Reversible Supracolloidal Self‐Assembly of Cobalt Nanoparticles to Hollow Capsids and Their Superstructures

Abstract

AbstractThe synthesis and spontaneous, reversible supracolloidal hydrogen bond‐driven self‐assembly of cobalt nanoparticles (CoNPs) into hollow shell‐like capsids and their directed assembly to higher order superstructures is presented. CoNPs and capsids form in one step upon mixing dicobalt octacarbonyl (Co2CO8) and p‐aminobenzoic acid (pABA) in 1,2‐dichlorobenzene using heating‐up synthesis without additional catalysts or stabilizers. This leads to pABA capped CoNPs (core ca. 5 nm) with a narrow size distribution. They spontaneously assemble into tunable spherical capsids (d≈50–200 nm) with a few‐layered shells, as driven by inter‐nanoparticle hydrogen bonds thus warranting supracolloidal self‐assembly. The capsids can be reversibly disassembled and reassembled by controlling the hydrogen bonds upon heating or solvent exchanges. The superparamagnetic nature of CoNPs allows magnetic‐field‐directed self‐assembly of capsids to capsid chains due to an interplay of induced dipoles and inter‐capsid hydrogen bonds. Finally, self‐assembly on air–water interface furnishes lightweight colloidal framework films.