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標題: Neurospora crassa真菌殘體對溶液中六價鉻的移除機制
Mechanism of Cr(VI) removal by dead fungal biomass of Neurospora crassa
作者: 林怡君
Lin, Yi-Chun
關鍵字: fungi
Neurospora crassa
hexavalent chromium
Neurospora crassa
出版社: 土壤環境科學系所
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摘要: 環境中的鉻通常以三價及六價兩種型態存在,其中,六價鉻為一強氧化劑,對生物體具毒性及致癌性,三價鉻的毒性較低,僅在高濃度下對植物會造成毒害,故必須將毒性較大的六價鉻吸附或還原成低毒性的三價鉻,以減低六價鉻對環境的危害。 許多研究已證實,酸性條件下,真菌殘體可有效地將溶液中的六價鉻完全還原成毒性較低的三價鉻,但其所需反應時間較長,故為提升真菌殘體對六價鉻的移除效率,本研究中將藉由UV光照及添加三價鐵離子等方式,評估其對真菌殘體移除六價鉻之效率。此外,由於過去研究中,對於真菌殘體表面的反應位置及途徑,仍尚未釐清,故本實驗中亦將透過光譜分析對反應機制部分做一深入的探討。因此,本研究之主要目的為探討非生長性的Neurospora crassa在各項參數,包含UV光照、初始溶液pH值及三價鐵的添加等影響下,對溶液中六價鉻的移除效率。此外,透過與六價鉻反應前後之真菌殘體的光譜分析,釐清主要參與反應的官能基團,推估可能的反應機制。 研究結果顯示,於初始溶液pH 1.0至3.0、避光條件下,經過六小時的反應,1.0 g L-1真菌殘體可移除20-54 %的六價鉻。然而經過UV光照後,六價鉻則可在相同反應時間內被完全移除。由XANES及XPS的分析結果顯示,鍵結在真菌殘體上的鉻皆以三價的型態存在,表示真菌殘體移除六價鉻的過程中確實發生還原反應。各項參數對真菌殘體移除六價鉻的影響則發現,當初始溶液pH值越低、添加三價鐵及UV光照條件下,真菌殘體對六價鉻的移除速率越快。而由FT-IR及13C-NMR之光譜分析可知,與六價鉻反應後,真菌殘體表面的-C=O、-NH、-CO和-CH等官能基可能減少或改變其鍵結型態,表示這些官能基與鉻的還原及鍵結有關。此外,真菌殘體移除六價鉻之過程中,其表面官能基會因為鉻的氧化而溶解,六價鉻亦可經由溶液中可溶性有機碳的氧化而還原。
Cr exists in the environment in two common oxidation states of Cr(III) and Cr(VI). These two Cr species exhibit significantly differences in charges, physicochemical properties as well as chemical and biochemical reactivities. Cr(VI) is toxic to both plants and animals, and it is a strong oxidizing agent and a potential carcinogen. While Cr(III) is less toxic or nontoxic to animals, and it may poison plants only at very high concentrations. Therefore, efforts to treating Cr(VI)-containing wastewaters through an adsorption or reduction technique are required to eliminate the hazard of Cr(VI) to the ecosystem. Recently, the dead fungal biomass have been confirmed to be effective bio-materials for converting Cr(VI) to Cr(III) at acidic conditions; however, the reaction time is often relatively long and the specific functional groups involved in Cr(VI) reduction are unclear. To enhance Cr(VI) removal and clarify the reaction mechanisms of Cr(VI) on biomaterials, a technique involving light and Fe(III) was developed to examine the interactions of Cr(VI) with Neurospora crassa as a model fungus. The objectives of this study were to evaluate the efficiency of Cr(VI) removal by a dead fungal biomass of Neurospora crassa as influenced by UV light, pHs and the addition of Fe(III). In addition, the possible functional groups involved in the process of Cr(VI) removal, either in the dark or exposure to the light, were identified and systemically investigated using spectroscopic analysis. The results show that 20-54 % of added Cr(VI) (96.15 μM) was removed by 1.0 g of dead fungal biomass at pH 1.0-3.0 after 6 h reaction in the dark. However, 96.15 μM Cr(VI) disappeared completely under the same reaction time and experimental conditions when light was present. The XANES and XPS spectra of the Cr-loaded biomass showed that most of the Cr on the fungus were Cr(III), a result indicating the occurrence of Cr(VI) reduction on the surfaces of the fungus. In addition, dissolved organic carbons (DOC) resulting from the dissolution of N. c.-biomass may also contribute to Cr(VI) reduction. The rates of Cr(VI) removal increased with a decrease in pH and with the addition of 89.5 μM Fe(III) under illumination. Spectroscopic studies, e.g., FTIR and NMR analysis, indicated that the -C=O, -NH, -CO and -CH of N. c.-biomass may be responsible for the reduction/adsorption of Cr.
其他識別: U0005-2306200915470200
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