Magnetic Nanoparticles Composite-modified By Deep Eutectic Solvents And Silica And Immobilization Research

In this research,superparamagnetic Fe₃O₄ nanoparticles aggregate?MNPs?were prepared by three methods of chemical co-precipitation,hydrothermal synthesis and sonochemistry.Magnetization,physical and chemical properties of MNPs were studied and compared,thus hydrothermal synthesis was chosen as the preferred way.Surface of MNPs was composite-modified by three kinds of deep eutectic solvents?DESs?and silica?SiO₂?.Studied and compared on micro structure and composite-modified effect,we selected the optimal composite-modified aggregates to be applied in the field of enzyme immobilization.?-Amylase and porcine pancreas lipase were immobilized based on composite-modified aggregates.We studied on the optimal process of immobilization in respect of temperature,enzyme concentration,glutaraldehyde concentration and time.In addition,the physical and chemical properties of immobilized enzyme and free enzyme were compared,and the performance of immobilized enzyme in heat-resisting,acid-resisting,operation stability were evaluated.The results of the study are as follows:The precipitated precursor of MNPs was made under the condition of n(Fe³⁺)/n?Fe2+?as 1.6,pH value as 9,ammonia as precipitant.The result showed that the optimum condition of above three methods,the prepared MNPs were monodispersed quasi-spherical nanoparticles with average diameter of about 8.49 nm,9.75 nm,8.79 nm,of which the saturation magnetization were 60.9 emu/g,67.5emu/g,65.4 emu/g,respectively.In the meanwhile,MNPs prepared by hydrothermal synthesis had higher saturation magnetization and MNPs prepared by chemical co-precipitation had better dispersion property and crystal structure.Furthermore,as high activity hydroxyl groups of nano-particles' surface was conducive to surface and functional groups modification.MNPs by the hydrothermal with high magnetic response were selected to be the follow-up basic material.Surface of MNPs was composite-modified by three kinds of deep eutectic solvents?DESs?and silica?SiO₂?.The structures and physicochemical properties of the aggregates were studied by transmission electron microscope?TEM?,scanning electron microscope?SEM?,infrared ray?IR?,thermal gravity analysis?TGA?,physical property measurement system?PPMS?,and determination of enzyme activity,respectively.The results of TEM and SEM indicated that the particles aggregates were spherical with irregular surface,and had properties of better dispersibility;meanwhile,MNP distributed inside them.The result of magnetic responsiveness as PPMS showed,the saturation magnetization of Fe₃O₄ and Fe₃O₄@SiO₂ were 65.42emu/g,42.57emu/g,respectively,the saturation magnetization of Fe₃O₄@SiO₂-DESs were decrease.The surface of particle aggregates owned abundant functional groups and stable structure estimated by IR and TGA,The IR spectrum of Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂-DESs showed that there were big differences,especially the band located at between 3600 cm-1and 3000 cm-1and the region of 1000-1200 cm-1.Because of hydroxyl groups or amino groups affected by hydrogen bonding,the movement of band position and broadening of peak occurred in original?-OH?or?-NH2?.In comparison of TGA curves,difference of weight loss between 150? and 800? exhibited the thermal stability and amount of DESs on the surface of Fe₃O₄@SiO₂was DES2?18.81±1.96?%,DES1?9.57±1.36?% and DES3?8.87±0.34?%,respectively.Composite-modified aggregates with DES3 were more beneficial to combine with ?-amylase.As for immobilization of ?-amylase,composite-modified aggregates with DES3 as carrier had better adsorption performance and higher more enzyme activity,too.Composite-modified aggregates with DES3 and SiO₂ is more suitable to be utilized in the carrier of immobilized enzyme.The composite-modified particle aggregates as the carrier,?-amylase and porcine pancreas lipase were immobilized by method of covalent linkage.The application performance of immobilized enzyme and free enzyme were studied.The temperature,pH value,the operation stability and the basic kinetics of them were compared,respectively.The optimal pH value and temperature of immobilized ?-amylase were 7 and 60 ?.Compared with the free ?-amylase,immobilized ?-amylase had stronger temperature and acid tolerance,and the half-time of repeated operation was 18.97 times.The optimal pH value and temperature of immobilized porcine pancreas lipase were 6 and 35 ?.Compared with the free porcine pancreas lipase,the thermal stability was improved,and the half-life of repeated operation was 7.03 times.In the study of enzyme kinetics,immobilized ?-amylase and immobilized porcine pancreas lipase have different characteristics,however,their affinity both decreased.