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. a 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 hierarchical porous structure of gel-based soft materials and the amorphous structure of low-coordinated active sites, which exhibits superior adsorption capacity for Pb(II) and excellent selectivity and reusability, indicating that it is a promising candidate to removal Pb(II) in practical water treatment. In addition, the transformation of amorphous Zr-MOG-12 to highly monodisperse Zr-MOF’ crystals was achieved by the solvothermal reorganization using glacial acetic acid as a crystallization promoter. The novel methods proposed in this study successfully connect crystalline MOF with amorphous MOG, providing new opportunities for facile preparation and transformation of MOFs and MOGs.