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Metal borides are known for their extraordinarily rich chemistry and extensive range of properties. Although their diversity and chemically tunable properties create abundant possibilities for several applications, their potential has not been fully realized. This is because metal borides have been primarily investigated in their bulk form. In this work, we present a chemical method to nanoscale MgB2—a representative from the family of layered metal diborides that comprise metal atoms sandwiched in between boron honeycomb planes. Their lattice structure offers a unique opportunity to obtain access to graphenic planes of boron upon exfoliation. We show that a treatment of MgB2 with acid followed by intercalation with organoammonium ions swells the crystals and partly delaminates these to multilayer thick (∼300–400 nm) lamellas, which resemble the shape of accordions. These nanoaccordions can be sonicated in water to yield few-layer-thick (∼3–5 nm) nanosheets. These nanostructures are found to be Mg-deficient and functionalized with oxygen-based moieties. We also present a preliminary study to demonstrate that these oxy-functionalized nanostructures have the potential to be utilized as flame retardant nanofillers. The thermogravimetric analysis reveals that a composite of epoxy resin with sonicated nanoaccordions exhibits an effective char residue gain of 6.0%. Furthermore, by adding only 2% sonicated nanoaccordions, the LOI value of epoxy was found to increase from 20.1 to 22.5, while the burning rate (determined by UL-94 horizontal burning test) decreased significantly from 31.7 to 15.1 mm/min. These flame retardant enhancement metrics are not only superior when compared with graphene and its analogues but also at the extremes of other flame retardant nanofillers at similar loadings. The ability to exfoliate a layered metal boride to obtain chemically functionalized nanoaccordions with flame retardant properties presents an unprecedented perspective to utilize MgB2 and showcases the rich prospects offered by the family of layered metal diborides.
Das et al. (Thu,) studied this question.