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The small molecule salicylaldehyde was used to sense hydrogen peroxide using fluorescence spectroscopy.

Little is known about airborne atmospheric aerosols containing emerging contaminants such as nano- and microplastics. A novel, minimum energy usage, synthetic protocol of plastic micro/nanoparticle...

Silver clusters consisting of ∼10 atoms are readily bound by and encapsulated within DNA strands to yield strong absorption and emission. The coordination environments, however, are poorly understood, so cluster adducts can only be empirically tuned. This work describes the C4AC4TC3G strand that templates a particular cluster adduct. Its sequence has three types of nucleobases with distinct roles—tracts of cytosines that collectively coordinate the cluster, thymine acting as a junction in the overall strand, and the adenine/guanine pair that exclusively forms the cluster. In relation to the native oligonucleotide, the DNA–silver cluster complex diffuses faster and is more compact, thus suggesting that the strands fold because of the cluster. The Ag106+ adduct emits with λex/λem = 490/540 nm, a 19% quantum yield, and a biexponential 1.1/2.1 ns lifetime. The electronic environment for the cluster is controlled by the heteroatoms in the adenine and guanine. Most significantly, the N7 and the N2 in the guanin...

Ice nucleation microphysical processes are identified to be of high importance in forecasting the magnitude of the Earth’s climate change. The environmental conditions often influence the ice nucleation processes in the Earth’s atmosphere. We herein study the impact of various environmental conditions on FeHg (maghemite–Hg2Cl2 composite), a highly efficient ice nucleating particle with similar freezing point to the best inorganic ice nuclei, AgI. FeHg is formed from FeCl2·4H2O and HgCl2, which are observed in the environment, in contrast to AgI, which is rarely found. The ice nucleation efficacy remained unchanged for FeHg under ambient conditions for a long duration. To mimic the atmosphere, we performed a series of experiments using a suite of complementary techniques, at various levels of radiation intensity, temperature, and pH for FeHg. Experiments were also performed in the presence of atmospheric pollutants, such as ozone (in the presence or absence of light), as well as nine emerging metal oxides ...

To evaluate the role of atmospheric heterogeneous reactions on the ice nucleation ability of airborne dust particles, we investigated the systematic study of ice nucleation microphysics with a suite of atmospherically relevant metals (10), halides (4), and oxyhalides (2). Within a minute, a kaolin–iron oxide composite (KaFe) showed efficient reactions with aqueous mercury salts. Among the different mercury salts tested, only HgCl2 reacting with KaFe generated HgKaFe, a highly efficient ice nucleating particle (HEIN). When added to water, HgKaFe caused water to freeze at much warmer temperatures, within a narrow range of −6.6 to −4.7 °C. Using a suite of optical spectroscopy, mass spectrometry, and microscopy techniques, we performed various experiments to decipher the physical and chemical properties of surface and bulk. KaFe was identified as a mixture of different iron oxides, namely, goethite, hematite, magnetite, and ε-Fe2O3, with kaolin. In HgKaFe, HgCl2 was reduced to Hg2Cl2 and iron was predominantly in maghemite form. Reduction of Fe2+ by NaBH4, followed by aerial oxidation, helped KaFe to be an exact precursor for the synthesis of HEIN HgKaFe. Kaolin served as a template for synthesizing iron oxide, opposing unwanted aggregation. No other metal or metal halide was found to have more efficient nucleating particles than HgCl2 with KaFe composite. The chelation of Hg(II) hindered the formation of HEIN. This study is useful for investigating the role of morphology and how inorganic chemical reactions on the surface of dust change morphology and thus ice nucleation activity. The understanding of the fundamentals of what makes a particle to be a good ice nucleating particle is valuable to further understand and predict the amount and types of atmospheric ice nucleating particles.

Molecular silver clusters are optical chromophores, and species with distinct spectra form with DNA strands. One such hybrid chromophore is a violet cluster bound to repeated C2X sequences where X ≠ C. We varied the number of C2X repeats and the X nucleobase and consider three observations. First, different lengths of (C2A)y and (C2T)y strands with y = 3–12 identify a minimal (C2X)6 scaffold that forms a specific Ag10 adduct. This cluster has a +6 oxidation state, absorbs between 400–450 nm, and folds its DNA host. Second, different X nucleobases alter the (C2X)6 binding site. The natural nucleobases preferentially form the Ag106+ cluster and yield strong circular dichroism. These ligands coordinate via their heteroatoms, and the N3 of thymine was identified via cluster fluorescence that varies with pH. In contrast, abasic sites and imidazole substitutions suppress circular dichroism and diminish the number of silver adducts. These observations suggest that a (C2X)6 coordinates Ag106+ via multiple nucleob...

Metal enhanced fluorescence of carbon dots has been reported in aqueous solution. Moderately fluorescing carbon dots (λex=360nm and λem=440nm) of 6-8nm diameters (CDA) have been synthesized from freshly prepared aqueous ascorbic acid solution under modified hydrothermal treatment. The CDA fluorescence is quenched at the close proximity with gold nanoparticles (AuNPs). Here, a substrate specific near-field electric field distribution is pronounced. Anticipating distance dependent fluorescence enhancement phenomenon, long-chain aliphatic thiol capped AuNPs are introduced to improve fluorescence of moderately fluorescing CDAs. The long-chain aliphatic thiols act as spacers between CDA and AuNP. Interestingly, the fluorescence of CDA is observed to be enhanced successively as the chain lengths of aliphatic thiols are increased. Fluorescing CDA, upon excitation, transfers energy to the nearby AuNP and a plasmon is induced. This plasmon radiates in the far-field resulting in fluorescence enhancement of CDAs. Such an interesting enhancement in emission with metallic gold is termed as gold enhanced fluorescence. This far-field effect for fluorescence enhancement of CDA particles becomes a general consensus in solution with varied long-chain aliphatic amine ligand capped silver nanoparticles (AgNPs). Finally, consequence of far-field effect of fluorescence enhancement has been observed while derivatized AuNP and AgNP are introduced into the CDA solution simultaneously which is described as reinforced fluorescence enhancement due to coupled plasmonic radiation.

A stable deliverable solid, carbon dot-MnO 2 adduct, has been exclusively synthesized from a solution phase redox reaction between KMnO 4 and moderately fluorescing carbon dot. Here, fluorescence resonance energy transfer (FRET) phenomenon happens within the adduct where energy is transferred from carbon dot to MnO 2 making the solid adduct non-fluorescent. The as-obtained non-fluorescing adduct can be used for N -acetyl- l -cysteine (NAC) detection (linear detection range is 67 nM–0.11 mM and limit of detection is 1.27 nM) through fluorescence “Turn On” phenomenon. Also in acidic medium the FRET system is disturbed and the fluorescence of carbon dots is regenerated. Inspired by these results, the carbon dot-MnO 2 adduct was engaged to perform preliminary logic operations, namely YES and AND using H + and NAC as inputs. Due to its fast response and ease of operation, the in situ generated carbon dot-MnO 2 adduct could be useful to design a molecular device for biomedical research. Also the as-synthesized carbon dot system was utilized to design NOT and IMPLICATION logic gates using KMnO 4 and NAC as inputs.

Silver cluster–DNA complexes are optical chromophores, and pairs of these conjugates can be toggled from fluorescently dim to bright states using DNA hybridization. This paper highlights spectral and structural differences for a specific cluster pair. We have previously characterized a cluster with low emission and violet absorption that forms a compact structure with single-stranded oligonucleotides. We now consider its counterpart with blue absorption and strong green emission. This cluster develops with a single-stranded/duplex DNA construct and is favored by low silver concentrations with ≲8 Ag+:DNA, an oxygen atmosphere, and neutral pH. The resulting cluster displays key signatures of a molecular metal with well-defined absorption/emission bands at 490/550 nm, and with a fluorescence quantum yield of 15% and lifetime of 2.4 ns. The molecular cluster conjugates with the larger DNA host because it chromatographically elutes with the DNA and it exhibits circular dichroism. The silver cluster is identifi...

Chemical dyes are used in a wide range of anthropogenic activities and are generally not biodegradable. Hence, sustainable recycling processes are needed to avoid their accumulation in the environment. A one-step synthesis of Fecore-maghemiteshell (Fe-MM) for facile, instantaneous, cost-effective, sustainable, and efficient removal of brilliant green (BG) dye from water has been reported here. The homogenous and monolayer type of adsorption is, to our knowledge, the most efficient, with a maximum uptake capacity of 1000 mg·g-1, for BG on Fe-MM. This adsorbent was shown to be efficient in occurring in time-scales of seconds and to be readily recyclable (ca. 91%). As iron/iron oxide possesses magnetic behavior, a strong magnet could be used to separate Fe-MM coated with BG. Thus, the recycling process required a minimum amount of energy. Capping Fe-MM by hydrophilic clay minerals further enhanced the BG uptake capacity, by reducing unwanted aggregation. Interestingly, capping the adsorbent by hydrophobic plastic (low-density polyethylene) had a completely inverse effect on clay minerals. BG removal using this method is found to be quite selective among the five common industrial dyes tested in this study. To shed light on the life cycle analysis of the composite in the environment, the influence of selected physicochemical factors (T, pH, hν, O3, and NO2) was examined, along with four types of water samples (melted snow, rain, river, and tap water). To evaluate the potential limitations of this technique, because of likely competitive reactions with metal ion contaminants in aquatic systems, additional experiments with 13 metal ions were performed. To decipher the adsorption mechanism, we deployed four reducing agents (NaBH4, hydrazine, LiAlH4, and polyphenols in green tea) and NaBH4, exclusively, favored the generation of an efficient adsorbent via aerial oxidation. The drift of electron density from electron-rich Fecore to maghemite shells was attributed to be responsible for the electrostatic adsorption of N+ in BG toward Fe-MM. This technology is deemed to be environmentally sustainable in environmental remediation, namely, in waste management protocol.

Silver clusters with ≲30 atoms are molecules with diverse electronic spectra and wide-ranging emission intensities. Specific cluster chromophores form within DNA strands, and we consider a DNA scaffold that transforms a pair of silver clusters. This ~20-nucleotide strand has two components, a cluster domain (S1) that stabilizes silver clusters and a recognition site (S2) that hybridizes with complementary oligonucleotides (S2C). The single-stranded S1-S2 exclusively develops clusters with violet absorption and low emission. This conjugate hybridizes with S2C to form S1-S2:S2C, and the violet chromophore transforms to a fluorescent counterpart with λex ≈ 490 nm/λem ≈ 550 nm and with ~100-fold stronger emission. Our studies focus on both the S1 sequence and structure that direct this violet → blue-green cluster transformation. From the sequence perspective, C4X sequences with X = adenine, thymine, and/or guanine favor the blue-green cluster, and the specificity of the binding site depends on three factors: the number of C4X repeats, the identity of the X nucleobase, and the number of contiguous cytosines. A systematic series of oligonucleotides identified the optimal S1 sequence C4AC4T and discerned distinct roles for the adenine, thymine, and cytosines. From the structure perspective, two factors guide the conformation of the C4AC4T sequence: hybridization with the S2C complement and coordination by the cluster adduct. Spectroscopic and chromatographic studies show that the single-stranded C4AC4T is folded by its blue-green cluster adduct. We propose a structural model in which the two C4X motifs within C4AC4T are cross-linked by the encapsulated cluster. These studies suggest that the structures of the DNA host and the cluster adduct are interdependent.

We herein present a novel and sustainable technology for mercury recycling, with the maximum observed uptake capacity. Facile synthesis of the most efficient (~1.9 gg−1) nano-trap, made of montmorillonite-Fe-iron oxides, was performed to instantaneously remove mercury(II) ions from water. Elemental Hg was recovered from the adduct, by employing Fe granules, at ambient conditions. Varied pHs and elevated temperatures further enhanced this already highly efficient recycling process. The reduction of Hg(II) to Hg(I) by the nano trap and Hg(I) to Hg(0) by Fe granules are the main driving forces behind the recycling process. Facile sustainable recycling of the nano-trap and Fe granules require no additional energy. We have further developed a recyclable model for Hg nano-trap, which is inexpensive (

Surface plasmon resonance (SPR) is the manifestation of a resonance effect due to the interaction of conduction electrons of metal nanoparticles with incident photons. The interaction relies on the size and shape of the metal nanoparticles and on the nature and composition of the dispersion medium. By understanding the mechanistic aspects of the interaction of altered nanoparticle morphologies together with the associated medium effect, a new technology has been developed for careful spectroscopic monitoring. Each change can be followed by various spectroscopic techniques, which lead to sensing applications and imaging events. From successful SPR band monitoring through spectroscopy, new optoelectronic technology and sensors, including color sensors and sensor devices, have been developed. In this review, we discuss the important role of SPR and its efficacy to heighten practical spectroscopic applications.

Synergism of gold and silver, causing enhanced fluorescence, has been reported in cluster science with higher photochemical stability and practical applications. The electronic factor, nuclearity, size effect etc., bring autofluorescence, doping/alloying, aggregation induced fluorescence, core–shell interaction, oxidation induced interaction and silver effect. The plausible interplaying mechanisms behind the synergism in the bimetallic clusters has been focused upon. Appropriate selection of the template is mandatory to achieving AuAg bimetallic clusters. Such templates are scarce and only a few are reported in the literature while templates to obtain individual Au and Ag clusters are numerous. Semi/complete reduced gold and non/complete reduced silver are one of the important features of such bimetallic clusters. Mingled Au and Ag has a profound effect on the stability, electronic structure and band energy of the bimetallic clusters. The arrangement of Au and Ag atoms in the bimetallic clusters is also a matter of interest. The bimetallic AuAg clusters are found to be superior to not only individual Au/Ag clusters but also carbon and semiconductor quantum dots, considering their emissive nature, toxicity, ease of synthesis, robustness etc. Water miscible as well as water immiscible solvents are equally efficient for the production of AuAg bimetallic clusters. Finally, such bimetallic clusters have proved to be unique candidates in the context of practical applications, namely sensing, catalysis, surface enhanced Raman spectroscopy (SERS), metal enhanced fluorescence (MEF), bio-imaging, synthesis of anti-bacterial cotton/papers etc. The ratio of Au and Ag not only tune the fluorescence behavior but also toxicity, as described.

The problem of poor electron conductivity is always associated with pseudocapacitive electrode material that deters full utilization of the active material. To have a viable solution to this problem, we report fabrication of a composite material bringing highly conductive carbon nanotube (CNT) wrapped pseudocapacitive with Co(OH) 2 nanoflakes. An in situ growth route evolves the supercapacitor via our laboratory developed modified hydrothermal reaction condition (MHT). An electrochemical investigation substantiates that the composite material electrode is highly active, which delivers a maximum specific capacitance of 603 F g −1 (at 1 mV s −1 scan rate), outstanding long-term cyclic stability with 96% retention at a constant current density of 1.5 A g −1 after 1000 cycles of operation. Thus it offers almost an effortless approach to fabricate high-power and high-energy density supercapacitors. By virtue of having high-capacity of pseudocapacitive hydroxides and desirable conductivity of carbon-based materials, the as-synthesized material could be a promising candidate for the development of supercapacitor electrode material.

Silver clusters with ∼10 atoms are molecules, and specific species develop within DNA strands. These molecular metals have sparsely organized electronic states with distinctive visible and near-infrared spectra that vary with cluster size, oxidation, and shape. These small molecules also act as DNA adducts and coordinate with their DNA hosts. We investigated these characteristics using a specific cluster-DNA conjugate with the goal of developing a sensitive and selective biosensor. The silver cluster has a single violet absorption band (λ(max) = 400 nm), and its single-stranded DNA host has two domains that stabilize this cluster and hybridize with target oligonucleotides. These target analytes transform the weakly emissive violet cluster to a new chromophore with blue-green absorption (λ(max) = 490 nm) and strong green emission (λ(max) = 550 nm). Our studies consider the synthesis, cluster size, and DNA structure of the precursor violet cluster-DNA complex. This species preferentially forms with relatively low amounts of Ag(+), high concentrations of the oxidizing agent O2, and DNA strands with ≳20 nucleotides. The resulting aqueous and gaseous forms of this chromophore have 10 silvers that coalesce into a single cluster. This molecule is not only a chromophore but also an adduct that coordinates multiple nucleobases. Large-scale DNA conformational changes are manifested in a 20% smaller hydrodynamic radius and disrupted nucleobase stacking. Multidentate coordination also stabilizes the single-stranded DNA and thereby inhibits hybridization with target complements. These observations suggest that the silver cluster-DNA conjugate acts like a molecular beacon but is distinguished because the cluster chromophore not only sensitively signals target analytes but also stringently discriminates against analogous competing analytes.

In this paper, we report the design, synthesis, and characterization of three different composite nanomaterials (Cu-ZnO, Cu-Cu2O-ZnO, and Cu2O-ZnO) with surface plasmon resonance (SPR) effect and n–p heterojunction for visible light photocatalysis. We have accounted for the first time the SPR effect of Cu in photocatalysis for promotion of efficient electron–hole separation that further enhances visible light induced photocatalytic activity. To make the composite efficient we have judiciously introduced cheap and common Cu and Cu2O in ZnO matrix individually and cojointly to make the composites visible light sensitizer. Furthermore, wide band gap barrier of ZnO crosses its UV limit in the composites and spreads over to visible region. By simply varying the complexing agents, here we achieve success to obtain three kinds of highly stable composite nanomaterials with three distinct structures from identical experimental condition. This synthetic strategy offers a radically different approach where oxidation...

A simple fluorometric technique has been adopted for cysteine (Cys) sensing in alkaline medium down to the nM level. The huge fluorescent signal of the solution is a consequence of fluorescent carbon dots (CDs) produced in situ from modified hydrothermal (MHT) reaction between Cys and dopamine (DA). It has been observed that the inherent fluorescence of DA is drastically quenched in alkaline solution. Cys can selectively rescue the fluorescence of DA. Thus, Cys determination in a straightforward way, but only to a micro molar (10(-7) M i.e. 0.1 μM) level is possible through such fluorescence enhancement. Sensitive Cys determination remains associated with the in situ generated CDs, but the external addition of pre-formed CDs to Cys solution fails miserably towards Cys detection. However, CDs prepared from the Cys-DA system in alkaline solution admirably increase the limit of detection (LOD) of Cys at least two orders higher (10(-9) M) than that observed without hydrothermal technique i.e., without CDs. This method finds applications for Cys determination in biological samples and pharmaceutical preparations.

Fluorescent carbon dots (NSCDs) with a size of ∼5 nm (λex = 320 nm and λem = 386 nm) have been synthesized under reflux from an alkaline mixture of dopamine and cysteine. The synthesized NSCDs are hybridized with in situ generated silver nanoparticles (AgNPs) obtained by mixing AgNO3 at room temperature. NSCDs enrich the plasmonic bands of AgNPs due to the localized surface plasmon resonance (LSPR) effect. Further enrichment of plasmon band, depending on the acetone concentration, enables acetone sensing down to 8 × 10(-5) M admixed in 1 M water. Thus, acetone induced hybrid particles with a sharp plasmon band (λex = 410 nm) become a sulfide sensing platform. Furthermore, vacuum dried stable particles (with or without acetone) have been proven to be an excellent catalyst for selective reduction of cationic dyes and they exhibit intriguing antimicrobial activity. These two types of dry particle act differently, which enables us to distinguish their altered surface functionalization in terms of catalysis and bacterial growth.

A modified hydrothermal protocol (MHT) has been adopted for the synthesis of a single-crystal of CoV2O6·2H2O. The crystals grew as a result of prolonged hydrothermal reaction between precursor salts of CoCl2 and ammonium vanadate. At first, the adopted reaction conditions resulted in nanowires of CoV2O6·4H2O. Then with increased reaction time, nanowires changed to single crystals of molecular formula CoV2O6·2H2O. The nanowires have lengths of several tens of micrometers and average diameter of 100 nm. The well defined structure crystallizes in the orthorhombic crystal system having space group Pnma and it displays a = 5.5647(2) A, b = 10.6870(5) A, c = 11.8501(5) A, α = β = γ = 90.00°. Here, each vanadium atom is tetrahedrally connected to four oxygens where two oxygens are connected to vanadium atoms and another two connected to cobalt atoms. Magnetic moment measurement of the nanowires indicates that antiferromagnetic ordering is observed at around 14.9 K and 6.8 K and field induced antiferromagnetic to ferromagnetic (spin-flop-type) transitions have been observed at a low temperature (5–8.8 K) range while these are absent in the as-synthesized single crystals.

Ultralong Ag1.92Mo3O10·H2O nanowires have been serendipitously obtained due to selective etching of ammonium phosphomolybdate (APM) only by Ag+ ions in water under stirring conditions. The spherical yellow APM particle upon etching by Ag+ ions generates a hollow sphere, and PO43– ions are expelled as a consequence of etching. The etching and hollowing disrupt the APM structure. Concentration of the etching agent and reaction time are crucial for the formation of Ag1.92Mo3O10·H2O nanowire. The growth of nanowires occurs probably due to etching followed by Ostwald ripening, oriented attachment, and splitting process. Finally, the as-synthesized nanowire exhibits a high capacity to adsorb cationic dyes on its surface. It shows superb adsorption properties, with maximum adsorption capacity of 110 mg g–1, 175 mg g–1, 160 mg g–1 for Methylene Blue, Methyl Green, Crystal Violet, respectively. Moreover, the adsorption process of Methylene Blue on the nanomaterial was investigated taking it as a representative ads...

A mild, template free protocol has been demonstrated for SnS2 nanoflake formation at the gram level from SnCl2 and thioacetamide (TAA). The SnS2 nanoflakes congregate to nanoflowers and nanoyarns with variable TAA concentrations. BET measurements reveal that the synthesized nanomaterials are highly porous having very high surface area, and the nanoflower has higher surface area than the nanoyarn. The synthesized nanomaterial finds application for promoting photoreduction of extremely toxic and lethal Cr(VI) under visible light irradiation due to their porous nature. The nanoflowers photocatalyst is proved to be superior to nanoyarn due to the increased surface area and higher pore volume. It was also inferred that increased pH decreased the reaction rate. The present result suggests that the morphology-dependent photoreduction of Cr(VI) by SnS2 nanomaterial under visible light exposure will endorse a new technique for harvesting energy and purification of wastewater.

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Electrochemical processing has already manifested its prominence for obtaining well structured composite materials. The method is highly precise and is reduction potential driven. This methodology has resulted in a hierarchical Au–CuO nanocomposite from a chosen redox transformation reaction between the newly synthesized spherical and roughened Cu2O nanoparticles and HAuCl4. Thus the attractive shape as well as reducing capability of Cu2O made it promising as a starting material. The proposed redox transformation reaction does not need any additional reducing or stabilizing agents. The reduction potential value of CuO/Cu2O (+0.66 V vs. SHE) supports the quantitative reduction of Au(III) ions because of its higher reduction potential (+1.69 V vs. SHE) i.e., for the AuCl4−/Au half cell. The prescribed conditions, spontaneous redox reaction and the morphology of Cu2O nanoparticles help to produce the unique Au–CuO nanoflowers. The formation of Au–CuO nanocomposites from Cu2O nanospheres is characterised by several physical techniques such as XRD, XPS and FTIR. Finally the flower like Au–CuO nanocomposite shows higher SERS activity with 4-aminothiophenol (4-ATP) as a probe molecule than what is evident from the individual components (Au or Cu2O or CuO). Additionally the derived Au–CuO nanocomposite has also been found to be an effective catalyst for the clock reaction employing methylene blue and ascorbic acid in solution.

We report a simple, facile, surfactant-free chemical route to fabricate morphologically different Cu2O nanoparticles such as octahedron, truncated octahedron, hollow octahedron, cube, and sphere by varying the hydrolyzing agents, complexing agent, and reducing agents. Then the componential and morphological evolution of Cu2O nanoparticles have been studied independently, employing different etching agents such as aqueous NaOH, triethylamine (TEA), and oxalic acid solution. Particles of varied shapes and compositions resulted from the etching, and those particles were characterized by different physical methods. The oxidative dissolution of morphologically different Cu2O nanoparticles with different etching agents depends on the exposed crystal planes. During oxidative dissolution in aqueous oxalic acid solution, it is realized that the stability of the (100) crystal plane is higher than that of the (111) crystal plane. Among all the etching reagents used, only oxalic acid exhibits shape transformation of ...

A facile, cost-effective, surfactant-free chemical route has been demonstrated for the fabrication of porous β-Co(OH)2 hierarchical nanostructure in gram level simply by adopting cobalt acetate as a precursor salt and ethanolamine as a hydrolyzing agent at room temperature. A couple of different morphologies of β-Co(OH)2 have been distinctly identified by varying the mole ratio of the precursor and hydrolyzing agent. The cyclic voltammetry measurements on β-Co(OH)2 displayed significantly high capacitance. The specific capacitance obtained from charge-discharge measurements made at a discharge current of 1 A/g is 416 F/g for the Co(OH)2 sample obtained at room temperature. The charge-discharge stability measurements indicate retention of specific capacitance about 93% after 500 continuous charge-discharge cycles at a current density of 1 A g(-1). The capacitive behavior of the other synthesized morphology was also accounted. The nanoflower-shaped porous β-Co(OH)2 with a characteristic three-dimensional architecture accompanied highest pore volume which made it promising electrode material for supercapacitor application. The porous nanostructures accompanied by high surface area facilitates the contact and transport of electrolyte, providing longer electron pathways and therefore giving rise to highest capacitance in nanoflower morphology. From a broad view, this study reveals a low-temperature synthetic route of β-Co(OH)2 of various morphologies, qualifying it as supercapacitor electrode material.

Attention has been directed toward electron deficient boron- doping in carbon dots (CDs) with the expectation of revealing new photophysical-aspects in accordance with varying amounts of boron content. It has been emphatically shown that boron uptake in CDs varies with different boron precursors evolving altered emissive CDs. Boron doping in CDs causes definite sulfate defect due to the generation of electron-deficient states. Modified hydrothermal treatment of a Mixture of ascorbic acid (AA) and different boron pecurs6t compounds (borax/boric acid/sodium borate/sodium- borohydride) produces different kinds of boron-clOped CDs (BCDs). These BCDs (

Silver clusters develop within DNA strands and become optical chromophores with diverse electronic spectra and wide-ranging emission intensities. These studies consider a specific cluster that absorbs at 400 nm, has low emission, and exclusively develops with single-stranded oligonucleotides. It is also a chameleon-like chromophore that can be transformed into different highly emissive fluorophores. We describe four characteristics of this species and conclude that it is highly oxidized yet also metallic. One, the cluster size was determined via electrospray ionization mass spectrometry. A common silver mass is measured with different oligonucleotides and thereby supports a Ag10 cluster. Two, the cluster charge was determined by mass spectrometry and Ag L3-edge X-ray absorption near-edge structure spectroscopy. Respectively, the conjugate mass and the integrated white-line intensity support a partially oxidized cluster with a +6 and +6.5 charge, respectively. Three, the cluster chirality was gauged by circular dichroism spectroscopy. This chirality changes with the length and sequence of its DNA hosts, and these studies identified a dispersed binding site with ∼20 nucleobases. Four, the structure of this complex was investigated via Ag K-edge extended X-ray absorption fine structure spectroscopy. A multishell fitting analysis identified three unique scattering environments with corresponding bond lengths, coordination numbers, and Debye-Waller factors for each. Collectively, these findings support the following conclusion: a Ag10(+6) cluster develops within a 20-nucleobase DNA binding site, and this complex segregates into a compact, metal-like silver core that weakly links to an encapsulating silver-DNA shell. We consider different models that account for silver-silver coordination within the core.

The condensation products of salicylaldehyde and different diamines constitute an important class of diiminic Schiff bases (DSBs). This class of compounds has been rediscovered as reducing as well as capping agents under UV irradiation. UV irradiation of alkaline DSB solutions in the presence of water-soluble copper salts has been employed to produce copper nanoparticles (CuNPs). Intriguing CuNP-stimulated fluorescence behavior of the solution has been observed. Depending upon the nature of the spacer in between two iminic bonds, fluorescence enhancement or quenching is observed. Such surprising fluorescence contrast has been ascribed to far-field radiation and lossy surface waves.

Straight chain amines of variable chain length offer steric stabilization to gold nanoparticles (AuNPs), and thereby, gold organosol is produced in nonpolar solvent. We have found that dodecylamine (DDA) becomes a preferred ligand over other amines, for extraction, stabilization, and preparation of gold organosol in hexane. In the same context, straight chain thiols also provide steric stabilization to the AuNPs and compete with amines. But, the extracting power of thiols is dramatically reduced while the size of AuNPs is increased, and amines accomplish success for variable sizes of AuNPs. Organosol system always remains admixed with excess free ligands, and it is true for amines also. Hence, free amines (unbound) conjecture false information and pose a problem during further course of investigation. Excess unbound ligands in the organosol system limit application of AuNPs in the organic medium. A simple heterogeneous separation technique is reported here to prepare amine stabilized organosol devoid of u...

Diiminic Schiff bases (DSBs) with a variety of spacers in between the two imine bonds have been prepared from salicylaldehyde and different diamines. Gold and silver nanoparticles (NPs) are photoproduced as stable hydrosol from the respective metal salts in the presence of alkaline DSBs. In solution, the capping capability of DSBs renders stability toward both the NPs. The phenomenon of capping of noble metal by DSBs is gifted with surprising alteration of the fluorescence property of DSBs. Varying concentration of the local field on the fluorophore as well as the coupling between the molecular dipole of the fluorophore and the surface plasmon band of the metal have been ascribed to be the key point of these stunning phenomena in solution phase.

We report a simple one-pot synthesis of highly fluorescent carbon dots (CDs) via modified hydrothermal (MHT) treatment of alkaline solution of dopamine and cysteine. These CDs (λex=320 nm, λem=390 nm, and quantum yield ∼ 5.1%) are of ∼ 2-3 nm in diameter. Further attempt of synthesizing CDs in some common water-miscible solvents ends up the fact that the MHT product from acetone medium is nonfluorescent. However, CDs, produced in aqueous medium, are so stable that they can be dried as a deliverable solid (WCD) without any alteration of fluorescing property if reversibly dispersed in water. Fluorescence of WCD is quenched selectively in acetone. Quenching occurs presumably due to the disruption of radiative recombination along with the hindrance in quantum confinement of the emissive energy traps to the particle surface. Successive quenching of fluorescence of WCD in different acetone concentration admixed in water paves the way to selective acetone sensing (LOD=8.75 × 10(-7) M). The synthesized CDs (in aqueous medium) are cytocompatible and are efficient fluorescent probe for cell imaging. Only living cells are recognized exclusively from fluorescence imaging leaving aside dead cells, while cells are treated with CDs.

Highly fluorescent Au(I)@Ag particles (emission maximum at 635 nm) have been obtained from a mixture of AgNO3, HAuCl4 and glutathione. Au(I)@Ag particles containing Ag2 and Ag3 clusters are produced when the reaction mixture is subjected to a modified hydrothermolysis (MHT) reaction. The silver clusters make the solution intensely fluorescent and the Au(I) moiety provides long term stability to the silver clusters by withdrawing electron density from the silver clusters. The vacuum-dried aqueous fluorescent solution leaves a yellow solid that exhibits higher emissive properties when re-dispersed in non-aqueous solvents. Fluorescent Au(I)@Ag particles have been found to be cytocompatible and efficient candidates for live cell imaging. Addition of S(2-) ions selectively and successively quenches the fluorescence of Au(I)@Ag particles without any significant interference from common anions. Thus, sensitive detection of S(2-) is possible with the fluorescent Au(i)@Ag particles in water and water-miscible non-aqueous solvents. Furthermore, Pb(ii) induced fluorescence enhancement of the solution containing Au(I)@Ag particles has been used to enable S(2-) detection free from interference by S2O3(2-) and I(-). The possibility of naked eye detection of S(2-) is also an additional advantage of this method as an orange color solution is developed exclusively with the S(2-) ion. Fluorometric determination of S(2-) has been rationalized for real environmental samples.

Metal enhanced fluorescence (MEF) from organic molecules has been the focus of plasmonic/photonic research. In this regard, silver and gold particle stimulated fluorescence has received much attention. However, the involvement of small organic molecules in solution has not been accounted for in MEF. We have reported here that the aqueous alkaline solution of salicylaldehyde exhibits highly enhanced fluorescence at room temperature (λem ∼ 420 nm, Stokes shift 120 nm, stability > a year) in the presence of Ag(I) or Au(III) after simple ageing for two days. The increased scattering cross-section of the in situ produced aggregated metal particles and the lightening rod effect of the metal aggregates that concentrate the electric field around the fluorophore (i.e., alkaline solutions of salicylaldehyde) are ascribed to such extraordinary fluorescence enhancement caused by Ag and Au particles. Finally, selective fluorescence enhancement due to silver particles alone has been made possible in the presence of ammonia or primary amines due to imine bond formation that eliminates Au enhanced fluorescence quantitatively. This finding allows us to design a highly selective Ag(I) sensor in the solution phase with a cheap and commercially available compound with LOD far below EPA-permissible levels. The imine induced selective silver enhanced fluorescence phenomenon becomes a general matter in our studies even with different Schiff bases.

This paper describes an effective method for a precursor salt assisted fabrication and reshaping of two different polyoxometalates [(NH4)2Cu(MoO4)2 (ACM) and Cu3(MoO4)2(OH)2 (CMOH)] into five distinctive shapes through straightforward and indirect routes. Explicit regulation of the structural arrangements of ACM and CMOH has been studied in detail with altered precursor salt concentration employing our laboratory developed modified hydrothermal (MHT) method. Morphologically different ACM 3D architectures are evolved with higher molybdate concentration, whereas 1D growth of CMOH is observed with increased copper concentration. Interesting morphological transformation of the products has been accomplished employing one precursor salt at a time without using any other foreign reagent. It has been proven that large ACMs become labile in the presence of incoming Cu(II) and NH4(+) ions of the precursor salts. A new strategy for the conversion of faceted ACMs (hexagonal plate, circular plate and hollow flower) to exclusive CMOH nanorods through a Cu(II) assisted reaction has been adopted. According to thermodynamic consideration, the synthesis of rare concave nanostructures with high index facet is still challenging due to their higher reactivity. In this study, concave hexagonal ACM with high index facet {hkl} has been successfully prepared for the first time from hexagonal ACM through simple etching with ammonium heptamolybdate (AHM), which is another precursor salt. Hexagonal ACM corrugates to a concave hexagon because of the higher reactivity of the {001} crystal plane than that of the {010} plane. It has been shown that high index facet exposed concave hexagonal ACM serves as a better catalyst for the photodegradation of dye than the other microstructures enclosed by low index facets.

Superhydrophobic surfaces prevent percolation of water droplets and thus render roll-off, self-cleaning, corrosion protection, etc., which find day-to-day and industrial applications. In this work, we developed a facile, cost-effective, and free-standing method for direct fabrication of copper nanoparticles to engender superhydrophobicity for various flat and irregular surfaces such as glass, transparency sheet (plastic), cotton wool, textile, and silicon substrates. The fabrication of as-prepared superhydrophobic surfaces was accomplished using a simple chemical reduction of copper acetate by hydrazine hydrate at room temperature. The surface morphological studies demonstrate that the as-prepared surfaces are rough and display superhydrophobic character on wetting due to generation of air pockets (The Cassie-Baxter state). Because of the low adhesion of water droplets on the as-prepared surfaces, the surfaces exhibited not only high water contact angle (164 ± 2°, 5 μL droplets) but also superb roll-off and self-cleaning properties. Superhydrophobic copper nanoparticle coated glass surface uniquely withstands water (10 min), mild alkali (5 min in saturated aqueous NaHCO3 of pH ≈ 9), acids (10 s in dilute HNO3, H2SO4 of pH ≈ 5) and thiol (10 s in neat 1-octanethiol) at room temperature (25-35 °C). Again as-prepared surface (cotton wool) was also found to be very effective for water-kerosene separation due to its superhydrophobic and oleophilic character. Additionally, the superhydrophobic copper nanoparticle (deposited on glass surface) was found to exhibit antibacterial activity against both Gram-negative and Gram-positive bacteria.

NanoCluster Beacons (NCBs), which use few-atom DNA-templated silver clusters as reporters, are a type of activatable molecular probes that are low-cost and easy to prepare. While NCBs provide a high fluorescence enhancement ratio upon activation, their activation colors are currently limited. Here we report a simple method to design NCBs with complementary emission colors, creating a set of multicolor probes for homogeneous, separation-free detection. By systematically altering the position and the number of cytosines in the cluster-nucleation sequence, we have tuned the activation colors of NCBs to green (C8–8, 460 nm/555 nm); yellow (C5–5, 525 nm/585 nm); red (C3–4, 580 nm/635 nm); and near-infrared (C3–3, 645 nm/695 nm). At the same NCB concentration, the activated yellow NCB (C5–5) was found to be 1.3 times brighter than the traditional red NCB (C3–4). Three of the four colors (green, yellow, and red) were relatively spectrally pure. We also found that subtle changes in the linker sequence (down to the single-nucleotide level) could significantly alter the emission spectrum pattern of an NCB. When the length of linker sequences was increased, the emission peaks were found to migrate in a periodic fashion, suggesting short-range interactions between silver clusters and nucleobases. Size exclusion chromatography results indicated that the activated NCBs are more compact than their native duplex forms. Our findings demonstrate the unique photophysical properties and environmental sensitivities of few-atom DNA-templated silver clusters, which are not seen before in common organic dyes or luminescent crystals.

Giant Au(I)@Ag2/Ag3-thiolate clusters with strong fluorescence (λex 400 nm, λem 564 nm, and quantum yield 8.3%) have been prepared in aqueous medium from glutathione and corresponding precursor salts at neutral pH under sunlight. An intriguing synergism between Au(I)core and Ag(0)shell imparts long-term stability to the fluorescent giant clusters (synthesized with a chemically green method) due to drifting of electron density towards core from shell. The strong fluorescence is selectively damped by cysteine (Cys) leaving aside all other essential amino acids ("Turn Off"). This quenched fluorescence is restored again on introducing Pb(II) ions in the system ("Turn On"). No other metal ion can cause such a recovery of the lost fluorescence. Such "Turn Off" and "Turn On" fluorescence helps in the design of a selective Cys as well as Pb(II) sensor in one pot. Detection of Cys and Pb(II) down to 5 × 10(-8) M and 15 × 10(-8) M, respectively, is possible following the present strategy.

Thermochromic properties of a series of non-ionic copper compounds have been reported. Herein, we demonstrate that Cu(II) ion with straight-chain primary amine (A) and alpha-linolenic (fatty acid, AL) co-jointly exhibit thermochromic properties. In the current case, we determined that thermochromism becomes ligand chain length-dependent and at least one of the ligands (A or AL) must be long chain. Thermochromism is attributed to a balanced competition between the fatty acids and amines for the copper(II) centre. The structure–property relationship of the non-ionic copper compounds Cu(AL)2(A)2 has been substantiated by various physical measurements along with detailed theoretical studies based on time-dependent density functional theory. It is presumed from our results that the compound would be a useful material for temperature-sensor applications.

Highly stable Au(I)(core)-Ag(0)(shell) particles have been synthesized in aqueous solution via a green chemistry pathway utilising sunlight irradiation. The shell of the particles is composed of fluorescent Ag2 and Ag3 clusters which make the large core-shell particles highly fluorescent. The Au(I) core of the particles offers long-term stability to the silver clusters, which are otherwise unstable in solution at room temperature, by the transfer of electron density from the shell. Successive additions of Hg(II) ions to the fluorescent solution cause efficient and selective quenching of the fluorescence with gradual red shifting of the emission peak. The metallophilic 5d(10)(Hg(2+))-4d(10)(Ag(δ+)) interaction as well as Hg(II) stimulated aggregation have been ascribed to causing the fluorescence quenching and red shift. The fluorescent Au(I)(core)-Ag(0)(shell) particles are a highly selective and sensitive sensing platform for the detection of Hg(II) down to 6 nM in the presence of various metal ions. The detection limit is far below the permissible level as determined by the EPA. Interferences due to Cu(II) and Fe(III) have been eliminated using Na2-EDTA and NH4HF2, respectively. The fluorescent particles are successfully transferred to various solvent systems making Hg(II) determination also possible in non-aqueous media. Finally, the temperature dependent fluorescence change with and without Hg(II) provides information about the metallophilic interaction.

In this work, we propose a systematic and delicate size- and shape-controlled synthesis of CuO-MnO2 composite nanostructures from time-dependent redox transformation reactions between Cu2O and KMnO4. The parental size and shape of Cu2O nanostructures are retained, even after the redox transformation, but the morphology becomes porous in nature. After prolonged reaction times (24 h), the product shapes are ruptured, and as a result, tiny spherical porous nanocomposites of ∼100 nm in size are obtained. This method is highly advantageous due to its low cost, its easy operation, and a surfactant or stabilizing agent-free approach with high reproducibility, and it provides a facile but new way to fabricate porous CuO-MnO2 nanocomposites of varied shape and size. The composite nanomaterials act as efficient recyclable catalysts for nitroarene reduction in water at room temperature. The time-dependent reduction kinetics can be easily monitored by using UV-vis spectrophotometer. The catalytic system is found to be very useful toward the reduction of nitro compounds, regardless of the type and position of the substituent(s). Furthermore, it is revealed that CuO-MnO2 composite nanomaterials exhibit facet-dependent catalytic activity toward nitroarene reduction, where the (111) facet of the composite stands to be more active than that of the (100) facet. The results are also corroborated from the BET surface area measurements. It is worthwhile to mention that porous tiny spheres (product of 48 h reaction) exhibit the highest catalytic activity due to pronounced surface area and smaller size.

Condensation product of salicylaldehyde and 1,3 propylenediamine becomes a diiminic Schiff base, which is oxidized by AgNO3 in alkaline solution, and in turn, stable Ag(0) is produced at room temperature. Under this condition, the solution exhibits intense silver nanoparticle enhanced fluorescence (SEF) with the λ(em) at 412 nm. Dopamine is selectively detected down to the nanomolar level via exclusive fluorescence quenching of the SEF. Dopamine-infested solution regains the fluorescence [i.e., SEF in the presence of Hg(II) ions]. Thus dopamine and Hg(II) in succession demonstrate "turn off/on" fluorescence due to the change in the scattering cross section of Ag(0) and gives a quantitative measure of dopamine in real samples. The proposed method is free from interferences of common biocompetitors.

Commercially available salicylaldehyde, in alkaline medium, exhibits strong fluorescence after one hour of UV exposure in the presence of Ag(I) . The phenolic group of salicylaldehyde is converted into the quinone form under alkaline conditions in the presence of AgNO3 , resulting in aggregated Ag(0), which causes approximately 250 times fluorescence enhancement of the in situ produced quinone. Such high silver-enhanced-fluorescence (SEF) is selectively quenched by cysteine, arginine, histidine, methionine, and tryptophan. In contrast to the other amino acids, ageing brings selectivity of the cysteine-induced quenching effect. Interestingly, Cu(II) is found to be the only metal ion that exclusively regenerates the lost fluorescence. Thus, quenching and recovery of fluorescence (Turn Off/On) can be used for the selective and sensitive detection of cysteine as well as Cu(II) ions in one pot. Alteration of the electric field density around the fluorophore (lightening rod effect) and scattering/absorption cross-section have been proposed to account for the Off/On fluorescence.

Synergistic evolution of fluorescent Au(I)@(Ag2/Ag3)-thiolate core-shell particles has been made possible under the Sun in presence of the respective precursor coinage metal compounds and glutathione (GSH). The green chemically synthesized fluorescent clusters are giant (∼600 nm) in size and robust. Among all the common water miscible solvents, exclusively DMSO exhibits selective fluorescence quenching (Turn Off) because of the removal of GSH from the giant cluster. Again, only Pb(II) ion brings back the lost fluorescence (Turn On) leaving aside all other metal ions. This happens owing to the strong affinity of the sulfur donor of DMSO for Pb(II). Thus, employing the aqueous solution containing the giant cluster, we can detect DMSO contamination in water bodies at trace level. Besides, a selective sensing platform has emerged out for Pb(II) ion with a detection limit of 14 × 10(-8) M. Pb(II) induced fluorescence recovery is again vanished by I(-) implying a promising route to sense I(-) ion.

Stable coinage metal nanoparticles (NPs) have been synthesized individually in an aqueous alkaline solution from the corresponding metal salts as precursors using the condensation product (CP) of salicylaldehyde and triethylenetetramine as a reagent. Silver and gold NPs are obtained with and without light illumination but UV irradiation is essential for Cu(0)NP formation. During nanoparticle formation the CP is oxidized to OCP which eventually becomes a fluorophore and also a stabilizer for the in situ produced NPs. It has been observed that silver and gold particle formation kinetics is accelerated by UV exposure. Thus the ease of evolution of coinage metal NP formation relates to their nobility. The as prepared OCP solutions containing coinage metals exhibit a fluorescence contrast behaviour (fluorescence enhancement by Cu and Ag; quenching by AuNP) due to the match and mismatch of wave vectors. The electric field evident from the FDTD simulation abreast of the scattering cross section of the NPs governed from Mie theory as a consequence of surface plasmon coupled emission (SPCE), near field electromagnetic intensity enhancement and lightening rod effect concentrating the electric field around the fluorophore are responsible for the Cu and AgNPs stimulated fluorescence. Again, lossy surface waves are anticipated for efficient quenching by the AuNPs. The most unprecedented observation is ‘Turn On’ fluorescence which is reported here as a result of the substitution of Au(0) or Cu(0) by Ag(0). Finally, the preferential fluorescence enhancement helps the selective detection of Ag(I) and Cu(II) well below the US Environmental Protection Agency (EPA) permissible level by tuning the experimental conditions.