Electron pulse radiolysis determination of hydroxyl radical rate constants with Suwannee River fulvic acid and other dissolved organic matter isolates.
ABSTRACT Pulse radiolysis experiments were conducted on dissolved organic matter (DOM) samples isolated as hydrophobic and hydrophilic acids and neutrals from different sources (i.e., stream, lake, wastewater treatment plant). Absolute bimolecular reaction rate constants for the reaction of hydroxyl radicals (*OH) with DOM (k*(OH), DOM) were determined. k*(OH, DOM) values are expressed as moles of carbon. Based on direct measurement of transient DOM radicals (DOM*) and competition kinetic techniques, both using pulse radiolysis, the k*(OH, DOM) value for a standard fulvic acid from the Suwannee River purchased from the International Humic Substances Society was (1.60 +/- 0.24) x 10(8) M(-1) s(-1). Both pulse radiolysis methods yielded comparable k*(OH, DOM) values. The k*(OH, DOM) values for the seven DOM isolates from different sources ranged from 1.39 x 10(8) M(-1) s(-1) to 4.53 x 10(8) M(-1) s(-1), and averaged 2.23 x 108 M(-1) s(-1) (equivalent to 1.9 x 10(4) (mgC/L)(-1) s(-1)). These values represent the first direct measurements of k*(OH, DOM,) and they compare well with literature values obtained via competition kinetic techniques during ozone or ultraviolet irradiation experiments. More polar, lower-molecular-weight DOM isolates from wastewater have higher k*(OH, DOM) values. In addition, the formation (microsecond time scale) and decay (millisecond time scale) of DOM* transients were observed for the first time. DOM* from hydrophobic acids exhibited broader absorbance spectra than transphilic acids, while wastewater DOM isolates had narrower DOM* spectra more skewed toward shorter wavelengths than did DOM* spectra for hydrophobic acids.
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ABSTRACT: UV irradiation-activated sodium persulfate (UV/PS) was studied to degrade florfenicol (FLO), a phenicol antibiotic commonly used in aquaculture, in water. Compared with UV/H2O2 process, UV/PS process achieves a higher FLO degradation efficiency, greater mineralization, and less cost. The quantum yield for direct photolysis of FLO and the second-order rate constant of FLO with sulfate radicals were determined. The effects of various factors, namely PS concentration, anions (NO3−, Cl−, and HCO3−), ferrous ion, and humic acid (HA), on FLO degradation were investigated. The results showed that the pseudo-first-order rate constant increased linearly with increased PS concentration. The tested anions all adversely affected FLO degradation performance with the order of HCO3− > Cl− > NO3−. Coexisting ferrous ions enhanced FLO degradation at a Fe2+/PS molar ratio under 1:1. HA significantly inhibited FLO degradation due to radical scavenging and light-screening effect. Toxicity assessment showed that it is capable of controlling the toxicity for FLO degradation. These findings indicated that UV/PS is a promising technology for water polluted by antibiotics, and the treatment is optimized only after the impacts of water characteristics are carefully considered.Environmental Science and Pollution Research 01/2015; DOI:10.1007/s11356-014-4054-6 · 2.76 Impact Factor
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ABSTRACT: In this study, ZnOOH was used as a catalyst and its efficiency in removing trace organic matter, 2-methylisoborneol (2-MIB), in conjunction with ozone was investigated. The catalyst was characterized by X-ray diffraction (XRD), the Brunauer-Emmet-Teller (BET) method and Fourier transform infrared spectrometry (FT-IR). The performance of the ozone oxidation process alone and the O-3/ZnOOH system were both studied. Factors such as ozone dose, catalyst dosage, radical inhibitor and water qualities were analyzed to investigate their effects on catalysis activity and 2-MIB removal efficiency. Results showed that the removal of 2-MIB was better in O-3/ZnOOH system. The removal efficiency increased with the increase of catalyst dosage. However, the increase became inconspicuous when the dose was higher than 400 mg. Tert-butanol inhibits the removal of 2-MIB, and this effect was even more obvious in O-3/ZnOOH system. This indicates that O-3/ZnOOH system promotes the hydroxyl radical production, and removal reaction process in this system follows the mechanism of hydroxyl radical reaction. The water qualities also affected the removal of 2-MIB. Tap water was better than distilled water in the degradation of 2-MIB, while the effect of Songhua River was the weakest.Aqua 02/2013; 62(1):35. DOI:10.2166/aqua.2013.016 · 0.52 Impact Factor
Conference Paper: InAs gate-all-around nanowire MOSFETs by top-down approach[Show abstract] [Hide abstract]
ABSTRACT: InAs gate-all-around (GAA) nanowire MOSFETs are experimentally demonstrated for the first time by a top-down approach [1-3]. Thanks to the well-controlled nanowire release process and the novel ALD high-k/metal gate stack process, InAs nFETs with channel length (Lch) ranging from 380 to 20 nm and nanowire width (WNW) from 60 to 20 nm are achieved. With an EOT of 3.9 nm, high drain current of 4.3 A/mm at Vds = Vgs = 2 V and maximum transconductance (gmax) of 1.6 S/mm at Vds = 1 V are obtained in a device with WNW = 20 nm and Lch = 180 nm, normalized by the perimeter of the nanowires. A detailed scalability study (VTH, gm, Ids vs. Lch) was carried out. The devices in this study show strong dependence on the nanowire width and smaller nanowire size offers much enhanced electrical performance and better immunity from the short channel effects (SCEs).2014 72nd Annual Device Research Conference (DRC); 06/2014