In modern nanotechnology one of the most exciting areas is the interaction between inorganic quantum dots and biological structures. For instance gold clusters surrounded by a shell of organic ligands covalently attach to proteins or other biological substances and can be used for labeling in structural biology. In the present report we show the possibility of using live plants for the fabrication of nanoparticles. Alfalfa plants were grown in an AuCl 4 rich environment. The absorption of Au metal by the plants was confirmed by X-ray absorption studies (XAS), and transmission electron microscopy (TEM). Atomic resolution analysis confirmed the nucleation and growth of Au nanoparticles inside the plant and that the Au nanoparticles are in a crystalline state. Images also showed defects such as twins in the crystal structure, and in some cases icosahedral nanoparticles were found. X-ray EDS studies corroborated that the nanoparticles are pure gold. This is the first report on the formation of gold nanoparticles by living plants and opens up new and exciting ways to fabricate nanoparticles. It shows how it is possible to link materials science and biotechnology in the new emerging field of nanobiotechnology.

Oat (Avena sativa) biomass was studied as an alternative to recover Au(III) ions from aqueous solutions and for its capacity to reduce Au(III) to Au(0) forming Au nanoparticles. To study the binding trend of Au(III) to oat and the possible formation of Au nanoparticles, the biomass and a solution of Au(III) were reacted for a period of 1 h at pH values ranging from 2 to 6. The results demonstrated that Au(III) ions were bound to oat biomass in a pH-dependent manner, with the highest adsorption (about 80%) at pH 3. HRTEM studies showed that oat biomass reacted with Au(III) ions formed Au nanoparticles of fcc tetrahedral, decahedral, hexagonal, icosahedral multitwinned, irregular, and rod shape. To our knowledge, this is the second report about the production of nanorods as a product of the reaction of a Au(III) solution with a biological material. These studies also showed that the pH of the reaction influenced the nanoparticle size. The smaller nanoparticles and the higher occurrence of these were observed at pH values of 3 and 4, whereas the larger nanoparticles were observed at pH 2.

Gold nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWNTs) functionalized with aliphatic bifunctional thiols (1,4-butanedithiol, 1,6-hexanedithiol, 1,8-octanedithiol, and 2-aminoethanethiol) through a direct solvent-free procedure. Small gold particles, with a narrow particle size distribution around 1.7 nm, were obtained on 1,6-hexanedithiol-functionalized MWNTs. For MWNTs functionalized with the aminothiol, the average Au particle size was larger, 5.5 nm, apparently due to a coalescence phenomenon. Gatan image filter (GIF) observations show that sulfur is at the nanotube surface with a non-homogeneous distribution. A higher sulfur concentration was observed around the gold nanoparticles' location.

It is shown that adsorption of the [Au(en)(2)](3+) cationic complex can be successfully employed for the deposition of gold nanoparticles (1.5 to 3 nm) onto SiO(2) with high metal loading, good dispersion, and small Au particle size. When the solution pH increases (from 3.8 to 10.5), the Au loading in the Au/SiO(2) samples increases proportionally (from 0.2 to 5.5 wt %), and the average gold particle size also increases (from 1.5 to 2.4 nm). These effects are explained by the increase in the amount of negatively charged sites present on the SiO(2) surface, namely, when the solution pH increases, a higher number of [Au(en)(2)](3+) species can be adsorbed. Extending the adsorption time from 2 to 16 h gives rise to an increase in the gold loading from 3.3 to 4.0 wt % and in the average particle size from 1.8 to 2.9 nm. Different morphologies of gold nanoparticles are present as a function of the particle size. Particles with a size of 3-5 nm show defective structure, some of them having a multiple twinning particle (MTP) structure. At the same time, nanoparticles with an average size of ca. 2 nm exhibit defect-free structure with well-distinguishable {111} family planes. TEM and HAADF observations revealed that Au particles do not agglomerate on the SiO(2) support: gold is present on the surface of SiO(2) only as small particles. Density functional theory calculations were employed to study the mechanisms of [Au(en)(2)](3+) adsorption, where neutral and negatively charged silica surfaces were simulated by neutral cluster Si(4)O(10)H(4) and negatively charged cluster Si(4)O(10)H(3), respectively. The calculation results are totally consistent with the suggestion that the deposition of gold takes place according to a cationic adsorption mechanism.

A series of Ir and Au-Ir supported on TiO 2 catalysts were prepared by deposition-precipitation with urea to study the activity and stability of these materials in the CO oxidation reaction. Bimetallic samples were prepared using two approaches: one by codeposition of the metal precursors and the other by sequential deposition being iridium the first to be incorporated on the support. Samples were submitted to calcination in air or reduction in hydrogen thermal treatments. Nominal gold and iridium loading were 4 wt %. Samples were characterized by EDS, H 2 -TPR, HRTEM, HAADF, and CO + O 2 adsorption followed by DRIFTS. It is shown for the first time that deposition-precipitation with urea is able to deposit Ir and Au-Ir nanoparticles on TiO 2 . Catalyst pretreatment had an important effect on the structure of the iridium phase. In calcined samples, Ir spreads over the TiO 2 mainly as a thin layer of IrO 2 particles preferentially deposited on the rutile phase of TiO 2 . In reduced samples, Ir particles were homogeneously dispersed on all of the TiO 2 crystals. It is shown that, even in the samples reduced at 300 °C, IrO 2 was present in the catalysts. Ir/TiO 2 samples prepared by deposition-precipitation with urea calcined or reduced in H 2 were not active at room temperature (light-off temperature above 250 °C). The preparation protocol in bimetallic catalysts (codeposition or sequential deposition of the metals and different pretreatments) had a strong influence on the catalytic performance of the catalysts. The most active sample was the one prepared by sequential deposition and thermally treated in hydrogen at 300 °C. An enhanced activity was observed when compared to Au/TiO 2 . Besides this synergetic effect, the bimetallic catalyst was more stable in time on stream and more stable against sintering after reaction. DRIFTS experiments showed that the interaction of Au and Ir could modify the adsorption properties of catalyst surface.