Hollow Spherical Nanostructures Research Articles

Rationally-designed sandwiched nanostructures boosting Fe-N based catalysts toward efficient oxygen reduction electrocatalysis in acidic medium

The development of acidic-available noble-metal-free oxygen reduction reaction (ORR) catalysts with high activity and good long-term durability is of significant importance for efficient proton exchange membrane fuel cells, but is still very challenging. Herein, we develop originally a facile wet-chemical-adsorption, pyrolysis and post-etching strategy to effectively intercalate Fe clusters among two nitrogen-doped carbon (NC) layers, forming unique hollow spherical nanostructures with sandwiched NC/Fe/NC shells as an active ORR catalyst. Thanks to the sandwiched nanostructure and the active Fe-N species, this as-prepared hollow sandwiched NC/Fe/NC catalyst could present superior ORR activity in an acidic medium, with a nice onset potential of 0.92 V and decent diffusion-limited current density of ~5.1 mA/cm2. The NC/Fe/NC catalyst manifests strong methanol tolerance and outstanding durability during a long-term acidic ORR operation, being a promising alternative to Pt-based catalysts toward efficient proton exchange membrane fuel cells. Synchrotron radiation characterizations and X-ray photoemission spectroscopy reveal at the atomic-level that the abundant robust Fe–N bonds presented in the sandwiched shells of hollow NC/Fe/NC spherical catalyst contribute substantially to high electrochemical activity and superior corrosion-resistance for efficient 4e¯ ORR in acidic electrolyte.

K- and Cu-doped CaTiO3-based nanostructured hollow spheres as alternative catalysts to produce fatty acid ethyl esters as potential biodiesel

New functional polycation oxide-type catalysts were synthesized by the ultrasonic spray-pyrolysis method. The catalytic activity in the production of fatty acid ethyl esters (FAEE’s) using soybean oil was studied. Catalysts are conformed by nanostructured hollow spheres of low density with a stoichiometric formula Ca1-xKxTiCux/2O3. The influence of the substitutional ratio (x) upon the catalytic activity was verified. The Ca1-xKxTiCux/2O3 sample with x = 0.3 showed the highest activity with a yield up to 89 % to produce fatty acid ethyl esters (FAEE’s) after 24 h reaction using 15 wt.% catalysts, 120 °C and 40 bars. The enhancement in the activity was ascribed to the substitution of the Ca+2 sites by K+ and Ti+4 by Cu+2 and to the hollow morphology favoring a more effective interaction between the soybean oil and the active basic sites of the catalysts.

One-step formation of TiO2 hollow spheres via a facile microwave-assisted process for photocatalytic activity

Mesoporous TiO2 hollow spherical nanostructures with high surface areas were successfully prepared using a microwave method. The prepared hollow spheres had a size range between 200 and 500 nm. The spheres consisted of numerous smaller TiO2 nanoparticles with an average diameter of 8 nm. The particles had an essentially mesoporous structure, with a pore size in the range of 2–50 nm. The results confirmed that the synthesised of anatase TiO2 nanoparticles with specific surface area approximately 172.3 m2 g−1. The effect of ultraviolet and visible light irradiation and catalyst dosage on the TiO2 photocatalytic activity was studied by measuring the degradation rate of methylene blue. The maximum dye degradation performances with low catalyst loading (30 mg) were 99% and 63.4% using the same duration of ultraviolet and visible light irradiation, respectively (120 min).

Cu 3 P nanotubes: controlled synthesis and their good photocatalytic activity for organic dye

Copper phosphide (Cu3P) nanotubes were successfully synthesised via a facile solvothermal route. The characterisation and analysis results indicate that the as-prepared sample is composed of a large quantity of Cu3P nanotubes with the mean diameter of about 100 nm, some nanotubes pass across each other and form the right angle morphology. Moreover, these nanotubes (sample II) can easily be changed to some irregular particles (sample I) or hollow spherical nanostructures (sample III) when the amount of cetyltrimethylammonium bromide is controlled in the experiments. Choosing methylene blue (MB) as a typical organic dye, Cu3P nanotubes exhibit a good photocatalytic activity, which may be that its large specific surface area enhances the oxidation–reduction ability of electron–hole.

Sodium hypophosphite induced a simultaneous P doping and hollowing process of TiO2 spherical nanostructures with enhanced photocatalytic activity.

Sodium hypophosphite induced a simultaneous P doping and hollowing process of TiO2 spherical nanostructures and produced P-doped hollow spherical nanostructures via a simple one-step hydrothermal method. The as-synthesized P-doped hollow spherical nanostructures demonstrated significantly enhanced photocatalytic activity for MB degradation compared to the undoped TiO2 and P25 under sunlight irradiation.

Rationally Controlling the Self-Assembly Behavior of Triarmed POSS–Organic Hybrid Macromolecules: From Giant Surfactants to Macroions

Two triarmed organic–inorganic hybrid materials based on carboxylic acid-functionalized polyhedral oligomeric silsesquioxane (APOSS) with/without PS linkers are designed and synthesized (tri-PS-APOSS and tri-APOSS). They can both self-assemble into hollow spherical nanostructures in water/organic mixed solvents, as confirmed by light scattering and TEM techniques, yet they possess completely different mechanisms and driving forces. With the PS linkers, the hybrid forms bilayer vesicles similar to surfactants; while without the PS linkers, the hybrid behaves like hydrophilic macroions and assembles into single-layered, vesicle-like “blackberry”-type structure. Consequently, the trend of the assembly size in response to the change of the solvent polarity is different for the two scenarios. This work shows a simple, universal approach of controlling the mechanism and product of the self-assembly process via minor adjustment of the organic–inorganic hybrid structures.

The Tunable and Well-Controlled Surface Plasmon Resonances of Au Hollow Nanostructures by a Chemical Route

Au plasmonic hollow spherical nanostructures were synthesized by electrochemical reduction (GRR, the Galvanic Replacement Reaction) using Ag nanoparticles as templates. From UV-visible absorption spectroscopy, it was found that the surface plasmon resonance (SPR) of gold hollow spherical nanostructures first showed red shift and then blue shift. However, further addition of gold precursor (HAuCl4) resulted into a red shift of SPR peak. The morphological changes from Ag nanoparticles to Au hollow nanostructures were assessed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX)analysis. The Mie Scattering theory based simulations of SPR of Au hollow nanostructures were performed which are in good agreement with the experimental observations. Based on the experimental observations and theoretical calculations, a complete growth mechanism for Au hollow nanostructures is proposed.

Kinetically Controlled Synthesis of LiNi0.5Mn1.5O4 Micro- and Nanostructured Hollow Spheres as High-Rate Cathode Materials for Lithium Ion Batteries

Spinel LiNi0.5Mn1.5O4 hollow spheres with micro- and nanostructures have been successfully synthesized based on the coprecipitation method followed by postheat treatment. A uniform and spherical precursor was obtained by controlling the reaction kinetics in the nucleation–crystallization process of forming nickel and manganese carbonates simply by employing NaHCO3 instead of Na2CO3 as precipitating agent. Single-shelled and double-shelled LiNi0.5Mn1.5O4 hollow spheres were derived of the spherical carbonate precursors via tuning the calcination kinetics. The as-prepared LiNi0.5Mn1.5O4 hollow spheres deliver a discharge capacity of 128.9 mAh g–1 at 0.1 C rate and maintain a capacity retention of 95% at 0.5 C after 100 cycles. Importantly, even at high rate of 30 C, it can still exhibit a discharge capacity of 100 mAh g–1. The excellent rate capability and cycling stability are mainly attributed to its hollow micro- and nanostructure, which could shorten Li+ ions’ diffusion path and buffer the volume change...

Synthesis of TiO2@WO3/Au Nanocomposite Hollow Spheres with Controllable Size and High Visible-Light-Driven Photocatalytic Activity

A new nanocomposite was reported as a good-performance photocatalyst, i.e., double-shelled, positively and negatively charged, nanostructured hollow spheres with supported Au nanoparticles (NPs). TiO2, WO3, and Au NPs were coated successively onto the functionalized polystyrene (PS) template spheres. The as-synthesized product PS@TiO2@WO3/Au nanocomposites were calcined at elevated temperature and then intact double-shelled TiO2@WO3/Au hollow spheres were obtained. The dispersity, morphology, size, and lattice of TiO2@WO3/Au hollow spheres were investigated by SEM and TEM. The presence of TiO2 hollow sphere and WO3/Au shell was proved by HAADF-STEM and XRD images. The photodegradation activity for rhodamine B and trimesic acid (i.e., color and colorless aromatic pollutants) in decreasing order were TiO2@WO3/Au, TiO2–WO3, P25. Under visible-light irradiation, the photodegradation rate of rhodamine B and trimesic acid for TiO2@WO3/Au was 94% and 95%, respectively, which exhibited a significant increase of 6...

Fabrication of positively and negatively charged, double-shelled, nanostructured hollow spheres for photodegradation of cationic and anionic aromatic pollutants under sunlight irradiation

A novel approach to prepare double-shelled, nanostructured hollow spheres with positively and negatively charged was proposed. If the difference in isoelectric points between MxO and NyO was large enough, at a certain pH range, the inner and outer shell of double-shelled MxO@NyO hollow spheres were positively and negatively charged, respectively. A proof-of-concept was shown, using WO3 and TiO2 as anionic and cationic building subunits, respectively. The nanoparticles of WO3 and TiO2 were coated successively onto the functionalized polystyrene (PS) template beads, the resulted PS@WO3@TiO2 nanocomposites were calcined at elevated temperature, and then double-shelled WO3@TiO2 hollow spheres were obtained. The dispersity, morphology, size, and lattice of these hollow spheres were tested by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The presence and purity of both WO3 and TiO2 phases were confirmed by electron energy loss mapping analysis and X-ray diffraction analysis (XRD). The specific surface area and the average pore diameter of these hollow spheres were 53.04m2/g and 8.042nm, respectively. The photocatalytic activity for the degradation of cationic and anionic aromatic pollutants was in the order of double-shell hollow spheres WO3@TiO2>single-shell WO3-TiO2>P25, i.e., the synergistic effect of coupling TiO2 with WO3 on photocatalytic performance was proved by us.

One‐Step Fabrication of Unique Mesoporous NiO Hollow Sphere Film on FTO for High‐Performance P‐Type Dye‐Sensitized Solar Cells

P‐type dye sensitized solar cells (p‐DSCs) deliver much lower overall efficiency than their inverse model, n‐DSCs. However, they have fundamental and practical significance, in particular, their tandem structured solar cells with both p‐ and n‐photoelectrodes could offer great potential to significantly improve the efficiency of existing solar cells. A facile and environmentally friendly method is developed to directly one‐step grow hollow NiO spherical structures on fluorine‐doped tin oxide (FTO) substrate, in which a Ni2+ and polymer complex spherical structure is self‐constructed through a controlled solvent evaporation process, followed by calcination‐converting to a unique NiO hollow sphere film. The prepared material is further used as a photocathode in p‐type dye sensitized solar cells, resulting in 41% increase of an open‐circuit voltage and 18% enhancement of power conversion efficiency than NiO nanoparticles photocathode. The improved performance can be ascribed to suppressed charge recombination at the photocathode/electrolyte interface. This template‐free approach could be universally used to fabricate other nanostructured hollow spheres for a wide range of energy conversion applications such as electrochemical capacitors, chemical sensors, and electrochromic devices.

Hydrothermal carbon-based nanostructured hollow spheres as electrode materials for high-power lithium–sulfur batteries

Carbon hollow spheres were produced using a sustainable approach, i.e. hydrothermal carbonization, using monosaccharides as carbon precursors and silica nanoparticles as hard-templates. Hydrothermal carbonization is an eco-efficient and cost-effective route to synthesize nanostructured carbonaceous materials from abundant biomass-derived molecules. After further thermal treatment under an inert atmosphere and removal of the silica-based core by chemical etching, porous hollow spheres depicting 5-8 nm thin shells were obtained. Subsequently, carbon-sulfur composites were synthesized via a melt diffusion method and used as nanostructured composites for cathodes in lithium-sulfur (Li-S) cells. The morphology of the hollow spheres was controlled and optimized to achieve improved electrochemical properties. Both high specific energies and high specific powers were obtained, due to the unique nanostructure of the hollow spheres. These results revealed that using optimized carbonaceous materials, it is possible to design sustainable Li-S cells showing promising electrochemical properties.

Recent advances in micro-/nano-structured hollow spheres for energy applications: From simple to complex systems

Hollow micro-/nano-structured materials are now playing an important role in cutting edge innovations for energy conversion and storage technologies such as solar cells, fuel cells, lithium ion batteries and super capacitors. These materials show great promise in addressing growing environmental concerns for cleaner power sources at a time of increasing global demand for energy. In this perspective, we show that complex multi-shelled micro-/nano-materials show significant material advantages in many applications over conventional simple hollow structures. We also summarize the vast array of synthetic strategies used to create multi-shelled hollow structures, and discuss the possible application of these novel materials for power generation and storage. Finally, the emergent challenges and future developments of multi-shelled hollow structures are further discussed.

Biomolecule-Assisted Synthesis of In(OH)3 Hollow Spherical Nanostructures Constructed with Well-Aligned Nanocubes and Their Conversion into C−In2O3

In this work, we demonstrate that indium hydroxide (In(OH)3) nanospheres with hollow interior, whose shells are constructed of oriented-attachment nanocubes, have been fabricated via a dl-asparagine-assisted synthesis route without any template. NH3 and dl-aspartic acid from the hydrolysis of dl-asparagine act as the OH− provider and the capping molecule, respectively. A detailed mechanism, involving dissolution−recrystallization and oriented aggregation processes, has been investigated on the basis of time-dependent experimental results. By annealing In(OH)3 precursors at 400 °C in air, cubic-phase indium sesquioxide (C−In2O3) nanocrystals, which inherit the morphology of their precursors, are also prepared.

Self-assembled zinc oxide nanostructures via a rapid microwave-assisted route

Self-assembled ZnO nanostructures with various morphologies were prepared via a rapid and simple microwave-assisted technique. The spherical, raspberry-like and hollow spherical nanostructures were synthesized in the presence of triethanolamine (TEA) as a capping agent and in different adjusted pHs. The volumetric amount of TEA has affected the particle size and crystallite size of the obtained nanostructures significantly. The ZnO nanostructures were obtained due to self-assembly of Zn 2+ ionic complexes, and the internal voids of the hollow spheres were formed by the Ostwald ripening mechanism. The obtained nanostructures were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The optical properties of the synthesized materials were investigated by Raman spectroscopy.

Large-scale production of self-assembled SnO2 nanospheres and their application in high-performance chemiluminescence sensors for hydrogen sulfide gas

Mesoporous SnO2 nanospheres with high thermal stability have been fabricated via reaction of sodium stannate with CO2 controllably released from urea under hydrothermal conditions. The resultant products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption and FTIR analysis. It was indicated that the products exhibited nearly monodisperse mesoporous or hollow spherical nanostructures with sizes in the range of ca. 25–50 nm, which were composed of nanocrystals with sizes of less than 10 nm. The formation mechnism of SnO2 nanospheres was also discussed. Urea not only acted as the CO2 resource for the formation of SnO2 primary nanocrystals, but also played an important role in their self-assembly into nanospheres. The as-prepared SnO2 nanospheres exhibited superior sensitivity, high selectivity, and extremely rapid response for detecting H2S gas based on catalytic chemiluminescence (CL) characteristics.

An in situ Template Route for Fabricating Metal Chalcogenide Hollow Spherical Assemblies Sonochemically

AbstractAn ultrasound‐assisted in situ template approach has been developed for fabricating a series of nanoscale metal chalcogenides in the form of well‐defined hollow spherical assemblies. These hollow spherical assemblies have well‐controlled dimensions and are composed of uniform nanoparticles. Initially, metal hydroxide particles self‐assemble into spherical templates generated in situ, and subsequent surface crystal growth leads to hollow spherical structures. Ultrasound irradiation plays a critical role both in the formation of the intermediate templates and in the crystal‐growth process. This approach provides a convenient and efficient one‐step pathway to the large‐scale fabrication of hollow spherical nanostructures. It also represents a new demonstration of sonochemical effects on the formation and assembly of crystalline particles on the nanometer scale. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)