Investigation of the Fate of Silver and Titanium Dioxide Nanoparticles in Model Wastewater Effluents via Selected Area Electron Diffraction

The
increasing use of manufactured nanomaterials (MNMs) and their
inevitable release into the environment, especially via wastewater
treatment plants (WWTPs), poses a potential threat for aquatic organisms.
The characterization of MNMs with analytical tools to comprehend their
fate and effect on the ecosystem is hence of great importance for
environmental risk assessment. We herein report, for the first time,
the investigation of physicochemical transformation processes during
artificial wastewater treatment of silver (Ag-NPs) and titanium dioxide
nanoparticles (TiO2-NPs) via selected area electron diffraction
(SAED). TiO2-NPs with an anatase/rutile ratio of ∼80/20
were found to not undergo any physicochemical transformation, as shown
via previous energy-dispersive X-ray analysis (EDX) elemental mapping
and crystal structure analysis via SAED. In contrast, Ag-NPs were
colocalized with substantial amounts of sulfur (Ag/S ratio of 1.9),
indicating the formation of Ag2S. SAED ultimately proved
the complete transformation of face-centered cubic (fcc) Ag-NPs into
monoclinic Ag2S-NPs. The size distribution of both nanomaterials
remained virtually unchanged. Our investigations show that cloud point
extraction of NPs and their subsequent crystal structure analysis
via SAED is another valuable approach toward the comprehensive investigation
of wastewater-borne MNMs. However, the extraction procedure needs
optimization for environmentally low NP concentrations.

随着制造纳米材料（MNMs）的广泛应用及其不可避免地排放至环境，尤其是通过废水处理厂（WWTPs），对水生生物构成潜在威胁。因此，利用分析工具对MNMs进行表征，以理解其命运及其对生态系统的影响，对于环境风险评估具有重要意义。本研究首次报道了通过选区电子衍射（SAED）技术对银纳米颗粒（Ag-NPs）和二氧化钛纳米颗粒（TiO2-NPs）在人工废水处理过程中的物理化学转化过程的研究。研究发现，具有金红石/锐钛矿比为约80/20的TiO2-NPs未发生任何物理化学转化，这通过先前的能量色散X射线分析（EDX）元素映射和SAED晶体结构分析得以证实。相比之下，Ag-NPs与大量硫（Ag/S比为1.9）共定位，表明形成了Ag2S。SAED最终证实了面心立方（fcc）Ag-NPs完全转化为单斜相的Ag2S-NPs。两种纳米材料的尺寸分布基本保持不变。本研究表明，云点萃取纳米颗粒及其随后的SAED晶体结构分析是全面调查废水携带的MNMs的另一有效方法。然而，为了对环境中低浓度的NP进行提取，提取程序需要进一步优化。