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A Keggin-type polyoxometalate (H3PW12O40) was incorporated into a mesoporous Zr-based MOF (NU-1000) via an impregnation method in aqueous media, resulting in the hybrid material, PW12@NU-1000. The POM@MOF composite was characterized by a suite of physical methods, indicating the retention of crystallinity and high porosity of the parent MOF. The hybrid material was also stable to leaching in aqueous media at varying pH. Finally, the material was tested as a heterogeneous catalyst for the oxidation of 2-chloroethyl ethyl sulfide using hydrogen peroxide as the oxidant. PW12@NU-1000 was shown to have a higher catalytic activity than either of the individual constituents alone.

Magnesium batteries are an energy storage system that potentially offers high energy density, but development of new high voltage cathode materials and understanding of their electrochemical mechanism are critical to realize its benefits. Herein, we synthesize the layered MnO2 polymorph (the birnessite phase) as a nanostructured phase supported on conductive carbon cloth and compare its electrochemistry and structural changes when it is cycled as a positive electrode material in a Mg-ion battery under nonaqueous or aqueous conditions. X-ray photoelectron spectroscopy and transmission electron microscopy studies show that a conversion mechanism takes place during cycling in a nonaqueous electrolyte, with the formation of MnOOH, MnO, and Mg(OH)2 upon discharge. In aqueous cells, on the other hand, intercalation of Mg2+ ions takes place, accompanied by expulsion of interlayer water and transformation to a spinel-like phase as evidenced by X-ray diffraction. Both systems are structurally quasireversible. The ...

The prevalent approach to developing new nanomaterials is a trial-and-error process of iteratively altering synthesis procedures and then characterizing the resulting nanostructures. This is fundamentally limited in that the growth processes that occur during synthesis can be inferred only from the final synthetic structure. Directly observing real-time nanomaterial growth provides unprecedented insight into the relationship between synthesis conditions and product evolution and facilitates a mechanistic approach to nanomaterial development. Here, we use in situ liquid-stage scanning transmission electron microscopy to observe the growth of mesoporous palladium in a solvated block copolymer (BCP) template under various synthesis conditions, and we ultimately determined a refined synthesis procedure that yields extended structures with ordered pores. We found that after sufficient drying time of the casting solvent (tetrahydrofuran, THF), the BCP assembles into a rigid, cylindrical micelle array with a hig...

Here we investigate the structure, photophysics, and photocatalytic water splitting properties of single-crystalline WO3 nanosheets (0.75 nm × 90 ± 38 nm), obtained by exfoliation from Bi2W2O9. Upon delamination, the nanosheets undergo a structural change from tetragonal symmetry in the parent material to monoclinic, as confirmed by powder X-ray diffraction and electron microscopy. Diffuse reflectance optical spectra show band gap energies consistent with quantum confinement in nano-WO3 (EG = 2.88 eV) and Bi2W2O9(EG = 2.81 eV), relative to bulk WO3 (EG = 2.68 eV). Surface photovoltage measurements on nano-WO3 films on a F:SnO2 substrate demonstrate photochemical carrier formation under band gap excitation and irreversible trapping of holes. Photochemical oxygen formation is observed with 50 mg of the material in aqueous AgNO3 and (NH4)2Ce(NO3)6 solutions under full spectrum (>250 nm) or visible only (>400 nm) irradiation. The highest initial O2 evolution rates (69.7 μmol h–1 for bulk and 35.5 μmol h–1 for...

K2Ti4O9 has been known as a photocatalyst for the oxidation of methanol under UV irradiation. Here we study the evolution of morphology, optical, and photocatalytic properties of this titanate as it is converted into H2Ti4O9 and subsequently exfoliated into individual tetrabutylammonium (TBA)-supported [Ti4O9]2- nanosheets. We find that proton exchange and exfoliation are accompanied by a red shift of the optical absorption edge and fluorescence maximum, suggesting a reduction of the bandgap in the series K2Ti4O9 (3.54 eV), H2Ti4O9 (3.25 eV), TBA2Ti4O9 (3.00 eV). Neither compound is active for photochemical water splitting, even after photochemical deposition of platinum nanoparticles. However, in aqueous methanol, all platinated compounds are moderately active for H2 evolution upon bandgap irradiation, and in 0.01 M AgNO3, they all produce moderate quantities of O2. From the onset potentials for photoelectrochemical methanol oxidation, the values for the valence band edges at pH = 7 are deduced to lie be...

CeO2 is a functional oxide known to conduct oxygen ions at elevated temperatures. Enhancement of the ionic conductivity can lead to its application as an electrolyte for solid oxide fuel cells that can operate at low temperatures. We report here a one-dimensional CeO2 nanostructure with a novel sheaflike morphology which exhibits the oxygen-ionic conductivity distinctively higher than that of conventional CeO2 electrolyte. The oxygen nonstoichiometry in the CeO2 nanowires constituting the sheaf was determined by electron energy loss spectroscopy (EELS) and was found to be very small. We thus attribute this anomalously high ionic conductivity to enhanced oxygen-ion mobility at the interfaces between CeO2 nanowires in the sheaf rather than to increased charge-carrier concentration which is often responsible for enhanced ionic conductivity in nanostructured ionic conductors.

Diluted magnetic semiconductors (DMS) are among the most intensely investigated materials in recent times in view of their great application potential. Yet, they are also the most controversial because of the possibility of extrinsic effects attributable to dopant solubility and clustering, point defects, incorporation of unintentional impurities, etc. This has highlighted the central role of materials chemistry in rendering a specific microstate and property response. In this work, we provide a combined window of high-resolution scanning transmission electron microscopy and electron energy-loss spectrometry, X-ray absorption (XAS)/X-ray magnetic circular dichroism (XMCD), and magnetization measurements on epitaxial rutile Co x Ti 1-x O 2 (x = 0-0.06) system (the first discovered oxide-DMS, which continues to be controversial) grown at low temperature (400 °C) under different ambient atmospheres. The study brings out a mixed-state scenario of ferromagnetism involving intrinsic DMS (uniform dopant distribution at low dopant concentration) and coupled cluster magnetism, involving cobalt associations within the matrix at higher concentrations. We also show that by matrix valence control during growth, it is possible to realize a uniform embedded cluster state and the related coupled cluster magnetism.

Incorporating a dopant into a nanoparticle is a nontrivial proposition in view of the size dependent surface versus bulk energy considerations and the intrinsic proximity of the surface to the interior, which facilitates migration to the surface. If realized and controlled, however, it can open up new avenues to novel nanomaterials. Some previous studies have shown the dopability of nanosystems but only with specific surface functionalization. Here, we demonstrate the successful dopant incorporation via a new route of pulsed high energy electron induced synthesis. We choose a system Co:CdS (dilutely cobalt doped cadmium sulfide) in view of the well-known application-worthy properties of CdS and the potential possibility of its conversion to a diluted magnetic semiconductor of interest to spintronics. By using various techniques, we show that matrix incorporation and uniform distribution of cobalt are realized in CdS nanocrystals without the need for additional chemical or physical manipulation. Optical an...

The combined application of HREM, HAADF STEM, and computer simulation techniques has proved to be a powerful tool for characterizing the structural modifications induced on ceria−zirconia mixed oxides by different thermochemical aging pretreatments. This is key information for better understanding the reversible changes of redox behavior exhibited by these materials.