Direct imaging of surface topology and pore system of ordered mesoporous silica (MCM-41, SBA-15, and KIT-6) and nanocast metal oxides by high resolution scanning electron microscopy.

We report here a detailed study on the surface topology of well-known ordered mesoporous silica (SBA-15, MCM-41, and KIT-6) and a series of nanocast Co 3O 4, Co 3O 4/CoFe 2O 4 composites by high resolution scanning electron microscopy (HR-SEM). Images of the MCM-41 structure were obtained at a resolution of the pore size, as well as a real space image of the gyroid silica surface of KIT-6 for two different aging temperatures, clearly revealing the differences of the aging procedures. By using the low voltage HR-SEM technique with extremely high resolution, we could very clearly show the influence of the template properties on the structure of the nanocast metal oxides.

Chemical and morphological consequences of acidification of pure, phosphated, and phosphonated CaO: influence of CO2 adsorption.

In situ Fourier transform infrared (FTIR) spectroscopy was employed to characterize the adsorption behavior (as a function of pressure or time) and surface species of CO2 molecules on pure, phosphated, and phosphonated CaO. Carbonate and bicarbonate species were found to form on the pure oxide, whereas on the phosphated and phosphonated oxide samples the carbonate species were found to substitute favorably some of the OH(-) and PO4(3-) groups thereon exposed, respectively. Before and after carbonation, the test samples were further examined by in situ FTIR spectroscopy of adsorbed pyridine species, scanning electron microscopy, and energy dispersive X-ray spectroscopy. Then they were in situ acidified by exposure to a wet atmosphere of HCl vapor at 673 K for 10 min and re-examined similarly to reveal the influence of CO2 adsorption on the chemical and morphological consequences of acidification. The results obtained show the carbonate substitution of PO4(3-) groups to enhance agglomeration of the otherwise fine, longitudinal material particles into much bulkier ones and to render the otherwise more stable phosphonate groups less stable to acid treatment than the phosphate groups. Moreover, the bulky particle agglomerates of the carbonated test samples were detectably eroded following the acid treatment.

Thermoresponsive polymer-stabilized silver nanoparticles.

Silver nanoparticles (Ag NPs) stabilized by a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), have been synthesized by the reduction of silver ions with NaBH(4) in aqueous solutions. The obtained Ag NPs are very stable at room temperature due to the extended coil conformation of the PNIPAM chain at temperatures below its volume phase transition temperature ( approximately 32 degrees C). At higher temperatures (such as 45 degrees C) above the phase transition of PNIPAM, only minute aggregation between Ag NPs was observed, showing that the collapsed PNIPAM chains still retain the ability to stabilize Ag NPs. The PNIPAM-stabilized Ag NPs were then characterized as a function of the thermal phase transition of PNIPAM by UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, and cyclic voltammeter. Consistent results were obtained showing that the phase transition of PNIPAM has some effect on the optical properties of Ag NPs. Switchable electrochemical response of the PNIPAM-stabilized Ag NPs triggered by temperature change was observed.

Micelle-assisted one-pot synthesis of water-soluble polyaniline-gold composite particles.

A micelle-based method to synthesize dispersed polyaniline (PANI)-Au composite particles by direct oxidation of aniline using AuCl4- as the oxidant is presented. The obtained composite particles have a core-shell structure, where Au nanoparticles of 20 nm mean diameter are encapsulated by PANI of well-defined tetrahedron shape with 150 nm average edge length. The polaron band of the dispersed PANI-Au composite particles is centered at 745 nm and is rather narrow compared to the broad 835 nm absorption of PANI synthesized by the IUPAC procedure. The surface plasmon absorption of Au nanoparticles normally centered at around 520 nm is absent in the composite particles with oxidized PANI. Our results point to a strong electronic interaction between the encapsulated Au nanoparticles and the shell of oxidized PANI. Films and pellets produced from these composite particles show a twofold higher conductivity than IUPAC PANI.

Influence of phosphonation and phosphation on surface acid-base and morphological properties of CaO as investigated by in situ FTIR spectroscopy and electron microscopy.

Pure, phosphated, and phosphonated CaO samples were prepared and characterized by X-ray powder diffractometry, FTIR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray microprobing. Surface acid-base properties were probed by in situ FTIR spectroscopy of adsorbed CO (at 85 K), CDCl3 (at RT), CO2 (at RT), and methyl butynol decomposition reactions (at 473 K). Results obtained have shown phosphate and, to a larger extent, phosphonate additives to enhance the strength of Lewis acid sites exposed on CaO surfaces, at the expense of the Lewis base site strength. The phosphonation has been found, moreover, to make CaO particles grow in a preferential direction and be less susceptible to rehydration. These findings may establish surface chemical attributes for the application of the methylene bisphosphonate (MBP) class of drugs to hamper acid-induced resorption of bone materials (osteoporosis).

Laser-assisted synthesis of Au-Ag alloy nanoparticles in solution.

By using laser-induced heating, we prepared Au-Ag nanoalloys via three different procedures: (i) mixture of Au nanoparticles and Ag(+) ions irradiated by a 532 nm laser, (ii) mixture of Au and Ag nanoparticles irradiated by a 532 nm laser, and (iii) mixture of Au and Ag nanoparticles irradiated by a 355 nm laser. Procedure i is advantageous for the production of spherical alloy nanoparticles; in procedures ii and iii, nanoalloys with a sintered structure have been obtained. The morphology of the obtained nanoalloys depends not only on the laser wavelength but also on the concentration of nanoparticles in the initial mixture. When the total concentration of Ag and Au nanoparticles in the mixture is increased, large-scale interlinked networks have been observed upon laser irradiation. It is expected that this selective heating strategy can be extended to prepare other bi- or multi-metallic nanoalloys.

Electron holography of thin amorphous carbon films: measurement of the mean inner potential and a thickness-independent phase shift.

The phase shift induced by thin amorphous carbon films with thicknesses between 1 and 16 nm was measured by electron holography in a transmission electron microscope. Large phase shifts Delta phi are observed as the thickness of the amorphous C films decreases which cannot be described by the well-known equation Delta phi = CE V0t (V0: mean inner Coulomb potential of the material, t: sample thickness). Data plotted in a Delta phi vs. t diagram can be well-fitted by a modified equation Delta phi=CE V0t + phi add. The mean inner Coulomb potential of the amorphous carbon with a density of 1.75 g/cm3 was determined to be 9.09 V which is consistent with previous experimental data for amorphous carbon with a higher density. The thickness-independent phase offset phi(add) of 0.497 rad is large for amorphous carbon under the given experimental conditions. We suggest that a surface-related electrostatic potential is responsible for the thickness-independent contribution phi add.

On the nature of the 'heterogeneous' catalyst: nickel-on-charcoal.

Results from aromatic aminations and Kumada couplings, together with spectroscopic analyses (TEM, EDX, ICP-AES, React-IR), reveal that catalysis using nickel-on-charcoal (Ni/C) is most likely of a homogeneous rather than heterogeneous nature. In the course of a reaction with Ni/C, nickel bleed from the support was calculated to be as high as 78%. However, the existence of an equilibrium for this homogeneous species between nickel located inside vs outside the pore system of charcoal strongly favors the former, thus leaving only traces of metal detectable in solution. This accounts for virtually complete recovery of nickel on the charcoal following filtration of a reaction mixture and allows for recycling of the catalyst. TEM and EDX data were used to explain different reactivity profiles of Ni/C, which depended upon the method of reduction used to convert Ni(II)/C to Ni(0) as well as the level of nickel loading on the support.