Hierarchical Nanospheres Research Articles

Hierarchical hollow MoS2 nanospheres with enhanced electrochemical properties used as an Electrode in Supercapacitor

MnCO3 nanospheres are employed as the template to prepare MoS2 hierarchical hollow nanospheres. The synthesis procedure involves the hydrothermal growth of MoS2 ultrathin nanosheets on the surface of MnCO3 nanospheres and subsequent selectively dissolving the template by acid washing. Galvanostatic charge-discharge measurements show that the MoS2 electrode has a specific capacitance of 142Fg−1 at a current density of 0.59Ag−1 and it retains 92.9% of capacitance even after 1000 cycles. These results indicate a promising potential application of hierarchical hollow MoS2 nanospheres for using as a suitable electrode material in Supercapacitors.

Adsorption and photocatalytic degradation of pharmaceuticals by BiOClxIy nanospheres in aqueous solution

BiOClxIy nanospheres have been synthesised via precipitation method in ethylene glycol (EG)-water (H2O) mixed solvent at 80°C and ambient pressure. Results of BiOClxIy characterisation showed that these composite materials well combined BiOCl with BiOI crystals, which displayed flower-like hierarchical nanospheres consisted of numerous nanosheets and possessed smaller particle size, higher surface area than those in previous papers. The great surface area resulted in its high adsorption abilities of hydroxyphenylacetic acid (p-HPA) in the dark, the adsorption process could be suitably described by a pseudo-second-order kinetics model and the adsorption isotherms could be well fitted with Freundlich and Langmuir equations. The photocatalytic degradation of p-HPA and acetaminophen (ACTP) were investigated under simulated solar and visible irradiation using BiOClxIy catalyst for the first time. The combination of BiOCl and BiOI to a certain extent has largely improved the remove efficiency, and BiOCl0.75I0.25 was the optimal catalyst with almost 100% removal of p-HPA and 80% removal of ACTP under solar light for 3h. Experimental results demonstrated that the photocatalytic degradation of p-HPA and ACTP followed pseudo-first-order kinetics and O2− and dissolved oxygen play predominant roles in photocatalytic process efficiency. This research will supply an environment-friendly photocatalyst for pharmaceutical wastewater treatment under sunlight.

Hierarchical mesoporous rutile TiO2/C composite nanospheres as lithium-ion battery anode materials

Hierarchical mesoporous rutile TiO2 nanospheres were successfully synthesized via a simple low-temperature template-free method. The rutile TiO2 electrode showed poor electrochemical anodic performance in a lithium-ion battery. In order to improve the performance, conductive polyaniline was synthesized and coated on rutile TiO2 nanospheres via in-situ polymerization and chemical etching. After carbonization, the TiO2/C composite electrode showed more stable cyclability and a higher rate performance. Additionally, the amorphous carbon layer provided an effective pathway for charge transport, leading to a lower charge-transfer resistance and a higher lithium-ion diffusion coefficient compared to those of untreated rutile.

Novel hollow SnO2 nanosphere@TiO2 yolk–shell hierarchical nanospheres as anode material for high-performance lithium-ion batteries

Hollow SnO2 nanosphere@TiO2 yolk–shell hierarchical nanospheres (h-SnO2@TiO2 YSHNSs) have been synthesized for the first time and evaluated as a high-performance anode material in lithium-ion batteries (LIBs). The h-SnO2@TiO2 YSHNS anode exhibited high reversible capacity (~520mAhg−1 at a current density of 100mAg−1 after 100 charge/discharge cycles), superior cyclic stability (capacity retention of ~63.3% after 100 cycles) and good rate performance (~172mAhg−1 at 2400mAg−1) due to the unique hierarchical yolk–shell nanostructure, comprised of a TiO2 shell surrounding an interspace and the hollow SnO2 yolk. These results suggest that the h-SnO2@TiO2 YSHNS should be a promising anode candidate for next-generation LIBs.

CdS nanowires decorated with Cu2O nanospheres: Synthesis, formation process and enhanced photoactivity and stability

CdS/Cu2O heterostructural materials were successfully synthesized by a solvent-thermal process followed by a chemical bath deposition process. Structures and morphologies of the obtained CdS/Cu2O composites were characterized by XRD, SEM, and TEM; the experimental results indicate that the surface of CdS nanowires (NWs) is decorated with spherical Cu2O whose diameter ranges from 100 to 200nm. Through crystal shape-evolution, the formation process of these hierarchical nanostructures was rationally proposed. Briefly, in the chemical bath deposition process, Cu(OH)2 colloids generate firstly, and then the colloids transform into nanobelts after adding ascorbic acid (AA). With the reaction time further increasing, nanobelts aggregate together to form the hierarchical nanospheres on the surface of CdS NWs. The photoactivity of CdS/Cu2O composite for methyl orange (MO) photodegradation was investigated in detail. The obtained high photocatalytic efficiency can be attributed to the heterojunction structure, which results in the efficient separation of photo-generated electrons and holes.

Synthesis of BiOI hierarchical nanospheres and their application in photocatalysis

We report the synthesis of BiOI hierarchical nanospheres in the presence of octadecene and oleic acid. The BiOI nanospheres show an average diameter of 150nm and are composed with nanocrystals of about 5nm in size, which is the smallest BiOI hierarchical nanospheres reported at present. The samples exhibit high photocatalytic activity on methyl orange, which was testified by the photoelectrochemical performance to be benefited from the effective separation of the photogenerated carriers.

High performance solid state flexible supercapacitor based on molybdenum sulfide hierarchical nanospheres

Molybdenum sulfide (MoS2) hierarchical nanospheres are synthesized using a hydrothermal method and characterized by X-ray powder diffraction, Brunauer–Emmett–Teller, scanning electron microscopy and transmission electron microscopy. The prepared MoS2 is used to fabricate solid state flexible supercapacitors which show excellent electrochemical performance such as high capacitance 368 F g−1 at a scan rate of 5 mV s−1 and high power density of 128 W kg−1 at energy density of 5.42 Wh kg−1. The fabricated supercapacitor presents good characteristics such as lightweight, low cast, portability, high flexibility, and long term cycling stability by retaining 96.5% after 5000 cycles at constant discharge current of 0.8 mA. Electrochemical impedance spectroscopy (EIS) results reveal low resistance and suggest that MoS2 nanospheres would be a promising candidate for supercapacitors. Three charged supercapacitors connected in series can light 8 red color commercial light emitting diodes (LEDs) for 2 min, demonstrating its capability as a good storage device.

Facile hydrothermal synthesis of NiMoO4@CoMoO4 hierarchical nanospheres for supercapacitor applications.

A novel binder-free electrode material of NiMoO4@CoMoO4 hierarchical nanospheres anchored on nickel foam with excellent electrochemical performance has been synthesized via a facile hydrothermal strategy. Microstructures and morphologies of samples are characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Besides, the effect of Ni/Co molar ratios of raw materials on electrochemical behaviors is also investigated by cyclic voltammetry, galvanostatic charge-discharge measurements, cycling tests and electrochemical impedance spectroscopy methods. Remarkably, the resulting NiMoO4@CoMoO4 hierarchical nanospheres with a Ni/Co molar ratio of 4 : 1 exhibit greatly enhanced capacitive properties relative to other components and display a high specific capacitance of 1601.6 F g(-1) at the current density of 2 A g(-1), as well as better cycling stability and rate capability. Moreover, a symmetric supercapacitor is constructed using NiMoO4@CoMoO4 nanospheres as the positive and negative electrodes with one piece of cellulose paper as the separator, which shows good electrochemical performance. Such enchanced capacitive properties are mostly attributed to the synergistic effect of nickel and cobalt molybdates directly deposited on the conductive substrate and their novel hierarchical structure, which can provide pathways for fast diffusion and transportation of ions and electrons and a large number of active sites. The results imply that the NiMoO4@CoMoO4 hierarchical nanospheres could be promising candidates for electrochemical energy storage.

Hierarchical Ru nanospheres as highly effective cathode catalysts for Li–O2batteries

Carbon-free, hierarchical Ru nanospheres as a cathode for Li–O2batteries can significantly reduce discharge/charge overpotential with a high capacity.

Mesostructure-tunable and size-controllable hierarchical porous silica nanospheres synthesized by aldehyde-modified Stöber method

Mesostructure-fine-tuned and size-controlled hierarchical porous silica nanospheres were synthesized by aldehyde-modified Stöber method in the TEOS–CTAB–NH3·H2O–aldehyde system.

Fabrication of hierarchical CdS nanosphere via one-pot process for photocatalytic water splitting

A hierarchical nanosphere assembled by CdS nanorods was fabricated via a simple one-pot hydrothermal route using (NH4)2MoS4, Cd(NO3)2 and ethanediamine as the initial reactant. The synthesized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. According to control experiments, it can be deduced that the (NH4)2MoS4 and ethanediamine may be predominantly responsible for the formation of hierarchical architecture, and a potential mechanism based on cation exchange reaction was proposed. For further investigation of the photocatalytic performance of the as-prepared samples, photocatalytic water-splitting experiment was carried out. The hierarchical CdS synthesized in the origin mol ratio of Mo:Cd = 0.3:1.4 exhibited the best performance for photocatalytic water splitting, and the hierarchical CdS with unique morphology, compared with the isolated CdS nanorod, showed an enhanced photocatalytic activity for water splitting arising from the intimate contact among CdS nanorods, incremental specific surface area and the high ratio of (002)/(100). A hierarchical nanosphere assembled by CdS nanorods was fabricated via cation exchange reaction and showed a superior photocatalytic water-splitting activity than isolated CdS.

Graphitized hierarchical porous carbon nanospheres: simultaneous activation/graphitization and superior supercapacitance performance

A novel graphitized porous carbon nanosphere material obtained by a simultaneous activation and graphitization route, which was realized by heating resorcinol–formaldehyde resin nanospheres immersed with ZnCl2and FeCl3in an inert atmosphere, has been reported.

Sonochemical synthesis of reduced graphene oxide uniformly decorated with hierarchical ZnS nanospheres and its enhanced photocatalytic activities

Reduced graphene oxide decorated with ZnS nanospheres was synthesized through the simple ultrasonic irradiation route which shows a significant enhancement in the photocatalytic degradation of methylene blue compared to the bare ZnS particles.

Hierarchical nanospheres based on Pd nanoparticles dispersed on carbon coated magnetite cores with a mesoporous ceria shell: a highly integrated multifunctional catalyst.

The design and fabrication of core-shell nanostructures with steerable morphologies and tailored performances have aroused abundant scientific studies for organic transformations. We here report the preparation of multifunctional and highly efficient core-shell microspheres, which bear a carbon-protected magnetic Fe3O4 core, a transition layer of active Pd nanoparticles (NPs) and an outer shell of mesoporous CeO2 (mCeO2). The composition and structure of the as-prepared Fe3O4@C-Pd@mCeO2 were thoroughly characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and Brunauer-Emmett-Teller measurements. The well-designed microspheres have high dispersibility, convenient magnetic separability and good reusability as heterogeneous nanoreactors due to their unique structure. We illustrate the high efficiency of these nanocomposites in mediating the Suzuki-Miyaura cross-coupling reaction and the reduction reaction of 4-nitrophenol (4-NP). The enhanced catalytic activity can be attributed to the synergistic effect between the CeO2 nanoparticles and noble metal NPs. A mechanism was further proposed to explain the improved catalytic activity. This peculiar core-shell nanostructure renders the nanospheres to be an approachable and attractive catalyst system for various catalytic organic industrial processes.

Morphological Influence of Polypyrrole Nanoparticles on the Performance of Dye–Sensitized Solar Cells

Polypyrrole (PPy) with various morphologies were synthesized by chemical oxidative polymerization and further used as the counter electrode (CE) in dye–sensitized solar cells (DSSCs). The conventional anionic surfactant, docusate sodium salt (AOT), cationic surfactant, cetylmethyl ammonium bromide (CTAB), and the newly developed polymeric dispersant, poly(oxyethylene)–imide (POEM), were employed in the PPy synthesis. Scanning electron microscopy images (SEM) revealed diversified morphologies of the synthesized PPy nanoparticles with irregular sheet (IS), hierarchical nanosphere (HNS), and nanosphere (NS), corresponded to the choice of the commercial surfactants AOT and CTAB, as well as the home–made POEM, respectively. Fourier transform spectroscopy (FT–IR) and X–ray diffraction (XRD) analysis were used to confirm the PPy structures and crystalline properties. When fabricated into films and used as CE in DSSCs, the PPy–HNS demonstrated the superior cell efficiency of 6.71±0.16% to those of PPy–IS (5.46±0.31) and PPy–NS (6.31±0.24), respectively. The excellent electrocatalytic ability of PPy–HNS was essentially attributed to its high electrochemical surface area (Ae), which was quantitatively calculated through a rotating disk electrode system by using the Koutecky–Levich equation. Brunauer–Emmett–Teller (BET) surface area measurement, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were also used to substantiate the explanation for the DSSC performances.

Preparation and electrocatalytic activity of 3D hierarchical porous spinel CoFe2O4 hollow nanospheres as efficient catalyst for Oxygen Reduction Reaction and Oxygen Evolution Reaction

Lithium-air battery has attracted extensively attention and now developing catalysts with high electrocatalytic activity is one of the challenges for lithium-air battery. In this paper, 3D hierarchical porous spinel CoFe2O4 hollow nanospheres were first prepared by a facile hydrothermal method. The hollow CoFe2O4 nanospheres have unique bimodal porous structure which consists of micropores and mesopores. The catalytic activity of the CoFe2O4 hollow nanospheres for oxygen reduction reaction (ORR) has been studied and compared with the acetylene black, the solid CoFe2O4 nanospheres and the commercial Pt/C by using rotating ring-disk electrode (RRDE) technique. The spinel CoFe2O4 hollow nanospheres exhibit superior catalytic activity for the ORR compared to the acetylene black and the solid CoFe2O4 nanospheres. Besides, the spinel CoFe2O4 hollow nanospheres also afford high catalytic activity for the oxygen evolution reaction (OER). Furthermore, the hollow CoFe2O4 nanospheres show the smallest overpotential between ORR and OER. The chronoamperometric studies show that the CoFe2O4 hollow nanospheres exhibit excellent stability for both the ORR and OER. The high ORR and OER activities and stabilities of CoFe2O4 hollow nanospheres could be attributed to their special 3D hierarchical porous structure. This material shows a significant potential application on lithium-air battery.

Highly-active copper oxide/copper electrocatalysts induced from hierarchical copper oxide nanospheres for carbon dioxide reduction reaction

Novel hierarchical copper oxide (CuXO) nanosphere particles are synthesized, and then coated onto gas diffusion layer (carbon) to form a working electrode for catalyzing CO2 electroreduction. When applying a negative voltage to the working electrode, the metal Cu nanoparticles which are induced by the CuXO nanospheres appear. CuXO and metal Cu together form the CuXO/Cu nanocatalysts which show high catalytic activity for CO2 electroreduction. The morphology, composition, crystal structure and surface area of the CuXO/Cu electrocatalysts are characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuXO/Cu nanoparticles are tested as the catalysts for CO2 electroreduction using cyclic voltammetry and linear sweep voltammetry in CO2-saturated 0.5M KHCO3 aqueous electrolyte. It is found that the CO2 electroreduction activity is highly improved using this CuXO/Cu nanocatalyst, which remains stable during 20h of electrolysis, along with the high selectivity with a ∼62% of Faradaic efficiency for formate production. Detailed kinetic information relevant to the catalysis is also discussed.

Synthesis of novel ZnV₂O₄ hierarchical nanospheres and their applications as electrochemical supercapacitor and hydrogen storage material.

Hierarchical nanostructures (Hs) have recently garnered enormous attention due to their remarkable performances in catalysis, electronic devices, energy storage and conversion. Considering the advantage of hierarchical nanostructures, we have formulated a facile and template free method to synthesize novel hierarchical nanospheres (NHNs) of ZnV2O4. Both zinc and vanadium are earth abundant, relatively economical and can offer several oxidation states, which can render a broad range of redox reactions favorable for electrochemical energy storage applications. Keeping these points in mind, we investigated for the first time the electrochemical supercapacitor performance of NHNs. The electrochemical measurements were performed in 2 M KOH solution. The measured specific capacitance of ZnV2O4 electrode is 360 F/g at 1 A/g with good stability and retention capacity of 89% after 1000 cycles. Moreover, the hydrogen storage properties of NHNs were measured at 473, 573, and 623 K with an absorption of 1.76, 2.03, and 2.49 wt %. respectively. These studies pave the way to consider ZnV2O4 as prospective material for energy storage applications.

Hollow nanospheres constructed by CoS2 nanosheets with a nitrogen-doped-carbon coating for energy-storage and photocatalysis.

Hierarchical CoS2 hollow nanospheres (HSs) with a nitrogen-doped-carbon coating (NC@CoS2 ) are fabricated by a simple solution method. The uniform 300 nm-sized NC@CoS2 HSs are composed of ultrathin nanosheet subunits with a thickness of around 2 nm. It was found that polyvinylpyrrolidone and ethylenediamine not only controlled the morphology of the products, but also provided the sources of nitrogen-doped carbon. Benefiting from their unique structural characteristics, hierarchical NC@CoS2 HSs can be applied in lithium-ion batteries, supercapacitors, and photocatalysis. When evaluated as an electrode material, NC@CoS2 with a coating of optimal thickness showed a high lithium-storage capability with a good cycling stability. Moreover, NC@CoS2 had a remarkable supercapacitive performance and photocatalytic activity. The attractive electrochemical and photocatalytic performances were attributed to the overall structural features of the NC@CoS2 hollow spheres: the N-doped-carbon (NC) coating, hollow interior, and ultrathin nanosheets.

Functionalization of Flower-Like ZnO Nanostructures With Au@CuO Nanoparticles for Detection of Ethanol

Hierarchical flower-like ZnO nanospheres were synthesized by a facile hydrothermal method using sodium citrate as soft template. The products were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray, inductively coupled plasma atomic emissions spectroscopy, and X-ray photoelectron spectroscopy techniques. The SEM and TEM results showed that the 3D ZnO nanospheres were consisted of 2D ZnO nanosheets. The diameter of the nanospheres was 3-4 μm and the thickness of the nanosheets was 60-70 nm. In order to improve the ethanol-sensing properties, the 3D ZnO nanostructures were functionalized with Au@CuO nanoparticles. Because of the protection of the CuO shell from aggregation, the size of the Au@CuO nanoparticles were smaller than that of the Au nanoparticles after annealing. The sensing response of 0.7% Au@0.3% CuO loaded ZnO was close to that of 1% Au loaded ZnO, and much higher than that of the unfunctionalized ZnO. The good performance was probably attributed to the high intensities of the chemical adsorption oxygen and the active sites of the Au@CuO functionalized ZnO nanostructures.