4 research outputs found

    Quantitative Determination the Role of the Intrabandgap States in Water Photooxidation over Hematite Electrodes

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    The intrabandgap states on the hematite (α-Fe2O3) electrodes are believed to play an important role in water photooxidation. Yet, it is not fully understood how the intrabandgap states are involved in the reaction. In this work, the intraband-gap states in water photooxidation on α-Fe2O3 electrodes are investigated by a combination of multiple (photo-) electrochemical techniques and operando spectroscopic methods. Two kinds of surface states are observed on the electrodes during water photooxidation, and their roles are quantitatively determined by the correlation with the steady-state photocurrent. It is demonstrated that the intrinsic electronic surface state close to the conduction band can act only as the recombination center for the photocarriers. However, the photogenerated surface state closer to the valence band is revealed to be the reactant in the rate-determining step in oxygen evolution reaction. These findings may be beneficial to elucidate the actual function of the surface states and provide insights into the kinetic and mechanism studies of water photooxidation on the α-Fe2O3 electrodes

    Quantitative Determination the Role of the Intrabandgap States in Water Photooxidation over Hematite Electrodes

    No full text
    The intrabandgap states on the hematite (α-Fe2O3) electrodes are believed to play an important role in water photooxidation. Yet, it is not fully understood how the intrabandgap states are involved in the reaction. In this work, the intraband-gap states in water photooxidation on α-Fe2O3 electrodes are investigated by a combination of multiple (photo-) electrochemical techniques and operando spectroscopic methods. Two kinds of surface states are observed on the electrodes during water photooxidation, and their roles are quantitatively determined by the correlation with the steady-state photocurrent. It is demonstrated that the intrinsic electronic surface state close to the conduction band can act only as the recombination center for the photocarriers. However, the photogenerated surface state closer to the valence band is revealed to be the reactant in the rate-determining step in oxygen evolution reaction. These findings may be beneficial to elucidate the actual function of the surface states and provide insights into the kinetic and mechanism studies of water photooxidation on the α-Fe2O3 electrodes

    Regenerated Dye-Sensitized Photocatalytic Oxidation of Arsenite over Nanostructured TiO<sub>2</sub> Films under Visible Light in Normal Aqueous Solutions: An Insight into the Mechanism by Simultaneous (Photo)electrochemical Measurements

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    TiO<sub>2</sub> photocatalysis has been demonstrated as an alternative pretreatment method for arsenic-contaminated water by oxidizing As­(III) to less toxic and less mobile As­(V). However, the lack of visible light absorption of the catalyst limits the utilization of sunlight. In this article, we report that As­(III) could be efficiently oxidized by visible light (λ ≥ 420 nm) over a typical ruthenium dye N719-sensitized nanostructured TiO<sub>2</sub> film in the normal aerated aqueous solutions. The amount of oxidation of As­(III) via the photo-oxidative (by dye cation, S<sup>+</sup>) and photoreductive (by electron-initiated reactive oxygen species, EIROS; O<sub>2</sub><sup>•–</sup> considered to be the dominant species) pathways was quantified by simultaneously measuring the oxidation rate and interfacial charge transfer rate of the film electrodes. The results in the absence of O<sub>2</sub> and under an anodic potential bias where EIROS is absent indicate that As­(III) can be highly efficiently oxidized by S<sup>+</sup> via a two-electron reaction with ∼100% Coulombic efficiency, while the results in the dark and under a cathodic bias where S<sup>+</sup> is absent suggest that EIROS could also efficiently oxidize As­(III) via a one-electron reaction with ∼100% Coulombic efficiency as well. Under open circuit and in the normal aerated aqueous solutions, nearly all of the interfacial transferred charge was utilized for the As­(III) photo-oxidation, and 33 and 67% of As­(V) production resulted from S<sup>+</sup> and EIROS-initiated oxidation, respectively. The mechanism of As­(V) formation under this situation was the direct two-electron oxidation of As­(III) by S<sup>+</sup> and indirect one-electron oxidation of As­(III) by EIROS to generate As­(IV), which further reacts with O<sub>2</sub>, producing As­(V). The dye could be completely regenerated in situ through the oxidation of As­(III) and consequently was photostable

    Enhanced Visible-Light Photoactivity of CuWO<sub>4</sub> through a Surface-Deposited CuO

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    Several papers have shown that CuWO<sub>4</sub> is active under visible light for water oxidation at an applied potential bias and for organic degradation in an aerated aqueous suspension. In this work, we report that the observed reduction of O<sub>2</sub> on the irradiated CuWO<sub>4</sub> is a multielectron transfer process with the formation of H<sub>2</sub>O<sub>2</sub>. More importantly, the surface modification of CuWO<sub>4</sub> with 1.8 wt % of CuO can increase the activity by approximately 9 times under UV light and by 5 times under visible light, for phenol degradation in aerated aqueous suspension. The catalyst was prepared by a hydrothermal reaction between Cu­(NO<sub>3</sub>)<sub>2</sub> and Na<sub>2</sub>WO<sub>4</sub>, followed by thermal treatment at 773 K. High-resolution transmission electron microscopy revealed that triclinic CuWO<sub>4</sub> (40 nm) was covered by monoclinic CuO (4 nm). Through a combination of photo- and electrochemical measurement, a plausible mechanism responsible for the activity enhancement is proposed, involving an interfacial electron transfer from CuO to CuWO<sub>4</sub> and an interfacial hole transfer from CuWO<sub>4</sub> to CuO
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