Modulated synthesized Ni-based MOF with improved adsorptive desulfurization activity

Metal-organic frameworks (MOFs) are promising adsorbents for adsorptive desulfurization (ADS) because MOF structure can be tuned to match the application. However, data on the ADS of liquid fuels using Ni-BDC are still scarce. In this study, modulated synthesis was used to prepare a group of Ni-doped MOF absorbents using formic acid as the modulator. The activities of these adsorbents for the ADS of model fuels were investigated, with initial sulfur concentrations of 150, 151, and 153 ppm for thiophene (TH), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6 DMDBT), respectively. Although Ni-doping decreased the crystallinity and crystallite size of the MOFs, the addition of formic acid significantly increased both the crystallite size and crystallinity of all the (xNi/Zn)-BDC materials. In addition, it was observed that modulated synthesis reduced the interpenetration of the MOF-5 crystallites. The adsorption experimental results showed that the modulated synthesis of Ni-BDC using formic acid improved the overall adsorptive activity of Ni-BDC almost twofold. This increase in activity was attributed to increased crystallinity and a higher number of atoms with low coordination for modulated Ni-BDC compared with MOF-5 (100). Formic acid as a modulator was observed to have three effects: i) accelerating MOF synthesis, ii) modulating crystallite size, and iii) controlling crystallinity. The most active adsorbent, Ni-BDC treated with formic acid, was observed to have higher activity toward TH than DBT and 4,6 DMDBT. The overall adsorption capacity and partition coefficient for this adsorbent were 4.14 mg/g and 0.053 mg/g/ppm, respectively.