Immobilized copper-layered nickel ferrite on acid-activated montmorillonite, [(NiFeO@Cu)(H-Mont)], as a superior magnetic nanocatalyst for the green synthesis of xanthene derivatives.

In this study, the immobilization of copper-layered nickel ferrite on the surface and in the cavities of acid-activated montmorillonite (H-Mont) was investigated. In this context, magnetic nanoparticles (MNPs) of NiFeO as the prime magnetic cores were prepared. Next, through the reduction of Cu ions with sodium borohydride, the nanoparticles of Cu were immobilized on the nanocore-surface of NiFeO, and the constituent NiFeO@Cu MNPs were obtained. Moreover, through the activation of montmorillonite K10 (Mont K10) with HCl (4 M) under controlled conditions, the H-Mont constituent was prepared. The nanostructured NiFeO@Cu was then intercalated within the interlayers and on the external surface of the H-Mont constituent to afford the novel magnetic nanocomposite (NiFeO@Cu)(H-Mont). The prepared clay nanocomposite was characterized using FTIR spectroscopy, SEM, EDX, XRD, VSM and BET analyses. The obtained results showed that through acid-activation, the stacked-sheet structure of Mont K10 was exfoliated to tiny segments, leading to a significant increase in the surface area and total pore volume of the H-Mont constituent as compared to those of montmorillonite alone. SEM analysis also exhibited that the dispersion of NiFeO@Cu MNPs in the interlayers and on the external surface of acid-activated montmorillonite was carried out successfully, and the nanoparticle sizes were distributed in the range of 15-25 nm. The BET surface analysis also indicated that through the immobilization of NiFeO@Cu MNPs, the surface area and total pore volume of the H-Mont system were decreased. The catalytic activity of (NiFeO@Cu)(H-Mont) was further studied towards the synthesis of substituted 13-aryl-5-dibenzo[,]xanthene-5,7,12,14(13) tetraones 3(a-k) and 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1-xanthene-1,8(2) diones 5(a-k) the pseudo-one-pot three-component cyclocondensation of 2-hydroxy-1,4-naphthoquinone (Lawsone)/dimedone and aromatic aldehydes in a mixture of HO-EtOH (1 : 1 mL) as a green solvent at 80-90 °C. The (NiFeO@Cu)(H-Mont) MNPs can be easily separated from the reaction mixture by an external magnetic field and reused for seven consecutive cycles without significant loss of catalytic activity.