Showing papers by "Indian Association for the Cultivation of Science published in 2019"
TL;DR: In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported.
Abstract: In a generic synthesis approach, all three CsPbX3 (X=Cl, Br and I) perovskite nanocrystals having near unity quantum yields is reported. This has been achieved by injecting the desired amount of preformed alkylammonium halide salts which acted as a dual source providing halide ions and the capping agent to an equimolar amount of non-halide Pb and Cs precursors in a reaction flask at an optimized reaction temperature. The composition sensitivity of Pb to Cs ratio, high temperature reaction, and injection of ammonium halide remained the key parameters for obtaining the high quantum yields. Details of the reaction process, use of different reagents and setting up the reaction parameters are reported.
240 citations
TL;DR: In this article, the role of carbon quantum dots (CQDs) as sensors for heavy metals in water is discussed and a comprehensive overview of CQDs' role in water sensing is provided.
Abstract: A diverse range of materials (e.g., metallic nanoparticles, semiconductor oxides, composites, polymers, and MOFs) have been reported for sensing applications in water samples based on several transduction techniques (e.g., absorbance, fluorescence, Raman, colorimetry, voltammetry, and plasmon resonance). Recently, carbon quantum dots (CQDs) have gained significant interest as fluorescent and small carbonaceous nanostructures for designing sensing devices (either as-produced or through modification) for heavy metals due to their excellent properties (e.g., photostability, facile surface modification, optical tunability, and environmental friendliness). This review provides a comprehensive overview on the role of CQDs as sensors for heavy metals in water. This work will help open up opportunities for the use of CQDs under the diverse field conditions.
140 citations
TL;DR: In this article, a review of porous organic polymers (POPs) and their application in CO2 adsorption and fixation into reactive organic molecules for the synthesis of fuels and value added fine chemicals is presented.
Abstract: To overcome the challenges of global warming and environmental pollution it is mandatory to reduce the concentration of atmospheric carbon dioxide (CO2), which is largely accumulated in air through the combustion of fossil fuels. Thus, sequestration of CO2 through physisorption on solid adsorbents and their successful conversion into value added fine chemicals are the major priority areas of research today. Innovation of efficient solid CO2‐philic adsorbents together with their high mechanical/chemical stability and regeneration efficiency are the most challenging objectives to achieve this goal. In this context, porous organic polymers (POPs) owing to their high specific surface area, chemical stability, nanoscale porosity and structural diversity have huge potential to play as selective CO2 adsorbent. POPs synthesized through large varieties of reactive monomers via simple and convenient chemical routes can be the ideal adsorbents for the CO2 storage and fixation reactions. A wide range of POPs can be synthesized from different multidentate amines, aldehydes, carboxylic acids or triazine monomers through the polycondensation reactions or solid state condensation reactions. Ease of synthesis, uniform pore width together with high surface area and surface basic sites (nitrogen and other heteroelements) play crucial role in the CO2 absorption and conversion reactions. This review provides a concise account in designing POPs and their application in CO2 adsorption and fixation into reactive organic molecules for the synthesis of fuels and value added fine chemicals.
133 citations
TL;DR: In this article, the phase stability of α-Cubic CsPbI3 nanocrystals has been investigated and shown to be stable even at room temperature under certain conditions.
Abstract: The semiconducting bulk α-cubic CsPbI3 phase is stable at high temperature. However, recent developments concluded that in nanodimensions this phase can also be stable even at room temperature. The unique feature of these α-CsPbI3 nanocrystals is their low-energy red color emission, which remained an essential part for the perovskite family of nanocrystals to cover the entire visible spectrum. Even though these were reported to be stable at room temperature, it is only under certain conditions. These are mostly phase-sensitive, and under ambient conditions, the α phase is transformed to a nonemitting phase. Hence, the phase stability in these nanocrystals remained one of the major challenges in current research. In this Perspective, the origin of phase instability, observations of change in optical properties along with phase transformation under different environmental conditions, insights of possible modulations in A, B, and X sites of the perovskites, precaution in the purification process, and the lig...
127 citations
22 Jan 2019
TL;DR: In this paper, a promising alternative of photocatalysis where the strained state of a piezoelectric material is exploited for electrochemical surface reactions under dark conditions is discussed.
Abstract: Piezocatalysis is a promising alternative of photocatalysis where the strained state of a piezoelectric material is exploited for electrochemical surface reactions under dark conditions. Among vari...
104 citations
TL;DR: In this paper, the surface defects of ZnO nanoparticles have been characterized by electron paramagnetic resonance (EPR), Raman and PL spectroscopy to reveal the origin of bulk and surface defects within the nanostructures.
103 citations
TL;DR: This Perspective focuses on the insights of doping and the photoluminescence properties of Mn2+-doped perovskite nanocrystals, and proposes possible future prospects of both synthesis and optical properties of these nanomaterials.
Abstract: Doping Mn2+ in semiconductor nanocrystals is widely known for its long-lifetime Mn d–d orange emission. While this had been extensively studied for chalcogenide nanostructures, recently this was al...
98 citations
TL;DR: In this article, the authors derived the differential equation governing the evolution of the photon sphere for dynamical black hole spacetimes with or without spherical symmetry, and presented the evolution for slowly rotating Kerr-Vaidya spacetime and associated structure of black hole shadow.
Abstract: We have derived the differential equation governing the evolution of the photon sphere for dynamical black hole spacetimes with or without spherical symmetry. Numerical solution of the same depicting evolution of the photon sphere has been presented for Vaidya, Reissner-Nordstr\"om-Vaidya and de Sitter Vaidya spacetimes. It has been pointed out that evolution of the photon sphere depends crucially on the validity of the null energy condition by the infalling matter and may present an observational window to even test it through black hole shadow. We have also presented the evolution of the photon sphere for slowly rotating Kerr-Vaidya spacetime and associated structure of black hole shadow. Finally, the effective graviton metric for Einstein-Gauss-Bonnet gravity has been presented, and the graviton sphere has been contrasted with the photon sphere in this context.
84 citations
TL;DR: An overview of the recent advances in the photophysical properties of MNCs is presented and it is revealed that the excited-state dynamics, nonlinear optical properties and aggregation induced emission of metal clusters offer exciting opportunities for potential applications.
Abstract: Photophysics of atomically precise metal nanoclusters (MNCs) is an emerging area of research due to their potential applications in optoelectronics, photovoltaics, sensing, bio-imaging and catalysis. An overview of the recent advances in the photophysical properties of MNCs is presented in this review. To begin with, we illustrate general synthesis methodologies of MNCs using direct reduction, chemical etching, ligand exchange, metal exchange and intercluster reaction. Due to strong quantum confinement, the NCs possess unique electronic properties such as discrete optical absorption, intense photoluminescence (PL), molecular-like electron dynamics and non-linear optical behavior. Discussions have also been carried out to unveil the influence of the core size, nature of ligands, heteroatom doping, and surrounding environments on the optical absorption and photophysical properties of metal clusters. Recent findings reveal that the excited-state dynamics, nonlinear optical properties and aggregation induced emission of metal clusters offer exciting opportunities for potential applications. We discuss briefly about their versatile applications in optoelectronics, sensing, catalysis and bio-imaging. Finally, the future perspective of this research field is given.
83 citations
TL;DR: In this article, the authors summarized the synthetic routes in designing key microporous and mesoporous phosphate and phosphonate molecular sieves for catalysis, adsorption, optoelectronics, electrochemical cells, fuel cells, and biomedical applications.
Abstract: Metal phosphate- and phosphonate-based nanoarchitectured materials offer a unique opportunity to design hierarchically porous nanomaterials consisting of interconnected micropores, mesopores, and macropores. Due to their strong affinity toward the metal centers, the phosphate and phosphonate moieties act as ligand sites/linkers to form a wide spectrum of nanoarchitectured materials. In this review, we have summarized the synthetic routes in designing key microporous and mesoporous phosphate and phosphonate molecular sieves. Designing novel nanoarchitectures of metal phosphate- and phosphonate-based microporous and mesoporous materials for catalysis, adsorption, optoelectronics, electrochemical cells, fuel cells, and biomedical applications will further enrich the chemistry of these porous solids in the future.
80 citations
TL;DR: Fe(II) doped CsPbBr3 perovskite nanocrystals showed enhanced catalytic activity and also predominantly led to evolution of CH4 than CO and the observation of reverse trend of predominated CH4 evolution in doped nanocry crystals rather than CO was correlated to the adsorption/desorption energy of respective products established theoretically earlier.
Abstract: Lead halide perovskite nanocrystals have recently emerged as an efficient optical material for light harvesting. While these have been extensively studied for obtaining bright emissions, their use as catalysts for enhancing the rate of chemical reactions has been explored little. Considering their importance in catalysis, herein, Fe(II)-doped CsPbBr3 perovskite nanocrystals have been explored for photocatalytic reduction of CO2. In comparison to undoped CsPbBr3, doped nanocrystals showed enhanced catalytic activity and also predominantly led to evolution of CH4 instead of CO. The observation of a reverse trend of predominated CH4 evolution in doped nanocrystals rather than CO observed for undoped nanocrystals was correlated to the adsorption/desorption energy of respective products established theoretically earlier. This selective evolution of major products on doping remained unique and also a step forward for understanding more regarding light to chemical energy conversions using perovskite nanocrystals.
TL;DR: In this paper, a wormhole-like mesoporous tin oxide (MTO) was synthesized by using sodium lauroyl sarcosinate as structure directing agent under hydrothermal reaction conditions followed by calcination and loading with IrO2 or Pt nanoparticles at its surface by simple wet-chemical methods.
Abstract: Electrocatalytic hydrogen and oxygen evolutions via water splitting are very demanding in the context of renewable energy and sustainable environment. We first report the synthesis of wormhole‐like mesoporous tin oxide (MTO‐S) by using sodium lauroyl sarcosinate as structure directing agent under hydrothermal reaction conditions followed by calcination and loading with IrO2 or Pt nanoparticles at its surface by simple wet‐chemical methods. These IrO2 and Pt‐loaded SnO2 nanomaterials are thoroughly characterized by small and wide‐angle powder XRD, nitrogen adsorption/desorption analysis, FTIR, XPS spectroscopy, UHR‐TEM, FE‐SEM, TG/DTA and NH3‐TPD analysis. The electrochemical water splitting measurements of the IrO2 and Pt doped mesoporous SnO2 nanostructured materials suggested fine dispersion of these metal/metal oxide nanoparticles at the mesopore surface and facile electron hopping could enhance the rate of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity of IrO2@MTO‐S and Pt@MTO‐S nanocomposites, respectively. As a result, the IrO2@MTO‐S modified electrode exhibits unprecedented OER activity with a very low overpotential of 240 mV at 10 mA cm−2, which is lower than the state‐of‐the‐art catalyst IrO2/C (360 mV) and other reported catalysis. Pt@MTO‐S also exhibit excellent HER activity with an ultralow overpotential of 73 mV at 10 mA cm−2. These findings may uncover new opportunities for IrO2@MTO‐S and Pt@MTO‐S as OER and HER electrocatalysts for future water electrolysis.
TL;DR: In this article, atomically precise copper nanoclusters (Cu NCs) were synthesized from nonluminescent plasmonic copper nanoparticles (Cu NPs) by core etching with excess reduced glutathione (GSH).
Abstract: Controlled synthesis of atomically precise metal nanoclusters (MNCs) and fundamental understanding of their physical properties have emerged as an active area of research because of their potential applications in healthcare and energy-related materials. In the present study, atomically precise copper nanoclusters (Cu NCs) have been synthesized from nonluminescent plasmonic copper nanoparticles (Cu NPs) by core etching with excess reduced glutathione (GSH). Electrospray ionization (ESI) mass spectrometry confirms the formation of kinetically controlled, polydisperse Cu34–32(SG)16–13 NCs at room temperature and monodisperse Cu25(SG)20 NCs at elevated temperature (70 °C). Cu34–32(SG)16–13 NCs exhibit weak red emission (625 nm), while Cu25(SG)20 NCs emit intense blue luminescence at 442 nm with 9.7% quantum yield. Rational tuning of reaction temperature, pH, GSH concentration, and reaction time are crucial for the composition and emission band tuning of atomically precise Cu NCs. Interestingly, Cu34–32(SG)16...
TL;DR: In this paper, a green synthesis of blue luminescent C-dots (CDs) using papaya waste (Carica papaya) as a precursor is presented. But the as-synthesized CDS exhibit a quantum yield of 23.7% and are of size
Abstract: The work presents the facile green synthesis of blue luminescent C-dots (CDs) using papaya waste (Carica papaya) as a precursor. The as-synthesized CDS exhibit a quantum yield of 23.7% and are of size
TL;DR: Formation of stable facets in polyhedron shaped nanostructures and their transformation to respective hexapods with under halide-deficient and halides-rich conditions add new fundamental concepts for these nanostructure and their shape evolutions.
Abstract: Highly emissive isotropic CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals are typically observed in a six-faceted cube shape. When a unique approach is adopted and the reaction medium is enriched with halides, arm growth on all six facets was carried out and reported. Analysis suggested that these armed nanostructures were obtained from intermediate polyhedron shaped structures having 26 facets, and these were formed under halide-deficient conditions. Surface energy calculations further supported the possible existence of all facets for both of these structures under different halide composition environments. The entire study was first explored for CsPbBr3 and then extended to CsPbCl3; however, for CsPbI3 nanocrystals, Sr(II) dopant was used for obtaining stable emission. Arm lengths could also be tuned with a function of reaction temperature for CsPbBr3. Formation of stable facets in polyhedron shaped nanostructures and their transformation to respective hexapods under halide-deficient and halide-rich conditions add new fundamental concepts for these nanostructures and their shape evolutions.
TL;DR: In this paper, Sb(III) was chosen as an effective dopant for occupying the Pb(II) position in CsPbI3 nanocrystals.
Abstract: B-site doping with various metal ions in α-CsPbI3 has been proven to be a potential approach in bringing phase stability to these nanocrystals. However, while the doping of various homovalent ions in replacing Pb(II) has been extensively studied, heterovalent doping was observed to be limited. To understand the impact of heterovalent doping, Sb(III) was chosen here as an effective dopant for occupying the Pb(II) position in CsPbI3 nanocrystals. Importantly, it was observed that insertion of Sb(III) also stabilized the crystal phase of these red-emitting nanocrystals, but only with limited doping. However, with more intake, the cube shape turned to platelet and therefore also reduced the stability. Details of the insights of formation of these doped nanostructures are investigated, and further, these were implemented for photovoltaic application and comparable efficiency was recorded.
TL;DR: In this article, a step-by-step progress of reactions in the synthesis of perovskite nanocrystals is discussed, and some synthesis tips and also some tricks for avoiding phase change or quenching of photoluminescence (PL) of these materials are also discussed.
Abstract: Making nanocrystals in a reaction flask is always exciting. This is even more fun with visible light-emitting nanocrystals. After the workhorse CdSe,(1) CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals emerged as the next all-visible color tunable emitters in nanodimensions.(2) While the synthesis of both of these types of semiconductor nanocrystals employed colloidal hot injection reactions, but perovskite nanocrystals showed unprecedented high photoluminescence quantum yield (PLQY). Hence, these nanocrystals remained in the forefront of current research and are considered as an efficient lighting material for energy conversion. However, the root of the performance in any kind of lighting application remains the quality of the material, which in turn depends on the synthetic strategy in the reaction flask. During the last four years, significant improvements have been achieved in optimizing the synthesis and obtaining near-unity PLQYs for all blue, green, and red emitting perovskite nanocrystals. The high-temperature synthetic approach, originally developed by Kovalenko et al.,(2) remained the benchmark protocol for obtaining these high-quality nanocrystals. This has been further modified, and the reaction chemistry for the formation of all three of these halide perovskite nanocrystals has been widely investigated.(3−11) Analysis of the chronological developments with variations of precursor ratios, ligands, reaction temperature, and also the solvent suggests that each successive modification has a logic behind the optimization of the reaction. This also helps in formulating the precise reaction parameters for obtaining the near-unity PLQY for all three CsPbX3 (X = Cl, Br, and I) nanocrystals in a reaction flask. Compiling all these developments, the step-by-step progress of reactions in the synthesis of these perovskite nanocrystals, is discussed in this Viewpoint. Some synthesis tips and also some tricks for avoiding phase change or quenching of photoluminescence (PL) of these nanocrystals are also discussed.
01 Mar 2019
01 Oct 2019
TL;DR: These luminescent Eu and Tb co-doped CQDs are also very useful to detect toxic Cr (VI) with excellent selectivity and sensitivity as compared to pure CQD.
Abstract: Although, great attention is paid to synthesize fluorescent carbon quantum dots (CQDs) for versatile applications, the field remains still attractive to achieve white light using these nano materials. In the present work, CQDs are synthesized from citric acid and lanthanide ions viz. Europium (Eu) and Terbium (Tb) are doped in CQD moiety to explore superior optical response for multifunctional applications. By proper tuning of excitation wavelength, perfect white light with Commission Internationale de l’Elcairage (CIE) index (0.345, 0.344) is obtained using these Europium Terbium co-doped CQDs (Eu-Tb-CQD). The observed photoluminescence of white light emitting lanthanide based CQD is pH dependent and will be used as a visual pH sensor. These luminescent Eu and Tb co-doped CQDs are also very useful to detect toxic Cr (VI) with excellent selectivity and sensitivity as compared to pure CQDs. It shows high quenching efficiency (∼95%) in presence of only 160 µM Cr(VI). The selectivity and lower detection limit are also obtained as ∼80% and 0.175 µM respectively.
TL;DR: DFT calculations provide a detailed insight into how the, apparently weak, 2nd sphere interactions lead to efficient CO2 activation for reduction and suggest that H-bonding alone can tune the rate of CO2 reduction by as much as 1000 fold.
Abstract: Iron porphyrins are potential catalysts for the electrocatalytic and photocatalytic reduction of CO2. It has been recently established that the reduction of CO2 by an iron porphyrin complex with a hydrogen bonding distal pocket involves at least two intermediates: a Fe(II)–CO22− and a Fe(II)–COOH species. A distal hydrogen bonding interaction was found to be key in determining the stability of these intermediates and affecting both the selectivity and rate of CO2 reduction. In this report, a series of iron porphyrins that vary only in the distal H-bonding network are further investigated and these exhibit turnover frequencies (TOFs) ranging from 1.0 s−1 to 103 s−1. The experimental TOFs correlate with the H-bonding ability of the distal superstructure of these iron porphyrin complexes and analysis suggests that H-bonding alone can tune the rate of CO2 reduction by as much as 1000 fold. DFT calculations provide a detailed insight into how the, apparently weak, 2nd sphere interactions lead to efficient CO2 activation for reduction. The ability to tune CO2 reduction rates by changing the H-bonding residue instead of the acid source is a convenient way to tune CO2 reduction electrocatalysis without compromising selectivity by introducing competitive hydrogen evolution reaction or formate generation.
TL;DR: In this article, the authors show 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.
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.
TL;DR: In this article, a generic solution-phase colloidal approach in the presence of alkylammonium salts was used to synthesize single-crystalline microcrystals of Mn-doped layered perovskites (L2PbX4, X = Cl, Br, I) with high quantum yield.
Abstract: While solution-processed doping of Mn ions in 3D lead halide perovskites is extensively studied, the chemistry for Mn doping in 2D layered perovskites is limited. Following a generic solution-phase colloidal approach in the presence of alkylammonium salts, formation of single-crystalline microcrystals of Mn-doped layered perovskites (L2PbX4, X = Cl, Br, I) is reported. While Mn was present in all microstructures, only L2PbBr4 led to Mn d–d emission with high quantum yield (∼61%). These doped layered structures showed robust stability and even retained the original emission in continuous thermocycling or constant heating at 200 °C in air for more than 24 h. Moreover, these materials also showed solid-state thermal annealing-induced 2D agglomeration leading to a larger structure, which was reflected from optical microscopic images and the enhanced intensity of powder XRD peaks that originated from the layered structure. Apart from the generic synthesis, these results also provided several new fundamental in...
TL;DR: By means of first-principles computations, it is demonstrated that dynamical as well as highly thermally stable single boron atom doped nanoporous carbon nitride materials, i.e. C2N monolayers, are a potential metal-free single atom catalyst for efficient N2 fixation under visible light absorption.
Abstract: The production of ammonia (NH3), an important carbon-free chemical, through nitrogen (N2) fixation under mild conditions, is one of the most challenging and attractive chemical processes for industrial applications. However, most N2 fixation occurs through transition-metal based systems and examples of metal-free catalysts remain elusive. Herein, by means of first-principles computations, we demonstrate that dynamical as well as highly thermally stable (up to 800 K) single boron atom doped nanoporous carbon nitride materials, i.e. C2N monolayers, are a potential metal-free single atom catalyst for efficient N2 fixation under visible light absorption. Based on the B-N synergistic effect, N2 strongly binds to the B/C2N surface through end-on and side-on modes respectively. Our computation reveals that the single B atom doped C2N-concept catalyst could effectively reduce N2 to NH3 with a record low onset potential (0.18 eV) through enzymatic pathways and can sufficiently suppress the competing hydrogen evolution reactions. Multimodal binding of gas phase N2 molecules with selective stabilization of NxHx by proton-electron (H+ + e-) pairs leads to the highest catalytic performance of B/C2N. Moreover, deposition of single B atoms on C2N dramatically enhances the absorption of light in the visible and IR regions, rendering it a promising solar light-driven N2 to NH3 reduction (NRR) catalyst. The excellent formation energy of B doped C2N advocates its experimental synthesis.
TL;DR: In this article, it was shown that the strong cosmic censorship conjecture holds even in the presence of a higher dimension Reissner-Nordstrom-de Sitter black hole and a rotating black hole on the brane.
Abstract: Strong cosmic censorship conjecture has been one of the most important leap of faith in the context of general relativity, providing assurance in the deterministic nature of the associated field equations. Though it holds well for asymptotically flat spacetimes, a potential failure of the strong cosmic censorship conjecture might arise for spacetimes inheriting Cauchy horizon along with a positive cosmological constant. We have explicitly demonstrated that violation of the censorship conjecture holds true in the presence of a Maxwell field even when higher spacetime dimensions are invoked. In particular, for a higher dimensional Reissner-Nordstrom-de Sitter black hole the violation of cosmic censorship conjecture is at a larger scale compared to the four dimensional one, for certain choices of the cosmological constant. On the other hand, for a brane world black hole, the effect of extra dimension is to make the violation of cosmic censorship conjecture weaker. For rotating black holes, intriguingly, the cosmic censorship conjecture is always respected even in presence of higher dimensions. A similar scenario is also observed for a rotating black hole on the brane.
TL;DR: It was established that Cu(II)Cl2 in the system helped to stabilize the reaction even at and above 260 °C and provided an adequate chloride source for obtaining the highly emitting host as well as doped nanocrystals.
Abstract: Pretreatment using metal chlorides during the formation of halide deficient free perovskite nanocrystals is reported. Among several metal chlorides, Cu(II)Cl2 was observed to be ideal for the synthesis of highly emitting CsPbCl3 nanocrystals at high reaction temperature. Because high temperature remained more favorable for the dopant insertion, doping of Mn(II) was carried out under this halide-rich system, and nearly 68% photoluminescence quantum yield was recorded. Analysis could not provide strong evidence of insertion of Cu(II) inside the nanocrystals; rather, it was established that Cu(II)Cl2 in the system helped to stabilize the reaction even at and above 260 °C and provided an adequate chloride source for obtaining the highly emitting host as well as doped nanocrystals. Details of the physical process involved for this metal ion-induced uplifting of the reaction temperature and the consequent impacts on the nanocrystal formation are studied in detail and reported in this Letter.
TL;DR: The decoration of silver nanoparticles (NPs) over the surface of a covalent organic framework (COF) material TpPa-1 synthesized through the polycondensation of 2,4,6-triformylphloroglucinol (TFP) and p-phenylenediamine exhibited excellent catalytic activity for the synthesis of tetramic acids from a variety of propargylic amine derivatives.
Abstract: CO2 fixation reactions by inserting it in reactive organic compounds are very challenging for the utilization of this abundant and harmful gas present in air and thus to mitigate this greenhouse gas responsible for global warming. This can be achieved by appropriate design of functionalized porous nanocatalysts having high surface areas and porosity and good CO2 uptake capacity. Herein, we first report the decoration of silver nanoparticles (NPs) over the surface of a covalent organic framework (COF) material TpPa-1 synthesized through the polycondensation of 2,4,6-triformylphloroglucinol (TFP) and p-phenylenediamine. The resulting material Ag@TpPa-1 was thoroughly characterized by N2 adsorption/desorption, powder X-ray diffraction (PXRD), FE-SEM, TEM, UV-Vis, FT IR and thermogravimetric techniques. This Ag NP decorated porous COF in the presence of DBU exhibited excellent catalytic activity for the synthesis of tetramic acids from a variety of propargylic amine derivatives at 60 °C under atmospheric pressure of carbon dioxide via formation of oxazolidinones, where CO2 acts as a C1 reagent. The Ag@TpPa-1 catalyst exhibited excellent recycling efficiency for the synthesis of tetramic acid with no leaching of Ag from the catalyst surface.
TL;DR: Kinetic study done at regular intervals of time revealed high percentage removal of lead throughout entire span of reactor operation, and the column reactor was efficient enough to treat lead containing actual industrial effluents.
TL;DR: P pH-responsive self-assembly and gelation of a highly biocompatible amphiphilic peptide PEP-1, an octa-peptide and double mutant of a naturally occurring β-strand peptide fragment of the protein Galectin-1 , available in bovine spleen is reported.
Abstract: Peptide-based hydrogels are highly promising for various biomedical applications owing to their precise self-assembly, biocompatibility, and sensitivity toward biologically relevant external stimuli. Herein, we report pH-responsive self-assembly and gelation of a highly biocompatible amphiphilic peptide PEP-1. This is an octa-peptide and double mutant of a naturally occurring β-strand peptide fragment of the protein Galectin-1, available in bovine spleen. PEP-1 was synthesized by using the Rink amide resin as the solid support in a homemade apparatus. At pH 7.4, it exhibits spontaneous gelation with very high yield stress of 88.0 Pa and gel-to-sol temperature of 84 °C at C = 2.0 wt %. Microscopy studies revealed entangled fibrillar morphology whereas circular dichroism, Fourier tranform IR, and Thioflavin T assay indicated formation of β-sheet rich secondary structure. The assembled state was found to be stable in neutral pH whereas either decrease or increase in the pH resulted in disassembly owing to the presence of the pH responsive Asp and Lys residues. The gel network showed ability to entrap water-soluble guest molecules such as Calcein which could be selectively released at acidic pH whereas under neutral condition the release was negligible. MTT assay revealed remarkable biocompatibility of the PEP-1 gel as almost 100% cells were alive after 48 h incubation in the presence of PEP-1 (2.0 mg/mL).
TL;DR: In this article, an iron porphyrin complex with four ferrocene groups in its distal site is demonstrated to reduce CO2 unabated in the presence of O2 as it can reduce O2 to benign H2O under the same conditions.
Abstract: Reduction of CO2 to value-added chemicals is a logical way of fixing the rising levels of CO2. Activation and reduction of CO2 requires low-valent transition metals as catalysts. A major challenge in this chemistry is sensitivity of these low-valent metal sites to more abundant O2. Since O2 is a stronger oxidant than CO2 and isolated from the obvious competitive inhibition of CO2, partial reduction of O2 leads to formation of reactive oxygen species like O2– and H2O2, which are deleterious to the catalyst itself. An iron porphyrin complex appended with four ferrocene groups in its distal site is demonstrated to reduce CO2 unabated in the presence of O2 as it can reduce O2 to benign H2O under the same conditions. Further investigations reveal that iron porphyrins, in general, reduce CO2 selectively in the presence of O2. The aforementioned selectivity is derived from a 500 times faster rate of reaction of CO2 with Fe(0) porphyrin relative to O2 despite a higher driving force for the latter.