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.

摘要

细胞外聚合物 (EPS) 由许多生物体分泌，是环境中天然有机物的重要组成部分。然而，对于 EPS 在纳米零价铁 (NZVI) 减少污染物中的作用，我们一无所知。该研究表明，NZVI 对硝基苯 (NB) 的降解动力学与 EPS (0.0272 ± 0.006 min ^-1 ) 比没有 EPS (0.0618 ± 0.006 min -1) 低 2.27^倍) 在第一个循环中，主要是由于对 NZVI 表面反应位点的竞争以及 EPS 与 Fe(II) 和 Fe(III) 的络合。在第二和第三个循环中，单独使用NZVI对NB的降解动力学明显下降，而在EPS存在下则保持或加速。与奎宁模型化合物的比较研究表明，EPS 不能作为电子穿梭来有效传输电子。X 射线光电子能谱、扫描电子显微镜和 X 射线衍射结果表明，EPS 可以防止 NZVI 的氧化，甚至在 NZVI 表面暴露更多的有效位点，从而导致 NZVI 在第二和第三阶段的反应性保持或增强NB 退化循环。此外，我们发现 EPS 还为 NZVI 颗粒提供胶体稳定性，通过空间机制或静电排斥。这些结果表明，EPS 可以在静置应用期间延长 NZVI 反应性方面发挥重要作用。