(510h) 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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