Defect-induced synthesis of nanoscale hierarchically porous metal-organic frameworks with tunable porosity for enhanced volatile organic compound adsorption

Abstract

Nanoscale hierarchically porous metal-organic frameworks (NH-MOFs) synergistically combine the advantages of nanoscale MOFs and hierarchically porous MOFs, resulting in remarkable characteristics such as increased specific surface area, greater porosity, and enhanced exposure of active sites. Herein, nanoscale hierarchically porous UIO-66 (UIO-66_X) was synthesized using a defect-induced strategy that employed ethylene diamine tetraacetic acid (EDTA) as a modulator. The introduced EDTA occupies the coordination sites of organic ligands, promoting the formation and growth of UIO-66 crystal nuclei and inducing defects during synthesis. The as-synthesized UIO-66_X crystals exhibit a uniform distribution with an average size of approximately 100 ​nm. In addition, the total pore volume attains a remarkable value of 0.95 ​cm³ ​g⁻¹, with mesopores constituting 36.8 % of the structure. Furthermore, the porosities of UIO-66_X can be easily tuned by controlling the molar ratio of EDTA/Zr⁴⁺. In addition, the as-synthesized UIO-66_X exhibits excellent adsorption capacities for n-hexane (344 ​mg ​g⁻¹) and p-xylene (218 ​mg ​g⁻¹), which are 44.5 % and 27.5 % higher than those of conventional UIO-66, respectively. Finally, the adsorption behavior of n-hexane and p-xylene molecules in UIO-66_X was investigated using density functional theory simulations.