Showing papers by "Indian Association for the Cultivation of Science published in 2021"

State of the Art and Prospects for Halide Perovskite Nanocrystals.

Abstract: Metal-halide perovskites have rapidly emerged as one of the most promising materials of the 21st century, with many exciting properties and great potential for a broad range of applications, from photovoltaics to optoelectronics and photocatalysis. The ease with which metal-halide perovskites can be synthesized in the form of brightly luminescent colloidal nanocrystals, as well as their tunable and intriguing optical and electronic properties, has attracted researchers from different disciplines of science and technology. In the last few years, there has been a significant progress in the shape-controlled synthesis of perovskite nanocrystals and understanding of their properties and applications. In this comprehensive review, researchers having expertise in different fields (chemistry, physics, and device engineering) of metal-halide perovskite nanocrystals have joined together to provide a state of the art overview and future prospects of metal-halide perovskite nanocrystal research.

A review on the recent advances in hybrid supercapacitors

Abstract: Presently, supercapacitors have gained an important space in energy storage modules due to their extraordinarily high power density, although they lag behind the energy density of batteries and fuel cells. This review covers recent approaches to not only increase the power density, rate capability, cyclic stability, etc. of supercapacitors, but also to increase their energy density using hybrid architectures. Electrodes are the most important component of a supercapacitor cell, and thus this review primarily deals with the design of hybrid supercapacitor electrodes offering a high specific capacitance, together with the elucidation of the mechanisms involved therein. The electrode performance significantly depends on the available surface area, porosity and conductivity of the component materials, and thus nano-structuring of the electrode is an elegant approach, which is discussed in the subsections for 0-, 1-, 2-, 3-dimensional hybrid materials, including some miscellaneous hybrids. The fabrication of different hybrid materials using metal oxides, metal sulfides, carbon materials, etc. with conducting polymers such as polyaniline and polypyrrole and their characterization are delineated from the literature data. Here, we primarily focus on the mechanism of energy storage by non-faradic electrical double-layer capacitance and faradaic pseudo-capacitance, discussing the contributions of different component mechanisms towards the total capacitance. In the hybrids, the impact of the component concentration operating via different mechanisms for charge storage on their final electrochemical performance is discussed. The specific capacitance, volumetric capacitance, charge–discharge cycles, Ragone plot, etc. of hybrid supercapacitors are described. Besides household and heavy-duty applications, the state-of-the-art future applications of supercapacitors in robotics, renewable and sustainable energy devices, wearable and self-healing supercapacitors, and biotechnology and their challenges in real-world applications with the scope of future work are elucidated.

Current and future perspectives of carbon and graphene quantum dots: From synthesis to strategy for building optoelectronic and energy devices

Abstract: Carbon quantum dots (CQDs) and graphene quantum dots (GQDs) are new carbon-based nanomaterials with unique electronic, optical, and physicochemical properties. Both CQDs and GQDs have received attention in different material research fields such as optoelectronics, energy harvesting, chemical sensing, and biosensing. The combination of edge effects and/or zero-dimensional quantum-confined structures make them a promising alternative for applications like LED emitters, photodetectors, solar cells, water splitting, and optoelectronic devices. Despite the great potential for using these materials in energy harvesters, their potential in energy applications has not yet been reviewed thoroughly. In this review, we particularly focused on the role of edge effects and attached functional groups on flexible optoelectronic devices for energy harvesting applications. In addition, we also discussed the underlying challenges and future prospects for CQD/GQD-based devices with respect to their performance, sustainability, durability, and cost-effectiveness to efficiently realize their industrial scale-up.

Biochemical and artificial pathways for the reduction of carbon dioxide, nitrite and the competing proton reduction: effect of 2nd sphere interactions in catalysis

Abstract: Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment. Substantial research has been dedicated to these areas in the last few decades. These reductions require both electrons and protons and their thermodynamic potentials often make them compete with hydrogen evolution reaction i.e., the reaction of protons and electrons to generate H2. These reactions are abundant in the environment in microorganisms and are facilitated by naturally occurring enzymes. This review brings together the state-of-the-art knowledge in the area of enzymatic reduction of CO2, NO2- and H+ with those of artificial molecular electrocatalysis. A simple ligand field theory-based design principle for electrocatalysts is first described. The electronic structure considerations developed automatically yield the basic geometry required and the 2nd sphere interactions which can potentially aid the activation and the further reduction of these small molecules. A systematic review of the enzymatic reaction followed by those reported in artificial molecular electrocatalysts is presented for the reduction of CO2, NO2- and H+. The review is focused on mechanism of action of these metalloenzymes and artificial electrocatalysts and discusses general principles that guide the rates and product selectivity of these reactions. The importance of the 2nd sphere interactions in both enzymatic and artificial molecular catalysis is discussed in detail.

Decision trees within a molecular memristor

Abstract: Profuse dendritic-synaptic interconnections among neurons in the neocortex embed intricate logic structures enabling sophisticated decision-making that vastly outperforms any artificial electronic analogues1–3. The physical complexity is far beyond existing circuit fabrication technologies: moreover, the network in a brain is dynamically reconfigurable, which provides flexibility and adaptability to changing environments4–6. In contrast, state-of-the-art semiconductor logic circuits are based on threshold switches that are hard-wired to perform predefined logic functions. To advance the performance of logic circuits, we are re-imagining fundamental electronic circuit elements by expressing complex logic in nanometre-scale material properties. Here we use voltage-driven conditional logic interconnectivity among five distinct molecular redox states of a metal–organic complex to embed a ‘thicket’ of decision trees (composed of multiple if-then-else conditional statements) having 71 nodes within a single memristor. The resultant current–voltage characteristic of this molecular memristor (a 'memory resistor', a globally passive resistive-switch circuit element that axiomatically complements the set of capacitor, inductor and resistor) exhibits eight recurrent and history-dependent non-volatile switching transitions between two conductance levels in a single sweep cycle. The identity of each molecular redox state was determined with in situ Raman spectroscopy and confirmed by quantum chemical calculations, revealing the electron transport mechanism. Using simple circuits of only these elements, we experimentally demonstrate dynamically reconfigurable, commutative and non-commutative stateful logic in multivariable decision trees that execute in a single time step and can, for example, be applied as local intelligence in edge computing7–9. Multiple redox transitions in a molecular memristor can be harnessed as ‘decision trees’ to undertake complex and reconfigurable logic operations in a single time step.

Recent Update on Targeting c-MYC G-Quadruplexes by Small Molecules for Anticancer Therapeutics.

Abstract: Guanine-rich DNA sequences have the propensity to adopt four-stranded tetrahelical G-quadruplex (G4) structures that are overrepresented in gene promoters. The structural polymorphism and physicochemical properties of these non-Watson-Crick G4 structures make them important targets for drug development. The guanine-rich nuclease hypersensitivity element III1 present in the upstream of P1 promoter of c-MYC oncogene has the ability to form an intramolecular parallel G4 structure. The G4 structure that forms transiently in the c-MYC promoter functions as a transcriptional repressor element. The c-MYC oncogene is overexpressed in a wide variety of cancers and plays a key role in cancer progression. Till now, a large number of compounds that are capable of interacting and stabilizing thec-MYC G4 have been reported. In this review, we summarize various c-MYC G4 specific molecules and discuss their effects on c-MYC gene expression in vitro and in vivo.

Studying the progress of COVID-19 outbreak in India using SIRD model.

Abstract: We explore a standard epidemiological model, known as the SIRD model, to study the COVID-19 infection in India, and a few other countries around the world We use (a) the stable cumulative infection of various countries and (b) the number of infection versus the tests carried out to evaluate the model The time-dependent infection rate is set in the model to obtain the best fit with the available data The model is simulated aiming to project the probable features of the infection in India, various Indian states, and other countries India imposed an early lockdown to contain the infection that can be treated by its healthcare system We find that with the current infection rate and containment measures, the total active infection in India would be maximum at the end of June or beginning of July 2020 With proper containment measures in the infected zones and social distancing, the infection is expected to fall considerably from August If the containment measures are relaxed before the arrival of the peak infection, more people from the susceptible population will fall sick as the infection is expected to see a threefold rise at the peak If the relaxation is given a month after the peak infection, a second peak with a moderate infection will follow However, a gradual relaxation of the lockdown started well ahead of the peak infection, leads to a nearly twofold increase of the peak infection with no second peak The model is further extended to incorporate the infection arising from the population showing no symptoms The preliminary finding suggests that random testing needs to be carried out within the asymptomatic population to contain the spread of the disease Our model provides a semi-quantitative overview of the progression of COVID-19 in India, with model projections reasonably replicating the current progress The projection of the model is highly sensitive to the choice of the parameters and the available data

Nanoparticle Size Effects in Biomedical Applications

Abstract: Nanoparticle size plays a central role in determining material properties and performance in biomedical applications. A wide variety of functional nanomaterials and nano-bioconjugates have been developed for monitoring biochemical activity, controlling biological functions, and therapeutic applications. This review focuses on the role of nanoparticle size (typically in the range of 1–100 nm) in various biomedical applications, the origin of such a size effect, and the optimum size requirement for the best performance in different biomedical applications. First, we discuss various nanoscale units present in life processes along with their size and functional role. Next, we discuss the size-dependent properties of some well-known nanoparticles and how those properties are exploited in different biomedical applications. Next, we discuss the size-dependent performance of functional nanomaterials and nano-bioconjugates that are used in various biomedical applications. Then, we highlight some of the best designed nanoparticles of optimum size for specific biomedical applications. Finally, we attempt to correlate the origin of the evolutionary selection of various nanoscale units in life processes toward specific biological functions.

Melting of hybrid organic-inorganic perovskites.

Abstract: Several organic–inorganic hybrid materials from the metal–organic framework (MOF) family have been shown to form stable liquids at high temperatures. Quenching then results in the formation of melt-quenched MOF glasses that retain the three-dimensional coordination bonding of the crystalline phase. These hybrid glasses have intriguing properties and could find practical applications, yet the melt-quench phenomenon has so far remained limited to a few MOF structures. Here we turn to hybrid organic–inorganic perovskites—which occupy a prominent position within materials chemistry owing to their functional properties such as ion transport, photoconductivity, ferroelectricity and multiferroicity—and show that a series of dicyanamide-based hybrid organic–inorganic perovskites undergo melting. Our combined experimental–computational approach demonstrates that, on quenching, they form glasses that largely retain their solid-state inorganic–organic connectivity. The resulting materials show very low thermal conductivities (~0.2 W m−1 K−1), moderate electrical conductivities (10−3–10−5 S m−1) and polymer-like thermomechanical properties.

Quantum Scars from Zero Modes in an Abelian Lattice Gauge Theory on Ladders.

Abstract: We consider the spectrum of a $U(1)$ quantum link model where gauge fields are realized as $S=1/2$ spins and demonstrate a new mechanism for generating quantum many-body scars (high-energy eigenstates that violate the eigenstate thermalization hypothesis) in a constrained Hilbert space. Many-body dynamics with local constraints has attracted much attention due to the recent discovery of nonergodic behavior in quantum simulators based on Rydberg atoms. Lattice gauge theories provide natural examples of constrained systems since physical states must be gauge invariant. In our case, the Hamiltonian $H={\mathcal{O}}_{\mathrm{kin}}+\ensuremath{\lambda}{\mathcal{O}}_{\mathrm{pot}}$, where ${\mathcal{O}}_{\mathrm{pot}}$ (${\mathcal{O}}_{\mathrm{kin}}$) is diagonal (off-diagonal) in the electric flux basis, contains exact midspectrum zero modes at $\ensuremath{\lambda}=0$ whose number grows exponentially with system size. This massive degeneracy is lifted at any nonzero $\ensuremath{\lambda}$ but some special linear combinations that simultaneously diagonalize ${\mathcal{O}}_{\mathrm{kin}}$ and ${\mathcal{O}}_{\mathrm{pot}}$ survive as quantum many-body scars, suggesting an ``order-by-disorder'' mechanism in the Hilbert space. We give evidence for such scars and show their dynamical consequences on two-leg ladders with up to 56 spins, which may be tested using available proposals of quantum simulators. Results on wider ladders point towards their presence in two dimensions as well.

Alkylammonium Halides for Facet Reconstruction and Shape Modulation in Lead Halide Perovskite Nanocrystals.

Abstract: ConspectusThe interactions of halides and ammonium ions with lead halide perovskite nanocrystals have been extensively studied for improving their phase stability, controlling size, and enhancing their photoluminescence quantum yields. However, all these nanocrystals, which showed intense and color tunable emissions, mostly retained the six faceted cube or platelet shapes. Shape tuning needs the creation of new facets, and instead of composition variations by foreign ions interactions/substitutions, these require facet stabilizations with suitable ligands. Among most of the reported cases of lead halide perovskites, alkyl ammonium ions are used as a capping agent, which substituted in the surface Cs(I) sites of these nanocrystals. Hence, new surface ligands having a specific binding ability with different facets other than those in cube/platelet shapes are required for bringing stability to new facets and, hence, for tuning their shapes.In this Account, interactions of alkyl ammonium ions on the surface of perovskite nanocrystals and their impact on surface reconstructions are reviewed. Emphasizing the most widely studied CsPbBr3 nanocrystals, the usefulness and impact of alkyl ammonium ions on the phase stability, high-temperature annealing, enhancement of the brightness and doping in these nanocrystals are first discussed. Then, nanocrystals formed under limited primary alkyl ammonium ions and also with specific tertiary ammonium ions having new facets are elaborated. Further, the treatment of excess alkyl ammonium halides to these newly formed multifaceted polyhedron nanocrystals under different conditions, which led to armed and step-armed structures, are discussed. The change in optical properties during these shape transformations is also presented. Finally, the shape-change mechanism with alkyl ammonium halide-induced dissolutions of {200} and {112} facets and formation of {110} and {002} facets are discussed. Further, in summary, future prospects of new ligand designing for stabilizing new facets of perovskite nanocrystals and obtaining new shapes and properties are proposed.

Metformin-Templated Nanoporous ZnO and Covalent Organic Framework Heterojunction Photoanode for Photoelectrochemical Water Oxidation

Abstract: Photoelectrochemical water-splitting offers unique opportunity in the utilization of abundant solar light energy and water resources to produce hydrogen (renewable energy) and oxygen (clean environment) in the presence of a semiconductor photoanode. Zinc oxide (ZnO), a wide bandgap semiconductor is found to crystallize predominantly in the hexagonal wurtzite phase. Herein, we first report a new crystalline triclinic phase of ZnO by using N-rich antidiabetic drug metformin as a template via hydrothermal synthesis with self-assembled nanorod-like particle morphology. We have fabricated a heterojunction nanocomposite charge carrier photoanode by coupling this porous ZnO with a covalent organic framework, which displayed highly enhanced photocurrent density of 0.62 mA/cm2 at 0.2 V vs. RHE in photoelectrochemical water oxidation and excellent photon-to-current conversion efficiency at near-neutral pH vis-a-vis bulk ZnO. This enhancement of the photocurrent for the porous ZnO/COF nanocomposite material over the corresponding bulk ZnO could be attributed to the visible light energy absorption by COF and subsequent efficient charge-carrier mobility via porous ZnO surface.

Activating the Fe(I) State of Iron Porphyrinoid with Second-Sphere Proton Transfer Residues for Selective Reduction of CO2 to HCOOH via Fe(III/II)-COOH Intermediate(s).

Abstract: The ability to tune the selectivity of CO2 reduction by first-row transition metal-based complexes via the inclusion of second-sphere effects heralds exciting and sought-after possibilities. On the basis of the mechanistic understanding of CO2 reduction by iron porphyrins developed by trapping and characterizing the intermediates involved ( J. Am. Chem. Soc. 2015, 137, 11214), a porphyrinoid ligand is envisaged to switch the selectivity of the iron porphyrins by reducing CO2 from CO to HCOOH as well as lower the overpotential to the process. The results show that the iron porphyrinoid designed can catalyze the reduction of CO2 to HCOOH using water as the proton source with 97% yield with no detectable H2 or CO. The iron porphyrinoid can activate CO2 in its Fe(I) state resulting in very low overpotential for CO2 reduction in contrast to all reported iron porphyrins, which can reduce CO2 in their Fe(0) state. Intermediates involved in CO2 reduction, Fe(III)-COOH and a Fe(II)-COOH, are identified with in situ FTIR-SEC and subsequently chemically generated and characterized using FTIR, resonance Raman, and Mossbauer spectroscopy. The mechanism of the reaction helps elucidate a key role played by a closely placed proton transfer residue in aiding CO2 binding to Fe(I), stabilizing the intermediates, and determining the fate of a rate-determining Fe(II)-COOH intermediate.

Ergoregion instability and echoes for braneworld black holes: Scalar, electromagnetic, and gravitational perturbations

Abstract: In the context of the higher dimensional braneworld scenario, we have argued that the occurrence of horizonless exotic compact objects, as an alternative to classical black holes, is more natural. These exotic compact objects carry a distinctive signature of the higher dimension, namely a tidal charge parameter, related to the size of the extra dimension. Due to the absence of any horizon, rotating exotic compact objects are often unstable because of superradiance. Interestingly, these higher dimensional exotic compact objects are more stable than their four-dimensional counterpart, as the presence of the tidal charge reduces the size of the extra dimension and hence results in a stronger gravitational field on the brane. A similar inference is drawn by analyzing the static modes associated with these exotic compact objects, irrespective of the nature of the perturbation, i.e., it holds true for scalar, electromagnetic and also gravitational perturbation. The postmerger ringdown phase of the exotic compact object in the braneworld scenario, which can be described in terms of the quasinormal modes, holds a plethora of information regarding the nature of the higher dimension. In this connection we have discussed the analytical computation of the quasinormal modes as well as their numerical estimation for perturbations of arbitrary spin, depicting existence of echoes in the ringdown waveform. As we have demonstrated, the echoes in the ringdown waveform depend explicitly on the tidal charge parameter and hence its future detection can provide constraints on the tidal charge parameter, which in turn will enable us to provide a possible bound on the size of the extra dimension.

Dark Self-Healing-Mediated Negative Photoconductivity of a Lead-Free Cs3Bi2Cl9 Perovskite Single Crystal.

Abstract: N.K.T. acknowledges a UGC Fellowship. S.S. acknowledges the Ministry of Electronics and Information Technology research grant DIC-1377-PHY.

Why Do Perovskite Nanocrystals Form Nanocubes and How Can Their Facets Be Tuned? A Perspective from Synthetic Prospects

Abstract: Lead halide perovskite nanocrystals have recently emerged as the workhorse in quantum dot research for their unprecedented high brightness and tunable colors in the most in-demand red–green–blue wi...

Supramolecular Engineering and Self-Assembly Strategies in Photoredox Catalysis

Abstract: Visible-light-mediated photoredox catalysis has evolved as an efficient and mild alternative to conventional organic synthesis. Inspired by the elegance and sophistication of natural photosynthetic...

Light-Emitting Metal-Organic Halide 1D and 2D Structures: Near-Unity Quantum Efficiency, Low-Loss Optical Waveguide and Highly Polarized Emission.

Abstract: Organic-inorganic metal-halide materials (OIMMs) with zero-dimensional (0D) structures offer useful optical properties with a wide range of applications. However, successful examples of 0D structural OIMMs with well-defined optical performance at the micro-/nanometer scale are limited. We prepared one-dimensional (1D) (DTA)2 SbCl5 ⋅DTAC (DTAC=dodecyl trimethyl ammonium chloride) single-crystal microrods and 2D microplates with a 0D structure in which individual (SbCl5 )2- quadrangular units are completely isolated and surrounded by the organic cation DTA+ . The organic molecular unit with a long alkyl chain (C12 ) and three methyl groups enables microrod and -plate formation. The single-crystal microrods/-plates exhibit a broadband orange emission peak at 610 nm with a photoluminescence quantum yield (PLQY) of ca. 90 % and a large Stokes shift of 260 nm under photoexcitation. The broad emission originates from self-trapping excitons. Spatially resolved PL spectra confirm that these microrods exhibit an optical waveguide effect with a low loss coefficient (0.0019 dB μm-1 ) during propagation, and linear polarized photoemission with a polarization contrast (0.57).

Hot Hole Cooling and Transfer Dynamics from Lead Halide Perovskite Nanocrystals Using Porphyrin Molecules

Abstract: A deep understanding of hot carrier (HC) dynamics is important to improve the performance of optoelectronic devices by reducing the thermalization losses. Here, we investigate the hot hole cooling ...

Chemically Spiraling CsPbBr3 Perovskite Nanorods.

Abstract: Light emitting lead halide perovskite nanocrystals are currently emerging as the workhorse in quantum dot research. Most of these reported nanocrystals are isotropic cubes or polyhedral; but anisotropic nanostructures with controlled anisotropic directions still remain a major challenge. For orthorhombic CsPbBr3, the 1D shaped nanostructures reported are linear and along either of the axial directions ⟨100⟩. In contrast, herein, spiral CsPbBr3 perovskite nanorods in the orthorhombic phase are reported with unusual anisotropy having (101) planes remaining perpendicular to the major axis [201]. While these nanorods are synthesized using the prelattice of orthorhombic Cs2CdBr4 with Pb(II) diffusion, the spirality is controlled by manipulation of the compositions of alkylammonium ions in the reaction system which selectively dissolve some spiral facets of the nanorods. Further, as spirality varied with facet creation and elimination, these nanorods were explored as photocatalysts for CO2 reduction, and the evolution of methane was also found to be dependent on the depth of the spiral nanorods. The entire study demonstrates facet manipulation of complex nanorods, and these results suggest that even if perovskites are ionic in nature, their shape could be constructed by design with proper reaction manipulation.

Reduced Graphene Oxide-Laminated One-Dimensional TiO2-Bronze Nanowire Composite: An Efficient Photoanode Material for Dye-Sensitized Solar Cells.

Abstract: A facile one-step hydrothermal method was developed to prepare reduced graphene oxide-laminated TiO2-bronze (TiO2-B) nanowire composites (TNWG), which contain two-dimensional graphene oxide nanosheets and TiO2-B nanowires. In the hydrothermal process, the functional groups of graphene oxide were reduced significantly. Dye-sensitized solar cells (DSSCs) were fabricated using TNWG as the photoanode material. The effects of different reduced graphene oxide contents in TNWG on the energy conversion efficiency of the dye-sensitized solar cells were investigated using J-V and incident photon-to-current conversion efficiency characteristics. DSSCs based on a TNWG hybrid photoanode with a reduced graphene oxide content of 8 wt % demonstrated an overall light-to-electricity conversion efficiency of 4.95%, accompanied by a short-circuit current density of 10.41 mA cm-2, an open-circuit voltage of 0.71 V, and a fill factor of 67%, which were much higher than those of DSSC made with a pure TiO2-B NW-based photoanode. The overall improvement in photovoltaic performance could be associated to the intense visible light absorption and enhanced dye adsorption because of the increased surface area of the composite, together with faster electron transport due to reduced carrier recombination.