Dye Removal Utilizing ZIF-71 and Hydrophobic ZIF-71(ClBr): Kinetic and Equilibrium Studies

In the present work, methylene blue (MB) was removed from aqueous solutions using ZIF-71 and ZIF-71-(ClBr) as adsorbents. The ZIFs were synthesized at room temperature, and their structures were confirmed by powder X-ray diffraction (PXRD). Nitrogen physisorption experiments showed high specific surface areas of 831.24 m² g^-1 and 815.17 m² g^-1 for ZIF-71 and ZIF-71-(ClBr), respectively. Adsorption optimal conditions of pH and contact time were evaluated. The adsorption data fitted well with the pseudo-first-order and the Langmuir isotherm model for ZIF-71, whereas ZIF-71-(ClBr) fitted well with the pseudo-second-order and the Freundlich isotherm model. The Langmuir model showed the ZIFs' maximum adsorption capacities (q_m ) of 597.92 mg g^-1 and 191.56 mg g^-1. Kinetic analysis showed that ZIF-71-(ClBr) reaches equilibrium faster than ZIF-71, revealing the effect of differences in their pore sizes. Moreover, density functional theory (DFT) calculations indicate that the minimal structural deformation required for ZIF-71-(ClBr) plays an important role in achieving this behavior. The efficiency of both ZIFs was evaluated by performing adsorption-desorption cycles, reaching four cycles.