Redox

About: Redox is a research topic. Over the lifetime, 26853 publications have been published within this topic receiving 862368 citations. The topic is also known as: reduction-oxidation & reduction-oxidation reaction.

Selective aerobic oxidation mediated by TiO(2) photocatalysis.

Abstract: TiO2 is one of the most studied metal oxide photocatalysts and has unparal-leled efficiency and stability. This cheap, abundant, and non-toxic material has the potential to address future environmental and energy concerns. Understanding about the photoinduced interfacial redox events on TiO2 could have profound effect on the degradation of organic pollutants, splitting of H2O into H2 and O2, and selective redox organic transformations. Scientists traditionally accept that for a semiconductor photocatalyst such as TiO2 under the illumination of light with energy larger than its band gap, two photocarriers will be created to carry out their independent reduction and oxidation processes. However, our recent discoveries indicate that it is the concerted rather than independent effect of both photocarriers of valence band hole (hvb(+)) and conduction band electron (ecb(-)) that dictate the product formation during interfacial oxidation event mediated by TiO2 photocatalysis. In this Account, we describe our recent findings on the selective oxidation of organic substrates with O2 mediated by TiO2 photocatalysis. The transfer of O-atoms from O2 to the corresponding products dominates the selective oxidation of alcohols, amines, and alkanes mediated by TiO2 photocatalysis. We ascribe this to the concerted effect of both hvb(+) and ecb(-) of TiO2 in contribution to the oxidation products. These findings imply that O2 plays a unique role in its transfer into the products rather than independent role of ecb(-) scavenger. More importantly, ecb(-) plays a crucial role to ensure the high selectivity for the oxygenation of organic substrates. We can also use the half reactions such as those of the conduction band electron of TiO2 for efficient oxidation reactions with O2. To this end, efficient selective oxidation of organic substrates such as alcohols, amines, and aromatic alkanes with O2 mediated by TiO2 photocatalysis under visible light irradiation has been achieved. In summary, the concerted effect of hvb(+) and ecb(-) to implement one oxidation event could pave the way for selective oxofunctionalization of organic substrates with O2 by metal oxide photocatalysis. Furthermore, it could also deepen our understanding on the role of O2 and the elusive nature of oxygen species at the interface of TiO2, which, in turn, could shed new light on avant-garde photocatalytic selective redox processes in addressing the energy and environmental challenges of the future.

Electrogenerated IrOx nanoparticles as dissolved redox catalysts for water oxidation

Abstract: We describe the first example of redox catalysis using a dissolved electroactive nanoparticle, based on the oxidation of water by electrogenerated IrOx nanoparticles containing IrVI states, in pH 13 solutions of 1.6 ± 0.6 nm (dia.) IrIVOx nanoparticles capped solely by hydroxide. At potentials (ca. +0.45 V) higher than the mass transport-controlled plateau of the nanoparticle IrV/IV wave, rising large redox catalytic currents reflect electrochemical generation of IrVI states, which by +0.55 V and onward to +1.0 V are shown by rotated ring disk electrode experiments to lead with 100% current efficiency to the oxidation of water to O2. O2 production at +0.55 V corresponds to an overpotential η of only 0.29 V, relative to thermodynamic expectations of the four electron H2O→O2 reaction. The Ir site turnover frequency (TO, mol O2/Ir sites/s) is 8−11 s−1. Controlled potential coulometry shows that all Ir sites in these nanoparticles (average 66 Ir each) are electroactive, meaning that the nanoparticles are smal...

Arsenic and selenium chemistry as affected by sediment redox potential and pH

Abstract: The influence of sediment redox potential and pH on As and Se speciation and solubility was studied. Hyco Reservoir (North Carolina) sediments were equilibrated under controlled redox (500, 200, 0, and −200 mV) and pH (5, natural, and 7.5) conditions. Redox potential and pH affected both speciation and solubility of As and Se. Under oxidized conditions As solubility was low and 87% of the As in solution was present as As(V). Upon reduction, As(III) became the major As species in solution, and As solubility increased. Total As in solution increased approximately 25 times upon reduction to −200 mV. No organic arsenicals were detected. In contrast to As, Se solubility reached a maximum under highly oxidized (500 mV) conditions and decreased significantly upon reduction. Selenium(VI) was the predominant dissolved Se species present at 500 mV. At 200 and 0 mV, Se(IV) became the most stable oxidation state of Se. Under strongly reduced conditions (−200 mV) oxidized Se species were no longer detectable and Se solubility was controlled by the formation of elemental Se and/or metal selenides. Biomethylation of Se was important under oxidized and moderately reduced conditions (500, 200, and 0 mV). More alkaline conditions (pH 7.5) resulted in both greater As and Se concentrations in solution. Dissolved As and Se increased up to 10 and 6 times, respectively, as compared to the more acidic equilibrations.

Adsorption and oxidation of PCP on the surface of magnetite: Kinetic experiments and spectroscopic investigations

Abstract: The oxidation of pentachlorophenol (PCP) on the surface of magnetite used as heterogeneous catalyst has been investigated under various experimental conditions (initial substrate concentration, H2O2 dose, solid loading and temperature) at neutral pH and correlated with the adsorption behavior. The surface reactivity of magnetite was evaluated by conducting the kinetic study of both H2O2 decomposition and PCP oxidation experiments. The occurrence of the optimum values of H2O2 and magnetite concentrations for the effective degradation of PCP could be explained by the scavenging reactions with H2O2 or iron oxide surface. The surface interactions with PCP in the absence and the presence of oxidant can be well described by Langmuir and Langmuir–Hinshelwood models, respectively. All batch experiments indicate that Fenton-like oxidation of PCP was controlled by surface mechanism reaction and the species compete with each other for adsorption on a fixed number of surface active sites. The apparent degradation rate was dominated by the rate of intrinsic chemical reactions on the oxide surface rather than the rate of mass transfer. Raman analysis suggested that the sorbed PCP was removed form magnetite surface at the first stage of oxidation reaction. The mineralization determined by TOC abatement was completed after 7 d, while total dechlorination was achieved at 4 d treatment time. The first reaction of PCP oxidation should be the dechlorination since 90% of chloride was formed at the first 30 h corresponding to the total disappearance of parent compound. All X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Mossbauer spectroscopy and chemical analyses showed that the magnetite catalyst exhibited low iron leaching, good structural stability and no loss of performance in second reaction cycle.