Synergistic effects of defect engineering and functionalizing ionic liquids within UiO-66(Zr)-NH2 frameworks towards improving removal efficiency of phosphate and methyl orange

Abstract

In this study, novel ionic liquid (IL)-entrapped UiO-66(Zr)-NH2 frameworks are proposed as efficient adsorbents to remove phosphate and methyl orange (MO). First, cetyltrimethylammonium bromide (CTAB) surfactant-defected UiO-66(Zr)-NH2 with tuned ligand deficiencies was produced using the continuous tubular reactor under microwave irradiation, making it a fast and scalable process. Upon changing the CTAB/ligand molar ratio from 0.5 to 1.5 and 2.5, the reaction yield deminised from ∼72–68 and 59 %, while the linker deficiency per Zr6 unit increased from ∼ 0.54–1.72 and 2.01, respectively. Defect-contained UiO-66(Zr)-NH2 was favourably entrapped with 1-butyl-3-methylimidazoliumbromide ([Bmim]+[Br]-) ionic liquid using a ship-in-bottle method to obtain host-guest [Bmim]+[Br]-@UiO-66(Zr)-NH2 composites, named Bmim@UN. Results revealed that IL-functionalized UiO-66(Zr)-NH2 comprised N-heteroaromatic rings and NH2 groups, creating a synergetic effect that enhanced the phosphate and MO adsorptions. At pH 4.5 and 27 °C, the Bmim@UN loaded 12 wt% IL had the equilibrium adsorbing capacity for phosphate and MO of ∼ 197 and ∼ 98 mg/g, respectively, and their corresponding adsorption rate constant of ∼ 0.0036 g mg−1min−1 and 0.0022 g mg−1min−1. Notably, the harvested Bmim@UN exhibited good simultaneous decontamination of phosphate and MO in their binary solution, where MO further accelerated the phosphate adsorption. The mechanism studies revealed that electrostatic interactions, hydrogen bonds, cation-π, and π-π interactions drove these adsorptions. The study demonstrates that combining defect engineering and IL-functionalizing of MOF has constructed efficient materials for wastewater remediation.