The optical absorption of colloidal suspensions made of silver nanoparticles with polyhedral shapes is studied experimentally and theoretically. The influence of the shape on the optical response is investigated by comparing the measured absorbance with theoretical results for icosahedral, decahedral, and cuboctahedral silver nanoparticles. The theoretical spectra are obtained within the discrete dipole approximation. We find that colloidal suspensions of silver nanoparticles with a small dispersion of size distribution show very few structural shapes.

Here we report a novel pathway for the synthesis of silver nanoparticles. Spontaneous reduction of silver 2-ethylhexanoate [Ag(ethex)] takes place in dimethyl sulfoxide (DMSO) at room temperature. The reaction is slow and markedly depends on temperature leading to the formation of silver nanoparticles (NPs) with a surface plasmon resonant band maximum centered at 424 nm. Colloidal silver is not stable in DMSO without stabilizing agents. When sodium citrate (1 × 10 -4 M) is utilized as a capping agent, the surface plasmon shifts to 414 nm and the surface-modified silver nanoparticles are stable for more than 6 months. The resulting nanoparticles are quite stable but at the same time reactive enough for catalytic purposes. An HR-TEM study shows a nanoparticles size distribution centered in 4.4 nm of diameter (SD ) 1.2) and a considerable number of defects such as stacking faults and twined particles. From ab initio quantum mechanical calculations, we propose a possible precursor for the spontaneous reduction of [Ag(ethex)] in DMSO. In addition, the interaction between NO and silver nanoparticles was tested. UV-visible spectra show the oxidation of silver and the reduction of NO at room temperature. The most probable products of this reaction are N 2 O, molecular nitrogen, and oxygen. Therefore, we have a simple catalytic colloidal system for NO.

Titanium dioxide nanoparticles have been prepared by solution-phase methods in the three phases that occur naturally, anatase, rutile, and brookite. The amorphous titania starting material was prepared from titanium(IV) iso-propoxide using iso-propanol as solvent and a small quantity of water. The resulting material was treated hydrothermally in an acid digestion vessel at temperatures between 175 ˚C and 230 ˚C with different reactants to obtain the three phases or controlled mixtures of two phases. The nanomaterials were characterized by a variety of techniques, including X-ray diffraction, Raman spectroscopy, electron microscopy, dynamic light scattering, and UV-Vis absorbance spectrophotometry. The results illustrate the relation between the properties of the nanoparticles in the colloid, in the powder, and in nanostructured thin films prepared with the materials. A thorough understanding of synthesis methods is essential for the preparation of nanomaterials with tailored structural, morphological, and ultimately, physical properties.

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