Evidence for a dual mechanism in the TiO2/CuxO photocatalyst during the degradation of sulfamethazine under solar or visible light: Critical issues

Juan Kiwi, César Pulgarin, Sami Rtimi, Jiajie Yu
ELSEVIER SCIENCE SA, 2019
Article

This study presents the photocatalytic degradation of sulfamethazine (SMT) on TiO2/CuxO nanotubes (NTs) by a differentiated mechanism under low intensity solar light and indoor visible light irradiation. In the presence of TiO2/CuxO nanotubes, the SMT-degradation was complete within 3 h (in acid aqueous solution). The surface of the photocatalyst used was registered by scanning and transmission electron microscopy SEM/TEM. By X-ray diffraction (XRD), the anatase and rutile phases were detected in the TiO2/CuxO(1%) materials. This photo catalyst led to the fastest SMT-degradation. By X-ray photoelectron spectroscopy (XPS) the TiO2 and CuxO species deconvoluted signals provided the evidence for the redox catalysis taking place during SMT-degradation. Cu2O was the major component in the TiO2/CuxO(1%) samples as detected by XPS. The SMT-degradation kinetics was monitored by high performance liquid chromatography (HPLC). The reactive oxidative species (ROS) generated by TiO2/CuxO surface under solar and visible light irradiation were unambiguously identified by appropriate scavengers. The band-gap of the TiO2/CuxO NTs prepared in this study is reported. The stability of the TiO2/CuxO leading to SMT-photodegradation was monitored. The interfacial charge transfer (IFCT) photo activated by solar light on the TiO2/CuxO surface is suggested to proceed via a Schottky barrier. But under visible light a mechanism involving surface plasmon resonance (SPR) mechanism is suggested to account for the observed IFCT.

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Juan Kiwi, César Pulgarin, Sami Rtimi, Jiajie Yu
ELSEVIER SCIENCE SA, 2019
Article

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https://infoscience.epfl.ch/record/266633?ln=fr

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Insights into the Photocatalytic Bacterial Inactivation by Flower-Like Bi2WO6 under Solar or Visible Light, Through in Situ Monitoring and Determination of Reactive Oxygen Species (ROS)

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This study addresses the visible light-induced bacterial inactivation kinetics over a Bi2WO6 synthesized catalyst. The systematic investigation was undertaken with Bi2WO6 prepared by the complexation of Bi with acetic acid (carboxylate) leading to a flower-like morphology. The characterization of the as-prepared Bi2WO6 was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area (SSA), and photoluminescence (PL). Under low intensity solar light (

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Duality in the Mechanism of Hexagonal ZnO/CuxO Nanowires Inducing Sulfamethazine Degradation under Solar or Visible Light

Juan Kiwi, César Pulgarin, Sami Rtimi, Jiajie Yu

This study presents the first evidence for the photocatalytic performance of ZnO/CuxO hexagonal nanowires leading to sulfamethazine (SMT) degradation. The chemical composition of the nanowires was determined by X-ray fluorescence (XRF). The sample with the composition ZnO/Cux=1.25O led to faster SMT-degradation kinetics. The SMT-degradation kinetics were monitored by high performance liquid chromatography (HPLC). The morphology of the hexagonal nanowires was determined by scanning electron microscopy (SEM) and mapped by EDX. The redox reactions during SMT degradation were followed by X-ray photoelectron spectroscopy (XPS). The interfacial potential between the catalyst surface and SMT was followed in situ under solar and indoor visible light irradiation. SMT-degradation was mediated by reactive oxidative species (ROS). The interfacial charge transfer (IFCT) between ZnO and CuxO is shown to depend on the type of light used (solar or visible light). This later process was found to be iso-energetic due to the potential energy positions of ZnO and CuxO conduction bands (cb). The intervention of surface plasmon resonance (LSPR) species in the SMT degradation is discussed.

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Photocatalytic Storing of O2 as H2O2 Mediated by High Surface Area CuO. Evidence for a Reductive-Oxidative Interfacial Mechanism

Paul Bowen, Juan Kiwi, Lucica Soare

CuO powders with a high specific surface area are shown to be able to produce H2O2 in aqueous solution under simulated light irradiation. The highest rate of peroxide production was observed under mild experimental conditions using O2 and a large surface area photocatalyst CuO irradiated with a solar simulator having light intensities between 60 and 90 mW/cm2. The CuO employed had a specific surface area (SSA) of 64.8-70.1 m2/g and was prepared in a tubular furnace by controlled thermal decomposition of precipitated copper oxalate. The CuOparticles produced were 1 μmcubes with primary particles around 15 nm. No peroxide was produced under the same conditions with commercial CuO, with SSA 200 times lower. The CuO synthesized during this work was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area [Brunauer-Emmett-Teller (BET)], porosity, and X-ray photoelectron spectroscopy (XPS). From XPS, it was observed that only CuII was present in the unused and used CuO. This indicates that the redox transient species involving other Cu oxidation states disappear very fast during the reaction, regenerating CuII during H2O2 production. Diverse experiments provided some evidence for the possible interfacial reaction mechanism leading to H2O2, following the initial step of O2-‚ formation on the CuO surface under irradiation with photons, with energies exceeding the band gap of CuO. A photocatalyzed degradation of a concentrated 4-chlorophenol (4-CP) solution was observed under solar-simulated light in the presence of CuO.

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