Facile Preparation of Well-Dispersed CeO₂–ZnO Composite Hollow Microspheres with Enhanced Catalytic Activity for CO Oxidation

In this article, well-dispersed CeO₂–ZnO composite hollow microspheres have been fabricated through a simple chemical reaction followed by annealing treatment. Amorphous zinc–cerium citrate hollow microspheres were first synthesized by dispersing zinc citrate hollow microspheres into cerium nitrate solution and then aging at room temperature for 1 h. By calcining the as-produced zinc–cerium citrate hollow microspheres at 500 °C for 2 h, CeO₂–ZnO composite hollow microspheres with homogeneous composition distribution could be harvested for the first time. The resulting CeO₂–ZnO composite hollow microspheres exhibit enhanced activity for CO oxidation compared with CeO₂ and ZnO, which is due to well-dispersed small CeO₂ particles on the surface of ZnO hollow microspheres and strong interaction between CeO₂ and ZnO. Moreover, when Au nanoparticles are deposited on the surface of the CeO₂–ZnO composite hollow microspheres, the full CO conversion temperature of the as-produced 1.0 wt % Au–CeO₂–ZnO composites reduces from 300 to 60 °C in comparison with CeO₂–ZnO composites. The significantly improved catalytic activity may be ascribed to the strong synergistic interplay between Au nanoparticles and CeO₂–ZnO composites

Adsorption of Dye Molecules on Single Crystalline Semiconductor Surfaces: An Electrochemical Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy Study

Adsorption of dye molecules on semiconductor surfaces dictates the interaction at and thus the electron transfer across the interface, which is a crucial issue in dye-sensitized solar cells (DSSCs). However, despite that surface enhanced Raman spectroscopy (SERS) has been employed to study the interface, information obtained so far is gathered from surfaces of irregularly arranged nanoparticles, which places complexities for precise attribution of adsorption configuration of dye molecules. Herein, we employ single crystalline rutile TiO₂(110) for Raman spectroscopic investigation of TiO₂–dye interfaces under electrochemical control by utilizing the enhancement of Au@SiO₂ core–shell nanoparticles. FD-TD simulation is performed to evaluate the localized electromagnetic field (EM) created by the core–shell nanoparticles while Mott–Schottky measurements are used to determine the band structure of the semiconductor electrode. Comparative investigations are carried out on nanoporous P25 TiO₂ electrodes. The potential-dependent Raman shift of ν­(NCS) suggests that the binding of the SCN group of N719 to the TiO₂ surface is the intrinsic nature of the TiO₂–N719 interaction, after removing the possible bonding complexity by surface roughness. Nevertheless, hydrogen bonding between COOH and the TiO₂ appears to be more favorable on the atomic flat rutile TiO₂(110) surface than on the surface of nanoporous P25 nanoparticle as revealed by the stronger Raman shift of ν­(CO) (COOH) on the former. Electrochemical SERS (EC-SERS) results show that photoinduced charge transfer (PICT) occurs for both the P25 and rutile(110) TiO₂ surfaces, and the potential to achieve PICT resonance depends on the band structure of the semiconductor. Our work demonstrates that EC-SERS can be applied to study the single crystalline semiconductor–molecule interfaces using core–shell based surface plasmonic resonance (SPR) enhancement strategy, which would promote fundamental investigations on interfaces of photovoltaic and photocatalytic systems