Formation Of Hollow Nanostructures Research Articles

Hollow metal island films as plasmonic sensors produced by galvanic replacement

Hollow nanoparticles show enhanced plasmonic response with respect to their solid counterparts. Formation of hollow nanostructures is usually carried out in nanoparticle solutions via galvanic replacement and Kirkendall effect driven by the redox potential difference between metals of a redox couple. In this work, the formation of hollow nanoparticle layers using metal island films fabricated by physical vapor deposition as templates is demonstrated. Ag metal island films on glass and silicon substrates are titrated with a solution containing tetrachloroauric acid as oxidizing agent. The islands morphology and their plasmonic properties gradually change with the increase of titration solution concentration due to the effects of galvanic replacement. In comparison to untreated samples, a four-fold enhancement of the refractive index sensitivity factor (360 nm/RIU vs 92 nm/RIU) and two and a half times increase of the figure of merit (1.37 vs 0.56) are observed for hollow island films obtained with large titration concentration. The presented approach merges the advantages of large area coverage and high particle density of island films with the plasmonic properties of hollow nanoparticles in a straightforward way that is suitable for cost-effective fabrication of plasmonic sensors.

Hierarchical Cu2O/CuO/TiO2 composite films with high superhydrophobicity and strong adhesion

ABSTRACT Hierarchical Cu2O/CuO/TiO2 hollow nanostructured films with petal effect (high superhydrophobicity and high adhesion to water droplets) have been synthesized through a facile solvothermal approach, and the wettability of the product films was studied. The protocol was carefully designed for the preparation of the multi-scaled nanostructures. Cu(OH)2 nanorod arrays were used as precursors, which decomposed to form CuO and H2O molecules at high temperature. The produced tiny amount of water molecules was beneficial for both the slow hydrolysis of Ti(OC4H9)4 to formTiO2 nanostructures and the reduction of CuO to form Cu2O. The formation of hollow nanostructures is suggested to be based on kirkendall effect. CuO diffuses outward to react with ethanol in the solution, producing Cu2O/CuO/TiO2 hollow nanostructured films with rough surfaces. The water contact angle of the product film was estimated to be around 152.8°, and the water droplet remained firmly stuck on the surface when the film was vertically tilted, indicating the superhydrophobicity and strong adhesion of the product films. The Cassie impregnating wetting state was suggested as the wetting state of the product films.

Formation of resorcinol-formaldehyde hollow nanoshells through a dissolution-regrowth process.

We report here that dissolution and regrowth of resorcinol formaldehyde (RF) colloidal particles can occur spontaneously when they are subjected to etching in solvents such as ethanol and tetrahydrofuran, resulting in the formation of hollow nanostructures with controllable shell thickness. The hollowing process of the RF particles is attributed to their structural inhomogeneity, which results from the successive deposition of oligomers with different chain lengths during their initial growth. As the near-surface layer of RF colloids mainly consists of long-chain oligomers while the inner part consists of short-chain oligomers, selective etching removes the latter and produces the hollow structures. By revealing the important effects of the condensation degree of RF, the etching time and temperature, and the composition of solvents, we demonstrate that the morphology and structure of the resulting RF nanostructures can be conveniently and precisely controlled. This study not only improves our understanding of the structural heterogeneity of colloidal polymer particles, but also provides a practical and universal self-templated approach for the synthesis of hollow nanostructures.

Facile Biopolymer Assisted Synthesis of Hollow SnO2 Nanostructures and Their Application in Dye Removal

AbstractHerein, we report the synthesis of SnO2 nanostructures by alkaline hydrolysis of the corresponding metal ions in presence of biopolymer additive such as carboxy methylcellulose at 65 °C. X‐ray diffraction studies confirmed the formation of pure crystalline tetragonal SnO2 nanostructures. Microscopic results revealed that addition of biopolymer results in the formation of hollow nanostructures. The sizes of such hollow nanostructures are controllable by varying the concentration of the biopolymer. The hollow nanostructures are further characterized by other spectroscopic techniques such as UV‐vis spectroscopy, photoluminescence spectroscopy, X‐ray photoelectron spectroscopy and energy dispersive X‐ray spectroscopy. These hollow SnO2 nanostructures are porous and show excellent adsorption capability in removal of organic dye, methylene blue from its aqueous solution at room temperature. The recovered SnO2 nanostructures can be reused in successive batches for dye adsorption without much losing its adsorption capacities.

Tuning the Morphology of Te 1D Nanostructures By Template-Free Electrochemical Deposition in an Ionic Liquid

Tellurium and its alloys are used in many applications such as photoconductors, piezoelectric devices, thermoelectric generators and coolers [1]. For thermoelectric applications, the transport properties (thermal conductivity, electrical resistivity, Seebeck coefficient) of tellurium and its compounds can be improved by nanostructuring [2]. One-dimensional nanostructures like nanowires [3] and core-shell nanowires [4] are particularly promising due to the high phonon interface scattering and the blocking of the phonon conduction along the wire axis which lead to an increase of the thermoelectric conversion efficiency. Te nanowires can represent a base to create core-shell structures, being the core that could be further capped with a shell to get arrays of Te-based thermoelectric nanostructures like BiTe [5], AgTe [6] or LaTe [7]. Template assisted electrodeposition is a low cost technique widely used in literature for the synthesis of nanowires but implies several preparation steps and the removal of the template after the growth of the nanowires. The aim of this work is to develop a template free synthesis route that would be more convenient. For this purpose, Room-Temperature Ionic Liquids (RTILs) appear as promising solvents. Indeed, it has been highlighted that they can act as stabilizing agents for nanoparticles and nanostructured films synthesis [8]. In a previous work ([9]), our laboratory showed that Te nanowires can be obtained in an ionic liquid binary mixture: 1-ethyl-1-octyl-piperidinium bis(trifluoromethylsulfonyl)imide:1-ethyl-1-octyl-piperidinium bromide (EOPipTFSI:EOPipBr). In the present work, several morphologies were obtained by varying the synthesis parameters (applied fixed potential, Te(IV) concentration, electrolyte composition). Under charge transfer control, micrometer faceted grains are formed. Under diffusion control, the deposits are composed of nanowires, which are single crystalline as proven by SAED (Selected Area Electronic Diffraction) and TEM (Transmission Electron Microscopy) analyses. In highest tested overpotential conditions, nanowires turn progressively into crystallized hollow nanostructures (HNs) when the coulometric charge increases. This phenomenon is more accentuated at low concentration and disappears when using a soluble anode, showing that the formation of HNs is due to a limitation by species supply. The geometry of HNs, with a high surface to volume ratio, is particularly interesting to create high performances thermoelectric materials. Indeed, this geometry could further decrease the lattice part of the thermal diffusion coefficient by phonon confinement. By decreasing the bromide content of the electrolyte, hair-like single crystalline nanowires with a high aspect ratio can be obtained. HRTEM (High Resolution Transmission Electron Spectroscopy) analyses reveal a growth along the c-axis, with a smooth interface. No surface contaminants were observed by STEM (Scanning Transmission Electron Microscopy), proving that halogenide ions do not play the role of capping agents, unlike observed in other works [10].

The Kirkendall Effect: its Efficacy in the Formation of Hollow Nanostructures

Kirkendall effect refers to the formation of the so-called ‘Kirkendall voids’ caused by the difference in diffusion rates between two species. It is a classical phenomenon in metallurgy and since its discovery, the Kirkendall effect has been observed in different alloy systems. The development of the hollow interior consists of two main steps. The first step is the formation of the small Kirkendall voids near the original interface via a bulk diffusion process. The second step is a consequence of the surface diffusion of the core material (the fast-diffusing species) along the pore surface. Since hollow and porous structures have attracted tremendous attention due to their common applications in sensor systems, chemical reactors, catalysis, drug delivery, environmental engineering, biotechnology, etc., the Kirkendall effect dominates in the fabrication of hollow nanostructures. These nanostructures play a key role in the biological applications of hollow materials such as labeling of cellular structures/molecules, drug loading, encapsulation, delivery and release, bio-labeling, biosensors, magnetic resonance imaging, and biomedicine vehicles.

CuGaS2 hollow spheres from Ga–CuS core–shell nanoparticles

A liquid gallium emulsion was prepared as a starting material using ultrasound treatment in ethylene glycol. Core–shell particles of Ga@CuS were successfully synthesized by deposition of a CuS layer on gallium droplets through sonochemical deposition of copper ions and thiourea in an alcohol media. The core and shell of Ga@CuS products were composed of amorphous gallium metal and covellite phase CuS, which transformed into chalcopyrite CuGaS2 hollow spheres after sulfurization at 450°C, which was the lowest crystallization temperature. The formation of hollow nanostructures was ascribed to the Kirkendall mechanism, in which liquid gallium particles play an important role as reactive templates. In conclusion, we obtained CuGaS2 hollow spheres with a 430nm outer diameter and 120nm shell thickness that had the same crystal structure and electrical properties as bulk CuGaS2.

Dopant induced hollow BaTiO3 nanostructures for application in high performance capacitors

In this work, large-scale single crystalline Nd-doped BaTiO3 hollow nanoparticles have been synthesized via a simple hydrothermal method without the assistance of a surfactant or high temperature sintering. With unique hollow structures, the nanoparticles not only exhibit excellent compatibility with poly(vinylidene fluoride) (PVDF), but significantly enhanced the dielectric properties of the nanocomposites. We demonstrated that the dielectric constant of the nanocomposite reached up to 480.3 with dielectric loss of 0.6 at 102 Hz. Design and optimization of the synthesis method have been achieved through a systematic study of the effect of reaction conditions on the size and morphology evolution of the hollow nanoparticles. The formation of hollow nanostructures is proposed to follow a Kirkendall induced hollowing mechanism which is governed by the differences in diffusion rates of dopant ions, water molecules and core ions during the synthesis reaction.

Oxidation Conversion of Carbon-Encapsulated Metal Nanoparticles to Hollow Nanoparticles

We synthesized α-Fe2O3 hollow nanoparticles by directly oxidizing the carbon-encapsulated iron carbide (Fe3C@C) nanoparticles in air. In this paper, the conversion mechanism of Fe3C@C to hollow nanoparticles was deduced in detail by comparatively investigating the morphologies and compositions of the oxidized products at different oxidation stages using transmission electron microscope (TEM), high resolution TEM (HRTEM), energy-dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It was found that both oxygen and carbon play important roles in the formation of hollow nanostructures, wherein oxygen is the driving force for the outward diffusion of core species and the carbon shell not only provides the diffusion vacancies but also effectively moderates the interdiffusion rates of metal core materials and oxygen. A growth model was proposed: during the oxidation process, three diffusion processes occur including the inward diffusion of oxygen along the carbon shell, o...