Zero-valent State Research Articles

Supporting of pristine TiO2 with noble metals to enhance the oxidation and mineralization of paracetamol by sonolysis and sonophotolysis

Pharmaceutical residues in fresh water bodies are of significant environmental concern due to their undesirable effects on aquatic organisms at very low concentrations. The present study is about the elimination and overall degradation of a common anti-inflammatory pharmaceutical-paracetamol (PCT) in water by catalytic oxidation using high-frequency ultrasound, UV-irradiation (254nm) and both. The catalysts were synthesized sonolytically by the reduction of Pd and Au to the zero-valent state followed by immobilization of the nanoparticles on the surface of commercial TiO2 (P-25) to improve the activity of the semiconductor under ultrasonic and UV irradiation. It was found that sonolytic oxidation of PCT during catalysis with Pd–TiO2 and Pd/Au–TiO2 was very effective owing to the significantly smaller size of these particles (than that of Au–TiO2), which promoted the formation and collapse of cavitation bubbles on their surface and the incidence of solute contact with the active sites. The addition of persulfate further enhanced the rate of PCT decay, signifying the role of ultrasound in activating the reagent and that of radical-initiated oxidation reactions in the decomposition of the parent compound. The activity of P-25 was low and almost equal under sonolysis and photolysis, but considerably higher under sono-photolysis, where the unfavorable properties of the semiconductor were minimized via combined effects of the two processes. Hybridization also induced a considerable synergy in carbon-mineralization, which was relatively low with single processes. The results were attributed to minimization of electron-hole pair recombination, surface corrosion and competition for photons and radical species. Au-supported particles exhibited higher activity in the presence of UV-irradiation than ultrasound, which was attributed to the unique activity of gold in the UV–vis region. Finally, Pd–TiO2 was found to be the most stable nanocomposite in terms of the ease of recovery and the efficiency of reuse.

Mechanisms of removal of heavy metals and arsenic from water by TiO2-heterogeneous photocatalysis

Abstract This article is an overview of recent work performed in our laboratory on TiO2 heterogeneous photocatalysis of aqueous systems containing toxic forms of chromium, arsenic, lead, uranium and mercury. The cases of chromium and arsenic are treated in profundity. Photocatalytic treatments can convert the ionic species into their metallic solid form and deposit them over the semiconductor surface, or transform them into less toxic soluble species. When a transformation to the zerovalent state is possible, this allows the recovery of the metal from the waters, with an important economical return. Three types of mechanisms can be considered, all of them taking place through successive thermodynamically allowed monoelectronic electron transfer steps: (a) direct reduction by photogenerated electrons; (b) indirect reduction by intermediates generated by hole or hydroxyl radical oxidation of electron donors (reducing radicals); (c) oxidative removal by holes or hydroxyl radicals. Fundamentals of oxidative or reductive heterogeneous photocatalysis are described, with special emphasis on the role of organic donors present in the medium acting as synergists. This indicates the possibility of simultaneous treatment of pollutants of different chemical structure and properties present in the same medium.

Examination of the Binding Mechanism of Mercury in Fluorescent Lamp Coatings

ABSTRACTThe mercury consumption during the operation of fluorescent lamps is not entirely understood. There are no publications that have reported in which chemical state the mercury is bound in alumina precoats. In the present study, alumina precoat lamps without a phosphor coating were built and seasoned for up to 8400 h. Parts from the seasoned lamps were analyzed using X-ray photoelectron spectroscopy (XPS) und thermal desorption mass spectrometry (TDMS). It could be shown that the state of the chemical binding of the mercury atoms changes with seasoning time. It appears that mercury is deposited in a zero-valent binding state that changes to an HgO-like binding state with increased seasoning time of the lamp.

Linear coordination fullerene C60 polymer [{Ni(Me3P)2}(μ-η(2),η(2)-C60)]∞ bridged by zerovalent nickel atoms.

Coordination nickel-bridged fullerene polymer [{Ni(Me3P)2}(μ-η(2),η(2)-C60)]∞ (1) has been obtained via reduction of a Ni(II)(Me3P)2Cl2 and C60 mixture. Each nickel atom is linked in the polymer with two fullerene units by η(2)-type Ni-C(C60) bonds of 2.087(8)-2.149(8) Å length. Nickel atoms are coordinated to the 6-6 bonds of C60 as well as two trimethylphosphine ligands to form a four-coordinated environment around the metal centers. Fullerene cages approach very close to each other in the polymer with a 9.693(3) Å interfullerene center-to-center distance, and two short interfullerene C-C contacts of 2.923(7) Å length are formed. Polymer chains are densely packed in a crystal with interfullerene center-to-center distances between fullerenes from neighboring polymer chains of 9.933(3) Å and multiple interfullerene C···C contacts. As a result, three-dimensional dense fullerene packing is formed in 1. According to optical and electron paramagnetic resonance spectra, fullerenes are neutral in 1 and nickel atoms have a zerovalent state with a diamagnetic d(10) electron configuration. The density functional theory calculations prove the diamagnetic state of the polymer with a singlet-triplet gap wider than 1.37 eV.

Platinum nanoparticles ion-implanted-modified indium tin oxide electrode for electrocatalytic oxidation of formaldehyde

A facile and low-cost method is developed to ion implant platinum nanoparticles (PtNPs) onto indium tin oxide (ITO) electrode. This modified electrode is eco-friendly without the use of any linking chemicals. The PtNPs formed on the electrode are in the zero-valent metallic state with a size distribution in the range of 5–12 nm. The modified electrode surface becomes smoother after platinum ion implantation and the PtNPs formed on the electrode. Electrochemical performances are measured by cyclic voltammetry (CV) and chronoamperometric. The PtNPs/ITO electrode shows prominent electrocatalytic activity towards the oxidation of formaldehyde with long-term stability, which could be useful in fuel cells.

The fabrication of silver ion implantation-modified electrode and its application in electrocatalytic oxidation of formaldehyde

In this work, we present a novel process for the fabrication of a silver-nanoparticle-modified electrode using silver ion implantation. This method is facile, low-cost and environmental friendly without the use of any linking chemicals. The modified electrode was verified by scanning electron microscope (SEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectra (EIS) and cyclic voltammetry (CV). The AgNPs formed on the electrode are in the zero-valent metallic state with a size distribution in the range of 3–6 nm. The modified electrode shows prominent electrocatalytic activity towards the oxidation of formaldehyde with long-term stability and could be useful in fuel cells.

Effects of nanocrystalline powders (Fe, Co and Cu) on the germination, growth, crop yield and product quality of soybean (Vietnamese species DT-51)

Superdispersive iron, cobalt and copper nanocrystalline powders were synthesized in a water–ethanol medium by the reduction method using sodium borohydride as a reducing agent and carboxymethyl cellulose as a stabilizer (for Fe and Co nanoparticles). Transmission electron microscopy micrographs and x-ray diffraction analyses of the freshly prepared nanocrystalline powders indicated that they were in a zerovalent state with particle sizes ranging from 20 to 60 nm. The soybean seeds were treated with an extra low nanocrystalline dose (not more than 300 mg of each metal per hectare) and then sowed on an experimental landfill plot consisting of a farming area of 180 m2. This pre-sowing treatment of soybean seeds, which does not exert any adverse effect on the soil environment, reliably changed the biological indices of the plant growth and development. In particular, in laboratory experiments, the germination rates of soybean seeds treated with zerovalent Cu, Co and Fe were 65, 80 and 80%, respectively, whereas 55% germination was observed in the control sample; in the field experiment, for all of the nanoscale metals studied, the chlorophyll index increased by 7–15% and the number of nodules by 20–49% compared to the control sample, and the soybean crop yield increased up to 16% in comparison with the control sample.

Enhanced arsenic removal at neutral pH using functionalized multiwalled carbon nanotubes

In this study, zerovalent iron nano-particles were immobilized on oxidized multiwalled carbon nanotubes (MWCNT) using EDTA as chelating agent (ZCNT). In addition to zerovalent iron (ZVI), the prepared composite had various surface functional groups including hydroxyl, amino and carboxyl groups. Presence of EDTA in the composite preserved the zerovalent state of iron. The prepared composite was characterized with various spectral techniques like Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDAX), Brunauer, Emmett, and Teller (BET) surface area analyzer, Fourier Transform Infra-red (FTIR) and Raman Spectroscopy. The equilibrium data were fitted to Langmuir model and maximum adsorption capacities at neutral pH were found to be 111.1±4.8 and 166.7±5.8mgg−1 for As(III) and As(V) respectively. Thermodynamic parameters such as ΔS, ΔH and ΔG indicated the suitability of ZCNT for the removal of As(III) and As(V). Recycling studies indicated the performance of ZCNT up to 5 cycles without appreciable depreciation in the capacity. The effect of commonly existing anions such as silicate, phosphate, sulfate, and humic acid were also tested. Finally, the adsorbent was successfully applied to the removal of total inorganic arsenic from arsenic contaminated ground water without resorting to any pretreatment.

Composite materials {glassy carbon/graphene/zero-valent metal (Pd0)} for building three-dimensional redox electrodes

When glassy carbon (GC) is mechanically covered with micrometric layers of graphene, the reduction of primary alkyl halides (RX) can shift to the catalytic mode due to the fact that cathodically charged graphene may act as a redox reducing agent triggering a classical redox catalytic process with a moderate gain (<0.2V) in potential. Alternatively, the injection of very small amounts of transition metals (not only Pd, but also Au, Ag or Pt) at zero-valent state into the graphene layer may induce catalytic reduction of RIs and RBrs that allows the formation of free radicals R and their concomitant grafting, not only at the GC/graphene interface but also in bulk graphene that plays the role of a three-dimensional radical scavenger. Therefore, by use of this simple process, GC/graphene layers could be converted into a 3D active interface. In order to quantify the global grafting/insertion of R, ferrocene and aryl probes (Fc-n-alkyl-I and pyrene-CH2-Br) were used, attesting to significant modification of the interface. Thus, for the first time, a bulky graphene–ferrocene layer (a redox system fully usable as a 3D modified electrode) was built. This model could quite hopefully be envisaged for electrochemically incorporating many other redox centers in graphene within the potential range of −2V to +1V vs. Ag/AgCl.

Molecular structure and spectroscopic properties of a nickel-bridged {Ni(Ph3P)}2(μ2-η(2), η(2)-C60)2 dimer.

A compound containing fullerene dimers bonded through two nickel atoms, {Ni(Ph3P)}2(μ2-η(2),η(2)-C60)2·2C6H4Cl2 (1), has been obtained as single crystals. The fullerenes are neutral in 1 , showing a zero-valent state of Ni. The nickel atoms are bonded in an η(2) coordination mode with Ni-C distances of 2.001(3)-2.037(3) Å and a close approach of the fullerenes with a 9.716 Å center-to-center distance. The DFT calculations showed a diamagnetic singlet ground state for this dimer.

Mononuclear Coordination Complexes of Fullerene C60 with Zerovalent Cobalt Having S = 1/2 Spin State: Co(η2-C60)(L)(C6H5CN)·(o-C6H4Cl2) (L = 1,2-bis(diphenylphosphino)ethane and 1,1′-bis(diphenylphosphino)ferrocene)

Two mononuclear coordination complexes of fullerene C60 with cobalt, Co(η(2)-C60)(dppe)(C6H5CN)·C6H4Cl2 (1) and Co(η(2)-C60)(dppf)(C6H5CN)·C6H4Cl2 (2) (dppe is 1,2-bis(diphenylphosphino)ethane and dppf is 1,1'-bis(diphenylphosphino)ferrocene) have been obtained by sodium fluorenone reduction of the Co(dppe)Cl2 or Co(dppf)Br2 and C60 mixtures. The IR and visible-NIR spectra of 1 and 2 indicate the neutral state of fullerenes. Therefore, cobalt atoms formally have the zerovalent state. Cobalt coordinates to the 6-6 bond of C60 by η(2)-type coordination with Co-C bond lengths in the 2.008(3)-2.060(3) Å range. Diphosphine and benzonitrile ligands additionally coordinate to cobalt to form a distorted square-pyramidal environment for the cobalt atoms. Complexes 1 and 2 are rare examples of fullerene coordination complexes with paramagnetic metal centers. Both complexes manifest intense asymmetric EPR signals attributed to zerovalent cobalt atoms, which can be fitted by three components with g = 2.261-2.124 (1) and g = 2.258-2.092 (2). Effective magnetic moments of 1 and 2 indicate the low-spin (S = 1/2) state of Co(0). In accordance with EPR spectra, DFT calculations show that the spin density is localized mainly on the central cobalt atoms and only slightly delocalized into C60, benzonitrile, dppe, or dppf ligands.

Ionic Liquids for the Synthesis and Stabilization of Metal Nanoparticles

The synthesis and stabilization of metal nanoparticles (M-NPs) from metals, metal salts, metal complexes and metal carbonyls in ionic liquids (ILs) is reviewed. The electrostatic and steric properties of ionic liquids allow for the stabilization of M-NPs without the need of additional stabilizers, surfactants or capping ligands. The synthesis of M-NPs in ILs can be carried out by chemical or electroreduction, thermolysis and photochemical methods including decomposition by microwave or sono-/ultrasound irradiation. Gas-phase syntheses can use sputtering, plasma/glow-discharge electrolysis and physical vapor deposition or electron beam and γ-irradiation. Metal carbonyl precursors Mx(CO)y contain the metal atoms already in the zero-valent oxidation state needed for M-NPs so that no extra reducing agent is necessary. Microwave-induced thermal decomposition of precursors in ILs is a rapid and energy-saving access to M-NPs because of the significant absorption efficiency of ILs for microwave energy due to their ionic charge, high polarity and high dielectric constant. M-NP=IL dispersions can be applied in catalytic reactions, e. g., in C-C coupling or hydrogenation catalysis.

Preparation and Study of Pd Catalysts Supported on Activated Carbon Cloth (ACC) for Direct Synthesis of H2O2 from H2 and O2

Activated carbon cloths (ACCs) were used as supports for Pd catalysts. The catalyst preparation was carried out by the impregnation method using acidic solution of palladium dichloride (PdCl2) as metal precursor. The effects of the oxidation state of the loaded metal, heat treatment of the catalysts in different atmosphere (H2, air) at different temperatures and surface chemistry of the support on the catalyst characterizations and the catalytic activities were investigated. Wet oxidation of ACC was done by nitric acid in order to induce oxygen-containing surface functional groups. Surface chemistry of the support and oxidation state of the metallic phase was investigated by means of XPS, TPD, SEM, DTA and TGA tests. Direct synthesis of hydrogen peroxide from H2 and O2 was performed batch wise in a stainless steel autoclave. The reactions were conducted under high pressure (38 bar) at 0 °C and methanol was used as reaction medium. The direct synthesis results showed that the oxygen-containing surface functional groups increase the selectivity of the catalysts by reducing the rate of water production. Existence of the oxidized state of Pd (PdO) also makes the catalyst more selective than the corresponding zerovalent state (Pd0). PdO affected on selectivity by increasing the rate of H2O2 production and reducing the amount of production of water, simultaneously.

Ruthenium Nanoparticles in Ionic Liquids – A Saga

Ionic liquids (ILs) are excellent media for the generation and stabilisation of metallic nanoparticles (NPs). Their ionic character coupled with 3-D structural pre-organisation in the liquid state, serves to direct the growth of transition metal NPs generated in situ, and to subsequently protect and stabilise them. Until now, many different NPs have been successfully synthesised within these media, however much attention has been paid to Ru-NPs. These have been prepared with small sizes and narrow size distributions by reduction of organometallic compounds with molecular hydrogen as well as decomposition of transition-metal complexes in the zero-valent state. These stable Ru-NPs immobilised in the ILs have proven to be efficient green catalysts for several reactions in multiphase conditions, including important energy-related processes such as biomass refinement. Furthermore, they present potential novel materials for use in the production of smarter electronic devices. In this review, the synthesis, stabilisation and size-control of Ru-NPs via various methods in different ILs is discussed, followed by their varied application in catalysis and potential in new fields. Keywords: Ionic liquids, Ruthenium, Nanoparticles, Catalysis

A novel method for producing hydrogen from water with Fe enhanced by HS− under mild hydrothermal conditions

In this paper, a novel method for producing hydrogen from water with Fe as a reductant promoted by HS− under mild hydrothermal conditions was proposed. Results showed that hydrogen production significantly increased in the presence of HS− compared to that in the absence of HS−. The obvious hydrogen production was achieved in a low reaction temperature of 250 °C and a very short reaction time (less than 2 h). The maximum yield of hydrogen production, which was defined as the percentage of produced hydrogen amount to theoretical one according to completive oxidation of Fe to Fe3O4 to produce hydrogen from water, was 34% at 300 °C. HS− may act as a catalyst and a possible HS−-catalyzed mechanism was proposed. This process may provide a promising solution for biomass-driven hydrogen production from water combined with the process of reducing iron oxide into their zero-valent state by bio-driven chemicals, such as glycerin.

A rugged, precise and accurate new gravimetry method for the determination of gold: an alternative to fire assay method

A new, rugged, precise, accurate and fast primary method of measurement has been proposed for the determination of gold in various gold articles. Precise and accurate measurement of gold is the primary requirement for hall marking and to trade gold internationally, as billions of dollars of gold are trading world wide for the various applications. At present Fire Assay ASTM E 1335–08 is the only Standard Test Method for the determination of Gold, which is accepted internationally. But the method is time consuming, cumbersome and required expertise to perform the test. In the present investigation, a method has been developed gravimetry based on direct determination of gold after reducing gold in zero-valent state by hydroxylamine hydrochloride. Gravimetry is the most reliable technique and having highest metrological qualities in comparison to titremetry and instrumental method and the results of gravimetry are directly traceable to SI unit. The results of gravimetric method are accepted without reference to a standard of the same quantity. Several experiments were carried out with and without impurities and it has been concluded that gold can be determined accurately and precisely in presence of several impurities. Five replicates of approximate 0.2 g gold samples were analyzed following method proposed and percentage purity were found to be 99.993 ± 0.0056 with 95% confidence level (k = 2). The combined uncertainty in gold measurement has also been evaluated using potential sources of the method according to the EURACHEM/GUM guidelines.

An Easy Route to Synthesize Novel Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;@Pt Core-shell Nanostructures with High Electrocatalytic Activity

In this work, the effect of changing the stirring method and temperature on the physicochemical properties of metallic nanoparticles and core-shell nanostructures is shown. Magnetic (MS), mechanical (UT) and ultrasonic (USS) stirring are the methods of synthesis. The effect that, temperatures between 0 and 50 °C, has on the structure and particle size of Fe3O4 nanoparticles is evaluated. The results indicate that Fe3O4 prepared by the three methods presents a spinel-type crystalline structure. An increase in the synthesis temperature leads to highly crystalline powders. Afterwards, Pt is deposited by the UT method on Fe3O4 to form Fe3O4@Pt core-shell nanostructures. It is important to mention that the time used for the synthesis of the nanoparticles and the core-shell nanostructures is only one minute. The presence of Fe3O4 and Pt is confirmed by XRD and XPS. The metallic Pt phase is confirmed because the binding energy of Pt 4f 7/2 is associated to platinum in the zero-valent state. We evaluated the electrochemical activity of the Fe3O4@Pt core-shell nanostructures for the oxygen reduction reaction (ORR). The novel materials show a high electrocatalytic activity and the Koutecky-Levich analysis indicates that the reaction follows a 4 electron transfer mechanism on the Fe3O4@Pt nanostructures prepared by the three stirring processes. Moreover, the mass specific activity of the core-shell materials is as high as that obtained from the Pt-alone catalysts, suggesting that the amount of Pt in these electrodes can be reduced without decreasing the performance.

Hydrodechlorination of chloromethanes with a highly stable Pt on activated carbon catalyst

A platinum catalyst with activated carbon-support (Pt/C) was prepared and showed a high activity for the deep gas-phase hydrodechlorination (HDC) of dichloromethane (DCM) and chloroform (TCM), with conversions of up to 70% and 100%, respectively (operating conditions: atmospheric pressure, reaction temperatures of 150–250 °C, and space–times of 0.08–1.7 kg h mol −1). The catalyst was highly selective to methane (the only non-chlorinated product) with selectivities of up to 85% for HDC of DCM and 93% for HDC of TCM. The catalyst showed exceptional stability with no loss of activity after 26 days on stream in the HDC of DCM. This can be ascribed to its high resistance to poisoning by organic compounds compared to Pd/C catalysts previously studied. This can be attributed to re-dispersion of Pt during the reaction and to the high proportion of metal in the zero-valent state (Pt 0) which disfavors the stabilization of chlorocarbon compounds at the active centers of the catalyst.

Surface modification of indium tin oxide films with Au ions implantation: Characterization and application in bioelectrochemistry

Indium tin oxide (ITO) thin film coated glass substrates have been implanted with 21keV Au ions at a fluence of 1.0×1017 ions/cm2 at room temperature. The resulting gold film was characterized with X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectra and electrochemical methods. The results reveal that the implanted Au atoms were in the zero-valent metallic state and these Au atoms precipitated to form nanoclusters on the ITO surface whose average radius was estimated between 2 and 5nm. The preferentially growing orientation was Au (111) plane during the formation process of gold film and the value of gold active surface area normalized by the geometric electrode areas was 0.48 for Au ion implanted ITO (Au/ITO) electrode. The potential utility of Au/ITO films was investigated. The Au/ITO electrode exhibited effective catalytic responses towards biomolecules such as ascorbic acid (AA) oxidation and lowered oxidation potential of AA by 0.6V when compared with the bare ITO electrode. Myoglobin (Mb) was also successfully immobilized on the Au/ITO electrode and the direct electron transfer between proteins and electrode surface was realized. It was demonstrated that the Au/ITO film offered a favorable microenvironment for the orientation of biomolecules. New biomaterials with specific electrocatalytic and electrochemical features could be fabricated using this method.

Hydrogenation of arenes and N-heteroaromatic compounds over ruthenium nanoparticles on poly(4-vinylpyridine): a versatile catalyst operating by a substrate-dependent dual site mechanism

A nanostructured catalyst composed of Ru nanoparticles immobilized on poly(4-vinylpyridine) (PVPy) has been synthesized by NaBH(4) reduction of RuCl(3)·3H(2)O in the presence of the polymer in methanol at room temperature. TEM measurements show well-dispersed Ru nanoparticles with an average diameter of 3.1 nm. Both powder XRD patterns and XPS data indicate that the Ru particles are predominantly in the zerovalent state. The new catalyst is efficient for the hydrogenation of a wide variety of aromatic hydrocarbons and N-heteroaromatic compounds representative of components of petroleum-derived fuels. The experimental data indicate the existence of two distinct active sites in the nanostructure that lead to two parallel hydrogenation pathways, one for simple aromatics involving conventional homolytic hydrogen splitting on Ru and a second one for N-heteroaromatics taking place via a novel heterolytic hydrogen activation on the catalyst surface, assisted by the basic pyridine groups of the support.