Indian Association for the Cultivation of Science

About: Indian Association for the Cultivation of Science is a education organization based out in Kolkata, India. It is known for research contribution in the topics: Excited state & Catalysis. The organization has 3867 authors who have published 10457 publications receiving 220098 citations.

Spin Exchange Coupling in Heterobimetallic MIIVIVO (M = Cu, Ni, Co, Fe, Mn) Macrocyclic Complexes. Synthesis, Structure, and Properties

Abstract: A series of heterobimetallic complexes [(VIVO)L1CuII(μ-OAC)(MeOH)](ClO4) (1) and [(VIVO)L1MII(μ-OAc)(H2O)](ClO4)·H2O (M = Ni (2), Co (3), Fe (4), Mn (5)) derived from a symmetric tetraaminodiphenol...

Optoelectronic and photovoltaic properties of graphene quantum dot–polyaniline nanostructures

Abstract: In aqueous dispersions of graphene quantum dots (GQDs) produced by a sono-Fenton method, aniline is in situ polymerized to produce different polyaniline (PANI)–GQD hybrids (PAGD) without using external dopant. FTIR studies indicate that the carboxylic acid groups of the GQDs dope PANI well. The UV-Vis spectra exhibit a π to polaron band transition of the PAGD hybrids and show a gradual red shift with increasing intensity for increasing amounts of GQDs due to the gradual uncoiling and increase of polarons in the doped PANI chains. The fluorescence intensity of the GQDs is drastically quenched in the PAGD hybrids suggesting effective charge transfer between the GQDs and PANI chains. The X-ray diffraction study suggests the presence of a lamellar structure with a lamellar thickness of 13.57 A. The morphologies of the PAGD hybrids studied using field emission scanning electron microscopy exhibit a change from flakes to rods with increasing GQD concentration, which has been attributed to the change from a flat to cylindrical lamella formation. The thermogravimetric analysis result indicates that, in comparison to HCl-doped PANI, the PAGD hybrids exhibit better thermal stability. In the PAGD composites the dc conductivity increases by three orders compared to that of the GQDs due to polaron formation in the PANI chains. The current–voltage (I–V) characteristics of the PAGD composites indicate semiconducting behaviour and on irradiation with light an almost reversible photoresponse occurs. Dye-sensitized solar cells (DSSCs) fabricated with the PAGD hybrids and N719 dye indicate a highest power conversion efficiency (PCE) of 3.12%. Impedance data of the PAGD hybrids exhibit semicircular Cole–Cole plots indicating the presence of a resistance (R)–capacitance (C) circuit where the capacitance is in parallel to the bulk resistance which increases with increasing GQD concentration. The Debye plot and the dielectric permittivity values also support the variation of the photovoltaic properties of the PAGD hybrids. The impedance spectra of the DSSCs indicate the presence of three semicircles exhibiting a complex equivalent circuit composed of three R–C circuits, and analysis of the data yields the lifetime values of photo-injected electrons supporting the PCE variation of the PAGD hybrids.

Inflationary universe in F (R ) gravity with antisymmetric tensor fields and their suppression during its evolution

Abstract: The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four- and in five-dimensional spacetime. The results here obtained reveal that the amplitude of the Kalb-Ramond field may be actually large and play a significant role during the early universe, while the presence of higher-order gravity suppresses this field during the cosmological evolution, so that it eventually becomes negligible in the current universe. Besides the suppression of the Kalb-Ramond field, the extra degree of freedom in $F(R)$ gravity, usually known as scalaron, also turns out to be responsible for inflation. Such $F(R)$ gravity with Kalb-Ramond fields may govern the early universe to undergo an inflationary stage at early times (with the subsequent graceful exit) for a wider range of $F(R)$ gravity than without antisymmetric fields. Furthermore, the models---in four- and five-dimensional spacetimes---are linked to observational constraints, with the conclusion that the corresponding values of the spectral index and tensor-to-scalar ratio closely match the values provided by the Planck survey 2018 data.

Solvent-adoptable polymer Ni/NiCo alloy nanochains: highly active and versatile catalysts for various organic reactions in both aqueous and nonaqueous media.

Abstract: The synthesis of solvent-adoptable monometallic Ni and NiCo alloy nanochains by a one-pot solution phase reduction method in the presence of poly(4-vinylphenol) (PVPh) is demonstrated. The elemental compositions of the as-prepared alloys are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS), which are matching well with the target compositions. The morphology analysis by TEM and FESEM confirms that the nanochains are made up of organized spherical monometallic Ni or bimetallic NiCo alloy nanoparticles (NPs). However, there is no nanochain formation when the alloy is prepared without the polymer PVPh. A possible mechanism for the formation of such NiCo alloy nanochains is discussed. The X-ray diffraction and selected area electron diffraction patterns reveal that the Ni/NiCo alloys are polycrystalline with fcc structure. The obtained Ni or NiCo alloy nanostructures are ferromagnetic with very high coercivity. The polymer Ni/NiCo ...