Formation Of Nanoflowers Research Articles

Aerosol-assisted chemical vapour deposition of α-Fe2O3 nanoflowers for photoelectrochemical water splitting

Abstract 3-dimensional (3D) nanostructures have gained broad attention in the field of microelectronics and nanotechnology owing to their fascinating properties and potential for novel applications. To enable successful fabrication of the nanostructure, deep understanding on their growth mechanism is an absolute prerequisite. In this study, thin film of hematite (α-Fe2O3) nanoflakes is successfully converted to nanoflowers using aerosol-assisted chemical vapour deposition (AACVD) technique simply by supplying high amount of oxygen and regulating the deposition time. The crystal structure and morphological properties including thickness and roughness of the film are thoroughly investigated to provide a clear explanation on the growth mechanism of α-Fe2O3 by AACVD. Results indicate that (110) crystal plane is the predominant factor that influence the formation of nanoflowers with unique pyramidal nanostructure. This structure causes the film thickness to increase linearly while the surface roughness shows a logarithmic growth trend. The samples are further employed in photoelectrochemical (PEC) water splitting as photoanode where 40 min deposition period is the optimum condition for achieving PEC photocurrent density of up to 585 μA/cm2 at 1.2 V vs. Ag/AgCl. The major contributor towards the performance enhancement is the large surface area and high light absorption of α-Fe2O3 nanoflowers as this parameter provides greater sites for photocatalytic activity, greater charge generation and enhanced charge carrier separation efficiency.

Unique 3D flower-on-sheet nanostructure of NiCo LDHs: Controllable microwave-assisted synthesis and its application for advanced supercapacitors

Two-dimensional (2D) nanostructures, though promising in energy storage, suffer from aggregation and subsequent deterioration of performance in practical applications. Hence, assembly of 2D nanostructures into three-dimensional (3D) architectures is highly desirable. Here, we report a microwave-assisted approach to the controllable synthesis of 2D materials with tunable 3D structures simply by adjusting the ratio of water/ethylene glycol (H2O/EG). Novel flower-on-sheet 3D hierarchical structures of nickel cobalt double hydroxide (NiCo LDHs) are obtained at EG content of 40%, while microspheres and 2D nanosheets are obtained when the EG content is 0% and 75%, respectively. We propose that under microwave irradiation, EG molecules disperse the nuclei and facilitate the initial formation of 2D sheets. Subsequently, the dominating hydrophobicity of the assembling results in the formation of nanoflowers on the sheets. When tested as electrode materials in supercapacitors, the flower-on-sheet NiCo LDH exhibits superior capacitance (1187.2 F g−1 at 1 A g−1), good rate capability (71% retention at 30 A g−1), and high stability (only 0.3% cyclic decay per cycle with respect to the first charge capacitance), which is ascribed to that ‘sheet’ could act as buffer substrate while ‘flower’ expose more active site. Our results demonstrate an energy-saving and one-pot approach for controllable construction of 2D derived 3D nanostructure that can be applied in next-generation energy storage materials.

Dependence of pH on phase stability, optical and photoelectrical properties of SnS thin films

This study reports the effect of pH value of the reaction solution (5, 5.8 and 6.5) on growth rate of SnS films deposited by chemical bath deposition and their characteristics such as X-ray diffraction (XRD), surface morphology, phase stability, optical and photoelectrical. XRD analysis reveals that the films exhibit an orthorhombic structure with polycrystalline nature, in addition to the presence of the secondary phase Sn2S3 at pH 6.5. Field emission scanning electron microscopy observations show the formation of nanoflowers. Raman spectra manifest the presence of Sn2S3 phase, where its peak intensity gradually reduces until disappearance with decreasing pH value from 6.5 to 5. Furthermore, the enhancement in the dark current (conductivity) value of the thin films occurs with decreasing pH value, as well as increasing in the value of photocurrent under illumination of near-infrared 750 nm. Conversely, the sensitivity value decreased with decreasing pH. Moreover, the energy gap value ranges from 1.34 to 1.51 eV with increasing pH. The as-obtained results demonstrate the key role of pH in controlling SnS films characteristics to achieve high quality films for the applications of photodetectors and solar cells.

Preparation and application of a chemically modified laccase and copper phosphate hybrid flower-like biocatalyst

In order to face the increasing demand of laccase with high stability and high performance, laccase was chemically modified by acid anhydride, and copper ion (Ⅱ) was coordinated with the hetero atom of the modified laccase to obtain the nanoflower biocatalyst. The effects of different reaction time, laccase concentration and copper sulfate concentration on the formation of nanoflowers were investigated in detail. Compared to free laccase, the enzyme activity, pH stability and thermal stability of nanoflowers increased by 165%, 375% and 430%, respectively. Furthermore, the catalytic properties of our nanoflower biocatalysts were investigated by catalyzing the synthesis of viniferin. The results showed that a higher yield of 45.0% was obtained in shorter period of time than that of the free laccase (21.6%), and the product was single without other by-products. What’s more, nanoflower biocatalyst exhibited excellent storage stability, repeatability and reproducibility in cycle operation. We believed that this study provided a feasible and efficient biocatalytic method for conversion of resveratrol to viniferin. These preliminary results indicated that nanoflowers would have great potential for application in biotransformation and biocatalysis.

Enzyme-free synthesis of cyclic single-stranded DNA constructs containing a single triazole, amide or phosphoramidate backbone linkage and their use as templates for rolling circle amplification and nanoflower formation.

Cyclic oligonucleotides are valuable targets with a broad range of potential applications spanning molecular biology and nanotechnology. Of particular importance is their role as templates in the rolling circle amplification (RCA) reaction. We describe three different chemical cyclisation methods for the preparation of single-stranded cyclic DNA constructs. These chemical cyclisation reactions are cheaper to carry out than the enzymatic reaction, and more amenable to preparative scale purification and characterisation of the cyclic product. They can also be performed under denaturing conditions and are therefore particularly valuable for cyclic DNA templates that contain secondary structures. The resulting single-stranded cyclic DNA constructs contain a single non-canonical backbone linkage at the ligation point (triazole, amide or phosphoramidate). They were compared to unmodified cyclic DNA in rolling circle amplification reactions using φ-29 and Bst 2.0 DNA polymerase enzymes. The cyclic templates containing a phosphoramidate linkage were particularly well tolerated by φ-29 polymerase, consistently performing as well in RCA as the unmodified DNA controls. Moreover, these phosphoramidate-modified cyclic constructs can be readily produced in oligonucleotide synthesis facilities from commercially available precursors. Phosphoramidate ligation therefore holds promise as a practical, scalable method for the synthesis of fully biocompatible cyclic RCA templates. The triazole-modified cyclic templates generally gave lower and more variable yields of RCA products, a significant proportion of which were double-stranded, while the performances of the templates containing an amide linkage lie in between those of the phosphoramidate- and triazole-containing templates.

Synthesis and electro-catalytic activity of Pt-Co nanoflowers

The study of metallic nanoflowers has attracted more and more attention because of their larger surface areas and active sites, which could be applied for surface-sensitive areas. Despite these excellent characteristics, it is still very hard to synthesize noble metal nanoflowers as the flower-like structure is apt to change into some more stable shapes which are covered by lower energy surfaces. In this study, Pt-Co nanoflowers were successfully synthesized by a two-step method via the reaction between Co nanoparticles and Pt precursor. From the transmission electron microscopy (TEM) images, it could be seen clearly that the products possessed a flower-like nanostructure. The morphology of the final products depended on a number of parameters, such as the reaction time and the reaction temperature. Based on the experimental results and theoretical calculation, the formation of nanoflowers could be attributed to the galvanic replacement reaction between Co nanoparticles and Pt precursor. In addition, the electrochemical catalytic activity of Pt-Co nanoflowers toward methanol oxidation was also evaluated in comparison with that of commercial Pt black. Owing to the special structure, the electro-catalytic activity and stability of Pt-Co nanoflowers were much better than those of commercial Pt black.

Effect of Annealing Temperature on Flowerlike Cu3BiS3 Thin Films Grown by Chemical Bath Deposition

For widespread application of thin-film photovoltaic solar cells, synthesis of inexpensive absorber material is essential. In this work, deposition of ternary Cu3BiS3 absorber material, which contains abundant and environmentally benign elements, was carried out on glass substrate. Flowerlike Cu3BiS3 thin films with nanoflakes as building block were formed on glass substrate by chemical bath deposition. These films were annealed at 573 K and 673 K in sulfur ambient for structural improvement. Their structure was characterized using Raman spectroscopy, as well as their surface morphological and optical properties. The x-ray diffraction profile of as-deposited Cu3BiS3 thin film revealed amorphous structure, which transformed to orthorhombic phase after annealing. The Raman spectrum exhibited a characteristic peak at 290 cm−1. Scanning electron microscopy of as-deposited Cu3BiS3 film confirmed formation of nanoflowers with diameter of around 1052 nm. Wettability testing of as-deposited Cu3BiS3 thin film demonstrated hydrophobic nature, which became hydrophilic after annealing. The measured ultraviolet–visible (UV–Vis) absorption spectra of the Cu3BiS3 thin films gave an absorption coefficient of 105 cm−1 and direct optical bandgap of about 1.42 eV after annealing treatment. Based on all these results, such Cu3BiS3 material may have potential applications in the photovoltaic field as an absorber layer.

Effect of silver doping on optical properties of nanoflower ZnO thin films prepared by spray pyrolysis technique

Silver doped zinc oxide (ZnO) thin films have been synthesized by spray pyrolysis method on the substrate at a temperature of 450 °C. The aqueous Zinc acetylacetonate (ZnC10H14O5) and silver nitrate (AgNO3) dissolved in ethanol were used as a starting material. The effect of sliver doping on the structural, surface morphological, electrical as well as optical properties of Ag: Zno thin films were studied. It is confirmed by the X-ray diffractogram that the Ag: ZnO thin films was polycrystalline nature with the preferential orientation along (002) plane in wurtzite structure. The Scanning Electron Microscope exhibited the surface formation of nanoflower shaped grains with an addition of silver (Ag) and compositional analysis by Energy Dispersive Spectroscopy confirmed the presence of Zinc (Zn), Oxigen (O) and silver (Ag). Atomic force microscopy revealed that surface roughness of the films was decreased with the increase of silver concentration. The films were found to exhibit high transmittance and low absorbance in the visible /new infrared region.

Effect of annealing process in TiO2 thin films: Structural, morphological, and optical properties

This work presents a study of the structural, morphological, and optical properties of titanium dioxide thin films prepared via chemical bath deposition method, after being submitted to annealing processes varying the temperature from 373 to 723K. The presence of the Rutile phase in all the samples was identified using X-ray diffraction measurements. When the annealing temperature increased to 723K, the presence of the Anatase phase was observed. From scanning electron microscopy measurements, the formation of nanoflowers was also perceived; these flower-like structures are composed of nanorods of around ∼10nm in length. With increasing annealing temperature, these structures disappear trans-forming into platelets distributed over the whole surface. A gap energy (Eg) of 3.0eV was determined, and this value decreased to 2.98eV after the temperature of T=723K was implemented, which is also where the Anatase phase was observed.

Rapid Formation and Evolution of Anodized-Zn Nanostructures in NaHCO3 Solution

Densely packed nanowires were fabricated by anodizing zinc foil in slightly basic sodium bicarbonate solution. The formation of different nanostructures was observed as a result from varying the reaction parameters such as voltage, electrolyte concentration and time. An in-depth analysis of these formation stages enables a growth mechanism to be proposed. The evolution of anodized-Zn nanostructures could be categorized into four stages, i.e. pitting, growth of nanofibers in pit, formation of nanoflowers and transformation to nanowires. The fabricated nanowires being amorphous in nature, whilst the FTIR measurement revealed the chemical bonds within the nanowires attributed to zinc hydroxy carbonate/hydrozincite. Hydrozincite nanowires were converted into hexagonal wurtzite ZnO after heat-treatment at 250°C for 1 h as verified by XRD measurement. The overall nanowires form was preserved after annealing but it displayed a granular surface. This surface texture will aid researchers to design/optimize the total expose surface area and yield device grade performances.

Organic-inorganic hybrid nanoflowers: types, characteristics, and future prospects.

Organic–inorganic hybrid nanoflowers, a newly developed class of flower-like hybrid nanoparticles, have received much attention due to their simple synthesis, high efficiency, and enzyme stabilizing ability. This article covers, in detail, the types, structural features, mechanism of formation, and bio-related applications of hybrid nanoflowers. The five major types of hybrid nanoflowers are discussed, i.e., copper–protein, calcium–protein, and manganese–protein hybrid nanoflowers, copper–DNA hybrid nanoflowers, and capsular hybrid nanoflowers. The structural features of these nanoflowers, such as size, shape, and protein ratio generally determine their applications. Thus, the specific characteristics of hybrid nanoflowers are summarized in this review. The interfacial mechanism of nanoflower formation is examined in three steps: first, combination of metal ion and organic matter; second, formation of petals; third, growth of nanoflowers. The explanations provided herein can be utilized in the development of innovative approaches for the synthesis of hybrid nanoflowers for prospective development of a plethora of hybrid nanoflowers. The future prospects of hybrid nanoflowers in the biotechnology industry, medicine, sensing, and catalysis are also discussed.

Spontaneous interfacial reaction between metallic copper and PBS to form cupric phosphate nanoflower and its enzyme hybrid with enhanced activity

We herein report the spontaneous interfacial reaction between copper foil with 0.01M phosphate buffered saline (PBS) to form free-standing cupric phosphate (Cu3(PO4)2) nanoflowers at ambient temperature. The underlying chemistry was thoroughly investigated and it is found that the formation of nanoflower is synergistically caused by dissolved oxygen, chlorine ions and phosphate ions. Enzyme-Cu3(PO4)2 hybrid nanoflower was further prepared successfully by using an enzyme-dissolving PBS solution and the enzymes in the hybrid exhibit enhanced biological activity. This work provides a facile route for large-scale synthesis of hierarchical inorganic and functional protein-inorganic hybrid architectures via a simple one-step solution-immersion reaction without using either template or surfactant, thus offering great potential for biosensing application among others.

Water-induced formation, characterization, and photoluminescence of carbon nanotube-based composites of gadolinium(III) and platinum(II) dithiolenes.

Understanding the nature of interactions of targeted drug-delivery vehicles, such as functionalized carbon nanotubes (f-CNTs) and their composites, with a cell or its organelles or DNA, where water is a major constituent, requires molecular-level understanding of f-CNTs with analogous chemical systems. The nature of interaction has not yet been explored within the scope of formation of giant aggregates by self-assembly processes. Crystals of platinum(II) dithiolene [Pt(mnt)2 ][PPh4 ]2 (1) and gadolinium(III) dithiolene [Gd(mnt)3 ][PPh4 ]3 (2) (mnt=maleonitrile dithiolate) form nanospheres (diameter 88 nm) and nanoflowers (400-600 nm) in acetonitrile/water and DMF/water solvent mixtures, respectively. The formation of nanospheres or nanoflowers is proposed to be a water-induced phenomenon. These nanospheres and nanoflowers interact with f-CNTs by forming either spherical supramolecular assemblies (3, diameter up to 45. 5 μm) in the case of platinum(II) dithiolene or composite flowers (4) with CNT buckling for gadolinium(III) dithiolene. Both nanostructures, (3) and (4), show emission upon excitation at a range of wavelengths (λex =385-560 nm). The fluorescence emissions of the composite materials 3 and 4 are proposed to be due to separation of energy states of the nanospheres of 1 or the nanoflowers of 2 by the energy states of the f-CNTs, leading to the possibility of new electronic transitions.

Facile synthesis of gold nanoflowers assisted by soybean peptides and their applications in surface enhanced Raman spectroscopy and catalysis

The controlled synthesis of gold nanoflowers demonstrates high yields and good monodispersity following reduction of hydrochloroauric acid and soybean peptides in alkaline aqueous solution. Proper pH is essential for the formation of nanoflowers. Gold microplates and branched and flower-like particles can be prepared by adjusting the pH of the aqueous solution. Moreover, maintaining an adequate soybean peptide concentration is important for the three-dimensional formation of monodisperse nanoflowers. The prepared gold flower-like nanoparticles are effective catalysts for the activation and reduction of methylene blue in the presence of NaBH4. Here, we also exhibit the effective application of gold nanoflowers for surface enhanced Raman scattering.

Large-scale preparation of ZnO nanoflowers from nanowires with high length/diameter ratio

ZnO nanoflowers were successfully prepared by a new non-catalytic method based on directly heating of Zn strip using a direct current power supply. The Zn strip was obtained by electrodeposition on silicon wafer with laser etching. The nanoflowers, with a size more than 15μm, are assembled by nanowires with a length of 10μm and a diameter of 100nm, and the length/diameter ratio is about 100. The samples were characterized by means of scanning electron microscope, X-ray diffraction and Raman. X-ray diffraction results show that the formation of nanoflowers is controlled by the current density. Raman modes of nanoflower corresponds well with X-ray diffraction result. Photoluminescence property of ZnO nanoflowers shows strong green emission and violet emission.

Strain relaxation defects in perovskite oxide superlattices

Abstract

Two-Step Synthesis of Narrow Size Distribution Nanoflowers Using a Tree-Type Multi-Amine-Head Surfactant as a Template

Unique, narrow polydispersity, hierarchical gold nanoflowers were synthesized by a two-step method using a tree-type multi-amine surfactant (C18N3) as the template and ascorbic acid (AA) as the reductant. Upon the addition of a stronger reductant AA, the C18N3–HAuCl4 composite changed to a black color, due to the gold nanoflower formation. Under a specific concentration ratio of C18N3, HAuCl4, and AA, narrow polydispersity flower-like gold structures were obtained. These nanoflowers were stable as an aqueous solution for months, with no deformation to particle size and no obvious change in the surface morphology. The experimental results demonstrated that the complexation between C18N3 and HAuCl4 is essential for the formation of gold nanoflowers with a narrow size distribution. The morphology and size of the composites can be easily adjusted by changing the concentration of C18N3, HAuCl4, and AA. The growth of nanoflowers is discussed in terms of two steps: the formation of complexes between C18N3 and HAuCl4, which determines the core size of the nanoflowers, and the surface nanocrystal growth, due to the reduction of HAuCl4 by AA, which determines the thickness and morphology of nanoflower surface layers. In the measurement of surface-enhanced Raman scattering (SERS) using rhodamine 6G, the gold nanoflowers exhibited a significant enhancement factor, indicating their potential in biosensing and nanodevice applications.

Synthesis and Catalytic Properties of Au–Pd Nanoflowers

Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 ± 0.1 nm) shell of Pd. UV-visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core-shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core-shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

Evolution of GaN nanoflowers from AlN–SiO 2 grains on a silicon substrate by chemical vapor reaction

Gallium nitride (GaN) nanoflowers were synthesized on a silicon (Si) substrate at growth temperatures of 650 and 600 °C and under HCl:NH 3 flow ratios of 1:20, 1:30, and 1:40 by hydride vapor phase epitaxy. Numerous nanorod and nanoneedle burs were formed within each nanoflower. The nanoflower size increased with increasing NH 3 gas flow rate. The nanoflower formation mechanism is proposed based on cross-sectional scanning electron microscopy images and bright field image of scanning transmission electron microscopy. Nanoflowers were evolved from irregular regions with AlN–SiO 2 grains on a Si substrate, i.e., the roughness of substrate affects nanoflower formation by causing nanoburs to protrude, exposing them to higher gas concentrations.

Controlled synthesis of gold nanoflowers assisted by poly(vinyl pyrrolidone)–sodium dodecyl sulfate aggregations

Gold nanoflowers with high-yield and good size monodispersity were synthesized in aqueous solution through a facile route under the assistance of poly(vinyl pyrrolidone) (PVP)–sodium dodecyl sulfate (SDS) aggregations. In this route, HAuCl 4 was directly reduced by PVP without any additional reducing agents and sodium hydroxide (NaOH) was added to induce the formation of nanoflowers. The synthesized nanoflowers are 100 nm in dimension consisting of a solid core and many short and obtuse protrusions (5–10 nm). UV–vis spectroscopy and transmission electron microscope (TEM) were used to monitor the shape evolutionary process of the nanoflowers to get a better understanding on their formation mechanism. The presence of PVP–SDS aggregations at a proper SDS concentration was essential to the synthesis of typical three-dimensional (3D) nanoflowers with many protrusions. Moreover, the influences of SDS, NaOH and HAuCl 4 concentrations on the morphology of the products were investigated in detail.