Core-shell Hybrid Nanostructure Research Articles

Synthesis and Raman Performance Enhancement of Multilayer AuAg Heterostructures with Magnetic Resonance

Significant amplification of surface enhanced Raman scattering (SERS) signals can be achieved mainly by the electric field enhancement in metal core-shell nanostructures, and the enhanced magnetic field is rarely studied. In this study, we prepared multi-gap Au/AgAu core-shell hybrid nanostructures by using gold nanocup as the core. The overgrowth processes to grow one, two, and three layers of AgAu hybrid nanoshells can produce Au/AgAu1, Au/AgAu2, and Au/AgAu3 heteronanostructures. The strong plasmon coupling between the core and shell leads to significant electromagnetic field enhancement. Under the synergistic effect of electromagnetic plasmon resonance and plasmon coupling, Au/AgAu core-shell hybrid nanostructures exhibit excellent SERS signals. We also investigate the effect of the interstitial position of the rhodamine B (RhB) molecule on Raman enhancement in Au/AgAu3 heteronanostructures. This study can provide new ideas for the synthesis of multi-gap Raman signal amplifiers based on magnetic plasmon coupling.

Electrochemical performance of binder-free Ni(OH)2/RGO battery type electrode materials for supercapacitor

ABSTRACT Ni(OH)2/reduced graphene oxide (RGO) core-shell hybrid nanostructure has been synthesized employing a facile and inexpensive chemical-precipitation technique. The synthesized core-shell nanostructures, comprising Ni(OH)2 at the core and RGO as shell, were then coated on commercially available Ni foam used as an electrode. Prepared Ni(OH)2/RGO nanospheres were analyzed by Raman analysis for structural information. In the Raman spectrum, the peaks at 1323 and 1612 cm−1 correspond to the D and G bands of RGO, respectively. The peaks at 468 and 335 cm−1 depict the characteristic bands of Ni(OH)2 . The core-shell morphology of the hybrid was established from Transmission Electron Microscope (TEM) images. The lattice fringes are measured to be 0.33 nm for RGO layers and 0.22 nm for Ni(OH)2 core, which correspond to (002) plane of RGO and (101) plane of Ni(OH)2. For electrochemical studies, the as-prepared Ni(OH)2/RGO hybrid was used as a battery-type electrode in supercapacitor. The results indicate that the Ni(OH)2/RGO core-shell hybrid nanostructure exhibits a maximum specific capacity of 513.8 Cg−1 at 10 mV/s with a maximum energy density of 119.4 Whkg−1 at 1250 Wkg−1 power density.

Light Harvesting in Magnetite-Coated Plasmonic Metal Nanospheres

The design of hybrid nanostructures composed of plasmonic metals and semiconductor oxides plays a major role in determining their efficiency for the conversion of solar energy. In this work, the light-harvesting properties of spherical core–shell hybrid nanostructures composed of a plasmonic metal core (Au, Ag, and Al) coated by a magnetite (Fe3O4) shell have been investigated through systematic discrete dipole approximation simulations. The diameter of the plasmonic core D was varied in the range of 5–90 nm, while the thickness of the Fe3O4 shell S was varied in the range of 2–40 nm. It was found that for a given set of D and S values, the absorbed photon flux within the Fe3O4 shell, ϕ, increases in the order Al, Au, and Ag. Furthermore, for a given size, which is D + 2S = constant, the largest ϕ value is approximately achieved when D/S = 3, 4, and 5 for Al, Au, and Ag as the core material, respectively. In addition, it was empirically found that ϕ correlates directly with the predictor K, a quantity that depends on D, S, and the resonance energy of the plasmon. The results presented contribute to expanding the tool kit that allows optimizing the design of hybrid nanostructures in order to improve their photoactive properties.

Photoluminescent carbon quantum dot/poly-l-Lysine core-shell nanoparticles: A novel candidate for gene delivery

Cationic polymers such as poly-l-lysine (PLL) are able to interact electrostatically with DNA to produce polymeric systems with nanometric diameters due to the neutralization and accumulation of DNA. This study integrates the outstanding properties of carbon quantum dots (CQDs) with PLL to develop a novel gene delivery vehicle with a core-shell hybrid nanostructure. The CQD/PLL core-shell nanoparticles (NPs) were, therefore, synthesized in such a way that they had narrow size distribution and an average diameter under 10 nm, both of which were confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy exhibited that the PLL passivation agents were formed on the CQDs through releasing amine groups on their surface. The positive charge of the CQD/PLL core-shell NPs reduced from +15 to nearly zero mV after being loaded with DNA at the weight ratio of 2:1. These traceable, water-soluble, biocompatible, and tunable photoluminescent NPs demonstrated a quantum yield of around 12% and a cellular uptake of nearly 70%. The NPs also showed no considerable toxicity to the human embryonic kidney (HEK)-293T cells. Hence, these novel CQD/PLL core-shell NPs hold great promise as a non-toxic and efficient gene delivery vector.

Enhanced blue photoluminescence and new crystallinity of Ag/organic rubrene core-shell nanoparticles through hydrothermal treatment

Light-emitting organic semiconductors have attracted considerable attention for the nanoscale fabrication of organic-based displays and their potential application in optoelectronics, plasmonics, and photonics. In this study, core-shell hybrid nanostructures of organic rubrene coated on Ag nanoparticles (NPs) have been synthesized using a chemical reduction method. The thickness of the rubrene shell was 2.6–6.0 nm and the diameter of the Ag core was 30–70 nm. The optical and structural properties of the Ag/rubrene core-shell NPs were tuned by hydrothermal (HT) treatment at 190 °C. The Ag/rubrene core-shell NPs were characterized by high-resolution transmission electron microscopy and energy-dispersive X-ray (EDX) spectroscopy before and after the HT treatment, and their structural properties were confirmed through X-ray diffraction (XRD) analysis. XRD peaks related to an orthorhombic phase were observed along with the original triclinic crystal structure of the rubrene shell, and the triclinic crystal domain size increased from 28.2 nm to 30.8 nm owing to the HT treatment. Interestingly, the green light emission (λem = 550 nm) of the Ag/rubrene core-shell NPs changed to blue light emission (λem = 425 nm), increasing in intensity through the HT treatment. This is caused by the crystal change with H-type aggregation and enhanced energy transfer from a surface plasmon resonance.

Effect of Polysaccharide Additions on the Anion-Exchange Deposition of Cobalt Ferrite Nanoparticles

A facile and rapid method easily reproducible in ordinary laboratory settings is proposed for preparing nanosized cobalt ferrite powders, where the precipitate used is a strongly basic anion exchange resin in the OH form. The effects caused by additions of polysaccharides having various chain natures and various molar weights on the composition, yield, and particle size of the deposition product are studied. Suggested mechanisms underlying these effects are studied. This method makes it possible to appreciably reduce the precursor annealing temperature compared to that in the state-of-art methods for preparing similar oxide systems due to the formation of highly reactive precursors. Optimal conditions are found to prepare stoichiometric precursors such that, once annealed at 600°C, would form a CoFe2O4 pure phase with particle sizes of 10–20 nm. The stability of hydrosols of the thus-prepared cobalt ferrite nanoparticles is studied by dynamic and electrophoretic light scattering. The prepared material is found to be useful for the design of magnetic core–shell hybrid nanostructures.

Electromagnetic induction derived micro-electric potential in metal-semiconductor core-shell hybrid nanostructure enhancing charge separation for high performance photocatalysis

The application of an external electric field is one of the most efficient approaches for photo-induced charge separation. However, the application of the electric-field- enhanced charge separation is limited in powder catalysts. In this study, the electromagnetic induction derived micro-electric potential in metal-semiconductor core-shell hybrid nanostructure was used to enhance charge separation in the shell semiconductor photocatalysts. The efficiency of photocatalytic hydrogen production can be improved around 110% by utilizing a core-shell nanostructure with a permanent magnet that moves under the normal photocatalytic reactor device. This electromagnetic induction derived electric field via the metal-semiconductor core-shell structure shows efficient conversions from relative motion to electric potential that provide a new opportunity to enhance photocatalytic performance with non-contacted interaction.

Morphology control of 3D-networked boron-doped diamond nanowires and its electrochemical properties

3D-networked boron-doped diamond (BDD) nanowire was synthesized using an electrostatic self-assembly technique and a chemical vapor deposition process. This BDD nanowire was a BDD-CNT core-shell hybrid nanostructure and applied as an active electrode material on electrochemical sensor. Because electrochemical sensing performance is generally affected by its surface structure and interface characteristics, the deposition time was controlled to identify the optimal morphology. As the deposition time increased, the BDD-CNT nanostructures became thicker, while their porosity and electron transfer resistance were smaller. The electrochemical properties of the BDD based electrodes were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The BDD-CNT electrodes had the significantly higher sensitivity and wider linear range than the BDD electrode due to large surface area and low electron transfer resistance. The BDD-CNT 40 electrode exhibited a highest sensitivity (275.27 μA/mM∙cm2). Therefore, the 3D-networked BDD nanostructures can be applied for electrochemical detection of various analytes as a promising electrode material.

In Situ Synthesis and Electrophoretic Deposition of NiO/Ni Core-Shell Nanoparticles and Its Application as Pseudocapacitor

A simple, low cost and transferable colloidal processing method and the subsequent heat treatment has been optimized to prepare binder-free electrodes for their application in supercapacitors. NiO/Ni core–shell hybrid nanostructures have been synthetized by heterogeneous precipitation of metallic Ni nanospheres onto NiO nanoplatelets as seed surfaces. The electrophoretic deposition (EPD) has been used to shape the electroactive material onto 3D substrates such as Ni foams. The method has allowed us to control the growth and the homogeneity of the NiO/Ni coatings. The presence of metallic Nickel in the microstructure and the optimization of the thermal treatment have brought several improvements in the electrochemical response due to the connectivity of the final microstructure. The highest specific capacitance value has been obtained using a thermal treatment of 325 °C during 1 h in Argon. At this temperature, necks formed among ceramic-metallic nanoparticles preserve the structural integrity of the microstructure avoiding the employment of binders to enhance their connectivity. Thus, a compromise between porosity and connectivity should be established to improve electrochemical performance.

MnO2-nanowire@NiO-nanosheet core-shell hybrid nanostructure derived interfacial Effect for promoting catalytic oxidation activity

Nanostructure-derived interfacial effect plays a great role in enhancing catalytic activities. Herein, a MnO2 nanowires@NiO nanosheets core-shell hybrid nanostructure was successfully prepared by uniformly decorating NiO nanosheets on the one-dimensional MnO2 nanowires. The physi-chemical properties of the MnO2 and MnO2@NiO were characterized by using XRD, BET, SEM, H2-TPR and XPS techniques. Compared to the single MnO2 nanowires, the MnO2@NiO nanocomposite with better low-temperature reducibility and more active surface oxygen species exhibited much better performance in complete oxidation of benzene, giving the temperatures for 100% benzene conversion of 320°C under the conditions of 1000ppm benzene in air and space velocity of 120,000mLg−1h−1 while the value over pure MnO2 was 380°C. The novel hetero-interface constructed between MnO2 and NiO core-shell nanostructures might make a great contribution on this significantly promoting effect.

Designing 3D interconnected continuous nanoporous Co/CoO core–shell nanostructure electrodes for a high-performance pseudocapacitor

A high-performance supercapacitor electrode is designed and fabricated with the 3D interconnected continuous nanoporous Co/CoO core–shell hybrid nanostructure grown on nickel foam. The Co/CoO core–shell hybrid nanostructures are obtained via a hydrothermal method, followed by high-temperature annealing in hydrogen atmosphere, and finally placed in air at 50 °C for 1 h. The Co/CoO core–shell nanostructure assembled by a conductive metal–core and a CoO shell, brings low resistance, high specific capacitance of 5.632 F cm−2 and good capability stability (81.5% capacitance retention after 6000 cycles). An asymmetric supercapacitor device built by the Co/CoO (positive electrode) and activated carbon (negative electrode) can deliver a working voltage of 1.7 V and display a high energy density of 0.002 67 Wh cm−2 at a power density of 0.001 62 W cm−2, which is far superior to that of a supercapacitor at a similar power density.

Influence of SiO2 layer on the plasmon quenched upconversion luminescence emission of core-shell NaYF4:Yb,Er@SiO2@Ag nanocomposites

β-NaYF4:Yb,Er@SiO2@Ag core-shell hybrid nanostructures are prepared and single core-shell hybrid particle is taken to investigate the influence of separation layer on the metal enhanced upconversion luminescence and corresponding mechanism. It is found that the green (4S3/2⿿4I15/2) and red (4F9/2⿿4I15/2) emissions of Er3+ increase first and then decrease with the increase of silica shell thickness. The best enhancement is observed at the silica thickness of 12nm. Time-resolved spectra study shows that the emission enhancement dominates when the silica thickness is 12nm, which leads to an enhancement factor of 1.28. But the enhancement factor reduces to 0.52 when the silica shell thickness is 5nm. Here, we define enhancement factor g(ϿF) as g(ϿF)=IF/I0, IF and I0 are fluorescence intensities of UCNPs with emission enhancement and without plasmon enhancement. The luminescence enhancement is owing to the enhanced emission process rather than the excitation process.

Metal-Organic Frameworks as Promising Photosensitizers for Photoelectrochemical Water Splitting.

Ti-based metal-organic frameworks (MOFs) are demonstrated as promising photosensitizers for photoelectrochemical (PEC) water splitting. Photocurrents of TiO2 nano wire photoelectrodes can be improved under visible light through sensitization with aminated Ti-based MOFs. As a host, other sensitizers or catalysts such as Au nanoparticles can be incorporated into the MOF layer thus further improving the PEC water splitting efficiency.

Hierarchical ZnO@MnO2 Core-Shell Pillar Arrays on Ni Foam for Binder-Free Supercapacitor Electrodes

Hierarchical ZnO@MnO2 core-shell pillar arrays on Ni foam have been fabricated by a facile two-step hydrothermal approach and further investigated as the binder-free electrode for supercapacitors. The core-shell hybrid nanostructure is achieved by decorating ultrathin self-standing MnO2 nanosheets on ZnO pillar arrays grown radically on Nickel foam. This unique well-designed binder-free electrode exhibits a high specific capacitance (423.5Fg−1 at a current density of 0.5Ag−1), and excellent cycling stability (92% capacitance retention after 3000 cycles). The improved electrochemical results show that the ZnO@MnO2 core-shell nanostructure electrode is promising for high-performance supercapacitors. The facile design of the unique core-shell array architectures provides a new and effective approach to fabricate high-performance binder-free electrode for supercapacitors.

A NEW CORE–SHELL HYBRID NANOSTRUCTURES OF GOLD NANOROD FOR ENHANCING FLUORESCENCE AND APPLICATION IN DUAL-COLOR IMAGING

A novel core–shell hybrid nanostructure was constructed by employing gold nanorod ( AuNR ) combined with rhodamine B (RB) as a core and silica as a shell. The poly(sodium 4-styrenesulfonate) (PSS), a negatively charged polyelectrolyte, played the role of linker to electrostatically trap RB on AuNRs . Due to the fluorescence spectral overlap between RB and AuNRs at 560 nm, the red fluorescence and enhanced green fluorescence of the hybrid nanostructures were observed obviously, which is capable for dual-color labeling. To reduce toxic side effects of AuNRs , silica was coated on AuNRs as a shell to fabricate the novel core–shell hybrid nanostructure function as a dual-color labeling for cancer-cell imaging. The fabricated composite structures were characterized by transmission electron microscopy (TEM), absorption spectrum, fluorescence spectrum, zeta potential measurements and laser scanning confocal microscope (LSCM). The experiment results confirmed that the obtained hybrid nanostructures provided excellent photostability, biocompatibility and active surface for further biological functionalization. The novel composite structures may have great potential application in cell multicolor labeling and imaging instead of traditional fluorescent dyes.

Core–Shell Noble Metal Nanostructures Templated by Gold Nanorods

The main research progress in core-shell noble metal nanostructures templated by gold nanorods (Au NRs) is summarized regarding synthesis, optical, and catalytic properties. Design and fabrication of core-shell hybrid nanostructures are demonstrated to be effective not only for optimizing and expanding intrinsic properties but also for creating novel localized surface plasmon enhanced optical and catalytic functionalities, thus providing great prospects in both fundamental research and potential applications.

Synthesis of Ag@ZnO core–shell hybrid nanostructures: an optical approach to reveal the growth mechanism

In this study, Ag@ZnO core-shell hybrid nanostructures (HNs) have been prepared by means of a very simple chemical methodology. In addition, their morphology and extinction properties have been characterized. It was found that the HNs consist in almost spherical Ag nanoparticle cores (mean diam- eter 56 nm) surrounded by a thin shell formed by small ZnO nanoparticles (mean size 6 nm). The changes in the extinction spectra during the formation of the hybrid nanostructures have been rationalized using electrodynamics simulations applying Mie theory for coated spheres along with the effective medium theory to describe the dielectric constant of the shell. By assuming a formation and growth mechanism of the shell, it was found that these simulations describe not only qualitatively but also quantitatively the changes in the extinction spectra.

Cylindrical PCL brushes on the surface of lanthanum hydroxide nanowires by ring-opening polymerization

A core-shell hybrid nanostructure, a hard core of single-crystalline lanthanum hydroxide nanowires and a soft shell of brushes of poly (ɛ-caprolactone) (PCL), has been successfully prepared by ring-opening polymerization (ROP) on the surface of nanowires. Such special structures were proved by TEM images. Meanwhile, the thickness of polymer layers was measured. The chemical component and the grafted PCL quantity of the sample were characterized by FTIR and TGA, which provides a simple and universal method to functionalize non-carbon nanowires. The modified lanthanum hydroxide nanowires can be well-dispersed in good solvents for PCL.

Gold/mesoporous silica-fiber core-shell hybrid nanostructure: a potential electron transfer mediator in a bio-electrochemical system

Mesostructured silica fibers synthesized by electrospinning silica sol were used as templates for the assembly of gold nanoparticles and the formation of continuous gold shells along the fiber axis. Dense and uniform spherical gold nanoparticles were formed by in situ reduction of hydrochloroauric acid absorbed on self-assembled polyelectrolyte film of silica fiber surface. The gold-seeded silica fibers were further coated by continuous gold shells via solution-phase reduction of an appropriate metal ion in PVP solution. The thickness and morphology of gold shell could be tailored by the molar ratio of repeating units of PVP to gold ions (R) and growth time. Experimental results showed that low R tended to form a thick gold layer with sharp tips, whereas high R favored obtaining thin and uniform Au shell. The SiO2@Au fiber hybrid nanostructures are further used as substrates for fabrication of a glucose biosensor, which exhibited excellent bio-electrochemical activity with high sensitivity and rapid response. These hybrid nanostructures are, therefore, regard as molecule wires for potential application in highly sensitive chemical or biological sensors.

Manganese-Based Nanoscale Metal−Organic Frameworks for Magnetic Resonance Imaging

Manganese-containing nanoscale metal-organic frameworks (NMOFs) with controllable morphologies were synthesized using reverse-phase microemulsion techniques at room temperature and a surfactant-assisted procedure at 120 degrees C with microwave heating. The nanoparticles were characterized using a variety of methods including SEM, TEM, TGA, PXRD, and ICP-MS. Although the nanoparticles gave a modest longitudinal relaxivity (r1) on a per Mn basis, they provided an efficient vehicle for the delivery of large doses of Mn2+ ions which exhibited very high in vitro and in vivo r1 values and afforded excellent MR contrast enhancement. The particle surface was also modified with a silica shell to allow covalent attachment of a cyclic RGD peptide and an organic fluorophore. The cell-targeting molecules on the Mn NMOFs enhanced their delivery to cancer cells to allow for target-specific MR imaging in vitro. The MR contrast enhancement was also demonstrated in vivo using a mouse model. Such core-shell hybrid nanostructures provide an ideal platform for targeted delivery of other imaging and therapeutic agents to diseased tissues.