Optomechanical properties of MoSe2 nanosheets as revealed by in situ transmission electron microscopy

Free-standing few-layered MoSe2 nanosheet stacks optoelectronic signatures are analyzed by using light compatible in situ transmission electron microscopy (TEM) utilizing an optical TEM holder allowing for the simultaneous mechanical deformation, electrical probing and light illumination of a sample. Two types of deformation, namely, (i) bending of nanosheets perpendicular to their basal atomic planes and (ii) edge deformation parallel to the basal atomic planes, lead to two distinctly different optomechanical performances of the nanosheet stacks. The former deformation induces a stable but rather marginal increase in photocurrent, whereas the latter mode is prone to unstable nonsystematic photocurrent value changes and a red-shifted photocurrent spectrum. The experimental results are verified by ab initio calculations using density functional theory (DFT).</p

New insights into synthesis of nanocrystalline hexagonal BN

Uncovering the mechanism behind nanocrystalline hexagonal boron nitride (h-BN) formation at relatively low temperatures is of great scientific and practical interest. Herein, the sequence of phase transformations occurring during the interaction of boric acid with ammonia in a temperature range of 25-1000 °C has been studied in detail by means of thermo-gravimetric analysis, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicate that at room temperature boric acid reacts with ammonia to form an ammonium borate hydrate (NH4)2B4O7x4H2O. Its interaction with ammonia upon further heating at 550 °C for 1 h leads to the formation of turbostratic BN. Nanocrystalline h-BN is obtained either during heating in ammonia at 550 °C for 24 h or at 1000 °C for 1 h. This result is important for the development of novel cost-effective and scalable syntheses of h-BN nanostructures, such as nanosheets, nanoparticles, nanofibers, and nanofilms, as well as for sintering h-BN ceramic materials

Elevated-temperature high-strength h-BN-doped Al2014 and Al7075 composites: experimental and theoretical insights

High-strength Al2014 (Al2) and Al7075 (Al7) series composites with and without addition of hexagonal BN (h-BN) flakes (1, 3, and 5 wt%) were fabricated from the powder mixtures of individual elements using a combination of high-energy ball milling (HEBM) and spark plasma sintering (SPS). Phase compositions of Al2 and Al7 composites were different from standard alloys obtained via casting and subsequent heat treatment. Thorough structural study revealed the presence of the following phases: Al(Mg,Si,Mn,Fe,Cu), AlCux, MgOx, and Al5Cu6Mg2 [Al2], Al(Mg,Si,Mn,Fe,Cu), AlCux, Al5Cu6Mg2, Al6CuMg4, MgO2, AlB2, and SiNx [Al2-BN], Al(Cu,Zn,Mg), Fe(Al,Cu), AlCu3, Al2Cu/Fe3Al, Al5Cu6Mg2, Al4Cu9, MgO2 [Al7], and Al(Cu,Zn,Mg), AlCux, MgOx, MgNxOy, MgB2, Mg3(BO3)2, BN, and BNO [Al7-BN]. The important role of h-BN additives in the microstructure formation during HEBM and SPS was demonstrated. Classical molecular dynamics simulations were carried out to estimate critical shear stress between Al nanoparticles with and without intermediate h-BN layers. The obtained results indicated that the h-BN nanosheets had provided solid lubrication, prevented nanoparticle agglomeration during HEBM, led to a reduced porosity and more homogeneous reinforcing phase distributions in the powder mixtures and resultant composites. Structural analysis showed, that during SPS, one part of BN additives had reacted with Al, Si, and Mg to form AlB2, SiNx, and MgB2/Mg3(BO3)2 inclusions, while the other part remained unreacted and contributed to the material strength. Doping with 3 wt% of BN led to an increase in hardness from 76 HV10 to 123 HV10 (Al2 series), and from 97 HV10 to 130 HV10 (Al7 series). The maximum room-temperature tensile strength of 310 MPa (Al7-BN) and 235 MPa (Al2-BN) was observed for the samples with 3 wt% of BN, which corresponds to an increase in strength by approximately 74% and 16%, respectively. At elevated temperatures, the tensile strength values were 227 MPa (350 °C) and 221 MPa (500 °C) for Al2–3%BN, and 276 MPa (350 °C) and 187 MPa (500 °C) for Al7–3%BN. The superior mechanical properties were attributed to the combination of high thermal stability of the reinforcing phases, solid solution hardening, and Orowan (precipitation) strengthening.</p

Microstructure evolution during AlSi10Mg molten alloy/BN microflake interactions in metal matrix composites obtained through 3D printing

Utilization of metal/ceramic powders opens new possibilities for 3D printing of metal matrix composites of complex shape with high strength, but it is still a great challenge. In this work, an AlSi10Mg matrix composite embedded with 1 wt.% of hexagonal BN phase microflakes (h-BN) was obtained by means of 3D printing. Then the present study elucidated microstructure evolutions occurring at the h-BN/melt interface during selective laser melting (SLM) of an h-BN-AlSi10Mg powder mixture. During short-term (0.15 ms) high-temperature (∼2900 K) processing the BN inclusions partly dissolved in the Al-Si melt. This process was accompanied by the formation of an AlN phase at the BN surfaces. The AlN crystallites, 100-200 nm in size, had spherical/semispherical shape and formed a continuous layer along the BN/metal grain boundaries. The peculiar growth of AlN grains along the metal/BN interfaces was governed by the specific features of localized N diffusion in the vicinity of interfaces. By contrast, B atoms, released from the dissolved BN phase, were randomly distributed over the melt. AlB2 nanocrystallites (∼10 nm in size) precipitated from the supersaturated Al-Si melt during cooling stage. With the addition of h-BN microflakes, the composite hardness and tensile strength increased by 32% and 28%, respectivelly. The observed experimental results were supported by ab initio molecular dynamics simulations. Our study demonstrates the possibility and wide prospects of obtaining a dense BN/AlSi10Mg material reinforced with h-BN, AlN, and AlB2 phases via SLM 3D printing and sheds a new light on fine morphological and microstructural features of thus obtained new composites

Oxygen-containing hexagonal boron nitride with an extremely small amount of Pt in CO oxidation

New simple and scalable method for the synthesis of nanocrystalline Pt-containing hexagonal boron oxynitride (Pt/BN(O)) is proposed. At a minimum content of 0.0085 wt.%, Pt is present only in the form of single atoms (SAs) and clusters. This sample demonstrates CO oxidation activity with specific CO2 productivity as high as 176 molCO2/gPt/h at 300 °C. The sample retains high catalytic activity after four cycles.</p

Synthesis and Characterization of Folate Conjugated Boron Nitride Nanocarriers for Targeted Drug Delivery

International audienceWe have developed advanced folate bonded to boron nitride (BN) nanocarriers with a high potential for targeted drug delivery. The folic acid (FA) molecules were successfully conjugated to BN nanoparticles (BNNPs) in three consecutive stages (i) FA preactivation by N,N'-dicyclohexylcarbodiimide (DCC), (ii) BNNP modification by AgNPs and their further NH2-functionalization with L-cysteine, and (iii) final conjugation of activated FA to modified BNNPs. To shed light on the FA-BNNPs binding mechanism, detailed energetic analysis of the atomic structure and stability of the FA-BNNPs system using density functional theory (DFT) calculations was carried out. The results indicated that the FA was successfully bonded with the BNNPs by a condensation reaction between amino groups of Cyst-Ag/BNNPs and carboxyl groups of FA using DCC. Theoretical analysis also demonstrated that the grafting of FA to the surface of BNNP does not affect FA targeting properties

Iron phthalocyanine derived Fe1/h-BN single atom catalysts for CO2 hydrogenation

Iron phthalocyanine-coated hexagonal boron nitride (FePc/h-BN) nanoparticles, obtained by FePcCl adsorption on the h-BN surface from a dimethylformamide solution, were subjected to heat treatment in order to form single atom Fe1/h-BN catalysts. Samples were characterized by means of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning and transmission electron microscopy, and temperature-programmed oxidation/reduction/desorption. The FePc deposition process was optimized to avoid the formation of nanoparticles. FePc exhibits high thermal stability in a hydrogen atmosphere and decomposes into a single iron atom when oxidizing in an O2 flow at 350 °C (sample Fe1-ox/h-BN). Subsequent reductive heat treatment in hydrogen (sample Fe1-red/h-BN) results in the formation of Fe-based nanoparticles due to Fe1 diffusion and association, resulting in a decrease in catalytic activity. Hydrogenation proceeds according to the Eley-Rideal mechanism with CO2 chemisorption on the Fe1 surface species (Fe1-ox/h-BN) and is changed to the Langmuir-Hinshelwood mechanism (Fe1-red/h-BN). Selectivity for hydrocarbons increases after reduction of the Fe1-ox/h-BN sample. Our results open up new possibilities for using metal phthalocyanine as a precursor for cheap, reproducible, and efficient single atom catalysts for CO2 hydrogenation.</p

Ball-milled processed, selective Fe/h-BN nanocatalysts for CO2 hydrogenation

Fe/h-BN nanocatalysts were obtained by a combination of precipitation and high-energy ball-milling (HEBM) techniques. Mechanical treatment at a rate of 300 and 500 rpm induced defects in the h-BN lattice and led to the formation of iron nitride nanoparticles when processing at a higher ball-milling mode. Lewis base centers formed as a result of the interaction of h-BN surface defects with water vapor from ambient air led to an increase in the activity of the Fe/h-BN catalyst in the CO2 hydrogenation. Iron carbides, 2-4 nm in size, formed during the activation stage in the Fe/h-BN nanocomposites after HEBM increased the selectivity toward hydrocarbon formation. Calculations based on the density functional theory showed a significant weakening of the CO bond on the surface of iron carbide and suggested the iron nitride → iron carbide transformation as the most energetically favorable route.</p

Probing electrochemical reactivity in an Sb2S3-containing potassium-ion battery anode: Observation of an increased capacity

Potassium-ion batteries are attracting considerable attention as a viable type of high voltage battery. Among available anode materials, composites containing Sb2S3are some of the most interesting high capacity candidates. A nanostructured Sb2S3-reduced graphene oxide composite anode material is evaluated in this study and compared with a structurally similar SnS2-reduced graphene oxide material reported previously by this team. The behaviour of the Sb2S3-based electrodes is assessed in both 1 M KPF6in ethylene carbonate-diethyl carbonate and 1 M KPF6in 1,2-dimethoxyethane electrolytes. Depotassiation capacities in excess of 650 mA h g−1are recorded for the composite electrodes, superior not only to SnS2-based electrodes but also to all previously reported Sb2S3-containing electrode materials for potassium-ion batteries. In order to establish insights into the reaction mechanism of the Sb2S3phase with potassium, post-cycling X-ray diffraction andin situtransmission electron microscopy are utilised. The recorded data suggest the presence of antimony alloys and potassium polysulphides as reaction products and intermediates; a possible conversion-alloying reaction mechanism is discussed. The results indicate that a capacity higher than previously believed is achievable in the Sb2S3active component of potassium-ion battery electrodes.</p

BN/Ag hybrid nanomaterials with petal-like surfaces as catalysts and antibacterial agents

BN/Ag hybrid nanomaterials (HNMs) and their possible applications as novel active catalysts and antibacterial agents are investigated. BN/Ag nanoparticle (NP) hybrids were fabricated using two methods: (i) chemical vapour deposition (CVD) of BN NPs in the presence of Ag vapours, and (ii) ultraviolet (UV) decomposition of AgNO3 in a suspension of BN NPs. The hybrid microstructures were studied by high-resolution transmission electron microscopy (HRTEM), high-angular dark field scanning TEM imaging paired with energy dispersion X-ray (EDX) mapping, X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (FTIR). They were also characterized in terms of thermal stability, Ag+ ion release, catalytic and antibacterial activities. The materials synthesized via UV decomposition of AgNO3 demonstrated a much better catalytic activity in comparison to those prepared using the CVD method. The best catalytic characteristics (100% methanol conversion at 350 °C) were achieved using the UV BN/Ag HNMs without preliminary annealing at 600 °C in an oxidizing atmosphere. Both types of the BN/Ag HNMs possess a profound antibacterial effect against Escherichia coli K-261 bacteria