Atomic and nanoscale imaging of a cellulose nanofiber and Pd nanoparticles composite using lower-voltage high-resolution TEM.

We have examined the advanced application of transmission electron microscopy (TEM) for the structural characterization of a composite of cellulose nanofiber (CNF) and palladium (Pd) nanoparticles. In the present study, we focused on electron-irradiation damage and optimization of high-resolution TEM imaging of the composite. The investigation indicates that the CNF breaks even under low-electron-dose conditions at an acceleration voltage of 200 kV. We then applied lower-voltage TEM at 60 kV using a spherical aberration corrector and a monochromator, in order to reduce electron-irradiation damage and improve the spatial resolution. The TEM observation achieved high-resolution imaging and revealed the existence of small Pd nanoparticles, around 2 nm in diameter, supported on the CNF. It is considered that the use of a monochromator in combination with spherical aberration correction contributed to the atomic and nanoscale imaging of the composite, owing to the improvement of the information limit under a lower-acceleration voltage.

Hydrocarbon decomposition on a hydrophilic TiO2 surface by UV irradiation: spectral and quantitative analysis using in-situ XPS technique.

This paper presents valuable evidence in support of the removal of a contaminant hydrocarbon layer adsorbed on photocatalytic TiO2 film by the latter's photo-oxidization. UV light was radiated on an anodic TiO2 film in an atmosphere-controlled chamber, and the film was then transferred to an ultrahigh-vacuum chamber for X-ray photoelectron spectroscopic (XPS) analysis; during the transfer, care was taken to ensure that the film was not exposed to air. This "in situ" setting eliminates the influence of carbon and water adsorptions during the transfer, thus enabling the accurate analysis of the UV-induced surface reaction. The spectral and quantitative results clearly revealed that the adsorbed hydrocarbon was removed from the photocatalytic TiO2 film when the film was irradiated in an oxygen atmosphere. Such removal occurs only in the case of TiO2 films that exhibit superhydrophilicity. This indicates that the removal of hydrocarbon is dependent on the UV-induced hydrophilicity on the film. In situ XPS measurement also presented evidence for UV-induced hydroxide group adsorption, where the adsorption was observed on both the surfaces showing superhydrophilicity and devoid of it.

Preparation of superparamagnetic magnetite nanoparticles by reverse precipitation method: contribution of sonochemically generated oxidants.

Magnetic iron oxide nanoparticles were successfully prepared by a novel reverse precipitation method with the irradiation of ultrasound. TEM, XRD and SQUID analyses showed that the formed particles were magnetite (Fe(3)O(4)) with about 10nm in their diameter. The magnetite nanoparticles exhibited superparamagnetism above 200K, and the saturation magnetization was 32.8 emu/g at 300 K. The sizes and size distributions could be controlled by the feeding conditions of FeSO(4).7H(2)O aqueous solution, and slower feeding rate and lower concentration lead to smaller and more uniform magnetite nanoparticles. The mechanisms of sonochemical oxidation were also discussed. The analyses of sonochemically produced oxidants in the presence of various gases suggested that besides sonochemically formed hydrogen peroxide, nitrite and nitrate ions contributed to Fe(II) ion oxidation.

Sonochemical immobilization of noble metal nanoparticles on the surface of maghemite: mechanism and morphological control of the products.

Aqueous sample solutions containing noble metal ions (HAuCl4, Na2PdCl4, H2PtCl6), polyethyleneglycol monostearate, and magnetic maghemite nanoparticles were irradiated with high power ultrasound. Analyses of the products showed that noble metal ions were reduced by the effects of ultrasound, and the formed noble metal nanoparticles were uniformly immobilized on the surface of the maghemite. The present "one pot process" significantly simplifies the immobilization of noble metal nanoparticles on the surface of supports, compared with the conventional impregnation method. The average diameter of immobilized Au was 7-13 nm, and the diameters of Pd and Pt were several nm. The diameters depended upon the concentration of polyethyleneglycol monostearate and the concentration of noble metal ions, but not upon the maghemite concentration, indicating the possibility of the morphological controls of the products by adjusting these preparation conditions. The measurements of the average diameters and the numbers of immobilized Au nanoparticles obtained under various conditions suggest that the nucleation of Au does not occur on the surface of maghemite, but it might occur in the homogeneous bulk solution.

Immobilization of noble metal nanoparticles on the surface of TiO2 by the sonochemical method: photocatalytic production of hydrogen from an aqueous solution of ethanol.

Sonochemically prepared Pt, Au and Pd nanoparticles were successfully immobilized onto TiO2 with the assistance of prolonged sonication. Their photocatalytic activities were evaluated in H2 production from aqueous ethanol solutions. Beside the sonochemical method, the conventional impregnation method was also employed to prepare photocatalysts. The sonochemically prepared catalysts showed higher activities than did the conventional ones. Their photocatalytic activities depended on the work functions and the dimensions of supported noble metal nanoparticles. Smaller Pt nanoparticles effectively restricted recombination of electrons and holes and provided H2 at a higher rate.

Sonochemical preparation of composite nanoparticles of Au/gamma-Fe2O3 and magnetic separation of glutathione.

We prepared Au/gamma-Fe2O3 composite nanoparticles by sonochemically reducing Au(III) ions employing no stabilizer in the aqueous solution to form stable Au nanoparticles and allowing them to attach onto the surface of gamma-Fe2O3 particles with an average size of 21 nm. Size of the formed Au nanoparticle depended on the initial concentration of Au(III) ions. The number of the Au nanoparticles, supported on each gamma-Fe2O3 particle was controlled by changing the relative amounts of Au(III) ions and gamma-Fe2O3 particles. The composite nanoparticles exhibited a high affinity with glutathione, a tripeptide with mercapto group so that separation and manipulation of glutathione in aqueous solutions could be performed by application of external magnetic field. Because the surfaces of the Au nanoparticles were not shielded by any stabilizers, or naked, sonochemically prepared Au/gamma-Fe2O3 composite nanoparticles seemed to show stronger affinity to the glutathione than those by the radiochemical method.

Structural analysis of sonochemically prepared Au/Pd nanoparticles dispersed in porous silica matrix.

Bimetallic Au/Pd nanoparticles supported on a silica matrix were prepared by an ultrasonic technique. The samples heat-treated at 100, 200, 300 and 400 degrees C were examined with techniques of XRD (X-ray diffraction), TEM and XAS (X-ray absorption spectrometry) for studying correlation between their structure and the catalytic activity of hydrogenation of cyclohexene. Even after the heat treatment at 400 degrees C, the particles were smaller than 20 nm and well dispersed in the matrix without agglomeration nor sintering. Results of the XRD, TEM and XAS indicated that the as-prepared particles have a core/shell structure of Au/Pd and transform into a random alloy at 300 degrees C. The catalysis seemed to be deactivated by alloying.