桉树叶绿色合成纳米铁修复地下水铬污染

Remediation of Cr(VI) from the contaminated groundwater is a great challenge. Significant potential has been demostrated for the application of nanoscale iron particles (nZVI) for groundwater remeidation. However, since nZVI tend to aggregate and to oxidize, and to produce nZVI by chemical method with a high cost, nZVI is limitd in its field application. Green synthesis of nZVI using plant extracts and iron ions has low cost and environmental friendly. Green nZVI also has good oxidation resistance and dispersibility. However, it is still unclear for the formation of nZVI by green synthesis and the reduction of Cr(VI) in ground water using green nZVI. Eucalyptus is one of three fast growing trees in the world, and eucalyptus leaves contain polyphenols, flavonoids, organic acids and other active substances. Therefore, eucalyptus leaf extracts can be acted as both reducing and stabilizing agents in the green synthesis of nZVI. For these reasons, the primary objective of the proposal is to 1) Understanding the green synthesis mechanism of nZVI using Eucalyptus leaf extracts; 2) explore the reduction mechanism of Cr(VI) by green synthesized nZVI; 3) investigate the factors such as organic matter and inorganic ions in groundwater, which could impacte the reduction of Cr(VI). Results of this study will provide fundamental knwledge on the application of green synthesis of nZVI used to remove Cr(VI) in ground water.

地下水Cr(VI)污染修复是当前急需解决的水环境污染问题之一，纳米铁用于修复地下水Cr(VI)污染具有潜在优势，然而存在成本高、易团聚沉降氧化等瓶颈问题。利用植物提取液作为还原剂与铁盐作用绿色合成多功能纳米铁，能够有效降低纳米铁合成成本，提高纳米铁的抗氧化性、分散性和吸附性，使得大规模原位修复成为可能。然而，植物提取液合成纳米铁的机理和绿色纳米铁还原Cr(VI)的影响机制尚不清楚。桉树是世界上三大速生丰产树种之一，桉树叶含有多酚、黄酮、有机酸等多种活性物质。本项目提出采用桉树叶提取液合成纳米铁，分析桉树叶提取液有效成分，揭示绿色合成纳米铁的机理；探讨绿色合成纳米铁还原Cr(VI)的影响机制；以及地下水中各类共存物质（如有机物、无机离子等）对绿色合成纳米铁去除Cr(VI)效率的影响。项目研究成果将为绿色合成纳米铁用于修复地下水Cr(VI)污染提供技术支持。

利用植物提取液绿色合成纳米铁具有快速、无毒、环保的特点，已经成为一种替代性强、环境友好的新技术。在本研究中，我们用桉树叶提取液成功合成了绿色纳米铁(EL-Fe NPs)，并用于从水溶液中Cr(VI)的去除。首先，对合成的EL-Fe NPs的形貌、表面和组成进行了探究。分析TEM谱图可知纳米铁的粒径约100 nm，表面覆盖着一层絮状物，结合FTIR、 XRD和XPS表征结果发现该絮状物主要成分为桉树叶提取液中的生物大分子。此外， GC-MS分析了桉树叶提取液中的主要成分，其中醇酚和烷基醛主要起到还原剂作用，而醇酸、烷醇、植物醇、乙酸酯和芳香酮则起稳定剂的作用。从而得出醛、酚和醇类化合物在EL-Fe NPs合成中起主导作用。最后，基于以上结果提出了EL-Fe NPs可能的合成机理。同时，还探究了温度、pH值、初始Cr(VI)浓度和EL-Fe NPs投加量等参数对Cr(VI) 去除效果的影响。结果表明，在最佳实验条件下，EL-Fe NPs对去除Cr(VI)和总铬的去除率分别达到98.6%和84.6%，重复使用4次后，Cr(VI)的去除率仍达到55.7%。应用SEM、EDS、FTIR、XRD、DLS等表征技术反应前后的对纳米颗粒进行表征，揭示了Cr吸附在了EL-Fe NPs的表面。条件实验拟合结果遵循还原动力学伪二阶模型，其中吸附过程更符合Langmuir模型(R2=0.9998)， 最大吸附量Qm和常数b分别为20.45 mg/g和3.596 L/mg。基于上述所有结果提出了EL-Fe NPs对Cr(VI)去除的机制。最后，为了进一步探究共存离子等环境因素对Cr(VI)的去除效率，研究了Cu（II）等存在下对Cr（VI）去除率的影响。结果表明，共存金属离子会与铬（VI）产生竞争作用，降低了Cr（VI）的去除率，在实际水体应用中，绿色合成纳米铁各类金属离子均具有去除作用。