Publications

Novel Metastable Structures of WO₃, MoO₃ and W_1‐<i>x</i>Mo_xO₃ Obtained by the Deintercalation of Layered Amine Adducts

Deintercalation of amines from the layered amine adducts of WO 3 , MoO 3 and W 1‐ x Mo x O 3 has been employed as a soft chemical route to produce unusual metastable structures of the oxides. After the adducts of WO 3 , MoO 3 and W 1– x Mo x O 3 ( x = 0.25, 0.5, 0.75) with amines such as triethylamine (TEA), pyridine, n ‐butylamine and n ‐octylamine had been characterized, deintercalation was carried out thermally as well as by acid leaching. Thermal deintercalation yielded novel metastable structures of WO 3 and MoO 3 that were significantly different from the stable forms, which contain distorted metal‐oxygen octahedra. Thus, ReO 3 ‐type cubic WO 3 was obtained by the thermal deintercalation of WO 3 · 0.5 TEA. Acid leaching of the amines gave metastable phases of WO 3 , MoO 3 and W 1‐ x Mo x O 3 , which were different from those obtained thermally. All the metastable phases transformed to the corresponding stable forms at higher temperatures.

Synthesis of multi-walled and single-walled nanotubes, aligned-nanotube bundles and nanorods by employing organometallic precursors

Pyrolysis of organometallic precursors such as metallocenes and iron pentacarbonyl as well as of their mixtures with hydrocarbons such as acetylene or benzene has been carried out under a variety of conditions to synthesize nanotubes. While the use of benzene as a hydrocarbon source generally yields multi-walled nanotubes, it has been possible to obtain single-walled nanotubes (∼1 nm diameter) by pyrolyzing a metallocene or a mixture of metallocenes along with acetylene under a high flow rate of Ar. These experiments show that the organometallic precursor produces small nanoparticles of ∼1 nm diameter which then catalyze the formation of the single-walled nanotubes. Copious quantities of aligned-nanotube bundles have been obtained by the pyrolysis of acetylene in the presence of high concentrations of ferrocene. Nanorods have been produced by the pyrolysis of ferrocene under vacuum. Single walled nanotubes can be filled or decorated by metals.

A Raman Study of CdSe and ZnSe Nanostructures

No abstract is provided for this article.

Electronic absorption and emission spectroscopic investigations of the interaction of the fullerenes, C60 and C70, with amines and aromatic molecules

Electronic absorption spectroscopy and fluorescence spectroscopy have been used to investigate the interaction of the fullerenes C60 and C70 with diethylaniline, and with aromatic solvents such as benzene. C60 interacts weakly with aromatic amines in the ground state while C70 does not interact at all. Steady state fluorescence emission and lifetime measurements show that both C60 and C70 form excited state complexes (exciplexes) with the amines in non-aromatic solvents such as methylcyclohexane, but not in benzene. In benzene, only fluorescence quenching is observed due to the interaction between the π systems of the aromatic solvent and the fullerene in the ground state. This is also borne out by the systematic study of solvent effects on the absorption and emission spectra of the fullerenes.

Strategies for the Synthesis of Graphene, Graphene Nanoribbons, Nanoscrolls and Related Materials

Single-layer graphene (SLG), the 3.4 Å thick two-dimensional sheet of sp2 carbon atoms, was first prepared in 2004 by mechanical exfoliation of graphite crystals using the scotch tape technique. Since then, SLG has been prepared by other physical methods such as laser irradiation or ultrasonication of graphite in liquid media. Chemical methods of synthesis of SLG are more commonly used; the most popular involves preparation of single-layer graphene oxide followed by reduction with a stable reagent, often assisted by microwave heating. This method yields single-layer reduced graphene oxide. Other methods for preparing SLG include chemical vapour deposition over surfaces of transition metals such as Ni and Cu. Large-area SLG has also been prepared by epitaxial growth over SiC. Few-layer graphene (FLG) is prepared by several methods; arc discharge of graphite in hydrogen atmosphere being the most convenient. Several other methods for preparing FLG include exfoliation of graphite oxide by rapid heating, ultrasonication or laser irradiation of graphite in liquid media, reduction of few-layer graphene oxide, alkali metal intercalation followed by exfoliation. Graphene nanoribbons, which are rectangular strips of graphene, are best prepared by the unzipping of carbon nanotubes by chemical oxidation or laser irradiation. Many graphene analogues of inorganic materials such as MoS2, MoSe2 and BN have been prepared by mechanical exfoliation, ultrasonication and by chemical methods involving high-temperature or hydrothermal reactions and intercalation of alkali metals followed by exfoliation. Scrolls of graphene are prepared by potassium intercalation in graphite or by microwave irradiation of graphite immersed in liquid nitrogen.

Superlattices of Metal and Metal−Semiconductor Quantum Dots Obtained by Layer-by-Layer Deposition of Nanoparticle Arrays

Superlattices formed by arrays of Pt or Au nanoparticles have been obtained by layer-by-layer deposition by using dithiols as cross-linkers. The superlattices have been characterized by X-ray diffraction, photoelectron spectroscopy, and scanning tunneling microscopy. The core-level intensities of the metal and of the dithiol in the X-ray photoelectron spectra show the expected increase with successive depositions. The formation of such structures has been confirmed by depositing Pt and Au layers alternatively. Layers of metal and CdS nanoparticles have been deposited alternatively to obtain heterostructures.

Importance of orientational rearrangement during vitrification of hydrocarbons: dependence on molecular shape

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTImportance of orientational rearrangement during vitrification of hydrocarbons: dependence on molecular shapeAparna Chakrabarti, S. Yashonath, and C. N. R. RaoCite this: J. Phys. Chem. 1992, 96, 16, 6762–6766Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://pubs.acs.org/doi/10.1021/j100195a043https://doi.org/10.1021/j100195a043research-articleACS PublicationsRequest reuse permissionsArticle Views57Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

ChemInform Abstract: Giant Magnetoresistance Phenomenon in Manganates

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Inorganic nanowires

Since the discovery of carbon nanotubes, there has been great interest in the synthesis and characterization of other one-dimensional materials. A variety of inorganic materials have been prepared in the form of nanowires with a diameter of a few nm and lengths going up to several microns. In order to produce the nanowires, both vapor-growth and solution-growth processes have been made use of. Besides physical methods, such as thermal evaporation and laser ablation, chemical methods including solvothermal, hydrothermal and carbothermal reactions have been employed for their synthesis. In this article, we describe the synthesis, structure and properties of nanowires of various inorganic materials, which include elements, oxides, nitrides, carbides and chalcogenides. Wherever possible, we have also included the relevant information on related one-dimensional materials, such as nanobelts.

Beneficial modification of the properties of multiferroic BiFeO3 by cation substitution

The effects of modifying the well-known multiferroic BiFeO3 by substituting Fe by Mn and Bi by La have been investigated. It is shown that both the substitutions have a favourable effect on the multiferroic properties of BiFeO3. Thus, both BiFe1−x Mn x O3 and Bi1−x La x FeO3 (x =0.0–0.3) show increased magnetization accompanied by hysteresis loops as well as improved dielectric properties. The ferroelectric transition temperature is lower than that of BiFeO3, but is in a more accessible range. In Bi1−x La x FeO3, there is a change in structure at x =0.2.

Positron lifetime studies in organic media

Lifetimes of positrons annihilating in a number of organic compounds consisting of aromatic hydrocarbons, substituted benzenes, phenols, anilines and ketones have been measured. Experimentally measured values of tau 2 and I2 are examined to determine whether positron annihilation takes place at a particular site of the molecule or whether it depends on average properties of the molecules. The intensity I2 seems to be related to the width of Ore gap in organic molecules; the tau 2 values in molecular liquids, however, can be interpreted in terms of additive atomic contributions to pick-off quenching. In substituted benzenes the results show changes due to substituent effects and these changes could be correlated with Hammett's sigma -constant. Results indicate that positron annihilation in organic media is determined by microscopic properties of the molecules such as ionization potentials (or width of Ore gap) and electron densities at the annihilation sites.

Inorganic Analogues of Graphene

The discovery of graphene has aroused great interest in the properties and phenomena exhibited by two‐dimensional inorganic materials, especially when they comprise only a single, two or a few layers. Graphene‐like MoS 2 and WS 2 have been prepared by chemical methods, and the materials have been characterized by electron microscopy, atomic force microscopy (AFM) and other methods. Boron nitride analogues of graphene have been obtained by a simple chemical procedure starting with boric acid and urea and have been characterized by various techniques that include surface area measurements. A new layered material with the composition BCN possessing a few layers and a large surface area discovered recently exhibits a large uptake of CO 2 .

Chemical approaches to the design of oxide materials

CCDC 112934: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Phase Transitions and the Chemistry of Solids

No abstract is provided for this article.

Reversible chemical storage of halogens in few-layer graphene

Few-layer graphene can be chlorinated up to 56 wt.% by irradiation with UV light in a liquid chlorine medium. The chlorinated sample decomposes on heating or on laser irradiation releasing all the chlorine. Similar results have been obtained with the bromination of few-layer graphene.

Investigations of carbon nanotubes

Experiments have been carried out to optimize the yields of carbon nanotubes obtained by the arc-evaporation of graphite. Other types of carbon particles such as nanocrystalline graphite usually present along with the nanotubes are readily removed by heating the material in oxygen around 763 K. Clean nanotubes so obtained have been characterized by X-ray diffraction. The clean tubes are thermally more stable than graphite or fullerenes. The tips of carbon nanotubes are opened by reaction with oxygen, but more interestingly, when the oxygen produced by the decomposition of a metal oxide is used to open the tube tips, the metal formed in the process enters the nanotube. Electrical resistance of pressed pellets of clean tubes is not unlike that of graphite. Tunnelling conductance measurements on isolated tubes characterized by means of scanning tunnelling microscopy however show that the conductance gap increases with decreasing tube diameter.

A novel method for synthesis of γ-graphyne and their charge transfer properties

Graphyne represents a family of layered artificial carbon allotropes wherein both sp and sp2 hybridized carbon atoms coexist in the lattice with γ-graphyne being the most stable member of the group. Theoretical studies predict γ-graphyne has high carrier mobility (104–105 cm2V−1s−1), exceptional flexibility, low thermal conductance, and charge transport comparable to graphene with a monolayer bandgap of ∼2.23eV. At present experimental exploration of γ-graphyne is still impeded due to the lack of suitable synthesis techniques. We report a simple one-pot Sonogashira cross-linking strategy for the synthesis of pristine γ-graphyne under mild conditions with high yields. As synthesized product was of high purity and exhibited a bandgap of 2.3eV. We believe this synthetic strategy will be helpful in designing similar strategies for the experimental realization of other members of this family. Charge transfer is a fundamental process for understanding a material's properties and tailoring them for various electronic and optoelectronic applications. In this work, UV–visible absorption studies were carried out to understand the charge transfer behavior and defect density of γ-graphyne with donor/acceptor molecules wherein few-layered γ-graphyne showed a comparable/better charge transfer behavior with organic acceptor molecules (TCNQ) than few-layered graphene.