Nanocrystals surface area

Thus, the authors theorized that the photorelease was initiated by electron transfer from the CdSe nanocrystal surface to 78 to form the anion of 78, which undergoes cis-trans isomerization, followed by lactonization to release 79. The authors suggested that photorelease from CdSe nanocrystals may have potential use in the areas of drug delivery and imaging. 

Although nanoscale materials promise to revolutionize many of our industries including electronics, health care, energy and more, the near term uses are in environmental remediation and green chemistry applications. One reason for this is that nanomaterials possess unique properties as adsorbents and catalysts, because (1) they possess high surface areas with large surface to bulk ratios so that the nanomaterial is used efficiently (2) nanocrystals have... 

Chemical reactivity The surface area of nanocrystals increases markedly with the decrease in size. Thus, a small metal nanocrystal of 1 nm diameter will have —100% of its atoms on the surface. A nanocrystal of 10 nm diameter on the other hand, would have only 15 % of its atoms on the surface. A... 

Feldhoff, A., C. Mendive, T. Bredow and D. Bahnemann (2007). Direct measurement of size, three-dimensional shape, and specific surface area of anatase nanocrystals. Chemphyschem, 8(6), 805-809. 

A novel method has been developed for controlling the particle size of inorganic nanocrystalls. For example, a monodispersed nanocrystalline YSZ with an average particle size of 4.7 nm is obtained by using this method [10]. A very high surface area of 165 m /g and a significant band gap increase from 4.13 to 5.44 eV are observed. Smaller SnOz nanocrystals are also prepared by this method [11]. Here we report the Raman spectra and UV-vis diffuse reflectance spectroscopy (DRS) results of the SnOz nanocrystals with different particle sizes. 

Assuming that the nanocrystals are spherical and have uniform size, the surface area (or roughness factor) may be expressed by ... 

Determination of surface atom density on nanocrystals can be difficult, and imprecise, especially for very small particles that cannot be easily characterized microscopically. Nevertheless, reasonable accuracy can be obtained by using theoretical calculations informed by empirical data. In this work, the CdTe nanocrystals that were prepared (2.5-6 nm diameter) were found to be in the zinc blende crystal structure, allowing the use of the bulk density and interplanar distances of zinc blende CdTe in these calculations. It is likely that a variety of crystalline facets are exposed on individual nanocrystals, each with a range of planar densities of atoms. It is also likely that there is a distribution of different facets exposed across an assembly of nanocrystals. Therefore, one may obtain an effective average number of surface atoms per nanocrystal by averaging the surface densities of commonly exposed facets in zinc blende nanocrystals over the calculated surface area of the nanocrystal. In this work we chose to use the commonly observed (Iff), (100), and (110) zinc blende planes, which are representative of the lattice structure, with both polar and nonpolar surfaces. For this calculation, we defined a surface atom as an atom (either Cd or Te ) located on a nanocrystal facet with one or more unpassivated orbitals. Some facets, such as Cd -terminated 111 faces, have closely underlying Te atoms that are less than 1 A beneath the surface plane. These atoms reside in the voids between Cd atoms, and thus are likely to be sterically accessible from the surface, but because they are completely passivated, they were not included in this definition. 

Next we calculated the effective volume of surface atoms within each quantum dot. We assumed a spherical geometry and used the interplanar distance d as the thickness of one monolayer of surface atoms in each nanocrystal. In this calculation, the surface volume was used, rather than the surface area, in order to yield a more realistic determination of surface atoms in very small nanocrystals (<2nm). For these high surface area nanocrystals, use of the surface area generally resulted in a surface atom number that was larger than the total number of atoms in each nanocrystal. Therefore,... 

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