2D Nanoplates Research Articles

One-step synthesis of micro/nano flower-like Ni3V2O8 as anode for Li-ion batteries

A micro/nano flower-like Ni3V2O8 superstructure composed of uniform two-dimensional (2D) nanoplates with thicknesses of 20–50nm had been successfully synthesized using a facile one-step hydrothermal approach. It was found that the pH value of the mixed precursor solutions played a key role in the formation of flower-like Ni3V2O8 structure. Importantly, the flower-like Ni3V2O8 exhibited a high reversible capacity, good cycling stability (1047.8mAhg−1 at 200mAg−1 after 300 cycles), and superior rate capability (640.8mAhg−1 at 3200mAg−1) as an anode material for Li-ion batteries. Furthermore, the lithium storage mechanism of Ni3V2O8 involving in a conversion reaction and an intercalation reaction was proposed by ex situ XRD analyses.

Synthesis and electrochemical properties of Fe3O4/MnO2/RGOs sandwich-like nano-superstructures

The Fe3O4/MnO2/RGOs (Reduced graphene oxide) sandwich-like nano-superstructures reported in this article were fabricated by using an eco-friendly mechanical stirring route at room temperature without any catalysts or templates. In this nano-superstructure, three-dimensional (3D) hierarchical MnO2 shell was assembled by two-dimensional (2D) nanoplates and Fe3O4/MnO2 core-shell was coated by RGO layers. The sandwich-like nano-superstructures show better electrochemical performance comparing to the pure MnO2 and Fe3O4/MnO2 nanoparticles. The maximum specific capacitance can reach 77.5 F/g at the current density of 0.5 A/g and maintain 35.0 F/g (55% of SC at 0.5 A/g) at the current density of 20 A/g. It was found that the electrocapacitive performances of the Fe3O4/MnO2/RGO electrodes are highly affected by the connection effectiveness between Fe3O4/MnO2 particles and graphene layers.

Sensitive and selective NO2 gas sensor based on WO3 nanoplates

Gas sensors based on a chemiresistive metal oxide semiconductor are widely used including nitrogen dioxide (NO2) at a moderate temperature. In this work efforts are taken to fabricate NO2 gas sensor using thin films of tungsten oxide (WO3) grown directly on to a soda-lime glass substrate without assistance of any seed layer by a simple and a facile hydrothermal technique. As per our knowledge, the deposition of nanostructured WO3 thin films without assistance of any seed layer on the glass substrate was rarely reported. The WO3 thin film samples were synthesized at various deposition times ranging from 3h to 7h and were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, UV–vis spectroscopy and Brunauer-Emmett-Teller techniques. The surface morphological and structural characterization showed the two dimensional (2D) nanoplate-like structure of as synthesized WO3 thin films with plate thickness ranging from 90 to 150nm and had an orthorhombic structure, respectively. Moreover, the 2D nanoplates of WO3 exhibited a gas response ∼10 for 5ppm for toxic NO2 gas at relatively low operating temperature. The new synthesis route and sensing behavior of as synthesized WO3 nanoplates revealed a promising candidate for the fabrication of the cost effective gas sensors.

Photocatalytic activity of Portland cement loaded with 3D hierarchical Bi2WO6 microspheres under visible light

In this work, photocatalytic cement was prepared by loading Bi2WO6 microspheres with Portland cement. 3D hierarchical Bi2WO6 microspheres were synthesized by self-assembly of 2D nanosheets and nanoplates firstly. Interestingly, Backscattered Electron (BSE) images showed Bi2WO6 hierarchical structure remained unchanged on the surface of hydration cement. The nanoplate and nanosheets which fell off from the Bi2WO6 microspheres distributed evenly on the surface of the hydration products. As to the inner structure of Bi2WO6/cement, a porous structure was observed and Bi2WO6 particles were located evenly in the pores. This result was in favor of enhancing photocatalytic performance and gas adsorption. The 15wt% Bi2WO6/cement showed the highest photocatalytic activity, which can degrade the HCHO completely within 80min under visible light. XRD and hydration heat results showed that Bi2WO6 hardly influences the hydration process. However, when the Bi2WO6 dosage was increased to beyond 15%, the hydration process was deterred and hydration heat decreased, which may influence the durability of the cement matrix.

Effective Chemical Route to 2D Nanostructured Silicon Electrode Material: Phase Transition from Exfoliated Clay Nanosheet to Porous Si Nanoplate

An efficient and economical route for the synthesis of porous two-dimensional (2D) nanoplates of silicon is developed via the magnesiothermically-induced phase transition of exfoliated clay 2D nanosheets. The magnesiothermic reaction of precursor clay nanosheets prepared by the exfoliation and restacking with Mg2+ cations yields porous 2D nanoplates of elemental silicon. The variation in the Mg:SiO2 ratio has a significant effect on the porosity and connectivity of silicon nanoplates. The porous silicon nanoplates show a high discharge capacity of 2000mAhg−1 after 50 cycles. Of prime importance is that this electrode material still retains a large discharge capacity at higher C-rates, which is unusual for the elemental silicon electrode. This is mainly attributed to the improved diffusion of lithium ions, charge-transfer kinetics, and the preservation of the electrical connection of the porous 2D plate-shaped morphology. This study highlights the usefulness of clay mineral as an economical and scalable precursor of high-performance silicon electrodes with tailorable nanostructures.

Photoinduced ultrafast charge separation in colloidal 2-dimensional CdSe/CdS-Au hybrid nanoplatelets and corresponding application in photocatalysis.

Multicomponent hybrid nanocrystals (HNC) consisting of a semiconductor and metallic domains are an important class of nanostructured materials demonstrating useful applications and interesting basic knowledge. In this scenario, Au nanoparticle (NP) islands of ∼2 nm have been grown on unique two dimensional (2D) CdSe/CdS core@shell hexagonal nanoheteroplatelets of 20 nm diameter to form unprecedented 2D CdSe/CdS-Au HNCs and detailed optical characterization has been carried out to determine the dimensionality based electron transfer dynamics on the ultrafast scale. Steady state optical absorption studies show that upon growing Au NPs onto the 2D nanoplates, a new band appears in the red region of the spectra (500-800 nm), which suggests a strong interaction between the exciton of the core-shell and the plasmon of the metal NPs. Fluorescence studies showed the quenching of emission of the semiconductor domains upon the growth of the metallic domains. Detailed optical and TRPL studies suggested efficient charge transfer from the 2D CdSe/CdS to the Au domains, irrespective of excitation wavelength. Femtosecond transient absorption studies suggest that the electron transfer from the 2D hybrid nanocrystals to the metal domain is on an ultrafast time scale (∼800 fs). No evidence is observed for charge transfer from the 2 nm Au domains to the semiconductor seeds. The broad absorption in the visible region of the hybrid nanocrystals and the ultrafast charge transfer facilitates very efficient photo-catalytic reactions under direct sun light, as a case study.

A general route to 2D nanoleaves and nanoplates of polyaniline

Novel 2D nanoleaves and nanoplates are synthesized by a facile and general method. A set of doping control experiments are carried out to show how PANI self-assemble to nanoleaves and nanoplates. Interestingly, the nanoleaves and nanorods have high crystallinity, according to their XRD patterns. The novel method will be readily scalable to produce polyaniline crystals with different morphologies with high quality and low cost. The polymer semiconductor crystals could be useful for next generation organic electronics such as nanotransistors.

Morphological and dimensional control via assembly of polyaniline crystals

A facile and general route to a new generation of polyaniline (PANI)-citric acid (CA) crystals such as 2D nanoplates, 2D nanosheets and 3D microrods self-assembled by the π-π stacking interaction is reported. Dramatic, 3D rectangular shaped microrods and 2D nanosheets are single crystals indicated by SAED patterns and HRTEM images. Moreover, the method does not depend on any specific equipment or heating, cooling and complex procedures. The novel polyaniline crystals will be useful for next generation organic electronics such as nano-transistors.

Oriented-attachment dimensionality build-up via van der Waals interaction

Molecular static calculation is carried out to evaluate the role of van der Waals interaction associated with different oriented attachment growth systems involving 0D nanoparticles, 1D nanorods, 2D nanoplates and 3D nanostrucutres.

Three‐dimensional hierarchical ZnO nanostructures with controllable building units: hydrothermal synthesis, growth process and photocatalytic activities for organic dyes

Two different morphologies of three-dimensional (3D) hierarchical ZnO nanostructures with different building units (1D nanowires and 2D nanoplates) have been successfully synthesised through a simple hydrothermal synthetic approach, namely nanourchins and nanoflowers. Moreover, the comparative photocatalytic studies have shown that the photocatalytic activities of the nanoflowers are both 10% higher than that of nanourchins in the photodegradation of organic dyes Methylene Blue and Rhodamine B. This study might be a useful basis for the study of other metal oxides from the perspective of basic theory and practical applications.

Controlled morphologies and growth direction of WO3 nanostructures hydrothermally synthesized with citric acid

Hexagonal tungsten oxide (h-WO3) nanorods have been synthesized by a hydrothermal process at 180°C using ammonium metatungstate and citric acid as starting materials. The phase constituent, morphology and growth direction of the h-WO3 nanocrystals were characterized by using XRD, SEM, HRTEM techniques. We found that the morphology, size and preferred orientation of the h-WO3 nanocrystals can be controlled by simply adjusting the amount of citric acid. In the absence of citric acid, 2-dimensional (2D) nanoplates or nanosheets 10–20nm thick were formed. With increasing the amount of citric acid, 1-dimensional (1D) nanorods or nanoneedles grew along [002] crystallographic orientation from some certain nanoplate crystallographic planes. The as-synthesized WO3 nanorods were up to 1μm in length and 40–50nm in diameter. It is suggested that the adsorption of carboxyl group on certain crystallographic faces leads to an anisotropic crystal growth and the formation of 1D morphology.

Surfactant Charge Mediated Shape Control of Nano- or Microscaled Coordination Polymers: The Case of Tetrapyridylporphine Based Metal Complex

In this work, CuTPyP (TPyP = 5,10,15,20-tetrapyridylporphine) single crystalline 2D nanoplates and 3D polyhedra of nano-octahedrons and microspindles can be selectively obtained by changing the type as well as the concentration of the surfactant via a simple surfactant-assisted chemical solution method at room temperature. Under anionic surfactant of sodium dodecyl sulfate (SDS), high purity uniform nanoplates were obtained, while under cationic surfactant of cetyltrimethylammonium bromide or tetrabutylammonium bromide, monodispersed microspindles and nano-octahedrons were obtained. The as synthesized products are characterized by UV–vis spectroscopy, fluorescence emission spectroscopy, X-ray diffraction pattern, scanning electron microscopy, and transmission electron microscopy. The crystal growth mechanism in the presence of either positively charged or negatively charged surfactant was studied by changing the preparation parameters. The rational shaping mechanism for different surfactants was thus promoted. This work provides a simple and mild approach to obtain high-quality 2D MTPyP nanocrystals through an anionic surfactant controlled synthesis process. It should be transferable to the shape control of nano- or microscaled metal–organic materials with related growth mechanisms.

A fast synthesis of hierarchical yolk–shell copper hydroxysulfates at room temperature with adjustable sizes

Hierarchical 3D yolk–shell copper hydroxysulfate microspheres were successfully synthesized by a fast synthesis method at room temperature. Both the core and the shell of the yolk–shell microspheres were assembled from 2D nanoplates or tiny nanoplatelets. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS), atomic absorption spectrophotometry (AAS) and thermogravimetric analysis (TG). The diameter of the yolk–shell microspheres can be tuned by simply adjusting the concentration of the chelating agent, 1,3-propanediamine. This reaction can be scaled up by a factor of 1000 with almost no loss in yield. An Ostwald ripening controlled formation mechanism was proposed. Furthermore, the yolk–shell copper hydroxysulfates were evaluated as catalysts for the oxidation of styrene to benzaldehyde.

CHISELED NICKEL HYDROXIDE NANOPLATES GROWTH ON GRAPHENE SHEETS FOR LITHIUM ION BATTERIES

The morphologies and structures of Ni ( OH )2–graphene hybrid materials were tailored by using different mineralizers in this work. It was revealed that the synergic effects of the highly oxidized graphene sheets and the mineralizers played a crucial role in controlling the morphology and structure of the nanocomposites, and Na 2 CO 3 is a very effective mineralizer for growing chiseled 2D nanoplates of Ni ( OH )2 on graphene sheets. When produced with NaOH , fragmental Ni ( OH )2 crystals with irregular shapes erratically decorated on graphene sheets. In contrast, chiseled Ni ( OH )2 hexagonal nanoplates grown on graphene sheets were obtained when Na 2 CO 3 was used as the mineralizer. These unique 2D–2D nanoarchitectures with higher contact area between the nanocrystals and graphene substrate can increase the interfacial interaction and then efficiently improve the structural stability of the composite material, thus exhibiting an enhanced Li storage capacity and excellent cycling performance of 562 mAh g-1 after the 36th cycle.

Morphology, structure and optical properties of 3D Bi2O3 hierarchical architectures

3D Bi2O3 hierarchical architectures were successfully fabricated from electrodeposited bismuth (Bi) film by controlling the ramp rate and reaction temperature of thermal oxidation process. Surface morphology observations show that the 3D Bi2O3 hierarchical architectures exhibit flower-like architectures assembled by dozens of 2D nanoplates with a thickness of 25nm. Characterizations of crystal structure reveal that the 2D nanoplates are well-crystallized β-Bi2O3. Furthermore, the 3D Bi2O3 hierarchical architectures exhibit a strong and wide photoluminescence (PL) signal in the range from 500 to 900nm, with a maximum peak at 759nm. Such unique architectures are expected to be utilized as next generation of nano-scale devices, such as sensors, optics and electronics.

Three-Dimensional Mesoscale Heterostructures of ZnO Nanowire Arrays Epitaxially Grown on CuGaO2 Nanoplates as Individual Diodes

We report a three-dimensional (3D) mesoscale heterostructure composed of one-dimensional (1D) nanowire (NW) arrays epitaxially grown on two-dimensional (2D) nanoplates. Specifically, three facile syntheses are developed to assemble vertical ZnO NWs on CuGaO2 (CGO) nanoplates in mild aqueous solution conditions. The key to the successful 3D mesoscale integration is the preferential nucleation and heteroepitaxial growth of ZnO NWs on the CGO nanoplates. Using transmission electron microscopy, heteroepitaxy was found between the basal planes of CGO nanoplates and ZnO NWs, which are their respective (001) crystallographic planes, by the observation of a hexagonal Moiré fringes pattern resulting from the slight mismatch between the c planes of ZnO and CGO. Careful analysis shows that this pattern can be described by a hexagonal supercell with a lattice parameter of almost exactly 11 and 12 times the a lattice constants for ZnO and CGO, respectively. The electrical properties of the individual CGO-ZnO mesoscale heterostructures were measured using a current-sensing atomic force microscopy setup to confirm the rectifying p-n diode behavior expected from the band alignment of p-type CGO and n-type ZnO wide band gap semiconductors. These 3D mesoscale heterostructures represent a new motif in nanoassembly for the integration of nanomaterials into functional devices with potential applications in electronics, photonics, and energy.

Synthesis of hierarchical Bi2WO6 microspheres with high visible-light-driven photocatalytic activities by sol–gel-hydrothermal route

Bi2WO6 samples with hierarchical microspheres structures built by higher order 2D nanoplate alignment were successfully synthesized by sol–gel-hydrothermal route. The structures and morphologies of the products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). UV–vis diffuse reflectance spectra indicated that as-prepared Bi2WO6 with hierarchical microspheres structures had enhanced absorption in both UV and visible light areas. Photocatalytic activities of the samples were evaluated by the degradation of methylene blue (MB) under visible light irradiation. Due to the unique morphology and porous structure, the hierarchical Bi2WO6 microspheres exhibited better photocatalytic activities than that of the Bi2WO6 prepared by hydrothermal routes.

Scalable Synthesis of Urchin- and Flowerlike Hierarchical NiO Microspheres and Their Electrochemical Property for Lithium Storage

A nickel salt-urea-H2O ternary system has been developed for the large-scale synthesis of hierarchical α-Ni(OH)2 microspheres, the solid precursor for the subsequent topotactic transition to NiO upon calcination. In this facile synthetic system, hierarchical structure is self-assembled under the cooperative direction of urea and anions in nickel salts. Thus, simply tuning the Ni salts leads to the selective construction of urchin and flowerlike hierarchical α-Ni(OH)2 and NiO microspheres consisting of radial 1D nanowires and 2D nanoplates, respectively. The obtained NiO microspheres possessing accessible nanopores, excellent structural stability and large surface area up to 130 m(2)/g show promising electrochemical performance in anodic lithium storage for lithium-ion battery.

Morphology-dependent photocatalytic removal of NO by hierarchical BiVO4 microboats and microspheres under visible light

In this study, hierarchical monoclinic BiVO4 three-dimensional (3D) superstructures with two kinds of morphologies, namely BiVO4 microboats and BiVO4 microspheres, have been controllably synthesized by adjusting reaction time in the template-free hydrothermal process using ethylene glycol as solvent. The nucleation, growth, and self-assembly of the BiVO4 superstructures could be readily controlled with reaction time, which brought different morphologies to the final product. The as-prepared BiVO4 superstructures were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption experimentation, and UV-vis diffuse reflectance spectra (UV-vis DRS). The monoclinic 3D BiVO4 catalysts are composed of two-dimensional (2D) nanoplates which intercross with each other. Nanoplates were firstly formed by aggregation of primary nanocrystallites and then self-assembly converted to microboats and microspheres via the oriented attachment mechanism. The prepared BiVO4 3D catalysts can respond to visible light and their optical and photocatalytic properties are relevant to their morphologies. The BiVO4 microspheres showed superior photocatalytic activity on removal of gaseous NO compared to the BiVO4 microboats. The morphology-dependent photocatalytic property of the BiVO4 superstructures is discussed. This work suggests that the synthesized BiVO4 micropheres are promising photocatalyst for environmental remediation.

Graphene‐Assisted Room‐Temperature Synthesis of 2D Nanostructured Hybrid Electrode Materials: Dramatic Acceleration of the Formation Rate of 2D Metal Oxide Nanoplates Induced by Reduced Graphene Oxide Nanosheets

A new prompt room temperature synthetic route to 2D nanostructured metal oxide-graphene-hybrid electrode materials can be developed by the application of colloidal reduced graphene oxide (RGO) nanosheets as an efficient reaction accelerator for the synthesis of δ-MnO2 2D nanoplates. Whereas the synthesis of the 2D nanostructured δ-MnO2 at room temperature requires treating divalent manganese compounds with persulfate ions for at least 24 h, the addition of RGO nanosheet causes a dramatic shortening of synthesis time to 1 h, underscoring its effectiveness for the promotion of the formation of 2D nanostructured metal oxide. To the best of our knowledge, this is the first example of the accelerated synthesis of 2D nanostructured hybrid material induced by the RGO nanosheets. The observed acceleration of nanoplate formation upon the addition of RGO nanosheets is attributable to the enhancement of the oxidizing power of persulfate ions, the increase of the solubility of precursor MnCO3, and the promoted crystal growth of δ-MnO2 2D nanoplates. The resulting hybridization between RGO nanosheets and δ-MnO2 nanoplates is quite powerful not only in increasing the surface area of manganese oxide nanoplate but also in enhancing its electrochemical activity. Of prime importance is that the present δ-MnO2 -RGO nanocomposites show much superior electrode performance over most of 2D nanostructured manganate systems including a similar porous assembly of RGO and layered MnO2 nanosheets. This result underscores that the present RGO-assisted solution-based synthesis can provide a prompt and scalable method to produce nanostructured hybrid electrode materials.