Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Institute of Environmental & Applied Chemistry, College of Chemistry , Central China Normal University , Wuhan 430079 , People's Republic of China.
Environ Sci Technol. 2019 Jul 16;53(14):8333-8341. doi: 10.1021/acs.est.9b01999. Epub 2019 Jun 26.
In this study, we report that liquid nitrogen treatment is a promising zero-valent iron activation method that does not remove the iron oxide shell; this can improve the apparent Cr(VI) removal rate constant of zero-valent iron by about 4-120 times, depending on the particle sizes and the suppliers of zero-valent iron. It was found that liquid nitrogen, with its low temperature of 77 K, could crack the iron oxide shell of zero-valent iron to produce abundant fractures because of the different thermal expansion coefficients of iron oxide and iron. These fractures provided suitable mass transfer channels for the inward transfer of water/oxygen molecules to the iron core and the subsequent in situ generation of Fe(II) for the reduction of Cr(VI) to Cr(III). More importantly, systematic characterizations confirmed the generation of an Fe(III)/Cr(III)/Cr(VI) composite on the surface of zero-valent iron during the removal, suggesting its environmental benignancy. This study provides a novel physical zero-valent iron activation method, sheds light on the importance of the iron oxide shell of zero-valent iron on Cr(VI) removal, and clarifies the intrinsic Cr(VI) removal mechanism of zero-valent iron.
在本研究中，我们报告液氮处理是一种有前途的零价铁活化方法，它不会去除氧化铁壳；这可以提高零价铁的表观六价铬去除速率常数约 4-120 倍，具体取决于零价铁的颗粒大小和供应商。研究发现，由于氧化铁和铁的热膨胀系数不同，液氮的低温 77K 可以使零价铁的氧化铁壳破裂，产生丰富的裂缝。这些裂缝为水分子/氧分子向内转移到铁核提供了合适的传质通道，随后原位生成 Fe(II)，将 Cr(VI)还原为 Cr(III)。更重要的是，系统的特性表明，在去除过程中，零价铁表面生成了一种 Fe(III)/Cr(III)/Cr(VI) 复合材料，表明其具有环境友好性。本研究提供了一种新的物理零价铁活化方法，阐明了零价铁氧化铁壳对六价铬去除的重要性，并澄清了零价铁内在的六价铬去除机制。
