Visible-light induced water detoxification catalyzed by PtII dye sensitized titania

A new dye sensitization system incorporating Pt(dcbpy)Cl2 on Degussa P-25 TiO2 for the photomineralization of aqueous organic pollutants under visible light irradiation is described. The representative wastewater pollutant, 4-chlorophenol (4-CP), is readily oxidized (ultimately to CO2) when the PtII dye sensitized TiO2 is exposed to visible light in the presence of dissolved O2, and the reaction is accelerated when the solution is purged with O2 gas at 1 atm. The sensitizer is regenerated during the photocatalysis; therefore, 4-CP effectively reduces the oxidized form of the surface bound dye. The experimental data are consistent with parallel oxidative decomposition pathways for 4-CP, one which operates using conduction band electrons to produce hydroxyl radicals and another where the oxidized sensitizer irreversibly oxidizes 4-CP.     

An efficient fluctuating charge model for transition metal complexes

A fluctuating charge model for transition metal complexes, based on the Hirshfeld partitioning scheme, spectroscopic energy data from the NIST Atomic Spectroscopy Database and the electronegativity equalization approach, has been developed and parameterized for organic ligands and their high‐ and low‐spin Fe^II and Fe^III, low‐spin Co^III and Cu^II complexes, using atom types defined in the Momec force field. Based on large training sets comprising a variety of transition metal complexes, a general parameter set has been developed and independently validated which allows the efficient computation of geometry‐dependent charge distributions in the field of transition metal coordination compounds. © 2013 Wiley Periodicals, Inc.     

Adsorptive properties of X zeolites modified by transition metal cation exchange

The ionic exchange of the NaX zeolite by Ni²⁺ and Cr³⁺ cations was progressively driven and studied by adsorption of nitrogen and carbon dioxide. For each cation-exchanged X zeolite sample, the development of characteristics such as profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot, was followed through the nitrogen adsorption. Results show that the cationic exchange process, in the case of Cr³⁺ introduced at middle degree, is accompanied by a textural damage for Cr(x)X, in contrast to Ni²⁺-exchanged X zeolites. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. The CO₂ adsorption isotherms were measured at intervals of 30 K from 273 K and the equilibrium pressures ranged from 0.5 to 600 Torr. The experimental data were correlated by the Toth model. The associated three adjustable parameters were estimated by nonlinear least-squares analysis. The effect of temperature on the model parameters and the Henry’s law slope, K _H , represented by the product of Toth parameters, are discussed.     

Phase transition and crystal growth of a titania layer on a titanium metal plate

Research on Chemical Intermediates - A titanium metal surface was heated with an alkali metal chloride in order to produce a phase transition from amorphous titania to crystalline titania on the...     

Mechanism of electrochemical charge transport in individual transition metal complexes

We used electrochemical scanning tunneling microscopy (STM) and spectroscopy (STS) to elucidate the mechanism of electron transport through individual pyridyl-based Os complexes. Our tunneling data obtained by two-dimensional electrochemical STS and STM imaging lead us to the conclusion that electron transport occurs by thermally activated hopping. The conductance enhancement around the redox potential of the complex, which is reminiscent of switching and transistor characterics in electronics, is reflected both in the STM imaging contrast and directly in the tunneling current. The latter shows a biphasic distance dependence, in line with a two-step electron hopping process. Under conditions where the substrate/molecule electron transfer (ET) step is dominant in determining the overall tunneling current, we determined the conductance of an individual Os complex to be 9 nS (Vbias = 0.1 V). We use theoretical approaches to connect the single-molecule conductance with electrochemical kinetics data obtained from monolayer experiments. While the latter leave some controversy regarding the degree of electronic coupling, our results suggest that electron transport occurs in the adiabatic limit of strong electronic coupling. Remarkably, and in contrast to established ET theory, the redox-mediated tunneling current remains strongly distance dependent due to the electronic coupling, even in the adiabatic limit. We exploit this feature and apply it to electrochemical single-molecule conductance data. In this way, we attempt to paint a unified picture of electrochemical charge transport at the single-molecule and monolayer levels.     

Synthesis and conversion of alcohols over modified transition metal sulphides

Alkali modified (Co/Ni)MoS systems are promising catalysts for higher alcohol synthesis from synthesis gas. The influence of various supports, modifiers and promoters on the activity of sulphide catalysts is reviewed. It is found that alkali metal reduces support acidity and affects the active phase morphology and active site functioning. Promotion of the catalyst with Co and Ni favours alcohol formation. KCoMoS catalyst activity in syngas conversion and hydrodesulphurization reactions is studied. An effect of organic compound additives such as methanol, ethanol, and ethylene on the catalyst behaviour is studied. It is suggested that alcohol formation may proceed in two steps: CO insertion and aldol condensation. Which of the two dominates depends on the reaction conditions.     

Dipolar and electronic effects on charge transport through single transition metal complexes

Charge transport through single molecular neutral monoand di-cobalt(II) complexes with π-conjugated macromolecular wire was investigated.Scanning tunnelling spectroscopy (STS) studies revealed that the mono-cobalt(II) complex showed a pronounced rectifying effect with a large rectification ratio and finely featured NDR peaks,while the di-cobalt(II) complex showed a relatively symmetric electron transport without clear NDR peaks.Th     

Catalysts based on cordierite modified with transition metal oxides

Catalysts active in ammonia oxidation have been obtained by the substitution of transition metal (Mn, Fe, Co, Ni, and Cu) ions for Mg ions in the cordierite structure 2MgO · 2Al₂O₃ · 5SiO₂ at 1100°C. Their phase composition, texture, and activity depend on the type and amount of introduced transition metal oxide. The Mn- and Cu-containing catalysts, which consist of substituted cordierites 2(Mg_{1 ? x} M _x )O · 2Al₂O₃ · 5SiO₂ and Mn₂O₃ or CuO crystallites located on their surface, are most active in ammonia oxidation. The catalysts are characterized by a small specific surface area and have large pores, whose total volume is small. The Fe-containing catalysts consist of the Fe-substituted cordierite phase and particles of an iron oxide phase. These particles are mostly located in internal pores of the catalysts and are, therefore, hardly accessible to ammonia molecules. The introduction of Co or Ni oxide leads to the formation of a low-active spinel phase rather than the cordierite phase.     

Study of the benzylation of benzene and other aromatics by benzyl chloride over transition metal chloride supported mesoporous SBA-15 catalysts

The benzylation of benzene by benzyl chloride to diphenylmethane over FeCl₃, InCl₃, GaCl₃, ZnCl₂, CuCl₂ and NiCl₂ supported on mesoporous SBA-15 at 353 K has been investigated. The redox property due to the impregnation of the SBA-15 by transition metal chloride seems to play a very important role in the benzene benzylation process. Among the catalysts, the FeCl₃/SBA-15 showed both high conversation and high selectivity for the benzylation of benzene. The activity of these catalysts for the benzylation of different aromatic compounds is in the following order: benzene > toluene > p-xylene > anisole. More interesting is the observation that this catalyst is always active and selective for large molecules like naphthenic compounds such as methoxynaphthalene and he can also be reused in the benzylation of benzene for several times. Kinetics of the benzene benzylation over these catalysts have also been investigated.     

First row transition metal ion-assisted ammonia-borane hydrolysis for hydrogen generation

Ammonia-borane (AB) hydrolysis for the generation of hydrogen has been studied using first row transition metal ions, such as Co (2+), Ni (2+), and Cu (2+). In the cases of cobalt- and nickel-assisted AB hydrolysis, amorphous powders are formed that are highly catalytically active for hydrogen generation. Annealing of these amorphous powders followed by powder X-ray diffraction measurements revealed the presence of Co(0) and Co 2B and Ni(0) and Ni 3B, respectively. On the other hand, copper-assisted AB hydrolysis was catalyzed by in situ generated H (+) and Cu(0) nanoparticles. The reduction ability of AB for the realization of coinage metal nanoparticles from the respective metal salts has also been studied. These reduction reactions were found to be facile, affording colloids of pure metal nanoparticles. Nanoparticles prepared in this manner were characterized by UV-visible spectroscopy and high-resolution electron microscopy.     

Reaction of vinyl chloride with late transition metal olefin polymerization catalysts

The reactions of vinyl chloride (VC) with representative late metal, single-site olefin dimerization and polymerization catalysts have been investigated. VC coordinates more weakly than ethylene or propylene to the simple catalyst (Me(2)bipy)PdMe(+) (Me(2)bipy = 4,4'-Me(2)-2,2'-bipyridine). Insertion rates of (Me(2)bipy)Pd(Me)(olefin)(+) species vary in the order VC > ethylene > propylene. The VC complexes (Me(2)bipy)Pd(Me)(VC)(+) and (alpha-diimine)Pd(Me)(VC)(+) (alpha-diimine = (2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMeCMe[double bond]N(2,6-(i)Pr(2)[bond]C(6)H(3))) undergo net 1,2 VC insertion and beta-Cl elimination to yield Pd[bond]Cl species and propylene. Analogous chemistry occurs for (pyridine-bisimine)MCl(2)/MAO catalysts (M = Fe, Co; pyridine-bisimine = 2,6-[(2,6-(i)Pr(2)[bond]C(6)H(3))N[double bond]CMe](2)-pyridine) and for neutral (sal)Ni(Ph)PPh(3) and (P[bond]O)Ni(Ph)PPh(3) catalysts (sal = 2-[C(H)[double bond]N(2,6-(i)Pr(2)-C(6)H(3))]-6-Ph-phenoxide; P[bond]O = [Ph(2)PC(SO(3)Na)[double bond]C(p-tol)O]), although the initial metal alkyl VC adducts were not detected in these cases. These results show that the L(n)MCH(2)CHClR species formed by VC insertion into the active species of late metal olefin polymerization catalysts undergo rapid beta-Cl elimination which precludes VC polymerization. Termination of chain growth by beta-Cl elimination is the most significant obstacle to metal-catalyzed insertion polymerization of VC.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Size and charge effects on the binding of CO to late transition metal clusters

We report on the size and charge dependence of the C-O stretching frequency, nu(CO), in complexes of CO with gas phase anionic, neutral, and cationic cobalt clusters (Co(n)CO(-0+)), anionic, neutral, and cationic rhodium clusters (Rh(n)CO(-0+)), and cationic nickel clusters (Ni(n)CO(+)) for n up to 37. We develop models, based on the established vibrational spectroscopy of organometallic carbonyl compounds, to understand how cluster size and charge relate to nu(CO) in these complexes. The dominating factor is the available electron density for backdonation from the metal to the CO pi* orbital. Electrostatic effects play a significant but minor role. For the charged clusters, the size trends are related to the dilution of the charge density at the binding site on the cluster as n increases. At large n, nu(CO) approaches asymptotes that are not the same as found for nu(CO) on the single crystal metal surfaces, reflecting differences between binding sites on medium sized clusters and the more highly coordinated metal surface sites.     

Tracer-diffusion of Co2+ ions in some transition metal chloride solutions

Tracer-diffusion coefficients of Co²⁺ ions have been determined in 1% agar gel containing transition metal chlorides, viz. ZnCl₂, NiCl₂ and MnCl₂ over the concentration range of 10^–6–0.15 M at 25°C using the zone-diffusion technique. The results are compared with calculated values on the basis of Onsager's theory and the deviations are accounted for on the basis of various types of interactions in the ion-gel water system. Further, activation energy for the tracer-diffusion of Co²⁺ ions in the above mentioned electrolytes has been obtained as a function of electrolyte concentration, using measurements in the temperature range of 25–50°C. The trend in activation energy is explained on the basis of the WANG's model.     

Thermal degradation of partly complexed poly(vinylpyridines) with transition metal chloride

The thermal degradation of poly(vinylpyridines), partly complexed with transition metal chlorides containing Co(II), Ni(II), Cu(II) and Zn(II) ions, was investigated using thermogravimetry, infrared spectrometry and gc/mass spectrometry. When poly(2-vinylpyridine) and poly(4-vinylpyridine) were partly complexed with transition metal ions, thermal degradation was initiated at low temperature. The complexes were decomposed even near the threshold temperature for weight loss. Degradations were modified by the complexation, particularly for poly(2-vinylpyridine). Yields of dimers, ethylpyridine, etc., increased linearly with degree of complexation, but that of monomer decreased linearly. The increase of the yield of dimer could be explained from the concept that polymer radicals reacted with metal chlorides, then dehydrochlorinated and underwent β-scission.     

Effect of transition metal chloride additives on the radiolysis of aqueous sodium nitrate

Radiolysis of aqueous sodium nitrate solution was studied as a function of concentration in the range 10^–4M to 1M NaNO₃. The radiolytic yield of nitrite was found to be linear with dose and concentration. The effect of transition metal chloride additives on the radiolysis of 0.01M NaNO₃ resulted in higher and lower yields of nitrite in the presence of cobalt and nickel chlorides, respectively, than that obtained in the pure nitrate system. The reduction of nitrate to nitrite is totally quenched even at very low concentration of copper chloride in the binary mixture. The results are explained on the basis of oxidizing and reducing properties of transition metal ions.     

The wetting-dewetting transition of monolayer water on a hydrophobic metal surface observed by surface-state resonant second-harmonic generation

The isothermal adsorption and desorption of monolayer water on a Ag(110) surface in the temperature range of 130-137 K were characterized by monitoring second-harmonic (SH) generation from the silver surface. The SH intensity resonantly enhanced by the silver surface-state transition is highly sensitive to the amount of silver surface area covered by water and allows the observation of an abrupt change in the adsorption/desorption behavior at 133.5 K. At temperatures below 133.5 K water wets the Ag surface in a two-dimensional structure with a measured desorption energy of 25.0 (+/-3.3) kJ/mol. At temperatures greater than 133.5 K water desorbs from three-dimensional clusters with a measured desorption energy of 48.3 (+/-2.2) kJ/mol, in agreement with temperature-programmed desorption measurements. This wetting-dewetting transition of water adsorbed on the silver surface at 133.5 K is supported by classical nucleation theory calculations.     

Basicity of transition metal carbonyl complexes: VIII. An infrared study of the reaction of aluminium chloride with some cyclopentadienyl and arenecarbonyl transition metal complexes

The interaction of cyclopentadienyl and arene derivatives of carbonyl complexes of Group V, VI and VII transition metals with AlCl₃ in benzene and CH₂Cl₂ solutions has been studied by IR spectroscopy.The formation of adducts involving the metal atom or the carbonyl oxygen atom was observed. The reaction path depends on the structure of the complex and on the nature of the solvent. In benzene the adduct formation at the CO ligand is more favourable than in CH₂Cl₂ solution. Introduction of a phosphine ligand in the place of the CO group or introduction of donor substituents into the π-ring increases the basicity of the central metal atom and makes adduct formation at the metal more probable.The basicity of the metal atom in complexes with the same ligands increases with increases of atomic number in the group. CpRe(CO)₂Br₂ forms adducts with AlCl₃ at the bromine atoms ($\text{1}\text{1}$ and $\text{sol1}\text{2}$). For Fe(CO)₄PPh₃ and Fe(CO)₃(PPh₃)₂ complex formation takes place at the iron atom.     

Electrochemical charge transfer mediated by metal nanoparticles and quantum dots

Electron transfer processes mediated by nanostructured materials assembled at electrode surfaces underpin fundamental processes in novel electrochemical sensors, light energy conversion systems and molecular electronics. Functionalisation of electrode surfaces with hierarchical architectures incorporating self-assembling molecular systems and materials, such as metal nanostructures, quantum dots, carbon nanotubes, graphene or biomolecules have been intensively studied over the last 20 years. Important steps have been made towards the rationalisation of the charge transfer dynamics from redox species in solution across molecular self-assembling systems to electrode surfaces. For instance, a unified picture has emerged describing the factors which determine the rate constant for electron transfer processes across rigid self-assembling molecular barriers. An increasing bulk of evidence has recently shown that the incorporation of nanomaterials into self-assembling monolayers leads to an entirely different electrochemical behaviour. This perspective rationalises some of the key observations associated with nanoparticle mediated charge transfer, such as the apparent distance independent charge transfer resistance observed for redox species in solution. This behaviour only manifests itself clearly in the case where the probability of direct charge transfer from the redox probe to the electrode is strongly attenuated by self-assembling molecular barriers. Here we will highlight specific issues concerning self-assembled monolayers as blocking barriers prior to discussing the effect of nanoparticles on the electrochemical response of the system. Selected examples will provide conclusive evidence that the extent of charge transfer mediation is determined by the overlap between the density of states of the nanostructures and the energy levels of redox species in solution. Only in the case where a strong overlap exists between the energy levels of the two components, the nanostructures behave as "electron launchers", allowing efficient charge transfer across insulating molecular layers.