Highly stable Ni8-pyrazolate metal-organic frameworks for adsorption of methylene blue from water

Three Ni-8-pyrazolate metal-organic frameworks, namely Ni-8-NiL1, Ni-8-CuL1 and Ni-8-CuL2, were prepared using metallosalen-based ligands (NiL1, CuL1, and CuL2). The octanuclear cubic clusters [Ni-8(OH)(4)(H2O)(2)] render these materials with sufficient robustness, enabling their reusability in water for the removal of methylene blue (MB) over three cycles. Because of & pi;-& pi; stacking interactions, these title materials can effectively adsorb MB and demonstrate an exceptional adsorption capacity (up to 1011.8 mg g(-1) for Ni-8-CuL2). Meanwhile, these materials show an adsorption preference for MB instead of methyl orange and eosin Y. The kinetic studies reveal that Ni-8-NiL1 and Ni-8-CuL1 conform to the pseudo second-order model, while Ni-8-CuL2 fits to the pseudo first-order model. The adsorption isotherms of the three materials were also determined to obey the Langmuir model. These results indicate that these title materials are promising adsorbents for removing MB from water.