Capping Reagent Research Articles

Fabrication of Hierarchical CuO Microspheres

Hierarchical microstructures of metal oxides comprised of nanoparticles, nanorods, and nanobelts as building blocks have been attracted great interests due to their novel structures, properties, and applications. In most systems, hierarchical assembly involves two distinct steps: 1) synthesizing the appropriate precursors, and 2) assembling them into larger structures. Copper oxide (CuO) is a narrow bandgap semiconducting oxide that has been widely used in electrochemical cells, in photothermal and photoconductive materials, and as a heterogeneous catalyst. Various techniques have been used to synthesize CuO nanostructures such as nanoparticles, nanorods, nanobelts, nanoribbons and nanotubes. However, the methods for fabricating CuO hierarchical microstructures were examined by a few groups. Dandelion-like CuO hollow microspheres have been synthesized by a solvothermal process. CuO microspheres have been generated by a simple solution method using sodium tartrate as a chelating agent and CuO whisker assemblies have been fabricated using a microwave-induced polyol process. Here we report a simple method for fabricating hierarchical CuO microspheres with an average diameter of 1.5-2.5 μm under the microwave irradiation. In this method, the CuO microspheres are built from small flakes, each comprised of several nanoplates of 15-25 nm wide and about 400 nm long. The effect of capping reagent concentration on the morphologies of the CuO products was also investigated.

Synthesis and Photoluminescence Properties of Truncated Octahedral Eu-Doped YF3 Submicrocrystals or Nanocrystals

Highly uniform and monodisperse Eu:YF3 nanosized and submicrosized truncated octahedra are successfully prepared in large quantities using a facile hydrothermal approach assisted by a capping reagent, ethylenediaminetetraacetic acid disodium salt (Na2H2EDTA). X-ray diffraction, field emission scanning microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction have been used to study the morphologies and crystal structure. The photoluminescence spectra at room temperature show that, in addition to the characteristic red emission peaks of Eu3+, an intense blue emission band centered at about 445 nm originating from the 4f65d to 4f7 configuration in Eu2+ is also observed when the crystals are excited at 393 nm, which is quite different from those reported previously. The results reveal that there should be a redox reaction during hydrothermal preparation of YF3:Eu at 180 °C, and some of the Eu3+ ions should have been reduced to the divalent state in the preparation process.

Additional Alkylsilanization of Aminosilane-modified Glass Slide: Effect of Alkylsilane Structure for Enhancing Surface Amine Functionality

Abstract Efficient amine-functionalized glass slides were developed by capping with alkylsilanes, which might reduce nonspecific interactions of amino groups with the surface silanol. We explored the types of alkylsilanes (used as silanol capping reagents) for designing high amine functionality on the glass slide.

A solution-phase approach to the chemical synthesis of ZnO nanostructures via a low-temperature route

A low-temperature and effective precursor-based method has been demonstrated to synthesize nanostructured ZnO and its precursors with controllable morphology. It is found that the morphology of ZnO precursors has a strong dependence on the reaction conditions that include the molar ratio of reagents, solvent, and reaction temperature. Ethylene glycol used as an organic capping reagent is the key to determine the two-dimensional petal-like ZnO nanostructure. The structures and properties of the obtained-samples are characterized by a scanning electron microscope, an X-ray diffractometer, and an energy dispersive X-ray spectrometer. The present technique is an easy and cheap method to synthesize nanoscale photonic and electronic materials.

Solid-phase synthesis of stereoregulated oligodeoxyribonucleoside phosphorothioates

An efficient stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates on a solid-support by an oxazaphospholidine method was achieved. A detailed investigation on the reagents and conditions for the solid-phase synthesis revealed that the use of the capping and sulfurizing reagents which are regularly used for the conventional synthesis of phosphorothioate DNA resulted in a sluggish removal of the chiral auxiliaries on the phosphorothioate internucleotidic linkages. After optimization of the capping and sulfurizing steps, the deprotection of the internucleotidic linkages were successfully conducted under the regular basic conditions, and P-stereoregulated phosphorothioate DNA oligomers were successfully obtained with excellent diastereopurity.

‘One-step’ controllable synthesis of Ag andAg2S nanocrystals on a large scale

Ag and Ag2S nanocrystals (NCs) were synthesized by a simple ‘one-step’ process. Dodecanethiol played threeimportant roles in the synthesis: as the capping reagent, reducer (for the synthesis of Ag) andS2− source (for thesynthesis of Ag2S). Due to the multifunctional characteristic of dodecanethiol, only two reactants (silvernitrate and dodecanethiol) are needed in the synthesis, avoiding the use of toxicorganic solvents and a complex reaction procedure. X-ray powder diffraction andtransmission electron microscopy studies indicated that both the phase (Ag orAg2S) and the particle size were controlled by reaction parameters. The infrared spectrastudies indicated that the nanoparticles were stabilized by dodecanethiol. Asa result, the particles were stable (no irreversible conglomeration) in the solidstate and in solution for several months. In addition, a large quantity of Ag andAg2S NCs could be readily obtained. A possible formation and size evolution mechanism for Ag andAg2S NCs was proposed.

Effect of phenylalanine on photoluminescence and stability of CdTe nanocrystals capped with thioglycolic acid

CdTe nanocrystals capped with thioglycolic acid in aqueous were conjugated with phenylalanine (Phe) in order to study the effect of Phe on the photoluminescence (PL) and stability of CdTe nanocrystals. The PL intensity of CdTe–Phe conjugate has enhanced greatly comparing with CdTe nanocrystals due to the interaction of CdTe and Phe. This interaction of Cd ion on the surface of CdTe nanocrystals with carboxyl group of Phe was identified by IR, TEM and PL spectra analyses. The effect of the reflux time, pH and the ratio of CdTe nanocrystals to Phe were also investigated. The results showed that Phe could prevent the aggregation of CdTe nanocrystals beside thioglycolic acid as a capping reagent of CdTe nanocrystals. The coordination between Phe and CdTe nanocrystals resulted in increasing both the PL intensity and the stabilization of CdTe–Phe conjugate. Furthermore, the phenyl group of Phe delayed the photo-oxidation of both CdTe nanocrystals and thiol ligands on the surface of CdTe nanoparticles. The pH value of the reaction system was an important factor for the reaction of CdTe nanocrystals and Phe because of the amphoteric property of Phe. The results of this paper was useful to understand the mechanism of the reaction between nanocrystals such as CdTe, CdSe, CdS and peptides or protein such as antibodies and enzymes composed of Phe or other apolar amino acids.

Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties

Cubic Pt nanoparticles were prepared from a solution of K 2PtCl 4 containing sodium polyacrylate as a capping reagent. The effects of the Pt/polymer molar ratio, the average molecular weight ( M w) of the polymer, and reaction temperature on the shape and size were investigated. When the polymer of M w = 5100 was added at a molar ratio of Pt/polymer = 1/12, cubic platinum nanoparticles of an average size of 10.3 nm were predominantly formed (ca. 50% in number) at 25 °C. The electron diffraction pattern of the cubic nanoparticles revealed that they are single crystals with Pt {1 0 0} faces on the surface. The cubic nanoparticles were electrochemically active, and showed strong features of Pt {1 0 0} faces on cyclic voltammogram under argon atmosphere. After repeated potential cycling in the range 0.05–1.4 V, the features of Pt {1 0 0} were gradually lost, and changed to those of polycrystalline Pt. Rotating ring disk electrode measurements in O 2-saturated H 2SO 4 solution revealed that the cubic nanoparticles had a high catalytic activity for oxygen reduction reaction (ORR). After polycrystallization by repeated potential cycling, the activity for ORR and hydrogen peroxide formation decreased slightly, which were attributed to the surface structural change from Pt {1 0 0} to polycrystalline.

2D nanostructure of gold nanoparticles: An approach to SERS-active substrate

Monolayer well-ordered close-packed 2D nanostructures of gold nanoparticles were fabricated without using any capping reagent or surfactant. The area of the 2D nanostructure obtained was as large as several 100 s μm 2 to mm 2. The individual gold nanoparticles of the 2D nanostructure are not in contact depicting the possible surface active site (i.e. hot site). The SERS-activity was measured by using crystal violet molecules adsorbed on the 2D nanostructure. The estimated enhancement was found as much as 10 8. Size-dependent SERS intensity of the well-ordered 2D nanostructures is discussed in detail.

Enabling routine fluorous capping in solid phase peptide synthesis

We describe here the use of polyfluorinated trivalent iodonium salts as efficient and robust capping reagents during solid phase peptide synthesis using either t-Boc or Fmoc chemistry. Standard protocols established for solid phase peptide synthesis can be utilized without any change in solvent or reagent conditions. The capping reaction was carried out at sites where amino acid coupling steps failed. At the termination of the synthesis, the crude peptide mixture obtained from release of materials from the resin, is either simply centrifuged in aqueous solution to yield pure peptide, or purified by passage through fluorous silica gel in solvents with high water content. We envision that the chemistry and reagents described here will find wide use in peptide and protein chemistry, and also in combinatorial library synthesis where terminal amines are coupled to reaction partners.

Conversion of Cu2O nanocrystals into hollow Cu2−xSe nanocages with the preservation of morphologies

With the use of PVP (polyvinylpyrrolidone) as capping reagent, cubic, octahedral and spherical Cu2O nanocrystals were obtained in aqueous media when different reducing agents were applied. After adding selenium sources at room temperature, these nanocrystals could be converted (based on the Kirkendall effect) into hollow Cu2-xSe nanocages that keep their corresponding orignial morphologies.

Preparation of Semiconductor/Polymer Coaxial Nanocables by a Facile Solution Process

AbstractWe report on the preparation of ultralong semiconductor tellurium/cross‐linked PVA coaxial nanocables with a core 20–30 nm in diameter and a surrounding sheath about 5–20 nm in thickness by a simple hydrothermal process. The length of these nanocables can be up to 500–800 μm. In the present synthesis PVA was used as the reducing agent to react with Na2TeO3, and it also serves as the capping reagent and the source of the sheaths. The synergistic effects of the interaction of cross‐linked PVA with the tellurium nanowires could play an important role in the formation of the morphology of the resulting products.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Large-Scale Self-Assembled Ag Nanotubes

A high yield of silver nanotubes with large aspect ratio were conveniently synthesized via an organic-assist solvothermal preparation technique using polyvinyl pyrrolidone (PVP) as a capping reagent and architecture soft-template. The molecular ratio between the repeating unit of PVP and AgNO 3 plays a crucial role in determining the geometric shape of the product. Such novel-type Ag nanotubes were self-assembled by Ag nanoparticles, which had largely similar crystallographic orientation, forming a texture. The fact that nanoparticles without anisotropic crystal structures can form such superstructures by self-assembly may open a window for understanding a range of nanotube formation processes.

Effects of chain length of polyvinylpyrrolidone for the synthesis of silver nanostructures by a microwave-polyol method

When silver nanostructures were prepared by a microwave(MW)-polyol method in the presence of polyvinylpyrrolidone (PVP) as a capping reagent, besides spherical nanoparticles, nanosheets, polygonal nanoplates, nanorods, and nanowires were synthesized within 8 min. Effects of chain length of PVP were examined by using three different molecular weights of PVPs (10, 40, and 360 k). When a short chain PVP (10 k) was used, nanosheets and nanoplates were dominantly prepared, while nanorods and nanowires were preferentially synthesized by using longer chain PVPs (40, 360 k). The maximum aspect ratios of nanorods and nanowires were ∼ 7, ∼ 130, and ∼ 200 for PVP (10, 40, 360 k), respectively. These results indicated that shape and size of Ag nanostructures can be controlled by changing chain length of PVP. On the basis of UV and visible absorption spectra of product solutions, the number density of Ag nanostructures including spherical nanoparticles increased rapidly with increasing chain length of PVP.

Rapid Formation of Novel Au Core–Ag Shell Nanostructures by a Microwave-polyol Method

Abstract Au core–Ag shell bimetallic nanoparticles, denoted as Au@Ag, have been prepared by a microwave(MW)-polyol method through the two-step reduction of AuCl4− and Ag+ ions in the presence of poly(vinylpyrrolidone) (PVP) as a capping reagent. When single crystal polygonal Au nanoplates and nanorods were used as seeds, a mixture of various Au@Ag core–shell nanostructures was prepared after MW heating for only 2 min. Among them, small amounts of novel polygonal and rod types of Au@Ag nanostructures, in which morphologies of Au core were conserved, were produced.

Fabrication of CdS Nanorods in PVP Fiber Matrices by Electrospinning

AbstractSummary: A controlled fabrication of rod‐like nanostructures of cadmium sulfide (CdS) incorporated into polymer fiber matrices has been developed by an electrospinning method. Here, poly(vinyl pyrrolidone) (PVP) was used as a polymer capping reagent, utilizing the interactions of cadmium ions with the carbonyl groups in the PVP molecules. The formation of CdS nanorods inside the PVP was carried out via the reaction of Cd2+ with H2S. SEM images showed that the electrospun films of PVP/CdS are composed of fibers with a diameter between 100 and 900 nm. TEM proved that most of the CdS nanorods are incorporated in the PVP fibrous film. The diameter of the rod is about 50 nm and the length is from 100 to 300 nm.TEM image of the CdS nanorods formed in the PVP fibrous film.imageTEM image of the CdS nanorods formed in the PVP fibrous film.

Preparation and characterization of the ZnS nanospheres with narrow size distribution

Abstract In this work, we report the synthesis of ZnS nanospheres with relatively narrow size distribution using polyvinyl pyrrolidone (PVP) as a capping reagent. The nanocrystallite powers were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), and UV–vis optical absorption spectra. The synthesized nanocrystallite show typical lattice spacings corresponding to the cubic phase of ZnS, as confirmed from HRTEM, ED, and XRD. The UV–vis spectra shows a blue shift of the first excitonic transition band compared with bulk ZnS, probably due to the quantum size effect.

Synthesis and characterization of flowerlike ZnO nanostructures via an ethylenediamine-meditated solution route

Flowerlike ZnO nanostructures were deposited on Si substrate by choosing hexamethylenetetramine as the nucleation control reagent and ethylenediamine as the chelating and capping reagent. Structural and optical measurements reveal that obtained ZnO exhibits well-defined flowerlike morphology, hexagonal wurtzite structure, uniform distribution on substrate, and strong photoluminescence in ultraviolet band. The well-arrayed pedals of each ZnO flower possess the typical tapering feature, and are built up by many well-aligned ZnO nanorods. Moreover, each single nanorod building up the pedal exhibits the single crystal nature and the growth direction along c-axis. Effects of the precursor composition on the morphology of ZnO were discussed.

A new approach to A,B-difunctionalisation of cyclodextrins using bulky 1,3-bis[bis(aryl)chloromethyl]benzenes as capping reagents

1,3-Bis[bis(4-tert-butylphenyl)chloromethyl]benzene and 1,3-bis[bis(4-anisyl)chloromethyl]benzene were employed as regioselective capping reagents for the preparation of C-6A,C-6B-bridged, permethylated alpha- and beta-CD derivatives; isolated yields up to 55% of proximally capped, methylated CDs were obtained, thus opening the way to the straightforward preparation of a wide range of A,B-functionalised CDs. As revealed by a single crystal X-ray diffraction study, the benzene-1,3-bis[bis(4-tert-butylphenyl)methyl] spacer is perfectly suited for A,B-capping of beta-cyclodextrin.

Chelating Ligand-Mediated Crystal Growth of Cerium Orthovanadate

An ethylenediaminetetraacetic acid (EDTA)-mediated hydrothermal route to cerium orthovanadate (CeVO4) microcrystals has been developed. The EDTA/Ce3+ ratio, solution pH, and temperature of the reaction systems are found to play important roles in determining the morphologies and growth process of the CeVO4 products. During the process of synthesis, EDTA plays important roles such as chelating ligand and capping reagent. These products have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, the results of X-ray photoelectron spectra (XPS) and magnetic measurements reveal the existence of Ce4+ induced by surface oxidation of air. The existence of Ce4+ ions may be helpful for oxidative dehydrogenation of propane of CeVO4. On the basis of the experimental results, we suppose this method may have wide applications in exploring the crystal growth process and may provide guidance for the morphology controllable synthesis.