Synergistically enhanced capture of perfluorooctanoic acid using a novel dual metal-organic framework adsorbent

Abstract

Metal-Organic Framework (MOF) have gained widespread attention as potential adsorbents for the removal of perfluorooctanoic acid (PFOA). However, single-component MOF often exhibit limitations in adsorption capacity, functionality, and pore structure. Hereby, we innovatively designed and synthesized a dual-metal core-shell MOF composite adsorbent, MIL-101(Cr)@ZIF-8 (a chromium-zinc bimetallic MOF, CZDM), which exhibits an excellent adsorption removal performance of PFOA from aqueous solutions. The results showed that the CZDM composite material has a high specific surface area (2091 m²/g), with pore structures exhibiting typical micropores (∼1.16 nm) and mesopores (∼3.4 nm), which are crucial for the efficient adsorption of PFOA. SEM and TEM images revealed that CZDM has a uniform core-shell morphology, with MIL-101(Cr) as the core and ZIF-8 as the shell, maintaining a stable and intact structure. EDX analysis further confirmed the successful incorporation of Cr and Zn elements. Batch experiments evaluated the effects of temperature, solution pH, and PFOA concentration on adsorption efficiency. The results demonstrated that the CZDM-3 adsorbent exhibited rapid adsorption kinetics and good PFOA removal efficiency across a wide pH range. The superior adsorption performance of CZDM is attributed to the synergistic effect of the dual-metal active sites, optimized pore structure, electrostatic interactions, and coordination bonds. The maximum adsorption capacity for PFOA reached 625.5 mg/g, with equilibrium achieved within 60 min, outperforming some related reported adsorbents. The experimental data of the adsorption process fit well with both Langmuir adsorption isotherms and pseudo-second-order kinetics models, indicating that the adsorption process is spontaneous, endothermic, and accompanied by an increase in entropy. Notably, even after five cycles, the CZDM material maintained high removal efficiency toward PFOA. This study advances a new synthesizing strategy of the MOF@MOF, and the CZDM exhibits a potential application in PFOA elimination from water.