Controlled Manipulation of Metal-Organic Framework Layers to Nanometer Precision Inside Large Mesochannels of Ordered Mesoporous Silica for Enhanced Removal of Bisphenol A from Water

Considerable attention has been paid on the design of hierarchical porous metal organic framework (MOF) composites, which not only enhances the performance but also broadens the applications of MOFs. So far, controlled manipulation of nanometer-thick MOF layers in ordered mesochannels, while retaining their respective intrinsic properties, is still a main challenge because of the difficulty of growing MOFs in confined space. Herein, using a step-by-step coordination method, the formation of a hierarchical micro-mesoporous hybrid with a wall (channel wall and coating layer) thickness of up to 8.0 nm and open pore size down to 7.7 nm has been achieved based on large mesoporous SBA-15, and the wall thickness with nanometer precision can be controlled by adjusting the growth cycles of zeolite imidazolate framework-8 (ZIF-8) coating layers. Compared to pure ZIF-8, the obtained ZIF-8@SBA-15 composites showed more than 2-fold enhancement in adsorption capacity and approximately 20-fold improvement in the adsorption rate constant for bisphenol A in water, which could be ascribed to the synergistic effects of the high adsorption ability from ZIF-8 and the fast diffusion property from SBA-15. More importantly, the degraded ZIF-8@SBA-15 composite can be completely restored by a simple immersion into 2-methylimidazole solution. The easy restorability and good reusability further enable ZIF-8@SBA-15 as a promising adsorbent for effectively removing organic contaminants from water.