There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Arsenic removal from water/wastewater using adsorbents—A critical review

5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

The ability to control the size, shape, and material of a surface has reinvigorated the field of surface-enhanced Raman spectroscopy (SERS). Because excitation of the localized surface plasmon resonance of a nanostructured surface or nanoparticle lies at the heart of SERS, the ability to reliably control the surface characteristics has taken SERS from an interesting surface phenomenon to a rapidly developing analytical tool. This article first explains many fundamental features of SERS and then describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates. In particular, we review metal film over nanosphere surfaces as excellent candidates for several experiments that were once impossible with more primitive SERS substrates (e.g., metal island films). The article also describes progress in applying SERS to the detection of chemical warfare agents and several biological molecules.

Surface-Enhanced Raman Spectroscopy

Bimetallic Pt–Ni nanoparticles (bi-MNPs) have been prepared at room temperature by a wet chemical technique from a micellar solution containing the corresponding metal salts. Co-reduction of the salts produced alloyed particles in bulk quantity. Use of different ratios of the respective metal salts supported the synthesis of tunable compositions of the Pt–Ni alloys. These alloyed bi-MNPs of variable compositions were exploited to study their catalytic activities towards the reduction of aromatic nitro compounds. The kinetics of the reduction was monitored under different experimental conditions. The catalytic activity of the Pt–Ni bi-MNPs has been found to be superior to the activities of monometallic Pt nanoparticles. Moreover, it was found that the rate of reduction of nitroaromatics is sensitive to the composition of the alloy catalysts. This could be attributed to the electronic effect and the segregation behavior of the material in the alloy.

Bimetallic Pt–Ni nanoparticles can catalyze reduction of aromatic nitro compounds by sodium borohydride in aqueous solution

We report here the enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field up to 300K and a finite thermoremanent magnetization up to 340K for the annealed sample. We propose that magnetic moments can be formed at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagneticlike behavior below 10K.

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Magnetite nanoparticles with tunable gold or silver shell

We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.

Bimetallic gold and silver particles, a core−shell type structure, have been prepared by a UV-photoactivation technique. The optical absorption spectra are recorded and compared with various absorption profiles due to Au−Ag particles described in the literature. Initially Au particles formed by UV irradiation, which act as the seed particles, catalyzed the reduction of added silver ion in the presence of UV light to yield bimetallic (Aucore−Agshell) particles. Preferential dissolution of Au particles by cyanide and TEM images of the particles corroborates the “core−shell” type configuration.

Madhuri Mandal

Papers

Bimetallic Pt–Ni nanoparticles can catalyze reduction of aromatic nitro compounds by sodium borohydride in aqueous solution

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Magnetite nanoparticles with tunable gold or silver shell

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Seed Mediated Formation of Bimetallic Nanoparticles by UV Irradiation: A Photochemical Approach for the Preparation of “Core−Shell” Type Structures