Enhanced Water Purification Performance of Ionic Liquid Impregnated Metal-Organic Framework: Dye Removal by [BMIM][PF6]/MIL-53(Al) Composite.

Safiyye Kavak,Harun Kulak,Seda Keskin,Alper Uzun,H Mert Polat,Özce Durak

doi:10.3389/fchem.2020.622567

Abstract

We incorporated a water-stable ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], into a water-stable metal–organic framework (MOF), MIL-53(Al), to generate the [BMIM][PF6]/MIL-53(Al) composite. This composite was examined for water purification by studying its capacity for methylene blue (MB) and methyl orange (MO) removal from aqueous solutions having either single dye or a mixture of both. Data illustrated that the removal efficiency and the maximum adsorption capacity of MIL-53(Al) were increased several times upon [BMIM][PF6] incorporation. For instance, within 1 min, 10 mg of pristine MIL-53(Al) adsorbed 23.3% MB from 10 mg/L of MB solution, while [BMIM][PF6]/MIL-53(Al) composite was adsorbed 82.3% MB in an identical solution. In the case of MO, 10 mg of pristine MIL-53(Al) achieved 27.8 and 53.6% MO removal from 10 mg/L of MO solution, while [BMIM][PF6]/MIL-53(Al) composite removed 61.4 and 99.2% within 5 min and 3 h, respectively. Moreover, upon [BMIM][PF6] incorporation, the maximum MB and MO adsorption capacities of the pristine MOF were increased from 84.5 to 44 mg/g to 204.9 to 60 mg/g, respectively. The adsorption of dyes in pristine MIL-53(Al) and [BMIM][PF6]/MIL-53(Al) followed a pseudo-second-order kinetic model and a Langmuir isotherm model. In a mixture of both dyes, the IL/MOF composite showed a doubled MB selectivity after the IL incorporation. The composite was successfully regenerated at least two times after its use in water purification to remove MB, MO, and their mixtures. Infrared (IR) spectra indicated that the MB/MO adsorption occurs on [BMIM][PF6]/MIL-53(Al) by electrostatic interactions, hydrogen bonding, and π-π interactions. These results showed that [BMIM][PF6]/MIL-53(Al) composite is a highly promising material for efficient water purification.

Highlights

Increased industrialization causes various water pollution issues and gives rise to a global water shortage
By taking advantage of our previous findings demonstrating that the effect of ionic liquid (IL) on improving the separation performance of metal–organic framework (MOF) becomes more significant with an increase in IL loading, we incorporated the IL at the highest possible loading before reaching the incipient wetness point (Koyuturk et al, 2017; Kavak et al, 2020)
Complete characterization data of this ILimpregnated composite, [BMIM][PF6]/MIL-53(Al), along with that of the pristine MOF were already presented in a previous report, where the samples from same batch were considered for gas separation applications (Kavak et al, 2019)

Summary

Introduction

Increased industrialization causes various water pollution issues and gives rise to a global water shortage. Industries such as textile, plastic, paper, food processing, and cosmetics use dyes for coloring purposes and generate effluent wastewater containing various environmentally hazardous dyes (Özcan et al, 2004; Khan et al, 2015). Efficient water purification strategies should be generated to overcome this issue In this regard, various types of adsorbent materials have been investigated and reported for efficient dye removal from aqueous solutions, such as activated carbon, coal, clay, fly ash, and metal–organic frameworks (MOFs) (Gupta and Suhas, 2009; Li et al, 2013; Lin et al, 2014; Dias and Petit, 2015; Anastopoulos et al, 2018; Kausar et al, 2018; Arora et al, 2019; Dhaka et al, 2019)

Methods

Results

Conclusion