Hollow Microflowers Research Articles

Construction of CoNiFe Trimetallic Carbonate Hydroxide Hierarchical Hollow Microflowers with Oxygen Vacancies for Electrocatalytic Water Oxidation

AbstractIt is of great challenge to design transition multimetallic carbonate hydroxides with delicate hollow features and defects for efficient electrolytic oxygen evolution reaction (OER). Here, a sequential self‐templating method to synthesize CoNiFe trimetallic carbonate hydroxide hierarchical hollow microflowers (CN‐xFe HMs) with oxygen vacancies (VO) is reported. The synergistic merits of hollow structure, Fe substitution, and VO endow the CN‐xFe HMs with high active‐site exposure density and increased electrical conductivity. Specially, the optimized CN‐xFe HMs validate the excellent OER performance with an overpotential of 258 mV to drive 10 mA cm−2 and a Tafel slope of 48.7 mV dec−1. Theoretical calculations reveal that Fe substitution and VO can synergistically regulate the electronic states to achieve near‐ideal adsorption/desorption capacity for oxygenated intermediates. Moreover, the successful synthesis of other six metals substituted CoNiM (M = Cu, Zn, Cr, Mo, Er and La) carbonate hydroxides provides a universal protocol to construct transition multimetallic electrocatalysts with hollow structures for gaining highly efficient energy conversion reactions.

Synergic adsorption and catalytic conversion of polysulfides based on polar Mo2C and pyridinic N for the enhanced electrochemical performance of Li–S batteries

As a most promising potential next-generation energy storage system, lithium-sulfur batteries (Li–S batteries) received great attention in recent years. However, how to effectively prevent the shuttling effect and accelerate the redox reaction kinetics of polysulfides are still a challenge. Herein, a strategy of using the soft template as a pore-forming agent was proposed to prepare Mo2C/nitrogen-doped carbon hollow microflowers (marked as H–Mo2C/NC MFs), which was used as an efficient absorbent and electrocatalyst of polysulfides for Li–S batteries. Due to the physical limitations of assembling the special nanosheet into a hollow carbon matrix in the shape of a microflower, the H–Mo2C/NC MFs can be used as an appropriate S loading substrate. With the synergistic chemisorption from pyridine N sites and high content polar Mo2C nanoparticles, the as-prepared H–Mo2C/NC MFs can provide enhancing adsorption and catalytic conversion for polysulfides. As a result, the H–Mo2C/NC/S MFs-based cathode provides a high initial discharge capacity of 1104.8mAh/g at 0.2C. Even at the high rate of 1.0C, the initial capacity of 705.2mAh/g still shows good electrochemical performance, and in 1000 cycles, the average capacity decay rate is only 0.016%, with supercycle stability. This article provided a new strategy for a novel viewpoint for the reasonable design of conductive and polar materials for efficient and durable Li–S batteries.

High sensitivity and low detection limit of acetone sensor based on Ru-doped Co3O4 flower-like hollow microspheres

In this paper, we successfully prepared Ru-doped Co3O4 flower-like hollow microspheres by a simple hydrothermal method. The microstructure characterization results indicated the formation of well-organized microflowers with a size of 0.5–1 µm, which were composed of nanosheets. The gas sensing performances of sensors by using the synthesized Ru-doped Co3O4 hollow microflowers as sensing material were investigated. The 1 at% Ru-doped Co3O4 sensor showed the best acetone sensing performance and had a response 18.8–10 ppm acetone, which was almost 5.4 times that of pure Co3O4. Significantly, the sensor had an ultra-low detection limit, with a response value of 1.5–50 ppb acetone at 137.5 °C (30%RH). We propose a plausible mechanism for sensing performance improvement. Namely, the substitution of Ru4+ regulated the carrier concentration and induced the change of Co3O4 defect oxygen and chemisorbed oxygen.

V6O13 nanosheets self-assembled into 3D hollow microflowers for long-life and high-rate Li-ion batteries

Among vanadium-based materials, V6O13 is considered to be an ideal cathode candidate material due to its high theoretical capacity and energy density. However, as mixed-valence vanadium oxide, it faces the challenge of controllable synthesis, and suffers unsatisfactory cycle performance due to the unstable structure. Constructing 3D micro/nano-structures is a very effective method to solve the above problems. Herein, we report a simple template-free solvothermal method to controllably synthesize 3D hollow microflowers structure formed by self-assembly of thin nanosheets. The growth mechanism of the hollow microflowers is revealed by changing the solvothermal reaction time and the content of ethylene glycol. As a cathode material for Li-ion batteries, the V6O13 hollow microflowers exhibit an initial discharge specific capacity of 326 mAh/g at a current density of 0.1 A/g. Even at a high current density of 1 A/g, the V6O13 hollow microflowers still deliver a discharge capacity of 183.2 mAh/g, and display high capacity retention of 75.6% after 500 cycles. The excellent electrochemical performance benefits from the unique advantages of 3D hollow microflowers structure, that is, large specific surface area, abundant mesopores, and robust structure. These results indicate that the V6O13 hollow microflowers have great potential as the long-life and high-rate cathode materials for the next generation of Li-ion batteries.

Improvement toluene detection of gas sensors based on flower-like porous indium oxide nanosheets

In this study, by applying a hydrothermal method with a subsequent in situ reduction treatment, Ag/Pd@In2O3-based sensitive materials were designed and synthesised to investigate toluene sensing performance (e.g. optimum operating temperature, selectivity, response/recovery time and long-term stability). The samples presented the gas-accessible structure with hollow micro-flowers assembled by abundant porous nanosheets. The as-synthesised Ag0.4Pd0.6@In2O3 sensors possessed an ultra-high response (15.9–1 ppm) towards toluene gas at a low operating temperature (180 °C), with a short response/recovery time (7/13 s) and low detection limit (20 ppb). Additionally, excellent reproducibility and selectivity was acquired after a series of tests. Moreover, the underlying sensing mechanism of the Ag0.4Pd0.6@In2O3 sensor to toluene gas was also thoroughly explained. Overall, the findings of this study open a pathway for detecting toluene gas with low cost and more competitiveness and significantly benefit to public safety monitoring and health care.

Hollow Zinc Oxide Microflowers for Selective Preconcentration of Selenium Ions in Natural Water

Background: Selenium’s popularity in a wide variety of products and industries means that it has, unfortunately, become a common environmental pollutant, particularly from sources such as industrial wastewater discharge and agricultural runoff. Objective: Quantification of the selenium (IV) ion content of natural water sources via atomic fluorescence spectrophotometry (AFS) was performed using hollow ZnO microflowers as the enriched materials. The hollow ZnO microflowers were prepared via a hydrothermal method with polystyrene (PS) microspheres as the template. Methods: Since the pH of the selenium (IV) solution is known to influence the degree of adsorption onto the sorbent, both the acidity of adsorption and elution were studied at various pH values to obtain the adsorption isotherm and adsorption capacity of the sorbent. AFS was used to quantify the amount of selenium ion that was present in the samples. The structure of the hollow ZnO microflowers was characterized using XRD, SEM, and TEM characterization methodologies. Results: When the pH was between 6.0 and 7.0, the percentage of Se (IV) adsorption was as high as 93%. It was found that the amount of Se (IV) that was eluted from the sorbent exceeded 96% with 5.0 mL of a 0.01 mol L−1 NaOH solution over the course of 10 minutes. The maximum adsorption capacity was 31.5, 31.8, and 32.0 mg·g−1 at 273, 333, and 353 K, respectively. Conclusion: The LOD for Se (IV) detection via enrichment was achieved at 0.006 μg L−1 with a linear range between 0.1 and 200 μg L−1. Thus, this method is applicable to the analysis of natural water samples and GBW(E)080394.

Ultrathin hetero-nanosheets assembled hollow Ni-Co-P/C for hybrid supercapacitors with enhanced rate capability and cyclic stability

Nanohybrid-type Ni-Co-phosphide/C (Ni-Co-P/C) hollow microflowers with ultrathin nanosheets (HUNs) are constructed through a modified ethylene glycol-mediated self-assembly process and further phosphating treatment. The peculiar structure can availably provide affluent mass transfer channels and active sites, meanwhile inhibit the aggregation of nanosheets. The synergistic effects of the produced Ni-Co-P/C are demonstrated systematically through regulating the initial Ni/Co ratio. A remarkable specific capacity of 205 mAh g−1 can be achieved at 1 A g−1, and the optimized Ni1-Co2-P/C (referred to as NiCoP/CoP/C) still holds a superior rate capability with a capacity retention of 71% even at 50 A g−1. Notably, the electrode also reveals an attractive capacity of 133 mAh g−1 with a high mass loading of 9.1 mg cm−2. A hybrid supercapacitor assembled with Ni1-Co2-P/C cathode and N-doped porous carbon anode demonstrates outstanding electrochemical performance, such as a high energy density (43 Wh kg−1 at a power density of 818 W kg−1) and excellent stability (90% retention after 20,000 cycles at 12 A g−1). The facile fabrication process and attractive performance make Ni1-Co2-P/C HUNs promising in energy storage applications.

Interlayer-Expanded V6O13·nH2O Architecture Constructed for an Advanced Rechargeable Aqueous Zinc-Ion Battery

Rechargeable aqueous zinc-ion batteries have been intensively studied as novel promising large-scale energy storage systems recently, owing to their advantages of high abundance, cost effectiveness, and high safety. However, the development of suitable cathode materials with superior performance is severely hampered by the sluggish kinetics of Zn2+ with divalent charge in the host structure. In the present work, a highly reversible aqueous Zn2+ battery is demonstrated in aqueous electrolyte using V6O13·nH2O hollow microflowers composed of ultrathin nanosheets. Benefiting from the synthetic merits of its favorable architecture and expanded interlamellar spacing that results from its structural water, the V6O13·nH2O cathode exhibits outstanding electrochemical performances with a high reversible capacity of 395 mAh g–1 at 0.1 A g–1, superior rate capability, and durable cycling stability with a capacity retention of 87% up to 1000 cycles. In addition, the reaction mechanism is significantly investigated in ...

Facile molten salt synthesis of Cs-MnO2 hollow microflowers for supercapacitor applications.

A facile molten salt technique is an interesting preparation method as it enables mass production of materials. With the use of CsNO3 salt, Cs-intercalated MnO2 hollow microflowers are obtained in this work. δ-MnO2 with a layered structure, instead of other allotropes with smaller structural cavities, is formed and stabilized by large Cs+ ions. Formation of the hollow microflowers is explained based on the Ostwald ripening process. The salt to starting agent ratio has little effect on the crystal structure and morphologies of the products but does influence the crystallinity, the interlayer distance, and the intercalating Cs+ content. The capacity of Cs+ in the structure and the interlayer distance are maximized when the weight ratio of CsNO3 : MnSO4 is 7 : 1. Cs–MnO2 obtained from this optimum ratio has most suitable crystallinity and interlayer distance, and consequently shows a highest specific capacitance of 155 F g−1 with excellent cycling performance. The obtained specific capacitance is comparable to that of other alkaline-intercalated MnO2, suggesting that Cs–MnO2 could be another interesting candidate for supercapacitor electrodes.

Controllable synthesis of CuS hollow microflowers hierarchical structures for asymmetric supercapacitors

One of the major challenges of high-performance asymmetric supercapacitors is engineering electrode materials with high capacitance and good cycling stability. Hence, we have successfully prepared different CuS hierarchical structures including CuS tubular structures (T-CuS), CuS hollow microspheres (S-CuS) and CuS hollow microflowers (H-CuS) by adjusting the solvents, all of which are investigated as electrode materials for supercapacitors. Among them, the H-CuS electrode exhibits the best electrochemical performance involving a high capacitance of 536.7 F g−1 at a current density of 8 A g−1 and excellent cycling stability with 83.6% capacitance retention for 20,000 continuous cycles at a current density of 5 A g−1. In addition, an asymmetric supercapacitor has assembled with H-CuS as positive electrode and activated carbon (AC) as negative electrode, which exhibits a desirable energy density of 15.97 W h kg−1 when the power density is 185.4 W kg−1. These desirable electrochemical performances powerfully demonstrate that the H-CuS electrode has promising potential for applications in energy storage fields.

Hierarchical hollow microflowers constructed from mesoporous single crystalline CoMn2O4 nanosheets for high performance anode of lithium ion battery

Abstract Hierarchical hollow microflowers constructed from mesoporous single crystalline CoMn2O4 nanosheets were synthesized by a solvothermal route followed by calcination in air. It was found that the amount of deionized water plays a key role in the formation of the well-defined hierarchical hollow structure. A possible formation mechanism of the hierarchical hollow microflowers is proposed based on the time-dependent experimental results. In addition, the unique structure of CoMn2O4 microflowers exhibits superior electrochemical performances with an initial discharge specific capacity of 1024 mA h g−1 at 1000 mA g−1 and remains at 650 mA h g−1 with a coulombic efficiency of 98.7% after 500 cycles.

Cationic Surfactant-assisted Preparation and Characterization of Novel Hierarchical SnS Hollow Microflowers

A facile cationic surfactant-assisted hydrothermal route has been developed to fabricate novel hierarchical SnS hollow microflowers. The obtained products were characterized by XRD, SEM, and HRTEM....

Synthesis of novel hollow microflowers (NHMF) of Nb3O7F, their optical and hydrogen storage properties

A two step, facile surfactant free hydrothermal route was adopted to synthesize Nb3O7F novel hollow microflowers (NHMF). Time dependent experiments were performed which suggested Nb3O7F-NHMF were formed due to Ostwald-ripening process. Raman spectroscopy was conducted to understand different vibrational modes of Nb3O7F-NHMF. Its characteristic band at 692 cm−1 was observed which is associated to NbO6 octahedron sharing. The bandgap of 3.2 eV was calculated by using UV-VIS-NIR absorption spectrum. Considering importance of layered structures in energy storage applications, hydrogen storage ability of Nb3O7F-NHMF were measured for the first time. The maximum values of hydrogen absorption for Nb3O7F-NHMF at 373 K and 473 K were 0.789 wt.% and 1.08 wt.%, respectively. The hydrogen storage measurements revealed the potential of Nb3O7F-NHMF as prospective material for energy storage applications.

Poly(3,4-ethylenedioxythiophene) (PEDOT) hollow microflowers and their application for nitrite sensing

A film of poly(3,4-ethylenedioxythiophene) hollow microflowers (PEDOT-HMF) was electrodeposited on a fluorine-doped tin oxide (FTO) glass substrate by using a film of ZnO microflowers as the template. Each of the PEDOT hollow microflowers shows several 2D nanopetals. Various charge densities were applied for the deposition of the PEDOT film, intending to investigate the charge effect on the film's morphology. The FTO glass with the film of PEDOT-HMF (hereafter PEDOT-HMF modified electrode) was used as a nitrite sensor. A dramatic improvement was observed in the sensitivity of the PEDOT-HMF electrode, with reference to that of a flat PEDOT electrode. Through an amperometric detection, the sensitivity and limit of detection (LOD) of the sensor were found to be 255.2μAmM−1cm−2 and 0.59μM, respectively. The linear range of the PEDOT-HMF electrode was between 50 and 7500μM, and was observed to be larger than that of the corresponding PEDOT electrode. An interference effect was studied, using different kinds of salts that contain anionic interferences in the detection of nitrite. All the ions of the salts, except SO32−, showed negligible effect on the determination of nitrite.

Uniform V2O5 nanosheet-assembled hollow microflowers with excellent lithium storage properties

Hierarchical vanadium-based hollow microflowers are prepared by a facile solvothermal approach. This novel nanostructure can be easily converted to V2O5 without significant structural alteration by simple annealing. The as-derived V2O5 nanosheet-assembled hollow microflowers exhibit excellent lithium storage properties with high capacity and superior cycling stability.