Monomer Protonation-Dependent Surface Polymerization to Achieve One-Step Grafting Cross-Linked Poly(4-Vinylpyridine) Onto Core–Shell Fe3O4@SiO2 Nanoparticles

Functional polymer-grafting silica nanoparticles hold great promise in diverse applications such as molecule recognition, drug delivery, and heterogeneous catalysis due to high density and uniform distribution of functional groups and their tunable spatial distance. However, conventional grafting methods from monomers mainly consist of one or more extra surface modification steps and a subsequent surface polymerization step. A monomer protonation-dependent surface polymerization strategy is proposed to achieve one-step uniform surface grafting of cross-linked poly(4-vinylpyridine) (P4VP) onto core–shell Fe3O4@SiO2 nanostructures. At an approximate pH, partially protonated 4VP sites in aqueous solution can be strongly adsorbed onto deprotonated silanol groups (SiO−) onto Fe3O4@SiO2 nanospheres to ensure prior polymerization of these protonated 4VP sites exclusively onto Fe3O4@SiO2 nanoparticles and subsequent polymerization of other 4VP and divinylbenzene monomers harvested by these protonated 4VP monomers onto Fe3O4@SiO2 nanoparticles, thereby achieving direct grafting of cross-linked P4VP macromolecules onto Fe3O4@SiO2 nanoparticles.