Subsequent Chemical Reduction Research Articles

Silver confined within zeolite EMT nanoparticles: preparation and antibacterial properties.

The preparation of pure zeolite nanocrystals (EMT-type framework) and their silver ion-exchanged (Ag(+)-EMT) and reduced silver (Ag(0)-EMT) forms is reported. The template-free zeolite nanocrystals are stabilized in water suspensions and used directly for silver ion-exchange and subsequent chemical reduction under microwave irradiation. The high porosity, low Si/Al ratio, high concentration of sodium and ultrasmall crystal size of the EMT-type zeolite permitted the introduction of a high amount of silver using short ion-exchange times in the range of 2-6 h. The killing efficacy of pure EMT, Ag(+)-EMT and Ag(0)-EMT against Escherichia coli was studied semi-quantitatively. The antibacterial activity increased with increasing Ag content for both types of samples (Ag(+)-EMT and Ag(0)-EMT). The Ag(0)-EMT samples show slightly enhanced antimicrobial efficacy compared to that of Ag(+)-EMT, however, the differences are not substantial and the preparation of Ag nanoparticles is not viable considering the complexity of preparation steps.

Formic Acid Oxidation over Hierarchical Porous Carbon Containing PtPd Catalysts

The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that it allows the synthesis of materials having a multimodal porous size distribution, with each pore size contributing to the desired properties. On the other hand, the monolithic nature of the porous support also imposes new challenges for metal loading. In this work, the use of Hierarchical Porous Carbon (HPC) as support for PtPd nanoparticles was explored. Three hierarchical porous carbon samples (denoted as HPC-300, HPC-400 and HPC-500) with main pore size around 300, 400 and 500 nm respectively, are used as porous support. PtPd nanoparticles were loaded by impregnation and subsequent chemical reduction with NaBH4. The resulting material was characterized by EDX, XRD and conventional electrochemical techniques. The catalytic activity toward formic acid and methanol electrooxidation was evaluated by electrochemical methods, and the results compared with commercial carbon supported PtPd. The Hierarchical Porous Carbon support discussed here seems to be promising for use in DFAFC anodes.

Reduced graphene oxide/CoSe2 nanocomposites: hydrothermal synthesis and their enhanced electrocatalytic activity

Reduced graphene oxide (RGO)/CoSe2 nanocomposites were synthesized by self-assembly of CoSe2/DETA (DETA: diethylenetriamine) onto the surface of graphene oxide (GO), followed by subsequent chemical reduction of GO during a hydrothermal process. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectra, scanning electron microscopy, and transmission electron microscopy. The morphology of the CoSe2 on the RGO nanosheets can be well controlled by adjusting the reaction time during the hydrothermal process. The catalytic activities of the RGO/CoSe2 nanocomposites were investigated for oxygen evolution reaction (OER) in alkaline conditions. It was found that the as-formed RGO/CoSe2 nanocomposites show higher catalytic activity compared with the unsupported CoSe2. In addition, the loading amounts and morphologies of CoSe2 on RGO sheets have a great influence on the catalytic performance of RGO/CoSe2. Our studies raise promising possibilities for designing effective OER electrocatalysts for energy conversion.

Development of a Novel Method for the Determination of Aqueous Inorganic 129I Speciation

The objective of this research was to develop a method suitable for the determination of aqueous concentrations of radioactive iodine as I2, I(-), and IO3(-). As one of the primary risk-drivers and contaminants of concern at nuclear waste repositories, the accurate determination of (129)I in aqueous systems is of significant concern. The redox-active nature of iodine makes its mobility and fate in the environment difficult to predict, thus underscoring the importance of species-specific determination of iodine concentrations. The developed method couples solid phase extraction with liquid scintillation counting, and scintillating anion exchange with a flow-cell detection system for a sequential measurement of each iodine species. Solid phase extraction disks were impregnated with polyvinylpyrrolidone for the selective extraction and stabilization of I2 with subsequent analysis by liquid scintillation counting. Aqueous I(-) was concentrated and measured by a previously developed flow-cell system utilizing scintillating anion-exchange resin. A subsequent chemical reduction of IO3(-) to I(-) in the effluent was used to quantify IO3(-) by the same flow-cell system. Nearly quantitative results were found for standardized single-species samples of I2 (95%), I(-) (101%), and IO3(-) (91%), respectively, while consistent measurements were obtained for multispecies samples using the developed method and algorithm.

Precise Tuning of Surface Composition and Electron‐Transfer Properties of Graphene Oxide Films through Electroreduction

Graphene materials are generally prepared from the exfoliation of graphite oxide (GO) to graphene oxide, followed by subsequent chemical or thermal reduction. These methods, although efficient in removing most of the oxygen functionalities from the GO material, lack control over the extent of the reduction process. We demonstrate here an electrochemical reduction procedure that not only allows for precise control of the reduction process to obtain a graphene material with a well-defined C/O ratio in the range of 3 to 10, but also one that is able to tune the electrocatalytic properties of the reduced material. A method that is able to precisely control the amount and density of the oxygen functionalities on the graphene material as well as its electrochemical behaviour is very important for several applications such as electronics, bio-composites and electrochemical devices.

Facile Assembly of Graphene on Anion Exchange Resin Microspheres for Electrochemical Sensing and Biosensing

Graphene sheets were assembled on anion exchange resin (AER) microspheres based on the electrostatic interactions between graphene oxide and AER and subsequent chemical reduction. The prepared graphene-coated AER microspheres were characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. They were then embedded in the bores of pipette tips to fabricate disposable electrodes for electrochemical sensing. The workability and performance of the novel electrodes were examined by analyzing the electrochemical behavior of the electrodes for the sensing of ascorbic acid, dopamine, uric acid, acetaminophen, aniline, and glucose by cyclic voltammetry and amperometry. The advantages of the electrodes include ease of fabrication, low cost, pronounced electrocatalytic activity, and rapid response. Thus, they hold great promise for a wide range of applications.

Room-temperature synthesis of CuO/graphene nanocomposite electrodes for high lithium storage capacity

A facile approach for the synthesis of hybrid nanocomposite electrodes comprising pine-nut-shaped cupric oxide (CuO) particles and electrolytically exfoliated conducting graphene nanosheets (GNSs) for lithium ion battery applications is demonstrated. The GNSs were initially dispersed in aqueous solution, and then, Cu(OH)2 was synthesized by the reaction of CuSO4·5H2O, NH4OH, and NaOH. In the subsequent chemical reduction process, a controlled amount of hydrazine hydrate (N2H4·H2O) was added to the reaction mixture to obtain the CuO/GNS nanocomposite. Information about the phase, surface properties, and morphology of the CuO and CuO/GNS composite was obtained by X-ray diffraction, Brunauer–Emmett–Teller surface analysis, field-emission scanning electron microscopy, and high-resolution transmission electron microcopy. The electrochemical performance of the nanocomposite was evaluated by cyclic voltammetry and galvanostatic cycling. The nanocomposite synthesized by this method had a uniform morphology without aggregation and showed enhanced electrochemical performances.

Low-cost fabrication of graphene ball electrodes for the amperometric detection of capillary electrophoresis

Graphene-coated anion exchange resin (AER) spheres were facilely prepared based on the electrostatic interaction between graphene oxide and AER and subsequent chemical reduction. They were embedded in the bores of polypropylene pipette tips to fabricate graphene ball electrodes for the amperometric detection of capillary electrophoresis. The feasibility and performance of the novel electrodes were demonstrated by measuring parabens in combination with micellar electrokinetic chromatography. The advantages of the electrodes include higher sensitivity, favorable signal-to-background characteristics, low expense of fabrication, ease of operation, and satisfactory reproducibility, indicating great promise for a wide range of applications.

Organic/Metallic Nanohybrids Based on Amphiphilic Dumbbell-Shaped Dendrimers

In this study, we synthesized a series of amphiphilic dumbbell-shaped dendrimers through the addition reactions of a hydrophilic poly(oxyalkylene) with hydrophobic dendrons based on 4-isocyanate-4'-(3,3-dimethyl-2,4-dioxo-azetidine)diphenylmethane with different numbers of branching generations. The addition reaction of azetidine-2,4-diones of dendrons to amines of poly(oxyalkylene) was proceeded by stirring the reactants in dry tetrahydrofuran (THF) under nitrogen at 60 °C. In aqueous media, the dumbbell-shaped dendrimers self-assembled into micelles with their hydrophobic dendrons in the core and their hydrophilic poly(oxyalkylene) segments forming loops in the corona shell. Employing the unique self-assembled micelle structures as templates for subsequent chemical reduction of the Ag(+) ions, we generated new types of organic/metallic [silver nanoparticle (AgNP)] nanohybrid clusters. The long poly(oxyalkylene) loops that extended into the aqueous phase complexed with the Ag(+) ions, providing the suspension with steric stabilization to prevent the AgNPs from collision and flocculation. After reduction, the AgNPs were present in a homogeneous distribution in the round dendrimer micelle-stabilized nanoclusters. The diameter of each AgNP was less than 10 nm; the diameter of each round nanocluster was in the range of 50-200 nm. The encapsulation efficiency of the AgNPs in micelles was about 54-69% for the dumbbell-shaped dendrimer based organic/AgNP nanohybrid.

Interfacial Rheology and Structure of Tiled Graphene Oxide Sheets

The hydrophilic nature of graphene oxide sheets can be tailored by varying the carbon to oxygen ratio. Depending on this ratio, the particles can be deposited at either a water-air or a water-oil interface. Upon compression of thus-created Langmuir monolayers, the sheets cover the entire interface, assembling into a strong, compact layer of tiled graphene oxide sheets. With further compression, the particle layer forms wrinkles that are reversible upon expansion, resembling the behavior of an elastic membrane. In the present work, we investigate under which conditions the structure and properties of the interfacial layer are such that free-standing films can be obtained. The interfacial rheological properties of these films are investigated using both compressional experiments and shear rheometry. The role of surface rheology in potential applications of such tiled films is explored. The rheological properties are shown to be responsible for the efficiency of such layers in stabilizing water-oil emulsions. Moreover, because of the mechanical integrity, large-area monolayers can be deposited by, for example, Langmuir-Blodgett techniques using aqueous subphases. These films can be turned into transparent conductive films upon subsequent chemical reduction.

Microorganism mediated synthesis of reduced graphene oxide films

The wide-ranging industrial application of graphene and related compounds has led researchers to devise methods for the synthesis of high quality graphene. We recently reported on the chemical synthesis, patterning, and doping of graphene films by the chemical exfoliation of graphite into graphene oxide (GO) with subsequent chemical reduction into graphene films [1, 2]. Here, we describe a hybrid approach for the synthesis of reduced graphene sheets, where chemically derived GO was reduced by microorganisms extracted from a riverside near the University. Our procedure enabled the production of ∼100 μm sized reduced graphene sheets, which showed excellent Raman spectra associated with high quality reduced graphene. We give a detailed account of the relationship between the type of microorganisms and the properties of the resulting reduced graphene.

Graphene chiral liquid crystals and macroscopic assembled fibres.

Chirality and liquid crystals are both widely expressed in nature and biology. Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals. To date, chiral liquid crystals of 2D colloids have not been explored. As a typical 2D colloid, graphene is now receiving unprecedented attention. However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method. Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations. Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance. The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles.

In Situ Reversible Tuning of Photoluminescence of Mn2+-Doped ZnS Quantum Dots by Redox Chemistry

Herein we report the development of a new method for in situ reversible tuning of photoluminescence properties of quantum dots (Qdots) by partial oxidation of population of the emitting species and subsequent chemical reduction of the oxidized form. The concept has been demonstrated using Mn(2+)-doped ZnS Qdots stabilized by acetyl acetonate. Treatment of an aqueous solution of the Qdots (with Mn(OAc)(2) being the source of Mn used for the synthesis of the Qdots) by potassium peroxodisulfate (KPS) led to reduction of intensity of emission due to Mn(2+) ((4)T(1)-(6)A(1)). Subsequent treatment of the solution containing KPS-treated Qdots with NaBH(4) led to regaining of intensity, thus providing reversibility to the tuning, which was possible for more than one cycle. Electron spin resonance (ESR) spectroscopic investigations revealed reduction of the population of Mn(2+) upon treatment with KPS, whereas it went back up upon further treatment with NaBH(4). Interestingly, a mixed population of oxidation states of Mn was indicated to be present in the Qdots prepared using KMnO(4) as the source of Mn. The fluorescence intensity of the Qdots so prepared increased upon treatment with NaBH(4) following synthesis, which was not possible when the source of Mn was Mn(OAc)(2). Transmission electron microscopic and X-ray diffraction studies indicated that oxidation and reduction did not change the sizes of Qdots significantly.

Synthesis and kinetics of growth of metal nanoparticles inside ion-exchange polymers

Copper and silver nanoparticles have been obtained by means of saturation of a sulfostyrene-divinylbenzene cation-exchange polymer with metal ions and their subsequent chemical reduction. This procedure was repeated several times up to formation of a long-range conducting network (percolating cluster). Another system under study was an ensemble of Ag nanoparticles of various sizes on the silver electrode surface obtained by reduction of anodically formed layers of silver oxide. Recrystallization of deposited metal crystals inside the polymer matrix in contact with metal-ion containing solution is very slow for electrically separated particles. Formation of the electric network results in an enormous acceleration of this process via electron-ion mechanism, with growth of the average particle size, so that their potential will approach that of the compact metal with time. The initial period of the particle growth is well described by the parabolic law (Burke and Turnbull). The values of the particle-growth coefficient in this law, k, are drastically different for particles inside the matrix and on the electrode surface. Particle-to-particle electron transfer is impeded by insulating areas inside the polymer matrix. Besides, ionogenic centers of the matrix restrict the mobility of metal cations, thus slowing down the ion transfer within the recrystallization circuit. These observations have allowed us to establish the conditions resulting in long-term stabilization of metal nanoparticles inside the ion-exchange matrix with respect to their recrystallization.

Graphene Nanoplatelets via Exfoliation of Platelet Carbon Nanofibers and Its Electric Double Layer Capacitance

Abstract Graphite oxide nanoplatelets with thickness of approximately 1 nm were synthesized via exfoliation of platelet carbon nanofibers with average diameter of 150 nm. The lateral size of the graphite oxide nanoplatelets was in accord with the diameter of the parent platelet carbon nanofibers. Subsequent chemical reduction of the graphite oxide nanoplatelets resulted in graphene nanoplatelet aggregates. Specific capacitance of 132 F g−1 in sulfuric acid electrolyte was obtained for the graphene nanoplatelet electrodes, which is about 1.6 times higher than graphene nanosheet aggregates obtained from natural graphite. The capacitive properties are discussed based on the size of the graphene nanoplatelets.

Fabrication of Graphene‐Encapsulated Oxide Nanoparticles: Towards High‐Performance Anode Materials for Lithium Storage

Storage shells: The assembly of negatively charged graphene oxide and positively charged oxide nanoparticles by electrostatic interactions, and subsequent chemical reduction, leads to metal oxides encapsulated in flexible and ultrathin graphene shells (see picture). These electrochemically active nanoparticles show a remarkable lithium storage capacity, with an excellent cycle performance. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis and Characteristics of Graphene Oxide-Derived Carbon Nanosheet−Pd Nanosized Particle Composites

Carbon nanosheet (CNS)-Pd nanosized particle (NP) composites were synthesized by using graphite oxide (GO) and bis(ethylenediamine)palladium(II) (Pd(en)(2)(2+)) as the precursors, and their structure and adsorption properties were examined. It was found that the Pd(en)(2)(2+) complex ions can be intercalated into GO layers highly efficiently to form a layered structure containing a large amount of Pd (approximately 12 wt %). By the subsequent chemical reduction, Pd NPs (2-6 nm in size) are well dispersed between CNS to form a CNS-Pd NP composite and serve as spacers to increase the porosity of the composite. Hydrogen adsorption results demonstrate that both Pd NPs and CNS play important roles in hydrogen adsorption, particularly at a lower temperature and for CNS with deficient sites, which bring about a H(2) adsorption greater than those on other Pd-loaded nanocarbon materials reported so far. The unique composite nanostructure having large contents of Pd NPs (20-25 wt %) stabilized by CNSs is hopeful to be applied to the fields of H(2)-related catalysis, sensing, and so forth.

Carbon nanotube supported platinum nanoparticles for the voltammetric sensing of hydrazine

Electrochemical sensing of hydrazine using a highly sensitive platform based on nanosized Pt (nPt) particles is described. The sensing platform is developed by the pre-organization of metal precursor on multiwalled carbon nanotubes (MCNT) modified conducting substrate and subsequent chemical reduction of the precursor in aqueous solution. The Pt nanoparticles are characterized by transmission electron microscope, X-ray diffraction (XRD), spectral and electrochemical measurements. The nPt on MCNT modified electrode has spherical shape with 5–10 nm size. XRD and selected area electron diffraction pattern reveal the existence of (1 1 1), (2 0 0) and (2 2 0) planes of face centered cubic structure. The electrocatalytic activity of nPt on the MCNT modified electrode toward oxidation of hydrazine is examined. The nPt on the MCNT modified electrode exhibit significantly high electrocatalytic activity with respect to the polycrystalline Pt electrode. The nanoparticle coverage on the electrode has strong influence on the electrocatalytic activity. Gradual negative shift in the oxidation peak potential and increase in the peak current are observed while increasing the particle coverage. The nanoparticle-based electrode is highly stable and sensitive and it can sense as low as 0.5 nM hydrazine sulfate at the potential of −0.35 V without any redox mediator. The co-existence of hydrazine derivative N,N-dimethylhydrazine does not interfere the electrochemical sensing of hydrazine.

Silver nanoparticles dispersed in electrospun polyacrylonitrile nanofibers via chemical reduction

Silver (Ag) nanoparticles were prepared in PAN nanofibrous film by a sol–gel derived electrospinning and subsequent chemical reduction for 30 min in hydrazine hydroxide (N2H5OH) aqueous solution. Antimicrobial properties of the AgNO3/PAN precursor solution against gram positive Staphylococcus aureusATCC 6538 and gram negative Escherichia coli ATCC 25922 were investigated. The formation of clear zone suggested that the PAN solution containing Ag+ ions were effective on the inhibition of bacterial growth. The Ag/PAN nanocomposite film, characterized by XRD, TEM and UV absorption spectrophotometer, revealed that highly crystallized cubic Ag particles with diameters of less than 5.8 nm were dispersed homogeneously in PAN nanofibers.

Silver-hydroxyapatite nanocomposites as bactericidal and fungicidal materials

AbstractSilver-hydroxyapatite nanocomposites containing 1 wt.% of metallic silver have been obtained by a colloidal chemical route and subsequent chemical reduction process. The silver nanoparticles are supported on the hydroxyapatite surface without a high degree of agglomeration. The bactericidal effect against common Gram-positive and Gram-negative bacteria, as well as antifungal activity against yeast have been investigated. The results indicated a high antimicrobial activity for E. coli, M. Luteus and I. Orientalis, so this material can be a promising antimicrobial biomaterial for implant and reconstructive surgery, among other applications.