Facile synthesis of hierarchical micro-mesoporous HKUST-1 by a mixed-linker defect strategy for enhanced adsorptive removal of benzothiophene from fuel

Developing high-efficiency adsorbents is crucial for removing aromatic sulfur containing compounds from the fossil fuels. HKUST-1 is considered as a promising candidate of adsorbents for deep desulfurization. However, the typical HKUST-1 possesses only micropores, which restricts the diffusion and limits the desulfurization capacity. Herein, we proposed a mixed-linker defect strategy to construct a bimodal micro-mesoporous HKUST-1 to enhance adsorptive removal of benzothiophene (BT) from fuels. A rapid microwave-assisted synthetic route was developed for preparing a series of micro-meso porous OH-HKUST-1-x (x = 0.1, 0.2 and 0.3) by adjusting the ratio of 5-hydroxyisophthalic acid to benzene-1,3,5-tricarboxylate acid. This series of hierarchically porous metal-organic frameworks (MOFs) features 0.7-0.8 nm and 3.4-3.8 nm micropore and mesopore, respectively. The effects of linker defects on the chemical and physical properties of the materials were systematically studied. The X-ray diffraction patterns showed that the as-synthesized OH-HKUST-1-x containing hydroxyl defects still retained the original crystal structure. The OH-HKUST-1-x exhibited a higher desulfurization efficiency in comparison with HKUST-1, because with increasing the mole ratio of the mixed linkers, larger pore diameters were generated. The bimodal micro-mesoporous structure facilitates adsorbates diffusion and leads to higher exposure of the unsaturated adsorptive site of Cu2+ than the microporous structure. The as-synthesized OHHKUST-1-0.2 displayed the best performance towards adsorptive removal of BT, the static and breakthrough adsorption capacity achieved 26.30 mg S g-1 and 0.0490 mmol g-1, respectively. Additionally, after the OHHKUST-1-0.2 was regenerated six times it still had a desulfurization performance as 88.3% of the fresh adsorbent.