Identifying the Molecular Edge Termination of Exfoliated Hexagonal Boron Nitride Nanosheets with Solid-State NMR Spectroscopy and Plane-Wave DFT Calculations

Abstract

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 crosspolarization 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.

Hydroxylated boron nitride materials: from structures to functional applications

“…The treatment can generate some other defects in HO-BNs. If the temperature reaches 1500°C, the products have to be hydroxylated by the above methods [47][48][49][50][51][52][53] h-BNNSs Sonication-assisted exfoliation It is a facile method to directly exfoliate BN bulk into HO-BNNSs The hydroxyl degree is relatively low For a high hydroxyl degree, some additives have to be introduced, such as, acid, base, salt, etc [31,[55][56][57][58][59][60][61][62][63] Ball-milling-assisted exfoliation Situations similar to ''sonication-assisted exfoliation'' [64][65][66][67][68][69][70][71][72] Hummer's-like routes The use of strong oxidants (i.e., H 2 SO 4 , H 2 O 2 , KMnO 4 , and their mixtures) requires an extra attention Sometimes the oxidization process can lead to the presence of a few by-products of BN dots [73][74][75][76] Multi-step functionalization method It can be divided into two stages: one is from BN to BNNS and then to HO-BNNS, the other is from BN to HO-BN and then to HO-BNNS [82][83][84][85][86][87][88][89][90][91][92] Bottom-up routes It generally requires high temp...…”

“…One-pot sonication-assisted exfoliation h-BNs, hydroxylated nanosheets can be directly prepared by thermal oxidation of BNs in air, typically at 1000°C, followed by treatment in water [54]. Another simple way to obtain HO-BNNSs is to exfoliate h-BNs using water as dispersant solvent by sonication without any additional use of surfactants or organic functionalization [31,[55][56][57][58][59]. Sonication process can provide an intensive longitudinal shear force leading to complete exfoliation of the bulk into h-BNNSs with few layers and reduced lateral sizes, with attached OH groups ( Fig.…”

Boron Carbon Oxynitride as a Novel Metal-Free Photocatalyst

“…Herein, we present the first detailed structural characterization of BCNO at the molecular level utilizing solid-state MAS 13 Although hBN nanomaterials and their defect-induced electronic properties have attracted significant interest, the molecular structure of hBN edges and defects structure are largely unknown [50]. The lack of structural characterization of boron-related nanomaterials is due to the difficulty in analyzing the solid-state 11 B NMR spectrum because 11 B is a half-integer quadrupole nucleus (I = 3/2) [51,52]. Solid-state 11 B NMR is also challenging to interpret due to the second-order quadrupole coupling resulting in the signal's distortion, which can only be partially averaged via MAS NMR [53].…”

“…In this study, we performed 11 B solid-state NMR recorded at 9.4 T, and the spectrum was deconvoluted using topspin solid-line shaped analysis (SOLA). By following the CP-MAS 11 B NMR experiment reported in the literature, we obtained meaningful B-related chemical bonding information by taking into account the quadrupolar coupling constant (C Q ) and the electric field gradient (EFG) tensor asymmetry (η Q ) [51,52,55]. Figure 3f shows the solid-state 11 B spin-echo NMR spectra of BGH with three major peaks and δ iso centered at 28.3 ppm, 20 ppm, and 1.2 ppm, respectively.…”

The adsorption of 1-Chloro-1,2,2,2-tetrafluoroethane onto the pristine, Al-, and Ga-doped boron nitride nanosheet

“…Ahmadi et al reported the values of energy gap and B-N bond length for BNNS 5.93 eV and 1.45 Å, respectively, and for Al-doped BNNS the band gap as well as Al-N bond length are 5.39 eVand 1.74 Å, respectively [34]BNNS is also a very successful nanosorbent and has been studied in many theoretical studies to detect H2O [35] NO [36] , CO [37] , CH2O [38], COCl2 [39], C2H4 [40], and N2O [41]. This nanosheet and metal decorated BNNS have also been used in the manufacture of many electronic devices [42][43][44][45][46][47][48]. It can also be used as a valuable material in the coating industry and metal protection because it is impermeable to gases and liquids and is also an electrical insulator [49][50][51][52].…”