Novel melamine modified metal-organic frameworks for remarkably high removal of heavy metal Pb (II)

Abstract Novel melamine modified metal-organic frameworks (melamine-MOFs) were synthesized and then used as an absorbent for the removal of heavy metal Pb (II) from a low-salt solution. The melamine-MOFs showed high-intensity x-ray diffraction peaks and a UiO-66-like structure. It has a sphere-like morphology and a diameter of ~ 50 nm. The interactions between melamine and the MOFs were calculated by time dependent density function theory (TD-DFT), showing that there were charge transfer and orbital switching. Fourier transform infrared (FTIR) analysis showed successful incorporation of the melamine into the MOFs upon chemical reaction. Thermal gravimetric analysis (TGA) showed a limited weight-loss before 350 °C, indicating that the melamine was not physically mixed with the MOFs. Effects of adsorption time, pH, and temperature (T) were also investigated. The melamine-MOFs showed higher adsorption capacity (122.0 mg g− 1) than that of the pristine MOFs (72.1 mg g− 1) at 120 min, 40 °C and pH = 5. The adsorption capacity was remarkably high (about 205 mg g− 1) at pH of 6. The pseudo-second-order kinetic model fit the adsorption data best (R2 > 0.99). The adsorption mechanisms were confirmed as the coordination interaction between the amino groups (–NH2) and Pb (II). Therefore, the melamine-MOFs demonstrated a great potential in the treatment of heavy metal wastewater.