Hierarchically Ultrasmall Hf-Based MOF: Mesopore Adjustment and Reconstruction by Recycle Using Acid Etching Strategy

Abstract

Benefiting from their unique properties including faster mass transfer, more exposed active sites and large molecule recognition, hierarchically porous metal–organic frameworks (HP-MOFs), in the form of ultrasmall nanoparticles (NPs) and having self-assembled interparticle mesopores, have garnered greater attention in recent years that given to typical MOFs. However, controllable synthesis of HP-MOFs on the nanoscale remains a significant challenge. Herein, for the first time, a facile top-down acid etching strategy was developed to fabricate a series of nanosized (∼15 nm) mesoporous MOF, HP-UiO-66-NH2(Hf). The sizes of mesopores in this material can be effectively tuned by simply controlling the concentration of propionic acid (PA) utilized in the preparation solution. Interestingly, the generated mesoporous HP-UiO-66-NH2(Hf) has excellent stability and can be readily constructed by using PA etching solution that has been recycled at least four times. Remarkably, HP-UiO-66-NH2(Hf) displays a high size-selectivity for adsorption of enzymes. Associated with its highly matched mesopore size, the nanocomposite generated by complexation with glucose oxidase (GOD), GOD@HP-UiO-66-NH2(Hf) has a higher catalytic activity and a significantly enhanced stability (recycled at least 7 times) in promoting oxidation of glucose compared to its MOF counterpart, GOD@UiO-66-NH2(Hf) and native GOD.