Synthesis And Catalytic Properties Study Of Magnetic Solid Acid

Composite materials based on magnetic nanoparticles Fe₃O₄ for magnetic cores have received more and more attention in recent years,because they can be easily separated from the reaction mixture by permanent magnets.The surface of Fe₃O₄ can be modified with various functional groups to construct various magnetic catalysts.The most common is the synthesis of a magnetic solid acid with a core-shell structure（Fe₃O₄@SiO₂）functionalized sulfonic acid group as an environmentally-friendly,recyclable cellulose hydrolysis catalyst.Based on the above magnetic composite materials,three new magnetic solid acid catalysts were synthesized to catalyze diosgenin in Dioscoreaceae,and their structural characteristics and catalytic properties were studied.The contents are as follows:1.Using Fe₃O₄ as the 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（FT-IR）,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（mol/L）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.2.Fe₃O₄ was synthesized by hydrothermal method.We designed and synthesized a magnetic solid acid catalyst Fe₃O₄@SiO₂@AMPS-MBA.In the presence of potassium persulfate（KPS）as the initiator,2-acrylamide-2-form Propanesulfonic acid（AMPS）and N,N’-methylenebisacrylamide（MBA）were polymerized on the surface of Fe₃O₄@SiO₂.Used to catalyze saponins in Dioscorea zingiberensis C.H.Wright（DZW）.In order to improve the yield of diosgenin,the dried DZW root rhizome was crushed through a 200-mesh sieve,then mixed with an ethanol solution for 24 h,then filtered and concentrated to dryness on a rotary evaporator,and finally an ethanol extract saponin was obtained.Here,we discuss the synthesis,characterization,and catalytic performance of magnetic solid acids.DZW’s alcoholysis experiments show that the amount of magnetic solid acid,temperature and time will have a certain effect,and under the optimal conditions,the activity of the prepared magnetic solid acid is higher than sulfuric acid.It is worth mentioning that the magnetic solid acid can be easily separated from the mixture and remains highly active after five cycles.Moreover,the discharge of strongly acidic hydrolysis products can be avoided.It can solve environmental problems encountered in the field of DZW hydrolysis.3.A new magnetic solid acid Fe₃O₄@PEI@SO3H was synthesized.Diosgenin was then extracted from the pretreated DZW saponin.Finally,the magnetic solid acidolyses saponins to produce diosgenin.In this study,a new strategy for extracting diosgenin from dioscin was established.This method combines magnetic solid acidolytic saponin with Soxhlet extraction for the first time.The optimal alcoholysis conditions were determined by single-factor experiments,and the conditions were optimized by response surface method to improve the yield of diosgenin.The content of diosgenin was determined by UV-Vis method depending on the yellow solution formed by perchloric acid and measured at 410 nm.The results were further verified by liquid chromatography-mass spectrometry（LC-MS）.Under the optimal conditions determined by response surface method,magnetic solid acid has higher activity than sulfuric acid at 100°C for 6 h.In addition,the magnetic solid acid has an acidic site content of 2.01 mmol/g at 454.5°C,which is the strongest acidity.In addition,the new process reduces the consumption of water,acid and organic solvents,while increasing the yield of diosgenin.By applying an external magnet,the magnetic solid acid can be easily separated from the reaction mixture and reused three times without significantly reducing activity.The results show that the newly developed method is more effective and cleaner,and the technology for extracting diosgenin from DZW in industrial applications has broad prospects.