[en] Infrared fluorescence from the sensitized reaction in SF₆-UF₆-H₂ system induced by 10.6 μm P(24) line of a pulsed CO₂ laser is investigated. The time resolved IR fluorescence of vibrationally excited HF* is measured with an InSb photovoltic detector and is compared with that from the SF₆--H₂ system under similar experimental conditions. Our results show a linear dependence of fluorescence intensity with laser energy density. The time resolved IR fluorescence of HF* is dependent on the partial pressure of UF₆. The fluorescence intensity obeys the single exponential decay at lower P/sub =/, but non-single exponential decay is observed at higher P/sub =/. The time dependence of the HF* fluorescence intensity is explained with the infrared photo-sensitized reaction mechanism of the SF₆-UF₆-H₂ system

[en] The UV photodissociation of UF₆ excited in the B-x-tilde band is investigated with the 253.7 nm radiation from a filter Hg lamp. In the presence of H₂, the dissociation yields are measured as a function of the incident light intensity, the partial pressure of hydrogen and various gas additives (Ar, N₂ and SF₆). The apparent quantum yield of 1.8 +- 0.1 is observed for UF₆-H₂ system and of near unity for for UF₆-CO system. The UV photodissociation mechanism of UF₆ excited in the B-x-tilde band is discussed

[en] The transient changes in UV absorbance of the vibrationally excited UF₆ molecules in the UV region of 220-330 nm have been investigated. The UF₆ molecules are excited from pulsed CO₂ laser pumped SF₆ by a V-V energy transfer process. Under static condition, the influences of CO₂ laser fluence, SF₆ and UF₆ partial pressure upon the UV absorption changes have been measured. For a 2.0 Torr SF₆ and 2.0 Torr UF₆ mixture and at laser pulsed energy of 160 +- 10 mJ, the UV absorption spectrum of vibrationally excited UF₆ molecules shows existence of four absorption peaks at 240, 248, 290 and 313 nm, respectively. It may be related to the UV absorption of several higher vibrationally excited UF₆ molecules

[en] As a class, perfluorinated carboxylate (PFCA) was ranked among the most prominent organohalogen contaminants in environment with respect to thermal, chemical and biological inertness. Hydrated electron (e_aq^-), a highly reactive and strongly reductive species, has been reported to readily decompose perfluoroaromatic compounds via intermolecular electron transfer process in aqueous solution. Question then arose: what would happen if perfluorinated carboxylates encountered with hydrated electron? Original laboratory trial on the interaction between F(CF₂)_nCOO^- (n=1, 3, 7) and hydrated electron was attempted by using laser flash photolysis technique in this research work. Abundant hydrated electron (e_aq^-) could be produced by photolysis of 1.25 x 10^-4 M K₄Fe(CN)₆ in nitrogen saturated water. In the presence of F(CF₂)_nCOO^- (n=1, 3, 7), the decay of e_aq^- was observed to enhance dramatically, indicating e_aq^- was able to attack PFCAs. On addition of perfluorinated carboxylates, the loss of e_aq^- was mainly due to the following channels. By mixing the solution of K₄Fe(CN)₆ with excess K₃Fe(CN)₆ and PFCAs, e_aq^- turned to decayed corresponding to mixed first- and second-order kinetics. Rate constants for the reactions of e_aq^- with PFCAs could be then easily determined by monitoring the decay of e_aq^- absorption at 690 nm. Since perfluorinated carboxylates were salts, the influence of ionic strength on k₃ was examined systematically by carrying out experiments of varying ionic strength ranging from 0.009 up to 0.102 M by adding NaClO₄. In this manner, the second order rate constants for e-aq with CF₃COO^-, C₃F₇COO^-, C₇F₁₅COO^- were derived to be (1.9±0.2) x 10⁶ M^-1 S^-1 (μ=0), (7.1±0.2) x 10⁶ M^-1S^-1 (μ=0) and (1.7±0.5) x10⁷ M^-1S^-1 (μ=0.009 M) respectively. Apparently, the length of F(CF₂)_n group exerted substantial influence on the rate constant. Further study on byproducts analysis by ion chromatography showed that fluorine ion was generated in the mixed solution of K₄Fe(CN)₆ and PFCAs after irradiation. This phenomenon also proved that hydrated electron could attach to PFCAs and followed by efficient dissociation of PFCAs via heterolytic cleavage of C-F bond. Considering that a majority of hydrated electron are generated in the course of radiation and non-thermal plasma, such technologies are believed to be capable of serving to PFCAs abatement. . (authors)

[en] An outer combined plasma photolysis (OCPP) reactor that simultaneously utilized a dielectric barrier discharge (DBD) plasma and UV radiation from DBD-driven KrI* excimer was designed and constructed. Gas streams containing benzene were treated with normal DBD and OCPP at atmospheric pressure. In contrast to DBD, benzene removal efficiency increased by 15.9% in OCPP when applied voltage, gas flow rate and initial concentration of benzene were set at 9 kV, 35 L min^-1 and 800 mg m^-3, respectively. Thus, the applied voltage could be reduced to a certain extent in the plasma decomposition of pollutants with OCPP. In addition, the effects of various operational parameters including pressure of filled Kr, ratio of Kr/I₂ and quartz dielectric characteristics on OCPP performance were investigated. Finally, the likely reaction mechanisms for the removal of benzene by OCPP were suggested on the basis of the emission spectra of KrI* excimer and byproducts analysis. Those results would offer prospective commercial applications for pollutant decomposition with OCPP

[en] A combined plasma photolysis (CPP) reactor that utilized the dielectric barrier discharge (DBD) plasma together with DBD-driven KrI* excimer ultraviolet emission was applied to the decomposition of H₂S gas. The effects of applied voltage, input current, gas flow velocity, original concentration as well as the ratio of Kr/I₂ mixture on H₂S removal efficiency were investigated. Gas streams containing H₂S were separately treated with single DBD and CPP reactor under the same conditions. In comparison to DBD, CPP could greatly enhance the H₂S removal efficiency at the same applied voltage, inlet gas concentration and gas flow velocity. In addition, the reaction mechanism was also discussed in this paper.

[en] Bromate (BrO₃^-) is a disinfection by-product in drinking water, and its removal is very difficult especially at low levels. ⁶⁰Co gamma rays were used to remove BrO₃^- in aqueous solution in this study. The effects of absorbed doses, BrO₃^- initial concentration, gas saturation, pH value and coexisting anions (Cl^-, NO₃^-, SO₄^2- and HCO₃^-/CO₃^2-) on BrO₃^- reduction were evaluated. After 4.0-kGy irradiation of air-equilibrated solution of 30.7 μg/L BrO₃^-, the residual BrO₃^- was 8.3 μg/L, which is below the maximum contaminant level of drinking water. The BrO₃^- reduction rate increased with the dose, in the order of N₂ > air > O₂ > N2_O atmosphere under similar conditions. The results also show that high pH favored the BrO₃^- removal. According to the experimental results, it can be concluded that the efficiency of decomposing BrO₃^- by reactive species followed the order of ·e_aq^- > ·H > HO₂· > O₂^-·. Coexisting Cl^-, HCO₃^-/CO₃^2- and SO₄^2- ions have little effect on BrO₃^- removal, whereas NO₃^- can inhibit its removal as a result of competition with BrO₃^- for ·e_aq^-. (authors)

[en] The radical cation of C₆₀ is generated either via hole transfer from the radical cation of CCl₄ to C₆₀ or via electron transfer from triplet C₆₀ to CCl₄. The radical adduct of CCl₃ to C₆₀, [C₆₀CCl₃], was also produced via two different mechanisms, namely the radical addition reaction and the reaction between triplet C₆₀ and CCl₄, respectively

[en] Background: LiF-BeF₂ is used as coolants for Thorium Molten Salt Reactor (TMSR). The offgas from TMSR containing beryllium which is harmful to both human health and the environment must be purified before being discharged. Purpose: A new type wet duster-ultrasonic atomization-impinging stream foam tower was developed. Methods: The beryllium removal properties were investigated by sampling according to national standards. The increase of atomization amount is helpful for improving beryllium removal efficiency. Results: In order to control the absolute humidity offgas after purification, the optimal atomization amount is set at 80 mL·min^-1. The ultrasonic humidifier should be installed 3 m away from the foam tower. Particles with diameter bigger than 0.4 μm can be removed effectively. The beryllium removal efficiency of offgas increases with the initial beryllium concentration and the offgas velocity which is optimized at 12 m·s^-1. The optimal water level in the tower is 40 cm when the offgas velocity is 12 m·s^-1. Conclusion: The results indicate that ultrasonic atomization-impinging stream foam tower is suitable for purifying offgas containing beryllium in TMSR. (authors)

[en] This paper investigates the degradation of chlorobenzene by dielectric barrier discharge (DBD) coupled with MnO_x/γ-Al₂O₃ catalysts. MnO_x/γ-Al₂O₃ catalysts were prepared using the impregnation method and were characterized in detail by N₂ adsorption/desorption, x-ray diffraction and x-ray photoelectron spectroscopy. Compared with the single DBD reactor, the coupled reactor has a better performance on the removal rate of chlorobenzene, the selectivity of CO_x, and the inhibition of ozone production, especially at low discharge voltages. The degradation rate of chlorobenzene and selectivity of CO_x can reach 96.3% and 53.0%, respectively, at the specific energy density of 1350 J l^–1. Moreover, the ozone concentration produced by the discharge is significantly reduced because the MnO_x/Al₂O₃ catalysts contribute to the decomposition of ozone to form oxygen atoms for the oxidation of chlorobenzene. In addition, based on analysis of the byproducts, the decomposition mechanism of chlorobenzene in the coupled reactor is also discussed. (paper)