Rapid defect engineering of UiO-67 (Zr) via microwave-assisted continuous-flow synthesis: Effects of modulator species and concentration on the toluene adsorption

Defect engineering is a promising approach for tailoring the physicochemical properties, such as stability, pore structure, and surface area, of metal–organic frameworks (MOFs). In this study, some defective Zr-based biphenyl dicarboxylate (UiO-67 (Zr)) MOFs were prepared via fast modulated synthesis under microwave-assisted continuous flow by using HCOOH, CH₃COOH, CH₃CH₂COOH, and C₆H₅COOH as modulators. A surface-modified UiO-67(Zr) framework with high porosity and crystallinity could be rapidly produced in a few minutes due to the incomplete exchange between the bridging ligand and the modulator. The defect concentration in the products was tuned by controlling both the modulator species and concentrations utilized. The adsorption ability toward toluene of the prepared UiO-67(Zr) MOFs was found to be related to their structural defects; the defective UiO-67(Zr) MOF synthesized with HCOOH as the modulator exhibited the highest toluene adsorption capacity (467 mg g⁻¹), surpassing also most of the previously reported adsorbent materials, such as zeolites, activated carbon, Zr-based dicarboxybenzene (UiO-66(Zr)), H₂N-UiO-66(Zr), zeolitic imidazolates, and copper benzenetricarboxylate. Moreover, the experimental dynamic adsorption data were mathematically modeled to predict the adsorption behaviors of defective UiO-67(Zr) MOFs.