Publications

Investigation of polycrystalline samples synthesized at high pressures as well as thin films deposited by nebulized spray pyrolysis suggest that BiMnO3 is ferromagnetic with a T C of 105K and ferroelectric with a Curie temperature of around 450K. It remains ferroelectric down to low temperatures through the ferromagnetic transition.

Inorganic sheets: Graphene-like MoS2 and WS2 were prepared by three different chemical methods. Examination by microscopic techniques revealed that they consist of one or a few layers (see depicted TEM image of WS2 layers), and an atomic-resolution TEM image showed that layered MoS2 has a hexagonal arrangement of Mo and S atoms (see inset).

This article describes successful incorporation of multiwalled boron nitride nanotubes (BNNTs) and various functionalized BNNTs by Lewis bases such as trioctylamine (TOA), tributylamine (TBA), and triphenylphosphine (TPP), etc., in organogels formed by triphenylenevinylene (TPV)-based low molecular weight gelator (LMWG) in toluene and consequent characterization of the resulting gel nanocomposites. Functionalized BNNTs were synthesized first, and the presence of tubular structures with high aspect ratio and increased diameter compared to the starting BNNTs was confirmed by SEM, TEM, and Raman spectroscopy. The micrographs of composites of 1 and BNNTs showed evidence of wrapping of the gelator molecules on to the BNNT surface presumably brought about by pi-pi stacking and van der Waals interactions. This leads to the formation of densely packed and directionally aligned fibrous networks. Such "reinforced" aggregation of the gelator molecules in presence of doped BNNTs led to an increase in the sol-to-gel transition temperature and the solidification temperature of the gel nanocomposites as revealed from differential scanning calorimetry. Rheological investigations of the gel nanocomposites indicate that the flow properties of the resulting materials become resistant to applied stress upon incorporation of even a very low wt % of BNNTs. Finally, the increase in thermal conductivity of the nanocomposite compared to the gelator alone was observed for the temperature range of 0-60 degrees C which may make these composites potentially useful in various applications depending on the choice and the amount of BNNT loading in the composite.

Lewis acid–base adduct formation in antimonene and bismuthene with group 12 and 13 Lewis acids leads to the tuning of the band structure along with surface passivation.

Interaction of graphene, graphene oxide, and related nanocarbons with radiation gives rise to many novel properties and phenomena. Irradiation of graphene oxide in solid state or in solution by sunlight, UV radiation, or excimer laser radiation reduces it to graphene with negligible oxygen functionalities on the surface. This transformation can be exploited for nanopatterning and for large scale production of reduced graphene oxide (RGO). Laser‐induced dehydrogenation of hydrogenated graphene can also be used for this purpose. All such laser‐induced transformations are associated with thermal effects. RGO emits blue light on UV excitation, a feature that can be used to generate white light in combination with a yellow emitter. RGO as well as graphene nanoribbons are excellent detectors of infra‐red radiation while RGO is a good UV detector.

Magnetic, linear thermal expansion (LTE), anisotropic ($\lambda_t$) and volume ($\omega $) magnetostriction properties of Pr$_{0.5}$Sr$_{0.5}$MnO$_3$ were investigated. The LTE decreases smoothly from 300 K without a clear anomaly either around the Curie (T$_C$ = 270 K) or the Neel temperature (T$_N$ = 100 K) and it exhibits hysteresis over a wide temperature range (60 K-270 K) upon warming. Isothermal magnetization study suggests that 13 % of the ferromagnetic phase coexists with 87 % of the antiferromagnetic phase at 25 K. The parallel and perpendicular magnetostrictions undergo rapid changes during the metamagnetic transition. Contrary to the isotropic giant volume magnetostriction reported in manganites so far, this compound exhibits a giant anisotropic magnetostriction ($\lambda_t \approx 10^{-3}$) and smaller volume ($\omega \approx 10^{-4}$) magnetostrictions below T$_N$. We suggest that the field induced antiferromagnetic to ferromagnetic transition is accompanied by a structural transition from the d$_{x^2-y^2}$ orbital ordered antiferromagnetic (orthorhombic) to the orbital disordered ferromagnetic (tetragonal) phase. The metamagnetic transition proceeds through nucleation and growth of the ferromagnetic domains at the expense of the antiferromagnetic phase. The preferential orientation of the ferromagnetic (tetragonal) domains along the field direction increases the linear dimension of the sample in the field direction and decreases in the orthogonal direction leading to the observed giant anisotropic magnetostriction effect. Our study also suggests that nanodomains of the low temperature antiferromagnetic phase possibly exist in the temperature region T$_N$ < T < T$_C$.

A novel method for the purification of single-walled and multiwalled carbon nanotubes is described. The method involves acid washing followed by hydrogen treatment in the 700−1000 °C range. While acid washing dissolves the metal particles, the hydrogen treatment removes amorphous carbon as well as the carbon coating on the metal nanoparticles. The high quality of the nanotubes obtained after purification has been checked by electron microscopy, X-ray diffraction, and spectroscopic methods.

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In the light of the recent discovery that carbon-rich borocarbonitrides show electrocatalytic activity for generating hydrogen from water, we have synthesized nanocomposites by covalently cross-linking BC₇N with MoS₂ sheets to explore whether the HER activity can be significantly enhanced. In order to cross-link BC₇N and MoS₂ sheets, we have exploited the presence of different functional groups on the surfaces of BN (NH₂) and graphene (COOH) domains of the borocarbonitride, as quantitatively determined by FLOSS. We have thus obtained two nanocomposites differing in the location of the cross-linking and these are designated as BN/BCN–MoS₂ and G/BCN–MoS₂, depending on which domains in the borocarbonitride participate in cross-linking. These nanocomposites were characterized by various spectroscopic methods including fluorescence labeling and their electrochemical and photochemical HER activity investigated. The composite where the graphene domains are cross-linked to MoS₂ nanosheets, G/BCN–MoS₂ (1:2), exhibits outstanding electrochemical HER activity with an onset potential of −30 mV (vs RHE) and a current density of 10 mA cm–² at an overpotential of −35 mV. This performance is closely comparable to that of Pt. The composite where the BN domains were cross-linked show somewhat lower activity. The physical mixture of BCN and MoS₂, on the other hand, does not display any notable HER activity. The BCN–MoS₂ composites also exhibit good photochemical activity. It is noteworthy that 2H-MoS₂, which does not exhibit significant catalytic activity, can be rendered highly active by cross-linking with BCN.

The aim of the contribution is to introduce a high performance anode alternative to graphite for lithium-ion batteries (LiBs). A simple process was employed to synthesize uniform graphene-like few-layer tungsten sulfide (WS2) supported on reduced graphene oxide (RGO) through a hydrothermal synthesis route. The WS2–RGO (80:20 and 70:30) composites exhibited good enhanced electrochemical performance and excellent rate capability performance when used as anode materials for lithium-ion batteries. The specific capacity of the WS2–RGO composite delivered a capacity of 400–450mAhg−1 after 50 cycles when cycled at a current density of 100mAg−1. At 4000mAg−1, the composites showed a stable capacity of approximately 180–240mAhg−1, respectively. The noteworthy electrochemical performance of the composite is not additive, rather it is synergistic in the sense that the electrochemical performance is much superior compared to both WS2 and RGO. As the observed lithiation/delithiation for WS2–RGO is at a voltage≈1.0V (≈0.1V for graphite, Li+/Li), the lithium-ion battery with WS2–RGO is expected to possess high interface stability, safety and management of electrical energy is expected to be more efficient and economic.

Cyanuric acid (CA) forms a 2:1 hydrogen-bonded adduct with 4,4′-bipyridyl (BP) when co-crystallized from a methanol solution and a 1:1 adduct from an aqueous solution. The sheet structure of the 2:1 adduct involves cyclic hydrogen bonds between the amide units of adjacent CA molecules and N–H⋯N bonds between CA and BP. The 1:1 adduct crystallized from water has a chain structure with single N–H⋯O hydrogen bonds between the adjacent CA molecules. The structures of these hydrogen-bonded assemblies bear a close resemblance to the structures of CA crystallized from the corresponding solvents. N-methylcyanuric acid (MCA) forms a chain structure with single N–H⋯O bonds between the adjacent MCA molecules. The 1:1 hydrogen-bonded adduct of MCA with BP, crystallized from methanol or water solution, retains the chain structure. The structural sensitivity of the hydrogen-bonded assemblies to the solvent of crystallization and the relation between the supramolecular assembly of the adduct and the parent structure of CA are noteworthy.