Amine/acid composite Janus nanosheets

Janus materials have witnessed fast development due to their diversified promising performances and practical applications. Compared with their spherical counterparts, Janus nanosheets have gained more concerns for their highly anisotropic shape besides chemistry. Herein, 3.5 nm ultrathin and flexible Janus nanosheets with carboxyl group terminated onto one side are fabricated by surface sol-gel process of the self-assembled monolayer of an amphiphilic silane onto the template CaCO3 particle firstly. Amine/acid composite Janus nanosheets are further derived from these carboxyl group terminated silica Janus nanosheets by selective conjugation with amine groups onto the other side. The amine/acid composite Janus nanosheets are dually pH responsive, and well dispersible in aqueous solution at both low and high pH levels. The nanosheets are aggregated forming multi-layered face-to-back superstructures at intermediate pH levels. This is originated by the opposite electrostatic interaction between the carboxyl and the amine groups. This approach can be extended to other silanes, and a huge family of Janus nanosheets is expected with tunable composition and performance.