Surface modified novel magnetically tuned halloysite functionalized sulfonic acid: synthesis, characterization and catalytic activity

Abstract

This work presents preparation of a surface modified magnetically tuned solid acid where thiol groups were grafted on magnetic halloysite, followed by oxidation of thiol groups to sulfonic acid groups. The physicochemical properties of the catalyst were analyzed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM) elemental mapping, field emission gun scanning electron microscopy (FEG-SEM), energy dispersive X-ray analysis (EDX), the Brunauer–Emmett–Teller (BET) method and vibrating-sample magnetometry (VSM). The catalyst could be recovered and reused at least 5 times without substantial loss of its catalytic activity. This study delivers a green protocol for the synthesis of bisamides and 4H-pyrans without the need for further purification by column chromatography.