ABSTRACT
This work describes the electrochemical degradation of Reactive Black 5 (RB5) by two methods: electrochemical and photo-assisted electrochemical degradation with and without a Fenton reagent. Two anodes were used, Pt and boron-doped diamond (BDD, 2500â¯ppm), and the cathode was 3% MnO2 nanoflowers (NFMnO2) on a carbon gas diffusion electrode (GDE). An electrochemical cell without a divider with a GDE with 3% w/w NFMnO2/C supported on carbon Vulcan XC72 was used. The decolorization efficiency was monitored by UV-vis spectroscopy, and the degradation was monitored by Total Organic Carbon (TOC) analysis. For dissolution monitoring, aliquots (1â¯mL) were collected during the degradation. After 6â¯h of H2O2 electrogeneration, the manganese concentration in the RB5 solution was only 23.1⯱â¯1.2⯵gâ¯L-1. It was estimated that approximately 60⯵gâ¯L-1 (<0.2%) of manganese migrated from the GDE to the solution after 12â¯h of electrolysis, which indicated the good stability of the GDE. The photoelectro-Fenton-BDD (PEF-BDD) processes showed both the best color removal percentage (â¼93%) and 91% of mineralization. The 3% NFMnO2/C GDE is promising for RB5 degradation.
Subject(s)
Coloring Agents/chemistry , Electrolysis , Hydrogen Peroxide/chemistry , Iron/chemistry , Manganese Compounds/chemistry , Naphthalenesulfonates/chemistry , Oxides/chemistry , Water Pollutants, Chemical/chemistry , Boron/chemistry , Coloring Agents/isolation & purification , Diamond/chemistry , Electrodes , Naphthalenesulfonates/isolation & purification , Oxidation-Reduction , Water Pollutants, Chemical/isolation & purificationABSTRACT
In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understanding of the composition-dependent catalytic activity of these nanoparticles. AgAu nanoparticles were synthesized via the galvanic replacement method with controlled size and nanoparticle compositions. We studied extinction spectra with UV-Vis spectroscopy and simulations based on Mie theory and the boundary element method, and ultrafast spectroscopy measurements to characterize decay constants and the overall energy transfer dynamics as a function of AgAu composition. Electron-phonon coupling times for each composition were obtained from pump-power dependent pump-probe transients. These spectroscopic studies showed how nanoscale surface segregation, hollow interiors and porosity affect the surface plasmon resonance wavelength and fundamental electron-phonon coupling times. Analysis of the spectroscopic data was used to correlate electron-phonon coupling times to AgAu composition, and thus to surface segregation and catalytic activity. We have performed all-atom molecular dynamics simulations of model hollow AgAu core-shell nanoparticles to characterize nanoparticle stability and equilibrium structures, besides providing atomic level views of nanoparticle surface segregation. Overall, the basic atomistic and electron-lattice dynamics of core-shell AgAu nanoparticles characterized here thus aid the mechanistic understanding and performance optimization of AgAu nanoparticle catalysts.
ABSTRACT
We report the controlled alloying, oxidation, and subsequent reduction of individual AgAu nanoparticles in the scanning transmission electron microscope (STEM). Through sequential application of electron beam induced oxidation and in situ heating and quenching, we demonstrate the transformation of Ag-Au core-shell nanoparticles into: AgAu alloyed, Au-Ag core-shell, hollow Au-Ag2O core-shell, and Au-Ag2O yolk-shell nanoparticles. We are able to directly image these morphological transformations in real-time at atomic resolution and perform energy dispersive X-ray (EDX) spectrum imaging to map changing elemental distributions with sub-nanometre resolution. By combining aberration corrected STEM imaging and high efficiency EDX spectroscopy we are able to quantify not only the growth and coalescence of Kirkendall voids during oxidation but also the compositional changes occurring during this reaction. This is the first time that it has been possible to track the changing distribution of elements in an individual nanoparticle undergoing oxidation driven shell growth and hollowing.
ABSTRACT
O caso de um paciente portador de um grande condrossarcoma da parede toracica anterior e apresentado. A tecnica de resseccao do tumor, bem como a reconstrucao da parede toracica com tela de polipropileno e um retalho miocutaneo pediculado e apresentada em detalhes