Department of Civil Engineering, McGill University , Montreal, Quebec H3A 0C3, Canada.
Department of Chemical Engineering, McGill University , Montreal, Quebec H3A 0C5, Canada.
Environ Sci Technol. 2016 Feb 16;50(4):1812-20. doi: 10.1021/acs.est.5b05074. Epub 2016 Jan 27.
Nanoscale zerovalent iron (NZVI) particles are often coated with polymeric surface modifiers for improved colloidal stability and transport during remediation of contaminated aquifers. Doping the NZVI surface with palladium (Pd-NZVI) increases its reactivity to pollutants such as trichloroethylene (TCE). In this study, we investigate the effects of coating Pd-NZVI with two surface modifiers of very different molecular size: rhamnolipid (RL, anionic biosurfactant, M.W. 600 g mol(-1)) and carboxymethylcellulose (CMC, anionic polyelectrolyte, M.W. 700 000 g mol(-1)) on TCE degradation. RL loadings of 13-133 mg TOC/g NZVI inhibited deposition of Pd in a concentration-dependent manner, thus limiting the number of available Pd sites and decreasing the TCE degradation reaction rate constant from 0.191 h(-1) to 0.027 h(-1). Furthermore, the presence of RL in solution had an additional inhibitory effect on the reactivity of Pd-NZVI by interacting with the exposed Pd deposits after they were formed. In contrast, CMC had no effect on reactivity at loadings up to 167 mg TOC/g NZVI. There was a lack of correlation between Pd-NZVI aggregate sizes and TCE reaction rates, and is explained by cryo-transmission electron microscopy images that show open, porous aggregate structures where TCE would be able to easily access Pd sites.
纳米零价铁（NZVI）颗粒通常用聚合表面改性剂进行包覆，以提高胶体稳定性并改善受污染含水层修复过程中的迁移性。在 NZVI 表面掺杂钯（Pd-NZVI）可以提高其对三氯乙烯（TCE）等污染物的反应活性。在这项研究中，我们研究了两种具有非常不同分子大小的表面改性剂（鼠李糖脂（RL，阴离子生物表面活性剂，MW600gmol-1）和羧甲基纤维素（CMC，阴离子聚电解质，MW700000gmol-1））包覆 Pd-NZVI 对 TCE 降解的影响。RL 的负载量为 13-133mgTOC/gNZVI 以浓度依赖的方式抑制 Pd 的沉积，从而限制了可用 Pd 位的数量，并将 TCE 降解反应速率常数从 0.191h-1 降低至 0.027h-1。此外，RL 在溶液中的存在通过与形成后暴露的 Pd 沉积物相互作用对 Pd-NZVI 的反应性具有额外的抑制作用。相比之下，CMC 在负载量高达 167mgTOC/gNZVI 时对反应性没有影响。Pd-NZVI 聚集体大小与 TCE 反应速率之间缺乏相关性，这可以通过低温透射电子显微镜图像得到解释，这些图像显示了开放、多孔的聚集体结构，TCE 可以很容易地进入 Pd 位。
