Laser-initiated primary and secondary nuclear reactions in Boron-Nitride.
Ontology highlight
ABSTRACT:
SUBMITTER: Labaune C
PROVIDER: S-EPMC4756368 | biostudies-other | 2016
REPOSITORIES: biostudies-other
Similar Datasets
Project description:The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. Two growth modes of BNNT coexisting during the synthesis process have been proposed based on HR-TEM observation and length analysis. One is the root growth mode, in which boron nitride (BN) species formed via the surface interaction between surrounding N2 molecules and boron nanodroplets incorporate into the tubular structure. Another mode called open-end growth mode means the prolongation of tube growth from the exposed BN edge surrounding the surface of boron nanodroplets which is constructed by the heterogeneous nucleation of absorbed BN radicals from the gas plume. The statistical data, the proportions of end structures and the length of BNNTs, could be fitted to two growth modes, and the open-end growth mode is found to be especially effective in producing longer nanotubes with a higher growth rate. The scientific understanding of the growth mechanism is believed to provide the control for optimized production of BNNTs.
| S-EPMC6821736 | biostudies-literature
Project description:Developing efficient (co-)catalysts with optimized interfacial mass and charge transport properties is essential for enhanced oxygen evolution reaction (OER) via electrochemical water splitting. Here we report one-atom-thick hexagonal boron nitride (hBN) as an attractive co-catalyst with enhanced OER efficiency. Various electrocatalytic electrodes are encapsulated with centimeter-sized hBN films which are dense and impermeable so that only the hBN surfaces are directly exposed to reactive species. For example, hBN covered Ni-Fe (oxy)hydroxide anodes show an ultralow Tafel slope of ~30 mV dec-1 with improved reaction current by about 10 times, reaching ~2000 mA cm-2 (at an overpotential of ~490 mV) for over 150 h. The mass activity of hBN co-catalyst is found exceeding that of commercialized catalysts by up to five orders of magnitude. Using isotope experiments and simulations, we attribute the results to the adsorption of oxygen-containing intermediates at the insulating co-catalyst, where localized electrons facilitate the deprotonation processes at electrodes. Little impedance to electron transfer is observed from hBN film encapsulation due to its ultimate thickness. Therefore, our work also offers insights into mechanisms of interfacial reactions at the very first atomic layer of electrodes.
| S-EPMC10618520 | biostudies-literature
Project description:A low-cost, scalable and reproducible approach for the mass production of screen-printed electrode (SPE) platforms that have varying percentage mass incorporations of 2D hexagonal boron nitride (2D-hBN) (2D-hBN/SPEs) is demonstrated herein. These novel 2D-hBN/SPEs are explored as a potential metal-free electrocatalysts towards oxygen reduction reactions (ORRs) within acidic media where their performance is evaluated. A 5% mass incorporation of 2D-hBN into the SPEs resulted in the most beneficial ORR catalysis, reducing the ORR onset potential by ca. 200 mV in comparison to bare/unmodified SPEs. Furthermore, an increase in the achievable current of 83% is also exhibited upon the utilisation of a 2D-hBN/SPE in comparison to its unmodified equivalent. The screen-printed fabrication approach replaces the less-reproducible and time-consuming drop-casting technique of 2D-hBN and provides an alternative approach for the large-scale manufacture of novel electrode platforms that can be utilised in a variety of applications.
| S-EPMC9105127 | biostudies-literature
Project description:Boron nitride (BN) is a material with outstanding technological promise due to its exceptional thermochemical stability, structural, electronic, and thermal conductivity properties, and extreme hardness. Yet, the relative thermodynamic stability of its most common polymorphs (diamond-like cubic and graphite-like hexagonal) has not been resolved satisfactorily because of the crucial role played by kinetic factors in the formation of BN phases at high temperatures and pressures (experiments) and by competing bonding and electrostatic and many-body dispersion forces in BN cohesion (theory). This lack of understanding hampers the development of potential technological applications and challenges the boundaries of fundamental science. Here, we use high-level first-principles theories that correctly reproduce all important electronic interactions (the adiabatic-connection fluctuation-dissipation theorem in the random phase approximation) to estimate with unprecedented accuracy the energy differences between BN polymorphs and thus overcome the accuracy hurdle that hindered previous theoretical studies. We show that the ground-state phase of BN is cubic and that the frequently observed hexagonal polymorph becomes entropically stabilized over the cubic at temperatures slightly above ambient conditions (T c?h = 335 ± 30 K). We also reveal a low-symmetry monoclinic phase that is extremely competitive with the other low-energy polymorphs and that could explain the origins of the experimentally observed "compressed h-BN" phase. Our theoretical findings therefore should stimulate new experimental efforts in bulk BN and promote the use of high-level theories in modeling of technologically relevant van der Waals materials.
| S-EPMC6357755 | biostudies-literature
Project description:Boron nitride (BN) nanomaterials have been increasingly explored for potential biological applications. However, their toxicity remains poorly understood. Using Caenorhabditis elegans as a whole-animal model for toxicity analysis of two representative types of BN nanomaterials - BN nanospheres (BNNSs) and highly water-soluble BN nanomaterial (named BN-800-2) - we found that BNNSs overall toxicity was less than soluble BN-800-2 with irregular shapes. The concentration thresholds for BNNSs and BN-800-2 were 100 µg·mL-1 and 10 µg·mL-1, respectively. Above this concentration, both delayed growth, decreased life span, reduced progeny, retarded locomotion behavior, and changed the expression of phenotype-related genes to various extents. BNNSs and BN-800-2 increased oxidative stress levels in C. elegans by promoting reactive oxygen species production. Our results further showed that oxidative stress response and MAPK signaling-related genes, such as GAS1, SOD2, SOD3, MEK1, and PMK1, might be key factors for reactive oxygen species production and toxic responses to BNNSs and BN-800-2 exposure. Together, our results suggest that when concentrations are lower than 10 µg·mL-1, BNNSs are more biocompatible than BN-800-2 and are potentially biocompatible material.
| S-EPMC5571844 | biostudies-other
Project description:We investigated the effects of laser excitation wavelength on water-window emission lines of laser-produced boron-nitride plasmas. Plasmas are produced by focusing 1064 nm and harmonically generated 532 and 266 nm radiation from a Nd:YAG laser on BN target in vacuum. Soft x-ray emission lines in the water-window region are recorded using a grazing-incidence spectrograph. Filtered photodiodes are used to obtain complementary data for water-window emission intensity and angular dependence. Spectral emission intensity changes in nitrogen Ly-α and He-α are used to show how laser wavelength affects emission. Our results show that the relative intensity of spectral lines is laser wavelength dependent, with the ratio of Ly-α to He-α emission intensity decreasing as laser wavelength is shortened. Filtered photodiode measurements of angular dependence showed that 266 and 532 nm laser wavelengths produce uniform emission.
| S-EPMC3293343 | biostudies-other
Project description:One of the low-dimensional Boron Nitride (BN) forms, namely, cubic-BN (c-BN) nanodots (NDs), offers a variety of novel opportunities in battery, biology, deep ultraviolet light emitting diodes, sensors, filters, and other optoelectronic applications. To date, the attempts towards producing c-BN NDs were mainly performed under extreme high-temperature/high-pressure conditions and resulted in c-BN NDs with micrometer sizes, mixture of different BN phases, and containing process-related impurities/contaminants. To enhance device performance for those applications by taking advantage of size effect, pure, sub-100 nm c-BN NDs are necessary. In this paper, we report self-assembled growth of c-BN NDs on cobalt and nickel substrates by plasma-assisted molecular beam epitaxy. It is found that the nucleation, formation, and morphological properties of c-BN NDs can be closely correlated with the nature of substrate including catalysis effect, lattice-mismatch-induced strain, and roughness, and growth conditions, in particular, growth time and growth temperature. The mean lateral size of c-BN NDs on cobalt scales from 175?nm to 77?nm with the growth time. The growth mechanism of c-BN NDs on metal substrates is concluded to be Volmer-Weber (VW) mode. A simplified two-dimensional numerical modeling shows that the elastic strain energy plays a key role in determining the total formation energy of c-BN NDs on metals.
| S-EPMC5481407 | biostudies-literature
Project description:The fabrication of optically active heterostructures in the shape of mesostructured thin films is a highly challenging task. It requires an integrated process to allow in one-step incorporating the two-dimensional materials within the mesoporous ordered host without disrupting the pore organization. Hexagonal boron nitride (BN) nanosheets have been successfully introduced into titania mesoporous films using a template-assisted sol-gel synthesis and evaporation-induced self-assembly. Two types of BN sheets have been used, with and without defects, to investigate the role of defects in heterostructure properties. It has been found that the defects increase the ultraviolet radiation A (UVA) absorbance and enhance the photocatalytic response of the film. The BN sheets are optically transparent and do not exhibit any photocatalytic property but contribute to anatase crystallization via heterogeneous nucleation.
| S-EPMC8280735 | biostudies-literature
Project description: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.
| S-EPMC7352847 | biostudies-literature
Project description:High global incidence of prostate cancer has led to a focus on prevention and treatment strategies to reduce the impact of this disease in public health. Boron compounds are increasingly recognized as preventative and chemotherapeutic agents. However, systemic administration of soluble boron compounds is hampered by their short half-life and low effectiveness. Here we report on hollow boron nitride (BN) spheres with controlled crystallinity and boron release that decrease cell viability and increase prostate cancer cell apoptosis. In vivo experiments on subcutaneous tumour mouse models treated with BN spheres demonstrated significant suppression of tumour growth. An orthotopic tumour growth model was also utilized and further confirmed the in vivo anti-cancer efficacy of BN spheres. Moreover, the administration of hollow BN spheres with paclitaxel leads to synergetic effects in the suppression of tumour growth. The work demonstrates that hollow BN spheres may function as a new agent for prostate cancer treatment.
| S-EPMC5228389 | biostudies-literature