Synthesis of Dense Non Aqueous Suspension of Nano-Scale Zero Valent Iron

近年來，穩定懸浮之奈米零價鐵被使用在去除地下水中溶解態含氯有機污染物之研究上。但因水相奈米零價鐵懸浮液與含氯溶劑不能互溶，以致無法用於處理非水溶解態之含氯有機物污染。本研究之目的即為了克服此項缺點，發展對環境友善且可與非水相含氯溶劑互溶之重質非水相奈米零價鐵懸浮液。 本實驗經適當篩選後，選定碳酸二甲酯(DMC)做為奈米零價鐵之承載液。DMC具有低毒性、可生物分解性、與水不互溶、比重比水大、低黏滯性，符合本研究對奈米零價鐵承載液之需求性質。 本研究以市售之奈米零價鐵進行表面改質，使用的表面修飾劑分別為十八烷基磷酸酯(ODP)、十六烷基三甲基溴化銨(CTAB)與聚甲基丙烯酸甲酯(PMMA)。實驗結果顯示經三種表面修飾劑改質後之重質非水相奈米零價鐵懸浮液，皆可輕易與三氯乙烯混合，且經CTAB、PMMA改質後可以提升奈米零價鐵在碳酸二甲酯中的穩定懸浮性。改質後之奈米零價鐵粒徑約在50-100 nm，比表面積為16.54 m2/g，鐵元素的含量約佔83-85 wt%。 在飽和含水之碳酸二甲酯中的TCE降解反應試驗結果顯示，在TCE初始濃度為262 mg/L條件下以PMMA/Fe0重質非水相奈米零價鐵懸浮液10小時內的監測中並未發現TCE有降解的趨勢。 以濃度為10 Fe0g/L、比重為1.073，含有CTAB/Fe0或PMMA/Fe0之重質非水相奈米零價鐵懸浮液，注入飽和石英砂層之試驗中經提高重質非水相奈米零價鐵懸浮液之液位差，以克服飽和石英砂柱之毛細壓力，含有CTAB/Fe0者所需克服的毛細壓力為1788 N/m2，含PMMA/Fe0者所需克服的毛細壓力為1050 N/m2。In recent years, suspended colloidal zero valent iron nanoparticles have been applied to the dechlorination of aqueous chlorinated solvents in polluted groundwater. However, due that nonaqueous chlorinated solvents and water are immiscible, nonaqueous chlorinated solvents could not react with aqueous colloidal zero valent iron nanoparticles. To overcome the drawback, eco-friendly dense nonaqueous suspensions of nano-scale zero-valent iron (DNAPNZVI) were developed. In this study, dimethyl carbonate (DMC) was chosen as the surface-modified nano zero valent iron’s carrying liquid. DMC has low toxicity, high biodegradability, immiscibility with water, denser density than water and low viscosity, which meets the criteria of the carrying liquid. Octadecyl phosphate, cetyltrimethylammonium bromide or poly methyl methacrylate was used to modify the surfaces of commercial nano zero valent iron (NZVI). The results of demonstrated that three kinds of DNAPNZVI were easily miscible with chlorinated solvent. In addition, NZVI modified with CTAB or PMMA, were stably suspended in DMC. The mean particle size ranged from 50 to 100 nm, surface area was 16.54 m2/g and the content of iron was 83-85 wt%. The results of dechlorination experiment for 262 mg/L TCE in DMC-saturated water showed that there was not TCE degradation found during ten hours with PMMA/Fe0. DNAPNZVI, at the concentration of 10 Fe g/L and with a specific gravity of 1.073 was injected into with grain size from 200 to 250 μm saturated quartz sand column. The result of experiment revealed that the capillary force of the oil-water system in saturated quartz sand column to be overcome was 1050 N/m2 by PMMA/Fe0 was 1050 N/m2 and 1788 N/m2 for CTAB/Fe0