Composite Materials Based on a Zr4+ MOF and Aluminosilicates for the Simultaneous Removal of Cationic and Anionic Dyes from Aqueous Media

Abstract

Environmental pollution has been a reality for many decades, with its contamination intensifying daily due to rapid urbanization and the ever-increasing world population. Dyes, and especially synthetic ones, constitute a category of pollutants that not only affect the quality of water but also exhibit high toxicity toward living organisms. This study was thoroughly planned to explore the removal of two toxic dyes, namely the methylene blue (MB) and methyl orange (MO) compounds from contaminated aqueous media. For this purpose, we designed and synthesized two new composite materials based on ammonium-functionalized Zr⁴⁺ MOF (MOR-1 or UiO-66-NH₃⁺) and naturally occurring sorbents, such as bentonite and clinoptilolite. The composite materials displayed exceptional sorption capability toward both MB⁺ and MO^- ions. A key finding of this study was the high efficiency of the composite materials to simultaneously remove MB⁺ and MO^- under continuous flow conditions, also showing regeneration capability and reusability, thus providing an alternative to well-known mixed bed resins.

Keywords: alginate beads; clay; composite materials; dyes’ sorption; metal–organic frameworks; methyl orange; methylene blue; sorption column; zeolite.

Figure 1

Representation of the structure of MOR-1. Color code: C, grey; O, red; N, blue; Zr, cyan.

Figure 2

Schematic representation of the preparation of (MOR-1/Bentonite/Fe₃O₄)-10%CA beads.

Figure 3

(A) PXRD patterns of bentonite, MOR-1-HA, and (MOR-1/Bentonite)-HA. (B) PXRD patterns of clinoptilolite, MOR-1-HA, and (MOR-1/Clinoptilolite)-HA. The characteristic diffraction peaks of MOR-1 and aluminosilicates are highlighted in the green rectangles.

Figure 4

FT-IR spectra of (A) bentonite, MOR-1, and (MOR-1/Bentonite)-HA; (B) clinoptilolite, MOR-1, and (MOR-1/Clinoptilolite)-HA.

Figure 5

N₂ sorption isotherms (77 K) for MOR-1, (A) (MOR-1/Bentonite)-HA, and (B) (MOR-1/Clinoptilolite)-HA.

Figure 6

Fitting (red line) of the kinetics data with the Ho–Mckay’s pseudo-second-order equation for the sorption of (A) MB⁺ and (B) MO⁻ by (MOR-1/Bentonite)-HA; (C) MB⁺ and (D) MO⁻ by (MOR-1/Clinoptilolite)-HA.

Figure 7

(A) MB⁺ and (B) MO⁻ isotherm sorption data for (MOR-1/Bentonite)-HA; (C) MB⁺ and (D) MO⁻ isotherm sorption data for (MOR-1/Clinoptilolite)-HA.

Figure 8

Percentage of sorption of (A) MB⁺ and (B) MO⁻ by (MOR-1/Bentonite)-HA; (C) MB⁺ and (D) MO⁻ by (MOR-1/Clinoptilolite)-HA in the pH range of 1–10.

Figure 9

(A) MB⁺ sorption data for (MOR-1/Bentonite)-HA and (MOR-1/Clinoptilolite)-HA in the presence of various competitive anions (initial MB⁺ concentration = 18 ppm, pH ∼ 6.5) and in contaminated bottled water samples (initial MB⁺ concentration = 18 ppm, pH ∼ 7.8). For comparison, sorption results in distilled water (DH₂O) solutions (containing no antagonistic ions) are also provided. (B) MO⁻ sorption data for (MOR-1/Bentonite)-HA and (MOR-1/Clinoptilolite)-HA in the presence of various competitive anions (initial MB⁺ concentration = 18 ppm, pH ∼ 6.5), in contaminated bottled water samples (initial MB⁺ concentration = 19 ppm, pH ∼ 7.8), and in distilled water solutions. The composition of the bottled water was as follows: pH = 7.8, HCO₃⁻ = 244 ppm, Cl⁻ = 4.29 ppm, NO₃⁻ = 1.93 ppm, SO₄²⁻ = 9.16 ppm, Na⁺ = 2.24 ppm, K⁺ = 0.6 ppm, Ca²⁺ = 80.7 ppm, and Mg²⁺ = 5.34 ppm.

Figure 10

Column sorption data regarding the removal of (A) MB⁺ and (B) MO⁻ with (MOR-1/Bentonite/Fe₃O₄)-10%CA from the mixture solution. Column sorption data regarding the removal of (C) MB⁺ and (D) MO⁻ with (ΜOR-1/Clinoptilolite/Fe₃O₄)-10%CA from the mixture solution. The MB⁺/MO⁻ mixture solution circularly passed through the column up to 10 times.

Figure 11

PXRD patterns of (MOR-1/Bentonite)-HA along with those of (A) (MOR-1/Bentonite)-HA@MB⁺, (B) (MOR-1/Bentonite)-HA@MO⁻ and MOR-1/Clinoptilolite)-HA, (C) (MOR-1/Clinoptilolite)-HA@MB⁺, and (D) (MOR-1/Clinoptilolite)-HA@MO⁻.