Soft‐Chemical Exfoliation Route to Layered Cobalt Oxide Monolayers and Its Application for Film Deposition and Nanoparticle Synthesis

Abstract

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau-like height profile with nanometer-level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross-confirmed by X-ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in-plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected-area electron diffraction and Co K-edge X-ray absorption near-edge structure analysis. The zeta-potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of approximately 10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.

A Direct Hybridization between Isocharged Nanosheets of Layered Metal Oxide and Graphene through a Surface‐Modification Assembly Process

“…The protonation of layered LiCoO 2 induces a slight shift of (00l) reflections toward the low-angle side with the formation of a small amount of cobalt hydroxide phase, as reported previously. [14] The reaction of the protonated cobalt oxide with tetramethyl ammonium (TMA) cations yields the colloidal suspension of exfoliated CoO 2 nanosheets. [14] The surface charge of another precursor, that is, the rGO nanosheets, is modified with PDDA cations, leading to the cationic rGO + nanosheet.…”

“…[9][10][11][12][13] Redox active metal oxide nanosheets such as CoO 2 , MnO 2 , and [Mn 1/3 Co 1/3 Ni 1/3 ]O 2 can be used as efficient electrode materials for lithium-ion batteries, supercapacitors, redox catalysts, etc. [14][15][16] Many of these functionalities of the exfoliated inorganic nanosheets can be further improved by hybridization with highly conductive graphene nanosheets. In fact, hybridization between the cationic layered double hydroxide (LDH) nanosheet and the chemically prepared reduced graphene oxide (rGO) nanosheet is fairly effective in optimizing the photocatalytic and electrochemical activity of the LDH materials.…”

Mixed Colloidal Suspensions of Reduced Graphene Oxide and Layered Metal Oxide Nanosheets: Useful Precursors for the Porous Nanocomposites and Hybrid Films of Graphene/Metal Oxide

“…[7,8] A distinct surface charge of exfoliated colloidal nanosheets renders them powerful building blocks for many novel hybrid materials such as intercalative nanohybrids, layer-by-layer-ordered multilayer films, hollow spheres, and so on. [7][8][9][10] The reassembling of anionic transition-metal oxide nanosheets with cationic guest species yields highly porous pillared metal oxides with a tailored pore structure and strongly coupled electronic structure. [10][11][12][13] If we take into account the remarkably expanded surface area and redox capability of component transition-metal ions, the reassembled nanohybrids of transition-metal oxide nanosheets are supposed to show promising electrode performance for supercapacitors and lithium-ion batteries.…”

“…[3][4][5] One of the most useful chemical methods to synthesize 2D nanosheets is an exfoliation of layered inorganic solids into individual layers. [6][7][8] The exfoliated 2D nanosheets are obtained in the form of a stable colloidal suspension in aqueous media or organic solvent. [7,8] A distinct surface charge of exfoliated colloidal nanosheets renders them powerful building blocks for many novel hybrid materials such as intercalative nanohybrids, layer-by-layer-ordered multilayer films, hollow spheres, and so on.…”

“…[6][7][8] The exfoliated 2D nanosheets are obtained in the form of a stable colloidal suspension in aqueous media or organic solvent. [7,8] A distinct surface charge of exfoliated colloidal nanosheets renders them powerful building blocks for many novel hybrid materials such as intercalative nanohybrids, layer-by-layer-ordered multilayer films, hollow spheres, and so on. [7][8][9][10] The reassembling of anionic transition-metal oxide nanosheets with cationic guest species yields highly porous pillared metal oxides with a tailored pore structure and strongly coupled electronic structure.…”