Fe₃O₄@SiO₂ Core/Shell Nanoparticles: The Silica Coating Regulations with a Single Core for Different Core Sizes and Shell Thicknesses

Abstract

In this work, we present the coating regulations of Fe3O4 nanoparticles (NPs) by the reverse microemulsion method to obtain the Fe3O4@SiO2 core/shell NPs. The regulation produces the core/shell NPs with a single core and with different shell thicknesses, and it especially can be applied to different sizes Fe3O4 NPs and avoid the formation of core-free silica particles. Our results reveal that the silica coating parameters suitable for Fe3O4 NPs with certain size are not definitely applicable to that with other sizes, and the match of the number of Fe3O4 NPs with aqueous domain is essential. We found that the small aqueous domain is suitable to coat ultrathin silica shell, while the large aqueous domain is indispensable for coating thicker shells. To avoid the formation of core-free silica particles, the thick silica shell can be achieved by increasing the content of either TEOS through the equivalently fractionated drops or ammonia with a decreased one-off TEOS. The ligand exchange between the intermediate processes of the silica coating is evidenced. Our results provide not only a strategy for synthesizing uniform Fe3O4@SiO2 core/shell NPs with controlled shell thickness, but also a regulation that can be applied to preparation other core–shell NPs.

Fe3O4/SiO2 Core/Shell Nanocubes: Novel Coating Approach with Tunable Silica Thickness and Enhancement in Stability and Biocompatibility

“…The saturation magnetization value, extracted from the corresponding Reverse Microemulsion method > 16 h [8] General method > 16 h [9] Reverse Microemulsion method 48 h [7] Sol-gel method 6-48 h [1] Microemulsion method 24 h [6] Microemulsion method 20 h [5] Modified Sol-gel method (Our method) 4 h - hysteresis loop, for the uncoated magnetite sample at 300 K is 80 emu/g, and it decreased for the coated samples as expected to be 50.7, 46.1, 43.8, and 42 emu/g, respectively with increasing the thickness of silica shell. The decrement in magnetization value after coating with silica in all the samples may be attributed to the incorporation of nonmagnetic silica shell around the core magnetite nanocubes.…”

“…However, these methods are complicated and require long time for the coating of silica. [5][6][7][8]. And, Shiva et al have used the so-called general method for coating of silica to the iron oxide nanoparticles within 16 h [9].…”

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

“…Single core MNPs which are uniformly coated with silica are resulted through this process. [128] Zhao et al performed a modified reverse microemulsion synthesis to prepare MNPs coated by silica, with average size of 40 nm. TEOS molecules were immediately added to the resultant MNPs and the reaction was continued for 24 h at room temperature.…”

Синтез Кластеров Оксидов Железа В Мезопорах Монодисперсных Сферических Частиц Кремнезема

“…Другим способом решения проблемы агрегативной неустойчивости магнитных частиц и сохранения их магнитных характеристик является покрытие их оболоч-ками из немагнитного материала, в частности, наноча-стицы оксидов железа покрывают оболочкой кремнезема различной толщины [11]. Кремнезем имеет ряд преиму-ществ перед органическими оболочками, например, он менее подвержен биодеградации [12].…”