Stability and properties of the two-dimensional hexagonal boron nitride monolayer functionalized by hydroxyl (OH) radicals: a theoretical study

The Temperature Dependence of the Hexagonal Boron Nitride Oxidation Resistance, Insights from First-Principle Computations

In this work, we studied the oxidation stability of h-BN by investigating different variants of its modification by -OH, -O- and -O-O- groups using an atomistic thermodynamics approach. We showed that up to temperatures of ~1700 K, oxygen is deposited on the surface of hexagonal boron nitride without dissociation, in the form of peroxide. Only at higher temperatures, oxygen tends to be incorporated into the lattice of hexagonal boron nitride, except in the presence of defects N_v, when the embedding occurs at all temperatures. Finally, the electronic and magnetic properties of the oxidized h-BN were studied.

Oxygen-Induced Dissociation of a Single Water Molecule in Confined 2-D Layers: A Semiempirical study

Semiempirical quantum mechanical methods provides a middle ground between a computationally demanding full ab initio quantum chemistry calculations and force-field calculations in application to molecule-surface interactions. In this study, PM7 semiempirical method is used to evaluate adsorption energy values of X@h-BN monolayer [X= O, OH, and H 2 O] followed by a mechanistic study of oxygen-induced water dissociation on a free-standing h-BN monolayer. Based on oxygen adsorption configurations, two reaction pathways for water dissociation are studied that yield two distinct configurations of double OH-functionalized h-BN monolayer. We then investigated the effect of a cover layer graphene on these proposed mechanistic pathways by placing the graphene cover layer on the top of the h-BN monolayer and continuously tuning the separation ( d Gr/h-BN ) between these two layers.

Structures and Electromagnetic Properties of Boron Nitride Nanoribbons Doped with Transition Metals

Inspired by the recent discovery of the Ti-doped BN nanocages, here we report the design of novel BN nanoribbons (BNNRs) doped with fourth-row transition metals (Sc-Cu) and the prediction of their structural and electromagnetic properties. First-principles calculations and ab initio molecular dynamics simulations show that Ti-doped BNNR possesses both thermodynamic and kinetic stability at high temperatures for synthesis of BN materials. Metal doping may make the nonmagnetic pristine BNNR ferromagnetic or antiferromagnetic, depending on the metal. The doping with all considered metals reduces substantially the band gap of pristine BNNR. For example, Sc-doped BNNR is ferromagnetic with an indirect band gap of 1.18 eV, while V-doped nanoribbon is antiferromagnetic with a direct gap of 2.50 eV. Remarkably, the carrier mobility in both materials is significantly enhanced compared to the pristine BNNR. Our findings suggest that doping with different metals may endow BNNRs with versatile electronic and magnetic properties.

Radio-frequency-transmitting hexagonal boron nitride-based anti- and de-icing heating system

Anti- and de-icing heating systems are used to both prevent the accumulation of ice and to remove it and thus avoid damage. Typically, anti- and de-icing heating systems employ carbon-based materials, metal frames, and bulky ceramic structures. These structures generally lead to the loss of radio-frequency (RF) signals and are also relatively heavy. Therefore, RF equipment such as radar domes (radomes) and antennas require anti- and de-icing systems with high RF transmittance for normal operation. In this work, we fabricated a fluorine-doped tin oxide (FTO) wave pattern covered with hexagonal boron nitride (h-BN) layers (i.e., an h-BN/FTO wave pattern) on a glass substrate for use as an RF-transmitting heating system for anti- and de-icing. The FTO wave pattern and h-BN layer act as the heating element and heat spreader, respectively. The h-BN layer showed a transmittance of approximately 90% for RF waves on glass (X band: 8.2-12.4 GHz) (the 10% loss was attributable to the glass substrate). The differences in the temperatures of the FTO-patterned and non-patterned areas for the h-BN(3.6 nm)/FTO and FTO wave pattern were 19.3 and 25.5 °C, respectively. This means that the h-BN layer improved the heat-spreading performance by 6.2 °C. Furthermore, a de-icing test was performed using the h-BN(3.6 nm)/FTO wave pattern by applying a voltage of 40 V at -20 °C. The ice on the non-patterned area melted within 1 min while that on the FTO-patterned area melted within 30 s. These results suggest that the fabricated h-BN(3.6 nm)/FTO wave pattern for RF-transmitting heating systems is suitable for use with the radomes of drones, unmanned aerial vehicles, aircraft, and spaceships in extremely cold environments.

Mechanical and electromechanical properties of functionalized hexagonal boron nitride nanosheet: A density functional theory study

Hydroxylation as a technique is mainly used to alter the chemical characteristics of hexagonal boron nitride (h-BN), affecting physical features as well as mechanical and electromechanical properties in the process, the extent of which remains unknown. In this study, effects of functionalization on the physical, mechanical, and electromechanical properties of h-BN, including the interlayer distance, Young's modulus, intrinsic strength, and bandgaps were investigated based on density functional theory. It was found that functionalized layers of h-BN have an average distance of about 5.48 Å. Analyzing mechanical properties of h-BN revealed great dependence on the degree of functionalization. For the amorphous hydroxylated hexagonal boron nitride nanosheets (OH-BNNS), the Young's modulus moves from 436 to 284 GPa as the coverage of -OH increases. The corresponding variations in the Young's modulus of the ordered OH-BNNS with analogous coverage are bigger at 460-290 GPa. The observed intrinsic strength suggested that mechanical properties are promising even after functionalization. Moreover, the resulted bandgap reduction drastically enhanced the electrical conductivity of this structure under imposed strains. The results from this work pave the way for future endeavors in h-BN nanocomposites research.

Magnetism-tuning strategies for graphene oxide based on magnetic oligoacene oxide patches model

Graphene oxide (GO) has wide application potential owing to its 2D structure and diverse modification sites for various targeted uses. The introduction of magnetism into GO structures has further advanced the controllability of the application of GO materials. Herein, the concept of modular design and modeling was applied to tune the magnetism of GO. To obtain desirable magnetic properties, diradical-structured GO patches were formed by the introduction of two functional groups to break the Kekule structure of the benzene ring. In these diradical GO patches, the energy of the triplet state was lower than those of the open-shell broken-symmetry singlet state and closed-shell singlet state. To create such multi-radical patches, a practical approach is to determine a substantial spatial separation of the α and β spin densities in the molecule. Thus, systematic design strategies and tests were evaluated. The first strategy was extending the distance between the distribution center of the α and β spin densities; the second was controlling the delocalization directions of the α and β electrons; the third was controlling the delocalization extension of the α and β electrons by oxidative modification, and finally introducing multi-radical structures into the molecular system and controlling the position of each radical. Herein, successful molecular models with a large magnetic coupling constant (∼3600 cm^-1) were obtained. This study paves the way to explore ferromagnetic MGO guided by theoretical study, which may become reality soon.

Scalable exfoliation and dispersion of two-dimensional materials - an update

The preparation of dispersions of single- and few-sheet 2D materials in various solvents, as well as the characterization methods applied to such dispersions, is critically reviewed. Motivating factors for producing single- and few-sheet dispersions of 2D materials in liquids are briefly discussed. Many practical applications are expected for such materials that do not require high purity formulations and tight control of donor and acceptor concentrations, as required in conventional Fab processing of semiconductor chips. Approaches and challenges encountered in exfoliating 2D materials in liquids are reviewed. Ultrasonication, mechanical shearing, and electrochemical processing approaches are discussed, and their respective limitations and promising features are critiqued. Supercritical and more conventional liquid and solvent processing are then discussed in detail. The effects of various types of stabilizers, including surfactants and other amphiphiles, as well as polymers, including homopolymeric electrolytes, nonionic polymers, and nanolatexes, are discussed. Consideration of apparent successes of stabilizer-free dispersions indicates that extensive exfoliation in the absence of dispersing aids results from processing-induced surface modifications that promote stabilization of 2D material/solvent interactions. Also apparent paradoxes in "pristineness" and optical extinctions in dispersions suggest that there is much we do not yet quantitatively understand about the surface chemistry of these materials. Another paradox, emanating from modeling dilute solvent-only exfoliation by sonication using polar components of solubility parameters and surface tension for pristine graphene with no polar structural component, is addressed. This apparent paradox appears to be resolved by realizing that the reactivity of graphene to addition reactions of solvent radicals produced by sonolysis is accompanied by unintended polar surface modifications that promote attractive interactions with solvent. This hypothesis serves to define important theoretical and experimental studies that are needed. We conclude that the greatest promise for high volume and high concentration processing lies in applying methods that have not yet been extensively reported, particularly wet comminution processing using small grinding media of various types.

Preparation of ultra-thin hexagonal boron nitride nanoplates for cancer cell imaging and neurotransmitter sensing

A facile and convenient process was optimized for preparing water-soluble hydroxyl-functionalized hexagonal boron nitride (hBN-OH) from hBN. The hBN-OH (2-3 nm thickness) contains ∼40% oxygen and exhibits blue emission with a quantum yield of approximately 36%. The hBN-OH could be used for imaging cells and for the in vitro detection of biomolecules through electrochemical analysis.

Synthesis, characterization and performance of high energy ball milled meso-scale zero valent iron in Fenton reaction

Understanding contaminant degradation by different sized zero valent iron (ZVI) particles is one important aspect in addressing the long-term stability of these particles in field studies. In this study, meso zero valent iron (mZVI) particles were synthesised in a milling time of 10 h using ball milling technique. The efficacy of mZVI particles for removal of phenol was quantitatively evaluated in comparison with coarse zero valent iron (cZVI) and nano zero valent iron (nZVI) particles. Phenol degradation experiments were carried out in sacrificial batch mode at room temperature independently with cZVI, nZVI and mZVI under varied pH conditions of 3, 4, 6, 7, 8 and 10. Batch experiments substantiating the reactivity of mZVI under unbuffered pH system were also carried out and compared with buffered and poorly buffered pH systems. mZVI particles showed consistent phenol degradation at circum-neutral pH with efficiency of 44%, 67%, and 89% in a span of 5, 10 and 20 min respectively. The dissolved iron species and residual iron formation were also measured as a function of pH. Unbuffered systems at circum-neutral pH produced less residual iron when compared to buffered and poorly buffered systems. At this pH, oxidation of Fe(2+) produced a different oxidant Ferryl ion, which was found to effectively participate in phenol degradation.

Experimental and theoretical investigations of functionalized boron nitride as electrode materials for Li-ion batteries

The feasibility of synthesizing functionalized h-BN (FBN) via the reaction between molten LiOH and solid h-BN is studied for the first time and its first ever application as an electrode material in Li-ion batteries is evaluated.