ABSTRACT:

Extracellular polymeric substance (EPS) is secreted by many organisms and makes up a significant constituent of natural organic matter in the environment. However, nothing is known about EPS's role in the reduction of pollutants by nano-sized zero-valent iron (NZVI). This research showed that the degradation kinetics of nitrobenzene (NB) by NZVI with EPS (0.0272 +/- 0.006 min(-1)) were 2.27 times lower than that without EPS (0.0618 +/- 0.006 min(-1)) in the first cycle, mainly due to competition for reactive sites on the NZVI surface and the complexation of EPS with Fe(II) and Fe(III). In the second and third cycle, the degradation kinetics of NB by NZVI alone decreased obviously, while those in the presence of EPS were preserved or accelerated. Comparative studies with a quinine model compound indicated that EPS did not function as the electron shuttle to transmit electrons effectively. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction results suggested that EPS could prevent the oxidation of NZVI and even expose more effective sites on the NZVI surface, thus leading to the preservation or enhancement of NZVI reactivity in the second and third NB degradation cycles. Moreover, we found that EPS also provided colloidal stability to NZVI particles, either by steric mechanisms or electrostatic repulsion. These results indicate that EPS can play an important role in the prolongation of NZVI reactivity during standing application.

KEYWORDS: Zero valent iron, Nanoparticles, EPS, colloidal stability, reactivity

摘要: 胞外聚合物（EPS）是由生物分泌的、环境中天然有机物的重要组成部分。然而，关于其对纳米零价铁（NZVI）还原降解有机污染物的影响目前尚无报道。我们研究发现，第一个循环周期中，添加了EPS的nZVI系统对硝基苯（NB）的降解动力学常数（0.0272±0.006 min-1）比未添加EPS（0.0618±0.006 min-1）的低2.27倍。这主要归因于EPS与硝基苯对nZVI活性点位的竞争以及EPS与Fe（II）和Fe（III）的络合。在第二个和第三个循环中，nZVI对NB的降解速率明显下降，而添加了EPS的nZVI降解速率反而提高。与醌类模型化合物的比较研究表明，EPS不能起到有效传递电子的电子穿梭作用。X射线光电子能谱（XPS），透射电子显微镜（TEM）和X射线衍射（XRD）结果表明EPS可以防止nZVI的氧化，甚至可以暴露更多nZVI表面上的活性点位，从而导致第二和第三循环中nZVI反应活性的增强。此外，我们发现EPS还可以通过空间机制或静电排斥作用为nZVI颗粒增强胶体稳定性。这些结果表明，在实际应用中，EPS可以对nZVI反应性的延长发挥重要作用。

关键词: 零价铁，纳米颗粒，EPS，胶体稳定性，反应活性

原载于Environmental Technology（2019 Impact Factor = 2.213）

原文链接： https://doi.org/10.1080/09593330.2020.1772376