Selective Redox Reactions Research Articles

Detection of ascorbic acid by persistent luminescent nanoparticles based on CoOOH nanosheets modification.

Persistent luminescent nanomaterials (PLNPs) Zn0.8Ga2O4: Cr3+, Zr3+ with high brightness and good dispersion were prepared by hydrothermal method. The PLNPs were used as luminescent units, and CoOOH nanosheets were used as quenching agents. Based on the fluorescence internal filtering effect, the luminescence of PLNPs were effectively quenched by CoOOH modification on the surface of PLNPs. However, the introduction of ascorbic acid (AA) restored the luminescence of PLNPs and successfully achieved highly sensitive and selective detection of AA. This was due to a selective redox reaction between CoOOH and AA, in which CoOOH was reduced to Co2+. The degree of luminescence recovery of PLNPs showed a good linear relationship with AA concentration in the range 5-250 µM, with a detection limit of 0.72 µM. Therecovery of actualspikedsamples were 97.9-102.2%. This method isexpected to provide reference for the study of other redox substances in biological systems.

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium.

Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO-CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo-C-O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1-x, and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C-O (selective C combustion) and Mo-C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO-CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO-CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas-solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material-property relationship accordingly.

Switching and control mechanism between p-type and n-type in SnO2 nanorods using laser with added convex lens to control oxygen concentrations

In a significant advancement, a novel technology has been developed to precisely control the electronic sensitization of SnO2 nanorods. This control is accomplished in a matter of seconds through the external injection of energy via laser and convex lens pairs (LCP). Utilizing LCP, selective redox reactions can be induced on the surface of SnO2 nanorods. The study focused on the contrasting effects of NO2, an oxidizing gas, and H2, a reducing gas. In the presence of NO2, the electronic sensitization caused by LCP outweighs the chemical sensitization due to NO2, thereby resulting in both n-type and p-type behaviors. In contrast, when exposed to H2, the nanorods exhibit only n-type behavior, as the chemical sensitization effect of H2 is more significant than the electronic sensitization effect of LCP. The observed variations in electronic properties can be systematically accounted for by the differential bonding energies between oxidizing and reducing gases.

Carbon-Neutral Energy Cycle via Highly Selective Electrochemical Reactions Using Biomass Derivable Organic Liquid Energy Carriers

Abstract Efficient storage and transport of electric energy is essential to promote the use of renewable energy based electricity. We demonstrate an energy cycle based on highly selective redox reactions between lactic acid (Lac) and pyruvic acid (Pyr), both of which are liquid under ambient conditions and can be obtained from biomass resources, thus realizing a completely low-emission system. As an energy storage device, an electrosynthesis cell (LAEC) for the production of Lac from Pyr was constructed using a membrane electrode assembly (MEA) consisting of a TiO2 cathode catalyst for the electroreduction of Pyr and an IrOx anode catalyst for water oxidation. Our LAEC achieved highly efficient Lac production from 10 M Pyr aqueous solution with Faradaic efficiency (FE) of approximately 100% in the applied voltage range of 1.4–2.4 V, resulting in an energy conversion efficiency of 50% and a current density of −0.4 A cm−2 at 2.0 V. Direct Lac fuel cell (DLAFC) was also constructed and its FE values for the Pyr production reached approximately 100%, enabling direct electronic energy storage in bio-derivative liquid carriers and efficient energy circulation with minimal CO2 emissions.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Photocatalytic water splitting on BiVO4: Balanced charge-carrier consumption and selective redox reaction

Photocatalytic water splitting on BiVO4: Balanced charge-carrier consumption and selective redox reaction

Self‐healable, recyclable, ultrastretchable, and high‐performance NO2 sensors based on an organohydrogel for room and sub‐zero temperature and wireless operation

AbstractTo date, development of high‐performance, stretchable gas sensors operating at and below room temperature (RT) remains a challenge in terms of traditional sensing materials. Herein, we report on a high‐performance NO2 gas sensor based on a self‐healable, recyclable, ultrastretchable, and stable polyvinyl alcohol–cellulose nanofibril double‐network organohydrogel, which features ultrahigh sensitivity (372%/ppm), low limit of detection (2.23 ppb), relatively fast response and recovery time (41/144 s for 250 ppb NO2), good selectivity against interfering gases (NH3, CO2, ethanol, and acetone), excellent reversibility, repeatability, and long‐term stability at RT or even at −20°C. In particular, this sensor shows outstanding stability against large deformations and mechanical damages so that it works normally after rapid self‐healing or remolding after undergoing mechanical damage without significant performance degradation, which has major advantages compared to state‐of‐the‐art gas sensors. The high NO2 sensitivity and selectivity are attributed to the selective redox reactions at the three‐phase interface of gas, gel, and electrode, which is even boosted by applying tensile strain. With a specific electrical circuit design, a wireless NO2 alarm system based on this sensor is created to enable continuous, real‐time, and wireless NO2 detection to avoid the risk of exposure to NO2 higher than threshold concentrations.

Interface Molecular Functionalization of Cu2O for Synchronous Electrocatalytic Generation of Formate.

The electrocatalytic generation of valuable fuels and chemicals from carbon dioxide (CO2) and others with the assistance of clean solar energy is a highly promising way to realize the carbon-neutral cycle, which invokes the systematic development of advanced electrocatalysts for efficient and selective redox reactions of feedstocks. Herein, we demonstrate the interface modification of cuprous oxide with polyvinylpyrrolidone (PVP) to improve the electrocatalytic efficiency for the synchronous formate generation. Density functional theory calculations reveal that the interfacial properties can be effectively regulated by the PVP functionalization for the favorable formation of intermediates to improve the selectivity of formate generation. Importantly, the advanced electrocatalyts enable an efficient coupling of CO2 reduction with methanol oxidation in an electrochemical cell powered with a solar cell. The work provides a predictive link between the electrocatalytic redox reactions by applying the interfacial regulation strategies of electrocatalysts.

Electrophotocatalysis: Combining Light and Electricity to Catalyze Reactions.

Visible-light photocatalysis and electrocatalysis are two powerful strategies for the promotion of chemical reactions that have received tremendous attention in recent years. In contrast, processes that combine these two modalities, an area termed electrophotocatalysis, have until recently remained quite rare. However, over the past several years a number of reports in this area have shown the potential of combining the power of light and electrical energy to realize new catalytic transformations. Electrophotocatalysis offers the ability to perform photoredox reactions without the need for large quantities of stoichiometric or superstoichiometric chemical oxidants or reductants by making use of an electrochemical potential as the electron source or sink. In addition, electrophotocatalysis is readily amenable to the generation of open-shell photocatalysts, which tend to have exceptionally strong redox potentials. In this way, potent yet selective redox reactions have been realized under relatively mild conditions. This Perspective highlights recent advances in the area of electrophotocatalysis and provides some possible avenues for future work in this growing area.

Programmable chemical actuator control of soluble and membrane-bound enzymatic catalysis.

Enzyme catalyzed reactions can be started, stopped, and throttled by regulating ion concentration in solution. The flow of charge through solution is related to the flow of electrons through an electric circuit using electrochemistry. However, current electrochemical methods to vary ionic concentration are largely limited to the electrode surface, making it impractical to exploit ionic concentration as a control variable in traditional enzyme assays. This chapter presents an electrochemical cell, termed a programmable chemical actuator (PCA), that uses selective electrochemical REDOX reactions to regulate the concentration of ions that control enzyme catalyzed reaction kinetics. The PCA is a polypyrrole polymerized and equilibrated to impart Mg2+, Mn2+, or OH- ion selectivity to working electrodes. Duplex pulse amperometry demonstrated reversible control over the pH-dependent kinetics of alkaline phosphatase, a soluble homodimeric enzyme, during a spectrophotometric assay. PCAs were also used to extend electrochemical control to the membrane-bound enzyme complex rubber transferase by modulating Mg2+ and Mn2+ concentrations during a radiometric enzyme assay. PCAs demonstrated tunable control over rubber transferase activity and rubber molecular weight without dislodging either the elongating rubber molecule or irreversibly inhibiting the rubber transferase complex. This chapter presents methods to fabricate and operate PCAs to facilitate insights into the roles of ions in biochemical pathways and environmental responses in plants.

Multi‐interfacial catalyst with spatially defined redox reactions for enhanced pure water photothermal hydrogen production

AbstractPhotocatalytic overall water splitting is a promising strategy to store abundant solar energy as clean fuel, but recombination of photogenerated carriers is the key factor that reduces the efficiency. Herein, we report multi‐interfacial ternary CoP@ZnIn2S4@Co3O4 photocatalyst with coordinated structural and electronic band coupling to concurrently fulfill spatially decoupled redox centers and modulated electric field. For one, the realization of 3D open framework consists of 2D ZnIn2S4 nanosheets on 1D CoP co‐catalyst maximizes exposures apart from circumvents aggregation and shielding issues. Another is the spatially defined and selective redox reactions where CoP is designated for proton reduction and Co3O4 for water oxidation. And finally, constructed type II band structure and p‐n junction facilitates directional charge separation, thereby prohibiting the recombination of charge carrier and also increase the local charge density. Besides, small band gap CoP and Co3O4 exhibit photothermal effect to further enhance photocatalytic hydrogen production. As a result, the photocatalysts could achieve the respective half reaction and pure water hydrogen evolution rate of 4254 and 145 μmol g−1 h−1 under visible light illumination and further enhance to 10 740 and 308 μmol g−1 h−1 when subjected to full spectrum photoheating. This work presents a promising strategy in designing surface and interfacial dominated photocatalytic system to achieve efficient solar energy to chemical conversion.image

(Invited) Electrodeless Organic Electrosynthesis By Plasma-Liquid Interface

The plasma-liquid interface can promote selective redox reactions involving organic molecules without the need for solid electrodes. More specifically, our group’s work on model organic compounds has revealed that selective reduction occurs near the surface of water in contact with an RF plasma jet generated using helium or argon as working gas, for positions located near the centerline of the impinging free jet. The complementary oxidation half reaction occurs further away from the centerline, and the products of reduction and oxidation can be isolated by placing a semipermeable membrane between the reduction and oxidation zones, which are termed electrodeless cathode and anode respectively. The reduction potential in the liquid near the surface at the plasma jet centerline can be tuned by changing the plasma parameters. Correlations between reduction potential and plasma parameters, specifically electron density and temperature as characterized by Thomson scattering, will be presented and a simple model proposed to theoretically connect the two. Finally, envisioned applications for this unique type of electrodeless organic electrosynthesis will be discussed in the fields of water quality, renewable carbon utilization, and pharmaceuticals. The work described in this presentation is collaborative between research groups at Washington University in Saint Louis, Princeton Plasma Physics Laboratory, and the University of Michigan; and was supported by the Department of Energy under award DE-SC0020352, the Princeton Collaborative Low Temperature Plasma Research Facility (PCRF), and the National Science Foundation through grant CBET-2033714.

Photogenerated Charge Separation between Polar Crystal Facets Under a Spontaneous Electric Field

AbstractUntil now, the photogenerated charge separation mechanism is not clear in photocatalysis. Based on the structures at the atomic scale of the polar crystal facets with photocatalytic activities, a general separation model of photogenerated charge between polar facets under a spontaneous electric field is presented. This charge separation model is proven by photo‐induced selective redox reactions on polar planes, photovoltaic and rectification effects in the polar direction orientated thin films, and electric field assisted assembly and alignment of semiconductor nanowires grown along the polar direction. This polar structure is similar to a semiconductor p–n junction, which can control the movement of electronic carriers and can be used to fabricate high‐efficiency photocatalysts and electronic and optoelectronic devices based on a new principle.

Site-selective doping of ordered charge states in magnetite

Charge ordering creates a spontaneous array of differently charged ions and is associated with electronic phenomena such as superconductivity, colossal magnetoresistances (CMR), and multiferroicity. Charge orders are usually suppressed by chemical doping and site selective doping of a charge ordered array has not previously been demonstrated. Here we show that selective oxidation of one out of eight distinct Fe2+ sites occurs within the complex Fe2+/Fe3+ ordered structure of 2%-doped magnetite (Fe3O4), while the rest of the charge and orbitally ordered network remains intact. This ‘charge order within a charge order’ is attributed to the relative instability of the trimeron distortion surrounding the selected site. Our discovery suggests that similar complex charge ordered arrays could be used to provide surface sites for selective redox reactions, or for storing information by doping specific sites.

Synthesis of Ag/AgCuS/CuInS2 hybrid nanoparticles by reductive cation exchange and their asymmetric heterostructure

Ag/AgCuS/CuInS2 hybrid nanoparticles (HNPs) were synthesized via a reductive cation exchange method. In this reaction, selective formation of Ag+ vacancies was achieved via direct reduction of Ag+ ions in AgCuS using a mixture of 1-dodecanethiol and tri-n-octylamine. AgCuS underwent a phase transition from orthorhombic (β-) to superionic δ-AgCuS phase with a face-centered cubic sulfur sublattice. This phase transition increased cation mobility during the cation exchange process. Below the phase transition temperature, the lower ionic conductivity of the orthorhombic phase prevents cation and hole diffusions through the interface between AgCuS and CuInS2 to stabilize a AgCuS/CuInS2 heterostructure. Transmission electron microscopy analyses revealed that the β-AgCuS/CuInS2 interface was composed of (010) or (001) β-AgCuS and (112) CuInS2. Because of the band alignment of Ag/AgCuS/CuInS2, the Ag NP tended to deposit on the surface of the AgCuS domain of the HNP. This selective redox reaction on the AgCuS domain may induce an electromotive force that plays an important role in the formation of the asymmetric heterostructure. Our proposed method may provide a novel strategy for the synthesis and precise structural tuning of metal/semiconductor hetero-nanostructures.

One-step synthesis of cross-linked and hollow microporous organic-inorganic hybrid nanoreactors for selective redox reactions.

Hollow microporous nanostructures (HMNs) are powerful platforms for multiple promising applications, including energy storage, drug/gene delivery, nanoreactors/catalysis, adsorption, and separation. Herein, we report a facile one-step method to synthesize highly cross-linked organic-inorganic hybrid poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) HMNs via a salt-induced liquid-liquid separation process. The size of inner cavities can be properly tuned by modulating the concentration of the NaOH solution. The regulation mechanism of the PZS HMNs was further confirmed by encapsulating water-dispersed Pt nanoclusters into the cavities. Interestingly, the resulting yolk-shell Pt@PZS serves as nanoreactors and exhibits excellent substrate selectivity and recyclability for the catalytic oxidation of 1,3,5-trimethylbenzene.

Constructing a system for effective utilization of photogenerated electrons and holes: Photocatalytic selective transformation of aromatic alcohols to aromatic aldehydes and hydrogen evolution over Zn3In2S6 photocatalysts

In a reaction system, the simultaneously efficient utilization of photogenerated electrons and holes to realize the photocatalytic selective redox reactions of organics has been a hot topic. In this paper, the Zn3In2S6 samples were synthesized via a simple solvothermal method with different solvents, which could make full use of photogenerated electrons and holes to achieve the photocatalytic selective transformation of aromatic alcohols to aromatic aldehydes and hydrogen evolution under mild conditions. The results show that the Zn3In2S6 synthesized with water (Zn3In2S6-W) exhibits the highest photocatalytic performance among the selected samples, with which the yields of benzaldehyde and hydrogen reach up to 732 and 708.8 μmol under light irradiation (λ ≥ 380 nm) for 4 h, respectively. The molar ratios between aldehydes and hydrogen are close to 1: 1. The apparent quantum efficiency is about 6.48% for wavelength λ = 380 ± 10 nm over Zn3In2S6-W sample. A possible reaction mechanism for the photocatalytic selective transformation of benzyl alcohol to benzaldehyde and hydrogen evolution under light irradiation is proposed. This work highlights that a reaction system is developed to effectively make use of the photogenerated electrons and holes for selective transformation of aromatic alcohols to aromatic aldehydes and hydrogen evolution over Zn3In2S6 photocatalysts under mild conditions.

Charge Transfer within Metal-Organic Frameworks: The Role of Polar Node in the Electrocatalysis and Charge Storage

Metal-organic frameworks (MOFs) assembled from photo and redox active building blocks such as porphyrins and pyrenes, as well as numerous post-synthesis processes that enable incorporation of required chemical functionality within the pores, have signified these crystalline molecular assemblies as emerging class of compositions for energy conversion, and storage systems. In particular, electrocatalytic energy conversion and storage applications require efficient charge transport process within the framework. It is known that the difference in the redox potentials between the linkers and metal-oxo nodes enforces a self-exchange/hopping type charge transport processes. For example, porphinato-iron based frameworks are shown to provide high electrode-surface concentration of electrocatalytic reduction of CO2 to CO. However, in such processes, as counter ion migration accompanies a (electrochemical) charge transfer reaction within the narrow pores of the MOFs, it leads to unique situations including a slower kinetic and selective redox reaction [i.e. a modified self-exchange reaction: L⁺—PF₆̅ + L⁰ → L⁰—PF₆̅ + L⁺]. This paper will discuss how the charge-transfer process is inherently different within the pores and that the metal-oxo node can play a critical role in the CT kinetics.

Large magnetoelectric effects mediated by electric-field-driven nanoscale phase transformations in sputtered (nanoparticulate) and electrochemically dealloyed (nanoporous) Fe-Cu films.

Large magnetoelectric effects are observed in as-sputtered (nanoparticulate-like) and electrochemically dealloyed (nanoporous) 200 nm thick Fe-Cu films. Application of positive voltages decreases both the saturation magnetization (MS) and coercivity (HC) of the films, while negative voltages cause the reverse effect (increase of MS and HC). The relative variations are as high as 20% for MS and beyond 100% for HC, both for the as-sputtered and dealloyed states. These changes in magnetic properties are caused by controlled and reversible electric-field-driven nanoscale phase transformations between face-centered cubic (fcc) and body-centered cubic (bcc) structures. These phase transitions are in turn due to selective redox reactions induced by the applied voltage, which can be regarded as a "magnetoionic effect." The controlled tuning of HC and MS with the moderate values of applied voltage, together with the sustainable composition of the investigated alloys (not containing noble metals, as opposed to many previous works on magnetoelectric effects in thin films), pave the way towards the implementation of magnetic and spintronic devices with enhanced energy efficiency and functionalities.

Enzymatic Oxyfunctionalization Driven by Photosynthetic Water-Splitting in the Cyanobacterium Synechocystis sp. PCC 6803

Photosynthetic water-splitting is a powerful force to drive selective redox reactions. The need of highly expensive redox partners such as NADPH and their regeneration is one of the main bottlenecks for the application of biocatalysis at an industrial scale. Recently, the possibility of using the photosystem of cyanobacteria to supply high amounts of reduced nicotinamide to a recombinant enoate reductase opened a new strategy for overcoming this hurdle. This paper presents the expansion of the photosynthetic regeneration system to a Baeyer–Villiger monooxygenase. Despite the potential of this strategy, this work also presents some of the encountered challenges as well as possible solutions, which will require further investigation. The successful enzymatic oxygenation shows that cyanobacterial whole-cell biocatalysis is an applicable approach that allows fuelling selective oxyfunctionalisation reactions at the expense of light and water. Yet, several hurdles such as side-reactions and the cell-density limitation, probably due to self-shading of the cells, will have to be overcome on the way to synthetic applications.