Hierarchical Flower-like Structure Research Articles

Enhanced photocatalytic dye degradation activity of carbonate intercalated layered Zn, ZnNi and ZnCu hydroxides

Carbonate intercalated layered Zn, ZnNi and ZnCu hydroxides were synthesized by a facile hydrothermal method for the visible light driven photocatalytic methylene blue dye degradation. The crystalline phase, surface states, optical and morphological properties were studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (DRS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) measurements. The XRD measurement demonstrated that all the synthesized materials were in a regular layered structure. Optical spectra of the samples were revealed that layered ZnNi hydroxide showed the visible light absorption property. The photocatalytic activities of the prepared layered materials examined by the degradation of methyl blue (MB) dye solution under visible light illumination. Among the prepared layered hydroxide, ZnNi hydroxide exhibited the 90% removal rate for MB under visible light illumination. The enhanced photocatalytic activity of ZnNi hydroxide is due to combined visible light absorption nature and hierarchical flower-like structure with a large number of active sites. Moreover, the ZnNi hydroxide has very good recyclability until remain active after the complete fourth degradation cycle.

Hierarchical flower-like structures composed of cross-shaped vanadium dioxide nanobelts as superior performance anode for lithium and sodium ions batteries

Until now, both lithium ion batteries (LIBs) and sodium ion batteries (SIBs), have been broadly researched, which is either attractive or challenging. Among the transition metal oxides (TMOs), VO2 (B), with a high theoretical capacity and appealing rate capability, has been studied as anode materials. In our work, the flower-like structures composed of cross-shaped VO2 (B) nanobelts were synthesized via a simple solvothermal method. The electrochemical properties were investigated for lithium storage (with capacities of 529.2 mA h g−1 at current density of 0.2 A g−1 after 200 cycles and 683.1 mA h g−1 at 1 A g−1 after 1000 cycles) and sodium storage (225.2 mA h g−1 at 0.2 A g−1 after 200 cycles, 150 mA h g−1 at 5 A g−1). The reaction mechanisms were explored by ex-situ XRD and ex-situ TEM, which reveals the intercalation mechanism for both LIBs and intercalation combined with conversion mechanisms for SIBs.

Fe3O4/Fe/C composites prepared by a facile thermal decomposition method and their application as microwave absorbers

The Fe3O4/Fe/C composites used as microwave absorbers were synthesized by a facile thermal decomposition method using sodium chloride as a template. The hierarchical flower-like structure was obtained by thermally treating the precursors at 600 °C for 2 h under a nitrogen atmosphere with a heating rate of 5 °C/min. Based on the complex permittivity and permeability results, the Reflection loss (RL) of the Fe3O4/Fe/C composites were calculated. The Fe3O4/Fe/C composites show a RL peak of −51.3 dB for a 2 mm thick positioned at 17.2 GHz frequency. When the absorber thickness was adjusted to 2.3 mm, the effective adsorption bandwidth (RL ≤ −10 dB) is 5.6 GHz (12.4–18 GHz) frequency. Simultaneously, the RL peak of the absorber still reaches −40.8 dB at 14.7 GHz frequency. The RL peak is explained using the quarter-wave cancellation model. The microwave absorption behavior of Fe3O4/Fe/C composites can be attributed to the reasonable impedance matching and the existence of interfaces around the composites. Our findings offer an effective way to design and synthesis the excellent microwave absorber of Fe3O4/Fe/C composite.

Controlled synthesis of unique Co9S8 nanostructures with carbon coating as advanced electrode for solid-state asymmetric supercapacitors

Stimulated by both the rich electrochemical properties and unique structural merits, much attention is directed to construct novel cobalt sulfides nanoarchitectures for energy storage devices. Here, carbon-coated cobalt sulfide nanostructures are fabricated with the assistance of polyvinylpyrrolidone during hydrothermal process. The morphology of carbon-coated cobalt sulfide can evolve from well-defined uniform nanooctahedrons, nanoflowers to nanospheres by simply controlling the polyvinylpyrrolidone amount. Remarkably, the unique carbon-coated cobalt sulfide configuration takes full advantage of the synergistic contributions from both the homogeneous incorporated carbon layer and the ideal hierarchical flowerlike structures, thereby making it to be a suitable electrode for supercapacitors. By virtue of the intriguing structural features of carbon-coated cobalt sulfide, a solid asymmetric supercapacitor based on carbon-coated cobalt sulfide nanoflowers as the positive electrode and active carbon as the negative electrode achieves remarkable cycling stability (around 86% capacitance retention even up to 10,000 times), and outstanding energy density of 40 Wh kg−1 at power density of 850 W kg−1. The exceptionably electrochemical performance of the asymmetric supercapacitor is related to the enhanced electrical conductivity and increased electrode/electrolyte contact area of carbon-coated cobalt sulfide. Thus, the as-prepared carbon-coated cobalt sulfide nanoflowers is demonstrated to be a promising electrode for asymmetric supercapacitors.

Calcium extraction and synthesis of precipitated calcium carbonate from Mg-rich dolomite

Abstract A green-reaction assisted synthesis using a natural occurring dolomite is reported for precipitated calcium carbonate production over aloe barbadensis miller extract template under ambient condition. Uniform, hierarchical aragonite precipitated calcium carbonate stacked from nanoparticles was synthesized. The tainted Mg influence on resultant PCC purity was averted via D-glucose extraction of dolomite constituent calcium and subsequent precipitation using CO2. The as-synthesized PCC was characterized using SEM, XRD, PSD, and FTIR spectroscopy. Under ambient conditions using carbonation route and 1 L/min CO2 flowrate, aragonite polymorph with hierarchical flower-like structure was produced. Energy is conserved as heat is not required for phase transformation. Minerals & Environment (RAMM) 2018.

Surface Area- and Structure-Dependent Effects of LDH for Highly Efficient Dye Removal

The surface area and structure of adsorbents are crucially important to its adsorption capacity. Herein, we focused on the correlation between the structures of 2D/3D materials and its adsorption properties by taking three kinds of cobalt–aluminum layered double hydroxide (CoAl-LDH) as adsorbents, including a 3D hierarchical flower-like hollow/solid sphere (FH/FS-CoAl) and 2D plate (P-CoAl). As expected, FH-CoAl showed the highest adsorption capacity (∼2189.23 mg/g) for methyl orange (MO), benefiting from the highly accessible surface areas and more active sites of unique hollow structural characteristics inherited from the hierarchical flower-like hollow structures. Interestingly, compared with FS/FH-CoAl, P-CoAl exhibited the highest adsorption capacity enhancement times after being normalized with surface area, but displayed an inferior maximum adsorption capacity. The reasons could be mainly ascribed to (1) P-CoAl with 2D plate structures possessed more fully exposed active sites than FH-CoAl and (2) ...

Effect of solvents and reaction parameters on the morphology of Ta2O5 and photocatalytic activity

We report a facile and efficient hydrothermal method for the controlled preparation of tantalum oxide (Ta2O5) flower-like hierarchical structures. The formation of flower-like hierarchical structure is systematically studied by tuning the reaction parameters such as precursor amount, reaction time, reaction temperature, hydrofluoric acid (HF) volume, hydrochloric acid (HCl) concentration and propanol-HCl volume ratio. The results reveal that simply altering the reaction conditions can easily modulate the morphology of the resultant Ta2O5 product. The growth mechanism for the formation of flower-like hierarchical structures has been proposed, where HF and propanol play a key role. A comparative study for photocatalytic hydrogen production was conducted by calcinating the product at 450 °C and 700 °C. The product calcinated at 450 °C revealed a higher photocatalytic activity than that calcined at 700 °C. The successful and convenient preparation of flower-like hierarchical structures can be easily scaled up and extended for the designing and fabrication of 3D hierarchical structures and visible-light driven heterostructures nanomaterial for energy production, environmental remediation and optical devices.

Tuning the morphological structure, light absorption, and photocatalytic activity of Bi2WO6 and Bi2WO6-BiOCl through cerium doping

Pharmaceuticals and personal care products are recognized as new classes of water pollutants that receive considerable attention because of their negative environmental impact on aquatic life and humans. Because microbiological and/or conventional secondary physicochemical treatments cannot completely remove those water pollutants, effective advanced oxidation processes using semiconductor-based photocatalysts are needed to ensure their total elimination in water. Here, we report on the tuning of the morphological structure, light absorption, and photocatalytic activity of Bi2WO6 and Bi2WO6-BiOCl through cerium doping. Non-doped and Ce-doped Bi2WO6 and Bi2WO6-BiOCl powders are synthesized by a hydrothermal method, and their adsorption ability and photocatalytic activity are evaluated for the removal of salicylic acid in the dark and under visible light irradiation, respectively. The adsorption affinities and preferential sites of salicylic acid molecules on non-doped and Ce-doped Bi2WO6, BiOCl, and Bi2WO6-BiOCl are computationally predicted using molecular dynamics simulations. When ethylene glycol is replaced by dilute HCl as a solvent in a hydrothermal system, BiOCl is also formed along with Bi2WO6, confirming the successful formation of a Bi2WO6-BiOCl composite. The flower-like hierarchical structures of Bi2WO6 and Bi2WO6-BiOCl can absorb more photon energy due to multiple scattering, charge carriers can easily transfer to the surface/interface, and mesopores can improve the transfer rate of organic molecules, contributing to the overall enhancement in photocatalytic activity. The Bi2WO6-BiOCl samples show higher photocatalytic activity than that of the Bi2WO6 samples for the degradation of salicylic acid due to the formed p–n heterojunction. The optimum concentration of Ce doping is found to be 1 mol% in the Bi2WO6 and Bi2WO6-BiOCl, promoting the effective separation and transfer of photogenerated charge carriers, resulting in high photocatalytic performance, and the sample exhibited good stability.

A Facile Approach for the Synthesis of Zn₂SnO₄/BiOBr Hybrid Nanocomposites with Improved Visible-Light Photocatalytic Performance.

In this study, a novel Zn2SnO4/BiOBr hybrid photocatalyst was prepared via a mild hydrothermal synthesis combined with a chemical deposition method. The morphological structure, chemical composition, crystal structure, and optical properties were comprehensively characterized by a series of measurement techniques. Morphological observation showed that fine Zn2SnO4 nanoparticles were anchored on the nanoplate surface of a flower-like BiOBr 3D hierarchical structure. The experimental results of UV-vis diffuse reflection spectroscopy revealed that the visible-light absorptive capacity of the Zn2SnO4/BiOBr hybrid photocatalyst was promoted, as compared to that of pure Zn2SnO4. Evidenced by electro-negativity theoretical calculation, Zn2SnO4 and BiOBr possessed matched band edges for accelerating photogenerated charge separation at the interface. The Zn2SnO4/BiOBr hybrid photocatalyst exhibited enhanced photocatalytic performance in the degradation of Rhodamine B (RhB) under visible light irradiation. According to the band energy structure and the experimental results, the enhanced photocatalytic performance was ascribed to the improved visible-light absorptive capacity and the contact interface between Zn2SnO4 nanoparticles and BiOBr nanoplates, being able to favor the prompt charge migration and suppress the recombination of photogenerated carriers in the hybrid system.

Hierarchical layered double hydroxides with Ag nanoparticle modification for ethanol sensing

Layered double hydroxides (LDHs) have recently been revealed to be promising in gas sensor applications due to their compositional flexibility and unique 2D-interlayer channel for gas diffusion and adsorption. This work demonstrates highly porous hierarchical LDHs containing Mg2+ and Al3+ (MgAl-LDHs) for ethanol sensing at room temperature. These MgAl-LDHs, with unique flower-like hierarchical structure and mesoporous interlayer, were synthesized hydrothermally using sodium dodecyl sulfate as soft template as well as intercalating agent. Further modification by discrete Ag nanoparticles (NPs) was achieved via an environmentally friendly glucose-reduction method to improve the gas-sensing response of the LDH-based sensor. It is found that the hierarchical MgAl-LDHs show potential in sensing ethanol gas with rapid dynamic characteristics at room temperature; their response magnitude towards ethanol can be enhanced significantly by Ag NP modification. The gas-response value of the Ag-modified MgAl-LDH sensor is about twice that of pristine MgAl-LDH sensors, towards 5–200 ppm ethanol at room temperature. Meanwhile, rapid response-recovery characteristics are achieved, with response and recovery times shorter than 10 and 50 s, respectively. The satisfactory sensing performance and remarkable response enhancement by Ag NP modification are demonstrated in terms of the unique microstructure of the hierarchical MgAl-LDHs and a constructed conductive effect model of Ag functionalized LDHs.

Synthesis of hierarchical superhydrophobic zinc oxide nano-structures for oil/water separation

Superhydrophobic hierarchical ZnO nano-structures were prepared by a convenient, inexpensive and reproducible method using no low surface energy additives or modifiers. Chemical composition and morphological properties of samples were characterized by SEM, TEM, XRD, and Raman analyses. The SEM images of resulted ZnO particles exhibited a hierarchical flower-like micro-nano dual-scale structure composed of nano-needles. The average tip diameter and length of the needles were approximately 90 nm and 1.5 µm, respectively. The prepared hierarchical sample displayed considerably high water contact angle (WCA = 163.8 ± 1.5°) and low contact angle hysteresis (CAH = 1.2°), indicating excellent superhydrophobic properties. The surface wettability was reversibly switched between super hydrophilicity and superhydrophobicity by altering the annealing temperature. A packed layer of the superhydrophobic product was applied for oil/water separation exhibiting high separation efficiency (>95%) and a high flux (2540 Lm−2 h−1). The variations of WCA and CAH values versus water immersion time were evaluated to examine the durability of the particles. Results confirmed that the obtained samples have an extremely high robustness after 12 h dipping in water.

Hierarchical Structure Formation and Effect Mechanism of Ni/Mn Layered Double Hydroxides Microspheres with Large-Scale Production for Flexible Asymmetric Supercapacitors

In this study, Ni/Mn layered double hydroxides (LDHs) microspheres with three-dimensional flower-like hierarchical structure are fabricated by a large-scale and self-assembled chemical coprecipitation strategy (at 55 °C under normal pressure). In each integrated microsphere, the petals consist of ultrathin two-dimensional nanosheets. The self-assembly formation mechanism of this flower-like construction is systematically investigated according to the analysis results from the regulation of various reaction factors. The Ni/Mn LDHs microspheres show an optimal capacitance value as high as 1379 F·g–1 at 1 A·g–1. Sum frequency generation spectroscopy and charge storage behavior mechanism analysis further demonstrate that a favorable capacitive constitution is indeed dependent on the synergistic effect of active sites (different feed ratios) and surface area (different architectural features). Moreover, a novel flexible all-solid-state asymmetric supercapacitor is assembled by exploiting these microspheres and...

Photocatalytic degradation of organic pollutants using surfactant-free hydrothermally prepared flower-like BiOBr hierarchical structures under visible light irradiation

Flower-like BiOBr hierarchical structures were successfully prepared via a facile hydrothermal route in the absence of any surfactants. Various characterization tests were carried out to analyze the as-prepared BiOBr samples. By utilizing the flower-like BiOBr as photocatalysts, enhanced photocatalytic performance on the sunset yellow degradation was observed in comparison with the BiOBr nanosheets and commercial TiO2. The photocatalytic enhancement was ascribed to the unique hierarchical porous surface structure with good crystallinity and optical properties, which could improve the electron-hole pairs separation and led to high yield of reactive oxygen species for photocatalytic reaction. Other organic pollutants such as bisphenol A and methylparaben were also successfully degraded over flower-like BiOBr under similar experimental conditions.

Self-Assembled Hybrid Nanoflowers of Manganese Phosphate and l-Arabinose Isomerase: A Stable and Recyclable Nanobiocatalyst for Equilibrium Level Conversion of d-Galactose to d-Tagatose

We report on the synthesis and characterization of a novel hybrid nanoflower of manganese and l-arabinose isomerase and its application in synthesis of d-tagatose, a rare sugar of high commercial value. An open reading frame of 1425 base pairs from Lactobacillus sakai was used to synthesis recombinant l-arabinose isomerase of 474 amino acids in E. coli. A hierarchical flower-like spherical structure with several nanopetals was self-assembled by using purified recombinant l-arabinose isomerase as the organic component and manganese phosphate as the inorganic component. The hybrid nanoflower was characterized by scanning electron microscopy, high-resolution transmission electron microscopy, confocal laser scanning microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Circular dichroism documented no change in structural properties of l-arabinose isomerase assembled in the hybrid nanoflower. Kinetic parameters of l-arabinose isomerase were improved ...

Preparation of hierarchical β-Ni(OH)2 nanostructures and adsorption characterization of methyl orange dye

The β-Ni(OH)2 nanostructures have been prepared by hydrothermal with ammonia as alkali source. The morphology of β-Ni(OH)2 evolves from hexagon sheets to flower-like hierarchical structure built up from the nanosheets as increasing the amount of ammonia. Hierarchical β-Ni(OH)2 nanostructures have strong adsorption effect on methyl orange dyes. The adsorption mechanism of β-Ni(OH)2 has been investigated, which could be expressed by pseudo-second order kinetic model with best match.

Nickel hierarchical flower-like nanostructures: Controlled synthesis and catalytic hydrogenation of toluene

Nickel (Ni) nanocrystals with a flower-like shape were successfully fabricated through a low temperature solution-phase approach without using any template or surfactant. The structures and morphologies of the as-synthesized Ni nanocrystals were systematically characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller surface analysis. Further, the magnetic property was also analyzed using a vibrating sample magnetometer (VSM). The characterization results showed that the entire structure of the products with diameter of around 500 nm was composed of several nanocones connected with each other through the center to form the three-dimensional hierarchical flower-like structures. Moreover, the orientation and morphology of the products could be carefully controlled by adjusting the reaction temperature, the growth time, and the reaction solvent. Furthermore, a possible formation mechanism of the hierarchical flower-like Ni nanostructures was also proposed based on the detailed characterization analysis. Besides, the series of Ni nanocrystals was studied for the catalytic hydrogenation of toluene to methylcyclohexane. It was found that the hierarchical flower-like Ni nanostructures obtained at 80 °C for 2 h showed an optimal catalytic performance among all the Ni catalysts tested, and correspondingly a 100% hydrogenation of toluene was achieved with in 30 min under the relatively mild reaction conditions. The merits including excellent durability, sound productivity, and superior catalytic performance make the hierarchical Ni nanocrystals as promising catalysts for the practical industrial application.

Confining SnS2 Ultrathin Nanosheets in Hollow Carbon Nanostructures for Efficient Capacitive Sodium Storage

Summary Tin disulfide (SnS 2 ) is a promising anode material for sodium-ion batteries because of its high specific capacity. However, the low conductivity and large volume change during reaction with Na + ions greatly limit its practical application. Herein, a multistep templating method has been exploited for the rational design and synthesis of SnS 2 nanosheets confined in carbon nanotubes (SnS 2 @CNTs). To demonstrate the universality of this method, SnS 2 nanosheets confined in carbon nanoboxes (SnS 2 @CNBs) and hollow carbon nanospheres (SnS 2 @CNSs) have also been synthesized by simply changing the template in the reaction system. Due to their unique structural merits, the SnS 2 @CNTs, SnS 2 @CNBs, and SnS 2 @CNSs show improved sodium storage performance in terms of high specific capacity, good cycling stability, and superior rate capability.

Photocatalytic Activity of ZnV2O6/Reduced Graphene Oxide Nanocomposite: From Theory to Experiment

A nanocomposite of ZnV2O6 with hierarchical flower-like structure hybridized with reduced graphene oxide (rGO) was fabricated using a facile hydrothermal approach. The structure, morphology, optical and electronic properties were explored using comprehensive analytical techniques. The results revealed that the rGO sheets were decorated with the in situ-formed ZnV2O6 nanoparticles yielding a well-combined composite structure. The photocatalytic activity of as-prepared ZnV2O6/rGO hybrids is 2.48 times larger than that of pristine ZnV2O6 for the degradation of Rhodamine B (RhB). In parallel to the experimental results, the basic mechanisms of interfacial interaction, charge transfer/separation and subsequently their influence on the photocatalytic activity were theoretically studied by first-principles calculations. The photocatalytic enhancement is attributed to efficient interfacial electron transfer from ZnV2O6 to rGO, leading to a prolonged lifetime of photoinduced charge carriers. We anticipate that these results will lead to new insights in the judicious design of graphene-based semiconductor photocatalysts.

A Different View of Solvent Effects in Crystallization

Solvents are widely used in crystallization, but their effects on the shape development of crystals are under debate. Here, we report a view on how solvents play their role by considering the viscosity of solvents. We synthesize silver particles in a mixture of alcohol and water. The viscosity of the solvent is changed by varying the volume ratio of alcohol in water. With the variation of viscosity, diverse morphologies of silver particles are synthesized. Small cubic crystals are formed at low viscosity, while hierarchical flower-like particles are formed at high viscosity. Two alcohols are employed, namely ethanol and propanol. No matter which alcohol is employed, the results are similar. Due to the limitation of mass transfer at high viscosity, the particles synthesized in such solvent are smaller and stabilized by the solvent. When the solution containing these particles are dropped onto metal substrates, these tiny particles firstly aggregate, which is followed by classic crystallization, forming flower-like hierarchical structures. These findings show the importance of the viscosity of solvents in shaping particles, which is underestimated previously.

Fabrication and Enhanced Visible-light Photocatalytic Activity of Pt/Bi2WO6 Composite with Hierarchical Flower-like Structure

Visible light activated Bi2WO6 was synthesized by the precipitation method with hydrothermal techniques firstly. And then a series of Pt/Bi2WO6 composite micro-flowers (Pt mass concentration: 0.5%, 1.0%, 1.5%, 2.0%) assembled by Bi2WO6 nano-sheets were synthesized by photo-deposition method. The products were characterized by X-ray diffraction (XRD), UV-vis diffusion absorption spectroscopy (DRS), high resolution scanning electron microscopy (HRSEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the products was evaluated by degradation of rhodamine B (RhB) under a Xenon lamp irradiation (λ>420nm). The results showed that sample synthesized at 180°C for 12h (pH=4) had a 3D hierarchical flower-like structure and excellent photocatalytic activity. After photo-deposition of Pt on the surface, the morphology of the sample did not change obviously. However, its photocatalytic activity was greatly enhanced. The products with 1.0% mass ratio of Pt to Bi2WO6 exhibited the highest RhB degradation of 86.5% under visible light irradiation in 120 min, much higher than that of pure Bi2WO6 with RhB degradation of 36.4%. The stability test showed that no obvious loss of photocatalytic activity of the product was detected after four cycles.