Synthesis of pH‐responsive magnetic yolk–shell nanoparticles: A comparison between conventional etching and new deswelling approaches

• Published in: Applied organometallic chemistry 2018-04, Vol.32 (4), p.n/a
• Main Authors: Nikravan, Goolia, Haddadi‐Asl, Vahid, Salami‐Kalajahi, Mehdi
• Format: Article
• Language: English
• Subjects: Acrylic acid; Chemistry; Copolymerization; Crosslinking; Distillation; distillation precipitation polymerization; Electron microscopy; Etching; Ethylene glycol; Iron oxides; Magnetic measurement; magnetic nanoparticles; Nanoparticles; pH‐responsive polymers; Protonation; Seeds; Silicon dioxide; Synthesis; yolk–shell nanoparticles
• ISSN: 0268-2605; 1099-0739
• DOI: 10.1002/aoc.4272

Iron oxide (Fe3O4) magnetic nanoparticles as movable cores were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first more common route, Fe3O4 nanoparticles were coated with silica layer via the Stöber process to yield Fe3O4@SiO2 core–shell nanoparticles, subsequently used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe3O4@SiO2@P(AA‐EGDMA). The silica layer was selectively removed through alkali etching to yield Fe3O4@air@P(AA‐EGDMA). In the second route, Fe3O4 nanoparticles without any stabilization were used as seeds in the distillation precipitation copolymerization of AA and EGDMA to yield Fe3O4@P(AA‐EGDMA) core–shell nanoparticles. The nanoparticles were subsequently dispersed in acidic medium of pH = 2. Yolk–shell Fe3O4@air@P(AA‐EGDMA) nanoparticles were formed through deswelling of crosslinked PAA because of protonation of carboxyl groups at low pH values. Various techniques were utilized to investigate the characteristics of the synthesized core–shell nanoparticles. Formation of yolk–shell nanostructure was observed for both synthesis routes, namely etching of silica layer and deswelling approaches, from vibrating sample magnetometry and transmission electron microscopy results. Both types of nanoparticles showed pH‐responsive behaviour, i.e. decrease in absorption with increase in pH, as examined using UV–visible spectroscopy. Fe3O4 magnetic nanoparticles were used to synthesize yolk–shell nanoparticles with pH‐responsive shell composed of ethylene glycol dimethacrylate (EGDMA)‐crosslinked poly(acrylic acid) (PAA) via two different routes. In the first, Fe3O4@SiO2@P(AA‐EGDMA) was produced with the silica layer being selectively removed through alkali etching to yield Fe3O4@air@P(AA‐EGDMA). In the second, Fe3O4@P(AA‐EGDMA) was produced and by dispersing in acidic medium of pH = 2, yolk–shell Fe3O4@air@P(AA‐EGDMA) was formed through a deswelling approach.