Zero-valent State Research Articles

Synthesis of nickel entities: From highly stable zerovalent nanoclusters to nanowires. Growth control and catalytic behavior

Non-noble metal nanoclusters synthesis is receiving increased attention due to their unique catalytic properties and lower cost. Herein, the synthesis of ligand-free Ni nanoclusters with an average diameter of 0.7 nm corresponding to a structure of 13 atoms is presented; they exhibit a zero-valence state and a high stability toward oxidation and thermal treatment. The nanoclusters formation method consists in the electroreduction of nickel ions inside an ordered mesoporous alumina; also, by increasing the current density, other structures can be obtained reaching to nanowires of 10 nm diameter. A seed-mediated mechanism is proposed to explain the growth to nanowires inside these mesoporous cavities. The size dependence on the catalytic behavior of these entities is illustrated by studying the reduction of methylene blue where the nanoclusters show an outstanding performance.

Synthesis, Characterization and Reactivity of Nanostructured Zero-Valent Iron Particles for Degradation of Azo Dyes

Nanostructured zero-valent iron (NSZVI) particles were synthesized by the method of ferric ion reduction with sodium borohydride with subsequent drying and passivation at room temperature in technical grade nitrogen. The obtained sample was characterized by means of X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and dynamic light scattering studies. The prepared NSZVI particles represent 100–200[Formula: see text]nm aggregates, which consist of 20–30[Formula: see text]nm iron nanoparticles in zero-valent oxidation state covered by thin oxide shell. The reactivity of the NSZVI sample, as the removal efficiency of refractory azo dyes, was investigated in this study. Two azo dye compounds, namely, orange G and methyl orange, are commonly detected in waste water of textile production. Experimental variables such as NSZVI dosage, initial dye concentration and solution pH were investigated. The kinetic rates of degradation of both dyes by NSZVI increased with the decrease of solution pH from 10 to 3 and with the increase of NSZVI dosage, but decreased with the increase of initial dye concentration. The removal efficiencies achieved for both orange G and methyl orange were higher than 90% after 80[Formula: see text]min of treatment.

Removal of Pb(II) and Cr(VI) from aqueous solutions using the fly ash-based adsorbent material-supported zero-valent iron

In this study, a granular adsorbent material containing zero valent iron (ZVI-GAM) was made with fly ash as skeletal material, bentonite as binder and Enteromorpha prolifera as pore former. Zero-valent iron was synthesized by direct reduction of iron ore tailings with the coke as reductant at 900°C in the anoxic atmosphere. SEM/EDX, XRD, FTIR and BET analysis were used to characterize ZVI-GAM. SEM image showed that there were many different size pores in ZVI-GAM. XRD analysis indicated the presence of iron in zero-valent state. FTIR analysis revealed that the surface of ZVI-GAM owned the groups responsible for the heavy metals adsorption. The specific surface area of ZVI-GAM was 8.19m2/g. ZVI-GAM was used as reaction and adsorbent material for the removal of Pb(II) and Cr(VI) from aqueous solutions. The factors affecting Pb(II) and Cr(VI) ions removal by ZVI-GAM in a batch model were studied including initial heavy metal concentrations, contact time, adsorbent dosage, pH values and temperature. Maximum removal capacity for Pb(II) and Cr(VI) by ZVI-GAM was found to be 78.13mg/g and 15.70mg/g. ZVI-GAM had the best adsorption and reduction capacity for Cr(VI) and Pb(II) and could reduce Cr(VI) to Cr(III) and Pb(II) to Pb0. Therefore, ZVI-GAM was an effective, low-cost and recyclable material and had great potential to be a promising technique for heavy metal remediation.

Conversion of ferrous compounds in a flameless combustion wave of hexogen-based systems filled with iron formate and other additives

The thermal decomposition of the energetic component and chemical reactions occurring at elevated temperatures in a flameless combustion wave of systems based on hexogen (filled with iron(II) formate and polyisocyanurate binding agent) afford a mixture of iron oxides and iron nitride as nanosized particles. The purposeful change in the ratio of the indicated basis components can provide individual Fe2O3, Fe3O4, or FeO in the conversion products. Additives of anthracene and hydroquinone to the initial composition can result in the formation of predominantly iron carbide in the products, whereas mainly iron nitrides are formed upon the addition of guanidine nitrate or 5-aminotetrazole. The addition of aluminum hydride components to the initial mixture results in the reduction of iron to the zero-valence state in the form of iron—aluminum intermetallic compounds.

Low-Temperature Water–Gas Shift Reaction over Au Supported on Anatase in the Presence of Copper: EXAFS/XANES Analysis of Gold–Copper Ion Mixtures on TiO2

Cu-modified Au/TiO2 (anatase, 200 m2/g) has been prepared by the incipient-wetness technique with introduction of the modifier either before or after Au loading. Such catalysts gave higher catalytic activities for the water–gas shift (WGS) reaction when compared to the unmodified catalysts mainly because of the existence of a synergetic interaction between Cu and Au, as the activities of both Cu/TiO2 and Au/TiO2 are lower than that of the bimetallic system. The WGS activities of both the as-prepared Au/TiO2 and a Au–Cuc/TiO2 catalyst were found to be high and stable. The presence of nitrates on Cuc–Au/TiO2 was found to be detrimental to the activity of Au on TiO2, as a result of the poisoning of Au and enhanced Au agglomeration by NO2 formed during reaction. The activities of Au/TiO2 catalysts modified with Cu-containing acetate counterions were found to decrease during the first 30 min on stream, reaching a constant value of (45 ± 2)%. However, when the poisoning by the acetate anion was eliminated through calcination, the activity increased compared to those of the Au/TiO2 catalysts. An increase in Cu loading was found to lower the activity of Au as a result of the loss of the interaction between the Au and the support interface. The XANES spectra of uncalcined as-prepared catalysts exhibited a pre-edge feature (due to the 1s-to-3d transition) characteristic of Au in a tetrahedral environment. The water–gas-shift-treated sample showed a reduction in the intensity of the white line, indicating a reduction of Au (a partial reduction of Au3+ to Au+/Au0). The XANES spectrum of calcined Cuc–Au/TiO2 (0.44 wt % Cu/3.74 wt % Au) confirmed that Cu exists as ions (Cu+/Cu2+) before and during the WGS reaction. The Au catalyst was not stable and continuously deactivated with time, and the white-line region showed a decrease in peak intensity during use. An increase in gold activity on Cu2+-modified TiO2 was achieved because at least 90% of the gold was reduced to the zero-valent state whereas most of the stabilizing metal (Cu2+) remained in the ionic state. We concluded that the addition of a stabilizing metal in ionic form during the preparation of the Au–Cuc/TiO2 system has marked effects in improving the initial dispersion of the reduced gold and also in helping to maintain a highly dispersed state of gold during use. The atomic ratio of stabilizing metal ions to gold metal plays a crucial role in maximizing the dispersion/stabilizing effects. The formation of bimetallic particles was not detected by EXAFS data analysis. The observed effects can be interpreted as a mutual influence of gold and copper ions and reduced species of gold and copper because of their competion for ion-exchange sites. It is unclear at present how this is achieved. However, EXAFS data analysis of both metals suggests that it is not due to a direct interaction between Au and Cu. In contrast to the results for the WGS reaction, copper was found to show no promotional effect on low-temperature CO oxidation or on preferential CO oxidation (PROX) in excess hydrogen.

Utilization of Human Hair as a Synergistic Support for Ag, Au, Cu, Ni, and Ru Nanoparticles: Application in Catalysis

Human hair powder (HHP) after chemical treatment (e-HHP) has been successfully utilized as a unique catalyst support for immobilization of metal nanoparticles (MNPs). Ag, Au, Cu, Ni, and Ru NPs were used to prepare five different nanocatalysts (MNPs/e-HHP). High-resolution transmission electron microscopy results confirmed the excellent attachment of ultrafine MNPs on the surface of e-HHP. Actual loading of metal in MNPs/e-HHP was determined by energy-dispersive spectroscopy and X-ray photoelectron spectroscopy analyses. The zero-valent state of MNPs in MNPs/e-HHP and a very strong interaction between MNPs and e-HHP were also proven. The obtained AgNPs/e-HHP, AuNPs/e-HHP, CuNPs/e-HHP, NiNPs/e-HHP, and RuNPs/e-HHP catalysts were employed for the self-coupling of amines, N-oxidation of tertiary amines, aza-Michael reaction, imines synthesis, and oxidation of alcohols, respectively. Reaction conditions were optimized, and the scope of the catalytic systems was extended. The merit of the MNPs/e-HHP materials ...

A Tris(diisocyanide)chromium(0) Complex Is a Luminescent Analog of Fe(2,2'-Bipyridine)32.

A meta-terphenyl unit was substituted with an isocyanide group on each of its two terminal aryls to afford a bidentate chelating ligand (CNtBuAr3NC) that is able to stabilize chromium in its zerovalent oxidation state. The homoleptic Cr(CNtBuAr3NC)3 complex luminesces in solution at room temperature, and its excited-state lifetime (2.2 ns in deaerated THF at 20 °C) is nearly 2 orders of magnitude longer than the current record lifetime for isoelectronic Fe(II) complexes, which are of significant interest as earth-abundant sensitizers in dye-sensitized solar cells. Due to its chelating ligands, Cr(CNtBuAr3NC)3 is more robust than Cr(0) complexes with carbonyl or monodentate isocyanides, manifesting in comparatively slow photodegradation. In the presence of excess anthracene in solution, efficient energy transfer and subsequent triplet-triplet annihilation upconversion is observed. With an excited-state oxidation potential of -2.43 V vs Fc+/Fc, the Cr(0) complex is a very strong photoreductant. The findings presented herein are relevant for replacement of precious metals in dye-sensitized solar cells and in luminescent devices by earth-abundant elements.

Greener Approach To Prepare Electrospun Antibacterial β-Cyclodextrin/Cellulose Acetate Nanofibers for Removal of Bacteria from Water

This work reports the synthesis of β-cyclodextrin (β-CD)/cellulose (CA) nanofibers embedded with silver (Ag) and silver/iron (Ag/Fe) nanoparticles (NPs) via a benign process involving in situ electrospinning of the biopolymers with Ag and Fe salts. The electrospun nanocomposite fibers containing Ag+/Fe3+ ions were then subjected to UV photochemical reduction in the presence of water vapor under inert atmosphere to reduce the ions to zerovalent state. SEM and TEM revealed that the average diameter of the β-CD/CA nanofibers was 382.12 ± 30.09 nm and that the diameters of Ag and Ag/Fe NPs were 38.81 ± 8.21 nm and 56.29 ± 12.64 nm, respectively, after reduction. The XRD and EDS analysis confirmed the presence of the Ag and Fe NPs on the surface of the nanofibers. The effect of UV irradiation time on the reduction of the Ag+ and Fe3+ was studied by measuring the UV–vis absorbance of the reduced NPs. The biocidal effect of Ag and Ag/Fe was investigated using 12 different strains of bacteria. The Ag and Ag/Fe NP...

Theoretical study of structures and reactivities of the complexes of metals in the zero-valent state with fullerene ligands

Possible reaction routes of dimerization of intermediate fullerene-containing zero-valent metal complexes probably formed by the reduction of the phosphine-containing CoII and NiII complexes in the presence of C60 were analyzed using the density functional theory with the PBE functional. The found energetic effects of the formation of the binuclear complexes with different structures, including those containing the dimer of fullerene C120 performing a bridging function, together with the estimated energy barriers to the symmetry-forbidden 2+2 cycloaddition in the coordination sphere are crucial in the understanding of the structures of the observed reaction products.

Lignocellulose Fiber- and Welded Fiber- Supports for Palladium-Based Catalytic Hydrogenation: A Natural Fiber Welding Application for Water Treatment

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium–copper (Pd–Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5–10 nm), near-spherical crystalline nanoparticles were produced, and a Pd–Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd–Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd...

Formation of Ni/C based polyacrylonitrile nanocomposites under IR-radiation

The work deals with obtaining nickel metal-carbon nanocomposites based on IR-pyrolyzed polyacrylonitrile and nickel chloride hexahydrate and a study of the structural characteristics of the synthesized material. Nanocomposites have been prepared under IR-based precursor pyrolysis of polyacrylonitrile (PAN) and nickel chloride hexahydrate (NiCl2·6H2O). Pyrolysis has been carried out in the 150–700°C temperature range. The grown nanocomposites are a two-phase system of the carbon matrix formed during carbonization of PAN and distributed in the nickel nanoparticles (nickel oxide). The average size of the nanoparticles in the nanocomposite was 15–25nm. The effect of IR precursor pyrolysis temperature on the size of the nickel nanoparticles has been studied.We have determined that the size distribution of nickel nanoparticles is determined by the temperature of nanocomposite synthesis. While the temperature increases the prevailing average particle size of the metal increases and the distribution is blurred and shifts towards larger sizes.By calculating the total Gibbs energy of possible reduction reactions of nickel chloride and oxide pyrolysis PAN products we have shown the possibility of the formation of nanocomposites comprising nickel oxide nanoparticles which can be reduced to zero-valence state at higher temperature IR heating (more than 5000°C).

Deactivation of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the reaction of oxidative ethane dehydrogenation

The operational stability of a mixed oxide catalyst of Mo–V–Te–Nb–O composition in the oxidative dehydrogenation of ethane (ratio of C2H6: O2 = 3: 1) is studied in a flow reactor at temperatures of 340–400°C, a pressure of 1 atm, and a WHSV of the feed mixture of 800 h−1. It is found that the selectivity toward ethylene is 98% at 340°C, but the conversion of ethane at this temperature is only 6%; when the temperature is raised to 400°C, the conversion of ethane is increased to 37%, while the selectivity toward ethylene is reduced to 85%. Using physical and chemical means (XPS, SEM), it is found that the lack of oxidant in the reaction mixture leads to irreversible changes in the catalyst, i.e., reduced selectivity and activity. Raising the reaction temperature to 400°C allows the reduction of tellurium by ethane, from the +6 oxidation state to the zerovalent state, with its subsequent sublimation and the destruction of the catalytically active and selective phase; in its characteristics, the catalyst becomes similar to the Mo–V–Nb–O system containing no tellurium.

Colloidal europium nanoparticles via a solvated metal atom dispersion approach and their surface enhanced Raman scattering studies

Chemistry of lanthanide metals in their zerovalent state at the nanoscale remains unexplored due to the high chemical reactivity and difficulty in synthesizing nanoparticles by conventional reduction methods. In the present study, europium(0) nanoparticles, the most reactive of all the rare earth metals have been synthesized by solvated metal atom dispersion (SMAD) method using hexadecyl amine as the capping agent. The as-prepared europium nanoparticles show surface Plasmon resonance (SPR) band in the visible region of the electromagnetic spectrum. This lead to the investigation of its surface enhanced Raman scattering (SERS) using visible light excitation source. The SERS activity of europium nanoparticles has been followed using 4-aminothiophenol and biologically important molecules such as hemoglobin and Cyt-c as the analytes. This is the first example of lanthanide metal nanoparticles as SERS substrate which can possibly be extended to other rare-earth metals. Since hemoglobin absorbs in the visible region, the use of visible light excitation source leads to surface enhanced resonance Raman spectroscopy (SERRS). The interaction of biomolecules with Eu(0) has been followed using FT-IR and UV–visible spectroscopy techniques. The results indicate that there is no major irreversible change in the structure of biomolecules upon interaction with europium nanoparticles.

Enhanced Dechlorination of 1,2-Dichloroethane by Coupled Nano Iron-Dithionite Treatment

1,2-Dichloroethane (1,2-DCA) is a chlorinated solvent classified as a probable human carcinogen. Due to its extensive use in industrial applications, widespread contamination, and recalcitrance toward abiotic dechlorination, 1,2-DCA remains a challenging compound for the remediation community. Over the past decade, nano zerovalent iron (nZVI) has been efficiently used to treat many of the chlorinated compounds of concern. However, thus far, even nZVI (monometallic or bimetallic) has been unable to dechlorinate 1,2-DCA. Therefore, an alternative treatment coupling nZVI with dithionite to treat 1,2-DCA is proposed in this work. Coupled nZVI-dithionite was able to degrade >90% 1,2-DCA over the course of a year. The effects of dithionite and nZVI loadings, carboxymethyl cellulose (CMC) coating, addition of palladium, and other iron species as metal surfaces on the degradation kinetics were also investigated. Observed pseudo-first-order rate constants (kobs) ranged from 3.8 × 10(-3) to 7.8 × 10(-3) d(-1). Both nucleophilic substitution and reductive dechlorination are the proposed mechanisms for 1,2-DCA degradation by coupled nZVI-dithionite treatment. Characterization analysis of the nZVI-dithionite nanoparticles shows that most of the iron was still preserved in the zerovalent state even after more than one year of reactivity with some iron sulfide (FeS) formation. Scanning electron microscopy (SEM) analysis shows that the nanosized spherical particles were still present along with the FeS platelets. This novel treatment represents the first nZVI-based formulation to achieve nearly complete degradation of 1,2-DCA.

Enhancing the reactivity of bimetallic Bi/Fe0 by citric acid for remediation of polluted water

In this study, the environmentally benign citric acid (CA) was utilized to improve the aerobic degradation of 4-chlorophenol (4-CP) over bismuth modified nanoscale zero-valent iron (Bi/Fe0). The characterization results revealed the existence of bismuth covering on the Fe0 surface under zero-valent state. And, the Bi/Fe0-CA+O2 system performed excellent reactivity in degradation of 4-CP due to the generation of reactive oxygen species (ROS), which was confirmed by electron spin resonance (ESR) spectroscopy. After 30min of reaction, 80% of 4-CP was removed using Bi/Fe0-CA+O2 accompanying with high dechlorination rate. The oxidative degradation intermediates were analyzed by HPLC and LC-MS. We found that CA could promote the bismuth-iron system to produce much reactive oxygen species ROS under both aerobic and anaerobic conditions due to its ligand function, which could react with Fe3+ to form a ligand complex (Fe(III)Cit), accompanying with a considerable production of Fe2+ and H2O2. This study provides a new strategy for generating ROS on nZVI and suggests its application for the mineralization of many recalcitrant pollutants.

Antibacterial activity of single crystalline silver-doped anatase TiO2 nanowire arrays

Well-ordered, one-dimensional silver-doped anatase TiO2 nanowire (AgNW) arrays have been prepared through a hydrothermal growth process on the sputtering-deposited AgTi layers. Electron microscope analyses reveal that the as-synthesized AgNW arrays exhibit a single crystalline phase with highly uniform morphologies, diameters ranging from 85 to 95nm, and lengths of about 11μm. Silver is found to be doped into TiO2 nanowire evenly and mainly exists in the zerovalent state. The AgNW arrays show excellent efficient antibacterial activity against Escherichia coli (E. coli), and all of the bacteria can be killed within 1h. Additionally, the AgNW arrays can still kill E. coli after immersion for 60 days, suggesting the long-term antibacterial property. The technique reported here is environmental friendly for formation of silver-containing nanostructure without using any toxic organic solvents.

Antimicrobial activity of Ag0-nanocomposite copolymer of 1-vinyl-1,2,4-triazole with sodium acrylate

Hydrophilic copolymer was obtained by radical copolymerization of 1-vinyl-1,2,4-triazole with sodium acrylate and used as a stabilizing matrix for metallic silver nanoparticles. The synthesis of metallopolymer nanocomposite was performed by chemical reduction of silver ions up to the zerovalent state. The formation of the metallic phase in the nanoscale state was confirmed by UV spectroscopy and transmission electron microscopy. Silver nanoparticles have the sizes of 2–12 nm and are uniformly distributed in the volume of the polymer matrix. Antimicrobial activity of the initial copolymer and polymer nanocomposite in relation to grampositive and gram-negative microorganisms was studied. It was found that the obtained nanocomposite is characterized by a high antimicrobial activity: bacteriostatic concentration varies in the range from 0.5 to 8 g mL–1, the bactericidal concentration is from 1 to 18 g mL–1.

Применение наночастиц висмута для защиты текстильных материалов от СВЧ-излучения

Synthesis of metal nanoparticles which consisted in chemical restoration of solution of bismuth nitrate is carried out. Optimum parameters of bismuth restoration to a zero-valent metal state and its drawing on fabric are developed. Parameters are calculated and the design of the equipment for impact on the metallized textile materials microwave ovens by radiation is developed for the operating laboratory semi-plant. Processing of samples of natural textile fabrics is carried out by bismuth nanoparticles and researches of distribution of nanoparticles in volume of fabric, forms of particles, their size, a way of fixing in volume of material are conducted. Impact on a sample was carried out by the microwave oven in the camera with a standing wave of modular conveyor installation. It is shown that the modified fabric subjected to radiation allows to lower a radiation dose. After the microwave influence strength properties of cellulose materials were defined. Fabrics were exposed to washings by domestic laundry powder after which such physicomechanical properties as change of the linear sizes after wet processings, the explosive and tearing apart loading, rigidity were defined at a bend, air permeability, hygroscopicity, electric resistance, coefficient of weakening of electromagnetic radiation. Material can be used in radio protective clothes with the strengthened partial protection which includes overalls, a helmet, gloves and boot covers made from the radio reflecting materials.

A Trialkylphosphine-Driven Chemical Transformation Route to Ag- and Bi-Based Chalcogenides

From the standpoint of chemistry, the metastable nature of nanocrystals provides us plentiful ground for the research of new nanoscale structural transformations. Herein, we report a new phenomenon that trialkylphosphine (TAP) can extract the Ag(+) and Bi(3+) from their nanostructural chalcogenides and reduce them to the zerovalent state. Based on this principle, a trialkylphosphine-driven chemical transformation route has been developed for the synthesis of a series of metals and metal-sulfide heterostructures with multiple sulfides as the precursors. Using this reaction principle, Ag, Bi, Ag-Ni3S2, Ag-ZnS, Ag-AgInS2, Ag-Bi, and Bi-Cu7S4 nanostructures can be successively synthesized. These Ag- or Bi-based metal chalcogenide heteronanostructures with interesting optical properties or multifunctionalities could be of special interest for a variety of applications, including high-performance catalysis, biological and biomedical sensing, photovoltaic devices, and a new generation of optoelectronic devices.

FORMATION OF NANOCOMPOSITES NI/C BASED OF POLYACRYLONITRILE UNDER IR-RADIATION

The work is dedicated to obtaining nickel metal-carbon nanocomposites, based on IR-pyrolyzed polyacrylonitrile and nickel chloride hexahydrate, and the study of the structural characteristics of the synthesized material. Nanocomposites prepared under IR-based precursor pyrolysis of polyacrylonitrile (PAN) and nickel chloride hexahydrate (NiCl2 • 6H2O). Pyrolysis was carried out in the temperature range 150—700 °C. The grown nanocomposites are two-phase system of the carbon matrix formed during carbonization of PAN, and distributed in the nanoparticles of nickel (nickel oxide). The average size of the nanoparticles in the nanocomposite was 15—25 nm. The effect of temperature pyrolysis process IR precursor in the size of nickel nanoparticles obtained. It was determined that the distribution of nickel nanoparticles in size is defined by the temperature of the synthesis of the nanocomposite. So while the temperature increases prevailing average particle size of the metal increases and the distribution is blured and shifts toward larger sizes. By a calculation of the total Gibbs energy of possible reduction reactions of nickel chloride and oxide pyrolysis products PAN the possibility of formation of nanocomposites comprising nickel oxide nanoparticles, which are at a higher temperature infrared heating (more than 5000 °C) can be reducted up to zero-valent state at more higher temperature IR heatig.