Superior visible light-mediated catalytic activity of a novel N-doped, Fe3O4-incorporating MgO nanosheet in presence of PMS: Imidacloprid degradation and implications on simultaneous bacterial inactivation

Impressive Imidacloprid (IMD) degradation and bacterial inactivation were attained through the photocatalytic activation of peroxymonosulfate (PMS) via a novel, N-doped MgO@Fe3O4, under visible light. After complete characterization (XPS, XRD, FT-IR, FE-SEM, EDX, HRTEM, DRS, BET, VSM, and EIS), using [PMS]=75 mg/L, [N-MgO@Fe3O4]=150 mg/L at pH=5.6, around 95% of 10 mg/L IMD was degraded within 60 min; highly synergic interactions between the various catalytic routes were revealed. Extensive scavenger tests and EPR studies revealed that SO4 center dot-, HO center dot, and O-1(2) are generated and play a key role in IMD degradation. Tap water experiments proceeded unhindered, and only the presence of high HCO3- and PO(4)(3-)concentration resulted in a decrease in the IMD degradation efficiency, while negligible leaching, magnetization, notable separation, and reusability properties were well-preserved for six repetitive cycles. Finally, E. coli disinfection was achieved before IMD degradation, possibly affected by its transformation byproducts. The overall efficacy of N-MgO@Fe3O4 indicated the potential for implementation in contaminated waters.

A Study of Synthesis & [and] Performance of Flame-Made Semiconducting BiVO4 Nanoparticles for the Photocatalytic Degradation of Aqueous Organic Pollutants

Nikola Castillo

Semiconductor photocatalysis is an Advanced Oxidation Technology that uses light as a source of energy to accelerate the degradation of harmful organic pollutants. Current research addresses the development of photocatalysts capable of harvesting visible light (Chapter 1). Bismuth vanadate (BiVO4) is a semiconductor that can absorb visible light up to 500 nm. It has been successfully tested for the oxidation of water and some dyes. So far, this material has been synthesized with low specific surface areas (SSA). Flame Spray Synthesis is a cost-effective method for the synthesis of nanoparticles and can be easily scaled up. The Flame Spray Synthesis of BiVO4 nanoparticles is described in detail. Careful adjustment of the process parameters allowed to control particle size and crystallinity of the as-prepared BiVO4 powders. Temperature of the collection site was found to hold a critical role on the control of these two properties (Chapter 3). Photocatalytic activity of the as-synthesized powders was then evaluated for the degradation of the Methylene Blue dye under visible-light irradiation. Photocatalyst properties controlled by synthesis parameters were confronted with their photocatalytic activity. It was found that both crystalline and amorphous powders could carry out the N-demethylation of Methylene Blue. Higher SSA lead to higher activity. A crystalline sample with moderate SSA was also found to degrade phenol to some extent at acidic pH but was subject to deactivation. Addition of different electron acceptors improved its photocatalytic activity. In particular, hydrogen peroxide (H2O2) could be used as a powerful yet rapidly consumed electron scavenger that enabled the degradation of phenol and dichloroacetate at neutral pH (Chapter 4). Advanced electrochemical and photochemical methods gave evidence of the poor reducing power of conduction-band electrons of BiVO4. Besides, the presence of deep traps associated with the change of coordination geometry of vanadium surface atoms upon photoexcitation has been correlated with the apparent photocatalytic activity of flame-made BiVO4 at pH 2. Finally, a mechanism involving the regneration of MB after its reduction when used as an electron acceptor has been proposed (Chapter 5). The flame spray synthesis of BiVO4 might be developed to produce high-SSA amorphous photocatalysts for the selective N-demethylation of Methylene Blue. Regarding the development of novel photocatalysts, the understanding of the role of the atomic surface structure should become a priority to increase their activity.

EPFL2011

Synchronic coupling of Cu2O(p)/CuO(n) semiconductors leading to Norfloxacin degradation under visible light: Kinetics, mechanism and film surface properties

Michaël Bensimon, Juan Kiwi, Gcina Mamba, César Pulgarin, Sami Rtimi

The study presents the first evidence for Norfoxacin photodegradation by uniform, adhesive and robust CuOx-polystyrene (CuOx-PES) films under visible light. Repetitive Norfloxacin degradation was attained on CuOx-PES films activated by visible light. The smooth CuOx-PES surface properties were investigated by diffuse reflectance spectroscopy (DRS). The band-gap of the Cu2O and CuO making up CuOx films were estimated by Tauc's method. By atomic force microscopy (AFM) the CuOx micro-agglomerated size was determined as well as the relatively small roughness of 22.4 +/- 10% nm and the distance between the Norfloxacin anchoring points on the CuO peaks. Evidence is presented by transmission electron microscopy (TEM) for the uniform distribution of Cu-clusters on the PES. The degradation of Norfloxacin was monitored in the range 2-20 mg/L, a Norfloxacin concentration far above the concentrations found in treated wastewaters. Proof of redox processes occurring in the CuOx during Norfloxacin degradation were monitored by (XPS). Deconvolution of the Cu2p3/2 peaks revealed Cu2O and CuO in different percentages before and after Norfloxacin degradation. The CuOx-PES samples were made up by Cu2O(p) and CuO(n) with an approximate ratio of Cu2O: CuO = 3: 1 before Norfloxacin degradation. Highly oxidative radical species and photogenerated holes Cu(2)Ovb (h(+)) were identified during Norfloxacin degradation. A mechanism is suggested for the Norfloxacin degradation involving highly oxidative radicals detected by scavenging experiment and the limits for the validity of this method are discussed. (C) 2017 Elsevier Inc. All rights reserved.

Elsevier2017

Accelerated methylene blue (MB) degradation by Fenton reagent exposed to UV or VUV/UV light in an innovative micro photo-reactor

Juan Kiwi, Mengkai Li, César Pulgarin

This study presents the accelerated discoloration/degradation of methylene blue (MB) in solution by Fenton reagent under exposure to ultraviolet (UV) or Vacuum-UV/UV (VUV/UV) light in an innovative micro photo-reactor. The MB degradation was kinetically faster when using VUV/UV light at 254/185 nm compared to UV-irradiation at 254 nm. Oxidative radicals produced by the photo-Fenton process were identified with appropriate scavengers. The addition of benzoquinone (BQ) at millimolar (mM) concentrations to MB solutions precluded completely the MB photo-induced bleaching, while tert-butanol hindered to a lesser extent the MB degradation suggesting that HO2 center dot was the predominant intermediate leading to MB degradation. The VUV/UV micro photo-reactor comprised mercury resonance lines at 185 and 254 nm. The photon percentages absorbed by water were estimated to be 16.8% at 254nm and 78.3% at 185 nm by water, while those absorbed by H2O2 were 0.9% and 2.2%, correspondingly. The solution parameters affecting the features of MB degradation, such as MB, Fe, and H2O2 concentrations, were explored and reaction mechanism was proposed. The lifetimes of (OH)-O-center dot and HO2 center dot were estimated to be 2 ns and 0.38 s under an optimized solution with 0.016 mM MB, 0.147 mM H2O2 and 0.05 mM Fe3+. Moreover, an estimation of the mean free paths of these radicals in solution provided the evidence that it was the radical lifetimes and mean-free paths, not their oxidation potentials that controlled the MB degradation kinetics. This study shows the potential of this VUV/UV assistant photo-Fenton process for the degradation of diluted organic compounds in aqueous solution. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier2016

A Study of Synthesis & [and] Performance of Flame-Made Semiconducting BiVO4 Nanoparticles for the Photocatalytic Degradation of Aqueous Organic Pollutants

Nikola Castillo

EPFL2011