Preparation and characterization of new room temperature ionic liquids

A new series [C(n)O(m )mim][X] of imidazolium cation-based room temperature ionic liquids (RTILs), with ether and alcohol functional groups on the alkyl side-chain has been prepared. Some physical properties of these RTILs were measured, namely solubility in common solvents, viscosity and density. The solubility of LiCl, HgCl(2) and LaCl(3) in room temperature ionic liquids was also determined. The features of the solid-liquid phase transition were analysed, namely the glass transition temperature and the heat capacity jump associated with the transition from the non-equilibrium glass to the metastable supercooled liquid. These properties were compared with those reported for the 1-n-alkyl-3-methylimidazolium [C(n )mim][X] series. While the density and solid-liquid phase transition properties are similar for both series, the new RTILs present a considerably lower viscosity and an increased ability to dissolve HgCl(2) and LaCl(3) (up to 16 times higher).     

Synthesis and characterization of mondispersed CdSe nanocrystals at lower temperature

Nearly monodispersed CdSe quantum dots have been prepared by a soft solution approach using air-stable reagents at lower temperature. The temporal evolution of the absorption and room temperature photoluminescence spectra were used to follow the reaction process and to characterize the optical properties of as-prepared CdSe quantum dots. The results exhibited clear exciton peaks in absorption and bright band-edge luminescence. The structures of the CdSe nanocrystals were determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The influence of the temperature on the properties of the resultant CdSe nanocrystals was investigated. The distribution of properties within ensembles of CdSe nanocrystals was also studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed.     

Exciton spin relaxation in colloidal CdSe quantum dots at room temperature

Size dependence of spin dynamics in colloidal CdSe quantum dots (QDs) are investigated with circularly polarized pump-probe transmission spectroscopy at room temperature. The excitation energy is tuned to resonance with the lowest exciton (1S(h)1S(e)) energy of the CdSe QDs. The exciton spin dynamics of CdSe QD with the diameter of 5.2 nm shows monoexponential decay with a typical time constant of about 1-3 ps depending on the excitation energy. For the cases of CdSe QDs with smaller size (with the diameter of 4.0 and 2.4 nm), the exciton spin relaxation shows biexponential decay, a fast component with time constant of several ps and a slow one with time constant of hundreds of ps to nanosecond time scale. The fast spin relaxation arises from the bright-dark transition, i.e., J = ±1 ? -/+2 transition. This process is dominated by the hole spin flips, while the electron spin conserves. The slow spin relaxation is attributed to the intralevel exciton transitions (J = ±1 ? -/+1 transition), which is relevant to the electron spin flip. Our results indicate that the exciton spin relaxation pathways in CdSe QD are controllable by monitoring the particle size, and polarized pump-probe spectroscopy is proved to be a sensitive method to probe the exciton transition among the fine structures.     

Reversible photoswitching of ferromagnetic FePt nanoparticles at room temperature

There has been a great interest in developing photoswitchable magnetic materials because of their possible applications for future high-density information storage media. In fact, however, the examples reported so far did not show ferromagnetic behavior at room temperature. From the viewpoint of their practical application to magnetic recording systems, the ability to fix their magnetic moments such that they still exhibit room-temperature ferromagnetism is an absolute requirement. Here, we have designed reversible photoswitchable ferromagnetic FePt nanoparticles whose surfaces were coated with azobenzene-derivatized ligands. On the surfaces of core particles, reversible photoisomerization of azobenzene in the solid state was realized by using spacer ligands that provide sufficient free volume. These photoisomerizations brought about changes in the electrostatic field around the core-FePt nanoparticles. As a result, we have succeeded in controlling the magnetic properties of these ferromagnetic composite nanoparticles by alternating the photoillumination in the solid state at room temperature.     

Synthesis and characterization of photoluminescent In-doped CdSe nanoparticles

Indium-doped CdSe nanoparticles have been synthesized and characterized. Their light absorption, photoluminescence, and structure are similar to undoped CdSe nanoparticles. The greater part of the In associated with the nanoparticles is removed when the nanoparticles undergo ligand exchange by pyridine. As observed with undoped nanoparticles, a ZnS capping layer on the indium-doped nanoparticles results in enhanced nanocrystal photoluminescence. Also, the ZnS cap enhances the retention of In by the nanoparticles. Elemental analysis shows ligand exchange causes CdSe to be lost and capping with ZnS results in the loss of Se. We conclude that In-doped nanoparticles have most of the In on their surface, capping helps the nanoparticles retain the In, and they do not have altered electronic properties.     

Aqueous synthesis and characterization of TGA-capped CdSe quantum dots at freezing temperature

CdSe quantum dots (QDs) have traditionally been synthesized in organic phase and then transferred to aqueous solution by functionalizing their surface with silica, polymers, short-chain thiol ligands, or phospholipid micelles. However, a drastic increase in the hydrodynamic size and biotoxicity of QDs may hinder their biomedical applications. In this paper, the TGA-capped CdSe QDs are directly synthesized in aqueous phase at freezing temperature, and they prove to possess high QY (up to 14%).     

Synthesis and characterization of cuprous selenide nanocrystals at room temperature

A simple method has been developed to prepare cuprous selenide nanocrystals by the reaction of copper nitrate trihydrate with selenium and sodium mercaptoacetate in aqueous ammonia system. Cu_2Se nanocrystals were characterized by transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), electron diffraction (ED), fluorescence spectrum and ultraviolet-visible absorption spectrum. Cu_2Se nanocrystals showed berzelianite structure with 20-40 nm in length and 10-20 nm in width. A possible mechanism is also discussed.     

One-step synthesis of stoichiometrically defined metal oxide nanoparticles at room temperature

A great variety of metal oxide nanoparticles have been readily synthesized by using alkali metal oxides, M(2)O (M is Na or Li) and soluble metal salts (metal chlorides) in polar organic solutions, for example, methanol and ethanol, at room temperature. The oxidation states of the metals in the resulting metal oxides (Cu(2)O, CuO, ZnO, Al(2)O(3), Fe(2)O(3), Bi(2)O(3), TiO(2), SnO(2), CeO(2), Nb(2)O(5), WO(3), and CoFe(2)O(4)) range from 1 to 6 and remain invariable through the reactions where good control of stoichiometry is achieved. Metal oxide nanoparticles are 1-30 nm and have good monodispersivity and displayed comparable optical spectra. These syntheses are based on a general ion reaction pathway during which the precipitate occurs when O(2-) ions meet metal cations (M(n+)) in anhydrous solution and the reaction equation is M(n+) + n/2 O(2-) --> MO(n/2) (n=1-6).     

Preparation of CdSe quantum dots with full color emission based on a room temperature injection technique

High quality CdSe quantum dots are synthesized through a room temperature injection technique by using CdAc2 and Na2SeSO3 as precursors. In this synthesis approach, small CdSe clusters are formed after the injection at room temperature. Thereafter, CdSe quantum dots with emissions from the green to the red region can be obtained by transferring these clusters to different temperatures (40-150 degrees C) for particle growth. Meanwhile, CdSe quantum dots with emission in the blue-violet region (500-430 nm) are gained by an oxidation etching approach using H2O2 as oxidant. The advantage of this method is the natural separation of the nucleation and the growth process, which can provide a longer time for the preparation of the nuclei in simple operations and a well controlled fluorescence of the products, as the evolution of the fluorescence is slow at this low particle growth temperature.     

A novel strategy for boosting the photoluminescence quantum efficiency of CdSe nanocrystals at room temperature

Highly luminescent colloidal nanocrystals have wide applications in bioimaging and various optoelectronic devices.Herein we report a facile and mild procedure by combining S2-treatment and binary ligand passivation,which can efficiently enhance the luminescent property of CdSe nanocrystals at room temperature.The photoluminescence quantum yield of as-treated CdSe nanocrystals exhibits drastic enhancement(e.g.,188 times for CdSe nanorods)after this dual-passivation treatment.The methodology proposed here can be applied to various CdSe nanocrystals,regardless of their sizes,shapes,and crystal structures.     

磁性聚乙烯醇微球的制备及表征

为了制备表面具有羟基且有一定磁响应性的聚乙烯醇微球,本文采用反相乳化的方法,以液体石蜡为连续相,在Fe3O4磁流体存在下,通过戊二醛交联聚乙烯醇(PVA)。对微球的形貌,表面羟基含量,微球密度,微球Fe含量以及微球的磁响应性进行了研究。制得了粒径分布为25μm~150μm,表面羟值为11mmol/g~20mmol/g的磁性聚乙烯醇微球。     

聚醋酸乙烯类梳型分散剂的制备与表征

颜料在工业生产和人们的日常生活中起着重要的作用.由于颜料颗粒具有较大的比表面积和较高的比表面能,是热力学不稳定体系,当分散在介质中时容易发生团聚,影响其特性的发挥[1],因此需加入分散剂使其在分散介质中稳定分散.     

Synthesis and characterization of water-soluble CdSe nanoparticles capped by AOT

Water-soluble CdSe nanoparticles were synthesized using AOT (sodium bis(2-ethylehexyl)-sulfosuccinate) as stabilizer, cadmium acetate and Na2SeSO3 as precursors in aqueous phase. The influence of some key factors, such as reaction time, temperature, concentration and molar ratio of precursors on the optical properties of CdSe nanoparticles was systematically investigated through UV-Vis and PL spectra. Powder X-ray diffraction (XRD) was used to characterize the crystalline structure of synthesized CdSe nanoparticles. As-prepared CdSe nanoparticles exhibit an apparent quantum confinement effect and typical hexagonal wurtzite structures. Finally, the optimal experimental conditions were obtained.     

Germania nanoparticles and nanocrystals at room temperature in water and aqueous lysine sols

Facile synthesis of nanometer-sized germania crystals and amorphous germania nanoparticles (ca. 1 nm) is investigated through hydrolysis of germanium tetraethoxide and subsequent condensation of germania in both pure water and aqueous lysine solutions. Germanium tetraethoxide rapidly hydrolyzes in pure water, leading to solvated germanate species at lower germania concentrations and the onset of nanometer-sized germania crystals at room temperature with increasing germania content. In the presence of the basic amino acid L-lysine, amorphous germania nanoparticles (ca. 1 nm) spontaneously form with increasing germania content and coexist with nanometer-sized germania crystals at higher germania concentrations. Lysine and germania concentration both influence crystallite size and morphology (i.e., polyhedral, cubic). The facile, room-temperature crystallization of germania in the presence and absence of lysine is striking. The fact that the crystal morphology shows no signs of nanoparticle aggregative assembly, as has been observed in the formation of other oxide crystals, suggests that crystal growth takes place by addition of dissolved species rather than nanoparticles, and could have implications for other oxide systems.     

Synthesis and characterization of CdSe nanorods using a novel microemulsion method at moderate temperature

CdSe nanoparticles have been successfully synthesized using a novel microemulsion method at moderate temperature. It is found that with a combination of the surfactant AOT and hydrazine hydrate, it is possible to control the morphology of the nanoparticles. The hydrazine hydrate acts as both a reducing agent and a templating agent that favors the formation of a rodlike structure. The composition, morphology and optical properties of the CdSe nanoparticles were investigated using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FT-IR) spectroscopy. The nucleation and growth mechanism for this system is also proposed based on a time-dependent study. This synthesis route provides a moderate temperature (100 degrees C) method for synthesizing rodlike CdSe, hence reducing the possibility of oxidation of this chalcogenide compound.     

Size-controlled synthesis and characterization of polyvinyl alcohol coated palladium nanoparticles

In order to synthesize stable, catalytically active palladium nanoparticles with low polydispersity, a one-pot synthesis by the facile reduction of palladium chloride with citric acid in an aqueous solution of steric stabilizer polyvinyl alcohol (PVA) has been developed. The resulting nanoparticles are highly water-dispersible, excellent electro-catalysts, and have long shelf life. The palladium nanoparticles have been characterized by physico-chemical, spectroscopic, microscopic, and CV studies. The average size of the nanoparticles can be readily tuned from 8.1 to 53 nm by controlling the extent of reflux for mixtures containing suitable concentrations of metal ion, reducing agent and capping polymer, which also influence the size. Despite the surface-protecting action of PVA, the palladium nanoparticles are electro-catalytically active and exhibit size-dependent electro-catalytic behavior.     

Preparation and characterization of polyvinyl alcohol‐grafted Fe3O4 magnetic nanoparticles through glutaraldehyde

Magnetic nanoparticles (MNPs) are of great interest owing to their numerous existing and potential biomedical applications. To further explore the potential of MNPs in biomedical and other fields, we have designed and synthesized polyvinyl alcohol (PVA) polymer grafted Fe₃O₄ MNPs through glutaraldehyde (GLA) link. The success of this process has been ascertained using Fourier transform infrared (FT‐IR) analysis, thermogravimetric analysis (TGA), X‐ray diffraction (XRD) analysis and scanning electron microscopy (SEM) analysis. The FT‐IR analysis of resultant MNPs show infrared peak characteristics of PVA. TGA analysis clearly shows two major stages of thermal degradation, one corresponding to organic phase of PVA and GLA and another corresponding to Fe₃O₄ nanoparticles. XRD results and SEM images further support the FT‐IR and TGA results and confirm the presence of PVA layer surrounding Fe₃O₄ MNP surface. Under SEM examination, the magnetic cores exhibit somewhat irregular shapes varying from spherical, to oval to cubic. Copyright © 2012 John Wiley & Sons, Ltd.     

Preparation of macroporous polyHIPE foams via radiation-induced polymerization at room temperature

PolyHIPEs are highly porous, crosslinked polymer foams typically synthesized within high internal-phase emulsions (HIPEs). Two kinds of polyHIPEs including poly(styrene-divinylbenzene) [P(St-DVB)] and poly(methyl methacrylate-divinylbenzene) [P(MMA-DVB)] foams are synthesized in this work, which are fabricated from HIPEs template via radiation-induced polymerization at room temperature. Traditional free radical polymerization initiated by potassium peroxydisulfate (KPS) at 60 °C for producing polyHIPE P(St-DVB) foams is also conducted for comparison. It is found that the amount of emulsifier can be reduced greatly in the radiation-induced polymerization of HIPEs at room temperature, compared with the traditional polymerization approach. Besides, P(MMA-DVB) PolyHIPE foams with a fine microstructure of highly interconnected pores have been successfully fabricated via radiation-induced polymerization in this work, which is usually difficult to be prepared by thermal-initiation method because of the intermediate hydrophobicity of methyl methacrylate monomer. The influences of the fraction of internal aqueous phase and the concentration of emulsifier on the structure and performance of foams are carefully explored. The structure and compression strength of the foams are characterized by scanning electron microscopy and a mechanical testing machine, respectively.

Biosynthesis of iron and silver nanoparticles at room temperature using aqueous sorghum bran extracts

Iron and silver nanoparticles were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous sorghum extracts as both the reducing and capping agent. Silver ions were rapidly reduced by the aqueous sorghum bran extracts, leading to the formation of highly crystalline silver nanoparticles with an average diameter of 10 nm. The diffraction peaks were indexed to the face-centered cubic (fcc) phase of silver. The absorption spectra of colloidal silver nanoparticles showed a surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. Amorphous iron nanoparticles with an average diameter of 50 nm were formed instantaneously under ambient conditions. The reactivity of iron nanoparticles was tested by the H(2)O(2)-catalyzed degradation of bromothymol blue as a model organic contaminant.