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

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.

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

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.

ELSEVIER SCIENCE SA2019

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)

Stefanos Giannakis, Minoo Karbasi, Juan Kiwi, César Pulgarin, Sami Rtimi

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 (

2020

Quantification of the local magnetized nanotube domains accelerating the photocatalytic removal of the emerging pollutant tetracycline

Juan Kiwi, Henrik Moodysson Rønnow, Sami Rtimi, Jiajie Yu, Ivica Zivkovic

( )Evidence is presented for the enhanced photodegradation of tetracycline (TC) by AgxO/FeOx/ZnO nanotubes (NTs) compared to AgxO/ZnO nanotubes under low-intensity solar light irradiation. A higher amount of the local magnetic domains with random orientation in the AgxO/FeOx,/ZnO NTs lead to a faster TC-degradation. Fe introduces intra-gap states in the ZnO NTs facilitating the e-transport under light. The AgxO/FeOx/ZnO nanotubes were observed to present predominantly semiconductor behavior during the light induced TC-degradation. The nature of the interaction between non-polarized photos with the local domains due the addition of Fe is discussed. By X-ray photoelectron spectroscopy (XPS) redox reactions were observed on the nanotube surface NTs leading to the reactive oxygen radical species (ROS). The ROS-intermediates were identified by appropriate scavengers. Fast TC-degradation kinetics was attained by a catalyst with a composition AgOx(5.8%)FeOx(21.9%) ZnO (72.3%) as determined by X-ray fluorescence (XRF). A scheme for the interfacial charge transfer (IFCT) between the oxides on the nanotube surface is presented. Magnetized nanotubes present a practical potential in environmental cleaning avoiding the high cost separation of the catalyst from the reaction media at the end of the process

ELSEVIER SCIENCE BV2019