Highly Efficient and Selective Capture of Pb(II) through Lignin-Decorated Metal Organic Frameworks

Metal-organic frameworks (MOFs) and their composites have demonstrated efficient and selective capture of heavy metal ions from aqueous solutions. In this study, a novel AL@Fe-BTC (lignin in situ growth of iron-based metal-organic framework Fe-BTC) was prepared by a one-pot method to grow Fe-BTC (metal-organic framework) in situ with lignin as the main body. The resulting composite with a lignin-to-ligand ratio of 3:1 exhibited excellent adsorption capacity for Pb(II). Then the optimal adsorption conditions of AL@Fe-BTC were determined as follows: pH of 6.0, initial metal ion concentration of 400 mg/L, adsorbent dosage of 0.4 g/L, and adsorption time of 360 min, resulting in an equilibrium adsorption capacity of 144.1 mg/g Pb(II). Kinetic and isothermal models revealed that the adsorption process follows the pseudo-second-order kinetic model and conforms well to the Freundlich isotherm model. The adsorption thermodynamics showed that the adsorption of Pb(II) by AL@Fe-BTC was a feasible spontaneous heat-adsorbing process. In the presence of coexisting metal ions and interfering ions (K⁺, Ca²⁺, and Na⁺), AL@Fe-BTC also presented highly efficient and selective capture for Pb(II). Furthermore, AL@Fe-BTC also exhibited positive reusability with an adsorption capacity of Pb(II) after four cycles. The adsorption mechanism of Pb(II) involved the chelation interaction of Pb-O and ion-exchange interaction. This research focuses on the application of composites obtained by in situ growth of the MOF material Fe-BTC on lignin in heavy metal-contaminated wastewater, which provides a method for the preparation of green and simple biobased materials for the removal of heavy metals.