their particle size.     

Enforcing solution phase nanoscopic aggregation in a palindromic tripeptide

C-terminal dimerization of a tripeptide palindrome afforded fibrillation in solution through an assembly probably driven by hydrogen bonding and hydrophobic contributions; such an approach provides an expeditious entry into fabrication of fibrillating peptides from non-fibrillating peptide sequences.     

Size-dependent hydrogen storage properties of Mg nanocrystals prepared from solution

Mg nanocrystals of controllable sizes were prepared in gram quantities by chemical reduction of magnesocene using a reducing solution of potassium with an aromatic hydrocarbon (either biphenyl, phenanthrene, or naphthalene). The hydrogen sorption kinetics were shown to be dramatically faster for nanocrystals with smaller diameters, although the activation energies calculated for hydrogen absorption (115-122 kJ/mol) and desorption (126-160 kJ/mol) were within previously measured values for bulk Mg. This large rate enhancement cannot be explained by the decrease in particle size alone but is likely due to an increase in the defect density present in smaller nanocrystals.     

Size-controlled preparation of Cu2O octahedron nanocrystals and studies on their optical absorption

We report herein the size-controlled preparation of monodispersed cuprous oxide octahedron nanocrystals smaller than 100 nm. The method is based on the reduction of copper nitrate in Triton X-100 water-in-oil (w/o) microemulsions by gamma-irradiation. The average edge length of the octahedron-shaped nanocrystals varies from 45 to 95 nm as a function of the dose rate. The quantum confinement effect was illustrated by the blueshift in the optical absorption. In addition, the growth process was also traced by absorption spectra.     

General and facile synthesis of ceria-based solid solution nanocrystals and their catalytic properties

Uniform Ce_1−xZr_xO₂ (x=0.2–0.8) nanocrystals with ultra-small size were synthesized through a thermolysis process, facilitated by the initial formation of precursor (hydrated (Ce,Zr)-hydroxides) at low temperature. TEM, XRD, EDAX, and Raman spectra were employed to study the formation of the solid solutions with various Ce/Zr ratios. Ultraviolet–visible (UV–vis) spectra showed that the ratios of Ce³⁺ to Ce⁴⁺ in both surface and bulk for the as-prepared Ce_1−xZr_xO₂ nanocrystals increased with the zirconium content x. The well-distributed Zr and Ce in the hydrated (Ce,Zr)-hydroxides before their thermolysis became the crucial factor for the structural homogeneity of the products. In addition, this strategy was extended to the synthesis of Ce_1−xGd_xO_1−x/2, Ce_1−xSm_xO_1−x/2, and Ce_1−xSn_xO₂ solid solutions. Catalytic measurements indicated that the ceria-based catalysts were active for CO oxidation at temperatures beyond 250 °C and the sequence of catalytic activity was Ce_0.5Zr_0.5O₂>Ce_0.8Zr_0.2O₂>Ce_0.2Zr_0.8O₂>Ce_0.5Sm_0.5O_1.75.     

液相合成方形PbS纳米晶的光学特性

采用一种简单、温和的液相合成方法制备了PbS纳米晶，利用透射电镜和高分辨透射电镜对PbS纳米晶的形貌与晶型结构进行了表征．研究了PbS纳米晶的光学吸收和光致发光特性，并比较分析了包覆剂聚乙烯吡咯烷酮(PVP)和回流时间对产物光学特性的影响．结果表明：PVP分子链中的O原子与纳米晶表面吸附的游离态Pb原子形成Pb-O配位键，使产物的激子吸收大为减弱，同时引起了表面浅束缚态能量的升高，最终导致了荧光淬灭现象．     

Adsorption and aggregation properties of novel star-shaped gluconamide-type cationic surfactants in aqueous solution

The adsorption and aggregation behavior of novel star-shaped gluconamide-type cationic surfactants N-dodecyl-N,N-bis[(3-D-gluconylamido)propyl]-N-alkylammonium bromide (C_nDBGB, where n represents hydrocarbon chain lengths of 10, 12, and 14) has been studied on the basis of static/dynamic surface tension, conductivity, dynamic light scattering (DLS), and transmission electron microscopy (TEM) data. The static surface tension of the C_nDBGB aqueous solution measured at the critical micelle concentration (CMC) is observed to be significantly lower than that of the corresponding monomeric surfactants. The dynamic surface tension results indicate that adsorption process of above CMC is a mixed diffusion–kinetic adsorption mechanism. From the results of temperature dependent conductivity measurements, we could obtain the degree of counterion binding (β) and the thermodynamic parameters such as standard free energy (ΔG _mic ⁰ ), enthalpy (ΔH _mic ⁰ ), and entropy (ΔS _mic ⁰ ) of aggregation. With a combination of the DLS and TEM data, a size transformation of the micelles is suggested to occur with an increase in the concentration.     

From trifluoroacetate complex precursors to monodisperse rare-earth fluoride and oxyfluoride nanocrystals with diverse shapes through controlled fluorination in solution phase

We report the first systematic synthesis of monodisperse rare-earth (RE=La to Lu, Y) fluoride and oxyfluoride nanocrystals with diverse shapes (trigonal REF3 triangular, truncated-triangular, hexagonal, and polygonal nanoplates; orthorhombic REF3 quadrilateral and zigzag-shaped nanoplates; cubic REOF nanopolyhedra and nanorods) from single-source precursors (SSP) of [RE(CF(3)COO)(3)] through controlled fluorination in oleic acid (OA)/oleylamine (OM)/1-octadecene (ODE). To selectively obtain REF3 or REOF nanocrystals, the fluorination of the RE-O bond to the RE-F bond at the nucleation stage was controlled by finely tuning the ratio of OA/ODE or OA/OM, and the reaction temperature. For phase-pure REF3 or REOF naocrystals, their shape-selective syntheses could be realized by further modifying the reaction conditions. The two-dimensional growth of the REF3 nanoplates and the one-dimensional growth of the REOF nanorods were likely due to the selective adsorption of the capping ligands on specific crystal planes of the nanocrystals. Those well-shaped nanocrystals with diverse geometric symmetries (such as D(3h), D(6h), C(2h), O(h), and D(nh)) displayed a remarkable capability to form self-assembled superlattices. By manipulating the solvent-substrate combination, the plate-shaped REF3 nanocrystals could form highly ordered nanoarrays by means of either the face-to-face formation or the edge-to-edge formation. By using this SSP strategy, we also obtained high-quality LaF3:Eu and LaF3:Eu/LaF3 triangular nanoplates that showed photoluminescent red emissions of Eu3+ ions sensitive to the surface effect.     

Morphology syntheses and properties of well-defined Prussian Blue nanocrystals by a facile solution approach

Large-scale syntheses of Prussian Blue (PB) uniform nanocubes and nanospheres, together with an interesting PB micro-frame structure, have been achieved by direct dissociation of a single-source precursor K(3)[Fe(CN)(6)] with polyvinylprrolidone (PVP) as a capping and reducing agent. The reaction temperature has been proved to be a key factor for morphology development of PB nanocrystals, and the size of PB nanocrystals can be tuned by adjusting the feed ratio of K(3)[Fe(CN)(6)] to PVP and the concentration of K(3)[Fe(CN)(6)]. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and high resolution transmission electron microscopy (HRTEM) were used to characterize the resulting nanocrystals and investigate their growth mechanisms. Optical and magnetic studies showed size- and shape-dependent optical and magnetic properties in the PB nanocrystals. An excellent electro-catalytic property to hydrogen peroxide reduction was observed at the PB nanocube-modified electrode.     

A computational study of lithium ketone enolate aggregation in the gas phase and in THF solution

The aggregation state of several lithium enolates were calculated in the gas phase and in THF solution by the B3LYP DFT and MP2 methods. The gas phase free energies of aggregate formation were underestimated by the DFT calculations, compared to those obtained by the G3MP2 method, although DFT did correctly predict the hexamer to be the major gas phase species. The DFT calculations correctly predicted the tetramer to be the major species in THF, while MP2 underestimated the stability of the tetramer relative to the dimer.     

Self-assembly of tert-butyl silanetriol in solution and aggregation with tetrahydrofuran

tert-Butyl silanetriol behaves like a surfactant and self-assembles in aqueous and tetrahydrofuran (THF) solutions. Micelle formation was studied with pulsed field gradient stimulated spin echo (PFG-SSE) NMR, while multilayer lamellar vesicles can be concluded from small/wide angle X-ray scattering measurements in concentrated solutions at elevated temperature. The significant interaction between tert-butyl silanetriol and THF is further highlighted by a crystal structure featuring a 3:1 adduct of silanetriol and THF.     

Dilute solution properties and phase separation of branched low-density polyethylene

Viscosity, light scattering, and precipitation temperature measurements on dilute solutions of high-density and low-density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long-chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long-chain branching in low-density polyethylene.     

Tuning of copper nanocrystals optical properties with their shapes

Copper nanocrystals are obtained by chemical reduction of copper ions in mixed reverse micelles. A large excess of reducing agent favors producing a new generation of shaped copper nanocrystals as nanodisks, elongated nanocrystals, and cubes. By using UV-Visible spectroscopy and numerical optical simulations we demonstrate that the optical properties are tuned by the relative proportions of spheres and nanodisks.     

The aggregation of trichosanthin in aqueous solution

As a kind of cytotoxin extracted from the root tuber of Trichosanthes kirilowii Maxim (Cucurbitaceae), trichosanthin can selectively bind to and kill the placental trophoblastic cells, which leads to a number of biomedical applications including the inhibition of trophoblastic tumors. However, the stability of trichosanthin in living organism is still one of the problems hindering the effectiveness of its applications. In this study, laser light scattering has been used successfully to investigate the stability of trichosanthin in both deionized water and KSCN aqueous solution in terms of the hydrodynamic size distribution of the trichosanthin aggregates as a function of both time and the salt concentration. It is found that the size distribution is always a bimodal one. One peak corresponds to a single trichosanthin chain; the other corresponds to the trichosanthin aggregates, which have an average hydrodynamic radius of ∼ 49 nm and are composed of ∼ 127 trichosanthin molecules when C_KSCN is higher than 0.5 mol/L. This implies that there exists an equilibrium between the single trichosanthin chain and its aggregates [i.e., nT ⇄ (T)_n]. Our results also suggest that the aggregates are made of the loosely packed trichosanthin molecules and behave as flexible polymer chains in θ solvent. © 1996 John Wiley & Sons, Inc.