Facile Fabrication of Magnetic Metal-Organic Framework Composites for the Highly Selective Removal of Cationic Dyes.

In this work, we show a novel magnetic composite material Fe₃O₄@HPU-9 (HPU-9 = {[Cd(L)0.5(H₂O)](DMA)(CH₃CN)}n) (H₄L = 1,1′-di(3,5-dicarbonylbenzyl)-2,2′bimidazoline, DMA = N,N-dimethylacetamide) constructed by in situ growth of HPU-9 on Fe₃O₄, which has excellent absorption of cationic dyes from aqueous solution. The Fe₃O₄@HPU-9 particle possesses a well-defined core-shell structure consisting of a Fe₃O₄ core (diameter: 190 nm) and a HPU-9 shell (thickness: 10 nm). In the composite, the HPU-9 shell contributes to the capsulation of cationic dyes through electrostatic attractions between HPU-9 and cationic dyes, while the Fe₃O₄ core serves as magnetic particle. The maximum absorption capacity of Fe₃O₄@HPU-9 for R6G was 362.318 mg·g−1. The absorption kinetics data were well described by a psedo-second-order model (R² > 0.99), and the equilibrium data were also well fitted to Langmuir isotherm model (R² > 0.99). Our data confirmed that the proposed magnetic composite could be recycled and reused several times without centrifugal separation, making it more convenient, economic and efficient than common adsorbents.