Room temperature solid-state synthesis and ethanol sensing properties of sea-urchin-like ZnO nanostructures

ZnO gas-sensing materials were prepared by one-step solid-state reaction at room temperature. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to characterize the hierarchal ZnO nanocrystals. The results indicate that ZnO clusters are assembled with nanosheets when no surface-active agent is present. When surface-active agent PEG-10000 was added, sea-urchin-like ZnO are assembled from ZnO nodules. The rods have an average diameter of 33 nm and length of about 100 nm. The primary gas-sensing results show that sea-urchin-like ZnO have good gas sensitivity to ethanol vapor.     

Room temperature synthesis of 2D CuO nanoleaves in aqueous solution

A simple room temperature method was reported for the synthesis of CuO nanocrystals in aqueous solution through the sequence of Cu(2+) → Cu(OA)2 → Cu(OH)2 → Cu(OH)(2-)4 → CuO. Sodium oleate (SOA) was used as the surfactant and shape controller. The as-prepared samples were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible absorption spectroscopy (UV-vis) and differential thermal analysis (DTA). It can be seen that 1D Cu(OH)(2) nanowires were first obtained from Cu(OA)(2) and, at room temperature, converted into 2D CuO nanoleaves (CuO NLs) in a short time under a weakly basic environment. On prolonging the reaction time, the top part of these 2D nanoleaves branched and separated along the long axis to form 1D rod-like nano-CuO because of the assistance of SOA. A possible transformation mechanism of Cu(OH)(2) to CuO nanostructures at room temperature in aqueous solution is discussed. The transformation velocity can be controlled by changing the pH value of the system. The prepared CuO NLs were used to construct an enzyme-free glucose sensor. The detecting results showed that the designed sensor exhibited good amperometric responses towards glucose with good anti-interferent ability.     

Room temperature synthesis of BaCrO4 nanoplates through a NaCl-assisted aqueous solution method

BaCrO₄ nanoplates have been successfully synthesized by a NaCl-assisted aqueous solution method at room temperature without using any surfactants or templates. Scanning electron microscopy and transmission electron microscopy analyses show that large-scale, single-crystalline BaCrO₄ nanoplates with 300 nm in size and thickness of about 40 nm are obtained by this simple method. It suggests that NaCl is crucial to the formation of BaCrO₄ nanoplates, which might provide a favorable chemical environment for the growth of nanoplates. This simple method might be useful for the synthesis of nanostructures of other chromates.     

Cerium-based coordination polymers micro/nanostructures: Room temperature synthesis and their thermolysis to ceria

In this presentation, several cerium-based coordination polymers micro/nanostructures such as nanoparticles, nanorods, and microflowers were successfully prepared by a facile room temperature method using three isomers of benzenedicarboxylic acid as organic building block and Ce³⁺ as center metal ion. It turns out that the three products exhibit obviously different morphologies. Also, their crystal structures are different. Amorphous products were obtained when benzene-1,2-dicarboxylic acid was used. However, well-crystallized products were obtained with the other two isomers. After calcining at high temperature, ceria with retained morphologies were achieved. Various measurements were used to characterize the products and their UV absorption properties were studied.     

Morphology-controlled synthesis of silver nanostructures via a solvothermal method

Silver nanostructures have been synthesized by a simple solvothermal method in the presence of poly(vinylpyrrolidone) (PVP). Typically, different exotic agents (NaOH, KBr, NaCl) are added into the reaction system. The anions (OH⁻, Cl⁻, Br⁻) from these agents can combine Ag⁺ to form silver salt colloids (AgOH, AgBr and AgCl), decreasing the concentration of free Ag⁺ in the initial formation of silver seeds. However, different release rates of Ag⁺ from these colloids to the solution in the subsequent reaction may play different roles in the growth of silver seeds. The as-prepared silver nanostructures were characterized by UV–vis absorption spectrum, X-ray diffraction (XRD) and field emission scanning electron microscope (FSEM). It is found that silver nanostructures with various shapes can be obtained by the addition of different exotic agents. Finally, our work provides a simple route to synthesize silver nanostructures with controllable morphologies.     

Biomolecule assisted hydrothermal synthesis of chainlike network of silver sulfide nanostructures

A L-cysteine assisted hydrothermal route has been utilized for the growth of Ag2S nanostructures with chainlike network. It was observed that the experimental parameters such as the synthesis temperature and variation in the molar ratio of the anionic and cationic precursors play critical role in determining the morphology and crystal structure of the products. X-ray diffraction study revealed the formation of monoclinic acanthite Ag2S. L-cysteine was acting as complexing agent as well as sulfur source. The branching fractal morphology was explained through Cayley tree model and structure of L-cysteine.     

Room temperature synthesis of crystalline metal oxides

Crystalline titanium dioxide powders have been synthesized as either rutile or anatase from aqueous solutions at low temperatures (T≤100°C) and atmospheric pressure. First, a sol is prepared by the hydrolysis of a titanium alkoxide in an acidic solution. The sol is subsequently heated at different rates to produce the different crystalline phases of titanium dioxide. Powder characterization was carried out using X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. In general, the precipitate size was observed to be between 50 and 100 nm. Possible mechanisms involved in determining the crystal variants are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Room temperature synthesis of nanocrystalline NbC powder

Synthesis of nanocrystalline NbC was explored via mechanochemical processing. The reaction mixture comprised of NbCl₅ and CaC₂. Fifteen minutes of high energy milling was sufficient to effectively transform the reaction mixture into nanocrystalline NbC. CaCl₂ and elemental C which is formed as by-product was successfully separated and leached out using centrifuge and distilled water.     

Room temperature synthesis of colloidal platinum nanoparticles

Efficient preparation of stable dispersions of platinum nanoparticles from platinous chloride (K₂PtCl₄) was achieved by simultaneous addition of capping polymer material. The size of platinum nanoparticles was controlled by changing the ratio of concentration of capping polymer material to the concentration of platinum cation used. The morphology of colloidal particles were studied by means of UV-visible spectrophotometry and transmission electron microscopy (TEM). Particle size increased with low reagent concentration. The change in absorption spectra with the particle size was observed, i.e. blue shift attributed to decrease in particle size Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Room temperature solvent-free synthesis of monodisperse magnetite nanocrystals

We have successfully demonstrated a facile, solvent-free synthesis of highly crystalline and monodisperse Fe3O4 nanocrystallites at ambient temperature avoiding any heating. Solid state reaction of inorganic Fe(ll) and Fe(ll) salts with NaOH was found to produce highly crystalline Fe3O4 nanoparticles. The reaction, if carried out in the presence of surfactant such as oleic acid-oleylamine adduct, generated monodisperse Fe3O4 nanocrystals extractable directly from the reaction mixture. The extracted nanoparticles were capable of forming self-assembled, two-dimensional and uniform periodic array. The new process utilizes inexpensive and nontoxic starting materials, and does not require a use of high boiling point and toxic solvents, thus is amenable to an environmentally desirable, large-scale synthesis of nanocrystals.     

Preparation temperature effect on the synthesis of various carbon nanostructures

Various carbon nanostructures (CNs) have been prepared by a simple deposition technique based on the pyrolysis of a new carbon source material tetrahydrofuran (THF) mixed with ferrocene using quartz tube reactor in the temperature range 700–1100 °C. A detailed study of how the synthesis parameter such as growth temperature affects the morphology of the carbon nanostructures is presented. The obtained CNs are investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), electron dispersive scattering (EDS), thermogravimetry analysis (TGA), Raman and transmission electron microscope (TEM). It is observed that at 700 °C, normal CNTs are formed. Iron filled multi-walled carbon nanotubes (MWCNTs) and carbon nanoribbons (CNRs) are formed at 950 °C. Magnetic characterization of iron filled MWCNTs and CNRs studied at 300 K by superconducting quantum interference device (SQUID) reveals that these nanostructures have an enhanced coercivity (Hc = 1049 Oe) higher than that of bulk Fe. The large shape anisotropy of MWCNTs, which act on the encapsulated material (Fe), is attributed for the contribution of the higher coercivity. Coiled carbon nanotubes (CCNTs) were obtained as main products in large quantities at temperature 1100 °C.     

On the polyol synthesis of silver nanostructures: glycolaldehyde as a reducing agent

The polyol synthesis is a popular method of preparing metal nanostructures, yet the mechanism by which metal ions are reduced is poorly understood. Using a spectrophotometric method, we show, for the first time, that heating ethylene glycol (EG) in air results in its oxidation to glycolaldehyde (GA), a reductant capable of reducing most noble metal ions. The dependence of reducing power on temperature for EG can be explained by this temperature-dependent oxidation, and the factors influencing GA production can have a profound impact on the nucleation and growth kinetics. These new findings provide critical insight into how the polyol synthesis can be used to generate metal nanostructures with well-controlled shapes. For example, with the primary reductant identified, it becomes possible to evaluate and understand its explicit role in generating nanostructures of a specific shape to the exclusion of others.     

Room temperature synthesis of bismuth oxyfluoride nanosheets and nanorods

At room temperature, two different morphological nanoscaled BiO_xF_3 − 2x (BiOF nanosheets and Bi₂₆O₃₈F₂ nanorods) have been prepared via a simple solution-based route in the presence of diethanolamine (DEA) and NaOH. The compositions and morphologies of bismuth oxyfluoride can be selectively prepared by varying the type of additives. The products were characterized by X-ray diffraction (XRD), energy-disperse X-ray analysis (EDXA), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectrum (XPS). A possible mechanism was introduced to explain the formation of the products.     

Room temperature synthesis of CdS nanoflakes for photocatalytic properties

Herein, we report, preparation of cadmium sulphide (CdS) nanoflakes at room temperature by simple arrested precipitation method. The synthesized CdS nanoflakes were characterized by various techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, Fourier transform-infrared spectroscopy, and UV–Visible spectrophotometer. Nanoflakes of CdS were found to be a mixed-phases composed of cubic and hexagonal with average crystallite size of 20 nm. Surface morphology of CdS seems to be nanoflakes. The absorption spectrum was slightly shifted to blue region as compared to the bulk, this indicates that synthesized material is smaller in size. The band gap energy was found to be 2.48 eV. The photocatalytic results reveals that CdS nanoflakes exhibits excellent photocatalytic performance for methyl orange (20 ppm) degradation, under sunlight and UV within 120 min (83 and 95 % respectively).     

ZnO 1-D nanostructures: Low temperature synthesis and characterizations

ZnO is one of the most important semiconductors having a wide variety of applications in photonic, field emission and sensing devices. In addition, it exhibits a wide variety of morphologies in the nano regime that can be grown by tuning the growth habit of the ZnO crystal. Among various nanostructures, oriented 1-D nanoforms are particularly important for applications such as UV laser, sensors, UV LED, field emission displays, piezoelectric nanogenerator etc. We have developed a soft chemical approach to fabricate well-aligned arrays of various 1-D nanoforms like nanonails, nanowires and nanorods. The microstructural and photoluminescence properties of all the structures were investigated and tuned by varying the synthesis parameters. Field emission study from the aligned nanorod arrays exhibited high current density and a low turn-on field. These arrays also exhibited very strong UV emission and week defect emission. These structures can be utilized to fabricate efficient UV LEDs.     

Morphology and size-controllable preparation of silver nanostructures through a wet-chemical route at room temperature

In this letter a simple wet-chemical route was developed to prepare silver nanostructures. The formation of the silver nanostructures occurs in a single process, carried out by mixing an AgNO₃ aqueous solution and a para-phenylenediamine solution at room temperature without the introduction of other reducing agents and morphology controlling agents. It is found that both the morphology and the size of such silver nanostructures can be facilely controlled by the molar ratio and concentration of the reactants as well as the solvent that was used to dilute para-phenylenediamine aqueous solution. As-formed silver nanostructures were examined by scanning electron microscopy.     

Low dimensional silver nanostructures: synthesis, growth mechanism, properties and applications

This work presents a review of the recent advances on the low-dimensional (LD) silver nanostructures (e.g., one-dimensional nanorods and nanowires, and two-dimensional nanoplates and nanodisks). First, the methods, either physical or chemical, for the synthesis of silver LD nanostructures are introduced. Then, the use is discussed of advanced experimental techniques (e.g., transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, ultraviolet-visible and Raman spectra) and theoretical techniques at different time and length scales from quantum mechanics (e.g., ab initio simulation and density function theory) to molecular dynamics method for understanding the principles of governing particle growth, as well as discrete dipolar approximate method for understanding the optical properties of different shapes and sizes of silver LD nanostructures. Subsequently, the functional applications of the LD silver nanostructures in different areas such optical, electronic, and sensing, particularly for those related to surface plasma resonance are summarized based on the recent findings. Finally, some perspectives and comments for future investigation of silver nanostructures are also briefly discussed.     

Room temperature synthesis of crystalline alpha-Fe2O3 nanoparticles

A room temperature process for the production of crystalline hematite Fe2O3 nanoparticles with an indirect band gap of 2 eV and size range from 15 to 35 nm is presented. The material to have an optical band gap of 2 eV as determined by the Tauc relationship which makes it suitable for visible light photocatalysis. The XRD pattern of the material shows no secondary phases to be present for the low temperature processed material.     

Surface-enhanced fluorescence from silver fractallike nanostructures decorated with silver nanoparticles

Fluorescence emission of fluorophore molecules in the close vicinity of a nanostructured metal surface can be enhanced through a local electromagnetic field with the help of surface plasmon resonance. The fluorescence enhancement effect is very sensitive to the topography and dielectric property of the metal substrate. In the current work, metal substrates with complex structures, which are made of silver fractallike structures and nanoparticles (NPs), are prepared through electrochemical reduction followed by physical deposition. The surface-enhanced fluorescence of Rhodamine 6G monolayer molecules deposited on the prepared complex substrates are investigated with the laser spectroscopic technique. The experimental results show that the fractallike structure decorated with silver NPs presents stronger fluorescence enhancement, compared with silver NPs or pure silver fractallike structures.