Bulk synthesis of monodisperse Fe nanoparticles by electromagnetic levitational gas condensation method

A one-step bulk synthesis method for monodisperse Fe nanoparticles was developed by electromagnetic levitational gas condensation (ELGC) process. The Fe vapours ascending from the high temperature levitated droplet was condensed by cryogenic He-Ar gas mixture under atmospheric pressure. The spherical Fe nanoparticles with particle size of 72.1 ± 19.5 nm and a narrow size distribution were prepared using the He-20%Ar gas mixture with the flow rate of 20 l/min. The production rate of the one-step ELGC process was estimated as high as 10 g/h. The nanoparticles were passivated by the formation of a thin layer of Fe oxides with the thickness of 3 nm.     

Extracellular biosynthesis of silver nanoparticles by the culture supernatant of Bacillus licheniformis

Development of reliable and eco-friendly processes for synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. One of the options to achieve this objective is to use ‘natural factories’ such as biological systems. In this study, we report the synthesis of nanoparticles of silver by reduction of aqueous Ag+ ions with the culture supernatant of Bacillus licheniformis. The morphology of the nanoparticles was characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The Debye-Scherrer equation was used to calculate particle sizes and the silver nanoparticles of approximate size 40 nm were observed. The process of reduction is extracellular, which makes it an easier method for the synthesis of silver nanoparticles.     

Synthesis of monodisperse gold nanoparticles in ionic liquid by applying room temperature plasma

Sub-atmospheric dielectric barrier discharge (SADBD) plasma was used for the reduction of gold trichloride to synthesize gold nanoparticles. By introducing poly vinyl pyrrolidone (PVP) as a capping agent, the nanoparticle size has been controlled to be ~ 1.7 nm in average with a narrow size distribution. These nanoparticles show enhanced activity and stability for electro-oxidation of methanol.     

Synthesis of silver nanoparticles using surfactin: A biosurfactant as stabilizing agent

Surfactin, a lipopeptide biosurfactant, was used to stabilize the formation of silver nanoparticles. Synthesis of silver nanoparticles using a borohydrate reduction was performed at three pH levels (pH 5, 7 and 9) and two different temperatures in the presence of surfactin. The nanomaterials were characterized by UV-vis spectroscopy, X-ray diffraction and transmission electron microscopy. The nanoparticles were synthesized at different pH conditions and temperature and remained stable for 2 months. The UV-vis spectra showed a surface plasmon resonance vibration band at 428 nm for all samples. TEM micrographs revealed that the mean nanoparticle size decreased with increase of pH from 5 to 9 (i.e. 17.8 ± 9.8, 6.9 ± 1.5 and 4.3 ± 1.1 nm) at 4 °C. However, at room temperature, size increased with pH (4.9 ± 1.4, 6.5 ± 1.6, 9.7 ± 4.3 nm at pH 5, 7 and 9 respectively). This report describes the use of a renewable, environmentally compatible, biodegradable surfactant as a stabilizing agent for the synthesis of silver nanoparticles.     

A simple microemulsion based method for the synthesis of gold nanoparticles

The production of gold nanoparticles and nanoplates by enzymatically-synthesized lauroyl glucose, lauroyl fructose and lauroyl ascorbate is described. These emulsifiers formed oil-in-water microemulsions with toluene and the available reducing groups brought about a rapid reduction of chloroauric acid (HAuCl₄). Gold nanoparticles could thus be synthesized without the use of an additional reducing agent. Optical images, UV–visible spectroscopy, scanning electron microscopy, energy dispersive spectra (SEM–EDS) and X-ray diffraction (XRD) analysis revealed the presence of gold nanoparticles, which on further incubation aggregated into nanoplates. This paper thus describes a novel application of the enzymatically-synthesized esters.     

Continuous synthesis of controlled size carbon-encapsulated iron nanoparticles

Carbon-encapsulated iron nanoparticles were continuously and selectively synthesised in a thermal plasma jet from ethanol (carbon source) and Fe powders with different grain sizes. The grain size of the Fe powder influenced the size distribution of the as-produced carbon encapsulates. The products obtained from large Fe particles (50-78 μm) were comprised of small encapsulates with diameters between 5 and 10 nm. Larger carbon encapsulates with a broad diameter distribution (10-100 nm) were synthesised from the finest Fe particles (18 μm). It was also found that Fe particle size was the most crucial parameter for determining the encapsulation yield. The encapsulation yield was also influenced by the carbon to iron ratio and the thermal conductivity of the plasma gas.     

Stable water-soluble iron oxide nanoparticles using Tiron

Success in biological and nanomaterial applications that rely on magnetic iron oxide nanoparticles (IONPs) often depends on monodispersity, size, and aqueous stability of the synthesized particles. Here we report a simple and efficient strategy to prepare monodisperse, ultrasmall, water dispersible superparamagnetic IONPs. Monodisperse IONPs are initially synthesized in organic solvents using oleic acid as a dispersant. The subsequent ligand exchange of oleic acid for dopamine and Tiron (4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt) allows for superior colloidal stability in aqueous media. Zeta potential measurements confirm the stability of the nanoparticles upon redispersal in water or biologically relevant buffers. The synthesized particles also preserve their general shape, size, and crystallinity after ligand exchange as evidenced by TEM and SAED measurements. Magnetic properties are also maintained after the ligand exchange as verified by magnetometry and magnetic force microscopy (MFM). An analysis of potential issues regarding this and other prior ligand exchanges is also highlighted, which may aid others in future investigations.     

Characterization of copper sulfide nanostructured spheres and nanotubes synthesized by microwave-assisted solvothermal method

Copper sulfide nanostructured spheres and nanotubes were successfully synthesized, using a microwave-assisted solvothermal method, by the decomposition of [Cu(CH₃CSNH₂)₂]Cl₂ complexes, formed by the reaction of CuCl₂·2H₂O and CH₃CSNH₂ in ethylene glycol at different pH values, and identified by CHNS/O and FTIR analyses. The decrease in bonding energy of N-H revealed the coordination of copper ions and thioacetamide molecules. It was specified that nitrogen atoms of thioacetamide molecules were used to form Cu-thioacetamide complexes. XRD, SEM, TEM and SAED analyses show that the products were hexagonal CuS spheres in an extremely low pH solution, and hexagonal CuS nanotubes at a pH 13. Their Raman spectra show sharp peaks at 473 cm^− 1, identified as the S-S stretching mode of S₂ ions at the 4e sites.     

Morphology controllable synthesis of TiO2 by a facile hydrothermal process

Titanium dioxide nanoparticles were prepared via a facile hydrothermal approach with titanium tetrabutoxide as a precursor under strongly acidic condition. The transmission electron microscopy results showed that novel flower-like, leaf-like, and rod-like TiO₂ nanoscale materials could be easily obtained by tailoring the concentration of the precursor and the reaction temperature. And the analysis from X-ray diffraction revealed that all the as-prepared products under different experimental conditions possessed a mixed crystal phase of anatase and rutile. The reasons for the phase formation were discussed. Larger proportion of rutile phase should be ascribed to the strongly acidic conditions. The growth mechanisms of TiO₂ nanostructures with various morphologies were also proposed.     

Preparation and transformation to hollow nanospheres of wrapped CuS nanowires by a simple hydrothermal route

In this paper we reported the preparation of wrapped CuS nanowires via a simple hydrothermal reaction at 180 °C for 2 h, employing CuSO₄·5H₂O and thiourea as reactants in the absence of any structure-directing agent. SAED pattern showed that the wrapped CuS nanowires were polycrystalline, which was comprised of small nanoparticles. TEM observations showed that wrapped nanowires could grow and further transfer to hollow spheres with the prolonging of the reaction time from 2 h to 13. The UV-Vis spectra of CuS prepared at 180 °C for different times were studied. The possible transfer mechanism from wrapped nanowires to hollow spheres was suggested.     

Biosynthesis of gold nanoparticles using the bacteria Rhodopseudomonas capsulata

The use of microorganisms in the synthesis of nanoparticles emerges as an eco-friendly and exciting approach. In this study, the bacteria Rhodopseudomonas capsulata was screened and found to successfully produce gold nanoparticles of different sizes and shapes. The important parameter, which controls the size and shape of gold nanoparticles, was pH value. The R. capsulata biomass and aqueous HAuCl₄ solution were incubated at pH values ranging from 7 to 4. The results demonstrated that spherical gold nanoparticles in the range of 10-20 nm were observed at pH value of 7 whereas a number of nanoplates were observed at pH 4.     

Preparation of polyaniline nanotubes by a template-free self-assembly method

Polyaniline nanotubes were prepared by the template-free self-assembly method in various aqueous media. Typically, polyaniline synthesized in methanol solution has a carambola-like shape covered with some nanotubes, and those obtained in acetic acid are short nanotubes accompanied with lots of nanoparticles. When appropriate mixed solution was used, uniform and long polyaniline nanotubes were obtained. The impact of proportion of methanol and acid was illustrated as well as the synergetic effect of these two components. The morphology evolution during the polymerization process was also investigated. SEM images clearly demonstrate that polyaniline nanotubes form through a self-curling behavior. The structure features of end products in various aqueous media and intermediates in the optimum mixed solution were surveyed by FTIR.     

Biosynthesis of gold nanoparticles by the tropical marine yeast Yarrowia lipolytica NCIM 3589

The synthesis of gold nanoparticles by the non-conventional yeast Yarrowia lipolytica is described. Optical images, scanning electron microscopy (SEM) and energy dispersive spectrum analysis revealed the presence of gold crystals at pH 2.0. At pH 7.0 and pH 9.0, nanoparticles displayed a characteristic peak at 540 nm and their presence was confirmed by XRD studies. Both the yeast and filamentous forms synthesized nanoparticles under a variety of conditions. SEM and transmission electron microscopy (TEM) showed that nanoparticles were associated with the cell wall. This paper thus describes a novel application of the abundantly available biomass of Y. lipolytica.     

Catalytic synthesis of carbon nanofibers and nanotubes by the pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method

Carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were synthesized at different temperatures by the catalytic pyrolysis of acetylene with iron nanoparticles prepared using a hydrogen-arc plasma method. The obtained carbon nanomaterials were characterized by transmission electron microscopy and field-emission scanning electron microscopy. An iron nanoparticle was always located at the tip of CNFs or CNTs, whose diameter was approximately identical with the diameter of the iron nanoparticle. The structures of the products were closely related to the reaction temperature, and could be changed from fibers to tubes by simply increasing the temperature. CNFs were obtained at the reaction temperature of 550-650 °C. When the reaction temperature was increased to 710-800 °C, CNTs were obtained.     

Temperature effect on synthesis of different carbon nanostructures by sulfur-assisted chemical vapor deposition

The temperature effect on synthesizing different carbon nanostructures in the range of 820−1020 °C by sulfur-assisted chemical vapor deposition is investigated. When the growth temperature is no more than 900 °C (e.g. 820, 860, and 900 °C), carbon onions can be obtained, accompanying with some fishbone-like carbon nanofibers (CNFs), graphite sheet and carbon nanotubes (CNTs). When the growth temperature is increased to 940 °C or above (e.g. 980 and 1020 °C), the products are mainly CNTs. Furthermore, by comparing the nitrogen adsorption-desorption results of samples obtained with and without sulfur addition at each temperature, it is found that the specific surface area (SSA) of products can be remarkably enlarged after introducing small amount of sulfur during growth. This is favorable to their applications in areas like electrodes of supercapacitors, adsorbents, catalyst supports, and so on.     

Characterization of gold nanoparticles in organic or inorganic medium (ethanol/water) fabricated by spark discharge method

In this paper a method of spark discharge method (SDM) for producing gold nanoparticles in organic or inorganic medium (pure ethanol/deionized water) is proposed. The microstructure of SDM-produced gold nanoparticles was examined by Transmission Electron Microscopy. The crystal structure and surface plasmon resonance of the nanoscale gold particles were studied using X-ray diffraction and UV-Visible spectroscopy. Zeta potential analysis showed that negative charges on the particle surface may be contributing to the stability of the suspension. The experiment's results revealed that SDM is an alternative process to synthesize gold nanoparticle suspension with different particle sizes and shapes in different media without any surfactant.     

Characterization and optical properties of ZnO nanoparticles obtained by oxidation of Zn nanoparticles

Strong UV emission at about 399 nm (3.1 eV) and multiple blue emissions at 440-490 nm (2.70-2.53 eV) by ZnO nanoparticles have been observed. The characterizations of ZnO nanoparticles, obtained by oxidizing Zn nanoparticles prepared by arc-discharging, were investigated. The multiple blue PL becomes stronger as the oxidation temperature and time increase, which is attributed to the existence of various defects, in particular to interstitial zinc at the surface of the ZnO nanoparticles.     

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.     

Preparation of uncoated iron oxide nanoparticles by thermal decarboxylation of iron hydroxide cetylsulfonyl acetate in solution

A novel method for preparing uncoated iron oxide nanoparticles by thermal decarboxylation of iron hydroxide cetylsulfonyl acetate in solution followed by heating under the protection of nitrogen was presented. The thermal decarboxylation of the precursor and the formation of iron oxide were monitored by FTIR and XRD, the vibrations of alkyl and sulfonyl groups vanished after refluxing in tetraline and uncoated maghemite was obtained after heating treatment at 400 °C. The sizes and morphologies of the obtained samples were studied by TEM. The particles were about 3 nm after refluxing and 8 nm after calcining at 400 °C but agglomerated due to the absence of capping ligands.     

Nanosize stabilization of cubic and tetragonal phases in reactive plasma synthesized zirconia powders

Pure zirconium oxide powders with particle size 2–33 nm are synthesized by reactive plasma processing. Transmission electron microscopy investigation of these particles revealed size dependent behavior for their phase stabilization. The monoclinic phase is found to be stable when particle size is ≥20 nm; Tetragonal is found to be stabilized in the range of 7–20 nm and as the particle size decreases to 6 nm and less, the cubic phase is stabilized.