Efficient removal of environmentally hazardous heavy metal ions from water by NH2-MIL-101-Fe and MOF-808-EDTA based polyether sulfone adsorbents

The potential of metal-organic frameworks (MOFs) based polymeric composites for heavy metal removal was analyzed in this study. Two mixed matrix composites, along with NH2-MIL-101-Fe and MOF-808-EDTA, were synthesized. The MOFs were synthesized using the solvothermal method, and the mixed matrix spheres (MMSs) were prepared using the facile dropping method. The MMSs were characterized, and batch adsorption studies were performed at different pH and adsorbent dosages. For both MMSs, the optimum pH was between 5-5.5, and the highest removal rates were obtained for MOF-808-EDTA spheres (94 % Hg2+, 86 % As, 80 % Mn). The optimum adsorbent dosage for MOF-808-EDTA was found to be 5.42 g/L, while for NH2-MIL-101-Fe, it was 7.13 g/L, after which the metal ion removal efficiency was reduced. Langmuir adsorption isotherm was fitted with thermodynamic evaluation of Gibbs free energy, enthalpy, and entropy. MOF-808-EDTA demonstrated a greater adsorption capacity of 272.7 mg/g (Hg2+), 151.29 mg/g (As3+), and 125.9 mg/g (Mn2+) than the other MMP. The Gibbs free energy of -20.14 (Hg2+), -12.66 (Mn2+), and -52.61 kJ/mol (As3+) were obtained from the thermodynamic study. The results indicated that the process was exothermic and spontaneous. Breakthrough column studies were performed for MOF-808-EDTA spheres using the pore-surface-diffusion model. The transient column study was conducted for individual heavy metal ion solutions using AddesignTM software to evaluate column exhaustion time, breakthrough time and length of mass transfer zone. Studies with multicomponent solutions of heavy metals also gave potentially promising results in the separation of 92 % of Hg, 84 % As, and 75 % Mn which indicates the prepared adsorbents can be used to remove heavy metal ions from industrial wastewater samples.