In Situ Measurement of Aggregation Effect of Nanoscale Zero-valent Iron in the Presence of Natural Organic Matter Based on the Dynamic Light Scattering Technique
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摘要: 纳米零价铁原位修复地下水污染是近年发展起来的新技术，通过改性合成不同种类纳米零价铁可以克服其易团聚易氧化的问题，水体中存在的天然有机质也会对纳米铁的分散性和反应活性产生影响，因此开展原位测试并研究不同种类纳米铁在水中的团聚效应具有重要意义。本文对实验合成的纳米零价铁、羧甲基纤维素包覆纳米零价铁、膨润土负载纳米零价铁以及商用纳米零价铁，基于动态光散射技术（DLS），运用纳米粒度/Zeta电位分析仪，结合透射电子显微镜（TEM）和沉降光谱曲线等手段，对比研究了天然有机质（腐植酸HA）对纳米铁团聚效应的影响。结果表明，羧甲基纤维素包覆或膨润土负载改性提高了纳米零价铁颗粒的分散稳定性，有效抑制了团聚沉降，团聚体粒径分布在1000 nm以下。HA会吸附在纳米铁颗粒表面，从而增加静电排斥力，进一步减缓了团聚效应，尤其是对膨润土负载纳米零价铁的影响最为显著，其团聚体粒径能降至100 nm以下，沉降速率也极大减缓，分散稳定性表现最佳。本研究表明DLS结合TEM表征纳米颗粒是获得更加丰富的微观粒子信息的一种非常重要的手段。Abstract: Nanoscale zero-valent iron (nZVI) is a newly developed method for in-situ remediation of groundwater in recent years. To overcome easy oxidation and aggregation, modification on nZVI is widely adopted. In addition, the ubiquitous natural organic matters (NOM) in water also affect the scatter and reaction activity of nZVI. Therefore, it is of significance to study the aggregation effect of different kinds of nZVI in water by in-situ measurement method. Besides commercial nZVI (RNIP), normal nZVI, carboxymethyl cellulose coated nZVI (C-nZVI) and bentonite supported nZVI (B-nZVI) was synthesized. Nano particle size/Zeta potential analyzer based on the Dynamic Light Scattering (DLS) technique, Transmission Electron Microscope (TEM) and UV-Vis spectrum of sedimentation were employed to characterize the aggregation behavior of above four types of nZVI in the presence or absence of humic acid (HA), a representative NOM. The results showed that the dispersion stability of C-nZVI and B-nZVI was improved significantly after modification and the aggregation precipation was suppressed. And size distribution of aggregates stabilizes at below 1000 nm. Humic acid adsorbed onto the surface of nanoparticles, which can increase the electrostatic force to prevent aggregation of nZVI. The effect of HA on B-nZVI is most obvious for B-nZVI aggregates with diameters below 100 nm and the sedimentation was very slow, indicating the dispersion performed the best among all kinds of nZVI. It can be concluded that the combination of DLS technique and TEM to characterize nanoparticles is a valuable approach for more comprehensive information.
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表 1 有无腐植酸环境中几种纳米铁的粒径分布变化
Table 1. Aggregation size distribution of several types nano-iron samples in the presence or absence of HA
纳米铁种类 粒径分布 nZVI 500~1500 nm nZVI+HA 200~500 nm RNIP 500~1000 nm RNIP+HA 500~500 nm C-nZVI 400~400 nm C-nZVI+HA 100~100 nm B-nZVI 300~400 nm B-nZVI+HA 30~60 nm 
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