New method helps exfoliate hexagonal boron nitride nanosheets
Chinese researchers recently reported an innovative mechanical process for controllably exfoliating hexagonal boron nitride nanosheets (h-BNNSs). Physics (LICP) of the Chinese Academy of Sciences (CAS).
h-BNNSs, with a honeycomb-like structure similar to graphene, exhibit excellent chemical and physical properties, such as high thermal conductivity, good oxidation resistance, remarkable mechanical strength, low dielectric constant, excellent lubricity, excellent biocompatibility and optical properties.
Given these characteristics, h-BNNSs are promising materials for a variety of applications, including high-performance electronic devices, dielectric substrates, thermal management, lubrication, sensors, catalysts, and sorbents. As a result, there is an urgent need to develop a simple, manageable and scalable method to produce high quality h-BNNSs for commercial applications.
In their new study, ZHANG and his team proposed a scalable and controllable approach to exfoliate high-quality h-BNNSs from h-BN flakes.
“This method is based on efficient reduction of h-BNNS interlayer interaction through rapid volume expansion of water in ice formation,” Zhang said.
In general, h-BNNSs can be prepared using a chemical vapor deposition (CVD) and physical exfoliation process. CVD can produce wafer-scale monolayer h-BNNS while the physical exfoliation process can achieve scalable production of small h-BNNSs.
Based on molecular dynamics simulations, the researchers suggested that -OH groups can cause local structural deformation in the defects/edges of h-BN flakes to form an “entrance” for water molecules entering the h-BNNS interlayer. . This in turn yields a sufficient number of relatively long-lived hydrogen bonds that can generate fairly compact initial cores for ice nucleation.
The initial nuclei then slowly change in shape and size until they reach a stage that allows rapid expansion when the temperature drops sharply. This results in an increase in interlayer spacing and reduction in interlayer forces between adjacent h-BNNS layers, as well as efficient exfoliation of h-BNNSs during subsequent ultrasonication.
“By adjusting the parameters, this exfoliation process can be used to produce large amounts of different, high-quality h-BNNSs,” says Dr. An Lulu, lead author of the study.
“This method provides an environmentally friendly method to exfoliate controllable thickness h-BNNSs by rapid water freezing and subsequent ultrasonication. These as obtained h-BNNSs can be used as polymer additives, thermally conductive fillers and flame retardants,” said Prof. Yu Yuanlie, corresponding author of the study.
This study was published in Cell reports Physical Science†
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Lulu An et al, Water ice-induced scalable and controllable exfoliation of hexagonal boron nitride nanosheets, Cell reports Physical Science (2022). DOI: 10.116/j.xcrp.2022.100941
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