Preparation of Mg@MIL-101(Fe)/NH2-MIL-125(Ti) bis-MIL composites and their sorption performance towards Pb(II) from aqueous solution

MIL-101(Fe) has received more and more attention in wastewater treatment, and how to further improve its stability and sorption capacity has become a research focus. In this study, metal Mg was used to dope MIL-101(Fe) to construct Mg@MIL-101(Fe) with bimetallic sites, which was then mixed with NH2-MIL-125(Ti) to successfully fabricate Mg@MIL-101(Fe)/NH2-MIL-125(Ti) (MOM) bis-MIL composites. MOM not only contains a large number of sorption sites but also exhibits excellent stability and reusability, realizing efficient sorption of Pb(II) from aqueous solution. In addition, the sorption performance and mechanism of Pb(II) on MOM were investigated by the characterizations of SEM, BET, TG, XRD, FTIR and XPS, as well as the kinetic and thermodynamic analyses. The sorption of Pb(II) on MOM is in accordance with the Langmuir isothermal model and pseudo-second-order kinetic model. The maximum sorption capacity of Pb(II) on MOM derived from the Langmuir model fitting is 320.941 mg·g−1. The sorption of Pb(II) on MOM is strongly affected by pH, but not by ionic strength, which indicates that MOM has good resistance to salt interferences. The strong complexation of carboxyl, hydroxyl and amino functional groups with Pb(II) is the main sorption mechanism of Pb(II) on MOM, and electrostatic interaction and ion exchange also contribute to the sorption. In conclusion, MOM has strong practical application prospects in the treatment of Pb(II)-containing wastewater.