Free-standing δ-MnO2 atomic sheets

Abstract

δ-Manganese dioxide (δ-MnO₂) is a 2D material which possesses distinct properties and features due to its unique atomic structure and has already been utilized in numerous disciplines recently, especially in the field of magnetism, energy storage, magnetic resonance imaging, biocatalysts, and fluorescence sensing. Keeping an eye on the huge potential of this 2D material, we report our recent discovery of single-step synthesis of MnO₂ nanosheets via bottom-up laser crystallization (of aqueous KMnO₄ solution) and top-down sonochemical exfoliation of bulk MnO₂ powder. The successful synthesis of δ-MnO₂ nanosheets has been proved through the observation of characteristic Raman peaks at 173 and 634 cm⁻¹ and characteristic X-ray diffraction peaks. The optical band gap was found to be 1.64 and 1.45 eV for both methods. We also demonstrated that 2D-MnO₂ is a prominent candidate material for ammonia sensing and strain sensing. δ-MnO₂ powder, when employed as cathode material in Li-ion batteries, results in a stable voltage of ˜0.5 V and in contrast, gives ˜1 V when used in Li-S batteries and the attained voltage is stable even for >5 h. New methods of synthesis of δ-MnO₂ and its hybrids with graphene will lead to future generation devices, it is expected.