Colloids of Holey Gd₂O₃ Nanosheets Converted from Exfoliated Gadolinium Hydroxide Layers

Abstract This paper proposes a confined solid‐state conversion approach using layered metal‐hydroxides for the production of a colloidal suspension of porous 2D crystalline metal oxide layers with superior electrochemical H₂O₂ sensing performance. This study investigates the conversion chemistry of delaminated layers of gadolinium hydroxide (LGdH), [Gd₂(OH)₅]⁺, encapsulated in a silica nanoshell that provides an antistacking and antisintering environment during the phase‐transition at high temperature. Thermal treatment of the LGdH layers within the protected environment results in a dimensionally confined phase‐transition into crystalline Gd₂O₃ nanosheets with an isomorphic 2D structure. Furthermore, annealing at higher temperatures leads to the evolution of in‐plane mesoporous structure on the Gd₂O₃ nanosheet. Based on insight acquired from in‐depth investigation, the evolution of in‐plane porosity proceeds through the in‐plane dominant silicate‐formation reaction at the interface with the surrounding silica shell. Their 2D‐anisotropic and mesoporous morphological features are preserved, producing a colloidal suspension of holey nanosheets that can be used to fabricate a thin and porous film through wet‐coating deposition. This study also demonstrates the superior electrochemical H₂O₂ sensing ability of the resultant porous Gd₂O₃ film, which represents a ≈1000‐ and 10‐fold enhancement of the detection limit and sensitivity, respectively, in comparison to previously reported Gd₂O₃ films.