A straightforward strategy to synthesize supramolecular amorphous zirconium metal-organic gel for efficient Pb(II) removal

Abstract

The transformation of metal-organic frameworks (MOFs) to metal-organic gels (MOGs) is an attractive but challenging issue because they are generally regarded as the opposite, with the former being hard and the latter soft. Herein, a straightforward strategy was developed to synthesize amorphous Zr-MOG-12 by gelatinization of UiO-66-NH2 (i.e. Zr-MOF) via a facile standing time-controlled crystallization method. The precursor ZrCl4 obtains oxide and hydroxide bridges after standing at room temperature, which promotes the formation of [Zr6O4(OH)4]12+ clusters and induces rapid and excessive nucleation rate, and further leads to the coordination perturbation of UiO-66-NH2 nanoparticles to achieve Zr-MOG-12. The as-prepared Zr-MOG-12 integrates the more hierarchical porous structure of gel-based soft materials and the amorphous structure of lower-coordinated active sites, which exhibits superb adsorption capacity for Pb(II) with excellent selectivity and reusability, indicating that Zr-MOG-12 is more promising to removal Pb(II) in practical water treatment. In addition, the transformation of amorphous Zr-MOG-12 to highly crystaline Zr-MOF’ has been achieved by the solvothermal reorganization using glacial acetic acid as the crystallization promoter. The novel methods proposed in this study successfully link crystalline MOF with amorphous MOG, providing new opportunities for facile preparation and transformation of MOFs and MOGs.