In situ N-doped graphene and Mo nanoribbon formation from Mo2Ti2C3 MXene monolayers

Since the advent of monolayered 2D transition metal carbide and nitrides (MXenes) in 2011, the number of different monolayer systems and the study thereof have been on the rise. Mo2Ti2C3 is one of the least studied MXenes and new insights to this material are of value to the field. Here, the stability of Mo2Ti2C3 under electron irradiation is investigated. A transmission electron microscope (TEM) is used to study the structural and elemental changes in situ. It is found that Mo2Ti2C3 is reasonably stable for the first 2 min of irradiation. However, structural changes occur thereafter, which trigger increasingly rapid and significant rearrangement. This results in the formation of pores and two new nanomaterials, namely, N-doped graphene membranes and Mo nanoribbons. The study provides insight into the stability of Mo2Ti2C3 monolayers against electron irradiation, which will allow for reliable future study of the material using TEM. Furthermore, these findings will facilitate further research in the rapidly growing field of electron beam driven chemistry and engineering of nanomaterials.Web of Scienceart. no. 190711

Внедрение образовательных программ - перспективное направление в охране репродуктивного здоровья молодежи

ПОЛОВОЕ ПОВЕДЕНИЕРЕПРОДУКЦИ

Factors that affect the residents’ propensity to invest in tourism

The current study based on social exchange theory (SET) investigated the impacts of residents’ perception about tourism on their willingness to invest in tourism. Data for this study were collected from residents who reside in Antalya for at least 1 year through online questionnaire utilizing snowball sampling method. The factors that are included in the residents’ perception of tourism were confirmed by Exploratory Factor Analysis first and then Confirmatory Factor Analysis was applied. Hierarchical regression analysis was executed to test the hypotheses in several stages. The results of the study provided a support for the hypotheses that residents positive perception of economic, social and environmental benefits of tourism increases their motivation to invest in the tourism industry

1 D Hierarchical MnCo2O4 Nanowire@MnO2 Sheet Core–Shell Arrays on Graphite Paper as Superior Electrodes for Asymmetric Supercapacitors

Heterostructured metal oxide core–shell architectures have attracted considerable attention owing to their superior electrochemical performance in supercapacitors compared to a single structure. Here, we report a simple and effective synthesis of hierarchical MnCo2O4 nanowire@MnO2 sheet core–shell nanostructures anchored on graphite paper for use in supercapacitors. The proposed electrode exhibits a specific capacitance of 2262 F g−1 at 1 A g−1. In addition, good rate capability and excellent cycling performance are observed. An asymmetric supercapacitor with operating potential at 1.6 V is demonstrated using MnCo2O4@MnO2 as cathode and graphene/nickel foam (NF) as anode. The MnCo2O4@MnO2//graphene/NF asymmetric device shows a high energy density of 85.7 Wh kg−1 at a power density of 800 W kg−1 while maintaining a high energy density of 34.7 Wh kg−1 at 24 kW kg−1. Moreover, the device demonstrates a long-term cycling stability of 81.6 % retention of its initial specific capacitance

Fabrication and Mechanical Properties of Magnesium Alloy Composites Reinforced with TiC and Ti2AlC Particles

Herein we report on the fabrication and mechanical properties of Mg composites fabricated by pressureless melt infiltration of Mg and Mg alloys into porous preforms of TiC and Ti2AlC. The latter is a member of the MAX phases - viz. layered machinable ternary carbides and nitrides - some of which are relatively light and stiff. In this study, pure Mg and three, commercially available, aluminum-containing Mg alloys - AZ31, AZ61 and AZ91 - were used as matrices at a loading of ~ 50 vol.%. For the most part, increasing the Al content enhanced the elastic moduli, Vickers hardness values and yield and ultimate compressive strengths. Reducing the particle sizes of the TiC and Tisub>2AlC particulate reinforcements also had a large impact on the mechanical properties. At 1028±5 MPa, the ultimate compressive strength of a TiC-AZ61 composite, in which the TiC particle size distribution is Lorentzian and centered at, dc = 0.41±0.01 µm, was ~ 40% higher than that of the same composite with coarser TiC particles with bimodal size distributions centered around dc=1.6±0.1 µm, and 5.8±0.3 µm. In addition, the elastic modulus and Vickers hardness of the former composite were measured to be 174±5 GPa and 3.4±0.3 GPa, respectively. For the Ti2AlC reinforced composites, the best properties were obtained when AZ61 was reinforced with Ti2AlC particles with dc = 0.51±0.01 µm. The enhancements in elastic and mechanical properties are attributed to finer grained Mg-matrices, the presence of Al in the matrices which enhances the wetting of TiC and Ti2AlC by Mg to create a strong interface and finer reinforcement particle sizes. The latter two attributes, in turnlead to better mechanical interlocking. For the composites studied herein better elastic and mechanical properties, were obtained at the expense of damping. The TiC-reinforced Mg matrix composites despite their high mechanical properties, have very small energy dissipation capabilities. However, by using Ti2AlC, which inherently dissipates mechanical energy, it is possible to achieve higher damping while simultaneously enhancing the mechanical properties almost to the same levels as for the TiC reinforced composites. Using Mg alloys instead of pure Mg and reducing the reinforcement particle sizes also reduced the damping capabilities of these composites. There is a threshold stress below which the damping capacities of the Ti2AlC reinforced composites are comparable to those of their TiC reinforced counterparts. This was ascribed to the negligible damping of Ti2AlC below the threshold stress ( ~ 200 MPa). The Ti2AlC composites are slightly lighter and can be fabricated at lower temperature than comparable TiC composites; the former are also readily machinable but more expensive.Ph.D., Materials Science and Engineering -- Drexel University, 201

High capacity silicon anodes enabled by MXene viscous aqueous ink

The ever-increasing demands for advanced lithium-ion batteries have greatly stimulated the quest for robust electrodes with a high areal capacity. Producing thick electrodes from a high-performance active material would maximize this parameter. However, above a critical thickness, solution-processed films typically encounter electrical/mechanical problems, limiting the achievable areal capacity and rate performance as a result. Herein, we show that two-dimensional titanium carbide or carbonitride nanosheets, known as MXenes, can be used as a conductive binder for silicon electrodes produced by a simple and scalable slurry-casting technique without the need of any other additives. The nanosheets form a continuous metallic network, enable fast charge transport and provide good mechanical reinforcement for the thick electrode (up to 450 µm). Consequently, very high areal capacity anodes (up to 23.3 mAh cm−2) have been demonstrated

Highly Stable Nanolamellar MXene-derived Carbides by Phase Transformation of Ti3C2Tx and Mo2TiC2Tx MXenes

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Oxidized Ti3C2 MXene nanosheets for dye-sensitized solar cells

Porous TiO2 electrodes were prepared by oxidizing two-dimensional titanium carbide nanosheets (Ti3C2 MXene) and the electrodes were tested in dye-sensitized solar cells. The effects of oxidation temperature and duration time together with various thicknesses on the device performance were investigated. A power conversion efficiency of 2.66% was observed

Synthesis and physical properties of (Zr1−x,Tix)3AlC2MAX phases

MAX phase solid solutions physical and mechanical properties may be tuned via changes in composition, giving them a range of possible technical applications. In the present study, we extend the MAX phase family by synthesizing (Zr1−xTix)3AlC2 quaternary MAX phases and investigating their mechanical properties using density functional theory (DFT). The experimentally determined lattice parameters are in good agreement with the lattice parameters derived by DFT and deviate <0.5% from Vegard's law. Ti3AlC2 has a higher Vickers hardness as compared to Zr3AlC2, in agreement with the available experimental data

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer-substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes' interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole-dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet's thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes' interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes' tribological performance as solid lubricants can be significantly improved by avoiding -OH and -F terminations, which can be done by controlling terminations via post-synthesis processing