Bulk Boron Nitride Research Articles

Pressureless Welding of Temperature-Invariant Multifunctionality Body Based on Hydroxyl-Functionalized Boron Nitride Nanosheets and Bifunctional Monoethanolamine Cross-linker.

Bulk hexagonal boron nitride (h-BN) ceramics with structural integrity, high-temperature resistance and low expansion rate are expected for multifunctional applications in extreme conditions. However, due to its sluggish self-diffusion and intrinsic inertness, it remains a great challenge to overcome high-energy barrier for h-BN powder sintering. Herein, a cross-linking and pressureless-welding strategy is reported to produce bulk boron nitride nanosheets (BNNSs) ceramics with well-crystalized and dense B-N covalent-welding frameworks. The essence of this synthesis strategy lies in the construction of >B─O─H2C─H2C─H2N:→B< bond bridge connection structure among hydroxyl functionalized BNNSs (BNNSs-OH) using bifunctional monoethanolamine (MEA) as cross-linker through esterification and intermolecular-coordination reactions. The prepared BNNSs-interlaced ceramics have densities not less than 1.2gcm-3, and exhibit exceptional mechanical robustness and resiliency, excellent thermomechanical stability, ultra-low linear thermal expansion coefficient of 0.06ppm°C-1, and high thermal diffusion coefficient of 4.76mm2s-1 at 25°C and 3.72mm2s-1 at 450°C. This research not only reduces the free energy barrier from h-BN particles to bulk ceramics through facile multi-step physicochemical reaction, but also stimulates further exploration of multifunctional applications for bulk h-BN ceramics over a wide temperature range.

Mechanical Property and Fracture Behavior of Borazine-Derived Bulk Boron Nitride Ceramics Reinforced with Chopped Si3N4 Fiber

Mechanical Property and Fracture Behavior of Borazine-Derived Bulk Boron Nitride Ceramics Reinforced with Chopped Si3N4 Fiber

Twisted-layer boron nitride ceramic with high deformability and strength.

Moiré superlattices formed by twisted stacking in van der Waals materials have emerged as a new platform for exploring thephysics of strongly correlated materials and other emergent phenomena1-5. However, there remains a lack of research on the mechanical properties of twisted-layer van der Waals materials, owing to a lack of suitable strategies for making three-dimensional bulk materials. Here we report the successful synthesis of a polycrystalline boron nitride bulk ceramic with high room-temperature deformability and strength. This ceramic, synthesized from an onion-like boron nitride nanoprecursor with conventional spark plasma sintering and hot-pressing sintering, consists of interlocked laminated nanoplates in which parallel laminae are stacked with varying twist angles. The compressive strain of this bulk ceramic can reach 14% before fracture, about one order of magnitude higher compared with traditional ceramics (less than 1% in general), whereas the compressive strength is about six times that of ordinary hexagonal boron nitride layered ceramics. The exceptional mechanical properties are due to a combination of theelevated intrinsic deformability of the twisted layering in the nanoplates and the three-dimensional interlocked architecture that restricts deformation from propagating across individual nanoplates. The advent of this twisted-layer boron nitride bulk ceramic opens a gate to the fabrication of highly deformable bulk ceramics.

Distinguishing Different Stackings in Layered Materials via Luminescence Spectroscopy.

Despite its simple crystal structure, layered boron nitride features a surprisingly complex variety of phonon-assisted luminescence peaks. We present a combined experimental and theoretical study on ultraviolet-light emission in hexagonal and rhombohedral bulk boron nitride crystals. Emission spectra of high-quality samples are measured via cathodoluminescence spectroscopy, displaying characteristic differences between the two polytypes. These differences are explained using a fully first-principles computational technique that takes into account radiative emission from "indirect," finite-momentum excitons via coupling to finite-momentum phonons. We show that the differences in peak positions, number of peaks, and relative intensities can be qualitatively and quantitatively explained, once a full integration over all relevant momenta of excitons and phonons is performed.

Synthesis and characterization of new targeted pH-responsive heteroatom-doped hexagonal boron nitride nanosheets for controlled drug release

In this study, sulfur doped hexagonal boron nitride (S-h-BN) and fluorine doped hexagonal boron nitride (F-h-BN) were prepared via the exfoliation and heat treatment of bulk boron nitride (B-BN). Then, Human Serum Albumin (HSA) were immobilized onto the obtained hexagonal boron nitride nanolayer (NLs) surfaces to enhance irinotecan loading, which is a fluorescent molecule having excitation and emission at the wavelengths of 299 nm and 436 nm, respectively. The loading and release properties were studied at different pH values. Whereas the maximum loading amounts were achieved at the pH of 4.0 for all nanosheets, the pH value at which the maximum drug release was observed were found to be different for all samples. The physicochemical characterization of the nanosheets were conducted by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy methods. The XRD and FTIR results indicated the successful synthesis of h-BN and the 2D structure of the nanolayers were imaged using SEM and TEM methods. The F and S content inserted into the h-BN structure was determined to be about 2.45 and 0.1 at. % using the XPS method. In addition, the bonding structre of the modified h-BN monolayers were unraveled by the deconvulation of the XPS results.

Scalable synthesis of highly exfoliated, water-dispersible boron nitride nanosheets for nano-fibrillated cellulose membrane toughening

A very simple solid-state Diels Alder reaction of bulk boron nitride (BN) with maleic anhydride followed by ultrasonication in an aqueous solution was used to mass production of maleic acid functionalized highly exfoliated water dispersible single and few layers of boron nitride nanosheets (BNNS-MA). We demonstrate that as-synthesized BNNS-MA can be used to reinforce and toughen nano-fibrillated cellulose membranes.

Construction of novel Heat-conducting Cu-based MOF nanocomposite (HK-mBNNS/PVDF) film for highly efficient Ad-/desorption of toluene

Metal-organic frameworks (MOFs) modification and composite to chase high adsorption capacity and desorption efficiency for volatile organic compounds (VOCs) capture are a great challenge work. Seeking a suitable strategy to simultaneously promote the adsorption capacity and regeneration efficiency of MOFs is a significant practical challenge in this context. Herein, novel heat-conducting MOFs (HKUST-1) composite films were prepared for efficient and synchronous improvement of adsorption affinity and desorption efficiency. In our case, bulk Boron nitride (BN) was exfoliated into BN nano-sheets (BNNS), which were then spread as flakes on PVDF nanofibers to form a conductive network (BNNS/PVDF film, which was abbreviated as B/P film). With the aid of citric acid (CA) modification, HKUST-1 crystals were dispersed-grown on modified B/P (mB/P) film, resulting in the formation of a hierarchical pore structure in HK-mB/P film with a relatively high MOFs loading amount (45.8 wt%) and surface area (448 m2/g). Performance evaluation experiments showed that the toluene adsorption and desorption rates of the HK-mB0.4/P0.6 film were 5.5 and 5.3 times higher than those of the powder HKUST-1, respectively. The fast adsorption rate could be ascribed to the constructed heat-conducting network and porous stacked nanofibers. Furthermore, its adsorption capacity for toluene was significantly increased up to 4.69 mmol/g at low pressure (P/P0 = 0.01), which was approximately-two times higher than that of pure HKUST-1. This merit was mainly attributed to the newly formed interface between HKUST-1 and mBNNS, which could strengthen the adsorption affinity for toluene by the generated unsaturated metal sites of (BNNS-CA-O|Cu|O-ligand) and π-π attraction of B-N bonds. Besides, the HK-mB0.4/P0.6 film also displayed good cycling performance, with only a 3–4 % decrease in activity observed after five consecutive cycles.

Boron Nitride Thin Films with Anisotropic Optical Properties from Microscale Particle Density Distributions

Unusual optical anisotropy was experimentally observed in hexagonal boron nitride thin films produced from bulk boron nitride via ultrasonication. Both the linear and circular polarisation demonstrated a well-defined single axis of anisotropy over a large sample area. To understand this phenomenon, we employed statistical analysis of optical microscopy images and atomic force microscopy to reveal an ordered particle density distribution at the microscopic level corresponding to the optical axis observed in the polarisation data. The direction of the observed ordering matched the axis of anisotropy. Hence, we attribute the measured optical anisotropy of the thin films to microscopic variations in the particle density distribution.

Electronic Structure of Graphene on the Hexagonal Boron Nitride Surface: A Density Functional Theory Study

Poor electron-related cutting current in graphene-based field-effect transistors (FETs) can be solved by placing a graphene layer over a hexagonal boron nitride (BN) substrate, as established by Giovannetti et al. and other researchers. In order to produce high-quality results, this investigation uses 2 × 2 cells (~2.27% mismatch), given that larger cells lead to more favourable considerations regarding interactions on cell edges. In this case, the substrate-induced band gap is close to 138 meV. In addition, we propose a new material based on graphene on BN in order to take advantage of the wonderful physical properties of both graphene and BN. In this new material, graphene is rotated with respect to BN, and it exhibits a better mismatch, only ~1.34%, than the 1 × 1-graphene/1 × 1-BN; furthermore, it has a very small bandgap, which is almost zero. Therefore, in the bands, there are electronic states in cone form that are like the Dirac cones, which maintain the same characteristics as isolated graphene. In the first case (2 × 2-graphene/2 × 2-BN), for example, the resulting band gap of 138 meV is greater than Giovannetti’s value by a factor of ~2.6. The 2 × 2-graphene/2 × 2-BN cell is better than the 1 × 1-graphene/BN one because a greater bandgap is an improvement in the cutting current of graphene-based FETs, since the barrier created by the bandgap is larger. The calculations in this investigation are performed within the density functional theory (DFT) theory framework, by using 2 × 2-graphene/2 × 2-BN and 13 × 13-graphene/23 × 23-(0001) BN cells. Pseudopotentials and the generalized gradient approximation (GGA), combined with the Perdew–Burke–Ernzerhof parametrization, were used. Relaxation is allowed for all atoms, except for the last layer of the BN substrate, which serves as a reference for all movements and simulates the bulk BN.

Sustainable preparation of graphene-analogue boron nitride by ball-milling for adsorption of organic pollutants

The method of fabricating low-cost adsorbents with high activity and durability via a convenient and eco-friendly procedure is of great importance to wastewater treatment. Herein, a high-efficient mechanical exfoliation strategy was proposed to facilely prepare few-layered graphene-analogue boron nitride (BN) via a one-step non-organic solvent assisted wet ball mill procedure. Ball-milling treatment increased the specific surface area of BN 3.5-fold by reducing the thickness to ∼3 layers with 45 min. The exfoliated BN exhibited strikingly improved sorption performance to organic contaminants with around 124% and 116% increased removal efficiency respectively for oxytetracycline (OTC) and Rhodamine B (RhB) as compared to the bulk BN. Batches sorption experiments showed that the sorption processes were thermodynamic endothermic, and well fitted to pseudo-second-order kinetic model and Freundlich isotherm equation. The π-π stacking interaction, hydrophobic effect and electrostatic interaction were proposed as the dominated sorption mechanism. In addition, no significant decline in adsorptive removal ability for the sorbent after 5 times recycling. The results indicate that the ball-milling exfoliation is a fast, green, sustainable and promising strategy for synthesis of highly potent BN based two-dimensional layered adsorbents.

Dense additive-free bulk boron nitride ceramics developed by self-densification of borazine

Boron nitride (BN) ceramics are promising candidates for high-temperature structural and functional materials. However, it is difficult to sinter dense additive-free bulk BN monoliths because of the covalent bond and flake structure. Here, we report dense bulk BN with relative density higher than 95% without sintering additives achieved via a self-densifying approach of borazine within a wide temperature range from 800 °C to 1800 °C. A polyborazylene with a controlled degree of cross-linking was synthesized and press-molded into shaped green bodies, which were pressureless pyrolyzed into porous frameworks and then densified through repeated borazine infiltration and pyrolysis method. The microstructural and crystalline evolution of the bulk BN ceramics, as well as the corresponded mechanical, thermal and dielectric properties were investigated.

Low temperature synthesis of bulk Boron Nitride Nanoplatelets with and without metallic binder

Boron Nitride Nanoplatelets (BNNP) are consolidated into a bulk form using a low energy processing route that consisted of cryogenic milling, cold isostatic pressing, and a short, mild heat treatment. X-ray diffraction analysis was performed to confirm the presence of the secondary metallic constituent and the different phases of Boron Nitride (BN). Unique features of BNNP such as platelet stacking and kinking are retained. A secondary metallic constituent is also included to improve processability and to enhance structural support in the bulk structure. Mechanical properties were evaluated using microhardness testing and nanoindentation. Relative density, elastic modulus, and hardness increased with the incorporation of Al binder contents of as low as 10 vol %. A high degree of load transfer efficiency is demonstrated in higher metallic binder content composites (50 vol % Al) by comparing theoretical and experimentally measured microhardness values. This study presents a novel template for manufacturing bulk 2D nanomaterials using simple and low energy processing.

Electron transport within bulk cubic boron nitride: A Monte Carlo simulation analysis

Through the use of a semi-classical three-valley Monte Carlo electron transport simulation analysis, we analyze the nature of the steady-state and transient electron transport processes that occur within the zinc-blende phase of bulk boron nitride. For the purposes of our steady-state analysis, the dependence of the electron drift velocity on the applied electric field strength is examined. For our transient electron transport analysis, however, we study how an ensemble of electrons, initially in thermal equilibrium, i.e., zero-field, responds to the sudden application of a constant and uniform applied electric field. The results obtained, corresponding to the specific case of bulk zinc-blende boron nitride, are then contrasted with those corresponding to a number of other compound semiconductors of interest within the III–V nitride semiconductor genome.

Boron nitride for excitonics, nano photonics, and quantum technologies

AbstractWe review the recent progress regarding the physics and applications of boron nitride bulk crystals and its epitaxial layers in various fields. First, we highlight its importance from optoelectronics side, for simple devices operating in the deep ultraviolet, in view of sanitary applications. Emphasis will be directed towards the unusually strong efficiency of the exciton–phonon coupling in this indirect band gap semiconductor. Second, we shift towards nanophotonics, for the management of hyper-magnification and of medical imaging. Here, advantage is taken of the efficient coupling of the electromagnetic field with some of its phonons, those interacting with light at 12 and 6 µm in vacuum. Third, we present the different defects that are currently studied for their propensity to behave as single photon emitters, in the perspective to help them becoming challengers of the NV centres in diamond or of the double vacancy in silicon carbide in the field of modern and developing quantum technologies.

Improved polarization and energy density in boron nitride nanosheets/poly(vinylidene fluoride-chlorotrifluoroethylene) nanocomposite with trilayered architecture regulation

A polymer film capacitor with high energy density has attracted great attention in recent decades to fulfil the requirements of miniaturization and light weight for electronics and energy storage systems. The multi-layered nanocomposite exhibits an effective route for developing polymer film with large energy capability due to the advantage of each layer. Here, two sandwich constructions of boron nitride nanosheets (BNNSs)/poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) nanocomposite film were designed to investigate the effects of architecture regulation on energy storage performance, i.e. the nanocomposite serving as an inner layer with pristine films as outer layers, in which the nanocomposite film delivers a strongly polarized behavior and the pristine polymer provides a high breakdown strength. The BNNSs were liquid exfoliated from boron nitride bulk assisted with fluoro hyperbranched copolymer that was adsorbed on the surface of nanosheets via CH-π non-covalent interactions. The presence of fluoro segments improves the compatibility between the nanosheets and the P(VDF-CTFE) matrix. The maximum polarization of 7.9 μC cm−2 at 300 MV m−1 is achieved in the tailored sandwich film, and the discharged energy density of 9.1 J cm−3 is obtained in the current nanocomposite, which benefits from the barrier effect between adjacent layers induced by the redistribution of electric field and emerging charge traps at the interfaces. This sandwich BNNSs/P(VDF-CTFE) nanocomposite provides an insightful prospect for structural design with respect to the advanced application of the polymer film capacitor.

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

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.

Bactericidal behavior of chemically exfoliated boron nitride nanosheets doped with zirconium.

In this work, boron nitride nanosheets (BNNS) were produced through chemical exfoliation of bulk boron nitride (BN). Furthermore, hydrothermal technique was used to incorporate various concentrations (2.5, 5, 7.5, and 10 wt%) of zirconium (Zr) as a dopant. The prepared undoped and doped BN samples were evaluated for its antimicrobial activity against E. coli and S. aureus. Structural analysis was undertaken using x-ray diffraction which identified the presence of hexagonal BN. FTIR and Raman spectroscopy were utilized to outline IR fingerprint and electronic properties of the synthesized material. Morphological information was obtained through micrographs extracted using field emission scanning electron spectroscope (FESEM) and high resolution transmission electron microscope (HRTEM), while d-spacing was also calculated through HRTEM analysis. Optical properties and emission spectra were examined by applying UV–vis and photoluminescence spectroscope (PL); whereas, band gap analysis was carried out via Tauc plot. Zr-doped BN nanosheets at increasing concentrations (0.5, 1.0 mg/50 μl) revealed enhanced antibacterial activity against E. coli compared to S. aureus (p < 0.05).

Modification of TiO2 with hBN: high temperature anatase phase stabilisation and photocatalytic degradation of 1,4-dioxane

This paper examines the modification of anatase TiO2 with hexagonal boron nitride (hBN) and the impact this coupling has on the temperature of the anatase to rutile phase transition and photocatalytic activity. All samples were 100% anatase when calcined up to 500 °C. At 600 °C, all BN-modified samples contain mixed rutile and anatase phases, with 8% and 16% BN–TiO2 showing the highest anatase contents of 64.4% and 65.5% respectively. The control sample converted fully to rutile at 600 °C while the BN modified sample converted to rutile only at 650 °C. In addition to TiO2 phase composition, XRD also showed the presence of bulk boron nitride peaks, with the peak at 26° indicating the graphite-like hBN structure. Density functional theory calculations of hBN-rings adsorbed at the anatase (101) surface show strong binding at the interface; new interfacial bonds are formed with key interfacial features being formation of B–O–Ti and N–Ti bonds. Models of extended hBN sheets at the anatase (101) surface show that formation of B–O and N–Ti bonds along the edge of the hBN sheet anchor it to the anatase surface. 16% BN–TiO2 at 500 °C showed a significant increase in the photocatalytic degradation of 1,4-dioxane when compared with pure anatase TiO2 at 500 °C. This arises from the effect of hBN on anatase. The computed density of states (DOS) plots show that interfacing anatase with BN results in a red shift in the TiO2 energy gap; N-p states extend the valence band maximum (VBM) to higher energies. This facilitates transitions from high lying N-p states to the Ti-d conduction band. A simple photoexcited state model shows separation of electrons and holes onto TiO2 and BN, respectively, which promotes the photocatalytic activity.

Flexible, thermally conductive layered composite films from massively exfoliated boron nitride nanosheets

Flexible, electrically insulating and highly thermally conductive materials are desired in the thermal management application of next-generation electronic devices. In this work, bulk boron nitride are exfoliated in N-methyl-2-pyrrolidone solvent through a unique combination of large and small ball milling, generating large-volume dispersion with plane defect-free, few-layered boron nitride nanosheets. The exfoliated dispersion is concentrated through centrifugation and further processed into large-area, layered composite films with poly(vinylidene fluoride) through a scalable doctor-blading technique. The high quality of boron nitride nanosheets and their well-ordered layered arrangement imparts the composite film with high in-plane thermal conductivity and low through-plane thermal conductivity. With incorporation of 60 wt% boron nitride nanosheets, the in-plane thermal conductivity is as high as 11.88 W/m K, two orders of magnitude larger than neat poly(vinylidene fluoride). The through-plane thermal conductivity is only 0.41 W/m K, about the same as neat poly(vinylidene fluoride). Besides, the composite film is highly flexible and can be folded without fracture.

Quality Assessment of Bulk Boron Nitride Nanotubes for Advancing Research, Commercial, and Industrial Applications

Evaluating the quality of nanomaterials is essential for both basic research and industrial applications. Here, we describe a methodology for assessment of relative quality of boron nitride nanotub...