Facile functionalization by π-stacking of macroscopic substrates made of vertically aligned carbon nanotubes: Tracing reactive groups by electrochemiluminescence

We report a simple, fast and reliable non-covalent route of functionalization of macroscopic carbon nanotubes (CNTs) surfaces based on the π-stacking of CNTs sidewall with fluorescein derivatives (i.e., amino- and isothiocyanate-). The electrochemiluminescent emission of Ru(bpy)₃²⁺ labels bearing –COOH and –NH₂ side groups coupled with colorimetric and XPS measurements allowed to estimate the quantity of –NH₂ and –NCS functions obtained. The evaluation of reactivity suggests that functionalized CNTs substrates, in particular those carrying –NCS groups, are suitable to covalently bind probe molecules such as proteins and oligonucleotides, thus opening up the possibility of future application in genomics and proteomics fields.     

UV- and thermal-curing behaviors of dual-curable adhesives based on epoxy acrylate oligomers

Dual-curable adhesives were prepared using various epoxy acrylate oligomers, a reactive diluent, photoinitiators, a thermal-curing agent and a filler. The UV- and thermal-curing behaviors of the dual-curable adhesives were investigated using photo-differential scanning calorimetry (photo-DSC), Fourier transform infrared-attenuated total reflection (FTIR-ATR) spectroscopy, and the determination of the gel fraction, pendulum hardness and adhesion strength.The reaction rate and extent of UV curing were found to be strongly dependent on the concentration of CC bonds in the epoxy acrylate oligomers. The FTIR-ATR absorption peak areas representing the relative concentration of CC bonds in the epoxy acrylate oligomers and trifunctional monomer decreased with increase in UV dose because of photopolymerization. When the dual-curable adhesives were irradiated with UV light, the gel fraction increased with increase in CC bond contents in the epoxy acrylate oligomers. Also, after thermal curing, the gel fraction was highly enhanced due to the cross-linking reaction of the unreacted glycidyl groups in epoxy acrylate oligomers induced by the thermal-curing agent. This cross-linked structure of the dual-curable adhesives affects the pendulum hardness and adhesion strength.     

Cyclometalated platinum(II) complex with C^N^N tridentate ligand as sensitizer for lanthanide luminescence

The preparation, characterization and photophysical properties of heterobinuclear complexes {Pt(C^N^N)(CCbpy)}Ln(hfac)₃ (C^N^N = 2-(6-(naphthalen-3-yl)-4-phenylpyridin-2-yl)pyridine; HCCbpy = 5-ethynyl-2,2′-bipyridine; Ln = Nd, Eu, Yb; hfac = hexafluoroacetylacetonate) are described. With excitation at 390  λ_ex  500 nm which is the MLCT/LLCT absorption region of the Pt(C^N^N)(CCbpy) chromophore, lanthanide luminescence is successfully attained by Pt → Ln energy transfer from the platinum(II) antenna chromophore to the lanthanide center across the bridging CCbpy ligand.     

Oxidative dehydrogenation of ethane to ethylene over alumina-supported vanadium oxide catalysts: Relationship between molecular structures and chemical reactivity

The influence of vanadium oxide loading in the supported VO_x/Al₂O₃ catalyst system upon the dehydrated surface vanadia molecular structure, surface acidic properties, reduction characteristics and the catalytic oxidative dehydrogenation (ODH) of ethane to ethylene was investigated. Characterization of the supported VO_x/Al₂O₃ catalysts by XPS surface analysis and Raman spectroscopy revealed that vanadia was highly dispersed on the Al₂O₃ support as a two-dimensional surface VO_x overlayer with monolayer surface coverage corresponding to 9 V/nm². Furthermore, Raman revealed that the extent of polymerization of surface VO_x species increases with surface vanadia coverage in the sub-monolayer region. Pyridine chemisorption-IR studies revealed that the number of surface Brønsted acid sites increases with increasing surface VO_x coverage and parallels the extent of polymerization in the sub-monolayer region. The reducibility of the surface VO_x species was monitored by both H₂-TPR and in situ Raman spectroscopy and also revealed that the reducibility of the surface VO_x species increases with surface VO_x coverage and parallels the extent of polymerization in the sub-monolayer region. The fraction of monomeric and polymeric surface VO_x species has been quantitatively calculated by a novel UV–Vis DRS method. The overall ethane ODH TOF value, however, is constant with surface vanadia coverage in the sub-monolayer region. The constant ethane TOF reveals that both isolated and polymeric surface VO_x species possess essentially the same TOF value for ethane activation. The reducibility and Brønsted acidity of the surface VO_x species, however, do affect the ethylene selectivity. The highest selectivity to ethylene was obtained at a surface vanadia density of 2.2 V/nm², which corresponds to a little more than 0.25 monolayer coverage. Below 2.2 V/nm², exposed Al support cations are responsible for converting ethylene to CO. Above 2.2 V/nm², the enhanced reducibility and surface Brønsted acidity appear to decrease the ethylene selectivity, which may also be due to higher conversion levels. Above monolayer coverage, crystalline V₂O₅ nanoparticles are also present and do not contribute to ethane activation, but are responsible for unselective conversion of ethylene to CO. The crystalline V₂O₅ nanoparticles also react with the Al₂O₃ support at elevated temperatures via a solid-state reaction to form crystalline AlVO₄, which suppresses ethylene combustion of the crystalline V₂O₅ nanoparticles. The molecular structure–chemical characteristics of the surface VO_x species demonstrate that neither the terminal VO nor bridging VOV bonds influence the chemical properties of the supported VO_x/Al₂O₃ catalysts, and that the bridging VOAl bond represents the catalytic active site for ethane activation.     

Effects of sodium promoter on the mechanism of biphenol hydrogenation over Pd/C catalyst

The effect of sodium promoter on the catalytic hydrogenation of biphenol (BP) was investigated. Several reaction products were identified and the change in their distribution with time was analyzed to find the reaction mechanism. Different amount of sodium salt was impregnated on Pd/C to observe its effect on the composing reactions of BP hydrogenation. The existence of sodium metal decreased the CC bond hydrogenation, but accelerated the CO bond hydrogenation resulting in the increase of the yield to bicyclohexyl-4,4′-diol (BHD). The promotional effect of Na on the supported palladium on carbon catalysts were explained by electronic and geometric factors.     

Electro-oxidation of chlorophenols at glassy carbon electrodes modified with polyNi(II)complexes

The effect of the ligand macrocycle (phenylporphyrin (PP) or phthalocyanine (Pc)) and of the ligand substituent (NH₂ or SO₃⁻) on the catalytic activity for the electro-oxidation in a pH 11 buffer electrolyte of 2- and 4-chlorophenol (2-CP and 4-CP), 2,4- and 2,6-dichlorophenol (2,4-DCP and 2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) at glassy carbon electrodes modified with electropolymerized Ni(II) macrocycles was studied. The polyphenolic residue deposited at the electrode surface was characterized by cyclic voltammetry, impedance measurements, ex situ Fourier transform infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). A band of aliphatic CO stretching in the IR spectrum of the fouling film produced by potential cycling in 2,4,6-TCP indicated that the aromatic ring had been broken, yielding ketones, aldehydes and/or carboxylic acids. The sulphonated Ni(II) polymers, which showed the Ni(III)/Ni(II) process in the CV, had XP spectra typical of paramagnetic Ni(II), indicating that they contained Ni(OH)₂ clusters. On the contrary, the CVs of the amino Ni(II) did not show the Ni(III)/Ni(II) process at all, this process appearing only after previous activation by potential cycling, and only to a small extent. As was to be expected, the XP spectra of activated amino films corresponded to diamagnetic Ni(II), showing that the concentration of Ni(OH)₂ clusters was very small. The amino films were less active than the sulpho films for the oxidation of chlorophenols, in agreement with the lower concentration of Ni(OH)₂ clusters in the former films. For all electrodes the highest activity was observed for 2,4,6-TCP, since its oxidation yields a phenolic residue which is much more porous than those produced by the other CPs.     

The effect of crystallographic orientation and solution aging on the electrical properties of sol–gel derived Pb(Zr0.45Ti0.55)O3 thin films

Lead zirconate titanate—Pb(Zr_0.45Ti_0.55)O₃ thin films are grown on Pt_1 1 1/Ti/SiO₂/Si_1 0 0 substrates by a sol–gel method with 1 0 0/0 0 1 and 1 1 1 preferred orientations. Film orientation was controlled mainly by the annealing process and temperature. Films with 1 0 0/0 0 1 orientation consist of a uniform microstructure with micron size grains, whereas films with 1 1 1 orientation contain sub-micron grains. The electrical properties were influenced markedly by the microstructure and orientation of the films. The 1 1 1 oriented films exhibit a square-like hysteresis loop with remnant polarization (P_r) reaching 46 μC/cm² under 550 kV/cm, whereas 1 0 0/0 0 1 oriented films have a P_r of 20 μC/cm² with more slim hysteresis curves. Aging of the precursor solutions resulted in films growing with 1 0 0/0 0 1 texture and displaying inferior electrical properties.     

Comparison of the chemical composition of boron-doped diamond surfaces upon different oxidation processes

In spite of the high stability of polycrystalline diamond, oxidation of the hydrogenated surface is relatively easy to perform. This results in the introduction of ether (C–O–C), carbonyl (CO) and hydroxyl (C–OH) groups on the surface. For further surface functionalization, it is important to quantify the presence of each group on the diamond surface when different oxidation processes are used. In this paper, we investigate the composition of oxidized boron-doped diamond surfaces using X-ray photoelectron spectroscopy (XPS) when electrochemical, photochemical or oxygen plasma methods were employed to introduce oxygen functionalities on as-deposited diamond interfaces. Cyclic voltammetry and C–V measurements were additionally performed to identify more clearly the formation of C–OH, C–O–C and/or CO functions.     

Characterization and activity of vanadia-promoted Pt/ZrO2 catalysts for the water–gas shift reaction

Pt/ZrO₂ catalysts for the water–gas shift (WGS) were promoted with various amounts of vanadia. Analyses by XRD, N₂ adsorption, Raman, and UV–vis DRS showed that vanadia is present below monolayer coverage as monovanadate and polyvanadate, with the former dominating at lower loadings, and that following monolayer formation, VO₅ species appear, with the eventual generation of V₂O₅ and ZrV₂O₇ for a vanadia weight loading of 13%. Though in all cases vanadia induced an enhancement in WGS activity, the best catalyst, that contained 3 wt.% of vanadia, gave a rate that was nearly double that of the unpromoted Pt/ZrO₂. That superior global activity probably results from the monovanadate that is the main species at low loadings. It is believed that monovanadate promotes the WGS by rendering the support's surface more oxidizing through its VOZr bonds.     

Oxidative dehydrogenation of ethane over vanadium-based hexagonal mesoporous silica catalysts

Vanadium-containing hexagonal mesoporous silica catalysts were tested in oxidative dehydrogenation of ethane. V-HMS catalysts (0.3–9.0 wt.% V) were prepared by impregnation with solution of vanadyl acetylacetonate, and by incorporation of vanadium in the synthesis process. The prepared catalysts achieved a different distribution of vanadium species (isolated monomeric units with tetrahedral coordination, oligomeric units connected by VOV bonds up to distorted tetrahedral coordination, two-dimensional polymeric units in octahedral coordination, and bulk vanadium oxides). The contribution deals with the understanding of the relationship between the distribution of vanadium species and their activity in ODH of ethane. It has been found that both monomeric and oligomeric vanadium species play important role in ODH of ethane. The activity correlated with the population of oligomeric tetrahedrally coordinated vanadium species, which were evidenced by the UV–vis band at 315 nm. To analyze this effect, V-HMS catalysts were characterized by means of UV–vis spectroscopy, H₂-TPR and N₂-adsorption.     

Modification of electrodes with nanostructured functionalized thiadiazole polymer film and its application to the determination of ascorbic acid

We report the electropolymerization of 2-amino-1,3,4-thiadiazole (ATD) on glassy carbon (GC) and indium tin oxide (ITO) electrodes in 0.10 M H₂SO₄. The electropolymerized ATD (p-ATD) film was characterized by cyclic voltammetry, attenuated total reflectance (ATR)-FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The AFM image showed that the p-ATD formed a spherical-like structure with a thickness of 25 nm. XPS of the p-ATD film showed binding energies at 398.7, 400.3 and 401.3 eV in the N 1s region corresponding to –N, –NH– and –N⁺H–, respectively, and at 285.5 and 287.0 eV in the C 1s region corresponding to C–N and CN, respectively. The appearance of binding energies at 285.5 and 287.0 eV confirmed that the p-ATD film proceeded via C–N and CN linkages and not via C–C or CC linkages. The p-ATD film deposited on the GC electrode was successfully used for the determination of ascorbic acid (AA) at physiological pH. The amperometric current was increased linearly from 7.5 × 10⁻⁸ to 2.0 × 10⁻⁵, and the detection limit was found to be 0.28 nM (S/N = 3).     

Adsorption mechanism and property of novel composite material PMAA/SiO2 towards phenol

In this paper, functional macromolecule poly(methacrylic acid) (PMAA) was grafted on the surface of silica gel particles using 3-methacryloxypropyl trimethoxysilane (MPS) as intermedia, and the grafted particle PMAA/SiO₂ with strong adsorption ability for phenol was prepared. The adsorption mechanism and properties of PMAA/SiO₂ for phenol were researched by static and dynamic methods. The experimental results showed that PMAA/SiO₂ possesses strong adsorption ability for phenol with interaction of three kinds of hydrogen bonds including peculiar O–Hπ hydrogen bond (aromatic hydrogen bond) and O–HOC π hydrogen bond. The saturated adsorption amount could reach up to 162.88 mg g⁻¹. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and temperature were found to have great influence on the adsorption amount. Finally, PMAA/SiO₂ was observed to possess excellent reusability properties as well.     

Preparation and photocatalytic activity of hierarchically mesoporous-macroporous TiO2−xNx

Hierarchically mesoporous-macroporous N-doped titania materials were fabricated by the thermal treatment of spontaneously formed hierarchical mesoporous-macroporous titanias with urea solution, in order to extend their photocatalytic applications from ultraviolet to visible-light range. The resultant meso-macroporous TiO_2−xN_x exhibited a bicrystalline (anatase and brookite) framework with high surface area and large porosity. The content of the doped nitrogen increased with the urea solution and the nitridation temperature, and the band gaps narrowed from 3.14 to 2.48 eV. The formation of OTiN bonds in the meso-macroporous TiO_2−xN_x was confirmed by the XPS and FT-IR spectra. The photocatalytic activity was evaluated by the photodegradation of methyl orange and rhodamine B under UV and visible-light irradiation, respectively. The significant improvement of photocatalytic activity for water contaminant decomposition under both UV and visible-light irradiation was observed, which is due to the incorporation of nitrogen into the titania lattice and the presence of the hierarchical meso-macroporous structure.     

Topological analysis of catalytic reaction networks: Methanol decomposition on Pt(111)

We describe our new reaction route (RR) graph approach as a powerful new tool for topological mechanistic and kinetic analysis of catalytic reaction networks, illustrated here with the help of methanol decomposition on Pt(111). In this approach a graph-theoretic network of molecular reaction steps is first constructed for the overall reaction (OR), on which each mechanistic step is represented by a directed branch interconnected at nodes, such that all conceivable reaction pathways can then be traced on it simply as walks or paths. Further, the network is consistent with the basic laws of flow graphs, so that it is suitable for a quantitative analysis. In fact, a direct analogy can be made to an equivalent wiring diagram, which allows tools of electric circuit analysis, namely, Kirchhoff's laws of current (rate) and potential (affinity), to be directly utilized for a rigorous flux analysis of the network. As a result, the dominant pathways as well as the rate-limiting steps (RLS) become transparent. This furthermore facilitates network pruning to retain only the essential steps and pathways. The RR graph approach when combined with ab initio kinetics, thus, provides a rigorous new framework for analyzing the mechanism and kinetics of catalytic reactions. It is, thus, found that methanol decomposition proceeds exclusively via the initial CH dehydrogenation step rather than through OH bond activation.     

Mn(II), Co(II) and Ni(II) complexes of 4-(2-thiazolylazo)resorcinol: Syntheses, characterization, catalase-like activity, thermal and electrochemical behaviour

Manganese(II), cobalt(II) and nickel(II) acetates react with the ligand, 4-(2-thiazolylazo)resorcinol, to form complexes of general formula [ML₂] for MCo(II), Ni(II) and [ML₂]·2H₂O for MMn(II). Each of the azo complexes was characterized using elemental analysis, electrolytic conductance, UV–visible spectroscopy and magnetic susceptibility. An octahedral structure is proposed for all complexes prepared, which molar conductance data revealed to be non-electrolytes. IR spectra reveal that the ligand is coordinated to the metal ions in a tridentate manner via the resorcinol OH, azo N and thiazole N groups as donor sites. The electrochemical behaviour of the ligand and its complexes were obtained by cyclic voltammetry. Thermal decomposition studies were undertaken to secure additional information on the structure of the investigated compounds. The manganese(II) complex catalysed the disproportionation of hydrogen peroxide in the presence of imidazole.     

Self-assembly hydrothermal assisted synthesis of mesoporous anatase in the presence of ethylene glycol

Mesoporous nanocrystalline anatase was prepared hydrothermally employing P123 as structure-directing agent. Ethylene glycol was used as a key synthesis parameter to fine tune the morphology, crystal size and pore size of the resultant mesophases. The incorporation of EG in the synthesis gel resulted in the formation of 1–2 μm sphere-like shapes and led to an increase in the specific surface area from 95 to 170 m²/g, decrease in the average pore size from 11 to 4.8 nm, and decrease in the average crystallite size from 17 to 12 nm. These mesophases were used as photocatalysts for the UV degradation of methylene blue and methyl orange. The mesoporous anatase phases photodegraded MB 1.5–3× faster than commercially available P25 and showed limited photocatalytic behavior for methyl orange.     

Effects of zinc oxide on thermal shock behavior of zinc sulfide– silicon dioxide ceramics

Thermal shock resistances of ZnO and non-ZnO containing ZnS–SiO₂ composite ceramics are observed using water quenching method. The residual strengths are measured as function of quenching temperature differences. The thermal shock damage parameters R and R are evaluated to compare with experimental results. Specimens with low thermal shock damage parameters show acute strength degradation up to 76% at a lower quenching temperature difference of 250 °C. The 1% ZnO containing specimen with medium density and higher thermal shock damage parameter values demonstrates a minimal strength drop of 36% at a higher quenching temperature difference of 300 °C. The evaluated R and R values correspond well with the residual strength at elevated temperature difference. It implies that the good thermal shock resistance of ZnS–SiO₂ system can be achieved by improving fracture toughness with moderate ZnO addition and pores.     

A quantitative electron-microscopic investigation of α-phase lamellae in isotactic polypropylene fractions

Lamellar thicknesses and cross-hatching frequencies in α-isotactic polypropylene have been measured for two series of fractions using linear nucleation to provide large arrays of oriented lamellae in row structures for sampling. One series is of high tacticity polymers differing in molecular mass from 6 × 10⁴ to 8 × 10⁵, the other has low and high tacticity materials for 9 × 10⁴ and 2 × 10⁵ masses. These have allowed the differing influences of both molecular mass and tacticity to be evaluated. Lamellar thicknesses increase with molecular mass to 5 × 10⁵ then level off. This is consistent with the fold surface increasing its free energy by 20% for longer molecules as its structure becomes progressively more complex. Except for the lowest fraction, the thickness of cross-hatching lamellae is less than that of its radial neighbours because of differential thickening. The frequency of cross-hatching is greatest for the least tactic fraction but decreases linearly with molecular length. This dependence suggests that chain ends play a key role in initiation probably by laying down the first segment in epitaxial orientation. This suggestion could also account for the reduced thermal stability of spherulite centres and regions of high cross-hatching density where there is competition for chain ends between thickening and cross-hatching. The curvature of lamellae at the very end of a row mirrors the dependence of lamellae thickness with molecular mass and allows cilia pressure, the factor strongly involved in causing the lamellar divergence underlying spherulitic growth, to be estimated as 100 Pa.