Synthesis of benzo[a]furo[2, 3-c]phenazine derivatives through an efficient, rapid and via microwave irradiation under solvent-free conditions catalyzed by H₃PW₁₂O₄₀@Fe₃O₄-ZnO for high-performance removal of methylene blue

Figures & data

Figure 1. Biological activity of phenazine derivatives.

Scheme 1. Synthesis of benzo[a]furo[2, 3-c]phenazine derivatives in the presence of H₃PW₁₂O₄₀@Fe₃O₄-ZnO as heterogeneous catalyst.

Figure 2. Phase separation of Fe₃O₄ sediments from solution using a conventional magnet.

Scheme 2. Synthesis process of Fe₃O₄@ZnO nanoparticles.

Table 1. Optimization of reaction conditions of compound 6a.

^aReaction conditions: 2-hydroxynaphthalene-1,4-dione (1 mmol), arylglyoxal (1 mmol), indole (1 mmol) in the presence of different catalytic systems under various conditions.

Table 2. Sequential one-pot four-component synthesis of benzo[a]furo[2, 3-c]phenazine derivatives.

^aYields refer to the pure isolated products.

Figure 3. The investigation of the recycling of nano H₃PW₁₂O₄₀@Fe₃O₄–ZnO.

Table 3. Comparison of results obtained using H₃PW₁₂O₄₀@Fe₃O₄–ZnO with results obtained using other catalyst reported in the literature for the synthesis.

Entry	Catalyst (mol %)	Condition	Time (min)	Yield (%)^a, b	Ref.
1	PTSA (10)	PEG-400	120	88	[26]
2	H2SO4 (20)	EtOH/H2O	300	87	[27]
3	HPA (20)	EtOH/H2O	300	99	[27]
4	[NMP]H2PO4 (20)	Solvent-free	150	81	[27]
5	SiO2–SO3H (20)	Solvent-free	60	86	[28]
6	SiO2–SO3H (20)	Solvent-free (MW)	7	93	[28]
7	H3PW12O40@Fe3O4–ZnO (10)	Solvent-free (MW)	6	97	This work

^a Isolated yields.

^b The reaction was carried out under microwave irradiation (MW) conditions.

Figure 4. Thermogravimetric (TG) nano H₃PW₁₂O₄₀@Fe₃O₄–ZnO.

Figure 5. X-ray diffraction pattern of Fe₃O₄, ZnO, and H₃PW₁₂O₄₀@Fe₃O₄–ZnO samples.

Figure 6. FESEM and TEM images of Fe₃O₄ (a, c) and H₃PW₁₂O₄₀@Fe₃O₄–ZnO (b, d, e).

Figure 7. Hot filtration test for H₃PW₁₂O₄₀@Fe₃O₄–ZnO catalyzed.

Figure 8. VSM curves of Fe₃O₄, Fe₃O₄–ZnO, H₃PW₁₂O₄₀@Fe₃O₄–ZnO.

Figure 9. Comparison of the slope of the magnetization curve at high fields.

Table 4. Coercion field values, saturation magnetization and residual magnetization.

Sample	Ms (emu/g)	Hc (G)	Mr (emu/g)	Mr/Ms
Fe3O4	62.55	1.07	0.054	0.0008
Fe3O4–ZnO	58.1	3.4	0.199	0.0034
H3PW12O40@Fe3O4–ZnO	28.81	11	0.332	0.0301

Figure 10. AFM 3D and 2D images of H₃PW₁₂O₄₀@Fe₃O₄–ZnO nanocomposite.

Figure 11. Curve (αhυ)² by hυ for Fe₃O₄–ZnO (left) and H₃PW₁₂O₄₀@Fe₃O₄–ZnO (right) sample.

Figure 12. Diagram of effect of H₂O₂ concentration on photon fenton methylene blue degradation.

Figure 13. Proposed mechanism for the synthesis of benzo[a]furo[2, 3-c]phenazine derivatives.

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