| Summary: | 碩士 === 中興大學 === 土壤環境科學系所 === 94 === Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants in inflammables to ensure the life and property safety by decreasing the risk of fire accidents. PBDEs have been detected in human, wildlife, marine, and freshwater sediments. PBDEs become important environmental organic pollutants but the degradation studies of PBDEs in the environment are still limited.
In this study, the chemical debromination of DBDE (Decabrominated diphenyl ether) by zero-valent iron (ZVI) was studied. A scanning electron microscopy and a photon correlation spectroscopy were performed to characterize the surface properties and particle size of nanoscale ZVI, respectively. The nanoscale ZVI existed as spherical particles averaging 20~50 nm in diameter and its surface area was 52.0 m2/g. Within 40 minutes over 80 % of DBDE was transformed into lower bromo congeners by nanoscale ZVI under ambient conditions. During the initial reaction period (< 20 minutes), nonabromo BDEs were the most abundant products but hexa to heptabromo congeners were dominant after 130 minutes.
The effects of particle sizes of zero-valent iron, temperature (5, 25, and 45 ℃), pH value (5, 7, 8, and 10), and the existence of inorganic anions (Cl-, HCO3-, and H2PO4-) and cations (Na+, Cu2+, and Fe3+) in solutions on the dehalogenation were evaluated.
For nanoscale ZVI, the pseudo-first-order DBDE debromination rate constant (0.0583 min-1) was significantly faster than that of microscale ZVI (0.0077 min-1) due to the higher surface area and reactivity of nanoscale iron particles. The debromination rate constants of DBDE increased with the decreasing of aqueous pH values and with the increase of temperature. For anions, a high concentration of chloride ions enhanced the debromination of DBDE, whereas phosphate and carbonate ions hindered the debromination process. The cation species also affected the reduction reaction by ZVI except Na+. The debromination rate constants of DBDE increased in the presence of Cu2+ and decreased in the presence of Fe3+.
Lugang and Longgang soil solutions and Lugang and Longgang soils were chose as soil systems to evaluate the debromination rate of DBDE by nanoscale ZVI. The reduction rates of DBDE by nanoscale ZVI in soil solutions and soils were slower than those in pure water. Comparing the reaction rates between Longgang and Lugang soils, the reduction rate of DBDE in Longgang soil was faster than that in Lugang soil probably due to the lower pH of Loggang soil. The debromination pathway of DBDE by nanoscale ZVI was proposed via the analysis of byproducts. Nanoscale ZVI has the high potential values to remediate PBDEs in the environment.
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