Performance study of phosphate removal from water using synergistic interaction between lanthanum-magnesium bimetallic organic frameworks and polyethyleneimine

Aiming at the water solubility of Mg-MOFs and the problems of unstable adsorption performance and low life of pure MOFs caused by metal leakage, lanthanum and polyethyleneimine co-doped Mg-MOFs (2.0LMBP-2.5) were synthesized by solvothermal and impregnation methods. 2.0LMBP-2.5 not only has strong resistance for co-existing anions and acid-base, but also has excellent reusability and stability. Its maximum phosphate adsorption capacity was 514.15 mg·g−1. The phosphate removal rate reached 90.53 %-96.04 % in the pH range of 3.0–11.0. The results of kinetic, isothermal adsorption and thermodynamics showed that the phosphate adsorption process of 2.0LMBP-2.5 was a spontaneous heat absorption process and dominated by monolayer adsorption and chemisorption. FT-IR spectroscopy and XPS revealed a synergistic mechanism between MOFs and polyethyleneimine. The introduction of lanthanum improved the coordination metal bond strength of Mg-MOFs, effectively overcame the water solubility problem of Mg-MOFs. The introduction of lanthanum and polyethyleneimine significantly increased the adsorption capacity of Mg-MOFs, from 21.79 to 273.61 mg·g−1 and 273.61 to 514.15 mg·g−1, respectively.