Department of Environmental Science, Zhejiang University, Hangzhou, 310058, China.
Key Laboratory of Environmental Pollution and Ecological Health of Ministry of Education, Hangzhou, 310058, China.
Sci Rep. 2021 Mar 3;11(1):5037. doi: 10.1038/s41598-021-84685-w.
Biochar supported nanoscale zero-valent iron (NZVI/BC), prepared commonly by liquid reduction using sodium borohydride (NaBH), exhibits better reduction performance for contaminants than bare NZVI. The better reducing ability was attributed to attachment of nanoscale zero-valent iron (NZVI) on biochar (BC) surface or into the interior pores of BC particles due to observations by scanning electron microscopy (SEM) and plan transmission electron microscopy (P-TEM) techniques in previous studies. In this study, cross-sectional TEM (C-TEM) technique was employed firstly to explore location of NZVI in NZVI/BC. It was observed that NZVI is isolated from BC particles, but not located on the surface or in the interior pores of BC particles. This observation was also supported by negligible adsorption and precipitation of Fe/Fe and iron hydroxides on BC surface or into interior pores of BC particles respectively. Precipitation of Fe and Fe, rather than adsorption, is responsible for the removal of Fe and Fe by BC. Moreover, precipitates of iron hydroxides cannot be reduced to NZVI by NaBH. In addition to SEM or P-TEM, therefore, C-TEM is a potential technique to characterize the interior morphology of NZVI/BC for better understanding the improved reduction performance of contaminants by NZVI/BC than bare NZVI.
生物炭负载纳米零价铁（NZVI/BC）通常通过使用硼氢化钠（NaBH）的液相还原法制备，其对污染物的还原性能优于裸露的 NZVI。在之前的研究中，通过扫描电子显微镜（SEM）和投射电子显微镜（P-TEM）技术观察到，由于纳米零价铁（NZVI）附着在生物炭（BC）表面或进入 BC 颗粒的内部孔隙中，因此 NZVI/BC 表现出更好的还原能力。在这项研究中，首次采用截面 TEM（C-TEM）技术来探究 NZVI 在 NZVI/BC 中的位置。结果表明，NZVI 与 BC 颗粒分离，而不是位于 BC 颗粒的表面或内部孔隙中。这一观察结果也得到了以下支持：在 BC 表面或内部孔隙中，Fe/Fe 和铁氢氧化物的吸附和沉淀可忽略不计。Fe 和 Fe 的沉淀而不是吸附是导致 BC 去除 Fe 和 Fe 的原因。此外，NaBH 不能将铁氢氧化物沉淀还原为 NZVI。因此，除了 SEM 或 P-TEM 之外，C-TEM 还是一种用于表征 NZVI/BC 内部形态的潜在技术，有助于更好地理解 NZVI/BC 对污染物的还原性能优于裸露的 NZVI。
