Yuri Koltypin

The sonochemical preparation of amorphous silver nanoparticles

Amorphous silver nanoparticles of ca. 20 nm size have been prepared by the sonochemical reduction of an aqueous silver nitrate solution in an atmosphere of argon-hydrogen. The silver nanoparticles have been characterized by TEM, X-ray diffraction, absorption spectroscopy, differential scanning calorimetry and EPR spectroscopy. The mechanism of the sonochemical reduction has been discussed, and occurs through the generation of hydrogen radicals during the sonication process.

Preparation of nanosized cobalt hydroxides and oxyhydroxide assisted by sonication

An α-cobalt hydroxide with an interlayer spacing of 12.65 A has been synthesized in sheet shapes with dimensions of 100–120 nm with the aid of sonication. Acetate anions are intercalated into the interlayer region of the as-prepared α-cobalt hydroxide in the form of a free ion state. β-Cobalt hydroxide has also been prepared and formed as crystallized thin hexagonal platelets with a diameter of 100 nm. Pure cobalt oxyhydroxide with a particle size of 10–30 nm has also been obtained. Powder X-ray diffraction, thermogravimetric analysis, FT-IR spectroscopy, transmission electron microscopy, as well as elemental analysis, have been used in the characterization of the as-prepared samples.

Catalytic Aerobic Oxidation of Cycloalkanes with Nanostructured Amorphous Metals and Alloys

Under mild conditions (40 atm O(2), 28 degrees C, 10-15 h), an efficient aerobic oxidation of cycloalkanes to cycloalkanols can be achieved using nanostructured amorphous metals such as Fe and Co and an amorphous alloy like Fe(20)Ni(80) as catalysts. For example, cyclohexane is oxidized to cyclohexanol with 32-41 % conversion, while 1-adamantanol is formed from adamantane with 52-57 % conversion.

Selective synthesis of anatase and rutile via ultrasound irradiation

A simple and efficient methodology has been established for the selective synthesis of anatase and rutile as well as their mixtures with various precursors using ultrasound irradiation; the products, the particle sizes of which are nanometric (<9 nm), are dependent both upon the reaction temperature and the precursor used; a substantial reduction in reaction time as well as reaction temperature is observed as compared to the corresponding hydrothemal processes.

Oxidation of cyclohexane with nanostructured amorphous catalysts under mild conditions

The oxidation of cyclohexane with molecular oxygen (1 atm) in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron supported on titania has been studied. It was found that highly dispersed transition metals oxide is more effective for oxidation than the corresponding zero valent powders. In the titania supported catalysts iron exists as iron (III) oxide segregated to the surface layers and stabilized by titania. This form is the most active in the cyclohexane oxidation under mild conditions.

Using Sonochemical Methods for the Preparation of Mesoporous Materials and for the Deposition of Catalysts into the Mesopores

Ultrasound radiation can be used to synthesize a variety of mesporous materials. The reaction time is considerably shorter than the conventional methods. Ultrasonic waves can be further used for the insertion of amorphous nanosized catalysts into the mesopores. A detailed study demonstrates that the nanoparticles are deposited as a monolayer on the inner mesopores walls without blocking them. When the ultrasonically prepared catalyst/mesoporous-subtrate composite is used in catalysis a high conversion into product is obtained.

Sonochemical synthesis, structural and magnetic properties of air-stable Fe/Co alloy nanoparticles

Nanoparticles of the Fe/Co alloy have been prepared by sonolysis of a Fe(CO)5 and Co(NO)(CO)3 mixture in diphenylmethane solution under argon. The as-prepared product is an amorphous material having 10 nm diameter particles. Upon annealing in argon at 600 °C for 5 h, an air-stable Fe/Co alloy is formed with an increased particle size to ∼40 nm. The Fe/Co alloy nanoparticles have been characterized by XRD, TEM, TGA, DSC, XPS, EPR, MES and magnetic susceptibility measurements. Materials obtained under appropriate conditions possess a very high saturation magnetization of about 150–238 emu g−1 and good, soft magnetic properties (Hc = 70 − 30 G). The nanocrystalline particles have a core-shell structure in which the iron–cobalt core is surrounded by a carbon surface layer. The stability of the nanocrystalline particle has been discussed, based on the core-shell structure.

Preparation of La1−xSrxMnO3 nanoparticles by sonication-assisted coprecipitation

La{sub 1-x}Sr{sub x}MnO{sub 3} (x=0.3) (LSM) nanoparticles were prepared by a sonication-assisted coprecipitation method. The coprecipitation reaction is carried out with ultrasound radiation. Lower sintering temperatures are required for the sonication-assisted product. Fully crystallized LSM with an average particle size 24 nm is obtained after the as-prepared mixture is annealed at 900 deg. C for 2 h. Magnetic properties indicate that the transition temperature from the paramagnetic to ferromagnetic state of the sample is quite sharp and occurs at 366 K for samples annealed for 2 h at 900 and 1100 deg. C.

Preparation of porous cobalt and nickel oxides from corresponding alkoxides using a sonochemical technique and its application as a catalyst in the oxidation of hydrocarbons

Porous nickel and cobalt oxides were prepared using their alkoxides as inorganic precursors. The stabilization of the mesostructure is especially critical for divalent elements such as Ni and Co, which do not form any network structure, like silicates. The lack of a network-forming multivalent bond is the probable reason why no stable mesoporous oxides have been synthesized for divalent elements yet. Here we have reported our attempt to synthesize porous oxides of Ni and Co. Octadecylamine has been used as the organic structure-directing agent. The product obtained was put under solvent extraction and calcination at various temperatures to remove the surfactant, followed by characterization using XRD, TEM and BET measurements. The FT/IR and thermal analyses (TGA and DSC) were also carried out for supporting information, such as extent of removal of surfactant from the pores of the metal oxide. A relatively better surface area has been obtained for the Co oxide, but in Ni the surface area found is not as good. A possible reason for that has been discussed. The porous (solvent extracted) cobalt oxide has been used as a catalyst in the oxidation reaction of cyclohexane in mild conditions. The catalyst has shown relatively better conversion of cyclohexane into cyclohexanone and cyclohexanol than the nanostructured cobalt oxide catalyst of regular structure.

Sonochemical synthesis of tungsten sulfide nanorods

Amorphous WS2 has been prepared by ultrasound irradiation of W(CO)6 solution in diphenylmethane (DPhM) in the presence of a slight excess of sulfur at 90 °C under argon. Heating the amorphous powder at 800 °C under argon yields WS2 nanorods and their packings. The average size of WS2 nanorods was found to be 3–10 nm and 1–5 µm in thickness and length, respectively. The prepared WS2 has been characterized by elemental analysis, X-ray powder diffraction measurements, FTIR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy, atomic force microscopy and energy dispersive X-ray analysis.