Structure and physicochemical properties of MgB2 nanosheets obtained via sonochemical liquid phase exfoliation

We have performed ultrasonic liquid phase exfoliation (LPE) of MgB2 in ethanol and investigated the resulting nano-assemblies as a function of the ultrasound processing time. TEM morphological and structural analysis, along with STM topographic characterization, showed that for short sonication times the exfoliated grains preserve the MgB2 crystal structure, have a 2D character and produce Moiré patterns corresponding to stacked layers with rotational misalignment. On the other hand, the longest process times result in spheroidal nanoparticles with diameters of the order of 10 nm, which can also coalesce into larger agglomerates. Optical absorbance spectra confirmed that the exfoliated material preserves a metallic nature with a predominant 2D character corresponding to the ab-plane, whereas Raman spectra showed the presence of extra-modes induced by 3D symmetry breaking in the exfoliated products, along with indications of some B-H stretching modes. The detection of a positive zeta potential confirms that an active surface hydrogenation process has taken place during sonication. The mechanochemistry of the exfoliation mechanism has been attributed to particle–particle collisions and particle-shockwave interactions originating from the implosive bubble-collapse. The present study provides important information useful for implementing the LPE process in different contexts for MgB2, like few-layer superconductivity, antibacterial coating and nano-drug preparation.