One-spot Synthesis Of Hollow Mesoporous Silica Multifunctional Nanoparticles Based On Self-assembly Of Block Copolymers

Hollow mesoporous Si O₂ material is a new type of inorganic material with special structure.Its internal one or more of the cavity can be used as a storage and transporter for guest molecules,while its low density,high specific surface area,tunable pore size,good biocompatibility and other characteristics make it have broad application prospects in the fields of adsorption and storage,catalysis,drug release,cancer diagnosis and treatment.The template method is one of the most effective methods for preparing hollow mesoporous Si O₂ materials.The morphology and nanostructure of hollow mesoporous Si O₂ can be controlled by simply adjusting the chemical composition and morphology of the template.However,the removal of the template at the end of the reaction（high temperature calcination or solvent extraction）tends to destroy the integrity of the hollow mesoporous morphology.Self-assembly strategy is one of the important"bottom-up"methods for the preparation of ordered and fine nanostructures.Amphiphilic block copolymers can self-assemble in aqueous solution to form nanostructures with controlled size and shape.It provides a good template molecule for controlling the growth of Si O₂ nanospheres and the construction of uniform assemblies.Therefore,in this paper,amphiphilic diblock copolymer Poly（2-（Dimethylamino）ethyl methacrylate）-b-Poly（glycidyl methacrylate）（p DMAEMA-b-p GMA）（42/22、42/32、42/62、27/87）with different block ratios by continuous reversible addition-fragmentation chain transfer（RAFT）polymerization.In aqueous medium（25°C,p H=7,atmospheric pressure）,the p DMAEMA segment in the block copolymer tends to be surrounded by the more hydrophilic p GMA to form a relatively hydrophobic region,while the tertiary amine group[-N（CH₃）₂]can be used as a Si O₂ catalytic deposition site,so Si O₂ nanoparticles are limited to growth and assembly in the hydrophobic region of the polyamine segment p DMAEMA.By changing the block composition ratio of the template,polymer hybrid hollow mesoporous silica nanoparticles（PSHMNs）with multi-morphologies such as spherical,rod-shaped and hollow mesopores can be formed due to the difference in selectivity to the selective solvent between different blocks.In particular,p DMAEMA-b-p GMA self-assembled aggregates can undergo morphological transformation under external environmental stimuli（p H）,which also greatly enriches the hollow mesoporous Si O₂ nanostructure.At the same p H,the block ratio of 27/87 polymer is the largest,which is100.31nm.Under different p H environments,with the gradual increase of p H,the particle size of the polymer gradually decreases with the increase of p GMA segment;In p H=7 system environment,the block copolymer can self-assemble to form a vesicle structure.At the same time,based on the sensitivity of the copolymer to p H,by comparing the p H of the reaction system and the amount of silicon source,it was found by TEM and SEM that when the p H of the system is 7,the mass ratio of copolymer to TEOS is 1:100,it is the best.Under the reaction conditions,the obtained silica coating is spherical,the hollow inner cavity size of PSHMNs is 30～70nm,the shell wall thickness is in the range of 10～20nm,the average pore diameter of BJH desorption adsorption is 7.03nm,and the specific surface area is 341.256 m²/g,pore volume is 0.706 cm³/g.The rattle-type Au@PSHMNs and Au/Fe₃O₄@PSHMNs multifunctional nanoparticles were prepared by one-step encapsulation in DMF/THF/H₂O（1v/9v/40v）mixed solvent using the interactions of different chain segments in block copolymer with Au and magnetic Fe₃O₄ nanoparticles.With the encapsulation of metal nanoparticles,the particle size of the rattle-type composite nanoparticles increased to75-150 nm,and the inner cavity size further increased,but the thickness of the Si O₂shell layer was 10-25 nm,which did not change much.The catalytic efficiency of the rattle-type Au/Fe₃O₄@PSHMNs multifunctional nanoparticles was investigated using the 4-nitroaniline reduction reaction as the model.The experimental results show that the encapsulation of Au nanoparticles can improve the catalytic stability and catalytic efficiency.The first-order kinetic reaction constant k increased from 3.95×10^-3s^-1 of Au nanoparticle dispersion solution to 5.33×10^-3s^-1.The synchronous encapsulation of magnetic Fe₃O₄ nanoparticles can not only effectively increase the load capacity of Nano Au particles per unit volume,but also further increase the first-order kinetic reaction constant k to 6.75×10^-3s^-1.Moreover,Au/Fe₃O₄@PSHMNs can be recovered through simple magnets to improve the recovery rate of catalyst.After 5 times of catalytic cycle,the catalytic efficiency of composite nanoparticles can reach up to97.6%,and the recovery rate of magnetic composite nanoparticles can reach 96%,which is expected to be applied in wastewater treatment.