WO2023191609A1

WO2023191609A1 - Process for producing zif-8, the chitosan@zif-8 composite thereof, and the use of zif-8 and of the chitosan@zif-8 composite thereof

Info

Publication number: WO2023191609A1
Application number: PCT/MA2023/050003
Authority: WO
Inventors: Elhankari SAMIR; Moutanassim LAHBIB
Original assignee: Universite Mohammed VI Polytechnique
Priority date: 2022-03-29
Filing date: 2023-03-29
Publication date: 2023-10-05
Also published as: MA56279A1

Abstract

The present invention describes a process which makes it possible to synthesise the compound ZIF-8 and the chitosan@ZIF-8 composite thereof, in particular in bead form, from zinc oxide and in the presence of acetic acid. The present invention also relates to the industrial use of the compound ZIF-8 and the chitosan@ZIF-8 composite thereof. This process comprises the following steps: • dissolving ZnO in the presence of a small amount of acetic acid • adding 2-methylimidazole in the presence of water and/or methanol at mild temperatures, and recovering ZIF-8 at this stage, or • forming chitosan@ZIF-8 beads from chitosan, still using ZnO as a metal precursor of ZIF-8, in the presence of acetic acid.

Description

Process for producing zif-8, its composite chitosan@zif-8 and their application

BRIEF DESCRIPTION OF THE INVENTION

The invention firstly relates to a process for producing ZIF-8 in a single step, from ZnO and in the presence of acetic acid.

The invention also relates to a process for producing the chitosan@ZIF-8 composite in a single step, from ZnO and in the presence of acetic acid, leading in particular to obtaining said composite in the form of beads.

The invention further relates to the use of the above-mentioned products in the treatment of industrial effluents, in particular effluents loaded with toxic products or phosphates. The invention will be defined further in the claims and other characteristics and advantages thereof will appear on reading the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

For a good understanding of the invention, reference will be made to the appended drawings in which:

Figure 1 is a schematic representation of an in-situ synthesis of ZIF-8 and its composite CS@ZIF-8 using ZnO and acetic acid as additive, as well as their use in the adsorption of phosphates.

Figure 2 represents the ray diffractograms of different materials in the form of powder and beads obtained in water and methanol (MeOH)

Figure 3 represents the FT-IR spectra of different materials in the form of powder and beads obtained under different conditions

Figure 4 represents the SEM images of the ZIF-8 materials in the form of powder (a and b) and of the CS@ZIF-8 composite in the form of beads (c and d) obtained in MeOH.

Figure 5 presents the rate of phosphate removal by ZIF-8 and CS@ZIF-8 (water) and CS@ZIF-8 (methanol) and the kinetics of phosphate adsorption by the CS@ZIF- composite. 8 in the form of balls (b).

DETAILED DESCRIPTION OF THE INVENTION

With reference to Figure 1, the process according to the invention first comprises the synthesis of ZIF-8 in powder form (route a) by a complete conversion of zinc oxide (ZnO) into ZIF-8, in presence of a small amount of acetic acid to completely dissociate the zinc ions

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SUBSTITUTE SHEET (RULE 26) (Zr>2+) which then transform into ZIF-8, in a single step, after the addition of 2-methylimidazole in the presence of water and methanol, under mild temperatures.

Next, chitosan@ZIF-8 beads (path b) were synthesized using chitosan, still using ZnO as a metal precursor in the presence of acetic acid, which plays a dual role in dissociating both chitosan and ZnO.

The obtained materials were then used in the adsorption of phosphates from an aqueous solution and the bead shaping facilitated the material recovery process, while maintaining its high adsorption capacity (path c).

The examples below illustrate some of the implementations of the invention, without restricting it to the technical conditions set out.

EXAMPLES

Example 1 - ZIF-8 nanoparticle synthesis conditions.

Example: H2O as solvent {ZIF-8 water}

0.004 mole (0.333 g) of zinc oxide (ZnO) was dissolved in 0.114 mole (2.05 ml) of HzO and 0.0085 mole (0.487 ml) of acetic acid until ZnO was completely dissolved and obtaining a transparent solution.

0.064 mole (5.254 g) of 2-methylimidazole was dissolved in 8.9 ml of triethylamine (TEA) and 20 ml H2O. Then the two solutions were mixed and stirred for 30 min at room temperature. The solid obtained is separated from the reaction mixture by centrifuge, then washed 3 times with 15 ml of distilled water and dried at 60°C for 12 hours.

Example lb: Methanol as solvent {ZIF-8 methanol}

0.004 mole (0.333 g) of zinc oxide (ZnO) was dissolved in 0.114 mole (2.05 ml) of H2O and 0.0085 mole (0.487 ml) of acetic acid until the total dissolution of ZnO and obtaining a transparent solution.

0.016 mole (1.313 g) of 2-methylimidazole was dissolved in 40 ml of methanol to generate another clear solution. Then, the two solutions were mixed and stirred for 5 min. The solution was allowed to stand at room temperature for 24 hours. After that, the solid obtained is separated from the reaction mixture by centrifuge, then washed 3 times with 15 ml of methanol and dried at 60 °C for 12 h.

Example 2 - Conditions for preparing CS@ZIF-8

0.00001 mole (0.6 g) of chitosan was dissolved in a solution consisting of 0.5 ml acetic acid and 24 ml H2O.

For its part, 0.004 mole (0.333 g) of zinc oxide (ZnO) was dissolved in a solution composed of 0.0087 mole (0.5 ml) of acetic acid and 2.05 ml of H2O with stirring, then the two solutions were mixed and kept stirring for another 30 min to form a homogeneous solution.

Then, the solution was poured dropwise into 1 M NaOH. After 20 min, the CS/Zn2+ microspheres were removed and washed 3 times with deionized water to remove excess NaOH, and then they were soaked in 0.0243 mole (2 g) of 2-methylimidazole dissolved in 24 ml of water for 24 h at 120 °C to form the chitosan@ZIF-8 composite. Then the balls

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SUBSTITUTE SHEET (RULE 26) CS@ZIF-8 composite beads obtained were washed 3 times with deionized water, then freeze-dried for 2 days to obtain CS@ZIF-8 composite beads.

The same operational strategy was followed for the synthesis of the CS@ZIF-8 composite in methanol under the following conditions: 1.32 g (0.0161 mole) of 2-methylimidazole; 40 ml of methanol; ambient temperature ; 24h.

ANALYTICAL RESULTS AND RELATED OBSERVATIONS

As shown in Figure 2, the X-ray diffractograms (XRD) of different solids synthesized: ZIF-8 (water); ZIF-8 (methanol) synthesized in water and MeOH respectively, include the characteristic peaks of the simulated ZIF-8 material reported in the literature and absence of the ZnO peaks. Indeed, the patterns generated by the ordered structure of ZIF-8 particles between 5° and 40° can be easily observed. The relative intensities of the prominent peaks including 011, 002, 112, 022, 013 and 222 correspond to the positions of the angle of incidence, respectively.

2 theta 7.3°; 10.35°; 12.7°; 14.8°; 16.4°; 18° which are in good agreement with those found in the literature. This confirms the sodalite (SOD) structure, which is the typical structure of ZIF-8. Furthermore, the intense peaks of both materials indicate a high degree of crystallinity of the particles. On the other hand, the peaks attributed to ZnO completely disappeared, indicating a complete conversion of Zinc oxide and the formation of a pure phase of ZIF-8.

Concerning the synthesis of CS@ZIF-8 composites prepared in methanol and water, the XRD of these materials obtained compared with that of simulated ZIF-8 show the presence of the relative intensities of the peaks at the same positions and in good agreement with that of ZIF-8 in addition to the disappearance of the ZnO phases and that no impurities were detected, thus explaining the formation of the ZIF-8 phases in both conditions. The broadening of the peaks of these materials may be due to the dispersion of the MOFs particles in the biopolymer matrix.

In the mode of operation of the FT-IR spectra of different materials shown in Figure 3, the spectra {(ZIF-8 (water); ZIF-8 (methanol)} compared to that of 2-methylimidazole (Figure 3a) demonstrate that All modes characteristic of the imidazole chemical structure of ZIF-8 are present. This includes the mode observed at 3133 cm-i (stretching vibration of aromatic C-H), 2930 cm-i (stretching vibration of aliphatic C-H ) and 1568 cm-i (elongation vibration of C=N).i3 In addition, three individual vibrations 1422 cm-i, 1141 cm-i and 996 cm-i, all of which are associated with the C-N elongation vibration , were also found. Furthermore, the bands at 678 and 742 cm were attributed to the out-of-plane mixing of 2-methylhlimidazole rings while the specific modes in the range of 850 cm-i and 996 cm-i and 1302 cm -i due to deformation in the imidazole plane. However, the absence of a broad and strong band in the interval 2200-3250 cm-i (hydrogen bond N-H ••• N) and at 1843 cm-i (resonance between the out-of-plane deformation of N-H--N and the stretching vibration of N-H) proves that the imidazole is indeed deprotonated (2-mlm) in the ZIF-8 spectra. In addition, the stretching vibration of the coordination bung of Zn-N appeared at 424 cm-i. Therefore, these results imply that Znz+ and 2-mlm- were involved in the ZIF-8 particle network.

The FT-IR spectra of the CS@ZIF-8 composites are shown in Figure 3b Concerning the characteristic functions of CS, the OH- groups vibrate over a broad band of 3433 cm-i which is superimposed on the NH stretching vibration -, while the characteristic vibrational mode at 1660

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SUBSTITUTE SHEET (RULE 26) cm-i corresponds to the vibrations of the NH2- group.21 Otherwise, the absorption mode at 2929 cm-i is attributed to the stretching vibration of the CH bond of 2-methylimidazole of ZIF-8. The absorption peak at 1584 cm-i belongs to the C=N vibrations, while the peaks at 1146 and 990 cm-i are associated with the CN elongation vibration. In addition, the stretching vibration of the Zn-N bond appeared at 424 cm-i. These results proved that the Zn-lmidazole network in the CS@ZIF-8 composite is well formed successfully.

The SEM images in Figure 4 (a and b), concerning the morphology of ZIF-8 prepared in MeOH in powder form, show uniform particles in rhombic dodecahedron, typical for ZIF-8 and an average crystal size of 300 ±70 nm. The SEM images presented in Figure 4 (c and d) of the CS@ZI F-8 composite synthesized in MeOH show interfacial interactions between pure CS and ZIF-8 in the CS@ZIF8 composite as well as the size of the spherical beads. formed which is of the order of 2mm. The surface of pure Chitosan material shows a smooth pattern, however after hybridization with ZIF-8 the surface becomes rough due to the attachment of numerous ZIF-8 nanoparticles with dodecahedral morphology and SOD-like crystal structure. of ZIF-8 which are clearly visible on the surface and in the cracks created during the formation of the composite.

INDUSTRIAL APPLICATION

The device according to the invention is particularly intended for the treatment of industrial effluents such as the adsorption of phosphates and other nutritional or toxic elements.

Thus, preliminary tests were carried out on the adsorption of phosphate with different materials. The following conditions were applied: 5 ml of solution containing 1 mg/l of phosphorus is brought into contact with the adsorbents (20 mg for the CS@ZIF-8 composites and 5 mg for the ZIF-8 powder) at room temperature for 6am. The results illustrated in the graph in Figure 5a show that the ZIF-8 powder as well as the composites CS@ZI F-8 (water) and CS@ZIF-8 (methanol) in the form of beads have a better capacity to adsorption, with a phosphorus removal rate reaching 96.05%, 95.7% and 94.98 respectively.

Subsequently, we carried out the kinetic study of phosphate adsorption by CS@ZIF-8. As shown in Figure 5b which represents the evolution of adsorption as a function of contact time in the phosphate solution containing lmg/1 in P, there is a rapid evolution of the curve during the first minutes, which can be explained by the fact that at the start of adsorption there are more active adsorption sites on the solid phase, which become more and more saturated during the first 100 minutes, with maximum extraction after a contact time of 120 minutes.

REFERENCES

2. CN 109433032 A - Preparation method of ZIF-8 membrane The Lens - Free & Open Patent and Scholarly Search. The Lens - Free & Open Patent and Scholarly Search https://www.lens.org/lens.

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SUBSTITUTE SHEET (RULE 26) 3. US 2013/0313193 Al - Metal-Organic Framework Supported on Porous Polymer - The Lens - Free & Open Patent and Scholarly Search, https://www.lens.org/lens/patent/174-470-825-320- 778/frontpage.

4. Zhan, G. & Zeng, H. C. Alternative synthetic approaches for metal-organic frameworks: transformation from solid matters. Chem. Common. 53, 72-81 (2017).

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SUBSTITUTE SHEET (RULE 26)

Claims

1. Process for producing ZIF-8, characterized in that it comprises:

1) complete dissolution of zinc oxide in aqueous acetic acid;

2) addition to the solution obtained according to step 1 of 2-methyl-imidazole, in an aqueous and/or alcoholic medium; And

3) recovery of ZIF-8 by filtration of the reaction mixture obtained according to step 2.

2. Process for producing a chitosan@ZIF-8 composite, characterized in that it comprises:

1) complete dissolution of a mixture of zinc oxide and chitosan in acetic acid

3) recovery of the chitosan@ZIF-8 composite by filtration of the reaction mixture obtained according to step 2.

3. Method according to at least one of claims 1 and 2, characterized in that the zinc oxide and the acetic acid have a molar ratio of approximately 1:2.

4. Method according to at least one of claims 2 and 3, characterized in that the zinc oxide and chitosan have a molar ratio of approximately 400:1.

5. Method according to at least one of claims 1 to 4, characterized in that step 2 is carried out in the presence of water, methanol or a mixture of the two.

6. Method according to at least one of claims 1 to 5, characterized in that the addition of 2-methyl-imidazole to the solution obtained according to step 1 is carried out at room temperature and at 120°C in MeOH and l water respectively.

7. Method according to at least one of claims 2 to 6, characterized in that the chitosan@ZIF-8 composite is obtained in the form of millimeter-sized beads.

8. Use of ZIFD-8, respectively of the chitosan@ZIF-8 composite as obtained by means of the process according to at least one of claims 1 to 7 in the treatment of industrial effluents.

9. Use according to claim 8 in the treatment of industrial effluents loaded with phosphates