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-5H-dibenzo[b,i]xanthene-5,7,12,14(13H) tetraones 3(a–k) and 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H) 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.