Showing papers by "Thalappil Pradeep published in 2012"

Effect of nanoscale zinc oxide particles on the germination, growth and yield of peanut

Abstract: An investigation was initiated to examine the effects of nanoscale zinc oxide particles on plant growth and development. In view of the widespread cultivation of peanut in India and in other parts of the globe and in view of the potential influence of zinc on its growth, this plant was chosen as the model system. Peanut seeds were separately treated with different concentrations of nanoscale zinc oxide (ZnO) and chelated bulk zinc sulfate (ZnSO4) suspensions (a common zinc supplement), respectively and the effect this treatment had on seed germination, seedling vigor, plant growth, flowering, chlorophyll content, pod yield and root growth were studied. Treatment of nanoscale ZnO (25 nm mean particle size) at 1000 ppm concentration promoted both seed germination and seedling vigor and in turn showed early establishment in soil manifested by early flowering and higher leaf chlorophyll content. These particles proved effective in increasing stem and root growth. Pod yield per plant was 34% higher compared to...

Graphene from Sugar and its Application in Water Purification

Abstract: This paper describes a green method for the synthesis of graphenic material from cane sugar, a common disaccharide. A suitable methodology was introduced to immobilize this material on sand without the need of any binder, resulting in a composite, referred to as graphene sand composite (GSC). Raman spectroscopy confirmed that the material is indeed graphenic in nature, having G and D bands at 1597 and 1338 cm–1, respectively. It effectively removes contaminants from water. Here, we use rhodamine 6G (R6G) as a model dye and chloropyrifos (CP) as a model pesticide to demonstrate this application. The spectroscopic and microscopic analyses coupled with adsorption experiments revealed that physical adsorption plays a dominant role in the adsorption process. Isotherm data in batch experiments show an adsorption capacity of 55 mg/g for R6G and 48 mg/g for CP, which are superior to that of activated carbon. The adsorbent can be easily regenerated using a suitable eluent. This quick and cost-effective technique f...

Ag7Au6: A 13-Atom Alloy Quantum Cluster

Abstract: An alloy cluster containing a 13-atom core, with a composition Ag 7 Au 6 (H 2 MSA) 10 (H 2 MSA=mercaptosuccinic acid) was synthesized from silver clusters by a galvanic exchange reaction. The clusters were characterized by several spectroscopic and microscopic methods. The alloy cluster shows luminescence with a quantum yield of 3.5×10 -2 at room temperature. Theoretical calculations for Ag 7 Au 6 (SCH 3 ) 10 suggest a distorted icosahedral core.

Protein-protected luminescent noble metal quantum clusters: an emerging trend in atomic cluster nanoscience

Abstract: Noble metal quantum clusters (NMQCs) are the missing link between isolated noble metal atoms and nanoparticles. NMQCs are sub-nanometer core sized clusters composed of a group of atoms, most often luminescent in the visible region, and possess intriguing photo-physical and chemical properties. A trend is observed in the use of ligands, ranging from phosphines to functional proteins, for the synthesis of NMQCs in the liquid phase. In this review, we briefly overview recent advancements in the synthesis of protein protected NMQCs with special emphasis on their structural and photo-physical properties. In view of the protein protection, coupled with direct synthesis and easy functionalization, this hybrid QC-protein system is expected to have numerous optical and bioimaging applications in the future, pointers in this direction are visible in the literature.

Understanding the degradation pathway of the pesticide, chlorpyrifos by noble metal nanoparticles.

Abstract: Application of nanoparticles (NPs) in environmental remediation such as water purification requires a detailed understanding of the mechanistic aspects of the interaction between the species involved. Here, an attempt was made to understand the chemistry of noble metal nanoparticle–pesticide interaction, as these nanosystems are being used extensively for water purification. Our model pesticide, chlorpyrifos (CP), belonging to the organophosphorothioate group, is shown to decompose to 3,5,6-trichloro-2-pyridinol (TCP) and diethyl thiophosphate at room temperature over Ag and Au NPs, in supported and unsupported forms. The degradation products were characterized by absorption spectroscopy and electrospray ionization mass spectrometry (ESI MS). These were further confirmed by ESI tandem mass spectrometry. The interaction of CP with NP surfaces was investigated using transmission electron microscopy, energy dispersive analysis of X-rays, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS rev...

Luminescent, bimetallic AuAg alloy quantum clusters in protein templates.

Abstract: We report the synthesis of luminescent AuAg alloy quantum clusters (QCs) in bovine serum albumin (BSA), for the first time, with experimentally determined atomic composition. Mixing of the as-synthesized protein-protected Au and Ag clusters resulted in the formation of alloy AuAg clusters within the BSA. Mass spectrometric analysis of the product of a 1:1 molar ratio reaction mixture of AuQC@BSA and AgQC@BSA suggested that the alloy clusters could be Au38−xAgx@BSA. Further analyses by standard techniques revealed that the alloy cluster core of ∼1.2 nm diameter is composed of nearly zero valent Au and Ag atoms that exhibit distinctly different steady state and time resolved excited state luminescence profiles compared to the parent clusters. Tuning of the alloy composition was achieved by varying the molar ratio of the parent species in the reaction mixture and compositional changes were observed by mass spectrometry. In another approach, mixing of Au3+ ions with the as-synthesized AgQC@BSA also resulted in the formation of alloy clusters through galvanic exchange reactions. We believe that alloy clusters with the combined properties of the constituents in versatile protein templates would have potential applications in the future. The work presents interesting aspects of the reactivity of the protein-protected clusters.

The Superstable 25 kDa Monolayer Protected Silver Nanoparticle: Measurements and Interpretation as an Icosahedral Ag152(SCH2CH2Ph)60 Cluster

Abstract: A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH2CH2Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well-defined metal core of ∼2 nm measured with transmission electron microscopy (TEM). The cluster yields a single fraction in high-performance liquid chromatography (HPLC). Increased laser fluence fragments the cluster until a new peak near 19 kDa predominates, suggesting that the parent cluster—Ag152(SCH2CH2Ph)60—evolves into a stable inorganic core—Ag152S60. Exploiting combined insights from investigations of clusters and surface science, a core–shell structure model was developed, with a 92-atom silver core having icosahedral-dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 60 thiolates arranged in a network of six-membered rings resembling the geometry found in self-assembled monolayers on Ag(111). The structure is in agreement with small-angle X-ray scatt...

Selective Visual Detection of TNT at the Sub-Zeptomole Level

Abstract: Realizing the limits of sensitivity, while maintaining selectivity, is an ongoing quest. Among the multitude of requirements, national security, early detection of diseases, safety of public utilities, and radiation prevention are some of the areas in need of ultralow detection. Structural, functional, and electronic features of nanomaterials are used to develop reliable analytical methods. Several kinds of surfaceenhanced spectroscopy, surface-enhanced Raman in particular, can be used for such applications; the technique may be further enhanced by spatially separating the analyte and the active plasmonic nanostructure with an insulator, a method known as shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Creating uniform anisotropic structures with nanoscale attributes by simple solution chemistry and combining analyte-selective chemistry on such surfaces enables ultrasensitive and selective detection methods. Noble metal quantum clusters (QCs), a new family of atomically precise nanomolecules with intense luminescence, along with their protein protected analogues, are highly sensitive and selective for specific analytes. Anchoring such QCs on mesoscale (100 nm to a few mm) particles leads to surface-enhancement of their luminescence and can create a new platform for ultrasensitive detection, especially when combined with the use of optical microscopy. Gold mesoflowers (MFs) are anisotropic materials with unique five-fold symmetric stems containing surface-enhancing nanoscale features. An entire MF is only a few micrometers in size, and its distinct shape allows for unique identification by optical microscopy; thus, changes in the properties of an MF can be used for the immediate and efficient detection of analytes. Herein, we demonstrate the selective detection of 2,4,6trinitrotoluene (TNT) at the sub-zeptomole level (10 21 moles) through a combination of these strategies on a mesostructure. Our method involves anchoring silver clusters, which are comprised of fifteen atoms and embedded in bovine serum albumin (BSA), on silica-coated Au MFs, termed Au@SiO2@Ag15 MFs, and using this system for analyte detection. Syntheses of the various components are described in the experimental section. The Au@SiO2 MFs have a tip-totip length of ca. 4 mm (Supporting Information, Figure S1a). The BSA-protected silver cluster (Ag15), is a red luminescent water-soluble QC prepared by a previously reported procedure (see Figure S2 for essential characterization data). Apart from a high quantum yield (10.7%) in water, it is stable over a wide pH range and exhibits emission in the solid state. We exposed varying concentrations of TNT to Au@SiO2@Ag15 MFs and found that even a concentration of less than one zeptomole of TNT per mesoflower quenches the luminescence of the composite mesoflowers within 1 min. The simultaneous disappearance of the luminescence of Ag15 on theMFand the appearance of the luminescence of another embedded fluorophore allows for easy identification of the analyte. Characterization data for the various composite MFs used in this study are presented in the Supporting Information. The hybrid structures, Au@SiO2@Ag15 MFs, with unique structural attributes are observable under an optical microscope (see Figure S3 for a schematic of the setup used). Dark field microscopic images of theseMFs show their well-defined features; they are star-shaped in a two dimensional projection (Figure 1A). The fluorescence image of the same MF (ca. 490 nm excitation, emitted light was passed through a triplepass filter and imaged) shows a characteristic red emission owing to the QCs anchored on its surface (Figure 1A). Unlike with other spherical single particle sensors, which are difficult to locate and distinguish by light-based microscopy, the welldefined shapes of the MFs ensure that the desired particles alone are analyzed. Furthermore, the analyte adsorption capacity of theMFs is enhanced by the thin inert layer of silica employed as a base. Au core/silica shell structures of this type can provide enhanced fluorescence and Raman scattering. The better stability of the QCs on the silica layer, along with a reduction in the luminescence quenching of the QCs on the MF surface and ease of functionalization are among the added advantages of this material (see the Supporting Information). Exposure of the Au@SiO2@Ag15 MFs to TNT (2.5 mL) at a concentration of one part per trillion (ppt) decreases the luminescence intensity slightly without affecting the optical image (Figure 1B), whereas at one part per billion (ppb) of TNT the luminescence feature disappears completely (Figure 1C; note that the MFs shown in Figure 1A–C are different in each case). For spectral intensity data collected from the surface of these MFs, see the Supporting Information, Figure S4. The quenching of cluster luminescence is due to the formation of a Meisenheimer complex by the [*] A. Mathew, Dr. P. R. Sajanlal, Prof. T. Pradeep DST Unit of Nanoscience (DST UNS), Department of Chemistry, Indian Institute of Technology Madras Chennai 600036 (India) E-mail: pradeep@iitm.ac.in [] Current address: Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology Atlanta, GA 30332-0400 (USA)

The Superstable 25 kDa Monolayer Protected Silver Nanoparticle: Measurements and Interpretation as an Icosahedral

Abstract: A cluster obtained in high yield from the reduction of a silver-thiolate precursor, Ag-SCH2CH2Ph, exhibited a single sharp peak near 25 kDa in the matrix-assisted laser desorption mass spectrum (MALDI MS) and a well- defined metal core of ∼2 nm measured with transmission electron microscopy (TEM). The cluster yields a single fraction in high-performance liquid chromatography (HPLC). Increased laser fluence fragments the cluster until a new peak near 19 kDa predominates, suggesting that the parent cluster Ag152(SCH2CH2Ph)60evolves into a stable inorganic core Ag152S60. Exploiting combined insights from investigations of clusters and surface science, a core−shell structure model was developed, with a 92-atom silver core having icosahedral- dodecahedral symmetry and an encapsulating protective shell containing 60 Ag atoms and 60 thiolates arranged in a network of six-membered rings resembling the geometry found in self-assembled monolayers on Ag(111). The structure is in agreement with small-angle X-ray scattering (SAXS) data. The protective layer encapsulating this silver cluster may be the smallest known three-dimensional self-assembled monolayer. First-principles electronic structure calculations show, for the geometry-optimized structure, the development of a ∼0.4 eV energy gap between the highest-occupied and lowest-unoccupied states, originating from a superatom 90-electron shell-closure and conferring stability to the cluster. The optical absorption spectrum of the cluster resembles that of plasmonic silver nanoparticles with a broad single feature peaking at 460 nm, but the luminescence spectrum shows two maxima with one attributed to the ligated shell and the other to the core.

Low-energy ionic collisions at molecular solids.

Abstract: ion mechanism, discussed in section 1.1.2. Figure 27 illustrates the reactive scattering mechanism with four representative snapshots of a Cs scattering trajectory in a classical MD simulation. The abstraction reaction is driven by the ion−dipole attraction force between the Cs ion and an adsorbate molecule. The impinging projectile first releases part of its initial energy to the surface (Figure 27b) even without direct collision with the adsorbate. Subsequently, the projectile pulls the adsorbate gently away from the surface in its outgoing trajectory (parts c and d of Figures 27 in sequence), leading to the formation of a Cs−molecule complex. The velocity of the outgoing Cs must be slow enough to accommodate the inertia of the adsorbate. As a result, adsorbates of low mass and small binding energy are efficiently abstracted. A heavier projectile like Cs transfers more energy to the target surface, and its lower velocity in the outgoing trajectory enhances the efficiency of reactive scattering events. Detailed aspects of Cs reactive scattering and its application for surface analysis have been reviewed. Table 9. Hyperthermal Energy Collisions at Condensed Molecular Solids method (projectile ion) system aim/observations refs reactive scattering and LES (Cs) H2O−D2O rate and activation energy of self-diffusion and H/D exchange of water 462, 476, 479, 496 H3O −water ice affinity of protons for the ice surface and proton transfer mechanism 478−480 H3O −H2O−D2O hydronium ion-mediated proton transfer at the ice surface 495 OH−H2O−D2O hydroxide ion-mediated proton transfer at the ice surface 497 HCl−water ice molecular and ionized states of HCl on ice 457, 477 Na−water ice hydrolysis of Na 484 H3O −NH3−water ice incomplete proton transfer from H3O to NH3 on the ice surface 454, 458 H3O −amine−water ice proton transfer efficiency on ice is reversed from the order of amine basicity 502 CO2−Na−water ice CO2 hydrolysis is not facilitated by a hydroxide ion 463 NO2−water ice NO2 hydrolysis produces nitrous acid 465 SO2−water ice SO2 hydrolysis occurs through various intermediates 511 C2H4−HCl−water ice electrophilic addition reaction mechanism at the condensed molecular surface 466 ethanol/2-methylpropan-2-ol−water ice SN1 and SN2 mechanisms at the condensed molecular surface 505 NH3−water ice and UV irradiation ammonium ion formation 608 CH3NH2−water ice and UV irradiation protonated methylamine formation 483 CH3NH2−CO2−water ice and UV irradiation glycine and carbamic acid formation 464 NaX−water ice (X = F, Cl, Br) surface/bulk segregation and transport properties of electrolyte ions 472−474 reactive scattering (Cs) CO and CO2 on Pt(111) mechanism of Cs + reactive ion scattering 89 Ar, Kr, Xe, and N2 on Pt(111) adsorbate mass effect on the reactive ion scattering cross-section 609 C2H4 on Pt(111) dehydrogenation mechanism of ethylene to ethylidyne 459, 610 C2D4 and H on Pt(111) ethylidene intermediate in H/D exchange reaction with ethylene 80, 610 reactive scattering (H) water ice and alcohol H2 + formation 469 CS (Ar) water ice−chloromethanes (CCl4, CHCl3, CH2Cl2) except CCl4, others undergo diffusive mixing 174 water ice−simple carboxylic acids structural reorganization on the ice film 175 water ice micropore collapse in the top layers of the ice film 176 water ice−butanol 494 Figure 27. Illustration of the reactive scattering mechanism of a Cs ion in four snapshots of a scattering trajectory from a Pt(111) surface: (a) initial positions before impact, (b) impact of the Cs and energy release to the surface, (c) Cs pulling the adsorbate away in its outgoing trajectory, (d) slow outgoing Cs dragging the adsorbate along and forming a Cs−molecule association product. Reprinted with permission from ref 88. Copyright 2004 John Wiley and Sons, Inc. Chemical Reviews Review dx.doi.org/10.1021/cr200384k | Chem. Rev. 2012, 112, 5356−5411 5388 Figure 28 shows an example of reactive collision mass spectra, which were obtained on a D2O ice film exposed first to 0.5 L of HCl gas and then to varying amounts of NH3 gas at 140 K. The spectra show peaks at higher masses than Cs (m/z 133), viz., CsNH3 + at m/z 150, Cs(D2O)n + (n = 1, 2) at m/z 153 and 173, and CsHCl at m/z 168, indicating the presence of the corresponding molecules on the surface. The intensities of H/D-exchanged species represent their original concentrations on the surface, because H/D isotopic scrambling does not occur during the ion/surface collision time (<1 × 10−12 s). The conversion efficiency of a neutral adsorbate (X) into a gaseous ion (CsX) ranges from ∼10−4 for chemisorbed species to ∼0.1 for physisorbed small molecules. Typical product ion signal intensities for ice film surfaces are much stronger than those for chemisorbed species. Also, it is worthwhile to point out that reactive collisions of Cs are ineffective for detecting large molecules such as polymers or long-chain SAM molecules. The mass spectra in Figure 28 also show LES signals corresponding to pre-existing ions on the surface. The hydronium ions seen are produced by the spontaneous ionization of HCl on the ice surface, and they undergo proton transfer reactions with NH3 to generate ammonium ions. The spectra show characteristic H/D isotopomers of each species produced by H/D exchange reactions with D2O molecules. The LES signals due to preformed hydronium and ammonium ions exhibited sputtering thresholds at Cs impact energies of 17 and 19 eV, respectively. On the other hand, on pure H2O and NH3 surfaces, these ions were emitted only above ∼60 eV due to their formation during secondary ion emission. It was also found that ultra-low-energy (a few electronvolts) collision of H with the ice surface can produce H2 +. The reaction proceeds more efficiently on amorphous solid water than crystalline water, reflecting differences in the surface concentration of dangling O−H bonds. Simple alkanols also behave in the same manner. The combined occurrence of reactive scattering and LES provides a powerful means to probe both neutral molecules and ions on surfaces and, therefore, to follow reactions on ice surfaces such as the ionization of electrolytes and acid−base reactions, which are described below. 7.2. Surface Composition and Structure Impurities in ice become concentrated in the quasi-liquid layers in the surface and at grain boundary regions due to the “freeze concentration effect”, and this has important consequences for atmospheric reactions on ice surfaces. However, there appear to be numerous exceptions to this general trend, where the surface segregation behavior of the dissolving species and their bulk solubility are determined by thermodynamic factors specific to individual chemical species. A good example is the formation of stable bulk phases of clathrate hydrates. Chemical specificity in the segregation phenomena can be studied by monitoring the surface populations of the dissolving species during the slow annealing of ice samples. Kang and coworkers examined these propensities in Na and halide ions at the surface and in the interior of ice films. They ionized NaF, NaCl, and NaBr molecules on ice films by the vapor deposition of the salts, and the variation in the surface population of the ions was monitored as a function of the ice temperature for 100−140 K by using LES. As shown in Figure 29, the LES intensities of Na and F− ions decrease with an increase in temperature above ∼120 K, whereas the Cl− and Br− intensities remain unchanged. The results indicate that Na and F− ions migrate from the ice surface to the interior at the elevated temperatures. The migration process is driven Figure 28. Cs reactive scattering and LES spectra monitoring the H3O −NH3 reaction on ice. The D2O film [3−4 bilayers (BLs), 1 BL = 1.1 × 10 water molecules cm−2] was exposed first to 0.5 L of HCl to generate hydronium ions and then to NH3 at varying exposures: (a) 0.02 L, (b) 0.3 L, (c) 0.7 L. The sample temperature was 100 K. The Cs collision energy was 30 eV. Reprinted with permission from ref 454. Copyright 2001 John Wiley and Sons, Inc. Figure 29. Surface populations of Na (□), F− (▲), Cl− (◇), and Br− (●) ions as a function of the ice film temperature measured from LES intensities of the ions. NaF, NaCl, and NaBr were deposited for a coverage of 0.8 ML for each salt on a D2O ice film grown at 130 K. The LES signals were measured at the indicated temperatures of salt adsorption. The LES intensities are shown on the normalized scale with the intensity at 100−105 K as a reference. The Cs beam energy was 35 eV. The figure is drawn on the basis of the data in refs 473 and 474. Chemical Reviews Review dx.doi.org/10.1021/cr200384k | Chem. Rev. 2012, 112, 5356−5411 5389 by the ion solvation energy, and it requires that surface water molecules have enough mobility to facilitate ion passage at temperatures above 120 K. It is worth noting that such a segregation behavior for ice agrees with the negative adsorption energy of these ions at water surfaces predicted by the Gibbs surface tension equation and MD simulations. An interesting property of hydronium ions observed in recent studies is that they preferentially reside at the surface of ice rather than in its interior. Evidence of this property has come from a variety of experimental observations over the past decade. The adsorption and ionization of HCl on an ice film promotes H/D exchange on the surface. However, vertical proton transfer to the film interior is inefficient. Continuous exposure of HCl gas on the ice film led to saturation in the hydronium ion population at the surface, and the amount of HCl uptake required for this saturation was independent of the thickness of the ice film. These observations suggest that protons stay at the ice surface and hardly migrate to the interior. This behavior can be attributed either to the active trapping of protons at the surface or to the lack of proton mobility to the ice interior. The observation of asymmetric

One-Step Route to Luminescent Au18SG14 in the Condensed Phase and Its Closed Shell Molecular Ions in the Gas Phase

Abstract: We report a one-step route for the synthesis of highly luminescent and water-soluble Au18SG14 (SG- glutathione in thiolate form) in nearly pure form using a slow reduction process. The cluster shows step-like behavior in its absorption profile. It emits red light in both aqueous and solid state under UV illumination. Quantum yield of the cluster is 0.053, nearly 25-fold higher than that of Au25SG18. The cluster exhibits distinct features corresponding to multiply charged ions in electrospray ionization mass spectrometry. This composition is also confirmed from MALDI MS along with other quantitative analyses. The cluster makes closed shell molecular ions in the gas phase. The possibility of making clusters of different core sizes is also demonstrated. The simplicity of this method and identification of the cluster with exact composition may facilitate the exploration of experimental and theoretical research on this material.

Protein-directed synthesis of NIR-emitting, tunable HgS quantum dots and their applications in metal-ion sensing.

Abstract: The development of luminescent mercury sulfide quantum dots (HgS QDs) through the bio-mineralization process has remained unexplored. Herein, a simple, two-step route for the synthesis of HgS quantum dots in bovine serum albumin (BSA) is reported. The QDs are characterized by UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, luminescence, Raman spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), circular dichroism (CD), energy dispersive X-ray analysis (EDX), and picosecond-resolved optical spectroscopy. Formation of various sizes of QDs is observed by modifying the conditions suitably. The QDs also show tunable luminescence over the 680-800 nm spectral regions, with a quantum yield of 4-5%. The as-prepared QDs can serve as selective sensor materials for Hg(II) and Cu(II), based on selective luminescence quenching. The quenching mechanism is found to be based on Dexter energy transfer and photoinduced electron transfer for Hg(II) and Cu(II), respectively. The simple synthesis route of protein-capped HgS QDs would provide additional impetus to explore applications for these materials.

Luminescent, Freestanding Composite Films of Au15 for Specific Metal Ion Sensing

Abstract: A highly luminescent freestanding film composed of the quantum cluster, Au15, was prepared. We studied the utility of the material for specific metal ion detection. The sensitivity of the red emission of the cluster in the composite to Cu2+ has been used to make a freestanding metal ion sensor, similar to pH paper. The luminescence of the film was stable when exposed to several other metal ions such as Hg2+, As3+, and As5+. The composite film exhibited visual sensitivity to Cu2+ up to 1 ppm, which is below the permissible limit (1.3 ppm) in drinking water set by the U.S. environmental protection agency (EPA). The specificity of the film for Cu2+ sensing may be due to the reduction of Cu2+ to Cu1+/Cu0 by the glutathione ligand or the Au15 core. Extended stability of the luminescence of the film makes it useful for practical applications.

Functional hybrid nickel nanostructures as recyclable SERS substrates: detection of explosives and biowarfare agents

Abstract: We present the synthesis of highly anisotropic nickel nanowires (NWs) and large area, free-standing carpets extending over cm2 area by simple solution phase chemistry. The materials can be post-synthetically manipulated to produce hybrid tubes, wires, and carpets by galvanic exchange reactions with Au3+, Ag+, Pt2+, and Pd2+. All of these structures, especially the hybrid carpets and tubes, have been prepared in bulk and are surface enhanced Raman scattering (SERS) active substrates. Molecules of relevance such as dipicolinic acid (constituting 5–15% of the dry weight of bacterial spores of Bacillus anthracis), dinitrotoluene, hexahydro-1,3,5-triazine (RDX), and trinitrotoluene at nanomolar concentrations have been detected. An enhancement factor of ∼1010 was observed for the Ni–Au nanocarpet. The reusability of the Ni–Au nanocarpet for SERS applications was tested 5 times without affecting the sensitivity. The reusability and sensitivity over large area have been demonstrated by Raman microscopy. Our method provides an easy and cost effective way to produce recyclable, large area, SERS active substrates with high sensitivity and reproducibility which can overcome the limitation of one-time use of traditional SERS substrates.

Graphene for environmental and biological applications

Abstract: The latest addition to the nanocarbon family, graphene, has been proclaimed to be the material of the century. Its peculiar band structure, extraordinary thermal and electronic conductance and room temperature quantum Hall effect have all been used for various applications in diverse fields ranging from catalysis to electronics. The difficulty to synthesize graphene in bulk quantities was a limiting factor of it being utilized in several fields. Advent of chemical processes and self-assembly approaches for the synthesis of graphene analogues have opened-up new avenues for graphene based materials. The high surface area and rich abundance of functional groups present make chemically synthesized graphene (generally known as graphene oxide (GO) and reduced graphene oxide (RGO) or chemically converted graphene) an attracting candidate in biotechnology and environmental remediation. By functionalizing graphene with specific molecules, the properties of graphene can be tuned to suite applications such as sensing, drug delivery or cellular imaging. Graphene with its high surface area can act as a good adsorbent for pollutant removal. Graphene either alone or in combination with other materials can be used for the degradation or removal of a large variety of contaminants through several methods. In this review some of the relevant efforts undertaken to utilize graphene in biology, sensing and water purification are described. Most recent efforts have been given precedence over older works, although certain specific important examples of the past are also mentioned.

Emergence of Multicolor Photoluminescence in La0.67Sr0.33MnO3 Nanoparticles

Abstract: Herein, we report the emergence of multicolor photoluminescence in a mixed-valence manganite nanoparticle La0.67Sr0.33MnO3 (LSMO NP) achieved through electronic structural modification of the nanoparticles upon functionalization with a biocompatible organic ligand, sodium tartrate. From UV–vis absorption, X-ray photoelectron spectroscopy (XPS), time-resolved photoluminescence study, and Raman spectroscopic measurements, it is revealed that ligand-to-metal charge transfer transitions from highest occupied molecular orbital (HOMO, centered in tartrate ligand) to lowest unoccupied molecular orbital (LUMO, centered in Mn3+/4+ of the NPs), and d–d transitions involving Jahn–Teller sensitive Mn3+ ions in the NPs plays the central role behind the origin of multiple photoluminescence from the ligand functionalized LSMO NPs.

Rapid identification of molecular changes in tulsi (Ocimum sanctum Linn) upon ageing using leaf spray ionization mass spectrometry

Abstract: Tulsi or Holy Basil (Ocimum sanctum Linn) is a medicinally important plant. Ursolic acid (UA) and oleanolic acid (OA) are among its major constituents which account for many medicinal activities of the plant. In the present work, we deployed a new ambient ionization method, leaf spray ionization, for rapid detection of UA, OA and their oxidation products from tulsi leaves. Tandem electrospray ionization mass spectrometry (ESI-MS) has been performed on tulsi leaf extracts in methanol to establish the identity of the compounds. We probed changes occurring in the relative amounts of the parent compounds (UA and OA) with their oxidized products and the latter show an increasing trend upon ageing. The findings are verified by ESI-MS analysis of tulsi leaf extracts, which shows the same trend proving the reliability of the leaf spray method.

Low-Temperature Thermal Dissociation of Ag Quantum Clusters in Solution and Formation of Monodisperse Ag2S Nanoparticles

Abstract: We report the effect of temperature on the stability of glutathione-protected Ag25 clusters. The clusters are stable up to 50 °C. Interestingly, above this temperature, they decompose to yield Ag2S nanoparticles with an average diameter of 3 ± 1 nm, crystallizing in monoclinic acanthite polymorph. Unlike conventional methods of syntheses of Ag2S, where a temperature of ∼200 °C is needed, our study shows the possibility of synthesis of Ag2S nanoparticles at much lower temperatures. This is in contrast with silver nanoparticles protected with thiolates, which typically give silver and alkyl/aryl disulfide upon thermal activation. The mechanism of cluster decomposition and formation of silver sulphide nanoparticles was investigated using various analytical techniques such as ultraviolet–visible spectroscopy, X-ray diffraction scanning electron microscopy, energy-dispersive analysis of X-rays, transmission electron microscopy, and electrospray ionization mass spectrometry. The monolayer of the cluster undergo...

Single container gravity-fed storage water purifier

Abstract: A gravity-fed storage water purifier is provided. The gravity-fed water purifier includes a filtration unit for receiving water. The filtration unit includes a housing unit, a first membrane cloth layer, a second membrane cloth layer, and a granular biocidal composition layer disposed between the first and second membrane cloth layers. The first and second membrane cloth layers remove dirt, sand and sediments from the contaminated water, using a depth filtration mechanism. The granular biocidal composition layer removes bacteria and virus from the contaminated water, through fast leaching of silver ions into the water. A single storage container is provided that collects the water filtered by the virtue of filtration unit and gravity. An adsorbent composition is disposed between the storage container and an outlet tap of the storage container.

Luminescent Silver Clusters with Covalent Functionalization of Graphene

Abstract: Brightly luminescent, atomically precise subnanometer clusters of silver protected by glutathione were covalently functionalized by solution phase thiolated graphene using ligand exchange. A hybrid molecule was formed, which was obtained in a nearly pure form by phase transfer from the aqueous to the organic phase. The resulting hybrid exhibited properties of both of these nanoscale materials. UV–vis, luminescence, XPS, EDAX, TEM, and Raman spectroscopy were used to characterize the hybrid structure, which showed the spectroscopic characteristics of both the constituents. The luminescence of the cluster was retained in the hybrid, along with features characteristic of graphene. Atomically precise clusters with covalently linked graphene will be useful for new applications in the areas of drug delivery, sensors, and catalysis.

Real time plasmonic spectroscopy of the interaction of Hg2+ with single noble metal nanoparticles

Abstract: In this work, we use dark-field optical microscopy (DFM) and hyper spectral imaging (HSI) to study the interactions of single Ag and Au nanoparticles (NPs) with Hg2+ in real time, at room temperature (25 °C). NPs were immobilized on glass substrates using 3-aminopropyltrimethoxysilane (APTMS) as the anchoring agent. Red, green and blue colors were assigned to the particles in hyper spectral images on the basis of their relative scattering intensities at 640, 550 and 460 nm, where the particles showed maxima in their scattering spectra. While Ag NPs showed all the colors, Au NPs were mostly red and rarely green in DFM images. The scattering spectra of Ag NPs were more blue shifted (with an average shift of 46 nm in the case of red particles) in a given time compared to Au NPs, after passing over Hg2+ solution and these shifts increased with time. Depending on the extent of blue shift, the colors of the particles got modified. Red particles appeared more reactive than green and blue, as revealed from the larger extent of shifts and their time dependence. The greater reactivity of red particles is attributed to their anisotropic nature possessing reactive tips, edges and more surface area due to their large size. The effect of quality of water on the scattering spectrum was checked by passing over deionized (DI) and tap waters separately, which showed that the effect is minimal compared to the presence of Hg2+, when data at a given time, flow rate and temperature were compared. Solution phase interactions of NPs with Hg2+ were also performed for comparison. These were characterized by UV-vis absorption spectroscopy, transmission electron microscopy (TEM) and energy dispersive analysis of X-rays (EDAX). Solution phase experiments showed citrate-induced aggregation of Ag NPs and partial reduction of Hg2+ to Hg0 upon exposure to Hg2+. Immobilized particles cannot aggregate and they show only reduction.

Sustained silver release composition for water purification

Abstract: Described herein are methods and compositions for preparing an adsorbent composition for sustained silver ion release is provided. The method comprises impregnating silver nanoparticles on an organic-templated-nanometal oxyhydroxide. Particle size of the silver nanoparticles is less than about 50 nm. The adsorbent composition is antimicrobial in water. In an aspect, the organic- templated-nanometal oxyhydroxide is organic-templated-boehmite nanoarchitecture (OTBN). The resultant adsorbent composition is used as a water filter in a water purification device.

Heterojunction double dumb-bell Ag2Te–Te–Ag2Te nanowires

Abstract: Growth of isolated axial heterojunction nanowires by a solution phase growth process is reported The dumb-bell shaped nanowires contain two silver telluride sections at the extremes joined by a tellurium section Reaction of silver nitrate with tellurium NWs in aqueous solution at a molar ratio of 1 : 1 leads to the formation of amorphous partially silver reacted Te NWs Low temperature (75 °C) solution phase annealing of these silver deficient NWs results in phase segregation producing crystalline Ag2Te and Te phases with clear phase boundaries along the wire axis Structural characterization of these dumb-bell shaped NWs was performed with different microscopic and spectroscopic tools Solution phase silver concentration over the course of annealing indicated leaching of silver into the solution during the formation of biphasic NWs Similar Ag : Te ratios were observed in both partially silver reacted Te NWs and phase segregated Ag2Te–Te–Ag2Te NWs and this was attributed to redeposition of leached silver on the amorphous NW tips which eventually resulted in complete phase segregation Successful integration of different chemical components in single NWs is expected to open up new application possibilities as physical and chemical properties of the heterostructure can be exploited

Water purification unit

Abstract: A sachet that can remove contaminates from a water sample. The sachet can comprise a nanomaterial. Any suitable amount of nanomaterial can be present in the sachet, for example, 1 %-30% by volume, preferably 1-10% or 2%-5%. In case of antimicrobial composition packed, a preferable quantity to be used in sachet is 2 to 5%. The nanomaterial in the sachet can release, for example, silver, into the water. The described sachet can be immersed in microbial contaminated water and then lifted out of water, such that water in the sachet can drain through the antimicrobial composition packed in the sachet. The composition can release trace quantity of silver ions in the water to be treated. The process of immersion-lift-drain can be repeated, to ensure that entire water volume has contacted the composition. The purification composition can comprise from about 50 vol% to about 99 vol% of the sachet.