Novel green sulfated phosphotungstic acid supported on MCM-41-coated NiFe₂O₄ MNPs for xanthene and coumarin synthesis

From an environmental and economic point of view, we focused on the preparation of simple catalysts with many advantages such as simple isolation, easy preparation, high stability, and well catalytic activity. Here, we prepared MCM-41-coated NiFe₂O₄ magnetic nanoparticles and modified their surface with phosphotungstic acid (PWA) and then sulfate. We tested the catalysts’ efficiency and reusability toward the formation of xanthene and coumarin derivatives. The prepared magnetic nanoparticles were found to be easily recovered from the reaction mixture and reused up to several runs without a noticeable decrease in the catalytic activity. The samples have been characterized by SEM, TEM, FTIR, XRD, VSM, and XPS. XPS indicated the presence of the inverse-cubic spinel phase of NiFe₂O₄ and the contribution of Fe(III)–O and Ni(II)–O bonds in tetrahedral (T_h) and octahedral (O_h) sites. The results indicated the good dispersion of sulfate and PWA nanoparticles on the surface and inside the pores of NF-MCM-41 which play an important role in increasing the acidity and activity of the catalyst toward the synthesis of xanthene and coumarin derivatives. The catalyst 20S-W/NF-MCM-41-II reveals the highest acidity (E_i = 586.3 mV) and yields 93.92% 14-aryl-14H-dibenzo[a, j]xanthene and 78.32% 7-hydroxy-4-methyl coumarin. (Figure presented.)