Thiophene Functionalized Magnetic Covalent Organic Frameworks For Selective Extraction Of Trace Heavy Metals Followed By ICP-MS Detection

Abstract

: Magnetic covalent organic frameworks (COFs) were prepared using aminated Fe 3 O 4 nanoparticles as the magnetic core and 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,5-dimethoxyterephthalaldehyde (DMTA) as monomers. The resultant Fe 3 O 4 @TPB-DMTP-COF was then post-modified with 3-ethynylthiophene through the “Aza D-A reaction”. The Fe 3 O 4 @COF-thiophene composite showed a high Brunauer-Emmett-Teller surface area of 898 m 2· g -1 , as well as a high content of S (5.27 w.t.%). Trace mercury (Hg), lead (Pb), and bismuth (Bi) ions were extracted from environmental water samples, followed by inductively coupled plasma mass spectrometry (ICP-MS) detection. Extraction conditions, such as extraction pH, sample volume, adsorbent amount, extraction/desorption time and elution volume, were optimized. Under the optimal conditions, the three heavy metal ions were extracted from 150 mL of aqueous solution within 20 min and eluted with 0.1 mol L -1 HNO 3 containing 8% cysteamine hydrochloride within 20 min. The method exhibited a high enrichment factor (188) and wide linear range of 3-5000 ng·L - 1 for Hg 2+ /Pb 2+ and 2-2000 for Bi 3+ , with the detection limits of 0.41, 0.97 and 0.47 ng∙L -1 , respectively. Furthermore, the reproducibility of the method was evaluated, and the relative standard deviations of Hg 2+ , Pb 2+ and Bi 3+ were found to be 7.5, 6.8 and 6.2% (n = 7, c = 3 ng∙L -1 ), respectively. The accuracy of this method was verified by analyzing certified reference materials in environmental water, including GSB 07-1185-2000 (202047), GSB 07-1185-2000 (201239) and BY 400143 (B2003113). The application potential of this method was further evaluated by analyzing real environmental water samples. Target Hg 2+ and Pb 2+ ions concentrations were found to be 4.91 and 62.5 ng∙L -1 , respectively, in the East Lake water sample and 10.2 and 103 ng·L - 1 , respectively, in the Yangtze River water sample. The recoveries of target three metal ions were found to be 86.1-104 % in the two environmental water samples at three spiked concentration levels.