Facile synthesis of near-monodisperse Ag@Ni core-shell nanoparticles and their application for catalytic generation of hydrogen

Magnetically recyclable Ag-Ni core-shell nanoparticles have been fabricated via a simple one-pot synthetic route using oleylamine both as solvent and reducing agent and triphenylphosphine as a surfactant. As characterized by transmission electron microscopy (TEM), the as-synthesized Ag-Ni core-shell nanoparticles exhibit a very narrow size distribution with a typical size of 14.9 ± 1.2 nm and a tunable shell thickness. UV-vis absorption spectroscopy study shows that the formation of a Ni shell on Ag core can damp the surface plasmon resonance (SPR) of the Ag core and lead to a red-shifted SPR absorption peak. Magnetic measurement indicates that all the as-synthesized Ag-Ni core-shell nanoparticles are superparamagnetic at room temperature, and their blocking temperatures can be controlled by modulating the shell thickness. The as-synthesized Ag-Ni core-shell nanoparticles exhibit excellent catalytic properties for the generation of H(2) from dehydrogenation of sodium borohydride in aqueous solutions. The hydrogen generation rate of Ag-Ni core-shell nanoparticles is found to be much higher than that of Ag and Ni nanoparticles of a similar size, and the calculated activation energy for hydrogen generation is lower than that of many bimetallic catalysts. The strategy employed here can also be extended to other noble-magnetic metal systems.     

核壳结构TiO2光催化剂的制备和性能

统一尺寸、结构上有序包覆的核壳型复合材料,具有高折射率以及独特的电磁、光学和机械性质.结构上的独特性可能导致其在近红外和可见光区有完整的带隙,利用核与壳之间的相互作用,以及核对降解物的吸附等作用,可提高复合体的光催化性能.本文着重介绍核壳型TiO2的几种类型、特点及其性能,并提出其今后的发展方向.     

Structural and spectral investigations of Rhodamine (Rh6G) dye-silica core-shell nanoparticles

Rhodamine (Rh6G) dye-silica core-shell nanoparticles (DSCSNPs) have been prepared by the controlled hydrolysis and condensation of single silica precursor tetraethylorthosilicate (TEOS) using the sol-gel method. Scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis reveal that dye molecules are entrapped in silica (SiO₂) shell resulting into core-shell particles of ∼30 nm diameter. These particles are also characterized by X-ray diffraction and Fourier transforms infrared spectroscopy. The results indicate that core-shell particles are all in spherical shape and have a narrow size distribution. The fluorescent and optical properties of core-shell particles have been investigated using fluorescence and UV-Visible absorption spectra. The photoluminescence in solid or liquid medium occurs at the same wavelength. The SiO₂ shell restricts the leakage and photobleaching of dye efficiently. These core-shell nanoparticles are found to be highly luminescent and stable.     

Preparation of controllable core-shell gold nanoparticles and its application in detection of silver ions

We report a novel shell technique to prepare controllable core-shell nanoparticles. In this technique, the shell is formed when the core reacts with metal ions and Na(2)S(2)O(3) and the size of the core and thickness of the shell can be controlled. Transmission electron microscopy and X-ray diffraction reveal that the shell consists of insoluble complex salts comprising Au(2)S, AuAgS, and Ag(3)AuS(2). The resulting core-shell nanoparticles obtained at different reaction stages demonstrate that the formation of Au(2)S, AuAgS, and Ag(3)AuS(2) shell proceeds from the outside. The morphological evolution of the particles changes significantly with reaction time demonstrating that formation of the shell results from diffusion in the solid shell. The core-shell nanoparticles produced by this technique can be used as nanosensors to detect Ag(+) in aqueous media with high selectivity and sensitivity. The excellent selectivity for Ag(+) is demonstrated by comparing the response to other metal ions. In addition, our evaluation indicates that gold nanorods offer higher sensitivity than gold nanospheres.     

Ferromagnetic resonance in nanomagnetic metal core and noble metal shell systems

The change in the line widths in the ferromagnetic resonance (FMR) spectra of Co and Ni nanoparticles upon shell formation with noble metals like gold or silver are described. The Ni(core)Ag(shell), Co(core)Ag(shell), and CO(core)Au(shell) nanoparticles were prepared by a simple transmetallation reaction between the Co and Ni nanoparticles and the Ag+ or AuCl4- ions. It is revealed that the FMR line width decreases upon Ag shell formation whereas it increases upon core-shell composite formation with Au. Several probable explanations such as the differences in size distributions before and after the reaction or the changes occurring in shape anisotropy of the particles due to the shell formation or the different extents of electronic interaction between the core and shell materials have been offered for this observation.     

介孔SiO2负载和包覆的纳米金属颗粒的制备与研究

制备了以SiO2为核、介孔SiO2为壳的核-壳颗粒负载纳米金属颗粒以及介孔SiO2壳层包覆SiO2负载的纳米金属颗粒。结果表明,十六烷基三甲基溴化胺(CTAB)作为模板剂,有助于介孔SiO2壳层包覆SiO2核的结构形成,介孔SiO2壳层的孔径方向垂直于SiO2核的表面;在聚乙烯吡咯烷酮(PVP)的稳定作用下,Pt纳米颗粒能均匀地分布在介孔SiO2壳层的表面。单分散SiO2颗粒经过3-氨丙基三乙氧基硅烷(APS)功能化后,可负载纳米金属颗粒。进一步研究表明,以SiO2负载纳米金属颗粒为核,NH3.H2O,乙醇和水为分散剂,CTAB为模板剂,正硅酸乙酯(TEOS)为硅源,还能制备介孔SiO2壳包覆SiO2负载的纳米金属颗粒,而且介孔SiO2壳层的厚度可通过TEOS的含量调节。     

Preparation and electromagnetic wave absorption properties of hollow Co,Fe@air@Co and Fe@Co nanoparticles

In this study, hollow Co, Fe@air@Co and Fe@Co nanoparticles (NPs) have been synthesized respectively by electroless plating Co shell on Fe core and controlling reaction time based on galvanic cell reaction between Co shell and Fe core in hydrochloric acid at room temperature. The electromagnetic (EM) wave absorption properties of these three NPs are also been investigated. The results indicate that the relationship between Fe core and Co shell is critical to the EM wave absorption properties of hollow Co, Fe@air@Co and Fe@Co nanoparticles when blended with 70?wt% in paraffin-based samples. Fe@air@Co nanoparticles shows the best EM wave absorption properties with minimum reflection loss of ?42.75?dB and effective bandwidth of 4.1?GHz under ?10?dB. The present work has a significant potential for the development of EM wave absorbing materials with core-shell structure.     

Al2O3/NiO包裹Ni纳米颗粒的结构和磁性

用电弧法蒸发Ni-Al合金(4%～5%Al,质量分数),制备了Al2O3/NiO包裹Ni及Ni-Al合金纳米颗粒.高分辨电镜显示该纳米颗粒具有壳核结构,核为纳米Ni及Ni-Al合金,壳为Al2O3/NiO复合氧化物.壳的厚度为2～4 nm,颗粒的尺寸为5～60 nm.壳核结构防止纳米Ni颗粒的进一步氧化和团聚.饱和磁化强度为29.6 Am2/kg,矫顽力为4.13 kA/m.由于铁磁和反铁磁性相界面处存在交换耦合作用,磁滞曲线出现小的偏置.     

核壳结构纳米颗粒的研究进展

核壳结构纳米颗粒具有不同于核和壳的物理和化学性能，通过调整核和壳的化学组成、尺寸和形貌，可以调控纳米颗粒的性能，扩展纳米颗粒的应用范围。系统总结了近年来制备核壳结构纳米颗粒的研究进展，讨论了核壳结构纳米颗粒对光学特性的影响。     

Enhanced emission from single component organic core-shell nanoparticles

By one-step mixed-solvent mediated approach, we have prepared fluorescent organic core-shell nanoparticles with an oligomer (1) derived from the Schiff base condensation reaction of 2,6-diformyl-4-methylphenol and o-phenylenediamine at room temperature. The core and shell structures are generated by the same oligomer (1) featuring the aggregation structure in core different from that in shell. The radial packing factor distribution of oligomer cluster depending on the solvent interaction in the time of nucleation is mainly responsible for the single component core-shell formation. Different morphologies of the core-shell nanospheres (CSNS) and core-shell nanohemispheres (CSNHS) were generated simply by changing the concentration of 1 in chloroform-methanol mixed solvent (1:2). We observed that fluorescent emission from those core-shell nanoparticles is intense whereas as-synthesized oligomer (1) itself is non-fluorescent in dilute solution. The enhanced emission in the core-shell form with more than 50 times increase in fluorescent quantum yield vis-à-vis 1 is a remarkable feature of the study. As UV absorption spectra of nanoparticles are blue-shifted relative to their properties in solution, the observed strong emission in the solid state makes the oligomer an outstanding exception to a well-established rule based on the molecular exciton model. The core-shell nanoparticles have been characterized by FE-SEM, TEM, XRD, nanosecond (ns) time-resolved fluorescence dynamics, UV-Vis and fluorescence spectroscopy. The longer fluorescence lifetimes (tau) of core-shell nanoparticles (3.50 ns and 3.52 ns for CSNS and CSNHS respectively) than 1 as-synthesized (1.28 ns) implies that the formation of the nanoparticles restricts the rotation and vibration of the groups in the molecules. The factor that induces fluorescent enhancement of nanoparticles is mainly ascribed to the increase of radiative rate constant (k(r)) and simultaneous decrease of nonradiative rate constant (k(nr)).     

Synthesis and Magnetic Properties of Nanoparticles of Fe-Co Alloys and Their Oxides Prepared by Chemical Vapor Condensation

Nanoparticles of Fe-Co alloys and their oxides with the particle size below 20 nm were prepared by chemical vapor condensation process. The pure Ar, Ar+1%O2, Ar+3%O2 and Ar+6%O2 were used as carrier gases, with iron carbonyl and cobalt carbonyl as the precursors. XRD patterns showed that Fe-Co metallic nanoparticles were synthesized by using pure Ar as carrier gas, and only metal oxides were obtained using Ar+(>3)%O2 as carrier gas. The HRTEM images and TG-DTA curves were used to study the core-shell structure of the different nanoparticles. The nanoparticles obtained in pure Ar consist of black core and light shell with thickness of 2~4 nm. However, in the particles obtained in Ar+6%02, the oxides core with visible lattice fringes are surrounded by thin shell.     

Synthesis of dendrimer-stabilized gold-polypyrrole core-shell nanoparticles

Core-shell composite nanoparticles consisting of a gold core and polypyrrole shell were prepared and stabilized with the poly(amidoamine) dendrimer. An in situ redox polymerization technique was used in which pyrrole reduced Au3+ to Au and then oxidized to polypyrrole. The presence of gold nanoparticles as a core was characterized by its surface plasmon absorption peak at 534 nm. Fourier transform infrared spectroscopy confirmed the presence of polypyrrole on the nanoparticle surfaces. The average diameter of the core-shell nanoparticle is 8.7 +/- 1.8 nm with a shell thickness of approximately 1.5-2.0 nm as estimated from the transmission electron microscopy image. Dissolution of the Au core using KCN enabled the formation of hollow polymer nanospheres.     

Zn/ZnO core/shell nanoparticles synthesized by laser ablation in aqueous environment: Optical and structural characterizations

Zn/ZnO core/shell nanoparticles are synthesized by pulsed laser ablation (PLA) of Zn metal plate in the aqueous environment of sodium dodacyl sulfate (SDS). Solution of nanoparticles is found stable in the colloidal form for a long time, and is characterized by UV-visible absorption, transmission electron microscopy (TEM), photoluminescence (PL) and Raman spectroscopic techniques. UV-visible absorption spectrum has four peaks at 231, 275, 356, and 520 nm, which provides primary information about the synthesis of core-shell and elongated nanoparticles. TEM micrographs reveal that synthesized nanoparticles are monodispersed with three different average sizes and size distributions. Colloidal solution of nanoparticles has significant absorption in the green region, therefore, it absorbs 514·7 nm light of Ar⁺ laser and emits in the blue region centred at 350 and 375 nm, violet at 457 nm and green at 550 nm regions. Raman shift is observed at 300 cm⁻¹ with PL spectrum, which corresponds to ³E_2N and E_3L mode of vibrations of ZnO shell layer. Synthesis mechanism of Zn/ZnO core/shell nanoparticles is discussed.     

Correlating electron tomography and plasmon spectroscopy of single noble metal core-shell nanoparticles

The 3D structure reconstruction of gold core-silver shell nanoparticles by electron tomography is combined with optical dark-field spectroscopy. Electron tomography allows segmentation of the particles into core and shell subvolumes and facilitates avoiding Bragg diffraction artifacts inherent in 2D images. This advantage proves essential for accurate correlation of plasmon spectra and structure. We find that for the nanoparticles of near-spherical shape studied here the plasmon resonances depend on the relative size of the core and shell, rather than on their exact shapes and concentricity. A remarkable dependence of the spectral shape on the permittivity of the surrounding medium is also demonstrated, suggesting that core-shell nanoparticles can be used as ratiometric sensors with a very high dynamic range.     

Synthesis of silica/Au core-shell nanostructures by galvanic replacement of silica/Ag in aqueous and alkaline medium

We present here a facile one-step method for the synthesis of silica/Au core-shell nanostructures by exploiting the potential difference of AuCl₄^? and Ag in aqueous as well as alkaline media. Initially, silica/Ag core-shell nanostructures were synthesised by coating Ag nanoparticles on silica core (size ～150 nm) in a two-step process (seeding and growth) and were characterised for their morphological, structural and optical behaviours. A complete coverage of silica core with Ag nanoparticles was seen from scanning electron microscope and transmission electron microscope images. The presence of resonance peaks in the optical spectrum manifests the nature of the shell (thin shell ～413 and 650 nm, thick shell ～434 nm). Galvanic replacement of silica/Ag core-shell nanostructures in chloroauric acid solution (HAuCl₄) was studied in both the aqueous and alkaline medium, where an aqueous environment results into fast and effective replacement as compared to an alkaline medium, which has been confirmed from optical absorption studies. The optical studies showed that in an alkaline environment, on galvanic replacement of Ag with Au, the individual absorption peak of Ag (～414 nm) and Au (～520 nm) disappeared, whereas new absorption wavelengths in higher region (600–800 nm) of electromagnetic spectrum were observed. A detailed mechanism is proposed for the same to explain this behaviour. A range of novel new plasmonic core-shell nanomaterials can be synthesised as an intermediate of this facile one-step reaction.     

Imparting biomimetic ion-gating recognition properties to electrodes with a hydrogen-bonding structured core-shell nanoparticle network

This paper presents findings of the creation of biomimetic ion-gating properties with core-shell nanoparticle network architectures. The architectures were formed by hydrogen-bonding linkages via an exchange-cross-linking-precipitation reaction pathway using gold nanoparticles capped with thiolate shell and alkylthiols terminated with carboxylic groups as model building blocks. Such network assemblies have open frameworks in which void space is in the form of a channel or chamber with the nanometer-sized cores defining its size, the geometric arrangement defining its shape, and the shell structures defining its chemical specificity. The formation of the network linkages via head-to-head hydrogen-bonded carboxylic terminals and the reversible pH-tuned structural properties between neutral and ionic states were characterized using infrared reflectance spectroscopic technique. The biomimetic ion-gating properties were demonstrated by measuring the pH-tuned network "open-close" responses to charged redox probes. Such redox responses were shown to depend on the degree of protonation-deprotonation of carboxylic groups at the interparticle linkages, core sizes of the nanoparticles, and charges of the redox probes. Differences in structural networking, pH-tuning, and electrochemical gating properties were identified between the network films derived from nanoparticles of two different core sizes (2 and 5 nm). The mechanistic correlation of these structural properties was discussed. These findings have added a new pathway to the current approaches to biomimetic molecular recognition via design of core-shell nanoparticle architectures at both nanocrystal and molecular scales.     

Core and shell sizing of small silver-coated nanospheres by optical extinction spectroscopy

Silver metal nanoparticles (Nps) are extensively used in different areas of research and technology due to their interesting optical, thermal and electric properties, especially for bare core and core-shell nanostructures with sizes smaller than 10?nm. Since these properties are core-shell size-dependent, size measurement is important in manipulating their potential functionalization and applications. Bare and coated small silver Nps fabricated by physical and chemical methods present specific characteristics in their extinction spectra that are potentially useful for sizing purposes. This work presents a novel procedure to size mean core radius smaller than 10?nm and mean shell thickness of silver core-shell Nps based on a comparative study of the characteristics in their optical extinction spectra in different media as a function of core radii, shell thickness and coating refractive index. From the regularities derived from these relationships, it can be concluded that plasmon full width at half-maximum (FWHM) is sensitive to core size but not to coating thickness, while plasmon resonance wavelength (PRW) is related to shell thickness and mostly independent of core radius. These facts, which allow sizing simultaneously both mean core radius and shell thickness, can also be used to size bare silver Nps as a special case of core-shell Nps with zero shell thickness. The proposed method was applied to size experimental samples and the results show good agreement with conventional TEM microscopy.     

Cytosolic delivery of membrane-impermeable molecules in dendritic cells using pH-responsive core-shell nanoparticles

Polycations that absorb protons in response to the acidification of endosomes can theoretically disrupt these vesicles via the "proton sponge" effect. To exploit this mechanism, we created nanoparticles with a segregated core-shell structure for efficient, noncytotoxic intracellular drug delivery. Cross-linked polymer nanoparticles were synthesized with a pH-responsive core and hydrophilic charged shell designed to disrupt endosomes and mediate drug/cell binding, respectively. By sequestering the relatively hydrophobic pH-responsive core component within a more hydrophilic pH-insensitive shell, nontoxic delivery of small molecules and proteins to the cytosol was achieved in dendritic cells, a key cell type of interest in the context of vaccines and immunotherapy.     

Synthesis and structure of Ag-Si nanoparticles obtained by the electron-beam evaporation/condensation method

Metal-semiconductor composite Ag-Si nanostructures, including Ag/Si core-shell nanoparticles, have been synthesized for the first time by a high-efficiency evaporation/condensation method using relativistic electron beam. In the Ag/Si core-shell nanoparticles, the core is crystalline, while the shell consists of amorphous silicon. It is found that the synthesis of these particles requires taking into account the difference in the saturated vapor pressures of evaporated components. The dependences of the particle size on the electron beam power at the evaporation stage and the pressure of argon at the condensation stage have been studied. It is established that (i) the main process of Ag/Si nanoparticle formation is coagulation and (ii) the Si shell formation decreases the size of particles.     

Synthesis of core-shell nanostructures of Co3O4@SiO2 with controlled shell thickness (5-20 nm) and hollow shells of silica

Synthesis of uniform silica shell over Co3O4 nanoparticles was carried out using the colloidal solutions of Tergitol and cyclohexane. The shell could be controlled to a thickness of up to 20 nm by varying different parameters such as the amount of tetraethylorthosilicate, concentration of Co3O4 nanoparticles, reaction time and the presence of water and 1-octanol. Control of the amount of water (required for hydrolysis) appears to be the key factor for controlling the shell thickness. The methodology used is suitable to form shell over nanoparticles (present in powder form; synthesized at high temperature) which have high degree of agglomeration. Hollow shells of silica were obtained by the dissolution of the oxide core of Co3O4@SiO2 core-shell nanostructures. The composition of these core-shell nanostructures was confirmed by high-resolution transmission electron microscopy and elemental mapping by energy dispersive X-ray analysis. The hollow shells were characterized by using TEM, EDX and IR. Electron paramagnetic resonance studies of the core-shell nanostructures indicate the presence of free radicals on silica shell due to the presence of dangling bonds in the silica. Increase in the magnetic susceptibility was observed for these core-shell nanostructures.