Hexagonal boron nitride nanosheets (h-BNNS), the isoelectronic analog to graphene, have received interest over the past decade due to their high thermal oxidative resistance, high bandgap, catalytic activity, and low cost. The functional groups that terminate boron and nitrogen zigzag and/or armchair edges directly affect their chemical, physical, and electronic properties. However, an understanding of the molecular edge termination present in h-BNNS is lacking. Here, high-resolution magic-angle spinning (MAS) solid-state NMR (SSNMR) spectroscopy, and plane-wave density-functional theory (DFT) calculations are used to determine the molecular edge termination in exfoliated h-BNNS. ¹H → ¹¹B cross-polarization MAS (CPMAS) SSNMR spectra of h-BNNS revealed multiple hydroxyl/oxygen coordinated boron edge sites that were not detectable in direct excitation experiments. A dynamic nuclear polarization (DNP)-enhanced ¹H → ¹⁵N CPMAS spectrum of h-BNNS displayed four distinct ¹⁵N resonances while a 2D ¹H{¹⁴N} dipolar-HMQC spectrum acquired with fast MAS revealed three distinct ¹⁴N environments. Plane-wave DFT calculations were used to construct model edge structures and predict the corresponding ¹¹B, ¹⁴N and ¹⁵N SSNMR spectra. Comparison of the experimental and predicted SSNMR spectra confirms that zigzag and armchair edges with both amine and boron hydroxide/oxide termination are present. The detailed characterization of h-BNNS molecular edge termination will prove useful for many material science applications. The techniques outlined here should also be applicable to understand the molecular edge terminations in other 2D materials.

中文翻译：

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用固态NMR光谱和平面波DFT计算确定剥离的六角形氮化硼纳米片的分子边缘终止

六方氮化硼纳米片（h -BNNS）是石墨烯的等电子类似物，由于其高的抗热氧化性，高带隙，催化活性和低成本而在过去十年中受到关注。终止硼和氮之字形和/或扶手椅边缘的官能团直接影响其化学，物理和电子性质。然而，缺乏对h -BNNS中存在的分子边缘终止的理解。在这里，高分辨率魔术角旋转（MAS）固态NMR（SSNMR）光谱和平面波密度泛函理论（DFT）计算用于确定剥离的h- BNNS中的分子边缘终止。¹小时→ ¹¹h -BNNS的B交叉极化MAS（CPMAS）SSNMR光谱显示，在直接激发实验中无法检测到多个羟基/氧配位的硼边缘位点。h -BNNS的动态核极化（DNP）增强的¹ H→ ¹⁵ N CPMAS光谱显示四个不同的¹⁵ N共振，而用快速MAS采集的2D ¹ H { ¹⁴ N}双极HMQC光谱显示三个不同的¹⁴ N环境。平面波DFT计算用于构造模型边缘结构并预测相应的¹¹ B，¹⁴ N和¹⁵N SSNMR谱。实验和预测的SSNMR光谱的比较证实，存在同时带有胺和氢氧化硼/氧化物末端的锯齿形和扶手椅状边缘。h- BNNS分子边缘终止的详细表征将证明对许多材料科学应用有用。这里概述的技术也应该适用于了解其他2D材料中的分子边缘终止。