MOF-525 and Fe-loaded MOF-525 for the selective adsorption removal of Cu(Ⅱ) and Cr(VI)

Two Zr-MOFs (including MOF-525 and MOF-525(Fe)) are synthesized and used to evaluate the adsorption performances for Cu(Ⅱ) and Cr(VI). Batch experiments demonstrate MOF-525 exhibits excellent adsorption removal for Cu(Ⅱ) and MOF-525(Fe) shows excellent adsorption removal for Cr(VI). The isotherms characteristic results indicate MOF-525 is micropores and conformed to type I, while MOF-525(Fe) is mesopores and conformed to type Ⅳ. The removal efficiency of Cu(Ⅱ) by MOF-525 is sharply increased from 26.1 % to 99.7 % and that of Cr(VI) by MOF-525(Fe) is decreased slightly from 99.6 % to 95.5 % as the pH increased from 3.0 to 8.0; besides, the adsorption capacity of Cu(Ⅱ) is enhanced in the presence of Cl− or PO43−, but that of Cr(VI) is significantly decreased. The adsorption processes of both MOF-525 for Cu(II) and MOF-525(Fe) for Cr(VI) are fitted better to the pseudo-second-order kinetic model and Langmuir model, indicating they are mainly monolayer chemisorption. In addition, adsorption thermodynamics results demonstrate the adsorption processes are endothermic and spontaneous physisorption. The adsorption mechanisms investigations further revealing that the electrostatic interaction, reducing action, and coordination interaction are involved in the adsorption removal of Cu(II) and Cr(VI); moreover, the surface precipitation is existed in the adsorption of Cu(II) and the hydrogen bonding is found in that of Cr(VI).