Co-Solvent Exfoliation of Hexagonal Boron Nitride: Effect of Raw Bulk Boron Nitride Size and Co-Solvent Composition

Abstract

Exfoliation of two-dimensional boron nitride nanosheets (BNNSs) from parent bulk material has been receiving intensive attention because of its fascinating physical properties. Liquid exfoliation is a simple, scalable approach to produce single-layer or few-layer BNNS. In this paper, water/propanol co-solvent exfoliation of bulk boron nitride under the assistance of sonication was investigated in detail. Special attention was paid on the effect of raw bulk boron nitride size and co-solvent composition. The results show that sonication of small-size hexagonal boron nitride tends to generate large nanosheets, due to a predominant solvent wedge effect. In addition, it is found that the composition of water/propanol co-solvent has an important effect on exfoliation efficiency. Interestingly, although two isomers of 1-propanol (NPA) and 2-propanol (IPA) have the same molecular weight and similar surface tension, their aqueous solutions allow the formation of boron nitride nanosheets dispersion with markedly different concentrations. It is proposed that due to their spatial configuration difference, NPA with its longer molecular chain and fewer hydrophobic methyl group tends to form dynamic water-NPA clusters with larger size than water-IPA clusters. The hydrodynamic radius of the co-solvent “clusters” was calculated to be 0.72 nm for water/NPA system and 0.44 nm for water/IPA system at their maximum, respectively. Their size changes, represented by two curves, indicate a strong “cluster size” effect on exfoliation efficiency. Our work provides an insight into co-solvent exfoliation of hexagonal boron nitride and emphasizes the importance of co-solvent cluster size in exfoliation efficiency.

Facile Mechanical-Induced Functionalization of Hexagonal Boron Nitride and Its Application as Vehicles for Antibacterial Essential Oil

“…Besides, nitrogen multilayers appear at 0.25 < P / P 0 < 0.70 which is made evident from the quasilinear region, and then, the curves grow rapidly owing to the filling of macropores, implying that typical adsorbents hold a wide pore size distribution including narrow slit-shaped mesopores or micropores originating from different forms of irregular stacking of multilayer flakes and macropores formed by agglomeration at a different direction, which is in agreement with Figure d and SEM and TEM images. The pore size distribution curves in Figure d exhibit a tripodal distribution calculated by the Barrett–Joyner–Halenda (BJH) method with the main characteristic pore diameters of 3.85, 26.76, and 57.00 nm for h-BN, 3.85, 26.76, and 43.70 nm for BNNS, and 3.85, 36.22, and 56.71 nm for CMC-SPI-BNNS, respectively, among which 3.85 nm correspond to approximately 9–10 layers in a stack . The increase of the latter two peaks once forming CMC-SPI-BNNS compared to BNNS is attributed to CMC-SPI stacked or incorporated on the surface and edge of BNNS to form a macroporous structure with slitlike pores. , The specific surface area (SSA) calculated by the multipoint Brunauer–Emmett–Teller (BET) method of BNNS after ball milling becomes higher (28.35 m 2 g –1 ) than the case of h-BN (13.64 m 2 g –1 ), which indicates that the mechanical force provided by the ball milling method leads to the fracture of h-BN.…”

“…The pore size distribution curves in Figure 7d exhibit a tripodal distribution calculated by the Barrett−Joyner−Halenda (BJH) method with the main characteristic pore diameters of 3.85, 26.76, and 57.00 nm for h-BN, 3.85, 26.76, and 43.70 nm for BNNS, and 3.85, 36.22, and 56.71 nm for CMC-SPI-BNNS, respectively, among which 3.85 nm correspond to approximately 9−10 layers in a stack. 66 The increase of the latter two peaks once forming CMC-SPI-BNNS compared to BNNS is attributed to CMC-SPI stacked or incorporated on the surface and edge of BNNS to form a macroporous structure with slitlike pores. 67,68 The specific surface area (SSA) calculated by the multipoint Brunauer−Emmett−Teller (BET) method of BNNS after ball milling becomes higher (28.35 m 2 g −1 ) than the case of h-BN (13.64 m 2 g −1 ), which indicates that the mechanical force provided by the ball milling method leads to the fracture of h-BN.…”

Preparation of Boron Nitride Nanoplatelets via Amino Acid Assisted Ball Milling: Towards Thermal Conductivity Application

“…A typical Raman signature was found for bulk h-BNs and exfoliated AA@BNNPs as a prominent peak in the region of 1364–1366 cm −1 . It was seen that the peak intensity of BNNPs was notably decreased compared to its raw material h-BN, indicating a reduction of the weaker interaction between layers and layer numbers [ 9 ]. The amino acid-assisted exfoliation had not broken up or created any large holes in the nanoplatelets.…”

“…With a similar filling amount (8.3 wt%), Lys@BNNP/PVA (0.83 W m −1 K −1 ) and Glu@BNNP/PVA (0.82 W m −1 K −1 ) also exhibited a higher thermal conductivity than that of h-BN/PVA (0.76 W m −1 K −1 ) and BNNP/PVA (0.77 W m −1 K −1 ), due to the thick AA@BNNPs flakes which assist thermal transport in the composite because they are less subject to thermal conductivity degradation due to phonon-boundary scattering. In the composite h-BN, nanosheets can form thermal links that interconnect the thick h-BN flakes [ 9 ], and the hydrogen-bonding interaction between −OH groups on the PVA chain and −COOH groups origin from amino acid grafts, leading to a better compatibility between the PVA matrix and AA@BNNPs [ 10 , 33 ].…”

“…BNNPs consist of sp 2 -bonded atomic layers where B and N atoms are alternately arranged into a hexagonal lattice. The regular atomic arrangement permits high phonon velocity and low phonon scattering, leading to an excellent thermal conductive property (~2000 W m −1 K −1 ) [ 9 ]. Compared to graphene, unique insulating properties make BNNPs especially promising in thermally conductive yet electrically insulating polymer composites [ 10 , 11 ].…”