The ability to synthesize multicomponent nanocomposites (NCs) is important for exploring their functional properties of not only individual single components but also their combinations in technological applications. This paper presents an investigation on the synthesis and characterization of water-soluble and bifunctional ZnO−Au NCs, of which ZnO provides fluorescence and Au is used for organic functionality for bioconjugation. ZnO nanocrystals were employed as seeding material for nucleation and growth of reduced gold by citrate to form the water-soluble ZnO−Au NCs. The morphology and components of the ZnO−Au NCs, characterized by the TEM and XRD, respectively, demonstrate a dumbbell-like shape and crystalline wurtzite ZnO together with face-center-cubic Au nanoparticles. The surface plasmon absorption band of ZnO−Au NCs in aqueous solution is distinctly broadened and red-shifted relative to monometallic Au nanoparticles, and the UV emission intensity is higher by about 1 order of magnitude in ZnO−Au NCs than in pure ZnO nanocrystals; these observations reflect the strong interfacial interaction between ZnO and Au. Moreover, multiphonon Raman scattering of ZnO is also largely enhanced by the strongly localized electromagnetic field of the Au surface plasmon.

Size and morphology controlled NaYF4:Yb, Er nanocrystals were synthesized via the hydrothermal method. Polydentate ligands, such as EDTA and citrate, were used in the synthesis of cubic and hexagonal Yb3+, Er3+ codoped NaYF4 nanocrystals as a means of controlling the size and morphology of the nanocrystals. Subsequently, the particle size was found to be dependent on the nucleation rate, which, in turn, was governed by the reactant concentration, molar ratio and choice of ligand. The phase transformation from cubic to hexagonal was found to be sensitive to reaction time and reactant concentration. The upconversion photoluminescence of the nanocrystals demonstrated morphology dependence, which provides a means to characterize their crystalline quality and structure.

We report a new class of porous liquids (PLs) using internally functionalized metal–organic framework (MOF) particles as pore carriers and poly­(dimethylsiloxane) as bulky solvents. Using a generalizable noncovalent surface-initiated controlled radical polymerization technique, a series of isoreticular UiO-66 particles were dispersed in a liquid PDMS matrix with excellent homogeneity and colloidal stability. Benefiting from the inherent properties of PDMS, the PLs exhibit low vapor pressure, high thermal stability, and fluidity down to −35 °C. Attributed to the bulkiness of PDMS and its inherent high permeability, the sorption properties of the MOF fillers can be largely retained in their respective PLs as confirmed by low-pressure CO2, N2, Xe, and H2O sorption isotherms. The permanent porosity of the PLs can also be largely preserved even after 15 months of storage. Finally, we demonstrate that by tuning the molecular weight and polymer chain architecture of PDMS, it is possible to preserve the permanent porosity of a mesoporous MOF, MIL-101­(Cr), within a PL.

The effect of annealing on the upconversion luminescence of ZnO:Er3+ nanocrystals was investigated in detail. The green and the red upconverted emissions under infrared 978-nm light excitation were remarkably enhanced with an increase of annealing temperature. Moreover, for the sample annealed at 500 °C, the ratio of the intensity of 2H11/2 → 4I15/2 emission to that of 4S3/2 → 4I15/2 emission increased from less than to more than unity with an increase of the excitation density. However, the same case did not occur to the sample annealed at 700 °C, where the ratio was independent of excitation density except when the excitation density was higher than 42 700 W/cm2. This distinction was attributed mainly to the difference in energy gap between the 2H11/2 and 4S3/2 states in the two samples, originating from the local microstructure variation around Er3+ ions. In addition, a high thermal sensitivity of 0.0062/°C was obtained in the ZnO:Er3+ nanocrystals based on the temperature-dependent fluorescence intensity ratio (FIR) of the green upconverted emission, which would make this material a promising candidate for the nanoscaled thermal sensor of high accuracy and resolution.

Through the use of ambient pressure X-ray photoelectron spectroscopy (APXPS) and a single-sided solid oxide electrochemical cell (SOC), we have studied the mechanism of electrocatalytic splitting of water (H 2 O + 2e − → H 2 + O 2− ) and electro-oxidation of hydrogen (H 2 + O 2− → H 2 O + 2e − ) at ∼700°C in 0.5 Torr of H 2 /H 2 O on ceria (CeO 2−x ) electrodes. The experiments reveal a transient buildup of surface intermediates (OH − and Ce 3+ ) and show the separation of charge at the gas−solid interface exclusively in the electrochemically active region of the SOC. During water electrolysis on ceria, the increase in surface potentials of the adsorbed OH − and incorporated O 2− differ by 0.25 eV in the active regions. For hydrogen electro-oxidation on ceria, the surface concentrations of OH − and O 2− shift significantly from their equilibrium values. These data suggest that the same charge transfer step (H 2 O + Ce 3+ ⇔ Ce 4+ + OH − + H • ) is rate limiting in both the forward (water electrolysis) and reverse (H 2 electrooxidation) reactions. This separation of potentials reflects an induced surface dipole layer on the ceria surface and represents the effective electrochemical double layer at a gas−solid interface. The in situ XPS data and DFT calculations show that the chemical origin of the OH − /O 2− potential separation resides in the reduced polarization of the Ce−OH bond due to the increase of Ce 3+ on the electrode surface. These results provide a graphical illustration of the electrochemically driven surface charge transfer processes under relevant and nonultrahigh vacuum conditions. ■ INTRODUCTIONUnderstanding the mechanisms of charge separation and charge transfer at electrochemical interfaces is essential for the rational development of electrochemical devices, such as batteries, fuel cells, electrolyzers, and supercapacitors. 1,2 However, the materials and operating conditions employed in real world applications of these technologies are usually quite different from those used in surface science studies on model systems (i.e., the "pressure and materials gap"). 3−5 This disconnect is particularly problematic with high temperature electrochemical energy conversion devices with multicomponent materials (e.g., solid oxide fuel cells, electrolyzers, and electrocatalytic fuel processors) 6 for which in situ surface experiments at cell operating temperatures (typically >500°C) are challenging. 7 Because of the experimental constraints of most surface science experiments, the knowledge and understanding of the surface processes at relevant conditions are limited and rely on extrapolations from ultrahigh vacuum (UHV) conditions and modeling studies. 8 As a result, the electrochemical surface processes are not well understood. For example, the nonFaradaic electrochemical modification of catalytic activity (NEMCA or EPOC) 9 can significantly enhance the rates of catalytic transformation of over 100 reactions, 3,10 yet the origins of this enhancement are not fully understood. 3 Even the mechanism ...

Dimethyl methylphosphonate (DMMP) is a common chemical warfare agent simulant and is widely used in adsorption studies. To further increase the understanding of DMMP interactions with metal oxides, ambient pressure X-ray photoelectron spectroscopy was used to study the adsorption of DMMP on MoO3, including the effects of oxygen vacancies, surface hydroxyl groups, and adsorbed molecular water. Density functional theory calculations were used to aid in the interpretation of the APXPS results. An inherent lack of Lewis acid metal sites results in weak interactions of DMMP with MoO3. Adsorption is enhanced by the presence of oxygen vacancies, hydroxyl groups, and molecular water on the MoO3 surface, as measured by photoelectron spectroscopy. Computational results agree with these findings and suggest the

A universal method to grow polymers on MOF surfaces with well-defined thickness, sequence and functionality.

Spatially resolved ambient pressure X-ray photoelectron spectroscopy has been used to measure and visualize regions of electrochemical activity, local surface potential losses, overpotentials, and oxidation state changes on single sided ceria/yttria-stabilized zirconia (YSZ)/Pt solid oxide electrochemical cells. When hydrogen electro-oxidation (negative applied bias) or water electrolysis (positive applied bias) is promoted on the ceria electrocatalyst, the Ce 3+ /Ce 4+ ratios shift away from equilibrium values and thereby demarcate electrochemically active regions on the ceria electrode. In addition to the ceria oxidation state shifts, inactive surface impurities with high photoelectron cross sections, such as Si, can provide local markers of activity through chemical and surface potential mappings under various electrochemical conditions. Localized removal of chemically active carbonaceous surface impurities also reveals regions of electrochemical oxidation activity on the ceria electrode. Finally, we show that electrochemical polarization of solid oxide electrochemical cells under different gas environments is used to control the ceria surface chemical state and oxygen vacancy density.