Showing papers by "National Chemical Laboratory published in 2013"
TL;DR: In this article, a functional microporous conducting carbon with a high surface area of about 1230 m2 g−1 is synthesized by single-step pyrolysis of dead plant leaves (dry waste, ground powder) without any activation and studied for supercapacitor application.
Abstract: Functional microporous conducting carbon with a high surface area of about 1230 m2 g−1 is synthesized by single-step pyrolysis of dead plant leaves (dry waste, ground powder) without any activation and studied for supercapacitor application. We suggest that the activation is provided by the natural constituents in the leaves composed of soft organics and metals. Although the detailed study performed and reported here is on dead Neem leaves (Azadirachta indica), the process is clearly generic and applicable to most forms of dead leaves. Indeed we have examined the case of dead Ashoka leaves as well. The comparison between the Neem and Ashoka leaves brings out the importance of the constitution and composition of the bio-source in the nature of carbon formed and its properties. We also discuss and compare the cases of pyrolysis of green leaves as well as un-ground dead leaves with that of ground dead leaf powder studied in full detail. The concurrent high conductivity and microporosity realized in our carbonaceous materials are key to the high energy supercapacitor application. Indeed, our synthesized functional carbon exhibits a very high specific capacitance of 400 F g−1 and an energy density of 55 W h kg−1 at a current density of 0.5 A g−1 in aqueous 1 M H2SO4. The areal capacitance value of the carbon derived from dead (Neem) plant leaves (CDDPL) is also significantly high (32 μF cm−2). In an organic electrolyte the material shows a specific capacitance of 88 F g−1 at a current density of 2 A g−1.
780 citations
TL;DR: Three thermally and chemically stable isoreticular covalent organic frameworks synthesized via room-temperature solvent-free mechanochemical grinding seemed to have a graphene-like layered morphology (exfoliated layers), unlike the parent COFs synthesized solvothermally.
Abstract: Three thermally and chemically stable isoreticular covalent organic frameworks (COFs) were synthesized via room-temperature solvent-free mechanochemical grinding. These COFs were successfully compared with their solvothermally synthesized counterparts in all aspects. These solvent-free mechanochemically synthesized COFs have moderate crystallinity with remarkable stability in boiling water, acid (9 N HCl), and base [TpBD (MC) in 3 N NaOH and TpPa-2 (MC) in 9 N NaOH]. Exfoliation of COF layers was simultaneously observed with COF formation during mechanochemical synthesis. The structures thus obtained seemed to have a graphene-like layered morphology (exfoliated layers), unlike the parent COFs synthesized solvothermally.
723 citations
TL;DR: The synthesized COFs were successfully delaminated using a simple, safe, and environmentally friendly mechanical grinding route to transform into covalent organic nanosheets (CONs) and were well characterized via transmission electron microscopy and atomic force microscopy.
Abstract: A series of five thermally and chemically stable functionalized covalent organic frameworks (COFs), namely, TpPa-NO2, TpPa-F4, TpBD-(NO2)2, TpBD-Me2, and TpBD-(OMe)2 were synthesized by employing the solvothermal aldehyde-amine Schiff base condensation reaction. In order to complete the series, previously reported TpPa-1, TpPa-2, and TpBD have also been synthesized, and altogether, eight COFs were fully characterized through powder X-ray diffraction (PXRD), Fourier transform IR (FT-IR) spectroscopy, 13C solid-state NMR spectroscopy, and thermogravimetric analysis. These COFs are crystalline, permanently porous, and stable in boiling water, acid (9 N HCl), and base (3 N NaOH). The synthesized COFs (all eight) were successfully delaminated using a simple, safe, and environmentally friendly mechanical grinding route to transform into covalent organic nanosheets (CONs) and were well characterized via transmission electron microscopy and atomic force microscopy. Further PXRD and FT-IR analyses confirm that the...
620 citations
TL;DR: In this article, the authors report high mobility (>60 cm2/Vs at room temperature) field-effect transistors that employ unencapsulated single-layer MoS2 on oxidized Si wafers with a low level of extrinsic contamination.
Abstract: Ultra-thin MoS2 has recently emerged as a promising two-dimensional semiconductor for electronic and optoelectronic applications. Here, we report high mobility (>60 cm2/Vs at room temperature) field-effect transistors that employ unencapsulated single-layer MoS2 on oxidized Si wafers with a low level of extrinsic contamination. While charge transport in the sub-threshold regime is consistent with a variable range hopping model, monotonically decreasing field-effect mobility with increasing temperature suggests band-like transport in the linear regime. At temperatures below 100 K, temperature-independent mobility is limited by Coulomb scattering, whereas, at temperatures above 100 K, phonon-limited mobility decreases as a power law with increasing temperature.
399 citations
TL;DR: A strategy based on intramolecular hydrogen-binding interactions in 2D covalent organic frameworks (COFs) is shown to improve the crystallinity, porosity, and chemical stability of the material.
Abstract: A strong bond: A strategy based on intramolecular hydrogen-binding interactions in 2D covalent organic frameworks (COFs) is shown to improve the crystallinity, porosity, and chemical stability of the material. The concept is validated by removing the hydrogen-bonding interaction in the methoxy analog which showed a lower stability and crystallinity.
370 citations
TL;DR: In this paper, the synthesis of phase pure CuO nanoparticles by controlled pyrolysis of Cu-based MOF was reported and the performance of half-cell assembly was evaluated.
243 citations
TL;DR: In this article, the authors used hydrate based gas separation (HBGS) process with silica sand and silica gel as contact medium to capture CO2 from fuel gas mixture.
224 citations
TL;DR: First-principles density functional calculations suggest that the enhanced field emission may also be due to an overalp of the electronic structures of WS2 and RGO, where graphene-like states are dumped in the region of the WS2 fundamental gap.
Abstract: We report here the field emission studies of a layered WS2-RGO composite at the base pressure of ~1 × 10−8 mbar. The turn on field required to draw a field emission current density of 1 μA/cm2 is found to be 3.5, 2.3 and 2 V/μm for WS2, RGO and the WS2-RGO composite respectively. The enhanced field emission behavior observed for the WS2-RGO nanocomposite is attributed to a high field enhancement factor of 2978, which is associated with the surface protrusions of the single-to-few layer thick sheets of the nanocomposite. The highest current density of ~800 μA/cm2 is drawn at an applied field of 4.1 V/μm from a few layers of the WS2-RGO nanocomposite. Furthermore, first-principles density functional calculations suggest that the enhanced field emission may also be due to an overalp of the electronic structures of WS2 and RGO, where graphene-like states are dumped in the region of the WS2 fundamental gap.
211 citations
TL;DR: In this article, the effect of additives on hydrate formation kinetics were also investigated, with a mesh size of 60-120, 100-200 and 230-400 having different surface area.
205 citations
TL;DR: This work isolated the endophytic fungi from Catharanthus roseus plant and found a fungus AA-CRL-6 which produces vinblastine and vincristine in appreciable amounts and was identified as Fusarium oxysporum based upon its cultural and morphological characteristics and internal transcribed spacer (ITS) sequence analysis.
Abstract: Endophytic fungi reside in a symbiotic fashion inside their host plants, mimic their chemistry and interestingly, produce the same natural products as their hosts and are thus being screened for the production of valuable compounds like taxol, camptothecin, podophyllotoxin, etc. Vinblastine and vincristine are excellent anti-cancer drugs but their current production using plants is non-abundant and expensive. In order to make these drugs readily available to the patients at affordable prices, we isolated the endophytic fungi from Catharanthus roseus plant and found a fungus AA-CRL-6 which produces vinblastine and vincristine in appreciable amounts. These drugs were purified by TLC and HPLC and characterized using UV-Vis spectroscopy, ESI-MS, MS/MS and 1H NMR. One liter of culture filtrate yielded 76 µg and 67 µg of vinblastine and vincristine respectively. This endophytic fungal strain was identified as Fusarium oxysporum based upon its cultural and morphological characteristics and internal transcribed spacer (ITS) sequence analysis.
196 citations
TL;DR: The biosynthesis of silver nanoparticles by the thermophilic fungus Humicola sp.
TL;DR: It is reported that silver nitrite (AgNO2) along with TEMPO can promote the regio- and stereoselective nitration of a broad range of olefins.
Abstract: Nitroolefin is a common and versatile reagent Its synthesis from olefin is generally limited by the formation of mixture of cis and trans compounds Here we report that silver nitrite (AgNO2) along with TEMPO can promote the regio- and stereoselective nitration of a broad range of olefins This work discloses a new and efficient approach wherein starting from olefin, nitroalkane radical formation and subsequent transformations lead to the desired nitroolefin in a stereoselective manner
TL;DR: In this article, the use of modified H-ZSM-5 by desilication was explored, and the increased LA conversion may be due to increase in total acidity from 43.14% to 84.31%.
Abstract: Levulinic acid (LA) is considered as a renewable platform chemical and can be used for the synthesis of variety of important fuels and chemicals. In particular, its esterification with ethanol produces ethyl levulinate (EL) would be green process, as it can be used as diesel miscible biofuel (DMB), preventing global warming by decreasing atmospheric CO 2 . This study explores the use of modified H-ZSM-5 by desilication viz.; DH-ZSM-5 and dodecatungstophosphoric acid (DTPA) loaded on DH-ZSM-5 for esterification of LA with ethanol aiming to EL. Different degree of desilication of H-ZSM-5 was performed by using aq. NaOH (0.2–1.5 M) at 338 K for 30 min and then DTPA was loaded on these desilicated H-ZSM-5 (DH-ZSM-5) support. H-ZSM-5, DH-ZSM-5 and DTPA on these DH-ZSM-5 samples were characterized by powder X-ray diffraction (XRD), N 2 adsorption–desorption, pyridine chemisorbed IR spectroscopy, Temperature Programmed Ammonia Desorption (TPAD). The increase in conversion of levulinic acid was observed from 28% to 94% with increase of DTPA loading from 0% to 15%. The increased LA conversion may be due to increase in total acidity from 43.14% to 84.31%. The use of DH-ZSM-5 as support for deposition of DTPA may be reported for the first time. The present work also extended to optimize process parameters such as DTPA loading on DH-ZSM-5, catalyst to LA ratio, LA to ethanol molar ratio, speed of agitation, particle size reaction temperature and catalyst reusability. Kinetic study based on pseudo-homogeneous (P-H) model is also presented. The experimental results follow second order kinetics.
TL;DR: The catalytic activity of ZIF-8 in the synthesis of styrene carbonate from carbon dioxide and styrene oxide was investigated in this paper, showing that the acid sites and nitrogen basic moieties from the imidazole linker promoted the adsorption of the CO 2 on the solid surface and its further conversion to the cyclic carbonate.
TL;DR: In this article, a polysulfone based porous asymmetric ultrafiltration (UF) membrane was synthesized by in situ growth followed by the LBL deposition of crystals without any need for pre-seeding or surface modification of the membrane.
Abstract: We demonstrate the synthesis of CuBTC and ZIF-8 on a polysulfone based porous asymmetric ultrafiltration (UF) membrane by in situ growth followed by the LBL deposition of crystals without any need for pre-seeding or surface modification of the membrane. In this way, the top surface of the UF membrane pores is completely covered by MOFs; while the remaining part of the membrane offers a flexible support to the MOFs. The pore apertures of the MOF nanoparticles located at the pore opening of the UF membrane act as channels for the entry of penetrants. The remaining porous sublayer of the membrane carries penetrants on the permeate side without significant resistance. These composite membranes were characterized by PXRD and SEM. The gas permeation study was performed using pure gases of industrial significance (H2, C3H6 and CO2). The performance of CuBTC@PSF showed enhanced selectivity, of 7.2 and 5.7 for H2/CO2 and H2/C3H6 respectively, to that of the pristine PSF membrane.
TL;DR: Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N-FeN(2+2)/C moieties, which are distributed along the carbon framework.
Abstract: The facile synthesis of a porous carbon material that is doped with iron-coordinated nitrogen active sites (FeNC-70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF-70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF-68 and ZIF-69, are also synthesized. The resulting active carbon material that is derived from ZIF-70, that is, FeNC-70, exhibits the highest BET surface area of 262 m(2) g(-1) compared to the active carbon materials that are derived from ZIF-68 and ZIF-69. The HR-TEM images of FeNC-70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X-ray photoelectron spectroscopy (XPS) reveals the presence of Fe-N-C moieties, which are the primary active sites for the oxygen-reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt.%, along with trace amounts of iron (0.1 wt.%), in the active FeNC-70 catalyst. This active porous carbon material, which is enriched with Fe-N-C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3-3.8 e(-) under acidic conditions, which is much closer to the favored 4 e(-) pathway for the ORR. The onset potential of FeNC-70 is significantly higher than those of its counterparts (FeNC-68 and FeNC-69) and of other reported systems. The FeNC-based systems also exhibit much-higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N-FeN(2+2)/C moieties, which are distributed along the carbon framework.
TL;DR: In this article, the authors outline the process of exploiting biomass for the production of polylactic acid, a biodegradable polymer which is well-known as a sustainable bioplastic material.
Abstract: Lignocellulosic biomass is renewable and cheap, and it has the potential to displace fossil fuels for the production of fuels and chemicals. Biomass derived lactic acid is an important compound that can be used as a chemical platform for the production of a variety of important chemicals on a large scale. The quality of the monomers of lactic acid and lactide, as well as the chemical changes induced during polymerization and processing, are crucial parameters for controlling the properties of the resulting polylactic acid (PLA) products. In this review, we outline the process of exploiting biomass for the production of polylactic acid, a biodegradable polymer which is well-known as a sustainable bioplastic material.
TL;DR: In this paper, the authors highlight the recent progress in the field of transition-metal-free direct C-C and C-heteroatom bond forming reactions via the use of a strong base and (or) an oxidant.
Abstract: The efficient generation of biaryl compounds and heterocycles via the advent of the transition-metal-free coupling reaction constitutes an important development in the last few years. Although early methods for the construction of such molecules involved transition metals, recent advances in the field have witnessed a myriad of elegant reports without the use of metal sources. The serendipitous discovery and observation of synthetic chemists have realized that there lies a great potential in exploiting the inherent reactivity of molecules in absence of transition metal. The key to the success of such coupling reactions is the use of a strong base, oxidant and a catalytic amount of N-donor ligands which contribute significantly. This review aims to highlight the recent progress in the field of transition-metal-free direct C–C and C–heteroatom bond forming reactions via the use of a strong base and (or) an oxidant.
TL;DR: A series of calcium hydroxyapatite (HAP) catalysts were synthesized with a Ca/P ratio ranging from 1.3 to 1.89 by a co-precipitation method that involved changing the pH of the calcium precursors.
TL;DR: A composite material consisting of silver nanoparticles deposited on graphene oxide (GO) nanosheets is prepared by chemical reduction of Ag metal ions by sodium borohydride (NaBH4) in the presence of trisodium citrate acting as a stabilizing agent to prevent agglomeration of the nanoparticles.
TL;DR: The binding of curcumin on the surface of gold nanoparticles (AuNPs) is reported, and it is proposed that it is the breakage of intramolecular H-bonding that probably leads to the increased availability ofCurcumin in the presence of gold ions and water molecules.
Abstract: Curcumin ((1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) is an active component of turmeric; it is responsible for its characteristic yellow color and therapeutic potential, but its poor bioavailability remains a major challenge. In order to improve the bioavailability of curcumin, various approaches have been used. One of the possible approaches to increase the bioavailability of curcumin is its conjugation on the surface of metal nanoparticles. Therefore, in the present study, we report the binding of curcumin on the surface of gold nanoparticles (AuNPs). The AuNPs were synthesized by the direct reduction of HAuCl4 using curcumin in the aqueous phase, without the use of any other reducing agents. We found that curcumin acts both as a reducing and capping agent, stabilizing the gold sol for many months. Moreover, these curcumin-capped AuNPs also show good antioxidant activity which was confirmed by the DPPH (2,2-diphenyl-l-picrylhydrazyl) radical test. Thus, the surface functionalization of AuNPs with curcumin may pave a new way of using the curcuminoids towards possible drug delivery and therapeutics. Apart from the experimental study, a detailed quantum chemical calculation using density functional theory (DFT) has been performed, in order to investigate the formation of a complex of curcumin with Au3+ ions in different possible conformational isomeric forms. Our theoretical calculations indicate the evidence of electron transfer from curcumin into the Au center and essentially indicate that as a consequence of complexation, Au3+ ions are reduced to Au0. Our theoretical results also propose that it is the breakage of intramolecular H-bonding that probably leads to the increased availability of curcumin in the presence of gold ions and water molecules.
Abstract: Silver nanoparticles (AgNPs) are currently among the most widely used man-made nanomaterials, present in a huge range of consumer products. Here we report a simple ‘green’ method of AgNP synthesis of using an anionic surfactant without use of any additional reducing agents. It was observed that synthesis of AgNPs at room temperature (25–35 °C) using sodium dodecyl sulphate (SDS) and sunlight. The nanoparticles have been characterised using high-resolution transmission electron spectroscopy (HRTEM), UV–vis spectrophotometry, X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) and are found to have an average diameter of 30 nm. The nanoparticles are water soluble and the nature of the process is amenable to scaling up.
TL;DR: In this paper, the effect of ligand nature on the resulting carbon porosity has been studied systematically using the MOFs synthesized from rigid and flexible ligands, and the linear relations between Zn/C ratio of the MOF versus surface area of resulting carbon, microporosity versus H2 uptake achieved in these carbons, and surface area versus specific capacitance of the end carbons have been verified from the gas adsorption, molecular composition, and electrochemical studies, respectively.
Abstract: Synthesis of porous carbons on direct carbonization of nonporous Zn-based MOFs has been achieved without using any additional carbon precursor. The effect of ligand nature on the resulting carbon porosity has been studied systematically using the MOFs synthesized from rigid and flexible ligands. The linear relations between Zn/C ratio of the MOF versus surface area of the resulting carbon, microporosity versus H2 uptake achieved in these carbons, and surface area versus specific capacitance of the end carbons have been verified from the gas adsorption, molecular composition, and electrochemical studies, respectively. Cyclic voltammetry and charge–discharge cycling have been carried out to study the capacitive behavior of the carbons. The interdependence of capacitive behavior on the surface area has been analyzed using data derived from N2 adsorption isotherms and charge–discharge curves. Among the carbons synthesized, C-MOF-2 shows maximal surface area of 1378 m2/g with a specific capacitance of 170 F/g ...
TL;DR: In this paper, the effect of CP (cyclopentane) as a promoter/additive, in the HBGS (hydrate based gas separation) process for pre-combustion gas mixture was investigated by employing an unstirred reactor configuration.
TL;DR: It is established a fact that hydrodynamic cavitation in combination with H2O2 can be effectively used for degradation of imidacloprid.
TL;DR: The catalytic activity of enzymes in combi-CLEAs during one pot starch hydrolysis was well maintained up to five cycles without performance changes and the biocatalyst was of spherical structure.
TL;DR: In this paper, the synthesis and Li-cyclability of α-Fe2O3 nanospindles derived from Fe based metal organic framework (MOF) were investigated through XRD and SEM/TEM analysis, respectively.
TL;DR: In this paper, a double front cone differential pumping arrangement and an aperture free design employed in the electrostatic lens regime improve the data collection and data quality of the Lab-APPES.
Abstract: The critical features of a custom-built laboratory version ambient pressure photoelectron spectrometer (Lab-APPES) are presented. A double front cone differential pumping arrangement and an aperture free design employed in the electrostatic lens regime improve the data collection and data quality. In contrast to the conventional X-ray photoelectron spectrometers (XPS) operating at ultrahigh vacuum (UHV), it is possible to explore the electronic structure of solid surfaces under working conditions or closer to working conditions with Lab-APPES. Especially surface-dependent phenomena can be explored up to 1 mbar pressure and up to 873 K by conventional heating methods and at least up to 1273 K by a laser heating method. Simultaneous XPS and reaction kinetic measurements on solid surfaces make the Lab-APPES an important tool to measure the dynamic electronic structure changes on material surfaces under reaction conditions. The interaction of O2 with polycrystalline foils of Cu, Ag, and Au from UHV to 1 mbar ...
TL;DR: Stabilizing GQDs inside the ZIF-8 nanocrystals results in tailoring of the photoluminescence emission of the GQD@ZIF- 8 nanocrystal composite even after 3 months of aging under normal laboratory conditions.
Abstract: Luminescent graphene quantum dots (GQDs) are encapsulated and stabilized in Zeolitic Imidazolate Framework (ZIF-8) nanocrystals. The GQDs are well confined due to the adsorption on the growing face of the ZIF-8 nanocrystals and have a profound effect on the shape of the nanocrystals from rhombic dodecahedron to spherical. Stabilizing GQDs inside the ZIF-8 nanocrystals results in tailoring of the photoluminescence emission (ca. 32 nm, bathochromic shift) of the GQD@ZIF-8 nanocrystal composite even after 3 months of aging under normal laboratory conditions. Also the water adsorption (at STP) capacity increased for the GQD@ZIF-8 composite as compared to the pristine ZIF-8.
TL;DR: Proton conductivity has been studied thoroughly in two isomeric In(III)-isophthalate based MOFs and it is shown that In-IA-2D-2 can conduct protons under humidified as well as anhydrous conditions.