Scalable exfoliation and gradable separation of boric-acid-functionalized boron nitride nanosheets

It is very challenging to effectively exfoliate and functionalize hexagonal boron nitride (h-BN). Here, an efficient exfoliation and functionalization of bulk h-BN was carried out by a ball-milling method using boric acid (BA) as a lubricant and modifier. A series of boric-acid-functionalized boron nitride nanosheets (BNNSs) was successfully produced using this approach. The obtained BNNS thermo-stable suspension can be easily condensed into a jelly-like dispersion with ultra-high concentration, up to 90 mg ml−1. The eco-friendly BA was readily and easily recyclable and remarkably reusable during the BNNS exfoliation. Interestingly, by means of a differential-centrifugation technique, the BNNSs could be easily separated and screened with different sizes and thicknesses. These screened BNNS samples also exhibited different levels of functionalization. As a result, filtration membranes made of various well-screened BNNSs exhibited an obviously different rejection rate for pollutant in water. In addition, the different screened BNNS products show a variable ability to dielectric behavior due to their different-level functionalization. We believe that our created boric-acid-functionalized BNNSs, combined with the smartly screened separation by differential centrifugation, can broaden the future practical applications of BNNS materials.