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Owing to its exceptional properties and wide‐ranging potential applications from aerospace to medicine, hexagonal boron nitride (h‐BN) has garnered considerable attention over the past decades. Boron nitride nanosheets (BNNSs), atomically thin h‐BN, not only inherit most of the outstanding properties of h‐BN but also exhibit superior characteristics compared to their bulk counterpart due to their reduced thickness, such as special adsorption behaviors and enhanced thermal conductivity. Furthermore, BNNSs display distinct thickness‐dependent properties from graphene and other 2D materials, such as unique mechanical response under indentation. This feature article provides an overview of the thickness‐related special properties of BNNSs, primarily derived from mechanically exfoliated h‐BN single crystals. These properties span various domains, including Raman signatures, molecule adsorption‐induced conformational changes, mechanical properties, thermal conductivity, and thermal expansion coefficients. Moreover, the feature article explores the underlying mechanisms governing these atomic‐scale thickness effects. Leveraging their unique properties, the feature article investigates diverse applications of BNNSs, encompassing surface‐enhanced Raman spectroscopy, metal‐enhanced fluorescence, and isotropic thermal management. [ABSTRACT FROM AUTHOR]

The rapid progress of high-performance microelectronic devices underscores the urgent necessity to develop materials possessing superior thermal conductivity for effectively dissipating heat in cutting-edge electronics. Boron nitride nanosheets (BNNSs) have garnered significant attention due to their exceptional thermal conductivity, combined with electrical insulation and low thermal expansion coefficient, offering a promising solution to heat-related challenges in electronic devices. While BNNSs share some common thermal behaviors with other two-dimensional (2D) materials, they also exhibit unique characteristics. For instance, BNNSs exhibit larger isotope disorders compared to graphene, yet their isotope enhancement in thermal conductivity is lower than that of their carbon counterpart. This review provides an overview of the thermal transport properties and mechanisms of BNNSs explored over the past decade, beginning with a brief introduction to the basic of thermal conductivity. It then delves into the thermal transport mechanisms in BNNSs, highlighting factors impacting the in-plane thermal conductivity of BNNSs, as well as the cross-plane thermal conductivity and the factors influencing it. Finally, the review discusses challenges associated with BNNS thermal conductivity measurement and outlines potential future research avenues. [ABSTRACT FROM AUTHOR]

Titanium-coated boron nitride nanotubes prepared by sputtering method have been heated under different conditions to investigate reaction phases at their interface. It is found that TiB 2 nanocrystals firstly nucleate on the surface of nanotubes at 800 °C for 30 min. By the time 1 h, these nucleated TiB 2 crystals grow larger by consuming inner walls of nanotubes and tend to transform into TiB phase. With an exposure to higher temperatures and longer periods, needle-like TiB whiskers and plate-like TiB 2 remain in the composite. [ABSTRACT FROM AUTHOR]

Atomically thin boron nitride (BN) is an important 2D nanomaterial, with many properties distinct from graphene. In this feature article, these unique properties and associated applications, often not feasible with graphene, are outlined. The article starts with characterization and identification of atomically thin BN. It is followed by demonstrating their strong oxidation resistance at high temperatures and applications in protecting metals from oxidation and corrosion. As flat insulators, BN nanosheets are ideal dielectric substrates for surface enhanced Raman spectroscopy (SERS) and electronic devices based on 2D heterostructures. The light emission of BN nanosheets in the deep ultraviolet (DUV) and ultraviolet (UV) regions is also included for its scientific and technological importance. The last part is dedicated to synthesis, characterization, and optical properties of BN nanoribbons, a special form of nanosheets. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) hexagonal boronnitride (BN) nanosheets are excellent dielectric substrate for graphene,molybdenum disulfide, and many other 2D nanomaterial-based electronicand photonic devices. To optimize the performance of these 2D devices,it is essential to understand the dielectric screening propertiesof BN nanosheets as a function of the thickness. Here, electric forcemicroscopy along with theoretical calculations based on both state-of-the-artfirst-principles calculations with van der Waals interactions underconsideration, and nonlinear Thomas–Fermi theory models areused to investigate the dielectric screening in high-quality BN nanosheetsof different thicknesses. It is found that atomically thin BN nanosheetsare less effective in electric field screening, but the screeningcapability of BN shows a relatively weak dependence on the layer thickness. [ABSTRACT FROM AUTHOR]

Abstract: Boron nitride (BN) nanomaterials are of great scientific and technological interest. Here we report formation of BN nanodisks which are only 1–2nm thick and have a relative uniform diameter of 30–40nm. The nanodisks are produced on surfaces of BN nanosheets by argon plasma treatment at room temperature. The nanodisks show a polycrystalline structure and some levels of oxidation. It is found that the oxidation (patched B3O bond) may serve as masks during the plasma etching and lead to the formation of the nanodisks. [Copyright &y& Elsevier]

Abstract: High-energy ball milling has been used to produce nanocrystalline and amorphous structures in nature graphite, but Raman spectroscopy analysis shows that the structure of the amorphous phase produced by ball milling is less disordered than the amorphous structures in ion-beam bombarded graphite and sputtered amorphous carbon. The band intensity ratio (I D/I G) increases first and then drops to 1.1 after 40h of milling treatment, and remains constant during extended milling up to 100h. Electron microscopy observation and surface area measurement show that the formation of some nanosized clusters during the extended milling period might be responsible for the less disordered structure in the milled graphite. [Copyright &y& Elsevier]

Light in deep ultraviolet (DUV) region has a wide range of applications and the demand for finding DUV light emitting materials at nanoscale is increasingly urgent as they are vital for building miniaturized optic and optoelectronic devices. We discover that boron nitride nanotubes (BNNTs) with a well-crystallized cylindrical multiwall structure and diameters smaller than 10 nm can have single DUV emission at 225 nm (5.51 eV). The measured BNNTs are grown on substrate in the form of a thin film. This study suggests that BNNTs may work as nanosized DUV light sources for various applications. [ABSTRACT FROM AUTHOR]

The effect of rolling and annealing on boron nitride nanotube (BNNTs) reinforced aluminum- composites is investigated in this study. Composites were fabricated via conventional sintering method with 0, 2 & 5 wt% BNNT addition in aluminum matrix. Addition of 2 wt% BNNT improved hardness and elastic modulus by 23% and 18%, respectively. Rolling the same composite at 200 °C with 60% reduction in single pass improved modulus and hardness of the composite by 60% and 31%, respectively, over Al. Addition of 5 wt% BNNT led to reduced properties due to agglomeration, which on rolling developed cracks. Annealing the rolled Al-BNNT composite further led to an improvement in strength and ductility. Annealed Al-2BNNT showed highest improvement in strength of 41% and 110% over rolled and sintered condition, respectively. In addition, the same composition has recorded 157% improvement in toughness in annealed condition, as compared to rolled condition. Uniformly distributed BNNTs restricted grain growth and grain boundary migration due to pinning, leading to presence of additional grain boundaries inside the old grains thus improving the strength further. Uniform distribution of BNNT is the prime reason behind the improved properties of Al-BNNT composites. [ABSTRACT FROM AUTHOR]

Boron Nitride Nanotube (BNNT) has emerged as a potential reinforcement for ceramic and metal matrices due to its excellent mechanical, chemical, and thermal properties. We have reinforced 5 vol % BNNT into the alumina (Al 2 O 3) matrix using the atmospheric plasma spraying technique in the present study. BNNTs have been successfully retained after experiencing extreme temperatures of the plasma plume. Reinforcement of BNNTs has improved the relative density of pure Al 2 O 3 coating from 90% to 94%, whereas the hardness, elastic modulus, and fracture toughness enhanced by 117%, 35% and 51%, respectively for the BNNTs reinforced coatings. The critical energy release rate increased from 3.90 ± 1.18 J/m2 to 6.50 ± 1.22 J/m2 with BNNT addition. The property enhancement reasons are attributed to improved densification, uniform distribution of BNNTs into the matrix, and toughening mechanisms, such as BNNT truss, nanotube pull-out, and crack bridging. This BNNT strengthened Al 2 O 3 coating could be a successful candidate for highly durable and strong structural material for automobile and aviation sector, high speed cutting tools and in bioimplant sectors. [ABSTRACT FROM AUTHOR]

Nano-perforated graphene sheets have emerged as exciting two-dimensional materials for a broad range of scientific and commercial purposes, due to their modified physicochemical properties as compared to native graphene materials. Nanoporous graphene sheets as a class of two-dimensional materials with thicknesses ranging from sub-nanometre to few tens of nanometres, possess high specific surface areas and porous mesh structures with tuneable porosity levels. These properties lead to high densities of unsaturated carbon edges around the pores, making them attractive candidates for applications such as energy storage, separation, sensing or catalysis. Several perforation methodologies have been reported to sculpt pores across graphene structures via etching or guided growth mechanisms. This review focuses on current and emerging nano-perforation methodologies for the two-dimensional graphene materials, and discusses controllable porosity parameters in terms of physical pore size and surface pore density across 2D materials. The relationship between perforation methodology and the achieved porosity level is also discussed and related to electronic or surface reactivity properties. Suggestions towards perforation methodologies in relation to targeted pore size and density, as well as the current challenges hindering scalability of engineering the nanoporous graphene and other similar two-dimensional materials are also highlighted. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Hexagonal boron nitride (BN) is electrically insulating and has a high in‐plane thermal conductivity. However, it has a very low cross‐plane thermal conductivity which limits its application for efficient heat dissipation. Here, large BN pellets with a quasi‐isotropic thermal conductivity are produced from BN nanosheets using a spark plasma sintering (SPS) technique. The BN pellets have the same thermal conductivity from both perpendicular and parallel directions to the pellet surface. The high quasi‐isotropic thermal conductivity of the bulk BN is attributed to a quasi‐isotropic structure formed during the SPS process in which the charged BN nanosheets form large sheets in all directions under two opposite forces of SPS compression and electric field. The pellet sintered at 2300 °C has a very high cross‐section thermal conductivity of 280 W m−1 K−1 (parallel to the SPS pressing direction) and exhibits superior heat dissipation performance due to more efficient heat transfer in the vertical direction. [ABSTRACT FROM AUTHOR]

The urgent need for ultrahigh thermally conductive materials to keep up with the rapid development of the electronics industry has led to the exploration of hexagonal boron nitride nanosheets (BNNSs) as an ideal material for thermal transport/dissipation applications. BNNSs possess outstanding mechanical strength, electrical insulation, thermal conductivity, and low density, as well as remarkable oxidation resistance. This article provides a comprehensive review of various fabrication methods for BNNSs and compares their advantages and disadvantages. Additionally, the article discusses the impact of several BNNS properties, including thickness, size, interface, isotopic concentration, and defects, on their thermally conductive properties. Lastly, the review delves into the use of BNNSs as highly thermally conductive fillers in polymer-based materials, highlighting the significant effects of the content, directionality, dispersibility, and structure of BNNSs within the polymer matrix on the composite's thermally conductive properties. This review aims to spark new fabrication methods and improvements to achieve BNNS/polymer composites and promote their practical application as thermal transport/dissipation materials. [ABSTRACT FROM AUTHOR]

Organometallic complexes with metal-nitrogen/carbon (M-N/C) coordination are the most important alternatives to precious metal catalysts for oxygen reduction and evolution reactions (ORR and OER) in energy conversion devices. Here, we designed and developed a range of molecule-level graphitic carbon nitride (g-C3N4) coordinated transition metals (M-C3N4) as a new generation of M-N/C catalysts for these oxygen electrode reactions. As a proof-of-concept example, we conducted theoretical evaluation and experimental validation on a cobalt-C3N4 catalyst with a desired molecular configuration, which possesses comparable electrocatalytic activity to that of precious metal benchmarks for the ORR and OER in alkaline media. The correlation of experimental and computational results confirms that this high activity originates from the precise M-N2 coordination in the g-C3N4 matrix. Moreover, the reversible ORR/OER activity trend for a wide variety of M-C3N4 complexes has been constructed to provide guidance for the molecular design of this promising class of catalysts. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) is a critical process due to its fundamental role in electrocatalysis. Practically, the development of high-performance electrocatalysts for HER in alkaline media is of great importance for the conversion of renewable energy to hydrogen fuel via photoelectrochemical water splitting. However, both mechanistic exploration and materials development for HER under alkaline conditions are very limited. Precious Pt metal, which still serves as the state-of-the-art catalyst for HER, is unable to guarantee a sustainable hydrogen supply. Here we report an anomalously structured Ru catalyst that shows 2.5 times higher hydrogen generation rate than Pt and is among the most active HER electrocatalysts yet reported in alkaline solutions. The identification of new face-centered cubic crystallographic structure of Ru nanoparticles was investigated by high-resolution transmission electron microscopy imaging, and its formation mechanism was revealed by spectroscopic characterization and theoretical analysis. For the first time, it is found that the Ru nanocatalyst showed a pronounced effect of the crystal structure on the electrocatalytic activity tested under different conditions. The combination of electrochemical reaction rate measurements and density functional theory computation shows that the high activity of anomalous Ru catalyst in alkaline solution originates from its suitable adsorption energies to some key reaction intermediates and reaction kinetics in the HER process. [ABSTRACT FROM AUTHOR]

Surface interaction is extremely important to both fundamental research and practical application. Physisorption can induce shape and structural distortion (i.e., conformational changes) in macromolecular and biomolecular adsorbates, but such phenomena have rarely been observed on adsorbents. Here, it is demonstrated theoretically and experimentally that atomically thin boron nitride (BN) nanosheets as an adsorbent experience conformational changes upon surface adsorption of molecules, increasing adsorption energy and efficiency. The study not only provides new perspectives on the strong adsorption capability of BN nanosheets and many other two-dimensional (2D) nanomaterials but also opens up possibilities for many novel applications. For example, it is demonstrated that BN nanosheets with the same surface area as bulk hexagonal BN particles are more effective in purification and sensing. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) is a useful multidisciplinary analytic technique. However, it is still a challenge to produce SERS substrates that are highly sensitive, reproducible, stable, reusable, and scalable. Herein, we demonstrate that atomically thin boron nitride (BN) nanosheets have many unique and desirable properties to help solve this challenge. The synergic effect of the atomic thickness, high flexibility, stronger surface adsorption capability, electrical insulation, impermeability, high thermal and chemical stability of BN nanosheets can increase the Raman sensitivity by up to two orders, and in the meantime attain longterm stability and extraordinary reusability not achievable by other materials. These advances will greatly facilitate the wider use of SERS in many fields. [ABSTRACT FROM AUTHOR]

Porous carbon nanotube/polyvinylidene fluoride (CNT/PVDF) composite material can be fabricated via formation and freeze-drying of a gel. The field emission scanning electron microscopy, nitrogen adsorption–desorption and pore size distribution analysis reveal that the introduction of a small amount of carbon nanotubes (CNTs) can effectively increase the surface roughness and porosity of polyvinylidene fluoride (PVDF). Contact angle measurements of water and oil indicate that the as-obtained composite material is superhydrophobic and superoleophilic. Further experiments demonstrate that these composite material can be efficiently used to separate/absorb the insoluble oil from oil polluted water as membrane/absorbent. Most importantly, the electrical conductivity of such porous CNT/PVDF composite material can be tuned by adjusting the mass ratio of CNT to PVDF without obviously changing the superhydrophobicity or superoleophilicity. The unique properties of the porous CNT/PVDF composite material make it a promising candidate for oil-polluted water treatment as well as water-repellent catalyst-supporting electrode material. [ABSTRACT FROM AUTHOR]

Abstract: Boron nitride nanotubes (BNNT) reinforced aluminum based composites are synthesized by spark plasma sintering (SPS). The concentration of BNNT is varied as 0, 2 and 5vol% in the aluminum matrix. Micro-pillar compression testing revealed that Al–5vol% BNNT has yield strength and compressive strength as 88MPa and 216MPa respectively, which is more than 50% improvement over unreinforced Al. BNNT play an active role in strengthening Al matrix through effective load bearing and transfer by crack bridging and sword in sheath mechanisms. Cold rolling of Al–5vol% BNNT with 75% thickness reduction in a single pass exhibited high deformability without cracking or disintegration. The deformation is dominated by slip signifying ductile behavior in sintered Al with and without BNNT. BNNT survives the extreme temperature and pressure conditions during SPS processing and heavy deformation during cold rolling. [Copyright &y& Elsevier]

Abstract: In this communication, the humidity sensing properties of single boron nitride nanotubes (BNNTs) with and without Au decoration have been investigated. The current–voltage measurement shows that the decoration of Au nanoparticles on the surface of BNNTs effectively improves the conductance. The resistance of single BNNT and Au-BNNT decreases slowly at the low relative humidity (RH) from 20% to 50%; but decreases fastly at the high RH from 50% to 90%. Moreover, the adsorption and desorption tests indicate that the Au-decorated boron nitride nanotube (Au-BNNT) has a fast and sensitive response and recovery to RH at room temperature. The good humidity-sensing properties of the Au-BNNT combined with its excellent chemical stability, make it a promising candidate for the fast detection of humidity in various wild environments. [Copyright &y& Elsevier]

On page 8202, Y. Chen, L. H. Li and co‐workers provide new perspectives on the strong surface adsorption capability of two‐dimensional nanomaterials. They demonstrate theoretically and experimentally that as an adsorbent, BN nanosheets experience conformational changes after surface adsorption of molecules with a resultant increase of adsorption energy and efficiency. This fundamental discovery is valuable for many applications. [ABSTRACT FROM AUTHOR]