Recent progress in the synthesis of inorganic nanoparticles.

Nanoparticles probably constitute the largest class of nanomaterials. Nanoparticles of several inorganic materials have been prepared by employing a variety of synthetic strategies. Besides synthesizing nanoparticles, there has been considerable effort to selectively prepare nanoparticles of different shapes. In view of the great interest in inorganic nanoparticles evinced in the last few years, we have prepared this perspective on the present status of the synthesis of inorganic nanoparticles. This article includes a brief discussion of methods followed by reports on the synthesis of nanoparticles of various classes of inorganic materials such as metals, alloys, oxides chalcogenides and pnictides. A brief section on core-shell nanoparticles is also included.

Self-assembly of C60, SWNTs and few-layer graphene and their binary composites at the organic-aqueous interface.

Self-assembly of C(60), single-walled carbon nanotubes (SWNTs) and few-layer graphene at the toluene-water interface has been investigated, starting with different concentrations of the nanocarbons in the organic phase and carrying out the assembly to different extents. Morphologies and structures of the films formed at the interface have been investigated by electron microscopy and other techniques. In the case of C(60), the films exhibit hcp and fcc structures depending on the starting concentration in the organic phase, the films being single crystalline under certain conditions. Self-assembly of the composites formed by pairs of nanocarbons (C(60)-SWNT, C(60)-few-layer graphene and SWNT-few-layer graphene) at the interface has been studied by electron microscopy. Raman spectroscopy and electronic absorption spectroscopy of the films formed at the interface have revealed the occurrence of charge-transfer interaction between SWNTs and C(60) as well as between few-layer graphene and C(60).

One-step synthesis of high-purity fluorous-capped inorganic nanoparticles.

Making use of the fact that perfluorohydrocarbon, and hydrocarbon solvents become miscible at high temperatures, highly pure inorganic nanoparticles capped with fluorous labels have been generated in a one-step synthesis. The procedure involves taking the reactants in a hydrocarbon+perfluorohydrocarbon mixture along with a fluorous reagent and carrying out the reaction at elevated temperatures. On cooling the reaction mixture, fluorous-capped inorganic nanoparticles dispersed in the perfluorohydrocarbon are obtained.

A simple method of separating metallic and semiconducting single-walled carbon nanotubes based on molecular charge transfer.

Interaction of as-prepared single-walled carbon nanotubes (SWNTs), containing a mixture of metallic and semiconducting species with the potassium salt of coronene tetracarboxylic acid, I, in an aqueous medium provides a simple method of separating semiconducting and metallic species. The metallic nanotubes precipitate out on interaction with I while the semiconducting nanotubes remain in solution. The method avoids centrifugation and is amenable for large-scale separation and can be used as a routine laboratory procedure. Interestingly, interaction with strong electron acceptor molecules brings about metal-semiconductor transitions in SWNTs.

New strategies for the enrichment of metallic single-walled carbon nanotubes.

Enrichment of metallic single-walled carbon nanotubes (SWNTs) has been accomplished by several means, including new extraction and synthetic procedures and by interaction with metal nanoparticles as well as electron donor molecules. In the presence of Fe(CO)5, the arc discharge method yields nearly pure metallic nanotubes. Fluorous chemistry involving the preferential diazotization of metallic SWNTs offers a good procedure of obtaining the pure metallic species. Interaction of gold or platinum nanoparticles as well as of electron-donor molecules such as aniline and tetrathiafulvalene (TTF) transform semiconducting SWNTs into metallic ones. Raman and electronic spectroscopies provide ideal means to monitor enrichment of metallic SWNTs.

Effect of electronic coupling between CdSe nanocrystals on the photoluminescence spectra.

Different types of aggregates of CdSe nanoparticles have been assembled by using bridging molecules such as thiolcarboxylic acids and alkanedithiols as by well as the click reaction involving cycloaddition between azido and acetylenic groups. The aggregates show photoluminescence spectra different from the pristine CdSe nanocrystals. The simplest situation is one where the spectrum has two bands one at longer wavelengths and another at lower wavelengths arising from dimeric units. More complex spectra arise from higher aggregates, but there is always some symmetry in the band positions. Fluorescence decay measurements have been carried out on the different CdSe aggregates. The results are interpreted in terms of electronic coupling between the nanocrystals.

Selective generation of single-walled carbon nanotubes with metallic, semiconducting and other unique electronic properties.

As-synthesized single-walled carbon nanotubes (SWNTs) are mixtures of semiconducting and metallic species and separation of the two is of crucial importance for many applications. In this article, the methods employed for the enrichment of semiconducting and metallic SWNTs are presented, along with possible procedures to prepare either of the species selectively. Equally important are the methods for chirality selection. The discovery of metal-semiconductor transitions in SWNTs induced by interaction with electron donor and acceptor molecules is not only of academic interest, but may also find applications. Synthesis of Y-junction SWNTs with unique electronic properties at the junction is yet to be fully accomplished.

Changes in the electronic structure and properties of graphene induced by molecular charge-transfer.

Interaction with electron-donor and -acceptor molecules such as aniline and nitrobenzene brings about marked changes in the D, G, G' and 2D bands of the Raman spectrum and the electronic structure of graphene, prepared by the exfoliation of graphitic oxide.

Use of fluorous chemistry in the solubilization and phase transfer of nanocrystals, nanorods, and nanotubes.

Fluorous chemistry, involving the use of a fluorous label for the functionalization of a substrate and a fluorous solvent for extraction of the functionalized substrate, is shown to be effective in solubilizing gold and CdSe nanoparticles in a fluorous medium, through phase transfer from an aqueous or a hydrocarbon medium. While these nanoparticles were functionalized with a fluorous thiol, single-walled carbon nanotubes and ZnO nanorods could be solubilized in a fluorous medium by reacting them with a fluorous amine. Fluorous chemistry enables the solubilization of the nanostructures in the most nonpolar liquid medium possible.