A novel solution-phase route for the synthesis of crystalline silver nanowires

A unique solution-phase route was devised to synthesize crystal Ag nanowires with high aspect-ratio (8-10 nm in diameter and length up to 10 μm) by the reduction of AgNO₃ with Vitamin C in SDS/ethanol solution. The resultant nanoproducts were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) and electron diffraction (ED). A soft template mechanism was put forward to interpret the formation of metal Ag nanowires.     

Synthesis of sub-micron silver and silver sulfide particles via solvothermal silver azide decomposition

Many transition-metal azides are thermodynamically unstable with respect to the elements and thus, may serve as energetic precursor sources in nanoscale metal particle synthesis. This report describes the use of silver azide (AgN₃) in nonaqueous, solvothermal decomposition reactions to produce crystalline sub-micron silver particles and interconnected structures. The thermal decomposition of AgN₃ directly produces silver and N₂ and no secondary chemical reducing agent is required. This solvothermal conversion was examined in toluene, tetrahydrofuran (THF), and trioctylamine below 250 °C. The coordinating solvents produced the smallest particles (150-500 nm), while the toluene reaction products were near 1 μm in size. The addition of soluble elemental sulfur to the THF reaction results in the growth of silver sulfide particles near 1 μm in size. The silver and Ag₂S products are crystalline by X-ray diffraction and show some faceting by scanning electron microscopy.     

A facile and novel way for the synthesis of nearly monodisperse silver nanoparticles

A facile and novel way was reported for the preparation of nearly monodisperse silver nanoparticles with controlled hydrophilic or hydrophobic surface, using trioctylphosphine as the surfactant and stabilizer. The synthesized nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and UV-vis spectroscopy. The monodisperse silver nanoparticles showed a strong surface plasmon resonance band at 402 nm from the UV-vis spectrum.     

One-step synthesis of reduced graphite oxide–silver nanocomposite

Here, a general approach for the preparation of reduced graphite oxide (rGO)–silver nanocomposite has been investigated. Graphite oxide (GO) sheets are used as the nanoscale substrates for the formation of rGO–silver composite. GO sheets and Ag ions can be reduced at the same time, under a mild condition using l-ascorbic acid (l-AA) as reducing agent. This simple approach should find practical applications in the production of rGO–silver nanocomposite. The SEM analysis indicates that the silver particles are dispersed on graphene sheets. Raman signals of rGO in the composite are increased by the attached silver nanoparticles, displaying surface-enhanced Raman scattering activity. The degree of enhancement can be adjusted by varying the quantity of silver nanoparticles in the composite. In addition, antibacterial activity of the composite against Escherichia coli was evaluated using zone of inhibition. Composites with Ag clearly showed antibacterial activity against E. coli. While GO alone has almost no effect against this bacteria.     

Plasmon-induced photochemical synthesis of silver triangular prisms and pentagonal bipyramids by illumination with light emitting diodes

We have grown silver prisms and pentagonal bipyramids, induced by plasmon excitation on a colloidal solution under the irradiation of light emitting diodes of different colors. Two methods of synthesis of the seeds were tested and their growth evolution recorded, in order to analyze the effect of the chemical synthesis and the color of the irradiation on the morphology and size of the final product. We show that the conversion rate into anisotropic nanoparticles is determined by the chemical environment and the shift of the irradiation wavelength with respect to the plasmon resonance of the seeds. The conversion rate defines the final morphology of the nanoparticles, whereas the size of the nanoparticles is univocally determined by the wavelength of irradiation, irrespective of the method to prepare the seed solution.     

Carbon-nanotube-supported Ag and Cu2O nanoparticles: Dendrimer-mediated synthesis and their broadband optical limiting properties

Multiwalled carbon nanotubes (MWCNTs) were covalently functionalized with fourth-generation poly(amido amine) (PAMAM) dendrimers with a trimesyl core (DT4), and the as-synthesized MWCNT-DT4 was used as the template for in situ growth of Ag and Cu₂O nanoparticles on MWCNTs. Extensive characterizations of the resultant hybrids have been performed using X-ray diffraction, transmission electron microscopy (TEM), high resolution TEM, energy dispersive X-ray spectroscopy, selected area electron diffraction, thermal gravimetric analysis, and X-ray photoelectron spectroscopy. The side-wall of the nanotubes was uniformly coated with the nanoparticles with mean sizes of 7–8 nm. The optical limiting property measurements of the nanoparticle-modified MWCNTs were carried out by the open-aperture z-scan technique. The results demonstrate that the samples suspended in water show broadband OL performance, and their OL behavior is better than that of MWCNT-DT4 in water due to the presence of Ag and Cu₂O nanoparticles.     

Investigation on one-pot hydrothermal synthesis,structural and optical properties of ZnS quantum dots

The advantage of hydrothermal synthesis of semiconductor quantum dots (QDs) over the control of particles size, morphology and stability is reported here. In a typical synthesis procedure, the zinc and sulfur precursor molar ratio of 1:3 was used in an aqueous solution at 150 °C. The cubic phase of ZnS with average particles size of 5 nm was confirmed and estimated from the X-ray diffraction (XRD) analysis. The composition and purity of the sample were analyzed from (energy dispersive-ray analysis) EDAX and (X-ray photoelectron spectroscopy analysis) XPS spectra. The absorption spectrum shows the large shift in the absorption band over 90 nm due to the quantum confinement of carriers. The emission spectrum of quantum dots carry more evidence on the presence of shallow trap, deep trap in the band gap of the material responsible for weak emission in the spectral region of 450–500 nm. High resolution transmission electron microscope and scanning electron microscope studies reveal the structural and morphological features of ZnS with slightly distorted spherical morphology. We found that the coordinating ability of solvent strongly influences the reaction process and morphology of the products.     

Synthesis and enhanced light absorption of alumina matrix nanocomposites containing multilayer oxide nanorods and silver nanoparticles

In this paper, multilayer oxide nanorods were deposited in the nanopores of anodic aluminum oxide (AAO) via solution infiltration followed by heat treatment. The nanorods have a core–shell structure. First, the shell (nanotube) with the thickness of about 40 nm was made of TiO₂ through the hydrolysis of (NH₄)₂TiF₆. Second, silver nanoparticles with the diameter of about 3 nm were added into the TiO₂ layer through thermal decomposition of AgNO₃ at elevated temperatures. Then, cylindrical cores (nanorods) of CoO and ZnO with 200 nm diameter were prepared, respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and composition of the nanorods. UV–vis light absorption measurements in the wavelength range from 350 to 1000 nm were performed to study the effect of nanorod and nanoparticle addition on the light absorption property of the alumina nanocomposites. It is found that CoO nanorods increase the light absorption of the alumina matrix composite in the wavelength range from 500 nm to 800 nm, but the TiO₂ shell does not increase the light absorption much. The ZnO nanorods do not change the light absorption either. However, the addition of silver nanoparticles significantly enhances light absorption of both AAO/TiO₂/Ag/CoO and AAO/TiO₂/Ag/ZnO nanocomposites. This increase in the visible light absorption reveals that there exists surface plasmon around the fine silver nanoparticles in the nanorods.     

Carbon-assisted synthesis of nanowires and related nanostructures of MgO

MgO nanowires and related nanostructures have been prepared by carbon-assisted synthesis, starting from polycrystalline MgO or Mg without the use of metal catalysts. The study has been carried out with different sources of carbon, all of them yielding the nanostructures with some differences. It has been possible to obtain nanotrees and other interesting nanostructures by this method. It has also been possible to obtain aligned MgO nanowires by carbon-assisted synthesis over Au-coated Si substrates. A vapor-solid mechanism of one-dimensional growth seems to be operative in the reactions carried out in bulk, but a vapor-liquid-solid mechanism applies when Si substrates are used.     

Formation of silver nanoparticles in low-alkali borosilicate glass via silver oxide intermediates

A successful procedure has been worked out for the subsequent colouration of low-alkali borosilicate glass that comprises silver doping by silver/sodium ion exchange below the glass transformation temperature followed by thermal processing well above, at 750 °C. The particle formation process as studied by electron microscopy and optical spectroscopy revealed the formation of silver nanoparticles proceeding via silver oxide intermediates. The intermediate nanoparticles are supposed to result from a phase separation within the silver ion-doped glass. Their formation and succeeding transformation to silver nanoparticles upon thermal processing is accompanied by characteristic absorption peaks in the visible range which gradually convert to the surface plasmon resonance of spherical silver nanoparticles. The optical density of the silver-based colouration achieved this way assumes values comparable to those usually obtained with soda lime silicate glass.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

Solvothermal synthesis of fusiform hexagonal prism SrCO3 microrods via ethylene glycol solution

Fusiform hexagonal prism SrCO₃ microrods were prepared by a simple solvothermal route at 120 °C, and characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. By controlling the content of ethylene glycol (EG), it was found that ethylene glycol (EG) played an important role in the formation of such SrCO₃ microrods. Finally, effects of other solvents on the products, including 1,2-propanediol and glycerin, were also investigated.     

Chitosan as template for the synthesis of ceria nanoparticles

Cerium oxide (CeO₂), nanoparticles were prepared using chitosan as template, cerium nitrate as a starting material and sodium hydroxide as a precipitating agent. The resultant ceria–chitosan spheres were calcined at 350 °C. The synthesized powders were characterized by, XRD, HRTEM, UV–vis, FTIR, and TG-DTA. The average size of the nanoparticles obtained was ∼4 nm and BET specific surface area ∼105 m² g⁻¹. Blueshifts in the ultraviolet absorption spectra have been observed in cerium oxide nanocrystallites. The band-gap was found to be 4.5 eV. The blueshifts are well explained for diameters down to less than a few nanometers by the change in the electronic band structure.     

Surfactant controlled synthesis of crystalline phosphovanadate nanorods

Phosphovanadate nanorods were obtained in a reaction of vanadium (V) oxide as a precursor and a cationic surfactant, dodecylpyridinium chloride, as structure directing template at pH ∼3 at room temperature. The composition and morphology of the nanorods was established by powder X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The obtained nanorods have diameters of 40-60 nm with lengths up to 1 μm. The effect of reaction parameters such as concentration of surfactant and pH of the solution on the growth of nanorods has been investigated. A plausible mechanism involving the coalescence of nanoparticle ‘seeds’ leading to one-dimensional nanorods is also discussed. The same reaction when performed under hydrothermal condition, keeping other reaction parameters unchanged, resulted in the formation of phosphovanadate nanospheres of diameter 10-15 nm.     

Sand flower layered double hydroxides synthesized by co-precipitation for CO2 capture: Morphology evolution mechanism,agitation effect and stability

Magnesium–aluminum layered double oxides (Mg–Al-LDO) derived from calcination of layered double hydroxides (LDH) is one of the most capable candidates for CO₂ capture. LDHs with sand flower and dense layered morphology are prepared by co-precipitation method at pH = 10 under different condition with and without stirring. The sand flower LDH prepared with stirring has better CO₂ adsorption performance. Additionally, the sand flower morphology under calcination can be preserved very well, while the morphology can only remain stable below 100 °C after hydrothermal treatment and reconstruction. The formation process of the sand flower LDH is investigated in detail and the related morphology evolution mechanism is proposed. This study can provide insight into the effect of mechanical interaction on chemical reaction and give a new way to control the morphology of layered materials.     

Low temperature growth of single crystalline germanium nanowires

Ge nanowires have been prepared at a low temperature by a simple hydrothermal deposition process using Ge and GeO₂ powders as the starting materials. These as-prepared Ge nanowires are single crystalline with the diameter ranging from 150 nm to 600 nm and length of several dozens of micrometers. The photoluminescence spectrum under excitation at 330 nm shows a strong blue light emission at 441 nm. The results of the pressure and GeO₂ content dependences on the formation and growth of Ge nanowires show that the hydrothermal pressure and GeO₂ content play an essential role on the formation and growth of Ge nanowires under hydrothermal deposition conditions. The growth of Ge nanowires is proposed as a solid state growth mechanism.     

Synthesis of uniform silver nanoparticles with a controllable size

A new method for the synthesis of uniform silver nanoparticles using a single silver reduction step is presented. Fine control over the nanoparticle's size is achieved by varying the concentration of tannic acid, one of the reducing agents, resulting in uniform nanoparticles in the range of 18 nm to 30 nm in diameter with a standard deviation of less than 15%. Changes in the optical properties of the nanoparticles are correlated with their diameter. As the diameter increases the absorption peak is red-shifted. Specifically, for six different sizes of nanoparticles, ranging from 18 nm to 30 nm in diameter, a red-shift from 401 nm to 410 nm in the absorption peaks is measured. In addition, the extinction coefficient increases as the third power of the nanoparticle radius. Rhodamine 123 adsorbed to 30 nm silver nanoparticles exhibits characteristic Raman spectrum suggesting that these nanoparticles are efficient substrate for surface-enhanced Raman spectroscopy.     

Formation of novel assembled silver nanostructures from polyglycol solution

This paper described a simple and mild chemical reduction approach to prepare novel silver nanostructures with different morphologies. Dendritic silver nanostructure was obtained by a fast reduction reaction using hydrazine as a reducing agent in aqueous solution of polyglycol, while both the zigzag and linear Ag nanostructures were slowly assembled using polyglycol as a reducing agent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and field emission scanning electron microscopy (FE-SEM) were used to characterize the obtained silver nanostructures. Fourier transform infrared absorption (FT-IR) spectra were recorded to show that there exists a certain coordination of the oxygen atoms in the polyglycol with Ag⁺ ions in aqueous solution of the AgNO₃/polyglycol. Furthermore, the examination of the morphologies of the products obtained at different stages of the reaction of Ag⁺ ions with polyglycol revealed that such a coordination is of utmost importance for the formation of the silver nanostructures, namely polyglycol provided lots of active sites for the coordination, nucleation, growth and serves as backbones for directing the assembly of the metal particles formed. The formation mechanism of the dendritic silver nanostructure was called a coordination–reduction–nucleation–growth–fractal growth process. The strong surface plasmon absorption bands at 470 nm for the zigzag silver and at 405 nm for the dendritic silver were found.     

Impact of reaction temperature,stirring and cosolvent on the solvothermal synthesis of anatase TiO2 and TiO2/titanate hybrid nanostructures: Elucidating the growth mechanism

One-dimensional anatase TiO₂ and hybrid TiO₂/titanate nanostructures are synthesized by a simple low temperature solvothermal route followed by the Na⁺/H⁺ ion-exchange and final calcination process. We investigated the impact of reaction temperature, stirring conditions and cosolvent on the morphologies of the as-prepared nanostructures. Nanotubes and nanorods are formed in alkaline solution, while nanorods/nanowires and nanoporous nanoribbons are formed in alkaline water–ethanol and alkaline water–ethylene glycol mixed solvents, respectively. X-ray diffraction, Raman scattering and high-resolution transmission electron microscopy studies are employed to identify the structure and phase composition. The formation of different morphologies of the as-synthesized nanostructures is investigated by field emission scanning electron microscopy and transmission electron microscopy. The growth mechanism and reaction process of the as-prepared nanostructures are explained based on the experimental observations. The photoluminescence, optical absorption and the tuning of band gap of the prepared samples are also studied. This work will be valuable for understanding the growth mechanism of various nanostructured TiO₂ and to explore the commercial applications of nanoporous nanoribbons of TiO₂.     

Rapid synthesis of pentagonal silver nanowires with diameter-dependent tensile yield strength

We synthesize silver nanowires (NWs) with pentagonal cross sections via a facile and rapid microwave-assisted polyol method in the presence of polyvinylpyrrolidone (PVP) and sodium sulfide (Na₂S). The synthesis does not use templates and needs only 2.5 min, which is 570 times faster than solvothermal preparation at 100 °C. The pentagonal Ag NWs grow along the <110> direction and reach lengths between 10 and 30 μm. Adjusting Na₂S concentration controls the wire diameters in a wide range from 60 to 480 nm. PVP and microwave irradiation both ensure the cross sections' pentagonal shape even at large diameters. We use different microwave irradiation times to investigate the morphology's evolution and to support the discussion of growth mechanisms. The electrical conductivity was measured in situ inside a transmission electron microscope. Their resistivity is diameter dependent and comparable to that of Ag NWs with round cross sections. Ultrasound fracturing analysis determined the NWs' tensile yield strengths, which is also diameter dependent and maximal around 220 nm.