Magnetic core–shell dendritic mesoporous silica nanospheres anchored with diamine as an efficient and recyclable base catalyst

Abstract

In the present study, diamine-functionalized magnetic core–shell dendritic mesoporous silica nanospheres have been successfully synthesized by an oil–water biphasic stratification-coating strategy. The shape, size and morphology of the synthesized magnetic nanocatalyst could be characterized by various physicochemical techniques such as, field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The characteristic information about the successful immobilization of various functionalities on the nanospheres could be obtained with the help of X-ray powder diffraction (XRD) patterns, Fourier transform-infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX) and thermo-gravimetric analysis (TGA). The details about the magnetic behaviour and surface area of the nanocatalyst could be acquired by vibrating sample magnetometry (VSM) and BET surface analysis, respectively. The synthesized diamine-functionalized magnetic nanoparticles were then explored as a highly efficient catalyst for the Knoevenagel condensation and one-pot synthesis of polyhydroquinolines using aromatic/heteroaromatic aldehydes and aliphatic aldehydes with active methylene compounds under very mild conditions. The synthesized magnetic core–shell dendritic mesoporous silica nanospheres had large surface areas. This large surface area and pore volume could facilitate a proper interaction and penetration of the reactant molecules with the basic amine groups present on the dendritic mesoporous silica nanospheres. The supported nanocatalyst revealed no sign of leaching of the amine groups present inside the dendrimers and therefore, could be reused up to nine times without any noteworthy loss in catalytic activity.