Scale-up Synthesis,Surface Functionalization And Applications Of Monodisperse Fe₃O₄@SiO₂

In recent years,magnetic Fe₃O₄ nanomaterials have been widely used in biomedicine,magnetic separation,biomolecular enrichment and detection due to their advantages of superparamagnetization,high specific area and biocompatibility.However,their potential applications are usually limited by oxidation and agglomerate of Fe₃O₄ due to their poor stability and dipole-dipole interactions.In order to enhance their stabilization,considerable modification strategies have been adopted to provide a shell to Fe₃O₄ nanoparticles with sufficient stability,such as silica,precious metals,small molecular surfactants,and polymers.Among many coating materials,silica not only improves the stability of Fe₃O₄ nanoparticles,but also facilitates the subsequent surface modification.When St（?）ber and the sodium silicate methods are used for silica quantitative coating,owing to the low surface charge density of bare Fe₃O₄ and the weak electrostatic repulsion among the particles,the related coating results are not ideal,the particles agglomerate and disperse poorly,which affects the subsequent use.In addition,in order to meet the needs of different application scenarios,appropriate surface functionalization of Fe₃O₄@SiO₂ is also required.Some problems such as low density of functional groups and insufficient modification process also occurred in the process of functionalization,which affect the properties of materials.Based on the above background and on the basis of the previous research work of our group,the following research work was carried out and centered on the quantitative preparation of Fe₃O₄@SiO₂ nanoparticles,surface functionalization and their applications:1.Scale-up synthesis and dispersion performance evaluation based on monodisperse Fe₃O₄@SiO₂Firstly,in order to solve the problems of particle agglomeration and poor dispersion in the process of mass synthesis,lactic acid,D-gluconic acid,sodium citrate and sodium alginate were used to modify Fe₃O₄ and improve the dispersion of Fe₃O₄ according to electrostatic repulsion and steric hindrance.On the basis of pre-modification,St（?）ber and sodium silicate methods were used for the attempt to quantitative synthesis.By means of scanning electron microscope,transmission electron microscope images,DLS and static sedimentation experiment,the feasibility of monodisperse Fe₃O₄@SiO₂ quantitative synthesis was evaluated.The results showed that sodium citrate,sodium alginate and sodium polystyrene maleate could significantly improve the dispersity of exposed Fe₃O₄,and the corresponding monodispersity synthesis of Fe₃O₄@SiO₂ was increased from 1 g/L to 6 g/L,7 g/L and 6 g/L by St（?）ber method,respectively.In the meantime,the corresponding monodispersity synthesis of Fe₃O₄@SiO₂ was all increased from 1 g/L to 5 g/L via silicate method.Based on the above analysis,this chapter proves the feasibility of the quantified preparation of Fe₃O₄@SiO₂ by sodium citrate,sodium alginate and polystyrene maleate modified Fe₃O₄,via St（?）ber method and sodium silicate method,which lays a good foundation for the subsequent material surface functionalization and related applications.2.Surface functionalization and characterization of monodisperse Fe₃O₄@SiO₂On the basis of the previously quantified synthesis of monodisperse Fe₃O₄@SiO₂,different modification strategies were adopted to functionalize Fe₃O₄@SiO₂ for different application scenarios.-NH₂,-COOH,-PO₄^3-groups and polyvinyl alcohol polymers were introduced to the surface of the material to endow different surface properties.As for the problem of low density functional groups and complicated modification procedures during the functional process,with the assistance of simplified modification strategies,different modification monomers were adopted to endow materials with different amino and carboxyl surface densities.The related amino and carboxyl densities were quantitatively determined by amino and coupling of nitrobenzene formaldehyde,UV-Vis spectrophotometry and conductance titration,respectively.The results showed that the amino and carboxyl densities were directly proportional to the number of amino and carboxyl groups in the modified monomer.Meanwhile,m AMNPs and mCMNPs possessed the highest density of amino and carboxyl groups.The corresponding values were 0.0334 mmol/mg and 0.236 mmol/g,respectively.The successful implementation of the above modification strategies not only broadens the application range of materials,but also provides reference for the surface functional modification process of materials.3.The preparation of core-shell Fe₃O₄@SiO₂ magnetic nanoparticles with different surface carboxyl densities and their application in the removal of methylene blueHerein,based on the surface functionalization of materials in the previous chapter,multi-carboxyl functionalized Fe₃O₄@SiO₂ magnetic nanoparticles（mCMNPs）have been adopted to evaluate the separation performance of Methyl blue（MB）and put a novel insight into the grafting density effects on the adsorption process.The results of UV-Vis spectrometry obviously showed that the increased carboxyl content on the surface of CMNPs resulted in the significant improvement in the removal process of MB.Among different types of CMNPs,mCMNPs were chosen for the separation of MB owing to possessing the highest surface carboxyl densities 0.236 mmol/g and exhibiting the highest removal efficiency of 96.18%.Several important factors including solution pH,initial MB concentration and sorption time were optimized to achieve the best removal efficiency.Desired adsorption capacity for MB（34.75 mg/g）was achieved using mCMNPs with the pH10,sorption time of 100 min and initial MB concentration of 50 mg/L.Meanwhile,the sorption isotherms and sorption kinetics can be well in agreement with the Langmuir model and pseudo-second-order kinetic model,respectively.Most importantly,the synthesized mCMNPs still exhibited high removal efficiency（63%）after 5 cycle numbers.As absorbents,it is noted that the prepared mCMNPs possessed the excellent regeneration ability and recyclability and could be a promising absorbent for the removal of MB in water treatment.4.Synthesis of polyvinyl alcohol coated Fe₃O₄@SiO₂ and evaluation of its performance in separating and enriching DNAFinally,in this chapter,polyvinyl alcohol modified Fe₃O₄@SiO₂ was used for the extraction and enrichment of microscale nucleic acid according to the problem of low DNA extraction and enrichment efficiency.Several factors including the amount of magnetic beads,binding time,the concentration of NaCl and PEG 8000 in the binding solution and elution temperature were optimized to determine the optimum conditions for DNA extraction and achieve the best extraction efficiency.Under the optimum conditions,the rapid and efficient separation of trace DNA could be achieved.Compared with SMNPs,phosphoric acid functionalized Fe₃O₄@SiO₂,commercial Medium Cobel and Sangon Biotech synthetic magnetic beads,the results showed that the PVA coated magnetic Fe₃O₄@SiO₂ via our preparation had better DNA extraction efficiency.More importantly,the real-time fluorescence PCR Ct value of PVA coated magnetic Fe₃O₄@SiO₂ was only 18 and the number of cycles reached the set threshold was less.Meanwhile,it can come to a conclusion that the method is highly sensitive for DNA extraction.To sum up,this study proves that PVA modified Fe₃O₄@SiO₂ has a great potential in the field of microscale acid separation and enrichment,and is expected to be quantitatively produced to meet the needs of daily analysis in the future.