We report the formation of high surface area hollow Mn 3 O 4 nanoparticles that form as a result of the galvanic reaction of Cu 2+ with MnO nanocrystals concomitant with a nanoscale Kirkendall effect. The MnO nanocrystals were prepared according to the ultralarge scale synthesis reported by Hyeon, which allowed the preparation of hollow Mn 3 O 4 in multigram quantities. Ex-situ analyses with transmission electron microscopy and powder X-ray diffraction show the morphology and phase stability of the hollow particles correlate with DSC-TGA data and show collapse of the hollow particles at temperatures greater than 200 °C. Electrodes fabricated from hollow Mn 3 O 4 exhibited excellent initial Li ion storage capability (initial discharge capacity = 1324 mAh/g) but poor cycling performance (97% loss of discharge capacity after 10th cycle), whereas Mn 3 O 4 -MWCNT electrodes exhibited good reversibility and discharge capacity of 760 mAh/g after 100 cycles.

We report a thermolytic reduction of silver precursors in the presence of anatase TiO2 nanorods to form Ag–TiO2 hybrid nanocrystals (HNCs). Upon changing the reaction conditions, the size and number density of Ag on the HNCs could be adjusted. The size and number density of Ag on the HNCs were found to have an inverse relation. We assess the hydrogen evolution of TiO2 nanorods, P25 TiO2, and Ag–TiO2 HNCs in methanol/water under xenon lamp irradiation. The turnover frequency for hydrogen evolution on silica-supported Ag–TiO2 was 1.4 × 10–4 s–1, greater than that of the anatase TiO2 nanorods (9.8 × 10–6 s–1) or the coupled anatase/rutile TiO2 (P25 catalyst; 5.2 × 10–5 s–1).

Hollow Mn 3 O 4 nanoparticles (diameter = 31 nm, cavity diameter = 16 nm, and shell thickness = 7 nm) were attached to the surface of multiwall carbon nanotubes (MWCNT). A suspension of hollow Mn 3 O 4 /MWCNT with Nafion™ was dropcast onto a glassy carbon electrode, and the electrochemical reduction of oxygen in aqueous solution was investigated with this electrode. We assess the role of MWCNT, hollow Mn 3 O 4 , and Nafion™ in the performance of the electrode, and investigate the kinetics of the oxygen reduction reaction. The electrode exhibits outstanding performance in measures of cathodic current density and onset potential, and performed similarly well in acidic, neutral, and alkaline conditions.

The concentration of nitrate in natural surface waters by agricultural runoff remains a challenging problem in environmental chemistry. One promising denitrification strategy is to utilize photocatalysts, whose light-driven excited states are capable of reducing nitrate to nitrogen gas. We have synthesized and characterized pristine and silver-loaded graphitic carbon nitrides and assessed their activity for photocatalytic nitrate reduction at neutral pH. While nitrate reduction does occur on the pristine material, the silver cocatalyst greatly enhances product yields. Kinetic studies performed in batch photoreactors under both UV and visible excitation suggest that nitrate reduction to produce aqueous nitrite, ammonium, and nitrogen gas proceeds via a cooperative water reduction on the silver metal domains to produce adsorbed H atoms. By varying the percentage of silver loading onto the g-C 3 N 4 , the density of metal domains can be adjusted, which in turn tunes the reduction selectivity toward various products.

We report the sequential, quantitative loading of transition-metal ions (Cr, Mn, Fe, Co, Ni, and Cu) onto the surface of rod-shaped anatase TiO nanocrystals in bimetallic combinations ( C = 15) to form M,M'-TiO nanocrystals. The materials were characterized with transmission electron microscopy (TEM), powder X-ray diffraction (XRD), elemental analysis, X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy. TEM and XRD data indicate that the sequential adsorption of metal ions occurs with the retention of the phase and morphology of the nanocrystal. Atomistic models of the M,M'-TiO nanocrystals were optimized with density functional theory calculations. Calculated UV-visible absorption spectra and partial charge density maps of the donor and acceptor states for the electronic transitions indicate the importance of metal-to-metal charge transfer (MMCT) processes.

No abstract

Graphitic carbon nitride (gCN) is a promising organic platform for driving light-activated charge-transfer reactions in a number of valuable photocatalytic cycles. A primary limitation of gCN as a photocatalyst is its short excited-state lifetime, which is mediated by a high density of trap and defect sites that result in rapid excited-state decay and low photocatalytic efficiency. To enhance the catalytic activity, gCN is often functionalized with a metal co-catalyst; however, the mechanism by which metal co-catalysts enhance the reactivity has not been clearly established. In this work, the excited-state dynamics of gCN and silver-modified gCN are compared using ultrafast transient absorption and time-resolved photoluminescence spectroscopies. In silver-modified gCN, an ultrafast spectral shift in the silver plasmon resonance provides direct spectral evidence of electron transfer from gCN to the silver nanoparticles. The electron-transfer rate is competitive with other non-radiative relaxation pathways, with electron-transfer yields approaching 50%, thus providing an effective strategy for mitigating losses associated with defects and trap sites.

Cobalt(ii) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal.