We have demonstrated that seeded growth of nanocrystals offers a convenient way to design nanoheterostructures with complex shapes and morphologies by changing the crystalline structure of the seed. By using CdSe nanocrystals with wurtzite and zinc blende structure as seeds for growth of CdS nanorods, we synthesized CdSe/CdS heterostructures nanorods and nano-tetrapods, respectively. Both of these structures showed excellent luminescent properties, combining high photoluminescence efficiency (~80% and ~50% for nanorods and nano-tetrapods, correspondingly), giant extinction coefficients (~2·10 7 M -1 cm -1 and ~1.5·10 8 M -1 cm -1 at 350 nm for nanorods and nano-tetrapods, correspondingly) and efficient energy transfer from the CdS arms into the emitting CdSe core. † Current address:

Using the principles of gas adsorption kinetics, we have developed a new theoretical model addressing the adsorption and breakthrough of contaminant vapors or gases with respect to solid sorbents. Specifically, we have applied the theory to predict respirator cartridge service life in connection with individual contaminant exposure to toluene, vinyl chloride, ethyl acetate, and each of several different trichlorinated hydrocarbons at several levels of concentration. Theoretical expressions and contaminant breakthrough curves derived from our new approach are compared with those published previously by Mecklenburg and by Wheeler. The breakthrough curves derived by Mecklenburg and by Wheeler have approximately the same shape as the corresponding experimental curves for 0% to 40% breakthrough. However, these curves deviate in varying degrees from the experimental data at breakthrough values exceeding 40%. By contrast, our new theory agrees with published experimental results over the entire range of 0% to 100% breakthrough. The new model not only agrees with experimental observation, it is also less complicated and easier to apply to practical industrial hygiene problems than theories developed previously.

Semiconductor photocatalysis has been identified as a promising avenue for the conversion of solar energy into environmentally friendly fuels, most notably by the production of hydrogen from water.[1-5] Nanometer-scale materials in particular have attracted considerable scientific attention as the building blocks for light-harvesting applications. [6,7] Their desirable attributes include tunability of the optical properties with size, amenability to relatively inexpensive low-temperature processing, and a high degree of synthetic sophistication leading to increasingly complex and multi-functional architectures. For photocatalysis in particular, the high surface-to-volume ratios in nanoscale materials should lead to an increased availability of carriers for redox reactions on the nanoparticle surface.Recombination of photoexcited carriers directly competes with photocatalytic activity.[3] Charge separation is often achieved with multi-component heterostructures. An early example is the case of TiO2 powders functionalized with Pt and RuO2 particles, where photoexcited electrons are transferred to Pt (the reduction site) and holes to RuO2 (the oxidation site).[8] More recently, many colloidally synthesized nanometer-scale metal-semiconductor heterostructures have been reported. [7,9,10] A majority of these structures are made by thermal methods. [7,10] We have chosen to study photochemical formation of metal-semiconductor heterostructures. The detailed understanding of the mechanisms involved in photodeposition of metals on nanometer-scale semiconductors is necessary to enable a high degree of synthetic control. At the same time, because the results of metal deposition can be directly observed by electron microscopy, it can be used to understand how factors such as nanocrystal composition, shape, carrier dynamics, and surface chemistry influence the photochemical properties of semiconductor nanocrystals.In this communication, we report on the photodeposition of Pt on colloidal CdS and CdSe/CdS core/shell nanocrystals. Among the II-VI semiconductors, CdS is of particular interest because it has the correct band alignment for water photolysis [2] and has been demonstrated to be photocatalytically active. [11][12][13][14][15][16] We have found that the photoexcitation of CdS and CdSe/CdS in the presence of an organometallic Pt precursor leads to deposition of Pt nanoparticles on the semiconductor surface. Stark differences are observed in the Pt nanoparticle location on the two substrates, and the photodeposition can be completely inhibited by the modification of the semiconductor surface. Our results suggest that tuning of the semiconductor band structure, spatial organization and surface chemistry should be crucial in the design of photocatalytic nanostructures.

To the Editors-Sanchez et al. 1 provide a viable technological roadmap for using biomass energy with carbon capture and storage (BECCS) in the western United States 1. However, they oversimplify emissions accounting by assuming a zero or negative carbon emissions factor. Accounting for total lifecycle emissions is perhaps the greatest challenge in deploying biomass (in solid, gaseous, or liquid form) to reduce carbon emissions 2,3. When utilized to generate electricity, emissions sinks and sources for biomass occur in two different sectors. As plants grow, they take up CO 2 and store it. When combusted, the stored CO 2 is