Hierarchical Flower-like Microspheres Research Articles

Unveiling a cutting-edge bi-ligand nickel metal-organic framework as an electrode material for symmetric supercapacitors

Perylene diimide (PDI)-based MOFs feature a substantial specific capacitance, terrific cycle durability, swift charge/discharge rates, exceptional chemical as well as thermal endurance, diversity in electrode design, and inexpensive production costs. In light of these benefits, PDI-based MOFs are intriguing options for utilization in energy storage. Inspired by the distinctive features of perylene diimide-based ligands, highly conjugated and nitrogen-rich organic ligands Perylene diimide-L-dopa (PDI-L-Dopa) were incorporated to create the Ni-MOF architecture. The resulting hierarchical flower-like microspheres of bi-ligand Ni-MOF had better electron transport, conductivity, and wettability. When applied as electrode material in a three-electrode system considering a specific capacitance of 198 F/g at a current density of 1 A/g, the Ni-MOF-24 h electrode showcased beneficial electrochemical efficiency. XRD, FT-IR, and XPS were used to validate the formation of Ni-MOF and disclose the exact chemical composition and valence state inside the material. The hierarchical flower-like microsphere structure of the Ni-MOF, formed of 2D petal-like nanosheets, was revealed by FE-SEM and TEM. Additionally, when Ni-MOF-24 h electrodes used to fabricate symmetric supercapacitor (SSC), it reveals a high energy density (Ed) of 23 Wh/kg at a corresponding power density (Pd) of 600 W/kg along with extraordinary cyclic stability over 10,000 charge/discharge cycles with retaining 99 % of the initial capacitance. This research sheds light on the design and manufacture of innovative materials for long-term and efficient energy storage devices based on MOFs.

Dual co-catalysts Ag/Ti3C2/TiO2 hierarchical flower-like microspheres with enhanced photocatalytic H2-production activity

Solar-powered semiconductor photocatalysis is considered a powerful strategy for addressing environmental pollution and energy crisis. Nevertheless, the separation and transfer abilities of photogenerated photocatalysts remain unsatisfactory. Herein, dual Ti3C2 nanosheets/Ag co-catalysts synergistically decorated hierarchical flower-like TiO2 microspheres for boosting photocatalytic H2 production were fabricated by electrostatic self-assembly and subsequent photoreduction procedures. The optimal Ag/Ti3C2/TiO2 composite demonstrated an excellent photocatalytic H2-production rate of 1024.72 μmol g−1 h−1 under simulated solar irradiation, achieving nearly 40, 2.3, and 1.8 folds with respect to that obtained on pristine TiO2, optimized Ti3C2/TiO2 composite, and Ag/TiO2 composite, respectively. The considerably improved photocatalytic H2-production activity is associated with the synergistic effect of the hierarchical flower-like structure of TiO2, excellent electrical conductivity of Ti3C2, and surface plasmon resonance effect of Ag, which enhances the light absorption capacity and promotes the separation and transfer of photogenerated carriers. This study provides insight into the design of high-efficiency photocatalysts with dual co-catalysts for solar H2 production.

Enhanced photocatalytic activity for degradation of ofloxacin and dye by hierarchical flower-like ZnS/MoS2/Bi2WO6 heterojunction: Synergetic effect of 2D/2D coupling interface and solid sulfide solutions

To strengthen the photocatalytic degradation of antibiotics and organic dyes, the band structure engineering serves as an efficient approach, which can be realized by constructing heterostucture photocatalysts. Herein, 0D/2D/2D ZnS/MoS2/Bi2WO6 (ZMB) hierarchical flower-like microspheres were smoothly prepared via in-situ growth of Bi2WO6 nanoparticles on ZnS/MoS2 surfaces. The results illustrated that the content of Bi2WO6 played a crucial role in regulating the photocatalytic activity of ZMB heterostructures. ZMB-7 showed a better degradation capacity compared to ZnS/MoS2 and other ZMB composites, and the degradation rates of ofloxacin (OFL) and rhodamine B (RhB) respectively reached 98.5% and 91.1% under light illumination. The enhanced photocatalytic activity could be attributed to the large specific surface, improved separation of photogenerated carriers, as well as rapid charge transfer by combining the advantage of 2D coupling interfaces generated from MoS2/Bi2WO6 and composition-controlled band gap in solid sulfide solutions. On the basis of active species trapping experiments and HPLC-MS tests, a possible photocatalytic mechanism and gradation pathway for OFL were further proposed. The ternary ZnS/MoS2/Bi2WO6 heterojunction with enhanced photocatalytic activities in the work may have vital applications for environmental purification owing to its synergistic effects between composition and microstructure.

Controllable preparation and photocatalytic activity of hierarchical flower-like microspheres clustered by ZnO porous nanosheets

• 3D hierarchical flower-like microspheres clustered by ZnO porous nanosheets were prepared. • The average pore size can be controlled by the calcination temperature. • The CV degradation rate of the optimum sample is high up to 77.6%. • The high photocatalytic activity originates from the high separation efficiency of photogenerated electrons and holes proved by the photocurrent, impedance and fluorescence emission decay. The zinc carbonate hydroxide hydrate was prepared by the hydrolysis reaction between zinc nitrate and urea at 90 °C for 12 h. Then, the hierarchical flower-like microspheres clustered by ZnO porous nanosheets are obtained by calcination of precursor zinc carbonate hydroxide hydrate without structure deformation. The ZnO porous nanosheets were characterized by XRD, TEM, SEM, BET, UV–Vis absorption, photocurrent, impedance and fluorescence emission decay. The average pore size can be controlled from 11.77 to 49.53 nm with the calcination temperature increased from 300 to 500 °C. The ZnO porous nanosheets show well photocatalytic activity for degradation of crystal violet. Besides, the ZnO porous nanosheets calcined at 400 °C exhibit the highest photodegradation rate, due to the highest separation efficiency of photogenerated charge carriers with the highest photocurrent, the lowest migration resistance and the longest fluorescence emission decay lifetime.

Alkaline aqueous rechargeable Ni-Fe batteries with high-performance based on flower-like hierarchical NiCo2O4 microspheres and vines-grapes-like Fe3O4-NGC composites

Aqueous rechargeable secondary Ni-Fe batteries have attracted extensive attention due to low cost, relatively outstanding safety and high energy density. However, the nickel/iron electrode materials also suffer from poor conductivity and week cycling performance. In this study, we have modified the CNT-S-PEGm as electron transport channels with methoxypolyethylene glycol (mPEG) via thiol-ene click to further provide more reactive sites, and then prepared the cathode materials of 3D flower-like hierarchical microspheres of NiCo2O4-CNT-S-PEGm composites by a solvothermal method. The as-prepared cathode materials reveal the capacity of 195.7 mAh g−1 at 0.5 A g−1. In addition, the anode materials of vines-grapes-like Fe3O4-N-rGO-CNT>N-PEGm (Fe3O4-NGC) ternary composites have been prepared in a typical hydrothermal method. Notably, the promising Fe3O4-NGC anode materials exhibit the highest capacity of 308.1 mAh g−1 at 1 A g−1. Due to such excellent attributes, the alkaline aqueous rechargeable Ni-Fe batteries of NiCo2O4-CNT-S-PEGm//Fe3O4-NGC have been successfully fabricated. Moreover, the as-assembled device displays the high capacity of 77.8 mAh g−1 at 0.5 A g−1 and the energy density of 64.4 Wh kg−1 at 414 W kg−1 for potential energy storage.

Cobalt ferrite microspheres as a biocompatible anode for higher power generation in microbial fuel cells

In the present study, spinel cobalt ferrite hierarchical flower-like microspheres (CoFe2O4-MS) are fabricated using a hydrothermal method and utilized as a biocompatible anode in microbial fuel cells (MFCs) for power generation. A maximum power density of 1964 mW m−2 is achieved with CoFe2O4-MS in a mediator-less MFC using Escherichia coli as a biocatalyst and glucose as a fuel. The unprecedented power generation by CoFe2O4-MS can be attributed to (i) the morphology of the flower-like CoFe2O4-MS, with a rough surface and large surface area suitable for biofilm formation, (ii) the rapid immobilization of negatively charged E. coli cells on the positively charged CoFe2O4-MS, facilitating stronger bacterial adhesion between the bacterial cells and CoFe2O4-MS, which leads to lower contact resistance and advantageous interfacial properties with rapid electron transfer, and, more importantly, (iii) enhanced interfacial charge transfer due to the presence of multi-valent cations and multiple valence states in the highly electrocapacitive CoFe2O4-MS. Thus, the enrichment of electroactive E. coli on CoFe2O4-MS produces a large number of electron-shuttling endogenous redox mediators, which promotes efficient extracellular electron transfer between E. coli and the electrocapacitive CoFe2O4-MS during the oxidation of the substrate, thus generating higher power output.

Novel Z-scheme MoS2/Bi2WO6 heterojunction with highly enhanced photocatalytic activity under visible light irradiation

In this study, novel Z-scheme MoS2/Bi2WO6 (MB) heterostructured hierarchical flower-like microspheres were successfully prepared via an in-situ growth method on exfoliated MoS2 nanosheets. Experimental results indicated that the content of MoS2 played a key role in controlling the morphology and photocatalytic activity of MB heterostructures. MB-9 exhibited a highly enhanced photocatalytic activity under visible light irradiation compared to pure MoS2, Bi2WO6 and other MB composites, which can be ascribed to the stable Z-scheme heterostructure, leading to the efficient transfer and the separation of photoinduced electrons and holes. The photocatalytic degradation efficiency of rhodamine B (RhB) can reach 100% within 90 min and almost all of Pseudomonas aeruginosa (P. aeruginosa) can be killed after 60 min by MB-9. In addition, MB-9 displayed a nice stability during the photocatalytic process, which favored a long-term use. Moreover, a possible photocatalytic mechanism was proposed based on the active species trapping experiments and electron spin resonance (ESR) tests, verifying that the photogenerated holes (h+) and ⋅O2− radicals were the dominating active species, which followed the Z-scheme reaction mechanism. It is hoped that this work can provide valuable information on developing novel Z-scheme heterostructures with enhanced photocatalytic activities for potential environmental purification and energy conversion.

Fabrication of Co3O4 and Au co-modified BiOBr flower-like microspheres with high photocatalytic efficiency for sulfadiazine degradation

For the first time, we fabricated Au-BiOBr-Co3O4 hierarchical flower-like microspheres by hydrothermal and photo-deposition methods. Au and Co3O4 nanoparticles (NPs) were selectively deposited on the {0 0 1} and {1 1 0} facets of BiOBr nanopetals, respectively. The light absorption, photoluminescence (PL), and electrochemical analyses revealed that the selectively deposited Au and Co3O4 can effectively enhance both the visible-light absorption and charge carrier separation in space. The photocatalytic degradation of sulfadiazine (SD) indicated that the degradation of SD follows the pseudo-first-order reaction and the reaction rate constant was increased 17 times from BiOBr flower-like microspheres (0.00014 min−1) to Au and Co3O4 co-modified Au-BiOBr-Co3O4 flower-like microspheres (0.00254 min−1). From the high performance liquid chromatography-mass spectrometry (HPLC-MS) measurement, it was disclosed that the desulfonated and bromized products are the main intermediates during SD degradation over Au-BiOBr-Co3O4. Meanwhile, the reactive species trapping experiments confirmed that Au-BiOBr-Co3O4 can produce h+, O2−, and Br0 reactive species responsible for antibiotic degradation. On the basis of these experiment results and discussion, the degradation mechanism of SD over Au-BiOBr-Co3O4 was tentatively discussed. We think this work provides a reference to fabricate novel photocatalytic materials for the effective degradation of antibiotics.

Fabrication of 3D Co-doped Ni-based MOF hierarchical micro-flowers as a high-performance electrode material for supercapacitors

Ni-based metal organic frameworks have attracted great interests as novel electrode materials for applications in supercapacitors, in virtue of their large specific surface area, high porosity and diverse coordination structure. Unfortunately, their specific capacitance and rate property are usually unsatisfying because of the poor conductivity of MOF materials. Herein, 3D Co-doped Ni-based MOF (Cox-Ni-MOF, x = 100n (Co/Ni) = 0.5, 2 and 5) flower-like hierarchical microspheres are prepared via a facile hydrothermal process. The introduction of Co promotes the electrochemical behaviors of Ni-MOF, especially Co2-Ni-MOF. It exhibits a prominent specific capacitance of 1300 F/g at 1 A/g along with a superb rate performance (1021 F/g at 10 A/g). Meanwhile, capacitance for Co2-Ni-MOF retains 71% of the original capacitance even after 3000 cycles. The improvement of electrochemical performance could be due to their unique structural and morphological characteristics including the 3D flower-like hierarchical microspheres structure, higher specific surface area and enhanced electrical conductivity. Moreover, a hybrid supercapacitor based on the Co2-Ni-MOF achieves an excellent energy density of 25.92 Wh/kg at a power density of 375 W/kg.

Anion De/Intercalation in Nickel Hydroxychloride Microspheres: A Mechanistic Study of Structural Impact on Energy Storage Performance of Multianion-Containing Layered Materials

Electrochemical cation de/intercalation has long been investigated for energy-relevant applications, while anion de/intercalation is comparatively highly challenging, although promising for promoting the performance of materials. Herein, layered nickel hydroxychloride was selected as a model multianion-containing inorganic functional material to study. Hierarchical flower-like microspheres self-assembled from nanosheets were synthesized via a solvothermal method. The as-prepared nickel hydroxychloride was built up from neutral layers of [Ni(OH)3/3Cl3/3] octahedra, showing an expanded interlayer spacing of 0.57 nm. With this unique microstructure, Cl– deintercalation and OH– intercalation were accomplished through an effective nonelectrochemical process. The nickel hydroxychloride Ni(OH)0.99Cl1.01 with a maximum Cl– ion content was found to possess the largest interlayer spacing, which when first employed as electrode materials for supercapacitor, delivered an ultrahigh specific capacitance of 3831 F/g at ...

A Facile Method To Prepare Novel Ag2O/Ag2CO3 Three-Dimensional Hollow Hierarchical Structures and Their Water Purification Function

A facile, green, and low-cost method to prepare novel Ag2O/Ag2CO3 three-dimensional hollow flowerlike hierarchical microspheres has been demonstrated. The microspheres were obtained by simple injection of Na2CO3 aqueous solution into AgNO3 ethanol solution. The surface morphology of the microspheres was relatively smooth, trumpet flowerlike hole, and flowerlike shallow hole when the reaction temperature was 8, 25, and 70 °C, respectively. They were assembled by nanoparticles. The microsphere prepared at 25 °C was composed of 86.3% Ag2CO3 and 13.7% Ag2O. The HTEM image indicates that the Ag2CO3 microsphere is wrapped by a thin Ag2O layer, and there is a heterojunction between Ag2CO3 and Ag2O. The study of the formation mechanism demonstrates the first example of using water-soluble Na2CO3 as templates to prepare 3D hierarchical microstructures. The Ag2O/Ag2CO3 microspheres prepared at 25 °C have excellent adsorption and photocatalysis activity for Congo red (CR). The adsorption behavior of the Ag2O/Ag2CO3 ...

Effect of Experimental Parameters on the Hydrothermal Synthesis of Bi2WO6 Nanostructures.

Bi2WO6 nanostructures were synthesized by a hydrothermal route, where the effect of various experimental parameters on the products was investigated. It is demonstrated that the sample morphology and size is highly dependent on the NaOH content (or pH value). At CNaOH = 0–0.0175 mol (pH range of 1–4), the prepared samples present flower-like hierarchical microspheres which are constructed from thin nanosheets via the self-assembly process. The size of the hierarchical microspheres exhibits a decreasing trend with increasing the NaOH content, from 7 μm at CNaOH = 0 mol to 1.5 μm at CNaOH = 0.0175 mol. At CNaOH = 0.03–0.0545 mol (pH: 5–9), the prepared samples exhibit irregular flake-like structures, and their size increases with the increase in NaOH content. At CNaOH = 0.055–0.05525 mol (pH: 10–11), the prepared samples are composed of uniform sphere-like particles with an average size of 85 nm. Compared to the NaOH content, the reaction temperature and time has a relatively small effect on the product morphology and size. The photocatalytic activity of the samples was evaluated by degrading rhodamine B (RhB) under irradiation of simulated sunlight. Among these samples, the samples composed of flower-like hierarchical microspheres have relatively high photocatalytic activity. In particular, the microspheres prepared at CNaOH = 0.01 mol exhibit the highest photocatalytic activity, and the degradation percentage reaches 99 % after 2 h of irradiation.

Poly(vinyl pyrrolidone)-assisted hydrothermal synthesis and enhanced visible-light photocatalytic performance of oxygen-rich bismuth oxychlorides

A series of novel oxygen-rich bismuth oxychloride (Bi12O17Cl2) were synthesized through a facile poly(vinyl pyrrolidone) (PVP)-assisted hydrothermal route. These obtained Bi12O17Cl2 samples were characterized by various physicochemical techniques. It was found that a proper addition amount of PVP could promote the transformation of Bi12O17Cl2 morphology from irregular clusters to three-dimensional hierarchical flower-like microspheres that were nominated as sample BP2. As-synthesized samples were subjected to a photocatalytic degradation of dye Rhodamine B (RhB) or 2,4-dichlorophenol (2,4-DCP) under visible light. Among all candidates, the sample BP2 with a hierarchical flower-like morphology showed the best degradation efficiency for RhB and 2,4-DCP. The apparent rate constant of sample BP2 in terms of degradation of RhB was nearly 5.7 and 45times that of unmodified BP0 and N-TiO2. The enhanced photocatalytic performance could be ascribed to synergetic effects including unique hierarchical morphologies, large specific surface area, small particle size, good crystallinity, and suitable band structures. A possible mechanism of catalytic degradation was finally proposed basing upon the active species trapping experiments.

Synthesis of CdS flower-like hierarchical microspheres as electrode material for electrochemical performance

We report in this paper, a facile hydrothermal route for the preparation of CdS nanocrystals at room temperature (RT). Composition, structure and morphology of the products were analyzed and characterized by X-ray diffraction (XRD) confirms that the hydrothermal treatment at 180 °C for periods ranging from 0 to 1440 min caused no significant modification of the long range order structure subjected to hydrothermal treatment. From the XRD analysis the diffraction peaks pertaining to 26.75°, 43.89° and 52.34° are attributed to the (111), (220) and (311) planes of cubic zinc blende structure. The Photoluminescence (PL) spectra are dominated by a strong narrow band edge emission tunable in the blue region of the visible spectra indicating the narrow size distribution of CdS nanocrystals. TEM observation shows that the CdS nanocrystals synthesized by hydrothermal synthesis are well dispersed and the average crystallite size was found to be ∼10 nm. The confocal microscopic studies reveal that each flower like spheres is due to Ostwald's ripening with numerous nanoparticles aggregating a surface.

Synthesis of 3D Flower-Like SnO2 with Hierarchical Nanostructure and High Reversible Capacity as Lithium-Ion Battery Anode

We report a route for large-scale synthesis of three-dimensional flower-like SnO2 microspheres. The prepared material was composed of special wedge-shaped nanorods with tetragonal and smooth square end planes. The obtained samples were characterized by x-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. A formation mechanism is proposed. The morphological evolution of a SnO2 sample from hierarchical flower-like microspheres to nanorods was observed. Time-dependent experiments illustrated that the hydrothermal reaction time and stirring time of the precursor were two key factors affecting the SnO2 shape. Compared with unorganized nanoparticles, the hierarchical flower-like SnO2 microspheres exhibited a significant improvement in electrochemical performance as the anode material for Li-ion batteries. The initial discharge capacity reached 1610.5 mAh g−1. In view of its unique structure, the prepared material is also expected to find interesting applications in other fields such as gas sensing or photocatalysis.

Ascorbic acid-assisted synthesis of cobalt ferrite (CoFe2O4) hierarchical flower-like microspheres with enhanced lithium storage properties

CoFe2O4 flower-like microspheres are prepared via a surfactant- and template-free method, involving the controlled hytrothermal synthesis firstly and a subsequent thermal decomposition treatment. The microspheres with diameters of 3–4 μm are characterized by the assembly of numerous porous and inter-connected lamella structures. Lithium-ion batteries electrodes based on the as-prepared CoFe2O4 microspheres show a high specific capacity of 733.5 mAh g−1 after 50 cycles at a current density of 200 mA g−1 and a good cyclic stability, as well as excellent rate capability. The enhanced electrochemical performance can be attributed to the hierarchical microsphere structure with high sufficient interfacial contact area between the microspheres and electrolyte, the short diffusion distance of Li+, better accommodation of structural stress and volume change with the lithiation/delithiation process. It is suggested that the CoFe2O4 microsphere is one of the most promising candidates for high-performance lithium-ion batteries.

Synthesis, characterization, and visible-light photocatalytic activity of BiOI hierarchical flower-like microspheres

BiOI flower-like microspheres prepared using N(Bu)4I as iodine source and template exhibit high photocatalytic activity under visible light.

Facile solvothermal synthesis of porous Bi2O3 microsphere and their photocatalytic performance under visible light

A facile template-free method has been developed for the controllable fabrication of novel hierarchical flower-like Bi2O3 microspheres via a solvothermal process in the presence of ethylene glycol. The products were characterised by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflection spectroscopy and nitrogen adsorption. The formation mechanism was proposed based on the evolution of morphology as a function of solvothermal time, which involves the initial formation of nanoparticles followed by their self-aggregation to microspheres and transformation into hierarchical flower-like microspheres by Ostwald ripening. The photocatalytic activities of as-prepared Bi2O3 hierarchitectures were six to nine times higher than that of the commercial sample, which was evaluated by the degradation of rhodamine B dye under visible light irradiation (λ>420 nm). The improved photocatalytic performance could be ascribed to the special hierarchical microsphere structure, good permeability, large surface area (58.2 m2g−1) and large bandgap (2.89 eV). The as-obtained products may have potential applications in water treatment and other related microscale or nano-scale devices.

Self-assembled 3D flower-like hierarchical Fe3O4/KxMnO2 core–shell architectures and their application for removal of dye pollutants

A simple method for fabricating hierarchical composite structures consisting of K-birnessite (KxMnO2) nanosheets on Fe3O4 microspheres was reported in this paper. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements indicated that the size of the three-dimensional (3D) flower-like hierarchical microspheres was about 420 ± 5 nm and the shell was composed of nanosheets with a thickness of about 5 nm. The experimental parameters such as reaction time, reaction temperature and the concentration of KMnO4 used in the solution were investigated for the growth of the core–shell hierarchical structures. These core–shell composites exhibited excellent removal efficiency (over 98% for rhodamine B (RB) and 94% for methylene blue (MB)) and rapid separation from aqueous solution by an external magnetic field, taking advantage of the combined benefits of hierarchical structured KxMnO2 nanosheets and magnetic microspheres. In addition, the adsorption behavior of this new adsorbent fitted well with both Langmuir and Freundlich isotherms and the pseudo-second-order kinetic model. All the results demonstrate that the core–shell composites are effective adsorbents for the removal of dye pollutants and thus could provide a new platform for dye decontamination.

Self‐Assembled 3D Flowerlike Hierarchical Fe3O4@Bi2O3 Core–Shell Architectures and Their Enhanced Photocatalytic Activity under Visible Light

Three-dimensional (3D) flowerlike hierarchical Fe(3)O(4)@Bi(2)O(3) core-shell architectures were synthesized by a simple and direct solvothermal route without any linker shell. The results indicated that the size of the 3D flowerlike hierarchical microspheres was about 420 nm and the shell was composed of several nanosheets with a thickness of 4-10 nm and a width of 100-140 nm. The saturation magnetization of the superparamagnetic composite microspheres was about 41 emu g(-1) at room temperature. Moreover, the Fe(3)O(4)@Bi(2)O(3) composite microspheres showed much higher (7-10 times) photocatalytic activity than commercial Bi(2)O(3) particles under visible-light irradiation. The possible formation mechanism was proposed for Ostwald ripening and the self-assembled process. This novel composite material may have potential applications in water treatment, degradation of dye pollutants, and environmental cleaning, for example.