Substrate Oxidation Enhances the Electrochemical Production of Hydrogen Peroxide

Hydrogen peroxide (H_2O_2) is electrochemically produced via oxygen (O_2) reduction on a carbon cathode surface. In order to enhance the production of H_2O_2, anodic loss pathways, which significantly reduce the overall H_2O_2 production rate, should be inhibited. In this study, we investigate the effects of organic electron donors (i.e., typical chemical contaminants) on the anodic loss pathways of H_2O_2 in a single-cell electrochemical reactor that employs an anode composed of TiO_2 over-coated on a mixed-metal oxide ohmic contact catalyst, Ir_(0.7)Ta_(0.3)O_2, deposited on a Ti-metal that is coupled with a graphite rod cathode in a sodium sulfate (Na_2SO_4) electrolyte that is saturated with oxygen (O_2). Organic electron donors are shown to enhance the electrochemical production of H_2O_2, while simultaneously undergoing oxidative degradation. The observed positive effect of organic electron donors on the electrochemical production of H_2O_2 is due in part to a preferential adsorption of organic substrates on the TiO_2 outer layer of the anode. The sorption of the organic electron donors inhibits the formation of surficial titanium hydroperoxo species ( Ti-OOH) on the anode surface. The organic sorbates also act as scavengers of surface-bound hydroxyl radical Ti-OH. As a result, the decomposition of H_2O_2 on the anode surface is significantly reduced. The cathodic production rate of H_2O_2 at low pH is enhanced due to proton coupled electron transfer (PCET) to O_2, while the anodic decomposition of H_2O_2 is inhibited due to electrostatic interactions between negatively-charged organic substrates and a positively-charged outer surface of the anode (TiO_2 pH_(zpc) = 5.8) at low pH

Peroxymonosulfate (PMS) activation on cobalt-doped TiO₂ nanotubes: degradation of organics under dark and solar light irradiation conditions

Peroxymonosulfate activation on cobalt-doped TiO₂ nanotubes (Co-TNTs) as applied for the degradation of organic pollutants in the absence of light and under solar light irradiation is investigated. Co-TNTs generate SO₄˙⁻ via PMS activation in the dark, while they result in SO₄˙⁻ formation via PMS activation and, at the same time, produce ˙OH via photocatalytic water oxidation under simulated solar light illumination. Radical generation is explored using electron paramagnetic resonance (EPR) spectroscopy. The catalytic activity is maintained over multiple catalytic cycles with negligible Co(II) leaching. The nanotube catalysts are easily recovered without loss of activity after water treatment. The Co-TNT/PMS reaction system can be used for wastewater treatment during the day and at night

Substrate Oxidation Enhances the Electrochemical Production of Hydrogen Peroxide

Hydrogen peroxide (H_2O_2) is electrochemically produced via oxygen (O_2) reduction on a carbon cathode surface. In order to enhance the production of H_2O_2, anodic loss pathways, which significantly reduce the overall H_2O_2 production rate, should be inhibited. In this study, we investigate the effects of organic electron donors (i.e., typical chemical contaminants) on the anodic loss pathways of H_2O_2 in a single-cell electrochemical reactor that employs an anode composed of TiO_2 over-coated on a mixed-metal oxide ohmic contact catalyst, Ir_(0.7)Ta_(0.3)O_2, deposited on a Ti-metal that is coupled with a graphite rod cathode in a sodium sulfate (Na_2SO_4) electrolyte that is saturated with oxygen (O_2). Organic electron donors are shown to enhance the electrochemical production of H_2O_2, while simultaneously undergoing oxidative degradation. The observed positive effect of organic electron donors on the electrochemical production of H_2O_2 is due in part to a preferential adsorption of organic substrates on the TiO_2 outer layer of the anode. The sorption of the organic electron donors inhibits the formation of surficial titanium hydroperoxo species ( Ti-OOH) on the anode surface. The organic sorbates also act as scavengers of surface-bound hydroxyl radical Ti-OH. As a result, the decomposition of H_2O_2 on the anode surface is significantly reduced. The cathodic production rate of H_2O_2 at low pH is enhanced due to proton coupled electron transfer (PCET) to O_2, while the anodic decomposition of H_2O_2 is inhibited due to electrostatic interactions between negatively-charged organic substrates and a positively-charged outer surface of the anode (TiO_2 pH_(zpc) = 5.8) at low pH

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO₂ and WO₃ (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O₂, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O₂ removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO₂•/O₂•– pair in the dark. The WO₃ fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight

In Situ-Generated Reactive Oxygen Species in Precharged Titania and Tungsten Trioxide Composite Catalyst Membrane Filters: Application to As(III) Oxidation in the Absence of Irradiation

This study demonstrates that in situ-generated reactive oxygen species (ROSs) in prephotocharged TiO₂ and WO₃ (TW) composite particle-embedded inorganic membrane filters oxidize arsenite (As(III)) into arsenate (As(V)) without any auxiliary chemical oxidants under ambient conditions in the dark. TW membrane filters have been charged with UV or simulated sunlight and subsequently transferred to a once-through flow-type system. The charged TW filters can transfer the stored electrons to dissolved O₂, producing ROSs that mediate As(III) oxidation in the dark. Dramatic inhibition of As(V) production with O₂ removal or addition of ROS quenchers indicates an ROS-mediated As(III) oxidation mechanism. Electron paramagnetic spectroscopic analysis has confirmed the formation of the HO₂•/O₂•– pair in the dark. The WO₃ fraction in the TW filter significantly influences the performance of the As(III) oxidation, while As(V) production is enhanced with increasing charging time and solution pH. The As(III) oxidation is terminated when the singly charged TW filter is fully discharged; however, recharging of TW recovers the catalytic activity for As(III) oxidation. The proposed oxidation process using charged TW membrane filters is practical and environmentally benign for the continuous treatment of As(III)-contaminated water during periods of unavailability of sunlight

Direct Conversion of Mouse Fibroblasts into Cholangiocyte Progenitor Cells

Disorders of the biliary epithelium, known as cholangiopathies, cause severe and irreversible liver diseases. The limited accessibility of bile duct precludes modeling of several cholangiocyte-mediated diseases. Therefore, novel approaches for obtaining functional cholangiocytes with high purity are needed. Previous work has shown that the combination of Hnf1β and Foxa3 could directly convert mouse fibroblasts into bipotential hepatic stem cell-like cells, termed iHepSCs. However, the efficiency of converting fibroblasts into iHepSCs is low, and these iHepSCs exhibit extremely low differentiation potential into cholangiocytes, thus hindering the translation of iHepSCs to the clinic. Here, we describe that the expression of Hnf1α and Foxa3 dramatically facilitates the robust generation of iHepSCs. Notably, prolonged in vitro culture of Hnf1α- and Foxa3-derived iHepSCs induces a Notch signaling-mediated secondary conversion into cholangiocyte progenitor-like cells that display dramatically enhanced differentiation capacity into mature cholangiocytes. Our study provides a robust two-step approach for obtaining cholangiocyte progenitor-like cells using defined factors

Simultaneous electrochemical production of hydrogen peroxide and degradation of organic pollutants

We investigated the effect of org. pollutants on the prodn. of hydrogen peroxide (H_2O_2) in the presence of Na_2SO_4 as an electrolyte under oxygen condition. TiO_2/IrO_2, graphite rod, and Ag/AgCl were used as an anode, a cathode, and a ref. electrode, resp. The electrochem. prodn. of H_2O_2 was significantly enhanced in the presence of org. pollutants. This result is ascribed to that the presence of org. pollutants reduces the anodic decompn. of H_2O_2. Org. pollutants prevent the surface complexation between hydroxyl group on the anode surface and H_2O_2. Furthermore, they can be acted as a scavenger of surface-bound hydroxyl radicals that decomp. H_2O_2. We also confirmed that the prodn. of H_2O_2 coupled with the degrdn. of org. pollutants at acidic pH than that at alk. condition. H_2O_2 is mainly produced via the proton coupled electron transfer (PCET) to oxygen. Org. pollutants are highly degraded at acidic condition, because they are electrostatically attracted with the anode surface and surface-bound OH radicals are more generated at a lower pH. This result indicates that the acidic pH provides a better condition for the degrdn. of org. pollutants and prodn. of H_2O_2

Simultaneous electrochemical production of hydrogen peroxide and degradation of organic pollutants

We investigated the effect of org. pollutants on the prodn. of hydrogen peroxide (H_2O_2) in the presence of Na_2SO_4 as an electrolyte under oxygen condition. TiO_2/IrO_2, graphite rod, and Ag/AgCl were used as an anode, a cathode, and a ref. electrode, resp. The electrochem. prodn. of H_2O_2 was significantly enhanced in the presence of org. pollutants. This result is ascribed to that the presence of org. pollutants reduces the anodic decompn. of H_2O_2. Org. pollutants prevent the surface complexation between hydroxyl group on the anode surface and H_2O_2. Furthermore, they can be acted as a scavenger of surface-bound hydroxyl radicals that decomp. H_2O_2. We also confirmed that the prodn. of H_2O_2 coupled with the degrdn. of org. pollutants at acidic pH than that at alk. condition. H_2O_2 is mainly produced via the proton coupled electron transfer (PCET) to oxygen. Org. pollutants are highly degraded at acidic condition, because they are electrostatically attracted with the anode surface and surface-bound OH radicals are more generated at a lower pH. This result indicates that the acidic pH provides a better condition for the degrdn. of org. pollutants and prodn. of H_2O_2