ABSTRACT
Environmentally persistent free radicals (EPFRs) are formed by the adsorption of substituted aromatic precursors on the surface of metal oxides and are known to have significant health and environmental impact due to their unique stability. In this article, the formation of EPFRs is studied by adsorption of phenol on ZnO, CuO, Fe2O3, and TiO2 nanoparticles (â¼10-50 nm) at high temperatures. Electron paramagnetic resonance indicates the formation of phenoxyl-type radicals. Fourier transform infrared spectroscopy provides further evidence of EPFR formation by the disappearance of -OH groups, indicating the chemisorption of the organic precursor on the metal oxide surface. These results are further confirmed by inelastic neutron scattering, which shows both ring out-of-plane bend and C-H in-plane bend motions characteristic of phenol adsorption on the studied systems. Also, the changes in the oxidation state of the metal cations are investigated by X-ray photoelectron spectroscopy, which shows that the direction of electron transfer (redox) during phenol chemisorption is strongly dependent on surface properties as well as surface defects of the metal oxide surface.
ABSTRACT
We demonstrate a chirped-pulse-amplified Ti:Sapphire laser system operating at 1 kHz, with 20 mJ pulse energy, 26 femtosecond pulse duration (0.77 terawatt), and excellent long term carrier-envelope-phase (CEP) stability. A new vibrational damping technique is implemented to significantly reduce vibrational noise on both the laser stretcher and compressor, thus enabling a single-shot CEP noise value of 250 mrad RMS over 1 hour and 300 mrad RMS over 9 hours. This is, to the best of our knowledge, the best long term CEP noise ever reported for any terawatt class laser. This laser is also used to pump a white-light-seeded optical parametric amplifier, producing 6 mJ of total energy in the signal and idler with 18 mJ of pumping energy. Due to preservation of the CEP in the white-light generated signal and passive CEP stability in the idler, this laser system promises synthesized laser pulses spanning multi-octaves of bandwidth at an unprecedented energy scale.
ABSTRACT
The surface-mediated reactions of 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene were studied using CuO/ SiO2 as a fly ash surrogate. These compounds served as model precursors that have been implicated in the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). With FTIR, we determined that reactions of the model precursors with a substrate composed of CuO dispersed on silica result in the formation of a mixture of surface-bound phenolate and carboxylate partial oxidation products from 200 to 500 degrees C. Chemisorption of 2-chlorophenol and 1,2-dichlorobenzene resulted in the formation of identical surface-bound species. Using X-ray absorption near-edge structure spectroscopy, we measured the time- and temperature-dependent reduction of Cu(II) in a fly ash surrogate during reaction with each precursor. It was demonstrated that CuI2O is the major reduction product in each case. The rate of Cu(II) reduction could be described using pseudo-first-order reaction kinetics with Arrhenius activation energies for reduction of Cu(II) of 112, 101, and 88 kJ mol(-1) for 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene, respectively. We demonstrate that chlorinated phenol and chlorinated benzene both chemisorb to form chlorophenolate. Although chlorinated phenols chemisorb at a faster rate, chlorinated benzenes are found at much higher concentrations in incinerator effluents. The implication is that chlorinated benzenes may form 10 times more chlorophenolate precursors to PCDD/Fs than chlorinated phenols in combustion systems.
