To assess the fate and long-term reactivity of bimetallic nanoparticles used in groundwater remediation, it is important to trace the physicochemical transformation of nanoparticles during aging in water. This study investigated the short-term (within 5 d) and long-term (up to 90 d) aging process of Fe/Ni bimetallic nanoparticles (Fe/Ni BNPs) in simulated groundwater and the consequent effect on the particle reactivity. Results indicate that the morphological, compositional and structural transformation of Fe/Ni BNPs happened during the aging. In the 5-d short-term aging, Fe⁰ corrosion occurred rapidly and was transformed to ferrous ions which were adsorbed onto the surface of Fe/Ni BNPs, accompanied by the elevation of solution pH and the negative redox potential. In the long-term aging, scanning electron microscopy (SEM) images show that the particles transformed from spherical to rod-like and further to sheet-like and needle-like. X-ray diffraction (XRD) analysis reveals that the main aging product was magnetite (Fe₃O₄) and/or maghemite (γ-Fe₂O₃) after aging for 60–90 d. Energy dispersive spectrometer (EDS) analysis demonstrates that the mass ratio of Fe/Ni increased with aging, revealing that Ni were possibly gradually entrapped and covered by the iron oxides. Besides, the release of Ni into solution was also detected during the aging. The reactivity of the aged Fe/Ni BNPs was examined by studying its performance in tetracycline (TC) removal. The aged Fe/Ni BNPs within 2 d kept similar removal efficiency of TC as the fresh particles. However, the removal efficiency of TC by Fe/Ni BNPs aged for 5–15 d dropped by 20–50% due to aggregation and oxidation of particles, and the removal efficiency further decreased slowly with the prolongation of aging time up to 90 d. This reveals that Fe/Ni BNPs were vulnerable to passivation in water environments.

中文翻译：

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Fe / Ni双金属纳米粒子在模拟地下水中的老化过程中的理化转变及其对污染物去除的影响

为了评估用于地下水修复的双金属纳米颗粒的命运和长期反应性，重要的是追踪在水中老化过程中纳米颗粒的物理化学转化。这项研究调查了模拟地下水中Fe / Ni双金属纳米颗粒（Fe / Ni BNPs）的短期（5 d内）和长期（长达90 d）老化过程及其对颗粒反应性的影响。结果表明，Fe / Ni BNPs在时效过程中发生了形态，组成和结构转变。在5 d短期时效中，Fe ⁰腐蚀迅速发生，并转化为亚铁离子，并吸附到Fe / Ni BNPs表面，伴随溶液pH升高和负氧化还原电位。在长期老化中，扫描电子显微镜（SEM）图像显示颗粒从球形转变为棒状，再转变为片状和针状。X射线衍射（XRD）分析表明，主老化产物是磁铁矿（铁₃ Ò ₄）和/或磁赤铁矿（γ-的Fe ₂ ö ₃）老化60-90天后。能量色散谱仪（EDS）分析表明，Fe / Ni的质量比随老化而增加，表明Ni可能逐渐被铁氧化物夹带和覆盖。此外，在时效过程中还检测到Ni释放到溶液中。通过研究其在四环素（TC）去除中的性能，检查了老化的Fe / Ni BNP的反应性。在2 d内老化的Fe / Ni BNP保持了与新鲜颗粒相似的TC去除效率。但是，由于颗粒的聚集和氧化作用，在5-15 d时效的Fe / Ni BNP去除TC的效率下降了20-50％，随着时效时间延长至90 d，去除效率进一步缓慢下降。这表明Fe / Ni BNPs在水环境中很容易钝化。