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Effect of the reaction atmosphere on component and reactivity of green synthesis of iron nanoparticles

摘要：成本低廉和无二次污染的"绿色"合成纳米材料是发展原位纳米环境修复技术的前沿研究课题之一.本文以绿茶提取液为还原剂和稳定剂进行"绿色"合成纳米铁,探讨在不同的气氛下"绿色"合成的纳米铁颗粒的主要成分,以期为调控合成纳米铁系材料提供基础研究.首先,利用扫描电子显微镜(SEM)、X射线能谱(EDS)、X射线光电子能谱分析(XPS)和傅里叶变换红外光谱(FTIR)等表征手段对不同反应气氛下合成的纳米铁颗粒的表面微观形貌、尺寸和价态结构进行分析.结果发现,在通入N₂情况下,合成的纳米铁颗粒粒径为(84.7±11.5) nm,其主要成分以纳米零价铁为主;在通入空气情况下,合成的纳米铁粒径为(117.8±26.2) nm,其主要成分是纳米零价铁、氧化铁和四氧化三铁的混合物;通入O₂时,合成的纳米铁粒径为(141.2±26.3) nm,其主要成分以四氧化三铁为主.其次,评价在不同气氛条件下合成纳米铁颗粒对去除亚甲基蓝(MB)的反应活性.结果表明,在反应温度313 K下降解初始浓度为50 mg · L^-1 的MB溶液,反应5 min时已达到平衡,通入N₂合成的纳米铁降解MB,去除率高达98.7%,而通入O₂合成的纳米铁反应效率低,对MB的去除率仅为65.3%.最后,从以上发现提出不同气氛下可以调控"绿色"合成的铁系纳米材料成分,从而导致不同的纳米修复环境中污染物的能力.

Abstract：Green synthesis of nanoparticles has received extensive attention for in situ environmental remediation due to its low cost and biocompatibility. In this study, the composition of iron-based nanoparticles (Fe NPs) at various atmospheres using green tea extract as reducing and stabilizing agent was investigated to understand the influence of the atmosphere during the plant-mediated synthesis. Firstly, SEM, EDS, XPS and FTIR were employed to confirm the morphology, size and surface composition of Fe NPs. In a nitrogen atmosphere, the size of as-prepared product is (84.7±11.5) nm and the main component is zero-valent iron. On the other hand, the product synthesized with air has a large size range of (117.8±26.2) nm, including zero-valent iron, iron oxide and iron hydroxide. Meanwhile, in an oxygen atmosphere, the product with the largest size range of (141.2±26.3) nm mainly contains iron oxide. Secondly, the activities of Fe NPs at various atmospheres were tested by removal of methylene blue (MB). The reaction process reached equilibrium within 5 minute at a temperature of 313 K and an initial concentration of 50 mg · L^-1 MB. The removal efficiency of Fe NPs by passing N₂ is more than 98.7% and the removal efficiency is only 65.3% using Fe NPs under O₂. Finally, we proposed that the composition of Fe NPs can be controlled at various atmospheres, thereby tuning the removal capacity for different contaminants in remediation.