SERS CHARACTERIZATION OF ADSORBED WATER AT VERY NEGATIVE POTENTIALS

Surface enhanced Raman scattering of water adsorbed at silver electrodes in very negative potential region was first observed and a simple model related to the adsorption configuration is proposed.

Promotion effect of adsorbed water/OH on the catalytic performance of Ag/activated carbon catalysts for CO preferential oxidation in excess H_2

Activated carbon （AC） supported silver catalysts were prepared by incipient wetness impregnation method and their catalytic performance for CO preferential oxidation （PROX） in excess H2 was evaluated. Ag/AC catalysts, after reduction in H2 at low temperatures （≤200 ℃） following heat treatment in He at 200 ℃ （He200H200）, exhibited the best catalytic properties. Temperature-programmed desorption （TPD）, X-ray diffraction （XRD） and temperature-programmed reduction （TPR） results indicated that silver oxides were produced during heat treatment in He at 200 ℃ which were reduced to metal silver nanoparticles in H2 at low temperatures （≤200 ℃）, simultaneously generating the adsorbed water/OH. CO conversion was enhanced 40% after water treatment following heat treatment in He at 600 ℃. These results imply that the metal silver nanoparticles are the active species and the adsorbed water/OH has noticeable promotion effects on CO oxidation. However, the promotion effect is still limited compared to gold catalysts under the similar conditions, which may be the reason of low selectivity to CO oxidation in PROX over silver catalysts. The reported Ag/AC-S-He catalyst after He200H200 treatment displayed similar PROX of CO reaction properties to Ag/SiO2. This means that Ag/AC catalyst is also an efficient low-temperature CO oxidation catalyst.

Saucer-and Rod-like WO_3 3-D Microstructures:Synthesis,Characterization,and Optical Properties

Three-dimensional（3-D）saucer-and rod-like WO3 microstructures have been synthesized by a simple hydrothermal route using tartaric acid as the assistant agent.X-ray powder diffraction（XRD）patterns indicate that the as-prepared samples are the pure hexagonal phase WO3.The morphologies are characterized by scanning electron microscope（SEM）and are found to be highly sensitized to the reaction temperature.A probable formation mechanism of the WO3 microstructures from saucer-like at low temperatures to rod-like at high temperatures is proposed.The optical properties of the novel WO3 microstructures are studied by UV-vis diffuse reflectance spectroscopy（DRS）.The mechanism of strong absorption at visible region and red shift of calcined sample is also discussed.

Elimination of Surfactants and Small Dyes from Water with Silicasupported Dendritic Amphiphiles

Silica-supported branched polyethylenimine（Sil@PEI） is a conventional adsorbent and shows a limited affinity to anionic surfactants and small dyes（K = 106？107 L/mol）. If the PEI is alkylated with cetyl groups（C16）, the K of the resulting adsorbents（Sil@PEI@C16-x, where x is the fraction of PEI units being alkylated） is significantly improved. Optimization shows that Sil@PEI@C16-0.15 can best reduce aqueous surfactants to a residue around 10？10 mol/L; while Sil@PEI@C16-0.6 can reduce even small aqueous dyes to a residue below 10？10 mol/L, nearly 105-fold lower than that by Sil@PEI. The adsorbents are well recyclable. It is believed that in the case of dyes, the dense cetyl shell can isolate the PEI from the bulky water and thus suppress the competitive binding by water; while in the case of surfactants, the semiclosed cetyl shell can simultaneously meet electrostatic complement and hydrophobic complement to the surfactants.