Effect of hydrophilic group on thin film formation using redox-active surfactants with an azobenzene group

Thin films of organic pigments were prepared at higher than pH 1 by the contact plating method using an anionic surfactant (AZNa, first figure of this article (part c) (n = 4)) containing an azobenzene moiety. The effects of hydrophilic group of the surfactants on the rate of following reaction of the reduction product were studied by cyclic voltammetry. The positive shift of the reduction peak potential of AZNa compared to those of cationic and non-ionic surfactants was ascribed to higher rate of following reaction of reduction product due to the presence of the anionic hydrophilic group of the surfactant. The present investigation revealed that the anionic hydrophilic group accelerates the cleavage of the NN bond of the azobenzene group. This phenomenon enabled us to prepare the organic thin film at higher pH condition.     

Aerobic oxidation of alcohols over novel crystalline MoVO oxide

Novel crystalline MoVO oxide was employed as the catalyst in the aerobic oxidation of alcohols to the corresponding carbonyl compounds. Reactions were mainly conducted at 353 K in pure oxygen or air (1 atm). The selectivities for benzaldehydes were more than 95% in all cases. The conversions of benzyl alcohols varied from 10% to 99% depending on the substituent. A Hammett plot gave a moderate ρ-value of −0.249 (r² = 0.98), suggesting that the reaction processes may involve hydride abstraction. The oxidation of primary alkanols afforded aldehydes, and secondary alcohols were mainly dehydrated to olefins. It was found that the conversion of linear alkanols decreased with the length of alkanols. Kinetic analysis showed that catalytic reaction rate was first-order dependent on the concentrations of substrate and of catalyst. The apparent activation energy was estimated to be 45.7 kJ mol⁻¹. Catalytic reactions took place on the 6- or 7-member rings on the a–b basal plane, where highly dense unsaturated metal cation centers and oxygen anion might serve as catalytic active sites.     

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.     

Two novel 3D bimetallic oxide framework with 16-membered wheel clusters based on {Mo5O16} ribbon-like chains

Two hybrid compounds based on {Mo₅O₁₆} ribbon-like chains, [M(3-pt)₂(Mo₅O₁₆)]·H₂O (M = Co, Mn) (1 and 2) {3-pt = 5-(3-pyridyl)-tetrazole}, have been hydrothermally synthesized and characterized by single crystal X-ray diffraction. Three-dimensional Mo/O/M^II/tetrazole frameworks of the title compounds are constructed from 1D infinite ribbon-like [Mo₅O₁₆]²⁻ chains covalently linked through [M(3-ptz)]²⁺ fragments via OM and NMo coordinate bonds. It is noteworthy that the isostructural compounds contain an unprecedented 3D bimetallic oxide network with 16-membered wheel clusters in which two parallel interdigitated stacks of 3-pt ligands are trapped. Remarkably, the title complexes represent the first two examples of the solid materials containing {Mo₅O₁₆} ribbon-like chains.     

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.     

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.     

Enhancing effect of S and F moieties on the performance of Fenton system in the selective oxidation of propane

The selective oxidation of propane to oxygenated products (isopropanol, n-propanol, propionic aldehyde and acetone) mediated by the Fe(II)/H₂O₂ Fenton system at 80 °C in the presence of solid acid and superacid promoters containing S and F moieties has been studied. The occurrence of a radical reaction pathway accounting for the activation of the CH bonds of the propane molecule by OH radicals has been proved by assessing the inhibiting effect of both Cl⁻ and NO₃⁻ radical scavengers and organic (CH₃COOH, CH₃CN, DMSO) reaction media on the reaction pattern. S and F functionalities of several solid agents promote the electron transfer processes controlling the H₂O₂ activation. Any effect of the Brönsted acid features of the solid promoters on the reaction kinetics and pathway has been disregarded.     

Decomposition of N2O over the surface of cobalt spinel: A DFT account of reactivity experiments

The DFT molecular modeling of N₂O decomposition over cobalt spinel (1 0 0) plane was performed using a cluster approach, and applied to rationalize the experimental reactivity data. The energetics of the postulated elementary steps such as N₂O adsorption, N₂O activation through dissociative electron or oxygen atom transfer, surface diffusion of resultant oxygen intermediates, and their recombination into O₂, was evaluated and discussed. The geometry and electronic structure of the implicated active sites and intermediates were determined. Three different transition states were found for the activation of nitrous oxide molecule. In the preferred electron transfer mechanism, involving a monodentate transition state, the N₂O activation and the formation of dioxygen are energetically the most demanding steps, whereas the barrier for the oxygen surface diffusion was found to be distinctly smaller. For the oxygen atom transfer the reaction is energetically constraint by the NO bond-breaking step. The inhibiting effect of co-adsorbed water and oxygen on the particular reaction steps was briefly addressed.     

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.     

Structural organization of catalytic functions in Mo-based oxides for propane selective oxidation

Several single phasic MoVO-based mixed oxides, all of which have a layer structure in the direction of c-axis and a high dimensional arrangement of metal octahedra in a–b plane, were synthesized by hydrothermal method and their catalytic performance in the selective oxidation of propane to acrylic acid were compared in order to elucidate structure effects on catalytic property and roles of constituent elements. It was clearly demonstrated that the catalyst with the particular arrangement of MO₆ (M = Mo, V) octahedra forming slabs with pentagonal, hexagonal and heptagonal rings in (0 0 1) plane of orthorhombic structure was exclusively superior both in the propane oxidation activity and in the selectivity to acrylic acid to the other related Mo- and V-based layer oxide catalysts consisting of either pentagonal or hexagonal ring unit. The role of constituent elements was clarified by the comparison of catalytic performance of MoVO, MoVTeO and MoVTeNbO, all of which have the same orthorhombic structure. Mo and V, which were indispensable elements for the structure formation, were found to be responsible for the catalytic activity for propane oxidation. Te located in the central position of the hexagonal ring promoted the conversion of intermediate propene effectively, resulting in a high selectivity to acrylic acid. The introduced Nb occupied the same structural position of V and the resulting catalyst clearly showed the improved selectively to acrylic acid particularly at high conversion region, because the further oxidation of acrylic acid to CO_x was suppressed.     

Catalytic reactions of dioxygen with ethane and methane on platinum clusters: Mechanistic connections,site requirements,and consequences of chemisorbed oxygen

C₂H₆ reactions with O₂ only form CO₂ and H₂O on dispersed Pt clusters at 0.2–28 O₂/C₂H₆ reactant ratios and 723–913 K without detectable formation of partial oxidation products. Kinetic and isotopic data, measured under conditions of strict kinetic control, show that CH₄ and C₂H₆ reactions involve similar elementary steps and kinetic regimes. These kinetic regimes exhibit different rate equations, kinetic isotope effects and structure sensitivity, and transitions among regimes are dictated by the prevalent coverages of chemisorbed oxygen (O^*). At O₂/C₂H₆ ratios that lead to O^*-saturated surfaces, kinetically-relevant CH bond activation steps involve O^*O^* pairs and transition states with radical-like alkyls. As oxygen vacancies (¹) emerge with decreasing O₂/alkane ratios, alkyl groups at transition states are effectively stabilized by vacancy sites and CH bond activation occurs preferentially at O^** site pairs. Measured kinetic isotope effects and the catalytic consequences of Pt cluster size are consistent with a monotonic transition in the kinetically-relevant step from CH bond activation on O^*O^* site pairs, to CH bond activation on O^** site pairs, to O₂ dissociation on ^** site pairs as O^* coverage decrease for both C₂H₆ and CH₄ reactants. When CH bond activation limits rates, turnover rates increase with increasing Pt cluster size for both alkanes because coordinatively unsaturated corner and edge atoms prevalent in small clusters lead to more strongly-bound and less-reactive O^* species and lower densities of vacancy sites at nearly saturated cluster surfaces. In contrast, the highly exothermic and barrierless nature of O₂ activation steps on uncovered clusters leads to similar turnover rates on Pt clusters with 1.8–8.5 nm diameter when this step becomes kinetically-relevant at low O₂/alkane ratios. Turnover rates and the O₂/alkane ratios required for transitions among kinetic regimes differ significantly between CH₄ and C₂H₆ reactants, because of the different CH bond energies, strength of alkylO^* interactions, and O₂ consumption stoichiometries for these two molecules. Vacancies emerge at higher O₂/alkane ratios for C₂H₆ than for CH₄ reactants, because their weaker CH bonds lead to faster scavenging of O^* and to lower O^* coverages, which are set by the kinetic coupling between CH and OO activation steps. The elementary steps, kinetic regimes, and mechanistic analogies reported here for C₂H₆ and CH₄ reactions with O₂ are consistent with all rate and isotopic data, with their differences in CH bond energies and in alkyl binding, and with the catalytic consequences of surface coordination and cluster size. The rigorous mechanistic interpretation of these seemingly complex kinetic data and cluster size effects provides useful kinetic guidance for larger alkanes and other catalytic surfaces based on the thermodynamic properties of these molecules and on the effects of metal identity and surface coordination on oxygen binding and reactivity.     

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.     

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.     

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.     

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.     

High efficient adsorption of gold ions onto the novel functional composite silica microspheres encapsulated by organophosphonated polystyrene

The novel functional composite silica microspheres encapsulated by organophosphonated polystyrene (SGPSNP) has been successfully synthesized. SGPSNP was employed to adsorb Au(III) from simulated wastewater, and it exhibited excellent performance, and the maximum adsorption capacity was 980.39 mg/g at 35 °C. The adsorption process optimization was performed using response surface methodology (RSM), and the analysis of variance (ANOVA) of the quadratic model demonstrated that the model was highly significant. Moreover, the regeneration capacities of SGPSNP were investigated, and it has been found that the adsorption capability remains high after several cycles of adsorption–desorption.