A novel strategy of approximate ligand substitution was proposed to introduce ionic liquids (ILs) into the porous framework of metal-organic frameworks (MOFs). With this approach, an efficient Bronsted-Lewis acidic catalyst RCH,COOH)(2)IM]HSO4@H-UiO-66 was successfully constructed via bidentate coordination between one-COO- group of [CH2COOH)(2)IM]HSO4 and two portions of unsaturated Zr ion defects of the hierarchically porous Zr metal-organic framework (H-UiO-66). The catalyst was systematically characterized by Fourier transform infrared spectroscopy, X-ray diffraction, nitrogen adsorption desorption, scanning electron microscopy, and thermal gravimetric analysis, proving the feasibility of this encapsulation mode. The fabricated [(CH2COOH)(2)IM]pH-UiO-66 catalyst was applied for synthesis of biodiesel, and the reaction conditions were optimized by response surface methodology. The resulting Bronsted-Lewis acidic RCH2COOH)(2)IM1Hso(4)@ H-UiO-66 catalyst exhibited excellent catalytic performance for the esterification of oleic acid with methanol. Under the optimum condition, the predicted yield of biodiesel reached 93.71% and the experimental value was 93.82%, which indicated the synthesized catalyst has high catalytic activity. Moreover, the catalyst could be easily recovered and reused, and the yield of biodiesel decreased from 93.82 to 90.95% after five runs, indicating good reusability. Besides, based on the synergistic effect of Bronsted acidic and Lewis acidic parts, the catalytic mechanism of [(CH2COOH)(2)IM]@H-UiO-66 was also discussed.
