Kinetically controlled synthesis of triangular and hexagonal nanoplates of palladium and their SPR/SERS properties

The rapid reduction of Na(2)PdCl(4) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) has recently been demonstrated as a convenient method of generating Pd cubooctahedra and twinned nanoparticles. Here we describe a new procedure where Pd triangular or hexagonal nanoplates could be selectively synthesized by manipulating the reduction kinetics of the polyol process. More specifically, the reduction rate was substantially reduced through the introduction of Fe(III) species and the O(2)/Cl(-) pair, two wet etchants for Pd(0). The etching power of the O(2)/Cl(-) pair could be further enhanced by adding an acid to lower the pH of the reaction solution. Unlike the previously reported synthesis of Ag and Au nanoplates, light was found to have no indispensable role in the formation of Pd nanoplates. Both triangular and hexagonal nanoplates of Pd exhibited surface plasmon resonance (SPR) peaks in the visible region, and their positions matched with the results of discrete dipole approximation (DDA) calculation. Thanks to their sharp corners and edges, these Pd nanoplates could serve as active substrates for surface-enhanced Raman scattering (SERS).     

Facile Synthesis of Porous Mn2O3 Nanoplates and Their Electrochemical Behavior as Anode Materials for Lithium Ion Batteries

Porous Mn₂O₃ nanoplates were prepared by a facile polyol solution method combined with a simple post‐annealing process. The porous Mn₂O₃ nanoplates were characterized by XRD, field‐emission SEM, high‐resolution TEM, and N₂ adsorption/desorption isotherm measurements. The formation process for the Mn₂O₃ nanoplates was proposed as a morphology‐conserved transformation strategy. These porous nanoplates exhibited improved electrochemical performance with excellent cycling stability and good rate capability when applied as anode materials in lithium ion batteries.     

Thermal aqueous solution approach for the synthesis of triangular and hexagonal gold nanoplates with three different size ranges

The synthesis of gold nanoplates was carried out in an aqueous solution by thermal reduction of HAuCl(4) with trisodium citrate in the presence of cetyltrimethylammonium bromide (CTAB) surfactant in just 5-40 min. The sizes of the gold nanoplates can be varied from as small as tens of nanometers in width, to several hundreds of nanometers, and even a few microns in width by changing the reagent concentrations, solution temperature, and the reaction time. A [CTAB]/[HAuCl(4)] ratio of 6 in the reaction solution was found to be favorable for the formation of gold nanoplates. The nanoplates possess well-defined shapes with sharp edges. The small nanoplates exhibit mainly a triangular shape, while larger nanoplates show a mixture of triangular, hexagonal, truncated triangular, and other symmetrical structures. The nanoplates are composed of essentially (111) lattice planes, as revealed by both XRD and TEM results. Nanoplates with widths from several hundreds of nanometers to a few microns absorb light strongly in the near-infrared region. The growth mechanism of these nanoplates was investigated. The ability to synthesize gold nanoplates with these different size ranges in large scale in aqueous solution using simple CTAB capping surfactant should allow more diverse applications of gold nanoplates.     

Use of Natural Monomer in the Synthesis of Nano- and Microparticles of Polyurethane by Suspension-Polyaddition Technique

Summary: Polyurethane nano- and microparticles were synthesized by suspension-polyaddition technique, using aqueous polymerization medium. Castor oil, a vegetable triglyceride possessing hydroxyl groups was used as natural polyol and methylene diphenyl diisocyanate (MDI) as isocyanate. The levofloxacin, an antibacterial drug was used as model drug to measure the particles encapsulation efficiency. The effect of the addition of a second polyol, the poly(ethylene glycol) (PEG), and the stirring rate on the mean diameter and morphology of particles was also investigated. The poly(ethylene glycol) has an important effect in the reduction of particles size and their porosity. On the other hand, the poly(ethylene glycol) reduced the yield of encapsulation from 70% for the formulation without PEG to 20% for formulations with PEG. FTIR analysis confirmed the polyurethane formation. Dynamic light scattering study, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to determine the nanoparticles size and shape. Spectrofluorimetric analysis was used to detect the levofloxacin.     

Synthesis and characterization of polyhedral Pt nanoparticles: their catalytic property, surface attachment, self-aggregation and assembly

In this paper, we presented the preparation procedure of Pt nanoparticles with the well-controlled polyhedral morphology and size by a modified polyol method using AgNO(3) in accordance with the reduction of H(2)PtCl(6) in EG at high temperature around 160°C. The methods of UV-vis spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution (HR) TEM measurements were used to characterize their surface morphology, size, and crystal structure. We have observed that the polyhedral Pt nanoparticles of sharp edges and corners were produced in the preferential homogenous growth as well as the formation of porous and large Pt particles by self-aggregation and assembly originating from as-prepared polyhedral Pt nanoparticles. It is most impressive to find that the arrangement of Pt nanoparticles was observed in their surface attachments, self-aggregation, random and directed surface self-assembly by the bottom-up approach. Their high electrocatalytic activity for methanol oxidation was predicted. The findings and results showed that the polyhedral Pt nanoparticle-based catalysts exhibited the high electrocatalytic activity for their potential applications in developing the efficient Pt-based catalysts for direct methanol fuel cells.     

Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

Glassy carbon electrode (GCE) coated with anisotropic gold nanoplates (aAuNPs) was used for the study of oxygen reduction reaction (ORR) in 0.5 M sulfuric acid instead of bulk gold electrodes. The electrode cleaning/activation procedure lead to the removal of any charged and uncharged residues on the gold nanoplates, leaving the nanostructured surface highly active towards oxygen reduction. The advantages: much lower overpotential and larger current densities of oxygen reduction are ascribed to the unique nanostructures present on the carbon electrode surface‐the gold nanoplates. They are rich in edges providing a large population of Au (100) sites with unsaturated coordination exposed to the solution, and catalytically active. Measurements performed using a rotating disc electrode, modified with the gold nanoplates, confirmed that ORR proceeds via two separate steps: oxygen is reduced to hydrogen peroxide, and the peroxide is further reduced in a two‐electron reduction to water.     

Mn3O4 nanoplates and nanoparticles: Synthesis, characterization, electrochemical and catalytic properties

Mn₃O₄ hexagonal nanoplates and nanoparticles were synthesized via a solvent-assisted hydrothermal oxidation process at low temperature and a solvothermal oxidation method, respectively. The synthesized product was characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (ED), Fourier transform infrared (FT-IR) spectroscopy. Their capability of catalytic oxidation of formaldehyde to formic acid at room temperature and atmospheric pressure and electrochemical properties by cyclic voltammogram (CV) were compared. The results showed that Mn₃O₄ hexagonal nanoplate is a better catalyst, and the hexagonal nanoplates and nanoparticles modified electrodes blended with carbon black have a higher specific capacitance.     

Controllable synthesis of nickel hydroxide and porous nickel oxide nanostructures with different morphologies

Alpha-Ni(OH)(2) nanobelts, nanowires, short nanowires, and beta-Ni(OH)(2) nanoplates have been successfully prepared in high yields and purities by a convenient hydrothermal method under mild conditions from very simple systems composed only of NaOH, NiSO(4), and water. It has been found that the ratio of NaOH to NiSO(4) not only affects the morphology of the Ni(OH)(2) nanostructures, but also determines whether the product is of the alpha- or beta-crystal phase. A notable finding is that porous NiO nanobelts were produced after exposure of the Ni(OH)(2) products to an electron beam for several minutes during transmission electron microscopy (TEM) observations. Another unusual feature is that rectangular nanoplates with many gaps were obtained. Furthermore, porous NiO nanobelts, nanowires, and nanoplates could also be obtained by annealing the as-prepared Ni(OH)(2) products. A sequence of dissolution, recrystallization, and oriented attachment-assisted self-assembly of nanowires into nanobelts is proposed as a plausible mechanistic interpretation for the formation of the observed structures. The method presented here possesses several advantages, including high yields, high purities, low cost, and environmental benignity. It might feasibly be scaled-up for industrial mass production.     

Synthesis of a PEG-PNIPAm thermosensitive dendritic copolymer and investigation of its self-association

A Novel thermosensitive dendritic copolymer based on polyethylene glycol(PEG) and poly(Nisopropylacrylamide)(PNIPAm) with a cloud point(CP) around 36 ?C was successfully synthesized by preparation of a dendritic polyol and followed by atom transfer radical polymerization(ATRP) of N-isopropylacrylamide. The dendritic copolymer was characterized using gel-permeation chromatography(GPC), FTIR and 1H-NMR spectroscopy. The selfassociation behavior of the copolymer in aqueous medium was investigated by dynamic light scattering(DLS) and transmission electron microscopy(TEM). These investigations confirmed that the dendritic copolymer showed different association behaviors at various temperatures.     

用双还原法制备三角形银纳米片及其光学性能

在硼氢化钠和柠檬酸三钠共存的体系中还原硝酸银, 以聚乙烯吡咯烷酮(PVP)为表面活性剂和保护剂, 水浴加热制备得到三角形银纳米片, 用X射线衍射(XRD)、透射电子显微镜(TEM)、紫外-可见(UV-Vis)吸收光谱、表面增强拉曼散射(SERS)光谱对其进行了表征. 结果表明: 三角形银纳米片产物为立方相金属银, 边长为(100±40) nm, 厚度为(10±5) nm; 产物表现出与球形银纳米粒子完全不同的吸收光谱; 柠檬酸根在银晶核不同晶面的选择吸附、PVP的包覆作用及Ag(111)晶面的层错对产物的形成起决定作用; 与球形纳米颗粒相比, 三角形银纳米片膜对吡啶(Py)分子有显著的SERS活性.     

Synthesis of Spin-Crossover Nano- and Micro-objects in Homogeneous Media

New methods are proposed for the synthesis of spin-crossover nano- and micro-objects. Several nano-objects that are based upon the spin-crossover complex [Fe(hptrz)(3) ](OTs)(2) (hptrz=4-heptyl-1,2,4-triazole, Ts=para-toluenesulfonyl) were prepared in homogeneous media. The use of various reagents (Triton X-100, PVP, TOPO, and PEGs of different molecular weights) as stabilizing agents yielded materials of different size (6?nm-2?μm) and morphology (nanorods, nanoplates, small spherical particles, and nano- and micro-crystals). In particular, when Triton X-100 was used, a variation in the morphology from nanorods to nanoplates was observed by changing the nature of the solvent. Interestingly, the preparation of the nanorods and nanoplates was always accompanied by the formation of small spherical particles. Alternatively, when PEG was used, 200-400?nm crystals of the complex were obtained. In addition, a very promising polymer-free synthetic method is discussed that was based on the preparation of relatively stable Fe(II) -triazole oligomers in CHCl(3) . Their specific treatment led to micro-crystals, small nanoparticles, or gels. The size and morphology of all of these objects were characterized by TEM and by dynamic light scattering (DLS) where possible. Their spin-crossover behavior was studied by optical and magnetic measurements. The spin-transition features for large particles (>100?nm) were very similar to that of the bulk material, that is, close to room temperature with a hysteresis width of up to 8?K. The effects of the matrix and/or size-reduction led to modification of the transition temperature and an abruptness of the spin transition for oligomeric solutions and small nanoparticles of 6?nm in size.     

Attachment-driven morphology evolvement of rectangular ZnO nanowires

The rectangular cross-sectional ZnO nanowires were synthesized in a solution method. An attachment-driven growth mechanism was proposed for the morphology evolvement of ZnO nanocrystals from nanoparticles to nanoplates and eventually to nanowires. Due to the pileup attachment of the nanoplates to recrystallize into nanowires, unique one-dimensional (1D) ZnO nanowires with the rectangular cross section were obtained, which is different from those nanowires in the previous reports. It is the first time the evidence that "oriented attachment" can occur not only for nanoparticles but also for nanoplates was obtained, suggesting that "oriented attachment" is an intrinsic behavior for nanosized materials. According to the growth model proposed based on the direct TEM observations, ZnO nanocrystals can be easily controlled as nanoparticles, nanoplates, or nanowires by tuning the synthetic parameters.     

UV irradiation induced formation of single-crystal gold nanonetworks with controllable pore distribution

Single-crystal gold nanonetworks and nanoplates with novel porous structures were synthesized through a continuous UV irradiation method. The structures of the porous nanonetworks and the nanoplates were found to be citric acid concentration dependent. Transmission electron microscopy (TEM) showed that the two-dimensional (2-D) nanonetworks prepared at the lower citric acid concentration (0.5 mM) had irregular pores and bigger area. Increasing the citric acid concentration resulted in formation of gold nanoplates with hexagonal, triangular or truncated triangular pores. When the acid concentration came to 2 mM, the nanoplates with single and double pores were observable. The selected area electron diffraction (SAED) patterns showed that both the nanonetworks and porous nanoplates were single-crystal. The presence of 1/3{4 2 2} reflections indicated that the surface of the gold nanonetwork and nanoplates is atomically flat.     

多元醇法形貌可控制备氧化亚铜微纳米颗粒

以硝酸铜、乙酸铜、乙酰丙酮铜为原料,采用多元醇还原法合成制备了氧化亚铜立方体、微球、空心球、核壳结构等微纳米颗粒。 利用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)和紫外可见吸收光谱(UV-Vis)等测试手段对样品的物相、形貌、元素组分及吸光性能进行了表征。 同时考察了铜源、反应时间、和多元醇类型对氧化亚铜微纳米材料形貌的影响,对产物形成机理进行了初步的探讨。 对产物形成机理进行了初步的探讨。 采用简单低廉的多元醇合成法,可以控制合成不同相貌的氧化亚铜微纳米结构。 对制备形貌可控的氧化物具有一定的指导意义。     

Influence of Temperature on the Formation of Silver Nanoparticles by using a Seed‐Free Photochemical Method under Sodium‐Lamp Irradiation

Silver nanoparticles can be prepared by using a seed‐free photo‐assisted citrate reduction method under the irradiation of a sodium lamp. Under the same irradiation intensity, bath temperatures are crucial in influencing the reaction rate, morphologies of final products, and shape evolution of the silver nanostructures. For example, when the bath temperature is 80 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 38±6 %, 35±10 %, and 12±8 %, respectively. However, when the bath temperature is 30 °C, the product yields of silver nanoplates, nanorods, and nanodecahedra are 6±3 %, 0 %, and 83±16 %, respectively. Time‐dependent UV/Vis spectra and TEM images show that silver nanoplates were formed at the earlier reaction stage and greatly decreased in amount at the later stage when the bath temperatures are less than or equal to 40 °C. This indicates that the silver nanoplates, which can be regarded as intermediates, are kinetically favored products. They are not thermodynamically favored products at these relatively low bath temperatures. The SERS spectra of crystal violet (CV) show that all the silver colloids synthesized at various temperatures exhibit good enhancement factors and that the colloids prepared at lower bath temperatures have a higher enhancement factor.     

Colloidal dispersions of monodisperse magnetite nanoparticles modified with poly(ethylene glycol)

Monodisperse magnetite nanoparticles modified with poly(ethylene glycol) (PEG) were synthesized using a silane functionalized PEG obtained by reacting 3-aminopropyl triethoxysilane with carboxylic acid-methoxy PEG (mPEG-COOH) using amide reactions. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential measurements show the particles are monodisperse (sigma(gv) approximately 0.2) and stable in water for pH of 3-9 and ionic strengths, up to 0.3 M NaCl. Thermogravimetric analysis coupled with TEM and DLS indicates formation of a dense graft layer on the particle surface. An analysis of the interparticle interaction energy indicates that the particles are stabilized by strong steric repulsions between PEG chains on their surface.     

Triangular Ag/Pd nanoplates with sawtooth edges: Displacement synthesis and optical and catalytic properties

Ag/Pd nanoplates with sawtooth edges were prepared via a galvanic displacement reaction in which added Pd(OAc)₂ slowly reacted with Ag nanoplates containing adsorbed hexadecyltrimethylammonium bromide. Control over the optical properties and catalytic activity of the Ag/Pd nanoplates for electroless copper deposition could be achieved by varying the Ag/Pd alloying ratio.     

Effect of polyethylene glycol-2000 on amino acid surfactant-based vesicles

Polyethylene glycol (PEG)-modified amino acid surfactant-based vesicles were prepared to improve the stability and cellular delivery of drugs. The vesicles comprised PEG-2000, sodium N-lauroylsarcosinate hydrate (SNLS), 1-decanol, and deionized water. The complex showed vesicular structures that were almost the same as the original vesicles, and their size distribution was (100–150 nm). Transmission electron microscopy (TEM) results revealed that no fusion occurred at 1.25 wt.% PEG concentration. The steric hindrance present among the vesicles prevented aggregation of the particles. No visual phase separation was observed for 6 months at room temperature 28?ºC. At higher molar concentration of PEG, fusion and wrinkling occurred owing to the association of PEG chains. The decreasing bending curvature led to the formation of fused vesicles with multilayer structure, as revealed by TEM and differential scanning calorimetry (DSC).     

Facile and Efficient Fabrication of Photoresponsive Microgels via Thiol–Michael Addition

A photoresponsive microgel is designed by the combination of a noncovalent assembly strategy with a covalent cross‐linking method. End‐functionalized poly(ethylene glycol) with azobenzene [(PEG‐(Azo)₂)] was mixed with acrylate‐modified β‐CD (β‐CD‐MAA) to form photoresponsive inclusion complex through host–guest interaction. The above photoresponsive complex was cross‐linked by thiol‐functionalized PEG (PEG‐dithiol) via Michael addition click reaction. The photoreversibility of resulted microgel was studied by TEM, UV–Vis spectroscopy, and ¹H NMR measurements. The characterization results indicated that the reversible size changes of the microgel could be achieved by alternative UV–Vis irradiations with good repeatability.     

Effect of Chain Length of Polyethylene Glycol and Crosslink Density (NCO/OH) on Properties of Castor Oil Based Polyurethane Elastomers

The equilibrium swelling study of polyurethanes (PU) was carried out in various solvents in order to calculate their solubility parameter. The kinetics of swelling and sorption have also been studied in 1,4‐dioxane at 30°C. The PU was synthesized by reacting a novel polyol (castor oil derivative and epoxy based resin, EpxR) and one of the polyethylene glycols (PEG 200, PEG 400, PEG 600) with different weight compositions, with a toluene diisocyanate (TDI) adduct (derived from toluene diisocyanate and R60 polyol). Different NCO/OH ratio viz. 1, 1.3 and 1.7 were employed in the study. The results were found to vary with the weight composition of polyol components, as well as the crosslink density of the samples. The sorption behavior is also found to vary with the molecular weight of polyethylene glycol employed in the preparations of the polyurethanes. Kinetic studies of swelling revealed that the sorption is anomalous in nature. The diffusion coefficient (D) increased with an increase in the NCO/OH ratio and decreased with an increase in chain length of polyethylene glycol. The sorption coefficient (S) decreased with an increase in crosslink density (NCO/OH) and increased with increasing polyethylene glycol (i.e., PEG 200, PEG 400, and PEG 600) moieties in the polyurethanes. The molecular weight between two crosslink points was calculated using the Flory Rehner equation (24), and hence, the number of chains per unit volume (N) and degree of crosslinking (ν) in all the samples were determined.