Ionic double-shell magnetic covalent organic framework for sharp and fast adsorption of critical metals

The recovery of critical metals (CMs) from waste streams has garnered increasing attention in recent years due to their increased demand, engineering applications, and vulnerability to supply disruptions. Herein, we synthesize two novel ionic materials, namely GIEC704a (magnetic covalent organic framework consisting of Fe3O4/TAGH-Dha) and GIEC704b (double-shell magnetic material formed of Fe3O4/TAGH-Dha/TpPa) using the solvothermal method for the recovery of CMs. The experimental data supported Langmuir's isotherm model, and the results showed that both GIEC704a and GIEC704b exhibited remarkable adsorption capacities (qmax). GIEC704a exhibited adsorption capacities of 1531.8, 884.9, and 729.9 mg/g, while GIEC704b had 1681.5, 854.7, and 800 mg/g (Al3+, Fe3+ and Cu2+) capacities, respectively. Furthermore, GIEC704a and GIEC704b demonstrated approximately 80 % adsorption of REEs with high adsorption capacities of 53.6, 52.3, 41.2 mg/g and 55.3, 55.4, and 43.4 mg/g (Lanthanum, Yttrium, and Neodymium), respectively with excellent selectivity. The large surface areas of GIEC704a and GIEC704b—147.9 m2/g and 2143.1 m2/g, respectively—explain their excellent performance. The results of the kinetic study support the pseudo-second-order model with a high coefficient of (R2 = 0.9999), and an efficiency of over 90 % was achieved within 5 min. The findings of the thermodynamic analysis indicated that the adsorption process was spontaneous and endothermic. Furthermore, the outstanding reusability of GIEC704a and GIEC704b confirmed their suitability for environmental chemical engineering and industrial applications.