One-step Two-electron Reduction Research Articles

Hydroxyl-Bonded Co Single Atom Site on Boroncarbonitride Surface Realizes Non-sacrificial H2O2 Synthesis in the Near-Infrared Region.

Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 and H2O under near-infrared light is a sustainable renewable energy production strategy, but challenging reaction. The bottleneck of this reaction lies in the regulation of O2 reduction path by photocatalyst. Herein, we construct the center of the one-step two-electron reduction (OSR) pathway of O2 for H2O2 evolution via the formation of the hydroxyl-bonded Co single-atom sites on boroncarbonitride surface (BCN-OH2/Co1). Our experimental and theoretical prediction results confirm that the hydroxyl group on the surface and the electronic band structure of BCN-OH2/Co1 are the key factor in regulating the O2 reduction pathway. In addition, the hydroxyl-bonded Co single-atom sites can further enrich O2 molecules with more electrons, which can avoid the one-electron reduction of O2 to •O2 -, thus promoting the direct two-electron activation hydrogenation of O2. Consequently, BCN-OH2/Co1 exhibited a high H2O2 evolution apparent quantum efficiency of 0.8% at 850nm, better than most of the previously reported photocatalysts. This study reveals an important reaction pathway for the generation of H2O2, emphasizing that precise control of the active site structure of the photocatalyst is essential for achieving efficient conversion of solar-to-chemical. This article is protected by copyright. All rights reserved.

Insights into sunlight-driven transformation of tetracycline by iron (hydr)oxides: The dominating role of self-generated hydrogen peroxide

Iron (hydr)oxides are abundant in surface environment, and actively participate in the transformation of organic pollutants due to their large specific surface areas and redox activity. This work investigated the transformation of tetracycline (TC) in the presence of three common iron (hydr)oxides, hematite (Hem), goethite (Goe), and ferrihydrite (Fh), under simulated sunlight irradiation. These iron (hydr)oxides exhibited photoactivity and facilitated the transformation of TC with the initial phototransformation rates decreasing in the order of: Hem > Fh > Goe. The linear correlation between TC removal efficiency and the yield of HO• suggests that HO• dominated TC transformation. The HO• was produced by UV-induced decomposition of self-generated H2O2 and surface Fe2+-triggered photo-Fenton reaction. The experimental results indicate that the generation of HO• was controlled by H2O2, while surface Fe2+ was in excess. Sunlight-driven H2O2 production in the presence of the highly crystalline Hem and Goe occurred through a one-step two-electron reduction pathway, while the process was contributed by both O2-induced Fe2+ oxidation and direct reduction of O2 by electrons on the conduction band in the presence of the poorly crystalline Fh. These findings demonstrate that sunlight may significantly accelerate the degradation of organic pollutants in the presence of iron (hydr)oxides.

Schottky barrier height mediated Ti3C2 MXene based heterostructure for rapid photocatalytic water disinfection: Antibacterial efficiency and reaction mechanism

Schottky barrier plays a key role in determining the interface electron transfer of most Schottky junctions, but the relationship between schottky barrier height (SBH) and photocatalytic disinfection activity is not clearly revealed. Here, a well-designed tubular graphitic carbon nitride/hydroxyl terminated Ti3C2 MXene (TCN/TC(OH)) Schottky junction with controllable SBH was prepared as a model case for investigation. Experimental study and density functional theory calculation confirm that the surface hydroxyl termination of Ti3C2 can lower the SBH of TCN/TC(OH) by reducing its work function (0.23 eV). The lowered SBH ensures rapid interface transfer of photogenerated electron, which decreases the average surface recombination rate from 0.0077 s−1 (TCN/TC) to 0.0045 s−1 (TCN/TC(OH)-3) and increases the corresponding surface charge transfer efficiency from 48.2% to 53.2%. Rotating disk electrode measurement confirms that different from the two-step single-electron O2 reduction of TCN/TC (n = 1.54), TCN/TC(OH)-3 (n = 1.95) exhibits a one-step two-electron reduction route, which is more selective for the generation of the major antibacterial reactive oxygen species H2O2. Consequently, TCN/TC(OH)-3 presents much higher photocatalytic performance towards natural water disinfection, and can entirely inactivate 7 × 107 CFU/mL of Staphylococcus aureus even in complex water matrix (interfering ions, acidic solution and real water samples). Our work provides a feasible guidance for future natural water purification by interfacial engineering of the MXene-based Schottky junction.

Dual H2O2 production paths over chemically etched MoS2/FeS2 heterojunction: Maximizing self-sufficient heterogeneous Fenton reaction rate under the neutral condition

Sufficient generation of H2O2 played an essential role in boosting self-sufficient heterogeneous Fenton reaction. Herein, the dual H2O2 production paths were designed to maximize the yield over H2O2-etched MoS2/FeS2 Z-scheme heterojunction, whose surface was modified with abundant –OH groups and sulfur vacancies (SVs). Mechanism studies revealed that H2O2 was generated via two-step single-electron reduction by electrons on conduction band, where H2O2 production was significantly improved by the internal hole-scavenging effect from –OH groups. Additionally, electrons surrounding SVs served as another sites for H2O2 production via one-step two-electron reduction even in darkness. H2O2 yield in neutral aqueous solution reached 1.5 mM/g/h without external hole scavenger. Tetracycline and rhodamine B were effectively degraded under light or in darkness. The degradation performance was even comparable to the heterogeneous Fenton reaction. This work provides new insights for the design of self-sufficient heterogeneous Fenton system with exceptional degradation performance.

Fabrication of ultra-thin g-C3N4 nanoplates for efficient visible-light photocatalytic H2O2 production via two-electron oxygen reduction

Photocatalytic generation of hydrogen peroxide (H2O2) is a sustainable technique to realize the solar-energy conversion. Here, ultrathin graphitic carbon nitride (g-C3N4) nanoplates with thickness of 1–3 nm was introduced for the efficient H2O2 production. The as-obtained nanoplates demonstrated the H2O2 production rate of 43.07 μmol g−1 h−1 and about 4 times as high as the pristine g-C3N4. Experimental results reflected that the ultrathin morphology offered an increased surface area, more active sites, smaller charge transfer length and stronger redox ability than that of the bulk counterparts. Moreover, the introduction of ultrathin structure switched the H2O2 production pathway from a two-step single-electron reduction to a one-step two-electron reduction route. This study offered the deep elucidation of the influence of ultrathin structure on the photoactivity of semiconductor photocatalysts.

Sacrificial agent-free photocatalytic H2O2evolutionviatwo-electron oxygen reduction using a ternary α-Fe2O3/CQD@g-C3N4photocatalyst with broad-spectrum response

The developed α-Fe2O3/CQD@g-C3N4can perform a direct one-step two-electron reduction for efficient photocatalytic H2O2evolution in pure water.

Theoretical Determination of the Redox Potentials of NRH:Quinone Oxidoreductase 2 Using Quantum Mechanical/Molecular Mechanical Simulations

NRH:quinone oxidoreductase 2 (NQO2) is a flavoenzyme that catalyzes a one-step two-electron reduction of quinones. During this enzyme catalysis, the 7,8-dimethyl isoalloxazine (flavin) ring of the enzyme-bound cofactor, flavin adenine dinucleotide (FAD), shuttles between reduced and oxidized states as the enzyme passes through multiple cycles of binding/release of alternate substrates. These redox changes in NQO2, however, lead to unequal charge separation between the flavin ring and the active site, which must be stabilized by reorganization of the surrounding protein matrix. In this study, we have used a combined quantum mechanical/molecular mechanical method to simulate the electron and proton addition reactions of the flavin-bound NQO2. We have computed the redox potentials and pK(a)'s of the enzyme-bound flavin. The present work demonstrates that upon reduction, the NQO2 active site stabilizes the flavin anionic hydroquinone state. Simulation data has also allowed quantitative estimation of the electrostatic contributions of active site residues. Their significance in oscillatory redox transition of this flavoenzyme is discussed.

Two-Electron Reduction of a Rh−Mo−Rh Dithiolato Complex To Form a Triplet Ground State Associated with a Change in CO Coordination Mode

We synthesized a dithiolato-bridged heterometal trinuclear complex [{(eta(5)-C(5)Me(5))Rh(S(2)C(6)H(4))}(2)Mo(CO)(2)] (1) in which two rhodadithiolene complex units are bridged by a Mo(CO)(2) moiety. Complex 1 with a Rh(III)-Mo(0)-Rh(III) bond exhibits reversible one-step two-electron reduction with potential inversion. This redox process between 1 and 1(2-) accompanies a reversible structural change, which is an alternation in the CO coordination mode between semibridging and bridging. The ground state of dianion 1(2-) with a Rh(II)-Mo(0)-Rh(II) bond is assigned to spin triplet. These alternations of CO coordination mode and spin state are fully consistent with the density functional theory calculation results. This is the first example of multinuclear metalladithiolene complex which was successful in elucidating a reversible multielectron redox process associated with structural change and spin state change.

Preparation and Stille Cross‐Coupling Reaction of the First Organotin Reagents of Azulenes. Easy Access to Poly(azulen‐6‐yl)benzene Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Preparation and Stille cross-coupling reaction of the first organotin reagents of azulenes. Easy access to poly(azulen-6-yl)benzene derivatives

The first versatile organometallic reagents derived from azulenes, i.e., 6-(tri-n-butylstannyl)azulene (1a) and its 1,3-diethoxycarbonyl derivative (1b), have been prepared by Pd(0)-catalyzed direct stannylation of 6-bromoazulenes with bis(tri-n-butyltin). We demonstrate the utility of the reagents in the Stille cross-coupling reaction with aryl, acyl and azulenyl halides to afford 6-aryl-, 6-acyl- and bi-azulenes in good yield. Furthermore, the methodology was applied to the synthesis of poly(azulen-6-yl)benzene derivatives. The reaction of 1b with 1,4-di-, 1,3,5-tri-, 1,2,4,5-tetra- and hexabromobenzenes afforded 1,4-di-, 1,3,5-tri-, 1,2,4,5-tetra-, 1,2,4-tri- and 1,2,3,5-tetra(azulen-6-yl)benzene derivatives (18, 20, 22, 24 and 25). The redox behavior of 18 and 22 was examined by cyclic voltammetry (CV) and compared with those of 20 and 24 reported previously. In contrast to the three-step reduction of 20, the compound 18 exhibited a reversible one-step two-electron reduction wave at −1.30 V upon CV, which revealed the formation of a closed-shell dianion. The four azulen-6-yl substituents on benzene in a 1,2,4,5 relationship increased electron-accepting properties because of the formation of a closed-shell dianion stabilized by four azulen-6-yl groups. As expected, the compound 22 exhibited a color change during the electrochemical reduction. However, the reverse oxidation did not regenerate the spectrum of 22 due to the low stability of the presumed dianionic species under the conditions of the UV–vis measurement.

Electrocatalytic properties of vitamin B 12 towards oxidation and reduction of nitric oxide

This paper reports on the catalytic behaviour of cyanocobalamin (VB 12) towards the reduction and oxidation of nitric oxide. When VB 12 is adsorbed on glassy carbon electrodes, it catalyses the reduction of nitric oxide (NO) in pH 4 and 9 buffers. In the absence of NO, cyclic voltammetry shows that VB 12 is reduced by a one-step two-electron reduction from Co III to the Co I species. Addition of NO at pH 9 to solutions of VB 12 resulted in the splitting of the cyclic voltammetry peaks as a result of a consecutive one-electron reduction of the central Co III metal in VB 12 to Co II and finally to Co I. The catalytic peak for oxidation of NO on a glassy carbon electrode modified with VB 12 was observed at 1.21 V versus Ag∣AgCl, at pH 9. The products of the catalytic reduction of nitric oxide include ammonia and hydroxylamine.

Synthesis, crystal structure and redox properties of µ-oxo-bis(µ-acetato)-diruthenium(III) complexes having 2,2′-bipyridine and imidazole bases as terminal ligands

Three diruthenium(III) complexes, [{Ru(bipy)L}2(µ-O)(µ-O2CMe)2][ClO4]2, have been prepared and characterized (L = imidazole, 1- or 4-methylimidazole; bipy = 2,2′-bipyridine). The crystal structure of the 1-methylimidazole complex [Ru2O(O2CMe)2(bipy)2(1-mim)2][ClO4]2·H 2O·MeOH has been determined. The complex has a Ru2(µ-O)(µ-O2CMe)22+ core with terminal unidentate 1-mim and bidentate chelating bipy ligands. The imidazole is trans to the oxide ligand. The Ru ⋯ Ru distance and Ru–O–Ru angle are 3.285(2)A and 121.5(3)°. The 1H NMR spectra of the complexes are consistent with this crystal structure. The complexes show an intense charge-transfer band near 600 nm. They are redox active and display reversible one-electron oxidation and reduction processes. On addition of weak proton-donor imidazole bases the complexes undergo a one-step two-electron reduction process RuIIIRuIII–RuIIRuII along with the RuIIIRuIII–RuIIIRuIV oxidation couple.

Palladium-catalysed electrochemical reduction of vinyl and aryl triflates

Abstract The reduction of vinyl and aryl triflates 1 , in the presence of stoichiometric amounts of benzoic acid and catalytic amounts of PdCl 2 (PPh 3 ) 2 results in the formation of the corresponding alkenes and arenes 2 . Most probably, the reaction proceeds via a catalytic cycle initiated by the one-step two-electron reduction of the palladium complex followed by oxidative addition of unsaturated triflates to the low-ligated zerovalent palladium complex Pd 0 (PPh 3 ) 2 Cl − . The resultant σ-vinyl and σ-arylpalladium(II) intermediate undergoes a one-step two-electron reduction to afford 2 in moderate to good yield, regenerating the low-ligated zerovalent palladium complex.

Kinetics of oxidation of azide ion by bis(dihydrogentellurato)-cuprate(III) and -argentate(III) in alkaline media

The kinetics of the oxidation of azide ion by bis(dihydrogentellurato)-cuprate(III) and -argentate(III) has been studied in alkaline media. The rate of the reaction increases with increasing azide ion but decreases with the increasing of alkali concentration. The reactions proceed through initial 1 : 1 complex formation between the reactants followed by decomposition of the complex to give nitrogen. Copper(III) is reduced by the substrate in a one-electron process, whereas one-step two-electron reduction has been shown to occur with silver(III). Thermodynamic parameters associated with the complex-formation step and the activation parameters for the decomposition step have been evaluated. The mechanism of the reactions is discussed.

Redox behaviour of the oxo-bridged diruthenium(III) complex, [Ru2(µ-O)(µ-MeCO2)2(bpy)2(mim)2]2+in acetonitrile in the presence of various proton donors (bpy = 2, 2′-bipyridine, mim = 1-methylimidazole)

Redox potentials of the Ru2III,III–Ru2III,II and Ru2III,II–Ru2II,II processes of [Ru2(µ-O)(µ-MeCO2)2(bpy)(mim)2]2+ in acetonitrile, move to the positive direction remarkably on addition of a strong acid such as toluene-p-sulfonic acid, while two processes are coalesced to show apparent one-step two-electron reduction on addition of weaker proton donors.

Electrochemical behavior of the oxo complex of Ru(IV), trans-[RuCl(O)(py) 4] +, in both non-aqueous and aqueous solvents

The electrochemical behavior of trans-[Ru IVCl(O)(py) 4] +, and that of its related complexes, trans-[Ru IIICl(OH)(py) 4] + and trans-[Ru IICl(H 2O)(py) 4] +, were investigated in both acetonitrile and aqueous solvents. The reduction process of trans-[Ru IVCl(O)(py) 4] + was an irreversible one; it converted into trans-[Ru IICl(OH)(py) 4] 0 in CH 3CN and trans-[Ru IICl(H 2O)(py) 4] + in aqueous solvent by a one-step two-electron reduction. The oxo complex undergoes a one-electron oxidation to give a reactive trans-[Ru VCl(O)(py) 4] 2+, which is the species capable of oxidizing organic substances.

Electrochemical reduction of the antitumour anthrapyrazole Cl-941: mechanism of formation and isolation of the leuco form

The title compound undergoes two successive one-electron reductions in the aprotic solvent DMF and an apparent one-step two-electron reduction in the presence of proton donors. Both the leuco form, resulting from the addition of two electrons and two protons, and the product of its hydrolysis in acidic media, have been isolated. All of the observed reactions proceed according to thermodynamic and kinetic parameters (redox potentials, pKas and rate constants) which are quantitatively analysed.

Electrochemical reduction of some benzophenones in molten acetamide at 85°C

Benzophenones undergo a one-step two-electron reduction in molten acetamide containing sodium acetate, both at the mercury and the glassy carbon electrodes. The reduction process is irreversible. TheE 1/2 potentials of some of the benzophenones can be fitted into a Hammett plot. Theαn a andk f, h o are evaluated and discussed.

Electrochemical investigation of quinone-hydroquinone couples in molten acetamide at 85°C

Quinones undergo a one-step two-electron reduction in molten acetamide at the mercury and platinum electrodes. The reversibility of reduction increases in the order benzoquinone < napthaquinone = phenanthrquinone < anthraquinone.