Solvent induction and in-situ interfacial polymerization of novel polyamide-protected MOFs for the efficient adsorption of rare earths

With the improvement of environmental protection requirements, rare earth separation and purification technology is developing in the direction of green and high efficiency in recent years. The treatment of low-concentration mixed rare earth wastewater has significant resource and environmental values. MOFs had extremely high adsorption capacity for metal ions, but were implicated by poor water and acid stability, making them unsuitable for engineering applications. Herein, a smaller-sized fluorinated MOF (n-KAUST-8) was first fabricated by solvent-induced regulation, and then a thin layer of polyamide (PA) was constructed on the surface (PA-n-KAUST-8) by in situ interfacial polymerization. SEM, TEM, and DLS results well demonstrated that n-KAUST-8 and PA-n-KAUST-8 exhibited much smaller particle sizes of around 400 and 100 nm, respectively, than that of KAUST-8, proving that the solvent-induced regulation was effective. Additionally, coating of the PA layer helped PA-n-KAUST-8 maintain a stable crystalline structure in water from pH range 1 to 5 for 7 days, indicating its chemical stability meets the expectation for the adsorption of rare earth ions. The adsorption capacities of n-KAUST-8 for Pr 3+ , Nd 3+ , and Sm 3+ were as high as 484.5, 455.7, and 385.1 mg g −1 respectively, indicating that nano-sized n-KAUST-8 was an effective adsorbent for separating rare earth ions in aqueous environments. In addition, 0.5 mol L −1 HCl solution was appropriate for the desorption of Nd 3+ by PA-n-KAUST-8, whose desorption rate could be higher than 80 %.