Guimin An

In Situ Controllable Loading of Ultrafine Noble Metal Particles on Titania

Herein we present a novel and facile approach to controllably load ultrafine noble metal nanoparticles on titania through in situ redox reaction between the reductive titanium(III) oxide support and metal salt precursors in aqueous solution. A series of noble metal/TiO(2) nanocomposites with uniform metal dispersion, tunable metal particle size, and narrow metal particle size distribution were obtained.

SnO2/carbon nanotube nanocomposites synthesized in supercritical fluids: highly efficient materials for use as a chemical sensor and as the anode of a lithium-ion battery

SnO2/multi-walled carbon nanotube (MWCNT) nanocomposites were prepared via oxidation of SnCl2 in a supercritical CO2?methanol mixture containing MWCNTs. The as-prepared nanocomposites were characterized by means of x-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy. It was indicated that SnO2 nanoparticles with size of 3?5?nm were uniformly and tightly decorated on the MWCNTs. The chemiluminescence characteristic to H2S and electrochemical performance of the as-prepared SnO2/MWCNT composites were investigated. The SnO2/MWCNT composites exhibited extremely high efficiency for detecting H2S, and also displayed good electrochemical performance as the anode material in a lithium-ion battery.

Pd nanoparticles immobilized on sepiolite by ionic liquids: efficient catalysts for hydrogenation of alkenes and Heck reactions

Palladium-sepiolite catalysts were prepared by immobilizing Pd2+ on sepiolite using an ionic liquid containing a guanidine cation, followed by reduction with hydrogen at 150 °C. The resulting composites were characterized by different techniques. X-Ray photoelectron spectroscopy analysis showed that the loaded Pd existed mainly in the form of Pd0, with a small amount of its oxides, and distributed uniformly on sepiolite with particle size about 5 nm, as confirmed by transmission electron microscopy examination. X-Ray diffraction analysis indicated that the sepiolite retained its original structure after deposition of Pd nanoparticles. The activities of the Pd-sepiolite catalysts for hydrogenations of some alkenes (e.g., cyclohexene and 1,3-cyclohexdiene) and Heck reactions were investigated. It was demonstrated that the as-prepared catalysts exhibited very high efficiency for these reactions.

Study on the Anatase to Rutile Phase Transformation and Controlled Synthesis of Rutile Nanocrystals with the Assistance of Ionic Liquid

We developed a route to synthesize rutile TiO(2) nanocrystals (NCs) with the assistance of 1-butyl-3-methylimidazolium chloride (bmim(+)Cl(-)). The phase transformation from anatase to rutile phase was investigated, and a simple model to describe the phase transformation process was proposed considering that the nucleation and growth of rutile phase were determined by the aggregation manner of anatase NCs and Ostwald ripening process, respectively. It was demonstrated that the surfactant-like nature of the IL used was crucial for controlling the crystallization process via controlling the aggregation manner of the NCs. The phase, shape, and size of TiO(2) NCs could be tuned by the controlling the operating conditions, such as temperature, solution acidity, and reactant concentration of the bmim(+)Cl(-)/TiCl(4)/H(2)O reaction system. Phase-pure rutile multipods and 1D nanorods with different sizes were controllably obtained.

A simple route to coat mesoporous SiO2 layer on carbon nanotubes

Herein we present a simple method to coat a porous SiO2 layer on carbon nanotubes (CNTs) with the aid of the cationic surfactant cetyltrimethyl ammonium bromide (CTAB). The coating process was studied systematically, and a possible coating mechanism was proposed. Temperature and the ratio of CTAB/CNTs/H2O were found to play key role in the coating process. This method can be applied to both multiwalled carbon nanotubes (MWNTs) and single walled carbon nanotubes (SWNTs). The individualized nature of the CNTs (both MWNTs and SWNTs) was maintained during the coating process. Furthermore, Raman spectroscopy showed that this method is nondestructive to the electronic structure of CNTs. The CNT/porous SiO2 core/shell structure will serve as a platform for further surface functionalization of CNTs.

Large-scale production of self-assembled SnO2 nanospheres and their application in high-performance chemiluminescence sensors for hydrogen sulfide gas

Mesoporous SnO2 nanospheres with high thermal stability have been fabricated via reaction of sodium stannate with CO2 controllably released from urea under hydrothermal conditions. The resultant products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption and FTIR analysis. It was indicated that the products exhibited nearly monodisperse mesoporous or hollow spherical nanostructures with sizes in the range of ca. 25–50 nm, which were composed of nanocrystals with sizes of less than 10 nm. The formation mechnism of SnO2 nanospheres was also discussed. Urea not only acted as the CO2 resource for the formation of SnO2 primary nanocrystals, but also played an important role in their self-assembly into nanospheres. The as-prepared SnO2 nanospheres exhibited superior sensitivity, high selectivity, and extremely rapid response for detecting H2S gas based on catalytic chemiluminescence (CL) characteristics.

Supercritical CO2-facilitating large-scale synthesis of CeO2 nanowires and their application for solvent-free selective hydrogenation of nitroarenes

Ceria nanowires were synthesized on a large scale by a simple, efficient, and environmentally benign strategy using supercritical (SC) CO2 expanded ethanol as reaction medium. Morphological characterization by SEM and TEM showed that most of the nanowires were bundles composed of individuals oriented parallel to each other throughout the whole length of the nanowires. Statistical data from AFM measurements showed that approximately 10% ceria nanowires (bundles/individuals) were ultrafine ones with diameters less than 5 nm. The effects of precursor concentration, reaction time and CO2 pressure on the formation of nanowires were studied, and it was found that SC CO2 played a key role in the evolution of the nanowires. As such, a possible formation mechanism for the as-prepared nanowires was provided. Moreover, the synthesis strategy was proved to be applicable to other rare earth oxide (La2O3, Eu2O3) nanowire preparation. Additionally, we successfully decorated ceria nanowires with ultrafine Pt nanoparticles via a sonication-facilitating deposition method. The as-prepared Pt-CeO2 showed superior catalytic activity and good selectivity for the solvent-free hydrogenation of nitrobenene and o-chloronitrobenzene.

The Immobilization of Glycidyl-Group-Containing Ionic Liquids and Its Application in CO2 Cycloaddition Reactions

Covalent immobilization of glycidyl-group-containing ionic liquids (ILs) on organic and inorganic supports with functional surfaces was achieved, based on the fact that the glycidyl group can actively react with almost all nucleophilic, electrophilic, neutral, and free-radical species. By using polymer spheres with amino- and carboxyl-group-functionalized surfaces as organic supports and silicas (including SBA15 and silica gel) with amino groups attached as inorganic supports, the ionic liquid 1-glycidyl-butylimidazolium chloride was successfully grafted onto these polymer and silica supports, respectively, through reactions between the glycidyl group in the IL and the polar groups on the support surfaces. The resultant samples were examined by transmission electron microscopy, solid-state (13)C NMR spectroscopy, IR spectroscopy, and ion chromatography. The activities of these resultant polymer- and silica-based catalysts were investigated for CO(2) cycloaddition reactions with epoxides. It was demonstrated that these catalysts could effectively catalyze CO(2) cycloaddition. In particular, the polymer supports generated synergistic effects with the IL in the coupling reaction of CO(2) with propylene oxide, and the turnover frequency could reach about 1700 h(-1) when the IL attached to the NH(2)-functionalized polymer was used as the catalyst.

Controlled fabrication of rare earth fluoride superstructures via a simple template-free route

A new and simple route to fabricate rare earth metal fluoride superstructures has been investigated. Typically, doughnut- and shuttle-shaped EuF3 superstructures were controllably synthesized by using sodium tetrafluoroborate (NaBF4) as a fluorine source to react with metal nitrate in aqueous solution under ambient conditions. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that different superstructures can be obtained by changing the concentration of the reactants. The photoluminescence (PL) spectra of the as-synthesized EuF3 measured with an excitation source wavelength of 380 nm showed that the emission intensity at different wavelengths can be adjusted by changing the morphology of EuF3. Moreover, our experiments indicated that the fabrication of the rare earth metal fluoride superstructures could be readily scaled up to grams.

Preparation of porous chromium oxide nanotubes using carbon nanotubes as templates and their application as an ethanol sensor

Chromium oxide nanotubes were successfully prepared using multi-walled carbon nanotubes (MWCNTs) as a template via a supercritical fluid-mediated route. In this method, with chromium (III) nitrate nonahydrate as precursor, chromium oxide was first deposited on MWCNTs in supercritical ethanol in the presence of NH(4)HCO(3). The as-prepared chromium oxide/MWCNT nanocomposites were characterized by transmission electron microscopy, x-ray diffraction, infrared spectroscopy and thermogravimetric analysis. It was demonstrated that the MWCNTs were coated with a layer of amorphous Cr(2)O(3)·xH(2)O. The thickness of the Cr(2)O(3)·xH(2)O sheath on MWCNTs could be tuned by manipulating the ratio of precursor to MWCNTs. Calcining the composites at 550 °C, the MWCNTs were removed, producing polycrystalline α-Cr(2)O(3) nanotubes. The as-prepared α-Cr(2)O(3) sample was used as a sensor material to detect ethanol vapor, and it was demonstrated that the α-Cr(2)O(3) nanotubes exhibited good performance even at 400 °C.