The Center for NanoBioEarth, Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061, United States.
Department of Civil and Environmental Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
Environ Sci Technol. 2017 Feb 21;51(4):1973-1980. doi: 10.1021/acs.est.6b03173. Epub 2017 Feb 8.
Nanoscale cerium oxide is used as a diesel fuel additive to reduce particulate matter emissions and increase fuel economy, but its fate in the environment has not been established. Cerium oxide released as a result of the combustion of diesel fuel containing the additive Envirox, which utilizes suspended nanoscale cerium oxide to reduce particulate matter emissions and increase fuel economy, was captured from the exhaust stream of a diesel engine and was characterized using a combination of bulk analytical techniques and high resolution transmission electron microscopy. The combustion process induced significant changes in the size and morphology of the particles; ∼15 nm aggregates consisting of 5-7 nm faceted crystals in the fuel additive became 50-300 nm, near-spherical, single crystals in the exhaust. Electron diffraction identified the original cerium oxide particles as cerium(IV) oxide (CeO, standard FCC structure) with no detectable quantities of Ce(III), whereas in the exhaust the ceria particles had additional electron diffraction reflections indicative of a CeO superstructure containing ordered oxygen vacancies. The surfactant coating present on the cerium oxide particles in the additive was lost during combustion, but in roughly 30% of the observed particles in the exhaust, a new surface coating formed, approximately 2-5 nm thick. The results of this study suggest that pristine, laboratory-produced, nanoscale cerium oxide is not a good substitute for the cerium oxide released from fuel-borne catalyst applications and that future toxicity experiments and modeling will require the use/consideration of more realistic materials.
纳米氧化铈被用作柴油燃料添加剂，以减少颗粒物排放并提高燃油经济性，但它在环境中的命运尚未确定。由于含有添加剂 Envirox 的柴油燃料燃烧而释放的氧化铈，该添加剂利用悬浮的纳米氧化铈来减少颗粒物排放并提高燃油经济性，从柴油机的排气流中捕获，并使用一系列体分析技术和高分辨率透射电子显微镜进行了表征。燃烧过程导致颗粒的尺寸和形态发生了显著变化；燃料添加剂中由 5-7nm 面心立方晶体组成的约 15nm 聚集体在排气中变成了 50-300nm 的近球形单晶。电子衍射表明原始氧化铈颗粒为氧化铈（CeO，标准 FCC 结构），没有检测到 Ce(III)的存在，而在排气中，氧化铈颗粒具有额外的电子衍射反射，表明存在含有有序氧空位的 CeO 超结构。添加剂中氧化铈颗粒上的表面活性剂涂层在燃烧过程中丢失，但在排气中观察到的约 30%的颗粒中，形成了一种新的表面涂层，厚度约为 2-5nm。这项研究的结果表明，原始的、实验室生产的纳米氧化铈不是从燃料载催化剂应用中释放的氧化铈的良好替代品，未来的毒性实验和建模将需要使用/考虑更现实的材料。
