Ze’ev Porat

Ultrasonic cavitation of molten gallium: Formation of micro- and nano-spheres

Pure gallium has a low melting point (29.8°C) and can be melted in warm water or organic liquids, thus forming two immiscible liquid phases. Irradiation of this system with ultrasonic energy causes cavitation and dispersion of the molten gallium as microscopic spheres. The resultant spheres were found to have radii range of 0.2-5 μm and they do not coalesce upon cessation of irradiation, although the ambient temperature is well above the m.p. of gallium. It was found that the spheres formed in water are covered with crystallites of GaO(OH), whereas those formed in organic liquids (hexane and n-dodecane) are smooth, lacking such crystallites. However, Raman spectroscopy revealed that the spheres formed in organic liquids are coated with a carbon film. The latter may be the factor preventing their coalescence at temperatures above the m.p. of gallium.

Facile one-step sonochemical synthesis of ultrafine and stable fluorescent C-dots

This work describes a one-step synthesis of carbon dots (C-dots), which is carried out by sonication of polyethylene glycol (PEG-400) for 0.5-3h. The effect of the various experimental parameters, such as sonication time, amplitude and temperature on the size and the fluorescence of the C-dots was studied. It was found that the average diameter of the C-dots is between 2 and 9 nm, depending on the preparation conditions. The highest quantum yield of emission was ∼ 16%. These high fluorescence properties of the C-dots could be used for bioimaging and for solar cell applications.

The sonochemical synthesis of Ga@C-dots particles

This research article is focused on a one-step sonochemical fabrication of carbon dots (C-dots) doped with Ga atom (Ga@C-dots). The synthesis is carried out by sonicating in molten Ga, polyethylene glycol (PEG-400) as the reaction medium for 30–120 min. The produced Ga@C-dots is present in the PEG supernatant and has an average diameter of 5 ± 2 nm. Herein, fluorescence is used to probe the emission of Ga@C-dots and to examine if it differs from that of pristine C-dots. The new product was also characterized by fluorimetric, surface charge potential, and XPS (X-ray photoelectron spectroscopy) measurements. It was revealed that the physical properties of the Ga@C-dots are different from pristine C-dots. We attribute the fluorescence spectrum to energy transfer from the C-dots to the Ga particles. Ga@C-dots show high photosensitization with respect to pristine C-dots.

Sonochemical synthesis of CH3NH3PbI3 perovskite ultrafine nanocrystal sensitizers for solar energy applications.

The organic-inorganic hybrid perovskite CH3NH3PbI3 is becoming an interesting material in the field of energy harvesting. This material is one of the cleanest and cheapest components in solar cells which is available in ample amounts. However, most of the previous research work was done on thin film of this material. In the present work we describe the preparation of a powder containing nanoparticles of CH3NH3PbI3 using a sonochemical method. Characterization of the product was done by various methods, such as HRTEM, FTIR, PL, DLS and XRD. The particles were found to be highly crystalline (tetragonal crystal structure), polygonal in shape and having diameters of 10-40nm.

Facile synthesis of gallium oxide hydroxide by ultrasonic irradiation of molten gallium in water

This work describes the single-step synthesis of GaO(OH) by ultrasonic irradiation of molten gallium in warm water. The ultrasonic energy causes dispersion of the liquid gallium into micrometric spheres, as-well-as decomposition of some of the water into H and OH radicals. The OH radicals and the dissolved oxygen react on the surface of the gallium spheres to form crystallites of GaO(OH). These crystallites prevent the re-coalescence of the gallium spheres, and as the reaction proceeds all the gallium is converted into crystalline GaO(OH).

DSC measurements of the thermal properties of gallium particles in the micron and sub-micron sizes, obtained by sonication of molten gallium

The thermal behavior of gallium microparticles, in comparison with bulk gallium, was examined by differential scanning calorimetry. All the samples showed a single endothermic signal for melting near the known melting point of gallium. Cooling the molten samples showed super-cooling effect, which was more pronounced for the gallium microparticles than for the bulk metal.

Ga@C-dots as an antibacterial agent for the eradication of Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa causes infections that are difficult to treat by antibiotic therapy. This research article reports on the synthesis of gallium (Ga) doped in carbon (C)-dots (Ga@C-dots) and their antimicrobial activity against free-living P. aeruginosa bacteria. The synthesis of Ga@C-dots was carried out by sonicating molten Ga (for 2.5 h) in polyethylene glycol-400, which acts as both a medium and carbon source. The resultant Ga@C-dots, having an average diameter of 9±2 nm, showed remarkably enhanced antibacterial activity compared with undoped C-dots. This was reflected by the much lower concentration of Ga doped within Ga@C-dots which was required for full inhibition of the bacterial growth. These results highlight the possibility of using Ga@C-dots as potential antimicrobial agents.

Ultrafine Highly Magnetic Fluorescent γ-Fe2O3/NCD Nanocomposites for Neuronal Manipulations

In this work, we describe a low-cost, two-step synthesis of composites of nitrogen-doped carbon quantum dots (NCDs) with γ-Fe2O3 (NCDs/γ-Fe2O3), which is based on a hydrothermal cum co-precipitation method. The product is a fine powder of particles having an average diameter of 9 ± 3 nm. The physical and chemical properties of NCDs/γ-Fe2O3 were studied, as well as the superconducting quantum interference device and Mossbauer analysis of the magnetic properties of these nanocomposites. The interaction of NCDs/γ-Fe2O3 nanocomposites with neuron-like cells was examined, showing efficient uptake and low toxicity. Our research demonstrates the use of the nanocomposites for imaging and for controlling the cellular motility. The NCDs/γ-Fe2O3 nanocomposites are promising because of their biocompatibility, photostability, and potential selective affinity, paving the way for multifunctional biomedical applications.

Thermal and structural characterization of ultrasonicated BiSn alloy in the eutectic composition

Irradiation of the molten eutectic Bi43Sn57 alloy with ultrasonic energy produced different bismuthtin phases that were not reported in the equilibrium binary phase diagram. The X-ray powder diffraction data, refined using the Rietveld method, allowed the identification of these metastable phases and their crystal structure. The Bi2Sn and β′-Sn phases, with distorted β-Sn type structure, were obtained in the sample which was rapidly quenched after ultrasonication. On the other hand, the equiatomic phase BiSn was obtained in the quenched sample when the ultrasonication was continued during the rapid cooling below the eutectic point. The ultrasonicated samples were characterized by differential scanning calorimetry. The results suggested that the metastable phases, which were kinetically stable at RT, decomposed into equilibrium components during the heating treatment at 320xa0°C, and that this conversion is an irreversible process. Observations by scanning electron microscopy and energy dispersive X-ray analysis complete the characterization of samples.

Novel polymerization of aniline and pyrrole by carbon dots

The polymerization of aniline requires an initiator, such as ammonium persulfate, iron chloride (FeCl3), potassium persulfate, or silver nitrate. In this study, we introduced a novel one-pot synthesis of polyaniline using carbon dots (C-dots) and UV light that act as catalysts without any additional initiator. Chemical oxidative polymerization is a facile one-step process where C-dots are prepared from polyethylene glycol-400 (PEG-400). Polyaniline was also synthesized by employing carbon dots coated on a glass plate and irradiation of UV light. The synthesized polymer was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and solid-state NMR spectroscopy. A similar procedure also allowed the synthesis of polypyrrole from pyrrole. The approach using only carbon dots and UV light offers a novel and facile route towards the formation of polymers.