Sonochemical Exfoliation of AlB2 into Few-Layer-Thick Chemically Functionalized Borophene with Inherent Reducing Capability

Ultrasonication-assisted liquid-phase exfoliation of layered metal diborides has emerged as a promising path for obtaining metal-deficient quasi-2D nanostructures. In this study, we show that ultrasonication can be combined with chelation to achieve exfoliation of AlB₂ in high yields. We show that ultrasonicating AlB₂ crystals in a solution containing ethylenediaminetetraacetate results in nearly metal-free, few-layer-thick nanosheets rich in boron. These nanosheets exhibit crumpled morphology with several instances of crystalline regions. AFM indicates thickness values between 1 and 6 nm with lateral dimensions extending up to a few microns. Chemical analyses show ultra-low aluminum content (Al:B molar ratio as low as 0.04:2) and presence of oxy, hydroxy, and hydride functional groups, rendering these as chemically functionalized borophene (CFB) nanosheets. We found that the yield of nanosheets can be increased up to 30% by choosing an appropriate pH. We further show that these nanosheets exhibit an inherent reducing capability and can catalyze the reduction of gold salt into gold nanoparticles while simultaneously serving as templates to stabilize them, with the growth of nanoparticles up to 10 nm. This study lays the ground for top-down approaches to synthesize chemically functionalized borophene in high yield and presents its potential as an active reducing agent.