OH Complex Research Articles

Synergistic catalysis of Co3O4 and graphene oxide on Co3O4/GO catalysts for degradation of Orange II in water by advanced oxidation technology based on sulfate radicals

In this study, the synergistic catalytic mechanism of Co3O4 and graphene oxide (GO) nanocomposite in the heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals was studied. The activation of Co3O4/GO with different Co3O4 loadings in the catalyst [bare graphene oxide (GO), 20% Co3O4/GO, 30% Co3O4/GO, 50% Co3O4/GO, 70% Co3O4/GO, 90% Co3O4/GO, 95% Co3O4/GO, and pure Co3O4] were tested though the degradation of Orange II in water. The results show that the highest performance achieved using the Co3O4/GO catalyst was based on a synergistic catalysis between Co3O4 and GO. Furthermore, a proportional relation exists between Co3O4 and the catalyst. The highest catalytic activity is observed when the Co3O4 loading was about 50% in the catalyst. Co–OH complexes form on the surface of the GO sheet through the direct interaction of Co species with nearby hydroxyl groups or through the dissociation of H2O with Co2+. The formation is proposed to facilitate the heterogeneous activation of PMS. However, a high Co3O4 loading on the GO surface prevents the formation of Co–OH complexes, which is important in the catalytic reaction.

Role of Polarization in Halogen Bonds

A classical point-charge self-consistent polarization model has been used to investigate the role of polarization in the CF3Cl:OH2 complex. The polarised electron densities of the monomers component are shown to be a good representation of the electron densities of complexes, especially CF3Cl. The point-charge model overestimates the polarization of the water molecule, which is likely because exchange repulsion is unaccounted for in the classical model calculations.

Synthesis and Structural Characterization of a Series of MnIIIOR Complexes, Including a Water-Soluble MnIIIOH That Promotes Aerobic Hydrogen-Atom Transfer

Hydrogen-atom-transfer (HAT) reactions are a class of proton-coupled electron-transfer (PCET) reactions used in biology to promote substrate oxidation. The driving force for such reactions depends on both the oxidation potential of the catalyst and the pKa value of the proton-acceptor site. Both high-valent transition-metal oxo M(IV)═O (M = Fe, Mn) and lower-valent transition-metal hydroxo compounds M(III)OH (M = Fe, Mn) have been shown to promote these reactions. Herein we describe the synthesis, structure, and reactivity properties of a series of Mn(III)OR compounds [R = (p)NO2Ph (5), Ph (6), Me (7), H (8)], some of which abstract H atoms. The Mn(III)OH complex 8 is water-soluble and represents a rare example of a stable mononuclear Mn(III)OH. In water, the redox potential of 8 was found to be pH-dependent and the Pourbaix (E(p,c) vs pH) diagram has a slope (52 mV pH(-1)) that is indicative of the transfer a single proton with each electron (i.e., PCET). The two compounds with the lowest oxidation potential, hydroxide- and methoxide-bound 7 and 8, are found to oxidize 2,2',6,6'-tetramethylpiperidin-1-ol (TEMPOH), whereas the compounds with the highest oxidation potential, phenol-ligated 5 and 6, are shown to be unreactive. Hydroxide-bound 8 reacts with TEMPOH an order of magnitude faster than methoxide-bound 7. Kinetic data [kH/kD = 3.1 (8); kH/kD = 2.1 (7)] are consistent with concerted H-atom abstraction. The reactive species 8 can be aerobically regenerated in H2O, and at least 10 turnovers can be achieved without significant degradation of the "catalyst". The linear correlation between the redox potential and pH, obtained from the Pourbaix diagram, was used to calculate the bond dissociation free energy (BDFE) = 74.0 ± 0.5 kcal mol(-1) for Mn(II)OH2 in water, and in MeCN, its BDFE was estimated to be 70.1 kcal mol(-1). The reduced protonated derivative of 8, [Mn(II)(S(Me2)N4(tren))(H2O)](+) (9), was estimated to have a pKa of 21.2 in MeCN. The ability (7) and inability (5 and 6) of the other members of the series to abstract a H atom from TEMPOH was used to estimate either an upper or lower limit to the Mn(II)O(H)R pKa based on their experimentally determined redox potentials. The trend in pKa [21.2 (R = H) > 16.2 (R = Me) > 13.5 (R = Ph) > 12.2 (R = (p)NO2Ph)] is shown to oppose that of the oxidation potential E(p,c) [-220 (R = (p)NO2Ph) > -300 (R = Ph) > -410 (R = Me) > -600 (R = H) mV vs Fc(+/0)] for this particular series.

Reaction Mechanism of Water Oxidation Catalyzed by Iron Tetraamido Macrocyclic Ligand Complexes – A DFT Study

AbstractDensity functional calculations are used to elucidate the reaction mechanism of water oxidation catalyzed by iron tetraamido macrocyclic ligand (TAML) complexes. The oxidation of the starting TAML–Fe3+–OH2 complex by removing three electrons and two protons leads to the formation of a key intermediate, TAML·–Fe5+=O, which can undergo nucleophilic attack by either a water molecule or a nitrate ion. Both pathways involve attack on the oxo group and lead to the production of O2. The water attack is more favoured and has a total barrier of 15.4 kcal/mol. The alternative nitrate attack pathway has a barrier of 19.5 kcal/mol. Nitrate functions as a cocatalyst by first donating an oxygen atom to the oxo group to form O2 and a nitrite ion, which can then be re‐oxidized to regenerate a nitrate ion. Three possible competing pathways result in ligand modification, namely, water and nitrate attack on the ligand, as well as ligand amide oxidation. The water attack on the ligand has a low barrier of only 10.9 kcal/mol and leads to the opening of the benzene ring, which explains the observation of fast catalyst degradation. The lack of activity or lower activity of other catalysts with different substituents is also rationalized.

Dinuclear transition metal complexes in carbon nanostructured materials synthesis

Carbon nanomaterials (CNMs) were prepared with two similar techniques using organometallic complexes as catalysts precursors. Chemical vapour deposition (CVD) and pyrolysis with chlorine gas approaches were employed in order to explore the effect of dinuclear transition metal compounds [Fe2(CO)6(μ-S2C6H2X2), (X=OH, Cl)] in synthesis of CNMs. Our to-date results have shown these complexes generate different carbonaceous materials when they are used in bulk, it was also observed that their performances in synthesis differ even though these compounds are analogous. With X=OH complex used in CVD process, metal nanoparticles of ca. 20–50 nm in size and embedded in carbon matrix were obtained. X=C1 complex has been used in pyrolysis experiments and showed an entire volatilisation or no reaction, depending on selected temperature. Furthermore, obtaining of a new tetranuclear iron cluster is presented in this work.

Effects of Proton Acceptors on Formation of a Non-Heme Iron(IV)–Oxo Complex via Proton-Coupled Electron Transfer

Rates of formation of a non-heme iron(IV)-oxo complex, [Fe(IV)(O)(N4Py)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), via electron-transfer oxidation of [Fe(III)(OH)(N4Py)](2+) in acetonitrile (MeCN) containing H2O (0.56 M) were accelerated as much as 390-fold by addition of proton acceptors such as CF3COO(-), TsO(-) (p-MeC6H4SO3(-)), NsO(-) (o-NO2C6H4SO3(-)), DNsO(-) (2,4-(NO2)2C6H3SO3(-)), and TfO(-) (CF3SO3(-)). The acceleration effect of proton acceptors increases with increasing basicity of the proton acceptors. The one-electron oxidation potential of [Fe(III)(OH)(N4Py)](2+) was shifted from 1.24 to 0.96 V vs SCE in the presence of TsO(-) (10 mM). The electron-transfer oxidation of Fe(III)-OH complex was coupled with the deprotonation process by proton acceptors in which deuterium kinetic isotope effects were observed when H2O was replaced by D2O.

Heterogeneous activation of oxone with CoMg/SBA-15 for the degradation of dye Rhodamine B in aqueous solution

A novel heterogeneous Co catalyst CoMg/SBA-15 was prepared through a two-step incipient wetness impregnation of Mg and Co into mesoporous silica SBA-15 and used for the activation of oxone to generate sulphate radicals for degrading Rhodamine B (RhB) in aqueous solution. The CoMg/SBA-15 was characterized by several techniques such as XRD, N2 adsorption–desorption, CO2-TPD, TEM and SEM. It was found that the CoMg/SBA-15 existed as agglomerates with the particle size more than 0.3μm, and Co and Mg occurred mainly both inside and outside the support pores in the form of cubic spinel Co3O4 and Mg oxide crystallites, respectively. Loading Mg into the support increased the dispersion of Co3O4 on the support and generated the remarkable basicity of the catalyst surface promoting the formation of surface Co–OH complex. The CoMg/SBA-15 still displayed the long-range ordered arrangement of the channels in structure with the reduced pore diameter and surface area compared with the SBA-15. The Co/SBA-15–oxone–RhB system, as a test control, was demonstrated to be efficient for the activation of oxone producing sulphate radicals for the degradation of RhB in solution. And the increase of Co/SBA-15 and oxone dosages had the positive effect on the degradation efficiency and rate, with the almost complete RhB degradation in 60min and the Co leaching concentration less than 43μg/L and the leaching percent less than 0.40% at appropriate Co/SBA-15 and oxone dosages. In addition, the degradation followed the first-order kinetics. The CoMg/SBA-15 exhibited much higher activity than Co/SBA-15 and Co/MgO with the same Co loading in degrading RhB by sulphate radicals from oxone, with nearly 100% degradation in 5min, the Co leaching concentration of 80μg/L and the leaching percent of 0.96%, and almost 100% TOC removal under appropriate conditions achieved. The CoMg/SBA-15 also displayed stable performance during 25 runs of reuse. Based on the UV–vis spectra and TOC measurement, the degradation mechanism of RhB in the presence of CoMg/SBA-15 and oxone was proposed. It is believed that CoMg/SBA-15 can be widely applied in the catalytic oxidation with oxone for the degradation of the refractory organic pollutants such as dye RhB in water.

Electrooxidation of methanol in an alkaline fuel cell: determination of the nature of the initial adsorbate

It is essential to correctly determine the nature of the initial adsorbate in order to calculate the pathway for any given reaction. Recent literature provides conflicting information on the first step in the methanol decomposition pathway. This work sets out to establish what role the solution and the surface have to play in the initial adsorption-deprotonation process. Density functional theory (DFT) calculations, in combination with a cluster-continuum model approach are used to resolve the nature of the adsorbing species. We show that methanol is the dominant species in solution over methoxide, and also has a smaller barrier to adsorption. The nature of the surface species is revealed to be a methanol-OH complex.

Solvent rearrangements during the transition from hydrophilic to hydrophobic solvation

We present an ab initio Born–Oppenheimer molecular dynamics study of the early time solvent dynamics after electron abstraction from aqueous iodide. An initial response occurs within ∼75fs, corresponding to a water molecule sharing almost one electron with the iodine. This is followed by the formation of a transient I0⋯OH2 complex within ∼500fs. Further insight into the driving forces for this complex are obtained using an energy decomposition analysis and frequency calculations of small clusters. It is shown that the anisotropic solvation shell structure of iodide before electron abstraction is likely to be an important factor in the formation of the complex.

Metal complexes with varying intramolecular hydrogen bonding networks

Alfred Werner described the attributes of the primary and secondary coordination spheres in his development of coordination chemistry. To examine the effects of the secondary coordination sphere on coordination chemistry, a series of tripodal ligands containing differing numbers of hydrogen bond (H-bond) donors were used to examine the effects of H-bonds on Fe(II), Mn(II)–acetato, and Mn(III)–OH complexes. The ligands containing varying numbers of urea and amidate donors allowed for systematic changes in the secondary coordination spheres of the complexes. Two of the Fe(II) complexes that were isolated as their Bu4N+ salts formed dimers in the solid-state as determined by X-ray diffraction methods, which correlates with the number of H-bonds present in the complexes (i.e., dimerization is favored as the number of H-bond donors increases). Electron paramagnetic resonance (EPR) studies suggested that the dimeric structures persist in acetonitrile. The Mn(II) complexes were all isolated as their acetato adducts. Furthermore, the synthesis of a rare Mn(III)–OH complex via dioxygen activation was achieved that contains a single intramolecular H-bond; its physical properties are discussed within the context of other Mn(III)–OH complexes.

Preparation and structural properties of InIII–OH complexes

The use of the tripodal ligands tris[(N′-tert-butylureaylato)-N-ethyl]aminato ([H3buea]3−) and the sulfonamide-based N,N′,N″-[2,2′,2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzene-sulfonamidato) ([MST]3−) has led to the synthesis of two structurally distinct In(III)–OH complexes. The first example of a five-coordinate indium(III) complex with a terminal hydroxide ligand, K[InIIIH3buea(OH)], was prepared by addition of In(OAc)3 and water to a deprotonated solution of H6buea. X-ray diffraction analysis, as well as FTIR and 1H NMR spectroscopic methods, provided evidence for the formation of a monomeric In(III)–OH complex. The complex contains an intramolecular hydrogen bonding (H-bonding) network involving the In(III)–OH unit and [H3buea]3− ligand, which aided in isolation of the complex. Isotope labeling studies verified the source of the hydroxo ligand as water. Treatment of the [InIIIMST] complex with a mixture of 15-crown-5 ether and NaOH led to isolation of the complex [15-crown-5⊃NaI-(μ-OH)-InIIIMST], whose solid-state structure was confirmed using X-ray diffraction methods. Nuclear magnetic resonance studies on this complex suggest it retains its heterobimetallic structure in solution.

Family of Carboxylate- and Nitrate-diphenoxo Triply Bridged Dinuclear NiIILnIII Complexes (Ln = Eu, Gd, Tb, Ho, Er, Y): Synthesis, Experimental and Theoretical Magneto-Structural Studies, and Single-Molecule Magnet Behavior

Seven acetate-diphenoxo triply bridged M(II)-Ln(III) complexes (M(II) = Ni(II) and Ln(III) = Gd, Tb, Ho, Er, and Y; M(II) = Zn(II) and Ln(III) = Ho(III) and Er(III)) of formula [M(μ-L)(μ-OAc)Ln(NO(3))(2)], one nitrate-diphenoxo triply bridged Ni(II)-Tb(III) complex, [Ni(μ-L)(μ-NO(3))Tb(NO(3))(2)]·2CH(3)OH, and two diphenoxo doubly bridged Ni(II)-Ln(III) complexes (Ln(III) = Eu, Gd) of formula [Ni(H(2)O)(μ-L)Ln(NO(3))(3)]·2CH(3)OH have been prepared in one pot reaction from the compartmental ligand N,N',N"-trimethyl-N,N"-bis(2-hydroxy-3-methoxy-5-methylbenzyl)diethylenetriamine (H(2)L). Moreover, Ni(II)-Ln(III) complexes bearing benzoate or 9-anthracenecarboxylate bridging groups of formula [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN have also been successfully synthesized. In acetate-diphenoxo triply bridged complexes, the acetate bridging group forces the structure to be folded with an average hinge angle in the M(μ-O(2))Ln bridging fragment of ~22°, whereas nitrate-diphenoxo doubly bridged complexes and diphenoxo-doubly bridged complexes exhibit more planar structures with hinge angles of ~13° and ~2°, respectively. All Ni(II)-Ln(III) complexes exhibit ferromagnetic interactions between Ni(II) and Ln(III) ions and, in the case of the Gd(III) complexes, the J(NiGd) coupling increases weakly but significantly with the planarity of the M-(O)(2)-Gd bridging fragment and with the increase of the Ni-O-Gd angle. Density functional theory (DFT) theoretical calculations on the Ni(II)Gd(III) complexes and model compounds support these magneto-structural correlations as well as the experimental J(NiGd) values, which were found to be ~1.38 and ~2.1 cm(-1) for the folded [Ni(μ-L)(μ-OAc)Gd(NO(3))(2)] and planar [Ni(H(2)O)(μ-L)Gd(NO(3))(3)]·2CH(3)OH complexes, respectively. The Ni(II)Dy(III) complexes exhibit slow relaxation of the magnetization with Δ/k(B) energy barriers under 1000 Oe applied magnetic fields of 9.2 and 10.1 K for [Ni(μ-L)(μ-BzO)Dy(NO(3))(2)] and [Ni(μ-L)(μ-9-An)Dy(9-An)(NO(3))(2)]·3CH(3)CN, respectively.

Effects of a Single Water Molecule on the OH + H2O2 Reaction

The effect of a single water molecule on the reaction between H(2)O(2) and HO has been investigated by employing MP2 and CCSD(T) theoretical approaches in connection with the aug-cc-PVDZ, aug-cc-PVTZ, and aug-cc-PVQZ basis sets and extrapolation to an ∞ basis set. The reaction without water has two elementary reaction paths that differ from each other in the orientation of the hydrogen atom of the hydroxyl radical moiety. Our computed rate constant, at 298 K, is 1.56 × 10(-12) cm(3) molecule(-1) s(-1), in excellent agreement with the suggested value by the NASA/JPL evaluation. The influence of water vapor has been investigated by considering either that H(2)O(2) first forms a complex with water that reacts with hydroxyl radical or that H(2)O(2) reacts with a previously formed H(2)O·OH complex. With the addition of water, the reaction mechanism becomes much more complex, yielding four different reaction paths. Two pathways do not undergo the oxidation reaction but an exchange reaction where there is an interchange between H(2)O(2)·H(2)O and H(2)O·OH complexes. The other two pathways oxidize H(2)O(2), with a computed total rate constant of 4.09 × 10(-12) cm(3) molecule(-1) s(-1) at 298 K, 2.6 times the value of the rate constant of the unassisted reaction. However, the true effect of water vapor requires taking into account the concentration of the prereactive bimolecular complex, namely, H(2)O(2)·H(2)O. With this consideration, water can actually slow down the oxidation of H(2)O(2) by OH between 1840 and 20.5 times in the 240-425 K temperature range. This is an example that demonstrates how water could be a catalyst in an atmospheric reaction in the laboratory but is slow under atmospheric conditions.

Aluminium fractionation and speciation in bulk and rhizosphere of a grass soil amended with mussel shells or lime

Acid soils have a high proportion of Al in the exchange complex and are usually amended with lime to reduce the toxic effect of the free Al (Al3+). To this purpose, in some places like Galicia (NW Spain), there is a high production of wastes such as mussel shells that may substitute the lime. The aim of this work was to study the effect of different amending products derived from mussel shells on the Al chemistry in both bulk and rhizosphere, and on pasture production. The experiments were conducted on plots of an acid soil cultivated with grasses (Dactylis glomerata L., Trifolium repens L. and Lolium perenne L.). Each plot received its own treatment consisting of 1) commercial lime, 2) mussel shells dried and ground till 0–2mm (MDF), 3) mussel shells dried and ground till 2–4mm (MDC), 4) mussel shells heated (550°) and ground till <63μm (MHF), or 5) mussel shells heated (550°C) and ground till 0–2mm (MHC); one plot acted as control and was not treated. Each plot was replicated four times. The soil samples were collected after 16months and submitted to a general characterization. The Al was extracted from the soil by different solutions: ammonium oxalate (Alo=non-crystalline Al), sodium pyrophosphate (Alp=organically bound Al), copper chloride (Alcu=organo-Al complexes of low to medium stability) and ammonium chloride (exchangeable Al); the difference Alp-cu estimated the organo-Al complexes of high stability. From the soil water extracts, the Al was fractionated into acid-soluble (Al-polymers, colloids and organic complexes), non-labile Al (organic monomers) and labile Al (inorganic monomers, namely the species Al3+, Al–OH, Al–F and Al–SO4). For each plot, the production of the total dry matter and of that produced by the sown species, were also determined. With respect to the control, all the amending treatments increased the pH in the rhizosphere (5.11 in the control plots, 5.48–5.89 in the amended plots), which showed pH values higher than the bulk (5.13–5.60 in the amended bulk soil; 5.48–5.89 in the amended rhizosphere). Also the contents of C and N were higher in the rhizosphere than in the bulk, without difference among treatments. Concerning with Al chemistry, all the mussel shells derived products had effects similar to those of the commercial lime, with no difference among them. With respect to the control, in the soil solid phase all the treatments induced an increase in the formation of hydroxyl-aluminium complexes in the bulk (Alo: 3500mgkg−1 in the control, 3700–5500mgkg−1 in the amended plots) and organo-Al complexes of high stability in the rhizosphere (Alp-cu: 3563mgkg−1 in the control, 3550–5000mgkg−1 in the amended plots). The exchangeable Al diminished with all treatments, more in the rhizosphere (1.36cmol(+) kg−1 in the control, 0.24–0.47cmol(+) kg−1 in the amended plots) than in the bulk (2.83cmol(+) kg−1 in the control, 0.46–1.23cmol(+) kg−1 in the amended plots). Concerning the water extracts, the treatments induced an increase of organic complexes (polymers and monomers), more pronounced in the rhizosphere (non-labile Al: 0.17μmolL−1 in the control, 10.7–35.7μmolL−1 in the amended plots) than in the bulk (non-labile Al: 0.25μmolL−1 in the control, 0.25–3.57μmolL−1 in the amended plots). Further, in the treated plots the labile Al was dominated by Al–OH complexes, which are considered toxic but a lower level than the Al3+ and abounded in the control. The production of dry matter due to the sown species was about double in the plots treated with CL and MHF with respect to the control. We conclude that the products derived from mussel shells can substitute the commercial lime in the amending of acid soils, so increasing the value of the shells and limiting the environmental problems derived by their disposal.

Kinetics and Mechanism for Hydrolysis of α-Amino Acid Esters in Mixed Ligand Complexes with Zn(II)–Nitrilo-tris(methyl phosphonic Acid)

The kinetics of base hydrolysis of the alanine ethyl ester, in addition to glycine, histidine and methionine methyl esters in the presence of the Zn-NTP complex, were studied in aqueous solution by the pH-potentiometric technique, where NTP denotes the nitrilo-tris(methyl phosphonic acid) ligand. The kinetic data fits assumed that hydrolysis proceeds through formation of a M–OH complex, followed by an intramolecular OH− attack. The effect of an organic solvent on the hydrolysis of coordinated esters was investigated by measuring the rate of hydrolysis in dioxane–water solutions of different compositions at t=25.0 °C and I=0.1 mol⋅dm−3. The kinetics of base hydrolysis of the glycine methyl ester was studied at different temperatures. Activation parameters for the base hydrolysis of the complexes were evaluated.

Preparation of Organometallic Ruthenium–Arene–Diaminotriazine Complexes as Binding Agents to DNA

The reactions of two diaminotriazine ligands 2,4-diamino-6-(2-pyridyl)-1,3,5-triazine (2-pydaT) and 6-phenyl-2,4-diamino-1,3,5-triazine (PhdaT) with ruthenium-arene precursors led to a new family of ruthenium(II) compounds that were spectroscopically characterized. Four of the complexes were cationic, with the general formula [(η(6)-arene)Ru(κ(2)-N,N-2-pydaT)Cl]X (X=BF(4), TsO; arene=p-cymene: 1·BF(4), 1·TsO; arene=benzene: 2·BF(4), 2·TsO). The neutral cyclometalated complex [(η(6)-p-cymene)Ru(κ(2)-C,N-PhdaT*)Cl] (3) was also isolated. The structures of complexes 2·BF(4) and 3·H(2)O were determined by X-ray diffraction. Complex 1·BF(4) underwent a partial reversible-aquation process in water. UV/Vis and NMR spectroscopic measurements showed that the reaction was hindered by the addition of NaCl and was pH-controlled in acidic solution. At pH 7.0 (sodium cacodylate) Ru-Cl complex 1·BF(4) was the only species present in solution, even at low ionic strength. However, in alkaline medium (KOH), complex 1·BF(4) underwent basic hydrolysis to afford a Ru-OH complex (5). Fluorimetric studies revealed that the interaction of complex 1·BF(4) with DNA was not straightforward; instead, its main features were closely linked to ionic strength and to the [DNA]/complex ratio. The bifunctional complex 1·BF(4) was capable of interacting concurrently through both its p-cymene and 2-pydaT groups. Cytotoxicity and genotoxicity studies showed that, contrary to the expected behavior, the complex species was biologically inactive; the formation of a Ru-OH complex could be responsible for such behavior.

Origin of unipolarity in carbon nanotube field effect transistors

Several mechanisms have been proposed for the origin of unipolar p-type behavior in carbon nanotube (CNT) transistors including (i) O2 molecules trapped in the metal/CNT contact, (ii) OH radicals on the SiO2 surface, and (iii) O2/H2O coupling on the CNT surface. Nevertheless, the underlying mechanism is far from being clearly understood. Using density functional calculations, we propose that the SiO2 substrate induces wetting of moisture, which enhances the formation of CNT–OH complexes via several intermediate chemical reactions. As a consequence, the CNT–OH complex provides deep (occupied and unoccupied) acceptor levels near the valence band, acting as an electron trap center, which is the main cause of the asymmetric unipolar behavior of CNT transistors. Based on the theory, I–V characteristics are proposed in terms of gate bias and work function difference between metal and CNTs.

A heterogeneous Co3O4–Bi2O3 composite catalyst for oxidative degradation of organic pollutants in the presence of peroxymonosulfate

By using cobalt nitrate and bismuth nitrate as precursor salts and NaOH as a precipitation agent, Co3O4–Bi2O3 nanocomposite oxides (CBO) were prepared as a heterogeneous catalyst for the activation of peroxymonosulfate (PMS) by a conventional reverse co-precipitation method and post-calcination. The characterization with transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy demonstrated that there was a strong interaction between Bi and Co components in CBO. The presence of Bi increased the content of surface hydroxyl oxygen, which favored the formation of Co(II)–OH complexes that were vital for heterogeneous activation of PMS. CBO showed strong catalytic activity in the heterogeneous activation of PMS for degradation of organic pollutants such as methylene blue (MB), rhodamine B, phenol and 2,4-dichlorophenol. With the addition of 0.5 mmol L−1 PMS, CBO produced fast and full degradation of MB (20 μmol L−1) with the apparent rate constant of 0.36 min−1, being 8.6 fold of that (0.042 min−1) over nano-Co3O4. It decreased the cobalt leaching to 43 μg L−1, being much less than that (158 μg L−1) from Co3O4 under the same conditions. The effects of CBO loading, PMS concentration and calcination temperature on the degradation of MB and cobalt leaching were also investigated.

Influence of Doping on the Structural Transformations of the Proton Conducting Perovskite BaCe1xYxO3-D

From neutron diffraction it is known that the BaCeO3 perovskite undergoes a sequence of phase transformations from high temperature cubic C to rhombohedral R, to orthorhombic O1 (Imma) and to orthorhombic O2 (Pnma). Doping Y3+ on the Ce4+ site introduces charge compensating O vacancies (VO) that may be partially filled with OH complexes with exposition to H2O, so making the material an ionic conductor. Anelastic relaxation experiments have been carried out on samples doped with 2%Y and 10%Y; the real part s’(T) of the complex elastic compliance presents softenings at the transitions, and the loss s’’/s’ curves allow the content of VO and H to be monitored. Doping has a strong effect on the temperature of the Pnma/R transition: with 10%Y in the fully hydrated state TO1-R increases up to 750 K while after full outgassing falls to 500 K, meaning that the introduction of ~5% VO shifts the transition of 250 K. While the effect of cation substitution on the transitions temperature is easily explained in terms of simple arguments usually valid for perovskites based on bond length considerations, the remarkable stabilization of the R phase by VO requires to take into account the anomalous sequence of phase transitions of undoped BaCeO3, where the R structure transforms into orthorhombic Pnma on cooling with the loss of an octahedral tilt system.

A computational study on the relationship between formation and electrolytic dissociation of carbonic acid

Calculations at the B3LYP/6-311+G**, MPW1K/6-311+G**, and MP2/6-311+G** level theory were carried out for the CO2 + nH2O → H2CO3 + (n − 1)H2O chemical reaction, where n denotes the number of water molecules. For n = 1, 2, 3, and 4 water molecules, a concerted path (without intermediates) for the formation of H2CO3 was obtained. For n = 6(3 + 3) and n = 8(4 + 4) water molecules, the MPW1K and B3LYP/6-311+G** SCRF = PCM methods resulted in an ion-pair intermediate being formed. Here, +3 or +4 stands for the three or four catalytic water molecules. The catalytic water molecules are distinguished from the reaction participating ones (either three or four). For n = 3 + 5 and n = 3 + 10, two ion-pair intermediates were obtained using both the B3LYP and MPW1K DFT methods. In order to check the method and model dependence, furthermore, n = 3 + 17 and n = 3 + 27 reacting systems were examined. Here, a likely mechanism of formation and electrolytic dissociation of carbonic acid was found. First, the O2C–OH2 complex is formed. Second, it is isomerized to the Zundel cation H5O2 +. Third, the cation is converted to the carbonic acid. The isomerization, i.e., proton transfer, was computed to occur along the hydrogen-bonded network of the pentagon shape.