College of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China.
College of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, China; Institute for Combustion Science and Environmental Technology, Department of Chemistry, Western Kentucky University, Bowling Green, KY 42101, USA.
Talanta. 2019 Jun 1;198:501-509. doi: 10.1016/j.talanta.2019.01.113. Epub 2019 Feb 1.
As indispensable and strategic elements, Rare Earth Elements (REEs) have been found wide high-tech applications in many modern industries. Their mining, extraction and purification address on economic and environmental significances. This study was the first to report the successful determination and differentiation of rare earth metals using the Nitrogen-doped Carbon Dots (NCDs). NCDs were synthesized via the one-step hydrothermal treatment method starting from folic acid. The as-received NCDs can emit bright blue fluorescence at 440 nm in a high quantum yield of 85% due to the fluorescence enhancement effect of N dopant atoms on NCDs' surface. This as-received NCDs can not only determine REE ions based on the fluorescence quenching effect of the newly-formed REE-NCDs complexes, also distinguish two groups of REEs with significantly different electronic structures. It was found REE ions (Group II REEs: Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) can only quench fluorescence of the initial NCDs solution, but not change its fluorescence wavelengths. This was contrasted to the similar quenching effect of REE ions (Group I REEs: La, Y, Lu) on NCDs, but further 20 nm red-shift of the fluorescence wavelength (from 439 nm to 458 nm). Taking examples of the selected La and Sm, their detection limit were found to be 0.045 μM (the linear range of 0-6 μM, R =0.998) and 0.29 μM (the linear range of 0-10 μM, R =0.993), respectively. The characterizations of NCDs, based on the ultraviolet and visible spectrophotometry (UV-VIS), X-ray photoelectron spectrometer (XPS) and Fourier Transform infrared spectroscopy (FTIR), helped in revealing the coordination status of rare earth ions on the carboxyl group of the NCDs surface and also mechanisms of their electron and energy transfers.
作为不可或缺的战略元素，稀土元素（REEs）在许多现代工业中得到了广泛的高科技应用。它们的开采、提取和纯化具有经济和环境意义。本研究首次报道了成功使用氮掺杂碳点（NCDs）来测定和区分稀土金属。NCDs 通过从叶酸开始的一步水热处理方法合成。接收的 NCDs 由于 N 掺杂原子对 NCDs 表面的荧光增强效应，在 440nm 处以 85%的高量子产率发射明亮的蓝色荧光。接收的 NCDs 不仅可以基于新形成的 REE-NCDs 配合物的荧光猝灭效应来测定 REE 离子，还可以区分两组具有明显不同电子结构的 REEs。结果发现，REE 离子（II 族 REEs：Pr、Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、Tm、Yb）只能猝灭初始 NCDs 溶液的荧光，但不能改变其荧光波长。这与 REE 离子（I 族 REEs：La、Y、Lu）对 NCDs 的类似猝灭效应形成对比，但荧光波长进一步红移 20nm（从 439nm 到 458nm）。以选择的 La 和 Sm 为例，发现它们的检测限分别为 0.045μM（0-6μM 的线性范围，R=0.998）和 0.29μM（0-10μM 的线性范围，R=0.993）。基于紫外可见分光光度法（UV-VIS）、X 射线光电子能谱（XPS）和傅里叶变换红外光谱（FTIR）对 NCDs 的表征，有助于揭示稀土离子在 NCDs 表面羧基上的配位状态及其电子和能量转移机制。
