Study of Chemical and Morphological Transformations during Ni2Mo3N Synthesis via an Oxide Precursor Nitration Route

Chemical and morphological transformations during Ni2Mo3N synthesis were studied in this work. Nitride samples were synthesized from oxide precursors in H2/N2 flow and were analyzed by thermogravimetry, X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-ray spectroscopy methods. In addition, physical and chemical adsorption properties were studied using low-temperature N2 physisorption and NH3 temperature-programmed desorption. It was shown that nitride formation proceeds through a sequence of phase transformations: NiMoO4 + MoO3 → Ni + NiMo + MoO2 → Ni + NiMo + Mo2N → Ni2Mo3N. The weight changes that were calculated from the proposed reactions were in agreement with the experimental data from thermogravimetry. The morphology of the powder changed from platelets and spheres for the oxide sample, to aggregates of needle-like particles for the intermediate product, to porous particles with an extended surface area for the nitride final product. The obtained results should prove useful for subsequent Ni2Mo3N based catalysts production process optimization

Study of Chemical and Morphological Transformations during Ni2Mo3N Synthesis via an Oxide Precursor Nitration Route

Chemical and morphological transformations during Ni2Mo3N synthesis were studied in this work. Nitride samples were synthesized from oxide precursors in H2/N2 flow and were analyzed by thermogravimetry, X-ray diffraction analysis, scanning electron microscopy, and energy dispersive X-ray spectroscopy methods. In addition, physical and chemical adsorption properties were studied using low-temperature N2 physisorption and NH3 temperature-programmed desorption. It was shown that nitride formation proceeds through a sequence of phase transformations: NiMoO4 + MoO3 → Ni + NiMo + MoO2 → Ni + NiMo + Mo2N → Ni2Mo3N. The weight changes that were calculated from the proposed reactions were in agreement with the experimental data from thermogravimetry. The morphology of the powder changed from platelets and spheres for the oxide sample, to aggregates of needle-like particles for the intermediate product, to porous particles with an extended surface area for the nitride final product. The obtained results should prove useful for subsequent Ni2Mo3N based catalysts production process optimization

Recent Progress in Fabrication and Application of BN Nanostructures and BN-Based Nanohybrids

Due to its unique physical, chemical, and mechanical properties, such as a low specific density, large specific surface area, excellent thermal stability, oxidation resistance, low friction, good dispersion stability, enhanced adsorbing capacity, large interlayer shear force, and wide bandgap, hexagonal boron nitride (h-BN) nanostructures are of great interest in many fields. These include, but are not limited to, (i) heterogeneous catalysts, (ii) promising nanocarriers for targeted drug delivery to tumor cells and nanoparticles containing therapeutic agents to fight bacterial and fungal infections, (iii) reinforcing phases in metal, ceramics, and polymer matrix composites, (iv) additives to liquid lubricants, (v) substrates for surface enhanced Raman spectroscopy, (vi) agents for boron neutron capture therapy, (vii) water purifiers, (viii) gas and biological sensors, and (ix) quantum dots, single photon emitters, and heterostructures for electronic, plasmonic, optical, optoelectronic, semiconductor, and magnetic devices. All of these areas are developing rapidly. Thus, the goal of this review is to analyze the critical mass of knowledge and the current state-of-the-art in the field of BN-based nanomaterial fabrication and application based on their amazing properties

Synergistic Catalytic Effect of Ag and MgO Nanoparticles Supported on Defective BN Surface in CO Oxidation Reaction

Micron-sized supports of catalytically active nanoparticles (NPs) can become a good alternative to nanocarriers if their structure is properly tuned. Here, we show that a combination of simple and easily scalable methods, such as defect engineering and polyol synthesis, makes it possible to obtain Ag and MgO nanoparticles supported on defective hexagonal BN (h-BN) support with high catalytic activity in the CO oxidation reaction. High-temperature annealing in air of Mg-containing (h-BN micropellets led to surface oxidation, the formation of hexagonal-shaped surface defects, and defect-related MgO NPs. The enhanced catalytic activity of Ag/MgO/h-BN materials is attributed to the synergistic effect of h-BN surface defects, ultrafine Ag and MgO NPs anchored at the defect edges, and MgO/Ag heterostructures. In addition, theoretical simulations show a shift in the electron density from metallic Ag towards MgO and the associated decrease in the negative charge of oxygen adsorbed on the Ag surface, which positively affects the catalytic activity of the Ag/MgO/h-BN material

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

A New Insight into the Mechanisms Underlying the Discoloration, Sorption, and Photodegradation of Methylene Blue Solutions with and without BNOx Nanocatalysts

Methylene blue (MB) is widely used as a test material in photodynamic therapy and photocatalysis. These applications require an accurate determination of the MB concentration as well as the factors affecting the temporal evolution of the MB concentration. Optical absorbance is the most common method used to estimate MB concentration. This paper presents a detailed study of the dependence of the optical absorbance of aqueous methylene blue (MB) solutions in a concentration range of 0.5 to 10 mg&middot;L&minus;1. The nonlinear behavior of optical absorbance as a function of MB concentration is described for the first time. A sharp change in optical absorption is observed in the range of MB concentrations from 3.33 to 4.00 mg&middot;L&minus;1. Based on the analysis of the absorption spectra, it is concluded that this is due to the formation of MB dimers and trimers in the specific concentration range. For the first time, a strong, thermally induced discoloration effect of the MB solution under the influence of visible and sunlight was revealed: the simultaneous illumination and heating of MB solutions from 20 to 80 &deg;C leads to a twofold decrease in the MB concentration in the solution. Exposure to sunlight for 120 min at a temperature of 80 &deg;C led to the discoloration of the MB solution by more than 80%. The thermally induced discoloration of MB solutions should be considered in photocatalytic experiments when tested solutions are not thermally stabilized and heated due to irradiation. We discuss whether MB is a suitable test material for photocatalytic experiments and consider this using the example of a new photocatalytic material&mdash;boron oxynitride (BNOx) nanoparticles&mdash;with 4.2 and 6.5 at.% of oxygen. It is shown that discoloration is a complex process and includes the following mechanisms: thermally induced MB photodegradation, MB absorption on BNOx NPs, self-sensitizing MB photooxidation, and photocatalytic MB degradation. Careful consideration of all these processes makes it possible to determine the photocatalytic contribution to the discoloration process when using MB as a test material. The photocatalytic activity of BNOx NPs containing 4.2 and 6.5 at.% of oxygen, estimated at ~440 &mu;mol&middot;g&minus;1&middot;h&minus;1. The obtained results are discussed based on the results of DFT calculations considering the effect of MB sorption on its self-sensitizing photooxidation activity. A DFT analysis of the MB sorption capacity with BNOx NPs shows that surface oxygen defects prevent the sorption of MB molecules due to their planar orientation over the BNOx surface. To enhance the sorption capacity, surface oxygen defects should be eliminated

Electrospun Polycaprolactone/ZnO Nanocomposite Membranes with High Antipathogen Activity

The spread of bacterial, fungal, and viral diseases by airborne aerosol flows poses a serious threat to human health, so the development of highly effective antibacterial, antifungal and antiviral filters to protect the respiratory system is in great demand. In this study, we developed ZnO-modified polycaprolactone nanofibers (PCL-ZnO) by treating the nanofiber surface with plasma in a gaseous mixture of Ar/CO2/C2H4 followed by the deposition of ZnO nanoparticles (NPs). The structure and chemical composition of the composite fibers were characterized by SEM, TEM, EDX, FTIR, and XPS methods. We demonstrated high material stability. The mats were tested against Gram-positive and Gram-negative pathogenic bacteria and pathogenic fungi and demonstrated high antibacterial and antifungal activity

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

Amorphous MoSxOy/h-BNxOy Nanohybrids: Synthesis and Dye Photodegradation

Molybdenum sulfide is a very promising catalyst for the photodegradation of organic pollutants in water. Its photocatalytic activity arises from unsaturated sulfur bonds, and it increases with the introduction of structural defects and/or oxygen substitutions. Amorphous molybdenum sulfide (a-MoSxOy) with oxygen substitutions has many active sites, which create favorable conditions for enhanced catalytic activity. Here we present a new approach to the synthesis of a-MoSxOy and demonstrate its high activity in the photodegradation of the dye methylene blue (MB). The MoSxOy was deposited on hexagonal boron oxynitride (h-BNO) nanoflakes by reacting h-BNO, MoCl5, and H2S in dimethylformamide (DMF) at 250 &deg;C. Both X-ray diffraction analysis and high-resolution TEM show the absence of crystalline order in a-MoSxOy. Based on the results of Raman and X-ray photoelectron spectroscopy, as well as analysis by the density functional theory (DFT) method, a chain structure of a-MoSxOy was proposed, consisting of MoS3 clusters with partial substitution of sulfur by oxygen. When a third of the sulfur atoms are replaced with oxygen, the band gap of a-MoSxOy is approximately 1.36 eV, and the valence and conduction bands are 0.74 eV and &minus;0.62 eV, respectively (relative to a standard hydrogen electrode), which satisfies the conditions of photoinduced splitting of water. When illuminated with a mercury lamp, a-MoSxOy/h-BNxOy nanohybrids have a specific mass activity in MB photodegradation of approximately 5.51 mmol g&minus;1 h&minus;1, which is at least four times higher than so far reported values for nonmetal catalysts. The photocatalyst has been shown to be very stable and can be reused