Fe-Mn 복합물을 이용한 펜톤유사반응에서의 산화 및 환원 분해경로에 대한 연구

Abstract

산업이 발달하고 도시화가 진행됨에 따라 다양한 오염물질이 인위적으로 생성, 배출되기 때문에 지하수에는 다양한 오염물질이 존재하고 있다. 이러한 다양한 오염물질을 동시에 제거하기 위해 Fe-Mn 복합물을 제작하고 이를 산화제(과산화수소, 과황산)와 반응시키는 Fenton-like 반응을이용하여 오염물질을 분해하는 것이 이 연구의 최종 목표이다. Fe-Mn 복합물을 제작하기 위하여 산화수가 다른 MnO,Mn2O3 그리고 MnO2를 [≡Fe-Mn]NaOH 및 [≡Fe-Mn]Ca(OH)2을 이용하여 제작하였으며, 최적의 복합물을 선정하기 위해 다양한 물리·화학적 분석을 시도해보았다. EDS 분석을 통해 NaOH를 주입한 3가지 복합물 중에서 특히 [≡Fe-MnO2]NaOH가 81%로 가장 많은 철이 존재하고 있었으며, XRD 분석을 통해서 [≡Fe-MnO]NaOH, [≡Fe-Mn2O3]NaOH 그리고 [≡Fe-MnO2]NaOH가 모두 공통적으로 jacobsite(MnFe2O4)의 철 산화물로 존재하는 물질임을 확인할 수 있었다. 또한 TEM분석을 통해서 망간표면에 막대 형태의 결정을 확인할 수 있는데, 이는 망간 표면에 존재하는 철임을 예측할 수 있었다. 더불어 XPS 분석을 통해 [≡Fe-Mn]NaOH로 결합된 복합물은 Fe 3p의 경우 56 eV근처에서, Fe 2p 의 경우에는 710 eV과 725 eV로 일반적인 철 산화물과 유사한 값을 가져 이는 망간 표면에 철이 존재하는 Fe-Mn 복합물임을 알 수 있었다. [≡Fe-Mn]Ca(OH)2는 TEM 분석을 통해 [≡Fe-MnO]Ca(OH)2, [≡Fe-Mn2O3]Ca(OH)2 그리고 [≡Fe-MnO2]Ca(OH)2 이 모두 바늘 모양의 결정이 망간 표면에 뭉쳐있는 형태로 존재하였으며, 이 복합물의 주된 결정물질이 calcite(CaCO3)의 물질임을 알 수 있었다. 더불어 [≡Fe-Mn]Ca(OH)2으로 결합된 물질은 일반적인 철 산화물이 갖는 binding energy의 값과 현저한 차이를 보이는데 이는 칼슘(Ca)의 존재로 때문인 것으로 사려 된다. 따라서 이렇게 제작한 [≡Fe-Mn]NaOH 및 [≡Fe-Mn]Ca(OH)2과 산화제(과산화수소, 과황산)을 다양한 pH영역에 적용하여 오염물질로 선정된 사염화탄소와 벤젠의 분해 실험을 수행해보았다. 사염화탄소는 과산화수소와는 반응하지 않는 물질로 알려져 있지만, Fe-Mn 복합물을 적용한 본 연구에서는 산성에서 알칼리 영역으로 갈수록 분해효율이 증가함을 확인할 수 있었다. [≡Fe-Mn]NaOH 및 [≡Fe-Mn]Ca(OH)2 모두 과산화수소에 비해 과황산을 적용하였을 때 높은 분해효율을 보였으며, 특히 pH 9 영역에서 과황산과 [≡Fe-MnO2]NaOH가 사염화탄소를 분해할 수 있는 가장 최적의 조건임을 알 수 있었다. 벤젠의 경우에는 과황산보다는 과산화수소와 반응하였을 때 가장 효율적인 분해가 이루어졌으며, 특히 pH 7에서 [≡Fe-MnO2]NaOH와 과산화수소와의 반응을 통해 63%의 벤젠이 분해되었다. 오염물질 분해 반응에 주된 영향을 미치는 라디컬을 규명하기 위하여 oxidant scavenger인 2-propanol과 reductantscaven ger인 chloroform을 주입하여 scavenger 실험을 진행하였다. Fenton 반응은 다양한 반응 생성물이 공존하지만, 본 연구에서는 사염화탄소의 경우에는 superoxide anion에 의한 환원 분해 경로를 갖는 물질임을 확인할 수 있었으며, 벤젠의 경우에는 hydroxyl radical이 주된 작용을 하는 산화 분해 경로를 가지 는 물질임을 규명해낼 수 있었다.결과적으로 본 연구에서는 다양한 복합물 중에서 오염물질을 분해하기 위한 가장 최적의 복합물은 [≡Fe-MnO2]NaOH로 선정하였으며, 이 복합물이 오염물질인 사염화탄소와 벤젠을 각각 과황산과 과산화수소를 적용하였을 때 가장 효율적으로 분해됨을 알 수 있었다. 더불어 이러한 반응 시스템에서 pH를 적절히 조절해준다면 지하수에 공존하는 여러 가지 오염물질을 동시에 제거할 수 있을 것이라고 사려 된다. |Contaminant of organic compounds is widely spread on soil and groundwater resulting from improper disposal such as carbontetrachloride and perchloroethylene and BTEX. Dissolution of NAPLs into groundwater and soil not only provide source of contaminant but also spread to non contaminated sites and then NAPLs might be persist for a long period. It must be immediately treated since it leads severe damage to public health and environmental problems. Thus, the purpose of this study was to investigate the acivity of Fe-Mn composite in Fenton-like reaction by evaluating their ability to degrade carbon tetrachloride and benzene. Fe-Mn complex were synthesized with reaction of Fe(II) and manganese oxide with various oxidation state. Based on the results of SEM, TEM, XPS and XRD analysis, iron oxides were identified and the types of synthesized iron oxides depended on the types of manganese oxide and hydroxide sources (NaOH or Ca(OH)2). EDS analysis reveals that the primary elements in [≡Fe-Mn]NaOH was Mn and Fe and specially Fe was contained 81% in [≡Fe-MnO2]NaOH. Results for XRD analysis [≡Fe-Mn]NaOH that manganese oxide reacted with Fe(II) is commonly indicated jacobsite (MnFe2O4) as a iron oxide. Morphologies were analyzed by TEM, all of manganese oxide synthesized with [≡Fe-Mn]NaOH have rod shape crystallization and it was expected Fe(II) attached manganese surface. Binding energies of [≡Fe-Mn]NaOH were similar with common iron oxide 56ev as Fe 3p and 710 and 725ev as Fe 2p by XPS. In case of [≡Fe-Mn]Ca(OH)2, morphologies demonstrated that needle shape agglomerate together on the particle through TEM. All of [≡Fe-Mn]Ca(OH)2 were detected calcite(CaCO3) because of Ca which is primary element. Moreover, binding energies of [≡Fe-Mn]Ca(OH)2 were different from common iron oxide, the peak might be shift due to binding of Ca. Thus, Fe-Mn composite was applied with oxidants such as H2O2 and persulfate to degrade of carbon tetrachloride and benzene. Carbon tetrachloride is known that it is non-reactive with H2O2 but when carbon tetrachloride reacted with [≡Fe-Mn]NaOH, [≡Fe-Mn]Ca(OH)2, it was gradually degraded cat various pH, especially it was efficiently degraded at pH 12. However, persulfate was the most optimum oxidant because it was remained after 6hr and a good oxidant for removing carbon tetrachloride. As a result carbon tetrachloride was decompose 30% when [≡Fe-MnO2]NaOH was reacted with persulfate. Benzene was approximately removed 63% when [≡Fe-MnO2]NaOH was reacted with H2O2 at pH 7 and it was the most optimum condition to degrade benzene. Chloroform and 2-propanol were selected as scavenger for respectively carbon tetrachloride and benzene because of its high reactivity with reductant and oxidant. The results suggest that the reductant can be scavenged by high concentrations of chloroform, which is likely superoixde anion. Carbon tetrachloride might be favored with superoxide anion. Oxidant scavenger like 2-propanol was reacted with hydroxyl radical, it was important role to degrade benzene. According to this study, Fe-Mn composite and two type of oxidants were properly reacted with carbon tetrachloride and benzene to degrade.; Contaminant of organic compounds is widely spread on soil and groundwater resulting from improper disposal such as carbontetrachloride and perchloroethylene and BTEX. Dissolution of NAPLs into groundwater and soil not only provide source of contaminant but also spread to non contaminated sites and then NAPLs might be persist for a long period. It must be immediately treated since it leads severe damage to public health and environmental problems. Thus, the purpose of this study was to investigate the acivity of Fe-Mn composite in Fenton-like reaction by evaluating their ability to degrade carbon tetrachloride and benzene. Fe-Mn complex were synthesized with reaction of Fe(II) and manganese oxide with various oxidation state. Based on the results of SEM, TEM, XPS and XRD analysis, iron oxides were identified and the types of synthesized iron oxides depended on the types of manganese oxide and hydroxide sources (NaOH or Ca(OH)2). EDS analysis reveals that the primary elements in [≡Fe-Mn]NaOH was Mn and Fe and specially Fe was contained 81% in [≡Fe-MnO2]NaOH. Results for XRD analysis [≡Fe-Mn]NaOH that manganese oxide reacted with Fe(II) is commonly indicated jacobsite (MnFe2O4) as a iron oxide. Morphologies were analyzed by TEM, all of manganese oxide synthesized with [≡Fe-Mn]NaOH have rod shape crystallization and it was expected Fe(II) attached manganese surface. Binding energies of [≡Fe-Mn]NaOH were similar with common iron oxide 56ev as Fe 3p and 710 and 725ev as Fe 2p by XPS. In case of [≡Fe-Mn]Ca(OH)2, morphologies demonstrated that needle shape agglomerate together on the particle through TEM. All of [≡Fe-Mn]Ca(OH)2 were detected calcite(CaCO3) because of Ca which is primary element. Moreover, binding energies of [≡Fe-Mn]Ca(OH)2 were different from common iron oxide, the peak might be shift due to binding of Ca. Thus, Fe-Mn composite was applied with oxidants such as H2O2 and persulfate to degrade of carbon tetrachloride and benzene. Carbon tetrachloride is known that it is non-reactive with H2O2 but when carbon tetrachloride reacted with [≡Fe-Mn]NaOH, [≡Fe-Mn]Ca(OH)2, it was gradually degraded cat various pH, especially it was efficiently degraded at pH 12. However, persulfate was the most optimum oxidant because it was remained after 6hr and a good oxidant for removing carbon tetrachloride. As a result carbon tetrachloride was decompose 30% when [≡Fe-MnO2]NaOH was reacted with persulfate. Benzene was approximately removed 63% when [≡Fe-MnO2]NaOH was reacted with H2O2 at pH 7 and it was the most optimum condition to degrade benzene. Chloroform and 2-propanol were selected as scavenger for respectively carbon tetrachloride and benzene because of its high reactivity with reductant and oxidant. The results suggest that the reductant can be scavenged by high concentrations of chloroform, which is likely superoixde anion. Carbon tetrachloride might be favored with superoxide anion. Oxidant scavenger like 2-propanol was reacted with hydroxyl radical, it was important role to degrade benzene. According to this study, Fe-Mn composite and two type of oxidants were properly reacted with carbon tetrachloride and benzene to degrade.