Z-BN: a novel superhard boron nitride phase

A superhard boron nitride phase dubbed as Z-BN is proposed as a possible intermediate phase between h-BN and zinc blende BN (c-BN), and investigated using first-principles calculations within the framework of density functional theory. Although the structure of Z-BN is similar to that of bct-BN containing four-eight BN rings, it is more energetically favorable than bct-BN. Our study reveals that Z-BN, with a considerable structural stability and high density comparable to c-BN, is a transparent insulator with an indirect band gap of about 5.27 eV. Amazingly, its Vickers hardness is 55.88 GPa which is comparable to that of c-BN. This new BN phase may be produced in experiments through cold compressing AB stacking h-BN due to its low transition pressure point of 3.3 GPa.     

Fluorinating hexagonal boron nitride into diamond-like nanofilms with tunable band gap and ferromagnetism

Cubic boron nitride (c-BN) possesses a number of extreme properties rivaling or surpassing those of diamond. Especially, owing to the high chemical stability, c-BN is desired for fabricating electronic devices that can stand up to harsh environments. However, realization of c-BN-based functional devices is still a challenging task due largely to the subtlety in the preparation of high-quality c-BN films with uniform thickness and controllable properties. Here, we present a simple synthetic strategy by surface fluorination of few-layered hexagonal boron nitride (h-BN) sheets to produce thermodynamically favorable F-terminated c-BN nanofilms with an embedded N-N bond layer and strong inbuilt electric polarization. Due to these specific features, the fluorinated c-BN nanofilms have controllable band gap by thickness or inbuilt and applied electric fields. Especially, the produced nanofilms can be tuned into substantial ferromagnetism through electron doping within a reasonable level. The electron-doping-induced deformation ratio of the c-BN nanofilms is found to be 1 order of magnitude higher than those of carbon nanotubes and graphene. At sufficient high doping levels, the nanofilm can be cleaved peculiarly along the N-N bond layer into diamond-like BN films. As the proposed synthesis strategy of the fluorinated c-BN nanofilms is well within the reach of current technologies, our results represent an extremely cost-effective approach for producing high-quality c-BN nanofilms with tunable electronic, magnetic, and electromechanical properties for versatile applications.     

Body-centered tetragonal B2N2: a novel sp3 bonding boron nitride polymorph

A novel polymorph of boron nitride (BN) with a body-centered tetragonal structure (bct-BN) has been predicted using first-principles calculations. The structural, vibrational, and mechanical calculations indicated that bct-BN is mechanically stable at zero pressure. When pressure is above 6 GPa, bct-BN becomes energetically more stable than h-BN. The bct-BN appears to be an intermediate phase between h-BN and w-BN due to a low energy barrier from h-BN to w-BN via bct-BN. Our results also indicated that the structure of unknown E-BN phase might be bct-BN.     

Structure, bonding, vibration and ideal strength of primitive-centered tetragonal boron nitride

First-principle calculations of the structural, electronic, vibrational and mechanical properties of the primitive-centered tetragonal boron nitride (pct-BN) structure are performed. Results reveal that pct-BN is more energetically favorable than h-BN above the pressure of 8.8 GPa and dynamically stable at up to 120 GPa. Electronic bonding indicates that pct-BN possesses a covalent character with near-tetrahedral sp(3)-hybridized electronic states. Vibrational property calculations show that its characteristic sp(3) Raman peaks are at 738 cm(-1), 1032 cm(-1) and 1155 cm(-1). The mechanical failure mode of pct-BN is dominated by the shear type. The lowest peak stress of 43.1 GPa under (110) [11(-)0] shear sets an upper bound for its ideal strength. The calculated minimum hardness of pct-BN is greater than that of w-BN. Its average hardness approached that of c-BN, indicating that this novel BN allotrope is a potential superhard material.     

Neutron damage of hexagonal boron nitride: h-BN

Hexagonal boron nitride (h-BN) was neutron damaged at an integral flux of 2.40 × 10¹² n cm⁻² s⁻¹ for 1, 2, 3 and 4 h. The h-BN samples undergo a transition from sp² to sp³ hybridization as a consequence of the neutron induced damage with the formation of cubic boron nitride (c-BN) spots, as suggested both by FT–IR and Raman spectroscopy. In addition to c-BN, also a certain degree of amorphization is achieved by h-BN already at the lowest neutron fluence of 8.64 × 10¹⁵ n cm⁻² as clearly evidenced by Raman spectroscopy. The Wigner or stored energy to the radiation-damaged h-BN samples was studied by DSC and also in this case there was a clear evidence that the neutron damage was partly irreversible and insensitive to the thermal annealing up to 630 °C. Electron spin resonance (ESR) was employed to further study the structural defects induced by the neutron bombardment of h-BN. Two kinds of paramagnetic defective structures centered on ¹¹B atoms were identified.

     

Enrichment and desalting of tryptic protein digests and the protein depletion using boron nitride

Sample preparation still remains a great challenge in modern bioanalysis and the interest in new efficient solid phase extraction (SPE) materials still remains high. In this work, hexagonal boron nitride (h-BN) is introduced as a new SPE material for the isolation and enrichment of peptides. The h-BN is isoelectronic and structurally similar to graphite. It has remarkable properties including good thermal conductivity, excellent thermal and chemical stability and a better oxidation resistance than graphite. BN attracts increasing interest because of its wide range of applicability. In the present work, the great potential of h-BN, as a new SPE-material, on the enrichment, preconcentration and desalting of tryptic digest of model proteins is demonstrated. A special attention was dedicated to the efficient enrichment of hydrophilic phosphopeptides. Two elution protocols were developed for the enrichment of peptides compatible for subsequent MALDI-MS and ESI-MS analysis. In addition, the recoveries of 5 peptides and 3 phosphopeptides with wide range of pI values utilizing h-BN materials with different surface areas were investigated. 84–106% recovery rate could be achieved using h-BN materials. The results were compared with those obtained using graphite and silica C18 under the same elution conditions, and lower recoveries were obtained. In addition, h-BN was found to have a capability of protein depletion, which is requisite for the peptide profiling.     

N,N-Dimethyl formamide facilitated formation of hexagonal boron nitride from boric acid

In this paper, we report on a promoting novel process for the formation of h-BN plates by using N,N-dimethyl formamide-treated boric acid (DMF-BA). Using this B source, the formation of h-BN can be indeed improved greatly compared to using pure boric acid (BA). This method effectively reduces the content of boric acid and amorphous boric oxide, enhancing the transformation rate of h-BN. For preparation of pure h-BN, it can obviously lower the resultant temperature without further purification process. Via graphitization index (G.I.) calculation and thermostability analysis, the pure h-BN plates obtained from the DMF-BA would be a promising candidate for raw material of c-BN and low-temperature applications in the air.     

First-principles study on the adhesive and electronic property of c-BN(111)/Cu(111) interface

The interface properties of c-BN/Cu composite play an important role in its application. In this work, we employed first-principles calculation to investigate the bonding properties and electronic characteristics of the c-BN(111)/Cu(111) interface. The adhesion properties, partial density of states (PDOS), charge density, and charge density difference of different interfaces were analyzed. The results show that the interface of B-termination “OT” stacking mode is the most stable one. The density of states at the c-BN(111)/Cu(111) interface is similar to that of c-BN bulk phase, indicating that the electronic states of the c-BN layer are not affected by the Cu atoms. The PDOS diagram shows that the 2p orbital of B atoms and the 2p orbital of N atoms are hybridized in the c-BN layer. Besides, 2p orbital of B(N) atoms and 3d orbital of Cu atoms are hybridized in the interface. The covalent bonds and ionic bonds in the interface of N-termination and B-termination OT stacking mode structures are stronger than that of “SL” and “TL” stacking mode. So, the OT stacking mode has larger adhesive energy. Furthermore, Cu and c-BN can form a good coherent interface, which can be used to prepare c-BN/Cu composites and functional materials with excellent mechanical properties.     

3D-Graphene/Boron Nitride-stacking Material: a Fundamental van der Waals Heterostructure

The 3D periodic graphene/h-BN(G/BN) heterostuctures were studied. The stacking forms between the graphene and h-BN layers were discussed. The varieties of the geometric and electronic configurations at the interface between graphene and h-BN layers were also reported. The metal-semiconductor transform of the G/BN material can be achieved by adjusting the stacking form of the h-BN layers or changing the proportion of graphene layers in the unit cell. An electrostatic potential well was found at the interface. Due to the potential well and the only dispersion correlation at the interface, the dielectric constant ε_zz in vertical direction was independent on the variety of the thickness or the proportion of the compositions in an unit cell.     

A simple method to synthesize polyhedral hexagonal boron nitride nanofibers

Hexagonal boron nitride (h-BN) fibers with polyhedral morphology were synthesized with a simple-operational, large-scale and low-cost method. The sample obtained was studied by X-ray photoelectron spectrometer (XPS), electron energy lose spectroscopy (EELS), X-ray powder diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), etc., which matched with h-BN. Environment scanning electron microscopy (ESEM) and transmission electron microscope (TEM) indicated that the BN fibers possess polyhedral morphology. The diameter of the BN fibers is mainly in the range of 100–500 nm.     

X-ray absorption near edge structure study of BN nanotubes and nanothorns

Two boron nitride (BN) nanostructures, the bamboo-like nanotubes and nanothorns where the nanosize h-BN layers are randomly stacked looking like thorns, were synthesized selectively via thermal chemical vapor deposition of B/B(2)O(3) under the NH(3) flow at 1200 degrees C. Electron energy-loss spectroscopy reveals the N-rich h-BN layers with a ratio of B/N = 0.75-0.85. Angle-resolved X-ray absorption near edge structure of these two N-rich nanostructures has been compared with that of h-BN microcrystals. The pi transition in the N K-edge shifts to the lower energy by 0.8-1.0 eV from that of h-BN microcrystals, and the second-order signals of N 1s electrons become significant. We suggest that the N enrichment would decrease the band gap of nanostructures from that of h-BN microcrystals. The Raman spectrum shows the peak broadening due to the defects of N-rich h-BN layers.     

Electron microscopic phase analysis of BN-thin films

A series of BN films was deposited by means of r.f. magnetron sputtering of a h-BN target onto Si(1OO) surfaces. Hereby, the substrate bias voltage was varied. Special interest is focussed to the influence of the deposition parameters on the orientation of the growing hexagonal BN film with respect to the substrate. For structural investigation, cross section samples were prepared. In addition to HRTEM and diffraction investigations, especially electron energy loss spectroscopy (EELS) was applied successfully for phase identification. For negative bias voltages of U _B =–300 V and U _B =–350V, we found a phase system consisting of a first-grown 25 nm thick layer of hexagonal structure with the c axis parallel to the substrate surface followed by the cubic phase.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

聚异丙胺基环硼氮烷裂解制备氮化硼及其抗氧化与介电性能

以异丙胺和三氯环硼氮烷(TCB)为原料,在较温和条件下合成了一种可溶可熔的聚异丙胺基环硼氮烷(PTPiAB),后经高温裂解制得六方氮化硼(h-BN).利用元素分析、TGA、FTIR、XRD和网络分析仪等对先驱体及裂解产物的组成、结构和性能进行了表征.结果表明,PTPiAB的结构中含有B3N3六元环,N-H、C-H和C-N键,其熔点约70 oC.1000 oC时在NH3和Ar中的陶瓷产率分别为45.9 %和52.8 %.NH3中裂解失重主要发生在800 oC以下,1000 oC左右开始结晶,1800 oC时得到BN的(002)晶面间距为0.334 nm,密度为2.03 g·cm-3.该BN表现出了较好的高温抗氧化性能,在空气中900 oC以下增重小于0.3%.此外,室温下测试频率为10 GHz时的介电常数实部和损耗角正切分别为2.48和0.03.     

Synergic nitrogen source route to inorganic fullerene-like boron nitride with vessel, hollow sphere, onion, and peanut nanostructures

In this paper we describe the large-scale synthesis of inorganic fullerene-like (IF-like) hexagonal boron nitride with vessel, hollow sphere, peanut, and onion structures by reacting BBr(3) with the synergic nitrogen sources NaNH(2) and NH(4)Cl at 400-450 degrees C for 6-12 h. The composition of products could be confirmed to be pure boron nitride with hexagonal structures by the XRD patterns and FT-IR, XPS, and EDXA spectra. The representative HRTEM images clearly reveal the layerlike features of the products. Here, the peanut-like structure of the IF-like BN is reported for the first time, and added to the list as one kind of new morphology of BN nanomaterials. The similarity in the structure between h-BN and graphite is responsible for the formation of IF-like BN with nanostructures of vessels, hollow spheres, peanuts, and onions.     

Thermal and physico-chemical studies on binary organic eutectic systems

The phase diagrams of binary systems of 4-aminoacetophenone (AAP) with each of benzoin (BN) and 4-nitrophenol (PNP) have been established by the thaw-melt method. This study shows the formation of eutectics. Accurate compositions of BN and PNP to form eutectic mixtures have been determined by the phase diagram study between BN?CAAP and PNP?CAAP in the entire range of compositions. The thermal properties of the eutectics, such as enthalpy of mixing, solid?Cliquid interfacial energy, entropy of fusion and excess thermodynamic functions were computed based on enthalpy of fusion values. The influence of undercooling on growth kinetics of pure components and their eutectics has been studied. The microstructural studies infer the influence of solid?Cliquid interfacial energy on the morphology of microstructures of eutectics.     

Origins of thermodynamically stable superhydrophobicity of boron nitride nanotubes coatings

Superhydrophobic surfaces are attractive as self-cleaning protective coatings in harsh environments with extreme temperatures and pH levels. Hexagonal phase boron nitride (h-BN) films are promising protective coatings due to their extraordinary chemical and thermal stability. However, their high surface energy makes them hydrophilic and thus not applicable as water repelling coatings. Our recent discovery on the superhydrophobicity of boron nitride nanotubes (BNNTs) is thus contradicting with the fact that BN materials would not be hydrophobic. To resolve this contradiction, we have investigated BNNT coatings by time-dependent contact angle measurement, thermogravimetry, IR spectroscopy, and electron microscopy. We found that the wettability of BNNTs is determined by the packing density, orientation, length of nanotubes, and the environmental condition. The origins of superhydrophobicity of these BNNT coatings are identified as (1) surface morphology and (2) hydrocarbon adsorbates on BNNTs. Hydrocarbon molecules adsorb spontaneously on the curved surfaces of nanotubes more intensively than on flat surfaces of BN films. This means the surface energy of BNNTs was enhanced by their large curvatures and thus increased the affinity of BNNTs to adsorb airborne molecules, which in turn would reduce the surface energy of BNNTs and make them hydrophobic. Our study revealed that both high-temperature and UV-ozone treatments can remove these adsorbates and lead to restitution of hydrophilic BN surface. However, nanotubes have a unique capability in building a hydrophobic layer of adsorbates after a few hours of exposure to ambient air.     

Hexagonal boron nitride adsorbent: Synthesis,performance tailoring and applications

Hexagonal boron nitride(h-BN), with unique structural and properties, has shown enormous potentitoward variety of possible applications. By virtue of partially-ionic character of BN chemical bonds anusually large specific surface area, h-BN-related nanostructures exhibit appealing adsorption propertiewhich can be widely applied for separation and purification towards energy and environment treatmenIn this review, recent progress in designing h-BN micro, nano-structure, controlled synthesis, performancoptimizing as well as energy and environment-related adsorption applications are summarized. Strategieto tailor the h-BN can be classified as morphology control, element doping, defect control and surfacmodification, focusing on how to optimize the adsorption performance. In order to insight the intrinsimechanism of tuning strategies for property optimization, the significant adsorption applications of h-Btowards hydrogen storage, CO_2 capture, pollutants removal from water and adsorption desulfurization arpresented.     

XPS investigations of thick,oxygen-containing cubic boron nitride coatings

Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen.     

Surface Chemistry and Catalytic Reactivity of Borocarbonitride in Oxidative Dehydrogenation of Propane

Borocarbonitride (BCN) materials are newly developed oxidative dehydrogenation catalysts that can efficiently convert alkanes to alkenes. However, BCN materials tend to form bulky B₂O₃ due to over-oxidation at the high reaction temperature, resulting in significant deactivation. Here, we report a series of super stable BCN nanosheets for the oxidative dehydrogenation of propane (ODHP) reaction. The catalytic performance of the BCN nanosheets can be easily regulated by changing the guanine dosage. The control experiment and structural characterization indicate that the introduction of a suitable amount of carbon could prevent the formation of excessive B₂O₃ from BCN materials and maintain the 2D skeleton at a high temperature of 520 °C. The best-performing catalyst BCN exhibits 81.9 % selectivity towards olefins with a stable propane conversion of 35.8 %, and the propene productivity reaches 16.2 mmol h⁻¹ g⁻¹, which is much better than hexagonal BN (h-BN) catalysts. Density functional theory calculation results show that the presence of dispersed rather than aggregated carbon atoms can significantly affect the electronic microenvironment of h-BN, thereby boosting the catalytic activity of BCN.