CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
CAS Key Laboratory of Urban Pollutant Conversion, Department of Chemistry, University of Science and Technology of China, Hefei, 230026, China.
Water Res. 2016 Dec 1;106:242-248. doi: 10.1016/j.watres.2016.10.004. Epub 2016 Oct 5.
Microbial extracellular polymeric substances (EPS) widely exist in natural environments and affect the migration and transformation of pollutants in aquatic environments. Previous works report that EPS have some reducing functional groups and can reduce heavy metals. However, because of the weak reducing capability of EPS, the reduction of heavy metals by EPS without cells is extremely slow, and its effect on heavy metals species is insignificant. In this work, the accelerated reduction of silver ions (Ag) by EPS from Shewanella oneidensis MR-1 under illumination was investigated. UV-visible spectroscopy, transmission electron microscopy (TEM) coupled with an energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to confirm the formation of silver nanoparticles (AgNPs) via the reduction of Ag by EPS under light illumination. The Ag reduction by EPS follows pseudo-first-order kinetics under both visible and UV light, and the light irradiation can significantly accelerate AgNPs formation. On the one hand, visible light can excite AgNPs for their surface plasma resonance (SPR) and accelerate the electrons from the EPS to adjacent Ag. On the other hand, EPS molecules may be excited by UV light to produce strong reducing species, which enhance Ag reduction. Moreover, pH, dissolved oxygen were found to affect the formation of AgNPs by EPS. This work proves the reducing capability of EPS on the reduction of Ag, and this process can be accelerated under light illumination, which may affect the speciation and transformation of heavy metals in natural waters.
微生物胞外聚合物（EPS）广泛存在于自然环境中，影响着水环境污染中污染物的迁移和转化。先前的研究报道 EPS 具有一些还原官能团，可以还原重金属。然而，由于 EPS 的还原能力较弱，没有细胞存在时 EPS 还原重金属的速度非常缓慢，其对重金属形态的影响也微不足道。在这项工作中，研究了光照下 Shewanella oneidensis MR-1 的 EPS 对银离子（Ag）的加速还原。通过使用紫外-可见光谱、透射电子显微镜（TEM）结合能量色散光谱仪（EDS）和 X 射线光电子能谱（XPS），证实了 EPS 在光照下还原 Ag 形成了银纳米颗粒（AgNPs）。EPS 还原 Ag 遵循可见和紫外光下的准一级动力学，并且光照可以显著加速 AgNPs 的形成。一方面，可见光可以激发 AgNPs 的表面等离子体共振（SPR），并加速 EPS 中的电子转移到相邻的 Ag 上。另一方面，EPS 分子可能被紫外光激发产生强还原物质，从而增强 Ag 的还原。此外，pH 值和溶解氧被发现会影响 EPS 对 AgNPs 的形成。这项工作证明了 EPS 对 Ag 还原的还原能力，并且该过程可以在光照下加速，这可能会影响天然水中重金属的形态和转化。
