Ultrathin Hexagonal Hybrid Nanosheets Synthesized by Graphene Oxide-Assisted Exfoliation of β-Co(OH)₂Mesocrystals

In the present study, we report the synthesis of a high-quality, single-crystal hexagonal β-Co(OH)₂nanosheet, exhibiting a thickness down to ten atomic layers and an aspect ratio exceeding 900, by using graphene oxide (GO) as an exfoliant of β-Co(OH)₂nanoflowers. Unlike conventional approaches using ionic precursors in which morphological control is realized by structure-directing molecules, the β-Co(OH)₂flower-like superstructures were first grown by a nanoparticle-mediated crystallization process, which results in large 3D superstructure consisting of ultrathin nanosheets interspaced by polydimethoxyaniline (PDMA). Thereafter, β-Co(OH)₂nanoflowers were chemically exfoliated by surface-active GO under hydrothermal conditions into unilamellar single-crystal nanosheets. In this reaction, GO acts as a two-dimensional (2D) amphiphile to facilitate the exfoliation process through tailored interactions between organic and inorganic molecules. Meanwhile, the on-site conjugation of GO and Co(OH)₂promotes the thermodynamic stability of freestanding ultrathin nanosheets and restrains further growth through Oswald ripening. The unique 2D structure combined with functionalities of the hybrid ultrathin Co(OH)₂nanosheets on rGO resulted in a remarkably enhanced lithium-ion storage performance as anode materials, maintaining a reversible capacity of 860 mA h g⁻¹for as many as 30 cycles. Since mesocrystals are ubiquitous and rich in morphological diversity, the strategy of the GO-assisted exfoliation of mesocrystals developed here provides an opportunity for the synthesis of new functional nanostructures that could bear importance in clean renewable energy, catalysis, photoelectronics, and photonics.