Investigation of electrical transport properties in solution-processed Bi2Se3-AgMnOOH nanocomposite.

In this paper, we report the fundamental electrical transport properties measured in Bi2Se3-AgMnOOH nanocomposite disc, which is prepared for the first time by convenient low temperature solution-phase chemistry in conjunction with redox-mediated methodology. The comparative structural and morphological analyses for the nanocomposite with pristine Bi2Se3 are comprehensively investigated by different material characterization techniques. The results demonstrate the successful in situ composite fabrication between the Bi2Se3, Ag and γ-MnOOH components. Besides, the present work introduces a systematic approach for the examination of electrical transport properties in Ohmic and non-Ohmic regimes over a wide temperature range. The results from the room temperature transport measurement exhibited that the nanocomposite demonstrated non-linearity after a certain current I0 (onset current), whereas Bi2Se3 was linear in the entire measured current range. An enhancement of the conductance was observed for Bi2Se3-AgMnOOH compared to the pure Bi2Se3 material, which is credited to the composite effect. The onset exponents xT (DC conductance) and xf (AC conductance) with phase-sensitive character demonstrate different values below and above 180 K separating two different phases with different conduction mechanisms. Also, flicker noise analysis established the correlation between the DC conductance in terms of Ohmic to non-Ohmic transition after the onset voltage V0. This transition phenomenon from Ohmic to non-Ohmic behaviour is explained from the structural point of view of the nanocomposite. The present investigation highlights the importance of using the bottom-up solution-phase strategy for the synthesis of high quality Bi2Se3-based nanocomposites for transport studies and their possible future applications.

Redox-Mediated Synthesis of a Fe3O4-MnO2 Nanocomposite for Dye Adsorption and Pseudocapacitance.

A logically chosen redox reaction of submerged Fe(0) in an aqueous KMnO4 solution has been reported. The template-free reaction conditions produced gram amounts of a hierarchical flowerlike Fe3O4-MnO2 nanocomposite. More precisely, freshly prepared Fe(0) nanoparticles were prepared from air-free hot water under submerged conditions using a door magnet. The black Fe(0) particles were oxidized in water quantitatively by KMnO4 in the solution phase and the nanocomposite was prepared. The material has been used as a dye adsorbent and the representative cationic dye uptake, recovery, and recycling of the dye becomes easy owing to the ferromagnetic properties and surface negative charge of the material. The nanocomposite also showed a higher specific capacitance (327 F g(-1) at 10 mV s(-1)) than the reported values of pure MnO2 and Fe3O4. The material exhibited a high energy density as well as a high power density, and remained stable even after a large number of charge-discharge cycles.

Solid-state transformation of single precursor vanadium complex nanostructures to V2O5 and VO2: catalytic activity of V2O5 for oxidative coupling of 2-naphthol.

A vanadium complex, [(C5H5N)2V2O3·H2O], of different morphologies has been obtained via a modified hydrothermal procedure using pyridine and VOSO4 salt as the starting material. The evolved [(C5H5N)2V2O3·H2O] nanobelts are of 50-200 nm in width and of a length up to several millimeters. At higher temperatures (600 °C), the solid [(C5H5N)2V2O3·H2O] nanostructures are converted to vanadium pentoxide (V2O5) and vanadium dioxide (VO2) when heated in air and nitrogen atmosphere, respectively. During growth, the mechanism of the evolution of octahedra, truncated octahedra, and hollow truncated octahedra of [(C5H5N)2V2O3·H2O] are reported for the first time. These types of well-structured morphology are also isolated while V2O5 and VO2 are evolved. The as-grown belt-like and octahedral morphologies of [(C5H5N)2V2O3·H2O] are retained during the solid-state transformation, suggesting a route to evolve crystalline nanomaterials. Again, the morphological evolution of the [(C5H5N)2V2O3·H2O] nanostructures has been examined to be pyridine and precursor vanadyl sulfate (VS) concentration dependent. Thus, we are able to isolate truncated octahedra as an intermediate during the formation of [(C5H5N)2V2O3·H2O] nanobelts and nanoflowers with a high pyridine (Py) concentration. Interestingly, longer reaction times successively featured the transformation of truncated octahedra into nanobelts. Nanobelt evolution is not observed at low pyridine concentrations. However, the formation of octahedral morphology takes place at low pyridine concentration. All of the nanostructures were critically examined and characterized thoroughly by various physical techniques to ascertain their purity, structure and composition. An interesting, thermodynamically stable, single crystalline product from DMF soluble [(C5H5N)2V2O3·H2O] has been characterized, which indirectly supports the composition of [(C5H5N)2V2O3·H2O]. Selectively, vanadium pentoxide nanobelts have been found to be an efficient catalyst for the oxidative coupling of 2-naphthol to binaphthols under a molecular oxygen atmosphere.

Evolution of amorphous selenium nanoballs in silicone oil and their solvent induced morphological transformation.

Selenium generally exhibits preferential habitual 1D growth as a result of redox reactions of selenium compounds. Commercial Se powder melts in silicone oil under refluxing conditions and upon subsequent cooling evolve amorphous Se nanoballs (SNBs). Further ultrapure crystalline 1D Se grows from SNBs due to solvent mediated oriented attachment.

Mn oxide-silver composite nanowires for improved thermal stability, SERS and electrical conductivity.

Redox transformation reaction between aqueous AgNO3 and Mn(CH3COO)2 at low temperature (∼80 °C) has been adopted for industrial-scale production of uniform Ag-MnOOH composite nanowires for the first time. Varying amounts of incorporated Ag in the composite retain the 1D morphology of the composite. Nanowires upon annealing evolve Ag-MnO2 nanocomposites, once again with the retention of the parental morphology. Just 4 % of silver incorporation in the composite demonstrates metal-like conducting performance from the corresponding semiconducting material. Transition of MnO2 to Mn2O3 to Mn3O4 takes place upon heat treatment in relation to successive increase in Ag concentrations in the nanowires. The composites offer resistance to the observed oxide transformation. This is evidenced from the progressive increase in transition temperature. In situ Raman, ex situ thermal and XRD analysis corroborate the fact. The composite with 12 % Ag offers resistance to the transformation of MnO2, which is also verified from laser heating. Importantly, Ag nanoparticle incorporation is proved to offer a thermally stable and better surface enhanced Raman scattering (SERS) platform than the individual components. Both the Ag-MnOOH and Ag-MnO2 nanocomposites with 8 atomic % Ag show the best SERS enhancement (enhancement factor ∼10(10)). The observed enhancement relates to charge transfer as well as electromagnetic effects.

Arsenate stabilized Cu2O nanoparticle catalyst for one-electron transfer reversible reaction.

The befitting capping capabilities of AsO4(3-) provide a stable Cu2O nanocatalyst from a galvanic reaction between a Cu(II) precursor salt and As(0) nanoparticles. This stable Cu2O hydrosol appears to be a suitable catalyst for the one-electron transfer reversible redox reaction between Eosin Y and NaBH4. The progress of the reaction relates to three different kinetic stages. In the presence of the new catalyst the reversible redox reaction of Eosin Y in air shows a periodic color change providing a new crowd-pleasing demonstration, i.e. a "clock reaction".

Silver nanoparticle decorated reduced graphene oxide (rGO) nanosheet: a platform for SERS based low-level detection of uranyl ion.

Herein, a simple wet-chemical pathway has been demonstrated for the synthesis of silver nanoparticle conjugated reduced graphene oxide nanosheets where dimethylformamide (DMF) is judiciously employed as an efficient reducing agent. Altogether, DMF reduces both silver nitrate (AgNO3) and graphene oxide (GO) in the reaction mixture. Additionally, the presence of polyvinylpyrolidone (PVP) assists the nanophasic growth and homogeneous distribution of the plasmonic nanoparticle Ag(0). Reduction of graphene oxide and the presence of aggregated Ag NPs on reduced graphene oxide (rGO) nanosheets are confirmed from various spectroscopic techniques. Finally, the composite material has been exploited as an intriguing platform for surface enhanced Raman scattering (SERS) based selective detection of uranyl (UO2(2+)) ion. The limit of detection has been achieved to be as low as 10 nM. Here the normal Raman spectral (NRS) band of uranyl acetate (UAc) at 838 cm(-1) shifts to 714 and 730 cm(-1) as SERS bands for pH 5.0 and 12.0, respectively. This distinguished Raman shift of the symmetric stretching mode for UO2(2+) ion is indicative of pronounced charge transfer (CT) effect. This CT effect even supports the higher sensitivity of the protocol toward UO2(2+) over other tested oxo-ions. It is anticipated that rGO nanosheets furnish a convenient compartment to favor the interaction between Ag NPs and UO2(2+) ion through proximity induced adsorption even at low concentration.

Synthesis of gold nanochains via photoactivation technique and their catalytic applications.

The article reports a simple photoactivation technique for the synthesis of chain like assembly of spherical Au nanocrystals using a nontoxic biochemical, ß-cyclodextrin under ~365 nm UV-light irradiation. Under UV irradiation, ß-cyclodextrin acts as a reducing as well as capping agent and eventually becomes a stabilizing linker for Au nanoparticles. The UV-visible spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), and X-ray photoelectron spectroscopic techniques are employed to systematically characterize the Au nanochains. Additionally, it is shown that the Au nanocrystals act as an effective catalyst for the reduction in nitrobenzene to aniline and methylene blue to leuco methylene blue in presence of suitable reducing agent. The catalytic reduction reactions and kinetic parameters are evaluated from UV-visible spectroscopy.

Large-scale solid-state synthesis of Sn-SnO2 nanoparticles from layered SnO by sunlight: a material for dye degradation in water by photocatalytic reaction.

Phase pure spherical Sn-SnO2 nanoparticles (∼ 50 nm) in gram level have been synthesized from well-defined SnO microplates (∼ 2.0 µm) using focused solar irradiation. The first step of the reaction involves simple stirring of a strong NaOH solution with fine SnCl2·2H2O powder. Precipitated blue black microplates of SnO are finally transformed into high band gap Sn-SnO2 nanoparticles with sunlight. During the solid-state photodecomposition of microplates, spherical SnO2 nanoparticles along with tiny Sn(0) particles are evolved simultaneously. Tiny Sn(0) particles, improved surface area, stability toward adverse environmental conditions, and inherited negative surface charge electrostatically stabilize the Sn-SnO2 particle rendering it excellent water dispersible. The presence of Sn(0) nanoparticles in spherical SnO2 nanoparticles improves the charge (electrons and holes) separation efficiency. Then, the as-prepared particles selectively invite cationic dye molecules to the particle surface due to negative surface charge and degrade the dyes at a faster rate under UV light.

Selective and sensitive recognition of Cu2+ in an aqueous medium: a surface-enhanced Raman scattering (SERS)-based analysis with a low-cost Raman reporter.

In the present study, surface-enhanced Raman spectra of a bifunctional Raman reporter, 2-mercaptobenzimidazole, has been found to be responsive exclusively towards Cu(2+) ions while the reporter remains anchored on the Au nanoparticle surface. Thus a specific Cu(2+)-ion-detection protocol emerges. The simplicity, sensitivity, and reproducibility of the method allow routine and quantitative detection of Cu(2+) ions. An interference study involving a wide number of other metal ions shows the procedure to be uniquely selective and analytically rigorous. A theoretical study was carried out to corroborate the experimental results. Finally, the method is promising for real-time assessment of Cu(2+) ions in aqueous samples and also has the ability to discriminate Cu(I) and Cu(II) ions in solution.

Redox-switchable superhydrophobic silver composite.

Unique packaging of Ag(2)O on the surface of polycrystalline AgCl allows fabrication of a new useful, superhydrophobic composite material. This pure inorganic material with surface porosity of submicrometer aperture size fabricates air pockets, which make the composite material superhydrophobic. The new material behaves like lotus leaves, butterfly wings, or water strider's leg in relation to superhydrophobicity. Visible light induces photoreduction of solid Ag(2)O surface layer and generates Ag(0), making the composite surface superhydrophilic. Reoxidation of Ag(0) on the composite surface gives back the hydrophobicity that represents the redox-switchable wetting property of the material.

Solvent effect on the optical property of uranyl acetylacetonate monohydrate.

The lability of the [UO2(acac)2H2O] complex has been exploited to decipher solvent composition of a medium. Successive blue shift of the π-π* band (λmax=282 nm) is observed due to alcohol substitution of increasing chain length in place of water. This observation helps to quantify the chain lengths of normal alcohol. The result has been accounted theoretically. However, in non-coordinating solvent, irregular red shift of the π-π* band is observed because of the molecular complexity. Again, charge transfer (CT) band at 211 nm has been identified employing polar-polar and polar coordinating-non-coordinating solvent systems.

Monoclinic CuO nanoflowers on resin support: recyclable catalyst to obtain perylene compound.

Monoclinic CuO crystallite in grams has been obtained from resin bound Cu(II)-1,10-phenanthroline complex, R(-)[Cu(1,10-phen)(2)](2+) that becomes a recyclable catalyst for oxidative phenol coupling (OPC) reaction. Thus an exclusively intuitive blue fluorescing perylene derivative is derived from colorless 2,7-dihydroxynaphthalene (2,7-DHN) in high yield.

An aminolytic approach toward hierarchical ß-Ni(OH)(2) nanoporous architectures: a bimodal forum for photocatalytic and surface-enhanced raman scattering activity.

A surfactantless, trouble-free, and gentle wet chemistry approach has been used to interpret the precisely controlled growth of ß-Ni(OH)(2) with the assistance of ammonia and nickel acetate from seedless mild hydrothermal conditions. A thorough investigation of the reaction kinetics and product morphology with varied concentration of NH(3) and different reaction times suggests that a putative mechanism of dissolution, recrystallization, and oriented attachment supports the intelligent self-assembly of nanobuilding blocks. Associated characterizations (FTIR, PXRD, FESEM, EDAX, HRTEM, and Raman) have identified it to be pure ß-Ni(OH)(2) without any signature of contamination. The assembled units result in porous frameworks (nanoflowers and nanocolumns) and are indeed full of communally intersecting nanopetals/nanoplates with both lengths and widths on the order of micrometer to nanometer length scale. The as-synthesized material could also be used as a precursor for nanometric black NiO under calcination. The hydroxide has been found to be a potent and environmentally benign material because it warrants its photocatalytic activity through dye mineralization. Finally, Ni(OH)(2) has been photochemically derivatized with dosages of silver nanoparticles bringing a competent composite authority Ag@Ni(OH)(2), to give a full-proof enhanced field effect of prolific SERS activity. In a nutshell, these results are encouraging and fetch new promise for the fabrication of a low-cost and high-yielding greener synthetic protocol for a functional material with promising practicability.

Electrostatic field force directed gold nanowires from anion exchange resin.

We have developed a polarization-induced growth process to synthesize gram quantity of gold nanowire (Au NW) on the outer surface of an anion exchange resin matrix. This new, simple, modified hydrothermolysis (MHT) procedure involving resin-bound HAuCl(4) produced micrometer long Au nanowire on resin surface. The charged resin matrix responsibly imposes electrostatic field effect (EFF) for 1D growth of Au NWs in the presence of different amines or derivatives of amines. The Au nanowire is separated from resin by sonication. Again, the synthesis of MnO(2) nanowire with resin support through similar MHT strengthens the 1D growth proposition, that is, EFF-induced polarization effect.

Evolution of hierarchical hexagonal stacked plates of CuS from liquid-liquid interface and its photocatalytic application for oxidative degradation of different dyes under indoor lighting.

Blue solution of copper(II) acetylacetonate complex, [Cu(acac)(2)] in dichloromethane (DCM) and an aqueous alkaline solution of thioacetamide (TAA) constitute a biphasic system. The system in a screw cap test tube under a modified hydrothermal (MHT) reaction condition produces a greenish black solid at the liquid-liquid interface. It has been characterized that the solid mass is an assembly of hexagonal copper sulfide (CuS) nanoplates representing a hierarchical structure. The as-synthesized CuS nanoplates are well characterized by several physical techniques. An ethanolic dispersion of CuS presents a high band gap energy (2.2 eV) which assists visible light photocatalytic mineralization of different dye molecules. Thus a cleanup measure of dye contaminated water body even under indoor light comes true.

Fabrication of large-scale hierarchical ZnO hollow spheroids for hydrophobicity and photocatalysis.

We report here the preparation of a crystalline, pure hexagonal phase of ZnO as hollow 500-800 nm spheroids in the presence of organic bases, such as pyridine, using zinc acetate as the precursor salt. The spheroids exhibit unique 3D hierarchical architectures, like cocoons, and demonstrate improved superhydrophobic (water contact angle, 150 degrees) character due to the inherited air-trapped capillarity within the cocoon structure. The simple synthetic strategy used in this process is modified hydrothermolysis (MHT), which represents a general approach and may contribute to the formation mechanism of the hollow nanostructures with highly improved porosity. Depending on the concentration of the precursor salt, it has been possible to cover glass plates or the inner wall of a reaction vessel with ZnO nanocrystals. A low salt concentration (<0.01 M) allows the easy preparation of a superhydrophobic glass surface, whereas a high salt concentration (>0.01 M) results in the precipitation of cocoons at the bottom of the reaction vessel as a solid mass together with a deposited thin film of ZnO nanocrystals covering the inner wall of the glass vessel. The thickness of the film successively grows through repetitive hydrothermolysis processes for which a low salt concentration (<0.01 M) was employed. Because of the hollow cocoon-like morphology, the surface area of the film is greatly increased, which makes it accessible for functionalization by incoming substrates from both sides (internally and externally) and helps to drive a competent photocatalytic dye degradation pathway. The heterocyclic base pyridine exclusively develops cocoons. Thus, the mechanism of self-aggregation of ZnO nanocrystals under MHT reaction conditions has been studied and the characterization of the compounds has been supported with physical measurements.

Layer-by-layer deposition of silver/gold nanoparticles for catalytic reduction of nitroaromatics.

A general method has been fabricated to achieve normal as well as inverted core-shell architectures of silver/gold through a layer-by-layer deposition technique on a commercial anion exchange resin. Electrostatic field force of the charged resin beads supports immobilization of anionic metal precursors [MX(n)]-, in turn deposition of silver/gold nanoparticles onto the solid resin matrix and reduction of 2-nitrobenzoic acid to obtain the corresponding amines through effective catalysis. The shell thickness has been tailored made by exploiting a new method of cyclic and repetitive deposition of the desired metal precursors. Thermodynamic parameters for the reduction reaction have been presented. Kinetic study reveals a comparative account of rates between the mono- and bi-metallic nanoparticles where silver stands to be a better catalyst for the reduction of nitroaromatics.

Hierarchical superparamagnetic magnetite nanowafers from a resin-bound [Fe(bpy)3]2+ matrix.

The brilliant red [Fe(bpy)(3)](2+) complex upon immobilization on a strongly acidic cation exchanger or in situ formation of the same cationic complex onto a resin matrix and subsequent modified hydrothermolysis (MHT) at approximately 110 degrees C produces unusually stable hierarchical magnetite (Fe(3)O(4)) nanowafers. The slow hydrothermolysis, oxidation, and subsequent dehydration of the complex on the solid-liquid interface produce stable hierarchical nanostructures. The isolation of neat Fe(3)O(4) (uncapped) particles from the resin matrix as hierarchical nanowafers was achieved by magnetically stirring a CH(3)CN suspension of nanocomposites. The solid resin support not only aids nanowafer formation on its surface but also provides unique stability to the magnetite particles, where nanowafer oxidation is largely retarded. The utility of the as-prepared porous nanocomposite and characterization of the nanoparticles are promising for nanotechnological and soft ferromagnetic applications.

Ligand-stabilized metal nanoparticles in organic solvent.

This critical review reports the fundamental behavior of metal nanoparticles in different organic solvents, i.e., metal organosol. An overview on metal organosol and then their smart synthetic approaches, characterization, and potential applications in the fields of catalysis and spectroscopy with special emphasis on SERS are embodied. Aspects of organosol fabrication, stabilization, morphology control, growth mechanisms, and physical properties as mono- and bimetallic nanoparticles are discussed. The article inspires the repetitive usage of metal nanoparticles as stable deliverable organic and molecular compounds.