Tailoring the topology of ZIF-67 metal-organic frameworks (MOFs) adsorbents to capture humic acids.

Chlorination is a versatile technique to combat water-borne pathogens. Over the last years, there has been continued research interest to abate the formation of chlorinated disinfection by-products (DBPs). To prevent hazardous DBPs in drinking water, it is decided to diminish organic precursors, among which humic acids (HA) resulting from the decomposition and transformation of biomass. Metal-organic frameworks (MOFs) such as zeolitic imidazolate frameworks (ZIFs) have recently received tremendous attention in water purification. Herein, customized ZIF-67 MOFs possessing various physicochemical properties were prepared by changing the cobalt source. The HA removal by ZIF-67-Cl, ZIF-67-OAc, ZIF-67-NO ₃ , and ZIF-67-SO ₄ were 85.6%, 68.9%, 86.1%, and 87.4%, respectively, evidently affected by the specific surface area. HA uptake by ZIF-67-SO ₄ indicated a removal efficiency beyond 90% in 4 <pH< 8, while a drop was observed when pH reached ∼10. A parametric study revealed that the adsorption efficiency was a function of dosage; moreover, the removal percentage remained > 90% after 60 min mixing the solution with 0.3 g L ^-1 ZIF-67-SO ₄ . Notably, an acceptable removal performance (∼72.3%) was obtained even at HA concentrations up to 100 mg L ^-1 . The equilibrium data fitted well with the isotherm models in the order of Langmuir> Hill > BET> Khan > Redlich-Peterson> Jovanovic> Freundlich > and Temkin. The maximum adsorption capacity q _m  for HA uptake by ZIF-67-SO ₄ was 175.89 mg g ^-1 , well above the majority of adsorbents. The pseudo-first-order model described the rate of HA adsorption by time. In conclusion, ZIF-67-SO ₄ presented promising adsorptive properties against HA. Further studies would be needed to minimize cobalt leaching from the ZIF-67-SO ₄ structure and improve its reusability safely, to ensure its effectiveness and the economy of adsorption system.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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