Controllable transformation from 1D Co-MOF-74 to 3D CoCO3 and Co3O4 with ligand recovery and tunable morphologies: the assembly process and boosting VOC degradation

Abstract

The controllable assembly of three-dimensional (3D) nanomaterials from a one-dimensional (1D) precursor has always been one of the difficulties in nanomaterial synthesis. Here, we use a gentle hydrolysis of 1D metal–organic frameworks (MOFs) to prepare 3D CoCO₃, with full and convenient recovery of costly organic ligands. For the first time, 1D nanowires of Co-MOF-74 were transformed into CoCO₃ with different 3D morphologies by introducing different modulators of urea or hexamethylenediamine (HMT). The formation mechanism (using urea as a modulator) has been elucidated and has revealed a conversion process from 1D nanowires of Co-MOF-74, subsequently to 1D rod-like stacked 3D Co-MOF-74 nanospheres through aggregate assembly, and then to 3D hydrangea like CoCO₃-H. After calcination, it was found that the obtained 3D Co₃O₄ catalyst derived from 3D CoCO₃ exhibited significantly enhanced catalytic performance for VOC degradation compared to 1D Co₃O₄ directly calcined from Co-MOF-74. In addition, the morphology and the catalytic performance of the catalysts prepared with the recycled ligands were consistent with those of catalysts made from fresh ligands.