Enhancing the remarkable adsorption of Pb 2+ in a series of sulfonic-functionalized Zr-based MOFs: a combined theoretical and experimental study for elucidating the adsorption mechanism

A series of Zr-based metal-organic frameworks was prepared the solvothermal route using sulfonic-rich linkers for the efficient capture of Pb ions from aqueous medium. The factors affecting adsorption such as the solution pH, adsorbent dosage, contact time, adsorption isotherms, and mechanism were studied. Consequently, the maximum adsorption capacity of Pb on the acidified VNU-23 was determined to be 617.3 mg g , which is much higher than that of previously reported adsorbents and MOF materials. Furthermore, the adsorption isotherms and kinetics of the Pb ion are in good accordance with the Langmuir and pseudo-second-order kinetic model, suggesting that the uptake of Pb is a chemisorption process. The reusability experiments demonstrated the facile recovery of the H ⊂VNU-23 material through immersion in an HNO solution (pH = 3), where its Pb adsorption efficiency still remained at about 90% of the initial uptake over seven cycles. Remarkably, the adsorption mechanism was elucidated through a combined theoretical and experimental investigation. Accordingly, the Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy connected to energy-dispersive X-ray mapping (SEM-EDX-mapping), and X-ray photoelectron spectroscopy (XPS) analysis of the Pb⊂VNU-23 sample and comparison with H ⊂VNU-23 confirmed that the electrostatic interaction occurs the interaction between the SO moieties in the framework and the Pb ion, leading to the formation of a Pb-O bond. In addition, the density functional theory (DFT) calculations showed the effective affinity of the MOF adsorbent toward the Pb ion the strong driving force mentioned in the experimental studies. Thus, these findings illustrate that H ⊂VNU-23 can be employed as a potential adsorbent to eliminate Pb ions from wastewater.