Crawford Scott E, Ellis James E, Ohodnicki Paul R, Baltrus John P
National Energy Technology Laboratory, 626 Cochrans Mill Rd, Pittsburgh 15236 Pennsylvania, United States.
ACS Appl Mater Interfaces. 2021 Feb 17;13(6):7268-7277. doi: 10.1021/acsami.0c20990. Epub 2021 Feb 3.
Rare earth elements (REEs) are critical to numerous technologies; however, a combination of increasing demand, environmental concerns, and monopolistic marketplace conditions has spurred interest in boosting the domestic REE production from sources such as coal utilization byproducts. The economic viability of this approach requires rapid, inexpensive, and sensitive analytical techniques capable of characterizing the REE content during resource exploration and downstream REE processing (e.g., analyzing REE separation, concentration, and purification production steps). Luminescence-based sensors are attractive because many REEs may be sensitized to produce element-specific emission. Hence, a single material may simultaneously detect and distinguish multiple REEs. Metal-organic frameworks (MOFs) can sensitize multiple REEs, but their viability has been hindered by sensitivity and selectivity challenges. Understanding how the MOF structure impacts the REE sensing efficacy is critical to the rational design of new sensors. Here, we evaluate the sensing performance of seven different anionic zinc-adeninate MOFs with different organic linkers and/or structures for the visible-emitting REEs Tb, Dy, Sm, and Eu. The choice of a linker determines which REEs are sensitized and significantly influences their sensitivity and selectivity against competing species (here, Fe(II) and HCl). For a given linker, structural changes to the MOF can further fine-tune the performance. The MOFs produce some of the lowest detection limits (sub-10 ppb for Tb) reported for the aqueous sensitization-based REE detection. Importantly, the most selective MOFs demonstrated the ability to sensitize the REE signal at sub-ppm levels in a REE-spiked acid mine drainage matrix, highlighting their potential for use in real-world sensing applications.
稀土元素（REEs）对众多技术至关重要；然而，需求增长、环境问题和垄断性市场条件的综合作用激发了人们对提高国内从煤炭利用副产品等来源生产稀土元素的兴趣。这种方法的经济可行性需要快速、廉价且灵敏的分析技术，以便在资源勘探和下游稀土元素加工过程中（例如分析稀土元素的分离、浓缩和提纯生产步骤）对稀土元素含量进行表征。基于发光的传感器很有吸引力，因为许多稀土元素可以被敏化以产生特定元素的发射。因此，单一材料可以同时检测和区分多种稀土元素。金属有机框架（MOFs）可以敏化多种稀土元素，但其可行性受到灵敏度和选择性挑战的阻碍。了解MOF结构如何影响稀土元素传感效率对于合理设计新型传感器至关重要。在这里，我们评估了七种不同的带有不同有机连接体和/或结构的阴离子锌腺嘌呤MOF对可见光发射稀土元素铽（Tb）、镝（Dy）、钐（Sm）和铕（Eu）的传感性能。连接体的选择决定了哪些稀土元素被敏化，并显著影响它们对竞争物种（这里是Fe(II)和HCl）的灵敏度和选择性。对于给定的连接体，MOF的结构变化可以进一步微调性能。这些MOF产生了一些基于水相敏化的稀土元素检测所报道的最低检测限（Tb低于10 ppb）。重要的是，最具选择性的MOF在添加了稀土元素的酸性矿山排水基质中，能够在亚ppm水平敏化稀土元素信号，突出了它们在实际传感应用中的潜力。
