Interaction of Au with Thin ZrO₂ Films: Influence of ZrO₂ Morphology on the Adsorption and Thermal Stability of Au Nanoparticles

The model catalysts of ZrO₂-supported Au nanoparticles have been prepared by deposition of Au atoms onto the surfaces of thin ZrO₂ films with different morphologies. The adsorption and thermal stability of Au nanoparticles on thin ZrO₂ films have been investigated using synchrotron radiation photoemission spectroscopy (SRPES) and X-ray photoelectron spectroscopy (XPS). The thin ZrO₂ films were prepared by two different methods, giving rise to different morphologies. The first method utilized wet chemical impregnation to synthesize the thin ZrO₂ film through the procedure of first spin-coating a zirconium ethoxide (Zr­(OC₂H₅)₄) precursor onto a SiO₂/Si­(100) substrate at room temperature followed by calcination at 773 K for 12 h. Scanning electron microscopy (SEM) investigations indicate that highly porous “sponge-like nanostructures” were obtained in this case. The second method was epitaxial growth of a ZrO₂(111) film through vacuum evaporation of Zr metal onto Pt(111) in 1 × 10^–6 Torr of oxygen at 550 K followed by annealing at 1000 K. The structural analysis with low energy electron diffraction (LEED) of this film exhibits good long-range ordering. It has been found that Au forms smaller particles on the porous ZrO₂ film as compared to those on the ordered ZrO₂(111) film at a given coverage. Thermal annealing experiments demonstrate that Au particles are more thermally stable on the porous ZrO₂ surface than on the ZrO₂(111) surface, although on both surfaces, Au particles experience significant sintering at elevated temperatures. In addition, by annealing the surfaces to 1100 K, Au particles desorb completely from ZrO₂(111) but not from porous ZrO₂. The enhanced thermal stability for Au on porous ZrO₂ can be attributed to the stronger interaction of the adsorbed Au with the defects and the hindered migration or coalescence resulting from the porous structures

Metal Charge Transfer Doped Carbon Dots with Reversibly Switchable, Ultra-High Quantum Yield Photoluminescence

As a class of the heteroatom-doped carbon materials, metal charge-transfer doped carbon dots (CDs) exhibited an excellent optical performance and were widely used as fluorescent probes. To improve fluorescence quantum yield (QY) remains one of the fundamental and challenging issues in the carbon dots field. Herein, we prepared a novel manganese doped CDs (Mn-CDs), which exhibited an ultrahigh quantum yield of 54%, the highest quantum yield for metal-doped CDs. Various spectroscopic measurements revealed an in situ change of dopant oxidation state during the synthesis. Our further study indicated the presence of metal–carbonate, which served as an important component for high quantum yield. We have also studied the reversibly switchable fluorescence property of Mn-CDs by adding Hg²⁺/S^2–, as well as elucidating the underlying mechanism of this switching fluorescence phenomenon. By using the Mn-CDs as fluorescent probes, we developed an extremely sensitive detection method for heavy metal Hg²⁺ detection at a nM detection limit level