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. 2018 Feb 12;8(13):6768-6780.
doi: 10.1039/c8ra00312b. eCollection 2018 Feb 9.

12-Molybdophosphoric acid anchored on aminopropylsilanized magnetic graphene oxide nanosheets (Fe3O4/GrOSi(CH2)3-NH2/H3PMo12O40): a novel magnetically recoverable solid catalyst for H2O2-mediated oxidation of benzylic alcohols under solvent-free conditions

Saeed Farhadi  1 , Mohammad Hakimi  2 , Mansoureh Maleki  2
Affiliations

12-Molybdophosphoric acid anchored on aminopropylsilanized magnetic graphene oxide nanosheets (Fe3O4/GrOSi(CH2)3-NH2/H3PMo12O40): a novel magnetically recoverable solid catalyst for H2O2-mediated oxidation of benzylic alcohols under solvent-free conditions

Saeed Farhadi et al. RSC Adv. .

Abstract

In this work, 12-molybdophosphoric acid (H3PMo12O40, HPMo) was chemically anchored onto the surface of aminosilanized magnetic graphene oxide (Fe3O4/GrOSi(CH2)3-NH2) and was characterized using different physicochemical techniques, such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, energy-dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), BET specific surface area analysis and magnetic measurements. The results demonstrated the successful loading of HPMo (∼31.5 wt%) on the surface of magnetic aminosilanized graphene oxide. XRD patterns, N2 adsorption-desorption isotherms and SEM images confirm the mesostructure of the sample. FT-IR and EDX spectra indicate the presence of the PMo12O40 3- polyanions in the nanocomposite. The as-prepared Fe3O4/GrOSi(CH2)3-NH2/HPMo nanocomposite has a specific surface area of 76.36 m2 g-1 that is much higher than that of pure HPMo. The selective oxidation of benzyl alcohol to benzaldehyde was initially studied as a benchmark reaction to evaluate the catalytic performance of the Fe3O4/GrOSi(CH2)3-NH2/HPMo catalyst. Then, the oxidation of a variety of substituted primary and secondary activated benzylic alcohols was evaluated with H2O2 under solvent-free conditions. Under the optimized conditions, all alcohols were converted into the corresponding aldehydes and ketones with very high selectivity (≥99%) in moderate to excellent yields (60-96%). The high catalytic performance of the nanocomposite was ascribed to its higher specific surface area and more efficient electron transfer, probably due to the presence of GrO nanosheets. The nanocomposite catalyst is readily recovered from the reaction mixture by a usual magnet and reused at least four times without any observable change in structure and catalytic activity.

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Conflict of interest statement

There are no conflicts of interest to declare.

Figures

Fig. 1
Fig. 1. Preparation process of the magnetic Fe3O4/GrOSi(CH2)3–NH2/HPMo catalyst.
Fig. 2
Fig. 2. FT-IR spectra of (a) pure HPMo and (d) Fe3O4/GrOSi(CH2)3–NH2/HPMo.
Fig. 3
Fig. 3. XRD patterns of (a) pure Fe3O4 and (b) Fe3O4/GrOSi(CH2)3–NH2/HPMo.
Fig. 4
Fig. 4. Raman spectra of (a) GO and (b) Fe3O4/GrOSi(CH2)3–NH2/HPMo.
Fig. 5
Fig. 5. SEM images of (a) GO, (b) and (c) Fe3O4/GrOSi(CH2)3–NH2/HPMo nanocomposite at different magnification and (d) EDX spectrum of the Fe3O4/GrO–NH2/HPMo nanocomposite.
Fig. 6
Fig. 6. Magnetic hysteresis loop of (a) Fe3O4 and (b) Fe3O4/GrOSi(CH2)3–NH2/HPMo at room temperature. The inset shows the behavior of the nanocomposite under an external magnetic field.
Fig. 7
Fig. 7. N2 adsorption–desorption isotherm of Fe3O4/GrOSi(CH2)3–NH2/HPMo. The inset shows the pore size distribution plot.
Scheme 1
Scheme 1
Fig. 8
Fig. 8. The conversion of benzyl alcohol and the selectivity to benzaldehyde at different catalyst dosage. Conditions: benzyl alcohol (10 mmol), H2O2 (15 mmol, 30%), catalyst (0.20 g) at reflux temperature 100 °C for 4 h.
Fig. 9
Fig. 9. The conversion of benzyl alcohol and the selectivity to benzaldehyde at different reaction time over Fe3O4/GrOSi(CH2)3–NH2/HPMo as the catalyst. Conditions: benzyl alcohol (10 mmol), H2O2 (15 mmol, 30%), catalyst (0.20 g) at 100 °C.
Fig. 10
Fig. 10. The conversion of benzyl alcohol and the selectivity to benzaldehyde over the Fe3O4/GrOSi(CH2)3–NH2/HPMo catalyst with different amount of H2O2 (30%). Conditions: benzyl alcohol (10 mmol), catalyst (0.20 g) at 100 °C for 4 h.
Fig. 11
Fig. 11. Effect of temperature on the conversion of benzyl alcohol using the Fe3O4/GrOSi(CH2)3–NH2/HPMo catalyst. Conditions: benzyl alcohol (10 mmol), H2O2 (15 mmol, 30%), catalyst (0.20 g) at 100 °C for 4 h.
Fig. 12
Fig. 12. Recyclability of the Fe3O4/GrOSi(CH2)3–NH2/HPMo catalyst. Conditions: benzyl alcohol (10 mmol), H2O2 (15 mmol, 30%), catalyst (0.20 g) at 100 °C for 4 h. Yields are for isolated pure benzaldehyde.
Fig. 13
Fig. 13. (a) XRD pattern, (b) FT-IR spectrum, (c) Raman spectrum and (d) SEM image of the recovered Fe3O4/GrOSi(CH2)3–NH2/HPMo nanocomposite after fourth run.
See this image and copyright information in PMC

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