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. 2020 Nov 2;10(66):40005-40018.
doi: 10.1039/d0ra07042d.

An organic-inorganic hybrid nanomaterial composed of a Dowson-type (NH4)6P2Mo18O62 heteropolyanion and a metal-organic framework: synthesis, characterization, and application as an effective adsorbent for the removal of organic dyes

Akram-Alsadat Hoseini  1 , Saeed Farhadi  1 , Abedin Zabardasti  1 , Firouzeh Siadatnasab  1
Affiliations

An organic-inorganic hybrid nanomaterial composed of a Dowson-type (NH4)6P2Mo18O62 heteropolyanion and a metal-organic framework: synthesis, characterization, and application as an effective adsorbent for the removal of organic dyes

Akram-Alsadat Hoseini et al. RSC Adv. .

Abstract

In this work, an inorganic-organic hybrid nanomaterial, P2Mo18/MIL-101(Cr), based on Wells-Dawson-type (NH4)6P2Mo18O62 polyoxometalate (abbreviated as P2Mo18) and the MIL-101(Cr) metal-organic framework was fabricated by the reaction of (NH4)6P2Mo18O62, Cr(NO3)3·9H2O and terephthalic acid under hydrothermal conditions. The as-prepared recyclable nanohybrid was fully characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) equipped with energy dispersive X-ray microanalysis (EDX), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and Brunauer-Emmett-Teller (BET) specific surface area studies. All the analyses confirmed the successful insertion of P2Mo18O62 6- heteropolyanion within the cavities of MIL-101(Cr). The encapsulated MIL-101(Cr) showed a considerable decrease in both pore volume and surface area compared with MIL-101(Cr) due to incorporation of the very large Dowson-type polyoxometalate into the three-dimensional porous MIL-101(Cr). The nanohybrid had a specific surface area of 800.42 m2 g-1. The adsorption efficiency of this nanohybrid for removal of methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) from aqueous solutions was evaluated. Surprisingly, the composite not only presented a high adsorption capacity of 312.5 mg g-1 for MB, but also has the ability to rapidly remove 100% MB from a dye solution of 50 mg L-1 within 3 min. These results confirmed that this adsorbent is applicable in a wide pH range of 2-10. The nanohybrid showed rapid and selective adsorption for cationic MB and RhB dyes from MB/MO, MB/RhB, MO/RhB and MB/MO/RhB mixed dye solutions. The equilibrium adsorption data were better fitted by the Langmuir isotherm. Kinetics data indicate that the adsorption of the dye follows a pseudo-second order kinetics model. Also, this material could be effortlessly separated and recycled without any structural modification. Accordingly, it is an efficient adsorbent for removing cationic dyes.

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Conflict of interest statement

There are no conflicts of interest to declare.

Figures

Scheme 1
Scheme 1. The preparation process of the P2Mo18/MIL-101(Cr) inorganic–organic hybrid nanomaterial.
Fig. 1
Fig. 1. The FT-IR spectra of (a) MIL-101(Cr), (b) P2Mo18, and (c) P2Mo18/MIL-101(Cr).
Fig. 2
Fig. 2. FT-Raman spectra of (a) P2Mo18, (b) MIL-101(Cr) and (c) P2Mo18/MIL-101(Cr).
Fig. 3
Fig. 3. XRD patterns of (a) MIL-101(Cr), (b) P2Mo18, and (c) P2Mo18/MIL-101(Cr).
Fig. 4
Fig. 4. FE-SEM images of (a) MIL-101(Cr) and (b and c) the P2Mo18/MIL-101(Cr) nanocomposite.
Fig. 5
Fig. 5. (a) SEM spectrum and (b–h) representative EDX photographs of the P2Mo18/MIL-101(Cr) with corresponding EDX elemental mappings.
Fig. 6
Fig. 6. (a) N2 adsorption–desorption isotherms and (b) BJH pore-size distribution plots for the MIL-101(Cr) and P2Mo18/MIL-101(Cr) samples.
Fig. 7
Fig. 7. The UV-Vis spectra during adsorption of dyes over P2Mo18/MIL-101(Cr): (a) MB, (b) RhB and (c) MO. (d) Comparison of the adsorption efficiencies of the dyes. Experimental conditions: C0(MB) = C0(RhB) = C0(MO) = 50 mg L−1, solution volume = 50 mL, adsorbent dosage = 30 mg, temperature = 25 °C and natural pH ≈ 6.5.
Fig. 8
Fig. 8. The selective adsorption capacity of the P2Mo18/MIL-101(Cr) toward the mixed dyes of (a) MB + MO, (b) RhB + MO, (c) MB + RhB, and (d) MB + MO + RhB. Experimental conditions: C0(MB) = C0(RhB) = C0(MO) = 50 mg L−1, solution volume = 50 mL, adsorbent dosage = 30 mg, temperature = 25 °C and natural pH ≈ 6.5.
Fig. 9
Fig. 9. (a) Effects of P2Mo18/MIL-101(Cr) dosage and (b) effects of initial pH on the removal efficiency of MB. Experimental conditions: C0(MB) = 50 mg L−1, solution volume = 50 mL and temperature = 25 °C at a fixed adsorption time of 3 min.
Fig. 10
Fig. 10. (a) The effect of the initial dye concentration, (b) pseudo-second-order kinetics, (c) Langmuir and (d) Freundlich isotherms for the adsorption of MB onto the P2Mo18/MIL-101(Cr) nanocomposite. Experimental conditions: solution volume = 50 mL, adsorbent dosage = 30 mg and temperature = 25 °C.
Fig. 11
Fig. 11. Proposed mechanism for the adsorption of cationic MB dye using the P2Mo18/MIL-101(Cr) nanohybrid.
Fig. 12
Fig. 12. (a) Recyclability of the P2Mo18/MIL-101(Cr) nanocomposite, (b) FT-IR, (c) XRD, (d) FT-Raman and (e) SEM images of the recovered P2Mo18/MIL-101(Cr) nanohybrid after the sixth run.
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