Flower-like Hierarchical Architectures Research Articles

Controllable synthesis of metastable γ-Bi2O3 architectures and optical properties

Metastable γ-Bi2O3 were successfully prepared via a controllable, facile and mild solution precipitation synthesis method in ethylene glycol-water mixed solvent systems without adding surfactant or template agents, at 80℃ and ambient atmospheric pressure in 40min. Ethylene glycol can facilitate the nucleation of γ-Bi2O3 as only α-Bi2O3 was observed in its absence. And by adjusting ethylene glycol (EG) volume fraction, metastable γ-Bi2O3 submicro hexahedrons, tetrahedrons, polyhedrons and three-dimensional self-assembled hierarchical flower-like architectures were obtained respectively. SEM, XRD, and EDS were used to characterize the microstructures. The flower-like metastable γ-Bi2O3 architectures with diameter of several micrometers were 3D self-assembled from tetrahedrons step by step. The formation of the hierarchical flower-like architectures was due to the controlling of crystal growth kinetics and the guidance of self-assembly approach by ethylene glycol. The possible formation mechanism of these metastable γ-Bi2O3 architectures was also discussed. And compared with α-Bi2O3, β-Bi2O3, δ-Bi2O3, and γ-Bi2O3 through other means reported previously, the as-prepared γ-Bi2O3 in this paper possesses more excellent optical performance.

Facile synthesis of flower-like hierarchical architecture of SnO2 nanoarrays

A novel structure of flower-like hierarchical SnO2 architecture consisted of nanorods array was successfully synthesized by facile one-step hydrothermal route only using sodium stannate tetrahydrate solution of ethanol–water mixed solvent. The morphology and microstructure of the hierarchical SnO2 architecture showed that flower-like hierarchical SnO2 architecture with six similar petals were organized by large scale uniformity and ordered dense nanorods arrays with a diameter of 10–15 nm and length of about 200 nm. Infrared absorption spectra (IR), Raman spectra and Ultraviolet–visible (UV–vis) absorption spectra were carried out to investigate the optical properties of the flower-like hierarchical SnO2 nanoarrays. The UV–vis spectrum of as-prepared layered SnO2 nanorod array assemblies showed the band gap blue-shifted compared with the band gap of bulk SnO2. A series of peculiar emission band positions of the room temperature photoluminescence properties of the hierarchical SnO2 nanoarrays were observed.

Assembly of 3D flower-like NiO hierarchical architectures by 2D nanosheets: synthesis and their sensing properties to formaldehyde

NiO flower-like hierarchical architectures were synthesized by a solvothermal route, which exhibited good formaldehyde gas sensing performance. The effect of reaction time and ethanol/water volume ratio on morphologies was investigated and a synthesis mechanism was proposed.

Retraction: Two-dimensional nanosheets associated with one-dimensional single-crystalline nanorods self-assembled into three-dimensional flower-like Mn3O4 hierarchical architectures.

Retraction of 'Two-dimensional nanosheets associated with one-dimensional single-crystalline nanorods self-assembled into three-dimensional flower-like Mn3O4 hierarchical architectures' by Mei Wang et al., Phys. Chem. Chem. Phys., 2014, 16, 21742-21746.

A unique semiconductor-carbon-metal hybrid structure design as a counter electrode in dye-sensitized solar cells.

The catalytic activity of counter electrodes (CEs) severely restricts the photovoltaic conversion efficiency of dye-sensitized solar cells. However, electrons trapped by bulk defects greatly reduce the catalytic activity of the CE. In this study, we report a novel In2S3-C-Au hybrid structure designed by simply decorating Au particles on the surface of carbon-coated hierarchical In2S3 flower-like architectures, which could avoid the abovementioned problems. This effect can be attributed to the unique contribution of indium sulfide, carbon, and Au from the hybrid structure, as well as to their synergy. Electrochemical measurements revealed that the hybrid structure possessed high catalytic activity and electrochemical stability for the interconversion of the redox couple I3-/I-. Moreover, this superior performance can be incorporated into the dye-sensitized solar cells system. We used this hybrid structure as a counter electrode by casting it on an FTO substrate to form a film, which displayed better photovoltaic conversion efficiency (8.91%) than the commercial Pt counterpart (7.67%).

Black N/H-TiO2 Nanoplates with a Flower-Like Hierarchical Architecture for Photocatalytic Hydrogen Evolution.

A facile two-step strategy was used to prepare black of hydrogenated/nitrogen-doped TiO2 nanoplates (NHTA) with a flower-like hierarchical architecture. In situ nitriding and self-assembly was realized by hydrothermal synthesis using tripolycyanamide as a N source and as a structure-directing agent. After thorough characterization, it was found that the hydrogenation treatment did not damage the flower-like architecture but distorted the anatase crystal structure and significantly changed the band structure of NHTA owing to the increased concentration of oxygen vacancies, hydroxyl groups, and Ti3+ cations. Under AM 1.5 illumination, the photocatalytic H2 evolution rate on the black NHTA was approximately 1500 μmol g-1 h-1 , which was much better than the N-doped TiO2 nanoplates (≈690 μmol g-1 h-1 ). This improvement in the hydrogen evolution rate was attributed to a reduced bandgap, enhanced separation of the photogenerated charge carriers, and an increase in the surface-active sites.

Superior adsorption performance for triphenylmethane dyes on 3D architectures assembled by ZnO nanosheets as thin as ∼1.5 nm

The 3-dimensional hierarchical ZnO flower-like architectures have been synthesized in a Zn(Ac)2·2H2O-Na2SeO3-KBH4-pyridine solvothermal system at 100°C for 24h. The flower-like architecture is assembled from ZnO nanosheets with a thickness of ∼1.5nm, and the flower-like architecture specific surface area is 132m2/g. When the ZnO flower-like architecture is used as the adsorbent for acid fuschin (AF), malachite green (MG), basic fuchsin (BF), congo red (CR) and acid red (AR) in water, the adsorption capacities for AF, MG, BF, CR and AR are 7154.9, 2587.0, 1377.9, 85.0 and 38.0mg/g, respectively. Evidently, the as-obtained ZnO flower-like architectures show excellent adsorption performances for triphenylmethane dyes, and the adsorption capacity of 7154.9mg/g for AF is the highest of all adsorbents for dyes. The adsorption mechanism can be attributed to the electrostatic attraction and the formation of ion-association complex between triphenylmethane dyes and ZnO hierarchical flower-like architectures.

Preparation and gas sensing properties of flower-like WO3 hierarchical architecture

Flower-like WO3 hierarchical architecture has been successfully synthesized through a facile hydrothermal method. The morphology and structure were investigated via X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The results indicated that the flower-like WO3 were self-assembled by many ultrathin petal-like nanosheets with thickness of several nanometers. A possible formation mechanism of 3D hierarchical architecture was proposed on basis of time dependent experiments. In addition, the well-defined WO3 hierarchical architectures exhibited high response and good selectivity to ethanol at 300 °C with fast response (5–7 s) and recovery (6–9 s) properties, which might substantially benefit from their layer-by-layer ultrathin petal structure.

A facile salicylic acid assisted hydrothermal synthesis of different flower-like ZnO hierarchical architectures with optical and concentration-dependent photocatalytic properties

Different flower-like ZnO hierarchical architectures with wurtzite structure have been prepared by a facile salicylic acid (SA) assisted hydrothermal method, especially four flower-like ZnO nanostructures can be obtained simultaneously by using 18.00mmol of SA. The petals of the flower-like ZnO architectures are mainly assembled by many of single nanorods, a mixture of single nanorods and bundle (cluster) of nanorods, or bundle of nanorods respectively. The nanorod exhibits the taper-like, hexagonal prism-like, tower-like or bamboo shoot-shaped body and the pyramid-like or pencil-like tip. Photoluminescence (PL) study shows two tunable wavelengths (542nm and 565nm). All the samples exhibit the similar Raman spectra. With increasing the amount of SA, the peak at 441cm−1 increases. The photodegradation rates of MB are more effective than these of MO, and the sample from 22.50mmol of SA decomposes 55% of MB within 140min. The activity of photocatalysts is significantly affected by the concentration of SA. With the increase of SA, the number of nanorods of the flower-like ZnO nanostructures increases, and leads to the improvement of photocurrent response and photocatalytic performance.

Formation of tungsten trioxide with hierarchical architectures arranged by tiny nanorods for lithium ion batteries

WO3 with hierarchical flower-like architectures has been obtained by calcination of WO3·0.33H2O, which is initially prepared via a hydrothermal method with formic acid as a structure directing agent.

Hydrothermal synthesis of WO3·H2O with different nanostructures from 0D to 3D and their gas sensing properties

In this paper, WO3·H2O with different nanostructures from 0D to 3D were successfully synthesized via a simple yet cost-effective hydrothermal method with the assistance of surfactants. The structures and morphologies of products were investigated by XRD and SEM. Besides, we systematically explained the evolution process and formation mechanisms of different WO3·H2O morphologies. It is noted that both the kinds and amounts of surfactants strongly affect the formation of WO3·H2O crystals, as reflected in the tailoring of WO3·H2O morphologies. Furthermore, the gas sensing performance of the as-prepared samples towards methanol was also investigated. 3D flower-like hierarchical architecture displayed outstanding response to target gas among the four samples. We hoped our results could be of great benefit to further investigations of synthesizing different dimensional WO3·H2O nanostructures and their gas sensing applications.

Synthesis of δ-Bi2O3 microflowers and nanosheets using CH3COO(BiO) self-sacrifice precursor

Bismuthyl acetate (CH3COO(BiO); BiOAc) dispersed nanosheets and flower-like hierarchical architectures were easily prepared from the reaction between Bi2O3 and glacial acetic acid (HAc) or Bi(NO3)3·5H2O and HAc and subsequent neutralization by Na2CO3 under ambient condition. The BiOAc could be completely soluble in HAc-water (0.04–250v/v) mixture but insoluble in pure HAc or water, and thus could be collected as a novel photocatalyst candidate because of its availability, non-toxicity and cheapness. Rhodamine B (RhB) could be completely degraded over BiOAc nanosheets within 4min of UV light irradiation. Especially, BiOAc nanosheets and microflowers could be converted to δ-Bi2O3 by thermal treatment, while the morphology remained unchanged. The as-prepared δ-Bi2O3 exhibited enhanced photocatalytic activity for RhB degradation under simulated sunlight illumination owing to its suitable band gap energy.

SnSex flowerlike composites as anode materials for sodium ion batteries

SnSex flowerlike composites have been synthesized by a facile single-step solvothermal method with the addition of 1,10-phenanthroline. As anode materials for sodium ion batteries, the SnSex flowerlike composites demonstrate a higher initial sodium ion storage capacities of 877.2mAhg−1 at 100mAg−1 and a better cycling performance (272.4mAhg−1 after 50 cycles at 200mAg−1) compared to bulk SnSex composites. The enhanced electrochemical performance can be attributed to the hierarchical flowerlike architecture which can increase the electrode/electrolyte contact area, shorten the electronic sodium ion pathway and limit the volume change of materials due to facile strain relaxation.

One-step synthesis of flower-like carbon-doped ZrO2 for visible-light-responsive photocatalyst

Carbon-doped ZrO2 photocatalysts with three-dimensional (3D) flower-like architecture were successfully prepared by one-step sol–gel-hydrothermal process using zirconatrane precursor for use as a high-performance material for the methylene blue (MB) degradation and the enhanced photoelectrochemical (PEC) properties compared with zero-dimensional ZrO2 nanoparticles and commercial TiO2 nanoparticles (P25). These mesoporous microflower structures consisted of ZrO2 nanopetals, implying good intercrystalline connections and effective light absorption. The synergy of carbon doping and flower-like hierarchical 3D architecture greatly promoted the photocatalytic efficiency for MB degradation under visible light. In view of these advantageous features inherited from the carbon-doped ZrO2 with flower-like structure can be used as photoanode materials. A high photoconversion efficiency of 3.17% was achieved from flower-like carbon-doped ZrO2, which increased by 575% and 1168% compared with those of the PEC devices based on ZrO2 nanoparticles and P25, respectively.

Synthesis and enhanced photoreactivity of metallic Bi-decorated BiOBr composites with abundant oxygen vacancies

Herein, a simple one-pot solvothermal strategy was put forward to obtain metal Bi-decorated BiOBr composites (Bi/BiOBr) with abundant oxygen vacancies. The metal Bi (Bi0) can be deposited into the BiOBr surface via reduction of glycerol solvent in solvothermal process. Precipitation of Bi on surface of BiOBr turned the morphologies of BiOBr from regular flower-like hierarchical architectures to scattered sheets with increase of Bi content, enhanced photoabsorption of BiOBr in whole light region. Interestingly, deposition of metallic Bi (Bi0) on the BiOBr surface could lead to formation of abundant surface oxygen vacancies. As-synthesized Bi/BiOBr composites showed better photocatalytic activity for phenol degradation under sunlight irradiation, as compared with that of BiOBr reference. The enhancement of photocatalytic activities for Bi/BiOBr composites can be attributed to the existence of Bi/BiOBr hetero-structure and abundant oxygen vacancies (as active electron trap), which causing efficient separation of electron–hole pairs in Bi/BiOBr composites.

Nanosheet-assembled flower-like SnO2 hierarchical structures with enhanced gas-sensing performance

Two type flower-like SnO2 hierarchical architectures with ultrathin nanosheets as building blocks have been controllably synthesized via tuning the presence or not of PEG under hydrothermal condition. Whether the sparsely assembled flower-like SnO2 hierarchical nanosheets or the closely assembled counterparts, the thickness of an individual nanosheet is about 50nm, which is less than twice Debye length of bulk SnO2 at 250°C, resulting in full electron depletion induced by oxygen adsorption. Interestingly, a comparison study reveals that an enhanced gas sensing performance for the sensor made of the closely assembled hierarchical nanosheets towards ethanol occurs over that of the other, which may be mainly attributed to the confined effect provided by numerous nano- or micro-reaction rooms for adequate gas-sensing reactions in closely assembled case.

Tartaric acid assisted hydrothermal synthesis of different flower-like ZnO hierarchical architectures with tunable optical and oxygen vacancy-induced photocatalytic properties

Different flower-like ZnO hierarchical architectures were prepared by tartaric acid assisted hydrothermal synthesis, especially four flower-like ZnO nanostructures were obtained simultaneously under the same reaction condition. The cauliflower-like ZnO is assembled by spherical shaped nanoparticles, and the chrysanthemum-like and other flower-like ZnO nanostructures are assembled by hexagonal rods/prisms with from planar to semi-pyramid, and to pyramid tips. TA acts as a capping agent and structure-directing agent during the synthesis. All ZnO possess the hexagonal wurtzite structure. The PL spectra can be tuned by changing TA concentration. XRD, PL and Raman spectra confirmed that oxygen vacancies mainly come from the ZnO surface. The flower-like samples of 1:4.5 and 1:3 with the largest aspect ratios have highest photocatalytic performance. They decompose 85% MB within 60min. Combining PL Gaussian fitting with K, the higher content of oxygen vacancy is, the higher photocatalytic activity is. The enhanced photocatalytic performance is mainly induced by oxygen vacancy of ZnO. The possible formation mechanism, growth and change process of flower-like ZnO were proposed.

Synthesis and controlled growth of NiO hierarchical bundle-like nanoflowers with the assistance of ethylene glycol

Monodisperse NiO hierarchical nanoflowers fabricated by nanobundles have been successfully synthesized under hydrothermal conditions followed by a calcination treatment. It is amazingly observed that the bundle-like nanoflowers possessed the emanative needle-like ends on the nanoscale, which was different from the previous 3D hierarchical architectures only fabricated by nanosheets, entire solid rod-like and emanative needle-like structures. Furthermore, based on the further experiments, the amount of ethylene glycol (EG, 99.5wt%) play a key role on the formation of emanative needle-like ends and constructions of the 3D hierarchical flower-like architectures, and the relative formation mechanism was primarily discussed. Such an unexpected morphology may provide a non-trivial behavior driven by the properties of emanative needle-like ends and electron transformation continuity.

Synthesis of WO3 flower-like hierarchical architectures and their sensing properties

WO3 flower-like hierarchical architectures were synthesized by hydrothermal process using sodium tungstate (Na2WO4·2H2O) as tungsten source and citric acid (CA) as an assistant agent. The morphology and crystal structure were investigated using scanning electron microscope and X-ray diffractometer. It is found that CA played a significant role in governing morphologies of product during hydrothermal process. The obtained products were identified as triclinic crystal WO3 structure. The ethanol gas sensing measurements showed that well-defined WO3 flower-like structures synthesized at CA/W molar ratio of 1 with large specific surface area exhibited the higher responses compared with others at all operating temperatures. Moreover, the reversible and fast response to ethanol gas at various gas concentrations and good selectivity were obtained. The results indicated that the WO3 flower-like hierarchical architectures are promising materials for gas sensors.

Photocatalytic properties of hierarchical BiOXs obtained via an ethanol-assisted solvothermal process

In this study, bismuth oxyhalide (BiOXs (XCl, Br, I)) semiconductors were prepared by a simple solvothermal method, with ethanol serving as solvent and a series of tetrabutylammonium halide surfactants as halogen sources. Under identical synthetic conditions, BiOBr was more readily constructed into regular flower-like hierarchical architectures. The photocatalytic properties of the materials were studied by monitoring the degradation of rhodamine B (RhB), with visible light absorption, and colorless salicylic acid (SA). It was found that both RhB and SA were rapidly degraded on the surface of BiOBr. BiOCl was rather active for the degradation of RhB, but ineffective toward the degradation of SA. However, neither RhB nor SA could be degraded effectively in the case of BiOI. Further experiments such as UV–visible spectroscopy and detection of OH and O2− radicals suggest that the electronic structure of the BiOX photocatalysts is responsible for the difference in their activities.