Phytic acid-encapsulated MIL-101(Cr): Remarkable adsorbent for the removal of both neutral indole and basic quinoline from model liquid fuel

Abstract

Phytic acid (PA) encapsulated metal-organic framework (MIL-101(Cr) or Cr-benzenedicarboxylate) was prepared for the first time; and applied in the adsorptive removal of nitrogen-containing compounds (NCCs) from liquid model fuel. The modified MIL-101(Cr)s resulted in very promising maximum adsorption capacities (Q0) for both the neutral indole (IND, Q0 = 543 mg/g) and basic quinoline (QUI, Q0 = 549 mg/g) compared to the pristine MIL-101(Cr) (IND; Q0 = 416 mg/g; QUI, Q0 = 409 mg/g). Or, the Qo values of PA(3)@MIL-101(Cr) for the adsorptions of IND and QUI stand at the second and fifth positions, respectively, among any previously reported results. Moreover, the new adsorbent showed around 8 times adsorption capacity to that of conventional activated carbon. PA encapsulation onto MIL-101(Cr) resulted in 86% and 91% increased adsorption (based on unit surface area of adsorbent) of IND and QUI, respectively. Moreover, PA(3)@MIL-101(Cr) showed more effective/selective adsorption than pristine MIL-101(Cr) towards the NCCs especially when toluene (as aromatics) was added as co-solvent. The extraordinary adsorptions could be described by the hydrogen bonding and the acid-base interactions between the NCCs and the PA functionalities of the adsorbents. Moreover, the PA@MIL-101(Cr)s could be regenerated via a simple manner and reused in adsorptions up to several cycles. Therefore, the novel PA@MOF materials could be suggested as a type of very efficient adsorbents for the adsorptive removal of both neutral and basic NCCs from liquid model fuel.