Hydroxide Microspheres Research Articles

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...

Hierarchical MgFe-layered double hydroxide microsphere/graphene composite for simultaneous electrochemical determination of trace Pb(II) and Cd(II)

Heavy metal contamination has been demonstrated to possess the severe threats toward the whole ecosystems and public security even at trace levels. Therefore, it is essential to exploit an ultrasensitive technique to determine the levels of heavy metal ions. In this work, hierarchical MgFe-layered double hydroxide (MgFe-LDH) microspheres have been successfully immobilized on the graphene nanosheets surface via a facile one-step hydrothermal route. Benefiting from the synergistic effects associated with high specific surface area, strong affinity of hierarchical MgFe-LDH architecture toward heavy metal ions, good electrical conductivity and effective electron transfer efficiency of graphene, the resulting composite (denoted as MgFe-LDH/graphene) is explored as an electrochemical sensor for simultaneous detection of Pb(II) and Cd(II) in aqueous medium. As a consequence, MgFe-LDH/graphene modified electrode exhibits low detection limit of 5.9 nM for Cd(II) and 2.7 nM for Pb(II), which are dramatically lower than the respective values of 3 ppb (27 nM) and 10 ppb (48 nM) in domestic water permitted by the World Health Organization (WHO). Meaningfully, the proposed electrochemical sensor shows specific recognition capability to Pb(II) and Cd(II), excellent reproducibility in repetitive measurements as well as feasibility in real water analysis.

Graphene-wrapped CoNi-layered double hydroxide microspheres as a new anode material for lithium-ion batteries.

High-performance electrode materials that can be easily prepared are imperative for obtaining highly efficient lithium-ion batteries (LIBs). In this study, graphene-wrapped CoNi-layered double hydroxide (LDH) microspheres were first fabricated and used as an anode material for LIBs. The composite electrode with a mass ratio of 2.5 : 1 (CoNi-LDH/graphene) showed a high reversible specific capacity of 1428.0 mA h g-1 at 0.05 A g-1, excellent rate performances (977.5, 670.8 and 328.1 mA h g-1 at 0.5, 2 and 10 A g-1, respectively) and long-cycling performance (75% retention at 10 A g-1 after 10 000 cycles). The excellent electrochemical performances could be due to the following reasons: CoNi-LDHs had high chemical reactivity, and the graphene shell improved the electrical conductivity of CoNi-LDHs, which facilitated charge transfer; the graphene shell also suppressed the volume expansion of metal hydroxides during charge-discharge cycling and enhanced the cycle stability of the electrode. More importantly, this is a significant study to directly use LDHs as a potential electrode for LIBs, which can promote applications of electro-active LDHs in energy storage and conversion fields.

One-step synthesis of copper-cobalt carbonate hydroxide microsphere for electrochemical capacitors with superior stability

Copper cobalt carbonate hydroxide (Cu-Co CH) microspheres were synthesized as a pseudocapacitive electrode material via a simple one-step hydrothermal method. Morphological characterization of the Cu-Co CH microspheres was carried out by scanning electron microscopy and transmission electron microscopy, showing their dandelion-like structure with the size approximately 4–7μm. The crystalline structure, morphology and electrochemical performances of Cu-Co CH materials could be readily dominated by the molar ratio of Cu to Co. Among various stoichiometries of Cu-Co CHs, sample Cu0.48Co1.52 CH delivered the highest specific capacitance of 397.3Fg−1 at 1Ag−1 with a good rate capability. Cu0.48Co1.52 CH electrode material also exhibited a remarkably excellent cycling stability, ~99% of initial capacitance retention even after 10,000 charge/discharge cycles at 2Ag−1. An asymmetric energy storage device was assembled by using Cu0.48Co1.52 CH as positive electrode and activated carbon as negative electrode in 2M KOH electrolyte. The hybrid capacitor device could deliver an energy density of 26.3Whkg−1 at a power density of 400.2Wkg−1, and remain 16.7Whkg−1 at 8374.2Wkg−1. Meanwhile, it also showed amazing stability with ~99% capacity retention after 10,000cycles. Based on the above results, Cu-Co CH microspheres possessed practical application as electrode materials for electrochemical capacitors due to their good structural stability in KOH electrolyte.

Template-free hydrothermal synthesis of 3D flower-like hollow Mg-Al layered double hydroxides microspheres for high-performance optical diffusers

A facile template-free hydrothermal method was proposed to synthesize 3D flower-like hollow Mg-Al layered double hydroxides (LDHs) microspheres. The structure and morphology characterization revealed that 3D flower-like hollow Mg-Al LDHs microspheres with a diameter of about 2.5 μm were assembled with numerous nanosheets. Interestingly, based on the optical diffusing test, 3D flower-like hollow Mg-Al LDHs microspheres exhibited suitable light transmittance, good diffusion capacity, and low incident angle dependence as light scattering materials for optical diffusers. Moreover, the possible light scattering mechanism was discussed and illustrated for the first time. Therefore, the results achieved in this study may provide valuable insights into the development of light scattering materials for high-performance optical diffusers.

Fabrication of layered double hydroxide microspheres by spray drying of nanoparticles: Effects of process conditions

Microspherical agglomerates of nano-sized layered double hydroxide (LDH) particles were prepared using a spray drying technique without addition of dispersant and binder. The effects of process conditions were investigated on the agglomerate size distribution, morphology and specific surface area. The spray-dried agglomerates were spherical in shape, with diameter of 2–15μm and with smooth surface without cracks and holes. The agglomerate surface area ranged from 49 to 101m2/g depending on process conditions. The smallest agglomerates with narrowest size distribution were obtained at the highest flow rate of spraying air, while the agglomerates of highest specific surface area were fabricated at the lowest spraying air flow rate. Drying at low temperature and using slurry of low concentration also resulted in formation of small agglomerates. The change in specific surface area was related to the variations in drying rate. Drying at low rate led to the fabrication of agglomerates with high surface area. Thus, by adjusting the spray drying parameters, one could produce LDH microspheres satisfying requirements and utilize them as an intermediate product in the manufacturing of functional materials.

A facile approach to synthesize 3D flower-like hierarchical NiCo layered double hydroxide microspheres and their enhanced adsorption capability

Uniform flower-like hierarchical NiCo-layered double hydroxide (NiCo-LDH) microspheres were fabricated by a facile hydrothermal method via the hydrolysis of hexamethylenetetramine (HMT). The diameter of the microspheres and thickness of the NiCo-LDH nanosheets are about 5–6μm and 25nm, respectively. The adsorption performance was estimated by the removal of methyl orange (MO) dye. The effects of Ni/Co mole ratios, adsorption time, initial dye concentration, pH and temperature on MO adsorption property were investigated. The results reveal that LDH with Ni/Co feeding ratio of 1:1 (Ni1Co1-LDH) possess the best adsorptive ability, exhibiting a short equilibrium time (5–50min) and an ultrahigh MO adsorption capability (497mg/g). The faster removal process and the higher adsorption capacity of the flower-like Ni1Co1-LDH than that of the stone-like LDH is ascribed to the speedy transport and porous structure of the 3D microspheres. Besides, the MO uptake behavior of Ni1Co1-LDH can be well described by the Langmuir isotherm and pseudo-second-order model, indicative of a monolayer and chemical adsorption that jointly derives from surface adsorption and anion exchange. Overall, the flower-like NiCo-LDH is potential cost-effective adsorbents to remove dye in wastewater.

Hierarchically mesoporous nickel-iron nitride as a cost-efficient and highly durable electrocatalyst for Zn-air battery

Rechargeable Zn-air battery is largely limited by the lack of low-cost and highly efficient bifunctional oxygen catalysts for both oxygen evolution and reduction reactions (OER and ORR). Herein, we report a promising bifunctional electrocatalyst, mesoporous nickel-iron nitride (Ni3FeN), which was synthesized by thermal ammonalysis of hierarchal NiFe layered double hydroxide microspheres. Different from the widely studied carbon/oxide composite catalysts, this metallic nitride does not need carbon as a conducting support, thus avoiding the issue of carbon corrosion at high potentials. The catalysts provide outstanding bifunctional performance with a low overpotential (0.355V) at 10mAcm−2, a low Tafel slope (70mVdec−1) for OER, and a positive half-wave potential (0.78V) for ORR under alkaline solution. More importantly, it delivers a lower voltage gap between charge and discharge and a better stability over 300 cycles compared to that of the more costly RuO2 air-cathode.

Hierarchical flower-like nickel(II) oxide microspheres with high adsorption capacity of Congo red in water

Monodispersed hierarchical flower-like nickel(II) oxide (NiO) microspheres were fabricated by a facile solvothermal reaction with the assistance of ethanolamine and a subsequent calcination process. The as-synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms, zeta potential measurement and Fourier transform infrared spectroscopy. Flower-like nickel(II) hydroxide microspheres with uniform diameters of approximate 6.3μm were obtained after the solvothermal reaction. After heat treatment at 350°C, the crystal phase transformed to NiO, but the hierarchical porous structure was maintained. The as-prepared microspheres exhibited outstanding performance for the adsorption of Congo red (CR), an anionic organic dye, from aqueous solution at circumneutral pH. The pseudo-second-order model can make a good description of the adsorption kinetics, while Langmuir model could well express the adsorption isotherms, with calculated maximum CR adsorption capacity of 534.8 and 384.6mgg–1, respectively, for NiO and Ni(OH)2. The adsorption mechanism of CR onto the as-synthesized samples can be mainly attributed to electrostatic interaction between the positively charged sample surface and the anionic CR molecules. The as-prepared NiO microspheres are a promising adsorbent for CR removal in water treatment.

Multiwalled carbon nanotubes twined α-nickel hydroxide microspheres as high-efficient urea electrooxidation catalysts

Multiwalled carbon nanotube (MWCNT) twined α-Ni(OH)2 microspheres, denoted as α-Ni(OH)2@MWCNT, are synthesized by a facile solvothermal method and are developed as a remarkably active catalyst for urea electrooxidation in alkaline media. Through optimizing the mass ratio between α-Ni(OH)2 and MWCNT, it is found that α-Ni(OH)2@MWCNT catalyst with a weight ratio of 2.5:1 affords the highest current density of 2503 mA cm−2 mg−1 at the potential of 0.58 V versus Hg/HgO and the largest exchange current density of 1.49 × 10−4 mA cm−2 among all the studied catalysts, which are much higher than that of pure α-Ni(OH)2 microspheres and are about one order of magnitude higher than that of reported Ni(OH)2 nanosheets. Additionally, the α-Ni(OH)2@MWCNT catalysts also present superior durability than pure α-Ni(OH)2. The exceptional catalytic performance of α-Ni(OH)2@MWCNT catalysts is attributed to the good electronic transport of MWCNT and favorable mass transport facilitated by α-Ni(OH)2 hollow porous microspheres. These results suggest the feasibility of an easy and low-cost solvothermal method to develop high-efficient catalyst for urea electrooxidation. Bird-nest-like microspheres of α-Ni(OH)2@MWCNT catalyst were synthesized with MWCNT twined α-Ni(OH)2 ultrathin nanosheets by an economical solvothermal method.

High-stable α-phase NiCo double hydroxide microspheres via microwave synthesis for supercapacitor electrode materials

Fast and low-cost fabrication of high performance electrode materials is of great importance for the application of supercapacitors. Herein, in our research, three-dimensional (3D) flower-like NiCo double hydroxide (NiCo DH) microsphere was successfully synthesized via a rapid, inexpensive and energy-saving microwave route without using any template or surfactant under atmospheric pressure. The as-obtained NiCo DH microsphere endowed with α-phase structure with CNO− ions intercalation in the interlayers (7.3Å) was composed of ultrathin nanosheets with thickness less than 10nm. Electrochemical test revealed the NiCo DH electrode showed a high specific capacitance of 1120Fg−1 at 1Ag−1 and remained 996Fg−1 at 10Ag−1 (88.9% retention). Moreover, after 2000 cycles, the capacitance reached 122.5% of its initial value at 10Ag−1 and still retained 93.8% at 30Ag−1 after another 1000 cycles, showing superb stability compared with reported α-phase hydroxides. The admirable stability could be attributed to the synergistic effect between Ni and Co elements, the ion exchange phenomenon between CNO− and OH− ions in the interlayer of NiCo DH during cycling test, and the coherent 3D superstructure. Besides, the asymmetric supercapacitor, with NiCo DH as positive electrode and activated carbon from coal as negative electrode, delivered a superior energy density of 42.5Whkg−1. Consequently, the pleasant synthesis procedure and excellent integrated performance of NiCo DH enable it to be a promising electrode material for the energy storage devices.

3D flower-like hierarchical Ag@nickel-cobalt hydroxide microsphere with enhanced electrochemical properties

The morphology and electrical conductivity are essential to electrochemical performance of electrode materials in renewable energy conversion and storage technologies such as fuel cells and supercapacitors. Here, we explored a facile method to grow Ag@nickel-cobalt layered double hydroxide (Ag@Ni/Co-LDHs) with 3D flower-like microsphere structure. The results show the morphology of Ni/Co-LDHs varies with the introduction of Ag species. The prepared Ag@Ni/Co-LDHs not only exhibits an open hierarchical structure with high specific capacitance but also shows good electrical conductivity to support fast electron transport. Benefiting from the unique structural features, these flower-like Ag@Ni/Co-LDHs microspheres have impressive specific capacitance as high as 1768 F g−1 at 1 A g−1. It can be concluded that engineering the structure of the electrode can increase the efficiency of the specific capacitance as a battery-type electrode for hybrid supercapacitors.

Facile Synthesis of Nickel Cobalt Layered Double Hydroxides Microspheres with High Pseudocapacitive Performance

To meet the ever-growing demand for peak-power assistance in portable electronics and electric vehicles,considerable efforts have been devoted to the development of pseudocapacitorelectrode materials with superiorspecific capacitance and excellent rate performance. Transition metal hydroxides such as Ni(OH)2 possesses hightheoretical specific capacitance, butits unsatisfactory ratecapability is confinedby the inferior intrinsic conductivity [1]. Encouragingly, theintegration of more conductive Co(OH)2 can significantly improvespecific capacitanceand rate capability [2]. In the present work, a facile one-step and cost-effective solvent thermal strategy was adopted to obtain Nickel–cobalt layered double hydroxides microspheres (LDHMs) with hierarchical architecture.Methanol without any other solvent was selected as reaction menstruumduring the whole reaction process, along with urea as alkaline source.Meanwhile, neither surfactant nor template was introduced.All electrochemical tests of all as-prepared microspheres with different Ni/Co atomic ratio (NixCo1-xLDHMs) were performed using 2M KOH aqueous electrolyte. This unique architecture was assembled by numerous ultrathin nanoflakes with an average thickness of about 30 nm randomly and tightly. Particularly, Ni0.6Co0.4LDHMs exhibitedthe most outstandingelectrochemical performance and rate performance, including an ultrahigh specific capacitance of 1624F/g at 0.5A/g,while even at a high current density of 10A/g,the specific capacitance still maintained as high as 1531F/g (~94.27% capacitance retention). Otherwise, the Ni0.6Co0.4LDHMs also exhibited an excellent long-term cycling stability. An ultrahigh retention about 89.94%of specific capacitance was acquired after 8000 cycles of continuousgalvanostaticcharge-discharge processes at 4A/g. The remarkable elecrochemical performance may arise from both the unique morphorlogy and the synergistic effect between the binary hydroxides components [3]. All these results demonstrate that our research can provide a novel way to easily fabricate the structure tunable materials with improved capacitance behavior for energy storage/conversion devices.

Microwave synthesis of nitrogen-doped mesoporous carbon/nickel-cobalt hydroxide microspheres for high-performance supercapacitors

A novel microsphere-like nitrogen-doped mesoporous carbon/nickel-cobalt layered double hydroxide (NMC/NiCo-LDHs-M) composites were successfully synthesized for the first time via a facile and cost-effective microwave method. The NMC/NiCo-LDHs-M electrode displays outstanding pseudocapacitance performances, including a high specific capacitance (2498 F g−1 at 1 A g−1), excellent rate capability and good charge-discharge stability, owing to the large surface area, appropriate pore size, rich mesoporous volume, low reaction resistance and high nitrogen amount. Moreover, an asymmetric supercapacitor using NMC/NiCo-LDHs-M as positive materials and NMC as negative materials was assembled to further investigate the electrochemical performances of NMC/NiCo-LDHs-M, which exhibited a high specific capacitance of 272.6 F g−1 at 1 A g−1 and outstanding electrochemical capacitance retention of 87.2% of initial capacitance after 10,000 cycles. These results indicated that the NMC/NiCo-LDHs-M microspheres were promising materials for high-performance supercapacitors and the microwave method was a potential approach for the design and preparation of diverse supercapacitor materials.

Cadmium-Aluminum Layered Double Hydroxide Microspheres for Photocatalytic CO2 Reduction.

We report the synthesis of cadmium-aluminum layered double hydroxide (CdAl LDH) using the reaction-diffusion framework. As the hydroxide anions diffuse into an agar gel matrix containing the mixture of aluminum and cadmium salts at a given ratio, they react to give the LDH. The LDH self-assembles inside the pores of the gel matrix into a unique spherical-porous shaped microstructure. The internal and external morphologies of the particles are studied by electron microscopy and tomography revealing interconnected channels and a high surface area. This material is shown to exhibit a promising performance in the photoreduction of carbon dioxide using solar light. Moreover, the palladium-decorated version shows a significant improvement in its reduction potential at room temperature.

Self-assembled lanthanum hydroxide microspheres within a reaction–diffusion framework: synthesis, characterization, control and application

The reaction–diffusion framework is used to synthesize lanthanum hydroxide microspheres with controlled particle size and fascinating surface topology and adsorption capacity.

UV-assisted, template-free synthesis of ultrathin nanosheet-assembled hollow indium oxide microstructures for effective gaseous formaldehyde detection

Hollow micro-/nanostructures, especially those with well-defined nanoscale subunits, have been widely used in a variety of areas including catalysis, sensing, energy storage, drug delivery, etc. Herein, we report a novel, UV-assisted, template-free synthesis of hollow indium oxide microstructures that are composed of ultrathin nanosheets (∼2.5nm). The two key steps for the synthesis of the materials being successful are: (i) the UV-induced conversion of a photoactive solid indium alkoxide precursor into hollow indium hydroxide microspheres composed of ultrathin nanosheets, and (ii) the thermal treatment of the resulting hollow hydroxide microspheres into the hollow In2O3 material with a morphological preservation. Moreover, we show that the as-obtained hollow nanomaterials exhibit excellent sensing performance (e.g., high response value, good stability, as well as fast response speed) for the detection of ppm-level gaseous formaldehyde. The efficient sensing performance of the material is attributed to their overall conducive structural features, including their hollow architecture and ultrathin nanoscale building blocks. These structural features can offer a large amount of active sites on the surface, facilitate the diffusion and adsorption of the target gas, and thus enhance the material's sensing performance.

Synthesizing NiAl-layered double hydroxide microspheres with hierarchical structure and electrochemical detection of hydroquinone and catechol

NiAl-layered double hydroxide microspheres with flowerlike hierarchical structure (H-NiAl/LDHs) were successfully synthesized via one-step hydrothermal method with the presence of ionic liquid (1-butyl-3-methyl imidazolium tetrafluoroborate, [BMIM]BF4). The XRD pattern confirms that the products are nickel aluminum hydrotalcites; SEM images show that microspheres with a size of 3–5μm consist of dozens of nanoflakes (about 20nm in thickness) intercrossed with each other. In addition, the H-NiAl/LDHs–modified electrode presents a significant electrocatalytic performance towards the oxidation of hydroquinone and catechol. The linear response range to hydroquinone is 0.01 to 140μM with high sensitivity (669.8 μAmM−1 cm−2) and low detection limit (0.003μM). For catechol, the linear response range is 0.01 to 400μM, sensitivity is 418.3 μAmM−1 cm−2 and detection limit is 0.003μM as well as good stability. The H-NiAl/LDHs showing enhanced electrocatalytic performance in this work can be used in electrochemical sensors and electroanalysis.

Facile synthesis of ZnAl-layered double hydroxide microspheres with core–shell structure and their enhanced adsorption capability

We have developed a simple solution route for the synthesis of hierarchical ZnAl-layered double hydroxide (ZnAl-LDH) microspheres with core–shell structure, which have great practical application as the efficient adsorbent for wastewater purification. The evolution of the morphology with time suggests that the hierarchical ZnAl-LDH microspheres formed by a stepwise growth mechanism. The results demonstrate that the as-prepared ZnAl-LDH microspheres exhibit more excellent adsorption capacity (523mg/g) towards methyl orange in aqueous solutions as compared with the LDH microspheres previously reported, result of which is attributed to their enhanced surface area and suitable mesopore distribution. This work provides a promising approach for the synthesis of hierarchical porous materials with excellent adsorption capacity, which can be potentially used in wastewater treatment.

Template growth of porous graphene microspheres on layered double oxide catalysts and their applications in lithium–sulfur batteries

The wise integration of individual two-dimensional graphene nanosheets into three-dimensional (3D) macroscopic architectures is essential for full exploration of their potential applications in electrochemical energy storage. Graphene microspheres (GMSs) with hierarchical porous architectures and high 3D electrical conductivities are highly expected to be the host carbon to accommodate sulfur cathode for lithium–sulfur batteries. Herein we reported the direct synthesis of GMSs assembled by 3D interconnected graphene with hierarchical pores by template chemical vapor deposition (CVD) on layered double oxide (LDO) microspheres. The LDO templates were derived from conformally calcined layered double hydroxide microspheres produced by spray drying. After methane-CVD, graphene was catalytically grown on LDO templates. Subsequent routine chemical etching of the LDO templates enabled as-obtained GMSs with a large diameter of ca. 11μm and a high surface area of 1275m2g−1. The GMS was employed as carbon scaffold to accommodate sulfur for rechargeable lithium–sulfur batteries. An initial areal discharge capacity of 2.67mAhcm−2 was obtained at a current density of 0.83mAcm−2 on flexible GMS paper electrode with an areal sulfur loading of 2.5mgcm−2.