Immobilized copper-layered nickel ferrite on acid-activated montmorillonite, [(NiFe 2 O 4 @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 NiFe 2 O 4 as the prime magnetic cores were prepared. Next, through the reduction of Cu 2+ ions with sodium borohydride, the nanoparticles of Cu 0 were immobilized on the nanocore-surface of NiFe 2 O 4 , and the constituent NiFe 2 O 4 @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 NiFe 2 O 4 @Cu was then intercalated within the interlayers and on the external surface of the H + -Mont constituent to afford the novel magnetic nanocomposite (NiFe 2 O 4 @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 NiFe 2 O 4 @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 NiFe 2 O 4 @Cu MNPs, the surface area and total pore volume of the H + -Mont system were decreased. The catalytic activity of (NiFe 2 O 4 @Cu)(H + -Mont) was further studied towards the synthesis of substituted 13-aryl-5 H -dibenzo[ b , i ]xanthene-5,7,12,14(13 H ) tetraones 3(a-k) and 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1 H -xanthene-1,8(2 H ) diones 5(a-k) via the pseudo-one-pot three-component cyclocondensation of 2-hydroxy-1,4-naphthoquinone (Lawsone)/dimedone and aromatic aldehydes in a mixture of H 2 O-EtOH (1 : 1 mL) as a green solvent at 80-90 °C. The (NiFe 2 O 4 @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.