Publications

Blue light emitting graphene-based materials and their use in generating white light

It has been demonstrated that acid-treated graphene samples as well as reduced graphene oxide show fairly intense blue emission centered around 440 nm. Reduction of graphene oxide can be carried out either chemically or by using different types of radiations. Blue emission from graphene-based materials can be combined with the yellow emission from materials like ZnO to produce white light sources.

Infrared and Electronic Spectra of Rare Earth Perovskites: Ortho-Chromites, -Manganites and -Ferrites

The electronic and ir spectra of rare earth perovskites of the general formula LnZO 3 , where Ln is the rare earth ion or yttrium and Z is Cr, Mn, or Fe, have been studied in detail. The results have been discussed in terms of crystallography, magnetic properties, covalency of Ln—O and Z—O bonds, and Goodenough's one electron energy diagrams. In all these compounds the rare earth ions do not markedly affect the electronic transitions of the transition metal ions; the 3 d electrons clearly exhibit localized behavior. Both the electronic and ir spectra of the LnZO 3 perovskites are comparable to the spectra of the corresponding transition metal sesquioxides, Z 2 O 3 .

Extraordinary synergy in the mechanical properties of polymer matrix composites reinforced with 2 nanocarbons

One of the applications of nanomaterials is as reinforcements in composites, wherein small additions of nanomaterials lead to large enhancements in mechanical properties. There have been extensive studies in the literature on composites where a polymer matrix is reinforced by a single nanomaterial such as carbon nanotubes. In this article, we examine the significant synergistic effects observed when 2 different types of nanocarbons are incorporated in a polymer matrix. Thus, binary combinations of nanodiamond, few-layer graphene, and single-walled nanotubes have been used to reinforce polyvinyl alcohol. The mechanical properties of the resulting composites, evaluated by the nanoindentation technique, show extraordinary synergy, improving the stiffness and hardness by as much as 400% compared to those obtained with single nanocarbon reinforcements. These results suggest a way of designing advanced materials with extraordinary mechanical properties by incorporating small amounts of 2 nanomaterials such as graphene plus nanodiamond or nanodiamond plus carbon nanotube.

Zirconia nanotubes

Hollow nanotubes of zirconia as well as of yttria-stabilized zirconia are successfully prepared by first coating the carbon nanotubes appropriately with the oxidic material and then burning off the carbon of the template.

Covalently Functionalized Nanoparticles of Semiconducting Metal Chalcogenides and Their Attributes

Covalent functionalization of the semiconducting chalcogenide nanoparticles ZnS, ZnSe and CdS by reaction with organic halides, specifically iodobenzenes, has been demonstrated. DFT calculations have thrown light on the electronic structure of the functionalized chalcogenides. Chalcogenides with bonded phenyl groups exhibit a long wavelength charge‐transfer band as predicted by theory. Functionalization has been carried out with fluorophores as well. Functionalization of semiconducting chalcogenide particles offers many possibilities for study of their properties and application.

MoO 3 /TiO 2 and Bi 2 MoO 6 as ammonia sensors

Size-Dependent Chemistry: Properties of Nanocrystals

Properties of materials determined by their size are indeed fascinating and form the basis of the emerging area of nanoscience. In this article, we examine the size dependent electronic structure and properties of nanocrystals of semiconductors and metals to illustrate this aspect. We then discuss the chemical reactivity of metal nanocrystals which is strongly dependent on the size not only because of the large surface area but also a result of the significantly different electronic structure of the small nanocrystals. Nanoscale catalysis of gold exemplifies this feature. Size also plays a role in the assembly of nanocrystals into crystalline arrays. While we owe the beginnings of size-dependent chemistry to the early studies of colloids, recent findings have added a new dimension to the subject.

Metallic ReO 3 nanoparticles

ReO3 nanoparticles in the diameter range of 8.5-32.5 nm have been prepared by decomposition of the Re2O7-dioxane complex under solvothermal conditions and characterized by X-ray diffraction, electron microscopy, optical spectroscopy, and scanning probe microscopy. The nanoparticles have the cubic (Pm3m {221} space group) structure with the lattice parameter increasing with decreasing size. The particles are metallic and show a plasmon band around 520 nm, which becomes blue-shifted with a decrease in size. The metallicity of the nanoparticles is also confirmed by tunneling conductance measurements. The nanoparticles show paramagnetic or diamagnetic behavior depending on the size, with evidence for superparamagnetism at low temperatures when the size is small.

ChemInform Abstract: Fullerenes, Nanotubes, Onions and Related Carbon Structures

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.

2D-GaS as a Photocatalyst for Water Splitting to Produce H₂

Using first-principles local and hybrid density functional theoretical calculations, a thickness-dependent electronic structure of layered GaS is determined, and it is shown that 2D GaS has an electronic structure with valence and conduction bands that straddle the redox potentials of hydrogen evolution reaction and oxygen evolution reaction up to a critical thickness (<5.5 nm). Here, simulations of adsorption of H2O on nanoscale GaS reveal that localized electronic states at its edges appear in the gap and strengthen the interaction with H2O, further activating the surface atomic sites. It is thus predicted that GaS synthesized with a controlled thickness and preferred edges may be an efficient catalyst for photocatalytic splitting of water. Experiments that verify some of the predictions in this study are presented, and it is shown that GaS is effective in absorption of light and evolution of H2 (887 μmol h−1 g−1) in the presence of aqueous solution of hydrazine (1% v/v). This study should open up the use of nanoscale GaS in conversion of solar energy into environment-friendly chemical energy in the form of hydrogen.

Clean WS₂ and MoS₂ Nanoribbons Generated by Laser‐Induced Unzipping of the Nanotubes

The preparation of 1D WS2 and MoS2 flexible nanoribbons by laser-induced unzipping of the nanotubes is reported. The nanoribbons are of high quality, uniform width, and devoid of surface contamination. The zig-zag edges in WS2 nanoribbons give rise to ferromagnetism at room temperature. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Effect of high-temperature shock-wave compression on few-layer MoS2, WS2 and MoSe2

Exposure of few-layer MoS2, WS2 and MoSe2 to high-temperature shock waves causes morphological changes and a significant decrease in the interlayer separation between the (002) planes, the decrease being greatest in MoSe2. Raman spectra show softening of both the A 1 g and the E 2 g 1 modes initially, followed by a slightly stiffening. Using first-principles density functional theoretical analysis of the response of few-layer MoS2 to shock waves, we propose that a combination of shear and uniaxial compressive deformation leads to flattening of MoS2 sheets which is responsible for the changes in the vibrational spectra.

Some Novel Attributes of Graphene

Graphene has generated great sensation due to its amazing properties, and extensive research is being pursued on single- as well as bi- and few-layer graphenes. In this Perspective, we highlight some aspects of graphene synthesis, surface, magnetic, and mechanical properties, as well as effects of doping and indicate a few useful directions for future research.

An infrared spectroscopic study of the incommensurate transitions and related phase changes in K2Pb[Cu(NO2)6] and [N(CH3)4]2MX4 (M = Mn, Co, Cu or Zn and X = Cl or Br)

K2Pb[Cu(NO2)6] and [N(CH3)4]2MX4 (M = Mn, Co, Cu or Zn and X = Cl or Br) undergo phase transitions which involve incommensurate phases. The transitions have been investigated by examining the changes in the NO2 and CH3 vibration bands in the i.r. spectra. Splitting and broadening of some of the bands across the incommensurate transitions are discussed in the context of geometrical restrictions in the incommensurate phases. The phase transitions have also been characterized using differential scanning calorimetry.

ChemInform Abstract: Charge-Ordering 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.

Preface to the second edition

The first edition of this book published in 1986 was well received by the chemistry and materials science communities and this resulted in the paperback edition published in 1989. We are most gratified by this warm reception to the book which has been found useful by students and teachers as well as practising solid state chemists and materials scientists. Since we first wrote the book, there have been many new developments in the various aspects of solid state chemistry covering synthesis, structure elucidation, properties, phenomena and reactivity. The discovery of high-temperature superconductivity in the cuprates created a great sensation and gave a boost to the study of solid state chemistry. Many new types of materials such as the fullerenes and carbon nanotubes have been discovered. We have now revised the book taking into account the new developments so that it reflects the present status of the subject adequately and points to new directions. In this edition, we have incorporated new material in all the chapters and updated references to the literature. New sections dealing with porous solids, fullerenes and related materials, metal nitrides, metal tellurides, molecular magnets and other organic materials have been added. Under preparative strategies, we have included new types of synthesis reported in the literature, specially those based on soft chemistry routes. We have a new section covering typical results from empirical theory and electron spectroscopy.

Synthesis, Characterization, and Properties of Few‐layer Metal Dichalcogenides and their Nanocomposites with Noble Metal Particles, Polyaniline, and Reduced Graphene Oxide

Few‐layer graphene‐like sheets of MoS 2 , WS 2 , MoSe 2 and WSe 2 were prepared by employing two methods. The first method uses microwave synthesis in ethylene glycol or water medium and the second method involves laser irradiation of the bulk samples dispersed in dimethylformamide. The few‐layer dichalcogenide samples were characterized by various microscopic and spectroscopic techniques. These graphene mimics show room‐temperature ferromagnetism and exchange bias besides magnetoresistance at room temperature. We have deposited nanoparticles of gold, silver, and platinum on few‐layer WS 2 and characterized the nanocomposites. Nanocomposites of MoS 2 with reduced graphene oxide show increase in resistivity with increasing amount of MoS 2 . The polyaniline MoS 2 composite prepared by in situ polymerization of aniline in the presence of few‐layer MoS 2 shows evidence of polaronic character.

The Y3−xBa3+xCu6O14+δ system of superconductors

Members of the Y3−xBa3+xCu6O14+δ system prepared at relatively low temperatures by nitrate decomposition have a tetragonal structure and show superconducting transitions (zero-resistance) around 50K.