反应气氛对绿色合成纳米铁的组分及其活性的影响

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.

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

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.