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The diameter distribution of the nanotubes produced by electric-arc discharge are measured using Raman spectroscopy at various wavelengths. These measurements agree with the results provided by two other techniques: high-resolution transmission electron microscopy and x-ray diffraction. The mean tube diameter shifts more than 0.1 nm with the increase of argon in the inert atmosphere. Some argon concentrations favored the synthesis of metallic tubes with specific diameters. Furthermore, the background gas influences the macroscopic characteristics of nanotube yield and bundle size, as determined by Brunauer–Emmett–Teller surface area measurements and x-ray diffraction. The information collected on nanotube diameter and arrangement is correlated with temperatures calculated using a numerical model of the plasma generated between the two electrodes. Indeed, plasma temperature control during the production process is achieved using argon–helium mixtures as buffer gases. The variation of the gas mixture from pure argon to pure helium changes the plasma temperature and hence the nanotube diameter.

The antimicrobial activity of nanoparticles (NPs) depends of the surface area in contact with microorganisms. The large surface area of the nanoparticles enhances their interaction with the microbes. In this work, a green, simple, rapid, and efficient ultrasound-assisted reduction method for silver nanoparticles (AgNP) synthesis is presented. For the synthesis, an aqueous solution of silver nitrate, ethanol, and ammonia was used. The adopted method can be easily implemented for any kind of scientific or industrial application due to its cost-effective nature. The effect of sonication time on the nanoparticle formation was investigated. Silver nanoparticles were analyzed through transmission electron microscopy and UV-vis spectroscopy. Antimicrobial additives can be incorporated in mass in different matrixes (polymeric or cellulosic), which is a convenient methodology to achieve antimicrobial activity. In this work, silver nanoparticles were incorporated in cellulose using an ultrasonic bath technique. The most important aspect of cellulose containing silver nanoparticles prepared by this method is its high antimicrobial efficiency. The microbiological study was carried out by a standard agar technique. The analysis showed that cellulose with incorporated silver nanoparticles exhibited strong antimicrobial activity against

We report on the effect of mixing on the morphology of ultrafine zinc oxide nanoparticles synthesized via a polyol process using zinc acetate and water in a diethylene glycol medium. Three mixing strategies were considered: stirred batch, T-mixer, and impinging free jets. The particle granulometry was accessed using the transmission electron microscopy and x-ray diffraction methods. The nanoparticle size and polydispersity decreased with an increase in the local dissipated energy. In particular, the polyol process conducted in the same chemical environment at 353 K did not lead to the observation of nanoparticles in the stirred batch reactor but resulted in unconventionally small 6-nm particles in the T-mixer and impinging jet configurations. This result is apparently related to the micromixing eddy geometry described by the Kolmogorov length. The hydrodynamic flow patterns and energy dissipation were obtained from computational fluid dynamics simulations, which are essential in the design, optimization, and scale-up of the polyol process.

In this article, we report on some of the fundamental chemical and physical processes responsible for the deposition of graphene by microwave plasma-enhanced chemical vapor deposition (PECVD). The graphene is grown by plasma decomposition of a methane and hydrogen mixture (CH 4 /H 2) at moderate pressures over polycrystalline metal catalysts. Different conditions obtained by varying the plasma power (300-400 W), total pressure (10-25 mbar), substrate temperature (700-1000°C), methane flow rate (1-10 sccm) and catalyst nature (Co-Cu) were experimentally analyzed using the in situ optical emission spectroscopy (OES) technique to assess the species rotational temperature of the plasma and the H-atom relative concentration. Then, two modeling approaches were developed to analyze the plasma environment during graphene growth. As a first approximation, the plasma is described by spatially averaged bulk properties, and the species compositions are determined using kinetic rates in the transient zero-dimensional (0D) configuration. The advantage of this approach lies in its small computational demands, which enable rapid evaluation of the effects of reactor conditions and permit the identification of dominant reactions and key species during graphene growth. This approach is useful for identifying the relevant set of species and reactions to consider in a higher-dimensional model. The reduced chemical scheme was then used within the self-consistent two-dimensional model (2D) to determine auto-coherently the electromagnetic field, gas and electron temperatures, heavy species, and electron and ion density distributions in the reactor. The 0D and 2D models are validated by comparison with experimental data obtained from atomic and molecular emission spectra.

Collarets rich in single-walled carbon nanotubes (SWCNTs) have been grown using a direct current arc method. Arc process parameters such as current, pressure, and anode to cathode distance were varied experimentally and by modeling to provide an optimal working window. The best collaret yields were obtained when helium was used as a buffer gas. Mixing helium with argon in the buffer permits controlling nanotube diameters. In addition to an experimental study, a modeling approach was developed assuming local thermal equilibrium and homogenous and heterogeneous neutral chemistry. The gas-phase chemical model involves 81 neutral carbon species (C1, C2, . . ., C79, C60F, C70F) and 554 reactions with rates taken from data of Krestinin and Moravsky. Axial profiles of temperature, C atom, C2 radical, and fullerene distributions in the reactor are predicted as a function of process parameters. Carbon nanotube growth is considered by a set of surface reactions simulating open nanotube growth. Because nanotube surface chemistry is controlled by the local terminated bond and not by the bulk nanotube bond, a mechanistic approach based on the formal resemblance between the bonding and the structure of open nanotube and other carbon surfaces is proposed to explain nanotube growth. Predicted growth rates are in the range of 100 to 1000 microm/min.

Bimetallic one-dimensional cobalt-nickel magnetic nanowires capped on both sides with conical heads were synthesized using the polyol process. Then, the process was scaled up to produce magnetic nanowires in sample aliquots of approximately 20 g. The scale-up strategy involved improving the mixing reagents using either axial or radial mixing configurations and was experimentally validated by comparing the structural and magnetic properties of the resulting nanowires. The results indicated a connection between the flow patterns and the size and shape of the nanowires. When a Rushton turbine was used, shorter nanowires with unconventional small heads were obtained. Because the demagnetizing field is strongly localized near or inside these heads, the coercive field was enhanced nearly twofold. These results were confirmed by micromagnetic simulations using isolated nanowires. In addition, the development of flow patterns at the small and pilot scales was predicted and compared using three-dimensional turbulent computational fluid dynamics simulations.