Hydrolysis extraction of diosgenin from Dioscorea nipponica Makino by sulfonated magnetic solid composites

Extraction of diosgenin from the rhizome of Dioscorea by catalytic hydrolysis over recyclable solid acids is one of the most enviromentally friendly ways for the conversion of biomass into chemicals. In this paper, a magnetic solid acid, Fe3O4@SiO2@NH-(CH2)2-NH2@SO3H with the particle size of about 80 nm, was synthesized by using Fe3O4 (~ 20 nm) as a magnetic core and then coated orderly with tetraethyl orthosilicate (TEOS) and N-{3-(Trimethoxysilyl) propyl} ethylenediamine (TMPED) by sol-gel reactions in water/ethanol solution, followed by the sulfonation of chlorosulfonic acid. The solid acid was characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and X-ray photoelectron spectroscopy (XPS). The content of acidic sites on the surface of the solid acid was 1.01 mmol/g, measured by back titration method. The prepared solid acid was used to hydrolyze and extract diosgenin from Dioscorea nipponica Makino (DNM). The results show that the magnetic solid acid has higher hydrolysis activity than 2.5 M hydrochloric acid under same hydrolysis conditions, at 110 °C for 5 h. In addition, the magnetic solid acid can be easily separated from the reaction mixture by the application of a magnet and reused several times without significant activity loss. This work has a potential application value for the extraction of diosgenin from plants.