Showing papers by "Indian Association for the Cultivation of Science published in 2016"

Soft-Nanocomposites of Nanoparticles and Nanocarbons with Supramolecular and Polymer Gels and Their Applications.

Abstract: Gel-nanocomposites are rapidly emerging functional advanced materials having widespread applications in materials and biological sciences. Herein, we review syntheses, properties, and applications of various gel-nanocomposites assembled from different metal-based nanoparticles or nanocarbons [fullerene, carbon nanotubes (CNTs), and graphenes] with tailor-made supramolecular (small molecular) or polymeric physical organogels and hydrogels. Dynamic supramolecular self-assembly of gelators prove to be excellent hosts for the incorporation of these dimensionally different nanomaterials. Thus, gel-nanocomposites doped with preformed/in situ synthesized nanoparticles show magnetic or near-infrared-responsive, catalytic or antibacterial properties. Fullerene-based gel-nanocomposites show applications in organic solar cells. Gel-nanocomposites based on CNTs and graphenes and their functionalized (covalent/noncovalent) analogues find interesting properties including electrical conductivity, viscoelasticity, therma...

Surface-Oxidized Dicobalt Phosphide Nanoneedles as a Nonprecious, Durable, and Efficient OER Catalyst

Abstract: Needle-shaped narrow hexagonal phase 1D nanostructures of dicobalt phosphide (Co2P) are reported as efficient electrocatalysts for the oxygen evolution reaction (OER). Without other metal incorporation, which was typically followed for enhancing the OER activity, the electrochemical performance was observed to be superior in comparison to all reported cobalt-based nanostructured metal phosphides. For anodic metamorphosis, these nanostructures, like all other metal phosphides, undergo surface oxidation but remain more active and superior to pure cobalt oxides as well as surface-oxidized different shaped monocobalt phosphides. Moreover, the synthesis was also followed by adopting a moderate synthetic protocol where PH3 gas was used as a phosphorus source and also scaled up to the gram level. In addition, the hydrogen evolution reaction (HER) performance of these phosphides was further studied, and the performance was observed to be comparable to that in the best reports.

Introducing Cu2O Thin Films as a Hole-Transport Layer in Efficient Planar Perovskite Solar Cell Structures

Abstract: In this work, we introduce Cu2O thin films as a hole-transport layer in planar perovskite solar cells. Here, a Cu2O layer was formed through successive ionic layer adsorption and reaction (SILAR) method. With methylammonium lead triiodide (MAPbI3) we form a direct structure (p–i–n), where the perovskite layer is sandwiched between a layer of p-type Cu2O and another layer of n-type PCBM (phenyl-C61-butyric acid methyl ester), which acted as hole- and electron-transport materials, respectively. We locate band edges of the materials with respect to their Fermi energy by recording scanning tunneling spectroscopy that has correspondence to their density of states (DOS). We observe that the energy levels of the materials form type II band alignments at each of the two interfaces (p–i and i–n) for charge separation and uninterrupted carrier transport upon illumination. Such a band alignment enabled charge transfer from MAPbI3 as evidenced from quenching of its photoluminescence emission when the perovskite was i...

Large magnetic cooling power involving frustrated antiferromagnetic spin-glass state in R 2 NiSi 3 ( R = Gd , Er )

Abstract: The ternary intermetallic compounds ${\mathrm{Gd}}_{2}{\mathrm{NiSi}}_{3}$ and ${\mathrm{Er}}_{2}{\mathrm{NiSi}}_{3}$ are synthesized in chemically single phase, which are characterized using dc magnetization, ac magnetic susceptibility, heat capacity, and neutron diffraction studies. Neutron diffraction and heat capacity studies confirm that long-range magnetic ordering coexists with the frustrated glassy magnetic components for both compounds. The static and dynamical features of dc magnetization and frequency-dependent ac susceptibility data reveal that ${\mathrm{Gd}}_{2}{\mathrm{NiSi}}_{3}$ is a canonical spin-glass system, while ${\mathrm{Er}}_{2}{\mathrm{NiSi}}_{3}$ is a reentrant spin cluster-glass system. The spin freezing temperature merges with the long-range antiferromagnetic ordering temperature at 16.4 K for ${\mathrm{Gd}}_{2}{\mathrm{NiSi}}_{3}$. ${\mathrm{Er}}_{2}{\mathrm{NiSi}}_{3}$ undergoes antiferromagnetic ordering at 5.4 K, which is slightly above the spin freezing temperature at 3 K. The detailed studies of nonequilibrium dynamical behavior, viz., the memory effect and relaxation behavior using different protocols, suggest that both compounds favor the hierarchical model over the droplet model. A large magnetocaloric effect is observed for both compounds. Maximum values of isothermal entropy change $(\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M})$ and relative cooling power (RCP) are found to be 18.4 J/kg K and 525 J/kg for ${\mathrm{Gd}}_{2}{\mathrm{NiSi}}_{3}$ and 22.6 J/kg K and 540 J/kg for ${\mathrm{Er}}_{2}{\mathrm{NiSi}}_{3}$, respectively, for a change in field from 0 to 70 kOe. The values of RCP are comparable to those of the promising refrigerant materials. A correlation between large RCP and magnetic frustration is discussed for developing new magnetic refrigerant materials.

Complete Transmetalation in a Metal–Organic Framework by Metal Ion Metathesis in a Single Crystal for Selective Sensing of Phosphate Ions in Aqueous Media

Abstract: A complete transmetalation has been achieved on a barium metal-organic framework (MOF), leading to the isolation of a new Tb-MOF in a single-crystal (SC) to single-crystal (SC) fashion. It leads to the transformation of an anionic framework with cations in the pore to one that is neutral. The mechanistic studies proposed a core-shell metal exchange through dissociation of metal-ligand bonds. This Tb-MOF exhibits enhanced photoluminescence and acts as a selective sensor for phosphate anion in aqueous medium. Thus, this work not only provides a method to functionalize a MOF that can have potential application in sensing but also elucidates the formation mechanism of the resulting MOF.

Two-Dimensional Group IV Monochalcogenides: Anode Materials for Li-Ion Batteries

Abstract: The selection of a suitable electrode material is a fundamental step in the development of Li-ion batteries (LIBs) to achieve enhanced performance. In the present study, we have explored the feasibility of monolayers of phosphorene analogues, namely, group IV monochalcogenides (SiS, SiSe, GeS, GeSe, SnS, and SnSe), to serve as anode materials in LIBs by density functional theory (DFT). Our exploratory study indicates that lithium binds efficiently to these monolayers, with Li@SiS and Li@SiSe showing appreciable stability comparable to that of phosphorene. The zero-point-energy-corrected minimum-energy pathway (MEP) for Li diffusion demonstrates high anisotropy for both SiS and SiSe, with a low diffusion barrier of ∼0.15 eV along the zigzag direction. Inclusion of corrections due to quantum effects such as the zero-point energy (ZPE) and quantum mechanical tunneling (QMT) increases the diffusion rates by 6–10% at room temperature and results in increasingly significant contributions as the temperature is r...

Capping Black Phosphorene by h-BN Enhances Performances in Anodes for Li and Na Ion Batteries

Abstract: Black phosphorus (BP), despite possessing a favorable direct band gap, suffers from structural instability at ambient conditions that limits its utility for lithium ion batteries (LIB). In this Letter, we have proposed h-BN as an effective capping agent for black-phosphorene (Pn) for application as an anode material in both LIBs and sodium ion batteries (SIBs). The binding energy of Li/Na in the h-BN/black-Pn heterostructure is greatly enhanced (2.81 eV/2.55 eV) vis-a-vis pristine Pn (1.80 eV/1.59 eV) along with reduction in the barrier for movement of Li/Na within the layers. Significantly, lithiation/sodiation of these heterostructures does not alter the packing patterns due to insignificant volume changes (∼1.5–2.0%). The theoretical specific capacities for h-BN/black-Pn is 607 and 445 mA h g–1 for LIB and SIB, respectively, which are larger than those for existing commercial anode materials. Clearly, the high capacity, low open-circuit voltage, small volume change, and high mobility of Li/Na within th...

Palladium nanoparticles in the catalysis of coupling reactions

Abstract: Palladium catalyzed coupling reactions have emerged as a versatile, convenient, selective and mild protocol that can usually be adapted in any synthetic scheme for important target molecules with various degrees of structural complexity. While anchored catalysts offer recycling advantages, palladium nanoparticles display an impressive ability to catalyse coupling reactions. Along with their successful applications in organic synthesis, controversy has also arisen concerning the exact nature – heterogeneous or homogeneous – of the reaction catalyzed by palladium nanoparticles.

A new triazine functionalized luminescent covalent organic framework for nitroaromatic sensing and CO2 storage

Abstract: A new hexagonally ordered covalent organic framework (COF), TRIPTA has been synthesized using Schiff base condensation reaction between 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 1,3,5-triformylphloroglucinol (TFP). TRIPTA exhibits high crystallinity, a large BET surface area (609 m2 g−1) and pore volume (0.351 cm3 g−1) and possesses high nitrogen content (14.97%). TRIPTA was found to be highly luminescent when suspended in polar solvents upon irradiation of UV light and can detect various nitroaromatic compounds with good sensitivity by fluorescence quenching at concentrations as low as in the range of 10−8 M. The maximum fluorescence quenching was observed for trinitrophenol (61.7% at 5.46 × 10−7 M) with a Stern–Volmer constant of 2.7 × 106 M−1. The COF also showed excellent CO2 uptake capacity of 57.07 wt% at 273 K and 16.02 wt% at 298 K up to 5 bar pressure, with an initial heat of adsorption (Qst) value 56.77 kJ mol−1.

Charge-Transfer-Induced Fluorescence Quenching of Anthracene Derivatives and Selective Detection of Picric Acid.

Abstract: 2,6-Divinylpyridine-appended anthracene derivatives flanked by two alkyl chains at the 9,10-position of the core have been designed, synthesized, and characterized by NMR, MALDI-TOF, FTIR, and single-crystal XRD. These anthracene derivatives are able to recognize picric acid (2,4,6-trinitrophenol, PA) selectively down to parts per billion (ppb) level in aqueous as well as nonaqueous medium. Fluorescence emission of these derivatives in solution is significantly quenched by adding trace amounts of PA, even in the presence of other competing analogues, such as 2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (NP), nitrobenzene (NB), benzoic acid (BA), and phenol (PH). The high sensitivity of these derivatives toward PA is considered as a combined effect of the proton-induced intramolecular charge transfer (ICT) as well as electron transfer from the electron-rich anthracene to the electron-deficient PA. Moreover, visual detection of PA has been successfully demonstrated in the solid state by using different substrates.

A Highly Sensitive ESIPT-Based Ratiometric Fluorescence Sensor for Selective Detection of Al3+

Abstract: An excited-state intramolecular proton transfer (ESIPT)-based highly sensitive ratiometric fluorescence sensor, 1H was developed for selective detection of aluminum (Al3+) in acetonitrile as well as in 90% aqueous system. Single-crystal X-ray diffraction analysis reveals almost planar and conjugated structure of 1H. Photophysical properties of the sensor as well as its selectivity toward Al3+ are explored using UV–visible, steady-state, and time-resolved fluorescence spectroscopic studies. The bright cyan (λem = 445 nm) fluorescence of 1H in acetonitrile turns into deep blue (λem = 412 nm) with ∼2.3-fold enhancement in emission intensity, in the presence of parts per billion level Al3+ (detection limit = 0.5 nM). Interestingly, the probe 1H exhibits increased selectivity toward Al3+ in H2O/acetonitrile (9:1 v/v) solvent system with a change in fluorescence color from pale green to deep blue associated with ca. sixfold enhancement in emission intensity. Density functional theoretical (DFT) calculations pro...

Amorphous molybdenum sulfide quantum dots: an efficient hydrogen evolution electrocatalyst in neutral medium

Abstract: To overcome the limitations of active edges, electrical conductivity and the surface area of MoS2 nanosheets, in the present work, we have successfully synthesized amorphous MoSx quantum dots with a larger number of edge atoms using a simple chemical reaction via a bottom-up approach. Structural and chemical characterizations are carried out by TEM, XRD, Raman and XPS measurements. XPS and EDX analyses indicate a larger number of unsaturated ‘S’ atoms in these ultrafine amorphous quantum dots. We have used this material as an efficient electrocatalyst for the hydrogen evolution reaction (HER) in neutral medium. The material shows a remarkably low overpotential (65 mV) towards HER compared to that of other crystalline MoS2 quantum dots or nanomaterials. The origin of such a low onset potential is the presence of more unsaturated sulfur (S22−) ligands and enhanced active edge sites. It also shows very high catalytic activity as well as good stability after 12 h of hydrogen generation in neutral water medium.

A Peptide-Based Mechano-sensitive, Proteolytically Stable Hydrogel with Remarkable Antibacterial Properties

Abstract: A long-chain amino acid containing dipeptide has been found to form a hydrogel in phosphate buffer whose pH ranges from 6.0 to 8.8. The hydrogel formed at pH 7.46 has been characterized by small-angle X-ray scattering (SAXS), wide-angle powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM) imaging and rheological analyses. The microscopic imaging studies suggest the formation of a nanofibrillar three-dimensional (3D) network for the hydrogel. As observed visually and confirmed rheologically, the hydrogel at pH 7.46 exhibits thixotropy. This thixotropic property can be exploited to inject the peptide. Furthermore, the hydrogel exhibits remarkable antibacterial activity against Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, which are responsible for many common diseases. The hydrogel has practical applicability due to its biocompatibility with human red blood cells and human fibroblast cells. Interestingly, this hydrogel shows high resistance toward proteolytic enzymes, making it a new potential antimicrobial agent for future applications. It has also been observed that a small change in molecular structure of the gelator peptide not only turns the gelator into a nongelator molecule under similar conditions, but it also has a significant negative impact on its bactericidal character.

Solving higher curvature gravity theories

Abstract: Solving field equations in the context of higher curvature gravity theories is a formidable task. However, in many situations, e.g., in the context of f(R) theories, the higher curvature gravity action can be written as an Einstein–Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent, provided the spacetime is regular. We also demonstrate that such an equivalence continues to hold even when the gravitational field equations are projected on a lower-dimensional hypersurface. We have further addressed explicit examples in which the solutions for Einstein–Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower-dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations.

Efficient Inhibition of Protein Aggregation, Disintegration of Aggregates, and Lowering of Cytotoxicity by Green Tea Polyphenol-Based Self-Assembled Polymer Nanoparticles.

Abstract: Green tea polyphenol epigallocatechin-3-gallate (EGCG) is known for its antiamyloidogenic property, and it is observed that molecular EGCG binds with amyloid structure, redirects fibrillation kinetics, remodels mature fibril, and lowers the amyloid-derived toxicity. However, this unique property of EGCG is difficult to utilize because of their poor chemical stability and substandard bioavailability. Here we report a nanoparticle form of EGCG of 25 nm size (nano-EGCG) which is 10-100 times more efficient than molecular EGCG in inhibiting protein aggregation, disintegrating mature protein aggregates, and lowering amyloidogenic cytotoxicity. The most attractive advantage of nano-EGCG is that it efficiently protects neuronal cells from the toxic effect of extracellular amyloid beta or intracellular mutant huntingtin protein aggregates by preventing their aggregation. We found that the better performance of nano-EGCG is due to the combined effect of increased chemical stability of EGCG against degradation, stronger binding with protein aggregates, and efficient entry into the cell for interaction with aggregated protein structure. This result indicates that the nanoparticle form of antiamyloidogenic molecules can be more powerful in prevention and curing of protein aggregation derived diseases.

Aerobic Radical‐Cascade Alkylation/Cyclization of α,β‐Unsaturated Amides: an Efficient Approach to Quaternary Oxindoles

Abstract: An efficient method for the aerobic radical-cascade alkylation/cyclization of α,β-unsaturated amides to afford functionalized oxindoles with a C3 quaternary stereocenter is described. The process is based on the generation of valuable alkyl radicals through sustainable aerobic C-H activation of aldehydes followed by decarbonylation using O2 as the sole oxidant. This method features a broad substrate scope, inexpensive alkyl radical precursors, and convenient reagents. Finally, the method was successfully applied to the synthesis of alkyl analogues of tetrahydrofuranoindoline and (±)-esermethole.

Combining Protons and Hydrides by Homogeneous Catalysis for Controlling the Release of Hydrogen from Ammonia–Borane: Present Status and Challenges

Abstract: Ammonia–borane (AB) has been in the spotlight for its much touted potential as an onboard vehicular hydrogen delivery material. Over the past decade, catalyzed dehydrogenation/dehydrocoupling reactions for releasing H2 from the maximum available 3 equiv in AB have gained significant momentum. In this Perspective, we focus on the homogeneous AB dehydrogenation catalysis, by both transition metal (TM)-based and metal-free systems. Several questions pertaining to underlying mechanisms, nature of intermediates, and catalyst efficacy have surfaced as the multitude of discoveries in the field has built up at a fast pace. The varied fate of the dehydrogenation reactions of AB with different catalysts yielding different end products ranging from polyaminoborane (PAB) to polyborazylene (PBZ) and the ability/inability of catalysts to release more than 1 equiv of H2 from AB have fuelled the genesis of several mechanistic hypotheses. However, the copious investigations on the experimental and theoretical fronts have ...

Red Fluorescent Carbon Nanoparticle-Based Cell Imaging Probe

Abstract: Fluorescent carbon nanoparticle-based probes with tunable visible emission are biocompatible, environment friendly and most suitable for various biomedical applications. However, synthesis of red fluorescent carbon nanoparticles and their transformation into functional nanoparticles are very challenging. Here we report red fluorescent carbon nanoparticle-based nanobioconjugates of <25 nm hydrodynamic size and their application as fluorescent cell labels. Hydrophobic carbon nanoparticles are synthesized via high temperature colloid-chemical approach and transformed into water-soluble functional nanoparticles via coating with amphiphilic polymer followed by covalent linking with desired biomolecules. Following this approach, carbon nanoparticles are functionalized with polyethylene glycol, primary amine, glucose, arginine, histidine, biotin and folic acid. These functional nanoparticles can be excited with blue/green light (i.e., 400-550 nm) to capture their emission spanning from 550 to 750 nm. Arginine and folic acid functionalized nanoparticles have been demonstrated as fluorescent cell labels where blue and green excitation has been used for imaging of labeled cells. The presented method can be extended for the development of carbon nanoparticle-based other bioimaging probes.

Morphology evolution of single-crystalline hematite nanocrystals: magnetically recoverable nanocatalysts for enhanced facet-driven photoredox activity

Abstract: We have developed a new green chemical approach for the shape-controlled synthesis of single-crystalline hematite nanocrystals in aqueous medium. FESEM, HRTEM and SAED techniques were used to determine the morphology and crystallographic orientations of each nanocrystal and its exposed facets. PXRD and HRTEM techniques revealed that the nanocrystals are single crystalline in nature; twins and stacking faults were not detected in these nanocrystals. The structural, vibrational, and electronic spectra of these nanocrystals were highly dependent on their shape. Different shaped hematite nanocrystals with distinct crystallographic planes have been synthesized under similar reaction conditions, which can be desired as a model for the purpose of properties comparison with the nanocrystals prepared under different reaction conditions. Here we investigated the photocatalytic performance of these different shaped-nanocrystals for methyl orange degradation in the presence of white light (λ > 420 nm). In this study, we found that the density of surface Fe3+ ions in particular facets was the key factor for the photocatalytic activity and was higher on the bitruncated-dodecahedron shape nanocrystals by coexposed {104}, {100} and {001} facets, attributing to higher catalytic activity. The catalytic activity of different exposed facet nanocrystals were as follows: {104} + {100} + {001} (bitruncated-dodecahedron) > {101} + {001} (bitruncated-octahedron) > {001} + {110} (nanorods) > {012} (nanocuboid) which provided the direct evidence of exposed facet-driven photocatalytic activity. The nanocrystals were easily recoverable using an external magnet and reused at least six times without significant loss of its catalytic activity.

Nanoparticle Multivalency Directed Shifting of Cellular Uptake Mechanism

Abstract: Although nanoparticle multivalency is known to influence their biological labeling performance, the functional role of multivalency is largely unexplored. Here we show that the folate receptor mediated cellular internalization mechanism of 35–50 nm nanoparticle shifts from caveolae- to clathrin-mediated endocytosis as the nanoparticle multivalency increases from 10 to 40 and results in the difference of their subcellular trafficking. We have synthesized folate functionalized multivalent quantum dot (QD) with varied average numbers of folate per QD between 10 and 110 [e.g., QD(folate)10, QD(folate)20, QD(folate)40, QD(folate)110] and investigated their uptake and localization into folate receptor overexpressed HeLa and KB cells. We found that uptake of QD(folate)10 occurs predominantly via caveolae-mediated endocytosis and entirely trafficked to the perinuclear region. In contrast, uptake of QD(folate)20 occurs via both caveolae- and chathrin-mediated endocytosis; uptake of QD(folate)40 and QD(folate)110 o...

Novel Nitrogen and Sulfur Rich Hyper-Cross-Linked Microporous Poly-Triazine-Thiophene Copolymer for Superior CO2 Capture

Abstract: A novel synthetic strategy has been developed for the preparation of hyper-cross-linked microporous copolymers, HMC-1, HMC-2, and HMC-3, by using 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine and thiophene monomers in their different molar ratios in the presence of anhydrous FeCl3 in chloroform under solvothermal conditions at 150 °C. These polymers are highly porous and robust materials, exhibiting very high BET surface areas and supermicroporosity. The presence of triazine and thiophene moieties within the copolymer network increases the electron donating basic N and S sites in the porous frameworks. Thus, these porous polymers displayed efficient adsorption of Lewis acidic CO2 molecules and showed good CO2/N2 adsorption selectivity. The maximum CO2 uptake of 14.2 mmol g–1 at 273 K under 3 bar pressure has been observed.

Pseudo-Jahn–Teller Distortion in Two-Dimensional Phosphorus: Origin of Black and Blue Phases of Phosphorene and Band Gap Modulation by Molecular Charge Transfer

Abstract: Phosphorene (Pn) is stabilized as a layered material like graphite, yet it possess a natural direct band gap (Eg = 2.0 eV). Interestingly, unlike graphene, Pn exhibits a much richer phase diagram which includes distorted forms like the stapler-clip (black Pn, α form) and chairlike (blue Pn, β form) structures. The existence of these phases is attributed to pseudo-Jahn–Teller (PJT) instability of planar hexagonal P66– rings. In both cases, the condition for vibronic instability of the planar P66– rings is satisfied. Doping with electron donors like tetrathiafulvalene and tetraamino-tetrathiafulvalene and electron acceptors like tetracyanoquinodimethane and tetracyanoethylene convert blue Pn into N-type and black Pn into efficient P-type semiconductors, respectively. Interestingly, pristine blue Pn, an indirect gap semiconductor, gets converted into a direct gap semiconductor on electron or hole doping. Because of comparatively smaller undulation in blue Pn (with respect to black Pn), the van der Waals inte...

Silver nanoparticles embedded over porous metal organic frameworks for carbon dioxide fixation via carboxylation of terminal alkynes at ambient pressure

Abstract: Ag nanoparticles (NPs) has been supported over a porous Co(II)-salicylate metal-organic framework to yield a new nanocatalyst AgNPs/Co-MOF and it has been thoroughly characterized by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), energy dispersive X-ray spectrometry (EDX), high-resolution transmission electron microscopy (HR-TEM), UV-vis diffuse reflection spectroscopy (DRS) and N2 adsorption/desorption analysis. The AgNPs/Co-MOF material showed high catalytic activity in the carboxylation of terminal alkynes via CO2 fixation reaction to yield alkynyl carboxylic acids under very mild conditions. Due to the presence of highly reactive AgNPs bound at the porous MOF framework the reaction proceeded smoothly at 1atm CO2 pressure. Moreover, the catalyst is very convenient to handle and it can be reused for several reaction cycles without appreciable loss of catalytic activity in this CO2 fixation reaction, which suggested a promising future of AgNPs/Co-MOF nanocatalyst.