不同有机分子改性羟基磷灰石用于甲醛催化氧化

分别采用十六烷基三甲基溴化铵(CTAB)、十二烷基硫酸钠(SDS)及柠檬酸钠(SC)对羟基磷灰石(HAP)进行了有机改性.柠檬酸钠改性的羟基磷灰石对甲醛催化氧化表现出最好的催化活性,在240℃实现了甲醛完全转化.通过X射线衍射、红外光谱、N2吸附-脱附、扫描电镜和热重/差重等手段对HAP结构进行了表征.结果表明,SC改性使得HAP比表面积和孔体积增加,孔径减小,更有利于吸附及传质,从而提高了其活性.此外,SC改性的HAP中羟基含量更多,更有利于甲醛与羟基之间发生相互作用,这是该样品活性提高的另一个原因.     

Organocatalyzed anodic oxidation of aldehydes

A method for the catalytic formation of electroauxiliaries and subsequent anodic oxidation has been developed. The process interfaces N-heterocyclic carbene-based organocatalysis with electro-organic synthesis to achieve direct oxidation of catalytically generated electroactive intermediates. We demonstrate the applicability of this method as a one-pot conversion of aldehydes to esters for a broad range of aldehyde and alcohol substrates. Furthermore, the anodic oxidation reactions are very clean, producing only H(2) gas as a result of cathodic reduction.     

Power-law blinking in the fluorescence of single organic molecules.

The blinking behavior of perylene diïmide molecules is investigated at the single‐molecule level. We observe long‐time scale blinking of individual multi‐chromophoric complexes embedded in a poly(methylmethacrylate) matrix, as well as for the monomeric dye absorbed on a glass substrate at ambient conditions. In both these different systems, the blinking of single molecules is found to obey analogous power‐law statistics for both the on and off periods. The observed range for single‐molecular power‐law blinking extends over the full experimental time window, covering four orders of magnitude in time and six orders of magnitude in probability density. From molecule to molecule, we observe a large spread in off‐time power‐law exponents. The distributions of off‐exponents in both systems are markedly different whereas both on‐exponent distributions appear similar. Our results are consistent with models that ascribe the power‐law behavior to charge separation and (environment‐dependent) recombination by electron tunneling to a dynamic distribution of charge acceptors. As a consequence of power‐law statistics, single molecule properties like the total number of emitted photons display non‐ergodicity.     

Synthesis of ZrO2 nanotubes in inorganic and organic electrolytes by anodic oxidation of zirconium

Present work reports on the results of the electrochemical growth of self-ordered zirconia nanotubes formed in aqueous Na₂SO₄?+?HF and nonaqueous electrolytes with glycerol addition. Anodization process was carried out in this inorganic water-based mixture with constant pH?=?2.5 and in the voltage range from 5 to 60 V. Similar experiments were repeated in an organic glycerol-based electrolyte with the voltage equal to 20 V and with variable glycerol concentration. All experiments were conducted at constant room temperature. The tube diameter dependence on the voltage of anodization process in an inorganic electrolyte was derived. It was found that when glycerol addition to water electrolyte was used, it takes more time to produce long zirconia nanotubes. However, they do not collapse as the similar structure of the same length formed in aqueous electrolyte.     

Artifacts in amine analysis from anodic oxidation of organic solvents upon electrospray ionization for mass spectrometry

Different phenylenediamines were used to explore anodic oxidation in solution during electrospray ionization (ESI) mass spectrometry analysis. In our experiments, a series of unknown ionic species was detected in the phenylenediamine solutions. Our results propose that reactions of phenylenediamines with species formed by anodic oxidation of typical ESI solvents during the electrospray ionization process such as formaldehyde are producing these peaks. Identification of these compounds inter alia suggests formal alkylation, a reaction not reported so far as a result of electrolytic oxidation in the prospective organic solvents.     

Theoretical mechanistic studies on oxidation reactions of some saturated and unsaturated organic molecules

This account describes the results collected by our group during the last years on some themes of environmental/mechanistic interest. Theoretical quantum-mechanical investigations have been carried out to help clarifying the mechanism of some oxidation reactions, which involve mainly unsaturated but also saturated organics as substrates, and, as reactive oxidants, triplet or singlet dioxygen, hydroxyl, ozone, and nitrogen oxides. Depending on the problem, the calculations are either multi-configurational (as CAS-MCSCF, CAS-PT2, MC-QDPT2), or based on the Density Functional Theory for the heavier systems. Research work has thus been developed along the following lines: hydrocarbon oxidations under atmospheric or combustion conditions; definition of a model for soot particles and their interaction with species as HO, O₂, O₃, NO, NO₂, NO₃, etc.; investigation on the reaction mechanism of ¹Δ_g dioxygen with organic unsaturated systems (cycloaddition and ene reactions).     

The anodic oxidation of gold + palladium alloys

The anodic oxidation of Au+Pd alloys has been studied in solutions of 1 M H₂SO₄ and 0.1 M K₂SO₄ by voltammetric methods. A linear relationship between oxide reduction maximum and bulk alloy composition, often used to determine the surface composition of homogeneous alloys, could be shown to hold only for alloys up to 60 at% gold. At higher gold content the Au oxide peak must be additionally evaluated. With continuous cycling in acid solution the anodic dissolution of Pd, especially from gold-rich places, leads to a rather heterogeneous surface. The O--chemisorption is not governed by a transfer mechanism from Pd to Au surface atoms. The alloys are able to absorb the oxygen species generated in the positive potential region; however, this ability decreases with increase of the gold content.     

A hierarchically ordered porous novel vanado-silicate catalyst for highly efficient oxidation of bulky organic molecules

A novel hierarchically ordered porous vanado-silicate nanocomposite with interconnecting macroporous windows and meso-microporous walls containing well dispersed vanadyl species has been fabricated and used as a heterogeneous catalyst for the oxidation of a bulky organic molecule, namely cyclooctene.     

Voltammetric study of the anodic oxidation of enolate carbanions

A voltammetric study of the anodic oxidation of the enolate carbanions of β-ketonitriles of the type

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has been carried out in DMSO. The variation of E_ox of these species as a function of the nature of R and Z was examined. Their anodic oxidation process could be identified by analysis of the voltamperometric curves obtained both at the rotated platinum electrode and at the stationary electrode. Cyclic voltammetry has confirmed that this is an ec overall irreversible provess. The electrochemical reaction e yielding a neutral radical is followed by the very fast dimerization (second-order chemical reaction C). The formation of different kinds of dimers, depending on the nature of the oxidized enolates, has been observed during controlled potential electrolysis.     

1,2-Shift in the anodic oxidation of aromatic compounds

The 1,2-shift observed during oxidation of organic substrates can arise by involvement of cation radicals.     

Direct electrochemical imidation of aliphatic amines via anodic oxidation

Direct electrochemical synthesis of sulfonyl amidines from aliphatic amines and sulfonyl azides was realized with good to excellent yields. Traditional tertiary amine substrates were broadened to secondary and primary amines. The reaction intermediates were observed and a reaction mechanism was proposed and discussed.     

Nickel surface anodic oxidation and electrocatalysis of oxygen evolution

The processes of nickel surface anodic oxidation taking place within the range of potentials preceding oxygen evolution reaction (OER) in the solutions of 1 M KOH, 0.5 M K₂SO₄, and 0.5 M H₂SO₄ have been analyzed in the present paper. Metallic nickel, thermally oxidized nickel, and black nickel coating were used as Ni electrodes. The methods of cyclic voltammetry and X-ray photoelectron spectroscopy were employed. The study was undertaken with a view to find the evidence of peroxide-type nickel surface compounds formation in the course of OER on the Ni electrode surface. On the basis of experimental results and literature data, it has been suggested that in alkaline solution at E ≈ 1.5 V (RHE) reversible electrochemical formation of Ni(IV) peroxide takes place according to the reaction as follows: This reaction accounts for both the underpotential (with respect to ) formation of O₂ from NiOO₂ peroxide and also small experimental values of dE/dlgi slope (<60 mV) at low anodic current densities, which are characteristic for the two-electron transfer process. It has been inferred that the composition of the γ-NiOOH phase, indicated in the Bode and revised Pourbaix diagrams, should be ∼5/6 NiOOH + ∼1/6 NiOO₂. The schemes demonstrating potential-dependent transitions between Ni surface oxygen compounds are presented, and the electrocatalytic mechanisms of OER in alkaline, acid, and neutral medium have been proposed.     

Modeling growth of organized nanoporous structures by anodic oxidation

Nanostructured porous oxides are produced by anodic dissolution of several metals. A scaling approach is introduced to explain pattern nucleation in an oxide layer, and a related microscopic model shows oxide growth with long nanopores. The scaling approach matches the time of ion transport across the thin oxide layer, which is related to metal corrosion, and the time of diffusion along the oxide/solution (OS) interface, which represents the extension of oxide dissolution. The selected pattern size is of order (dD(S)/v(O))(1/2), where d is the oxide thickness, v(O) is the migration velocity of oxygen ions across the oxide, and D(s) is the diffusion coefficient of H(+) ions along the oxide/solution interface. This result is consistent with available experimental data for those quantities, predicts the increase of pore size with the external voltage, and suggests the independence of pore size with the solution pH. Subsequently, we propose a microscopic model that expresses the main physicochemical processes as a set of characteristic lengths for diffusion and surface relaxation. It shows a randomly perturbed OS interface at short times, its evolution to pore nucleation and to stable growth of very long pores, in agreement with the mechanistic scenario suggested by two experimental groups. The decrease of the size of the walls between the pores with the interface tension is consistent with arguments for formation of titania nanotube arrays instead of nanopores. These models show that pattern nucleation and growth depend on matching a small number of physicochemical parameters, which is probably the reason for the production of nanostructured porous oxides from various materials under suitable electrochemical conditions.     

The anodic oxidation of 2,4,5-triarylimidazoles in aprotic medium

The anodic oxidation of 2-(p-dimethylaminophenyl)-4,5-diphenylimidazole and 2,4,5-tris-p-methoxyphenylimidazole in benzonitrile solutions has been studied, using rotating disc electrode, rotating double ring electrode, and coulometry as electrochemical techniques. ESR and UV-vis. spectroscopy were used for product analysis. The triarylimidazoles exhibit two or more oxidation waves. The first one is interpreted as a non-conventional e.c.e. mechanism where the parent molecule is involved in the chemical step. Further anodic waves are due to the oxidation of protonated triarylimidazole, produced in the e.c.e. mechanism.