Amorphous a-Cr2O3 Nanosheets for NO2 and NH3 Gas Sensing

The design of bidimensional materials with unique catalytic properties has recently focused on the synthesis and applications of layered (2D) amorphous (a) metal oxide (2D a-MOx) interfaces. Herein, we report an original strategy for synthesizing bidimensional (2D) amorphous Cr2O3 (2D a-Cr2O3) via “low-temperature” annealing of liquid-phase exfoliated anhydrous CrCl3 transition metal trihalide (TMTH), yielding p-type semiconductor interfaces with excellent NO2 and NH3 gas-sensing capabilities. By tuning the annealing time at temperatures below the recrystallization of a-Cr2O3, the removal of chlorine atoms and the complete oxidation/amorphization of CrCl3 into a-Cr2O3 are achieved. Moreover, the oxidation/amorphization proceeds from the flake’s edge toward the core, following a “Shrinking core” kinetic oxidation model, which preserves the shape of pristine 2D CrCl3. Gas-sensing characterization of a-Cr2O3 to NO2 and NH3 exhibits enhanced signal gains of 18% (1 ppm of NO2) and 45% (100 ppm of NH3) compared to pristine CrCl3. Our research offers valuable insight for extending the “low-temperature” amorphization strategy to the synthesis of 2D amorphous metal oxides (a-MOx where M = Ni, Co, Fe, Bi, Ti), departing from anhydrous transition metal chlorides, such as NiCl2, CoCl2, and oxychlorides, including FeOCl, BiOCl, and TiOCl, broadening the scope and applications of a-MOx interfaces.