Modulated synthesis of a novel nickel-based metal–organic framework composite material for the adsorptive desulfurization of liquid fuels

Abstract: Metal-organic frameworks (MOFs) are promising adsorbents for adsorptive desulphurisation (ADS), because of the ability to tune the MOF structure to match the application. However, the study of ADS of liquid fuels by using MOF-5 is still scarce. In this work, a group of Ni-doped MOF-5 absorbents were modulated synthesised by using formic acid as a modulator. Their activities for ADS of model fuels (with initial sulphur concentrations of 150 ppm, 151 ppm and 153 ppm for TH, DBT and 4,6 DMDBT respectively), were investigated. Although Ni-doping decreased the crystallinity and the crystallite size of MOF-5, the addition of the formic acid dramatically increased both the crystallite size and crystallinity of all the MOF-5(xNi/Zn) materials. In addition, it was observed that the modulated synthesis reduced the interpenetration of MOF-5 crystallites. The adsorptive experimental results showed that the modulated synthesis of MOF-5(Ni) by formic acid improved the overall adsorptive activity of MOF-5(Ni) almost twofold. This increase in activity was attributed to increased crystallinity, and an increase in the number of atoms with low coordination for modulated MOF-5(Ni) compared to MOF-5 (100). Formic acid as a modulator was observed to have three effects, namely: i) catalysing MOF synthesis; ii) modulating crystallite size; iii) controlling crystallinity. The most active adsorbent, MOF-5(Ni) treated with formic acid, was observed to have the highest activity towards thiophene (TH), rather than Dibenzothiophene(DBT) and 4,6-Dimethyldibenzothiophene (DMDBT). The overall adsorption capacity and partition coefficient for this adsorbent was 4.14 mg/g and 0.053 mg/g/ppm respectively