Incorporation of N-Methyl-D-Glucamine Functionalized Oligomer into MIL-101(Cr) for Highly Efficient Removal of Boric Acid from Water

Incorporation of N-methyl-D-glucamine functionalized oligomer into MIL-101(Cr) for highly efficient removal of boric acid from water

Jiawei Wang†, Zongbi Bao*†, Huabin Xing†, Baogen Su†, Zhiguo Zhang†, Qiwei Yang†, Yiwen Yang†, and Qilong Ren†

Key Laboratory of Biomass Chemical Engineering of Ministry of Education, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, P. R. China

Abstract

Water security is receiving an increasing attention and will remain a worldwide concern over next decades. An estimated, 80% of the world's population is exposed to high levels of threat to water security. The presence of appreciable quantities of boron species in drinking water deteriorates the quality of the water. Considering the health consequences of elevated levels of boron species, the World Health Organization (WHO) has set the tolerance limit in drinking water to 2.4 mg L^-1. Many approaches have been explored for the removal of boron species from water including precipitation-coagulation, reverse osmosis, electrodialysis, solvent extraction, membrane filtration, and adsorption. Among these methods, adsorption is a more efficient and economical technique. Polymeric resins are practically important adsorbents in a wide variety of applications, but generally suffer from low surface areas and limited functionalized adsorption sites due to their closely compacted and tangled polymeric chains. Metal-organic frameworks (MOFs), emerging as a new class of porous polymer materials, show great potential in adsorptive removal of contaminants from water. MOFs are structurally diverse and provide well-defined nanostructures, enabling the fabrication of hybrid composites with some special properties by incorporating some functional species into their pores.

Herein, we report a MOF composite poly(Si-NMDG)@MIL-101 by incorporating N-methyl-D-glucamine (NMDG) functionalized oligomer into MIL-101(Cr) for the exceptionally high adsorption of boron species and thus the removal of boric acid from water (Scheme 1). The poly(Si-NMDG)@MIL-101 remarkably takes up about 12 times boric acid (0.46 mmol g^-1) compared to the parent MIL-101(Cr) (0.04 mmol g^-1) when the equilibrium concentration of boric acid is 0.1 mg mL^-1 (Figure 1). Furthermore, the adsorption isotherm on the basis of dynamic saturated adsorption capacities obtained with different concentrations of boric acid solution shows a theoretical maximum adsorption capacity of 2.29 mmol B g^-1 (Figure 2). It outperforms all other boron-selective silica adsorbents and commercial resins, offering promising perspectives for boron removal applications in seawater desalination. Regeneration and breakthrough studies indicate that the poly(Si-NMDG)@MIL-101 is rather stable and practically feasible for the practical applications (Figure 3).

Scheme 1. Schematic illustration of the synthesis of poly(Si-NMDG)@MIL-101

 

Figure 1. Breakthrough curves for 0.1 mg mL^-1 boric acid aqueous solution for original MIL-101(Cr) (red), and poly(Si-NMDG)@MIL-101 (blue).

 

Figure 2. Boron adsorption isotherm of poly(Si-NMDG)@MIL-101 on basis of adsorption data obtained from breakthrough experiments. The curve represents a fit to the Langmuir equation.

Figure 3. Adsorption cycles of regenerated poly(Si-NMDG)@MIL-101

 

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