Pristine Structure Research Articles

Chemical Functionalization of Silicon Carbide Nanotube (SiCNT): First Principles DFT Study

In this study, a functionalized nano drug carrier design based on (5,5) silicon carbide nanotube and functional groups such as amine (−NH2), hydroxyl (−OH), and carboxylic acid (−COOH) were investigated using the first principles’ density functional theory. The critical need for a smart nanocarrier system aims to increase the concentration of medications to the particular tissues of interest with minimal toxicity to the patient. The simulations are carried out using Quantum ATK-Atomistic Simulation Software. The negative binding energy and the total energy difference obtained by optimization through random perturbation ensure the stability of the structures SiCNT and SiCNT-(X/2X) (X = −OH, −NH2, and −COOH). The energy bandgap obtained for the pristine structure is 1.99 eV indicating their indirect bandgap semiconducting characteristics. In comparison to SiCNT, the energy bandgap of SiCNT-(X/2X) structures decreases within a range of 0.06 eV to 1.95 eV, respectively. Partial charges and p-character were used to understand the nature of bonds between the nanotube and the functional moiety. The chemical potential analysis favors a blue shift of SiCNT-(X/2X) with respect to SiCNT. The higher values of ionic character and solvation energy predicts the solubility of nanostructures in the aqueous medium. In comparison to all analyzed systems, the findings of the ionic character, solvation, and sensing mechanism indicate SiCNT-(2NH2) system to be most favorable drug delivery nanocarrier. These findings suggest that increasing the concentration of −NH2 functional groups on the side wall of silicon carbide nanotubes helps to develop a promising and efficient targeted drug delivery system to deliver specific molecular cargo to the cells mitigating toxicity associated with nanotubes, thereby enhancing the outcomes of cancer treatment. Furthermore, surface functionalization of silicon carbide nanostructures could improve their potential solubility parameterized by higher values of dipole moment and solvation energy together with enhanced biocompatibility leading to the desired therapeutic effect.

Surface engineering of non-platinum-based electrocatalysts for sustainable hydrogen production: Encapsulation, doping, and decoration approach

The hydrogen evolution reaction's electrocatalytic reduction of water to molecular hydrogen may one day provide a long-term sustainable source of energy. However, the use of precious platinum catalysts makes it difficult to commercialize. So far, all alternatives to platinum are based on non-precious metals and transition metals. Hence, tuning the catalytic activity of nanomaterials through surface engineering might offer significant advantages. Herein, we step-wisely modulate the surface of all carbon fullerene nanomaterial by encapsulation, doping and decoration with alkali and transition metals to produce a hybrid catalyst which demonstrated excellent hydrogen evolution activity with comparable Gibbs free energy with both experimentally developed and theoretically modelled electrocatalyst. The adsorption of H* intermediate on the doped and decorated metal sites has been investigated in comparison with the pristine C24 fullerene structure. The electronic properties, the density of state (PDOS), reaction-free energy (ΔG) and transition states have all been carefully considered at appropriate theoretical levels. The ΔG of hydrogen adsorption on H@IndecNidopMgencC24 was found to be closer to zero (0.0328 eV) because of the concomitant effect of the encapsulation, doping and decoration with transition metals thus, demonstrating the effectiveness of this approach to tuning catalytic activity. The encapsulated metal enhanced the catalyst surface's conductivity and electronic attributes, leading to improved HER activity. The catalytic HER was also found to follow the Volmer-Tafel pathways, resulting in a lower free energy barrier. Overall, this work demonstrates a simple structure-activity relationship between metallic effects and substrate engineering and could open new dimensions for the development of novel non-platinum-based electrocatalysts.

A mixed city or an ancient historical city? The malleability of heritage in rebranding Lydd

At the national scale, Lydd is one of the “mixed cities” in Israel; however, to the Lydd municipality, the city is an “ancient historical city.” Through a discourse analysis of how the Lydd Municipality uses heritage as a tool to construct the city’s image as an “ancient historical city,” this article highlights how the two disparate urban identities align in producing and maintaining histories of colonial erasure. To the Lydd Municipality, the image of Lydd as an “ancient historical city” begins with the Shelby White and Leon Levy Lod Mosaic Archaeological Center, a pristine modern structure standing only a few blocks away from several abandoned and haphazardly cordoned-off ruins from the Ottoman era. Looking to municipal rhetorics and urban development plans for several of the heritage sites in the northeastern portion of the city, heritage is understood as a tool through which national priorities, municipal entrepreneurialism, and colonial erasure coalesce.

Microstructure evolution and mechanical properties of graphene reinforced Ti-6Al-4V matrix composites: Defective vs high-quality graphene

Graphene reinforced Ti6Al4V composites were fabricated by ball milling, fast hot press sintering, and hot rolling. Graphene with two defect states, high quality with pristine structure and low quality with defective structure, was introduced into the Ti6Al4V matrix. The microstructure evolution and mechanical properties of graphene reinforced Ti6Al4V matrix composites were investigated. The results indicated that the high quality graphene/Ti6Al4V composite exhibited good strength-plasticity compatibility while the low quality graphene/Ti6Al4V composite had a severe interface reaction with a wide TiC interlayer and showed poor ductility due to the weak interface bonding.

Investigations of electronic, elastic, and optical properties of (Ag, Cd)-doped LaAlO3: a computational insight

In this study, we used density functional theory to examine how the wide band gap optoelectronic properties of pure, silver-, and cadmium-doped LaAlO3 perovskites changed. Structural, electrical, elastic, and mechanical properties were calculated using generalized gradient approximation. Silver and cadmium incorporated at Al site demonstrated a decreasing trend in the band gap. Both impurities showed the reduction in band gap from 2.98 to 0.468 eV and from 2.98 to 2.0238 eV. The density of states was examined for pristine and doped structures to understand behavioral change of LaAlO3. It was observed that p states in upper valance band and d states in lower conduction band were contributing toward the reduction of band gap. Elastic properties were computed. Elastic parameters were used to calculate Born’s stability and it is predicted that the material is stable mechanically for both pristine and doped forms. Mechanical properties were also predicted and brittle nature was found for both pristine and doped materials. Optical responses such as dielectric function, absorption, and refractive index were also predicted. The impurity inclusion in pristine structure not only reduces the bad gap but also alters the optical behavior. Absorption edge shifted toward lower energy shows a clear redshift, whereas refractive index also reduces from 2.4 to 1.9, making the material more transparent. The absorption spectrum as well as electronic band gap makes this material more useful for solar cell application as well as photocatalytic applications.

Functionalized Copper Nanoparticles with Gold Nanoclusters: Part I. Highly Selective Electrosynthesis of Hydrogen Peroxide.

Copper nanoparticles (CuNPs) and gold nanoclusters (AuNCs) show a high catalytic performance in generating hydrogen peroxide (H2O2), a property that can be exploited to kill disease-causing microbes and to carry carbon-free energy. Some combinations of NPs/NCs can generate synergistic effects to produce stronger antiseptics, such as H2O2 or other reactive oxygen species (ROS). Herein, we demonstrate a novel facile AuNC surface decoration method on the surfaces of CuNPs using galvanic displacement. The Cu-Au bimetallic NPs presented a high selective production of H2O2 via a two-electron (2e-) oxygen reduction reaction (ORR). Their physicochemical analyses were conducted by scanning electron microscopy (SEM), transmitting electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). With the optimized Cu-Au1.5NPs showing their particle sizes averaged in 53.8 nm, their electrochemical analysis indicated that the pristine AuNC structure exhibited the highest 2e- selectivity in ORR, the CuNPs presented the weakest 2e- selectivity, and the optimized Cu-Au1.5NPs exhibited a high 2e- selectivity of 95% for H2O2 production, along with excellent catalytic activity and durability. The optimized Cu-Au1.5NPs demonstrated a novel pathway to balance the cost and catalytic performance through the appropriate combination of metal NPs/NCs.

Evaluating the appropriateness of γ-graphyne derivatives as electrode materials for supercapacitors

DFT calculations were used to study the quantum capacitance of pure, B/Al/Si/N/P-doped, and defective γ-graphyne. Due to the direct relationship between capacitance and electronic states around the Fermi level, structures' electronic properties were evaluated by DOS plots. The results of integrated specific quantum capacitance in the range of water stability potential show an improvement of capacity in each p and n-type doping. The calculated cohesive energies of doped structures reflect the stability enhancement. Also, the stability/capacitance of single and double vacancies in two distinct positions (sp and sp2) were examined. The results illustrate stability retention and quantum capacitance improvement of these defective structures. Among the doped structures, the maximum quantum capacitance is 2251.10 F/gr belonging to the aluminum doped structure (in the sp position). For the defective structures, the maximum quantum capacitance is 4221.69 F/gr belonging to removing two sp carbon atoms. These quantum capacitances significantly improved compared to the pristine structure (1216.87 F/gr) and many other structures. These stunning results can contribute to the design of appropriate structures as electrode materials for high-efficiency supercapacitors.

Probing Active Sites on Pristine and Defective MnPX3 (X: S and Se) Monolayers for Electrocatalytic Water Splitting.

The state-of-the-art density functional theory approach was used to study the structural and electronic properties of pristine and defective MnPX3 monolayers as well as their activity toward water and hydrogen evolution reaction (HER) catalytic performance. The adsorption behavior of H2O on a pristine MnPX3 structure is of physisorption nature, whereas the adsorption energy is significantly increased for the defective structures. At the same time, the water dissociation process is more energetically favorable, and the reactivity of MnPX3 is determined by the vacancy configuration. Following Nørskov's approach, the HER catalytic performance is evaluated by calculating the hydrogen adsorption free energy on the respective MnPX3 surface. Our calculation results demonstrate that defective 2D MnPX3 with low coordinated P shows significantly higher HER performance compared to the pristine counterpart.

Influence of laser texturing on interfacial bonding strength of W/Cu joint by spark plasma sintering

In this study, a spark plasma sintering(SPS) technique is used to bond tungsten(W) and copper(Cu) based on the laser texturing tungsten surface. Five microstructures, namely pristine structure, micropores1, micropores2, microgrooves, and nanoripples, were fabricated on the tungsten surface, and the effect of the microstructures on the shear properties, thermal shock resistance, and thermal conductivity of the tungsten/copper joints was investigated. W with the original planar morphology did not form an effective connection with copper, while the W with other surface structures connected well with copper. The results of the shear resistance experiments showed that the micro/nano interface structure significantly improved the shear resistance of W/Cu, where the microgroove structure presented the highest shear strength of 88.19 MPa. It was found that the volume of copper infiltrated into the microstructures had the greatest effect on the thermal shock resistance of the tungsten/copper joint. The highest number of microgroove thermal shock resistance was 297 times. The highest thermal diffusion coefficient of 82.31 mm²/s was obtained for the nanoripple specimens.

Local Structure in Sodium Antiperovskite Ionic Conductors

Antiperovskites, which can serve as solid state electrolytes, have recently received great attention due to their high ionic conductivity[1]. Compared to typical solid-state ionic conductors, Na3OCl antiperovskite exhibits a unique ionic conductivity behavior that deviates from a linear Arrhenius behavior, in which the ionic conductivity increases rapidly with increasing temperature[2,3]. Many different structural origins affecting the ion conduction mechanism in antiperovskite have been proposed using calculation, such as vacancy/dumbbell migration[4]. The lack of direct experimental local structural investigations makes it challenging to fully understand the structural origins for high ionic conductivity, even resulting in limitations in the development of material designs for good ionic conductors. Complicating their investigation, these materials are also extremely sensitive to air, preventing many structural studies.Here, local structural investigations of Na3OCl are performed using aberration corrected scanning transmission electron microscopy (STEM) to elucidate the atomistic mechanisms underlying its high ionic conduction. To avoid degradation in air, we use an inert gas transfer system that has several advantages. First, transfer in an inert gas environment without air/moisture exposure enables the sample to retain the on-stoichiometry. Second, both room temperature and cryo experiments are possible, which allows pristine structure investigation at application relevant temperatures. Beyond the environment, Na3OCl is also very electron beam sensitive. We will show that low-dose imaging methods, such as parallel beam electron diffraction and electron ptychography, can provide new insights and allow for direct imaging of the local structure. For example, diffuse electron scattering (scattering between the Bragg reflections) is used to investigate subtle differences resulting from local structure, atomic defects, and phonon dispersion relations through combination with electron scattering simulations and Molecular Dynamics (MD) using machine learned potentials. We will then demonstrate how electron ptychography can achieve deep sub-angstrom spatial resolution with low dose conditions and provide direct insights into the migration of Na-ions. Overall, the inert gas transfer system and low-dose diffraction and STEM ptychography enable direct imaging of local structures even for reactive and electron beam sensitive materials, such as antiperovskite electrolytes. The understanding of local structure related to the high ionic conductivity will be crucial for designing high-performance solid electrolytes.

Electronic structure and physical properties of the monolayer Kagome lattice system AV3Sb5 (A = K, Rb, Cs)

In this study, we employ density functional theory to investigate the electronic structure and physical properties of the monolayer Kagome lattice system of AV3Sb5 (A = K, Rb, Cs). Our results reveal that charge density wave (CDW) states are present not only in the bulk, but also in the monolayer systems. Notably, we find that the monolayer system exhibits a higher stability of the CDW states compared to the corresponding bulk system. Additionally, we find that external pressure can induce the instability of the CDW states, driving the pristine structure to a stable phase. Our band unfolding and phonon calculations also provide additional support for these findings. Our study suggests that manipulating the dimensions of Kagome lattice materials as well as applying external pressure can lead to desired physical properties, thereby paving the way for material design advancements in the family of AV3Sb5 Kagome lattice systems.

Highly Stable MWCNT@NVP Composite as a Cathode Material for Na-Ion Batteries.

A 3D framework with Nasicon structured polyanionic Na3V2(PO4)3 (NVP) has been emphasized as a leading cathode material for sodium-ion batteries (SIBs) due to its high working voltage plateau, structural stability, and good rate performance. Herein, pristine NVP and MWCNT@NVP composite synthesized via a facile solid-state method are examined and compared as cathode materials for Na-ion batteries. The morphological study confirms the uniform distribution of MWCNTs in the pristine NVP structure. Impedance spectroscopy clearly confirms more diffusion of Na ions for the MWCNT@NVP composite as compared to pristine NVP, considering its diffusion coefficient which directly implies on an increase in specific capacity. MWCNT@NVP (FNV-2) showed specific discharge capacity 110 mAhg-1 at 0.1C current rate which is almost stable at higher current rates with marginal fading. However, the pristine NVP shows capacity loss at a higher current rate. It is noteworthy that the MWCNT@NVP composite shows stable performance with marginal specific capacity fading (1%) compared to pristine (15%). This is because of the mechanical integrity and stability afforded to the composite by the intertwined MWCNT framework in the MWCNT@NVP composite matrix against electrode degradation during the electrochemical reaction. More significantly, even at a higher current rate, that is, at 10 C, the composite recorded a very stable and excellent Columbic efficiency of 97% with a reversible specific capacity of 94 mAhg-1 after 2000 cycles. An enhanced electrochemical performance, that is, rate capability and cycling stability, demonstrates the high potential of the MWCNT@NVP composite for Na-ion storage. Moreover, a sodium-ion full cell with hard carbon demonstrated a reversible capacity of 103 mAhg-1 at C/20 current rate, which clearly demonstrates that MWCNT@NVP is a promising cathode material for sodium-ion batteries.

Cork-Derived Carbon Sheets for High-Performance Na-Ion Capacitors.

S-doped carbon sheets have been easily prepared by deconstructing the 3D cellular structure of a fully sustainable and renewable biomass material such as cork through a mild ball-milling process. S-doping of the material (>14 wt % S) has been achieved by using sulfur as an earth-abundant, cost-effective, and environmentally benign S-dopant. Such synthesized materials provide large Na storage capacities in the range of 300-550 mAh g-1 at 0.1 A g-1 and can handle large current densities of 10 A g-1, providing 55-140 mAh g-1. Their increased packing density compared to the 3D pristine structure allows them to also provide good volumetric capacities in the range of 285-522 mAh cm-3 at 0.1 A g-1 and 53-133 mAh cm-3 at 10 A g-1. In addition, highly porous carbon sheets (SBET > 2700 m2 g-1) have been produced from the same carbon precursor by rationally designing the chemical activation approach. These materials are able to provide good anion storage capacities/capacitances of up to 100-114 mAh g-1/163-196 F g-1. A sodium-ion capacitor assembled with the optimized S-doped carbon sheets and the highly porous carbon sheets with mass matching ratios provided the best energy/power characteristics (90 Wh kg-1 at 29 kW kg-1) in combination with robust cycling stability over 10,000 cycles, with a capacity fade of only 0.0018% per cycle.

Thermal-protective and oxygen-resistant nanocoating using silica-nanocomposites for laser thinning of polymorphic molybdenum ditellurides

Laser irradiation has been investigated as a method of fabricating atomically thin crystals from layered two-dimensional (2D) materials with precise thickness control. However, during laser irradiation, inevitable structural changes can occur in the 2D materials due to the high thermal energy, altering their physical and chemical properties and introducing disorder, which has hindered the study and use of the intrinsic properties of atomically thin materials. In this study, we report a laser thinning method using a new coating material, a layered silica-based nanocomposite (SNC), that preserves the pristine crystal structure of a polymorphic 2D material, MoTe2, down to an atomically thin geometry. We confirmed that the nano-porous coating of layered silica-based nanocomposite (SNC) behaved as a good thermal-protective and oxygen-resistant material during the laser thinning process using various experimental techniques, atomic force microscopy, Raman spectroscopy and scanning photoelectron microscopy with synchrotron radiation. Accordingly, our SNC coating of 2D materials is a promising way to engineer the phase and geometry of polymorphic 2D materials, enabling versatile applications in various optoelectronic, spintronic, and electronic devices.

Stable antiferromagnetic property and tunable electronic structure of two-dimensional MnPX3 (X = S and Se) from pristine structure to Janus phase

Transition-metal phosphorus trichalcogenides have been considered as very promising two-dimensional (2D) magnetic candidates up-to-date. We performed a systematical first-principles study on the electronic structures and magnetic properties of pristine MnPX3 (X = S and Se) and Janus Mn2P2S3Se3 monolayers. All monolayers behave as a direct-band-gap semiconductor in antiferromagnetic ground state which is caused by strong direct and indirect exchange interactions. It is found that the electronic structures and magnetic properties can be manipulated by Janus phase. The calculated band gap is 2.44 eV, 1.80 eV and 1.86 eV for MnPS3, MnPSe3 and Mn2P2S3Se3 with a valley polarization with consideration of spin–orbital coupling (SOC), respectively. In particular, significant energy-splittings emerge in the SOC-band structures of Janus Mn2P2S3Se3 due to its broken-inversion-symmetry. Estimated by Monte Carlo simulations, the Néel temperature is 96 K, 71 K and 79 K based on Ising model while halved down to 41 K, 33 K and 36 K on the basis of XY model for MnPS3, MnPSe3 and Mn2P2S3Se3, respectively, indicating the XY model should be more reliable to describe the spin dynamics. Our research offers an insight into the magnetic mechanism and paves a feasible path to modulate the magnetism for 2D magnets in realistic applications on spintronics.

Stable 2R van der Waals heterostructures of NbS2 and MSe2 for M=Mo and W

In this letter, we investigate the stable and commensurate van der Waals heterostructures of metallic and semiconducting $1H$ transition-metal dichalcogenides, NbS$_2$ and MoSe$_2$ (WSe$_2$), which possess almost the same lattice constant of the pristine honeycomb structure. In the most stable structure, the metallic and semiconducting layers are stacked in a similar manner to $3R$ stacking but the period is a pair of a metallic layer and a semiconducting layer. The heterostructure aligns the spin-polarization in each valley among all layers and induces spin-selective charge transfer between the metallic and semiconducting layers. Especially in hetero-trilayers, the electronic spin is conserved due to mirror symmetry along the out-of-plane axis in contrast to the $3R$ stacking structure. A drastic enhancement of spin Hall effect is numerically shown as an example of electronic spin transport phenomena in the hetero-trilayers.

Reduced graphene oxide-functionalized zinc oxide nanorods as promising nanocomposites for white light emitting diodes and reliable UV photodetection devices

We present a breakthrough in the development of novel nanocomposites based on reduced graphene oxide (RGO)-functionalized zinc oxide (ZnO) nanorods that hold exceptional promise for their use in white light emitting diodes (LEDs) and reliable UV photodetection. The nanorods had a pristine hexagonal wurtzite structure, as confirmed by XRD analysis. SEM images revealed sandwich-like nanocomposites with ZnO nanorods coated in reduced graphene oxide and embedded between two layers of RGO. The study also confirmed the hybridization and interactions between the layers using Raman measurements. The resulting nanocomposites displayed a lower band gap energy than ZnO and exhibited unique photoluminescence spectra with a white PL light. The photodetector based on RGO/ZnO/RGO sandwich structures demonstrated exceptional photoresponse, with higher photocurrent under UV illumination, making it highly promising for a wide range of optoelectronic applications. Overall, this study offers a novel and powerful approach to create nanocomposite structures with enhanced optical characteristics.

Determination of γ-aminobutyric acid in fermented soybean products by HPLC coupled with pre-column derivatization

This study reports a pre-column derivatization HPLC stragety to determine the content of GABA in fermented soybean products. 9-Fluorenylmethyloxycarbonyl chloride (Fmoc-Cl) is employed as the derivative reagent with chromophore linked to GABA, which lacks of chromophore for UV/DAD analysis in its pristine structure. After the detection wavelength was confirmed, the derivatization and analysis conditions were also optimized, including pH and amount of boric acid buffer, amount of derivative reagent, the mobile phases and their gradient. Methodological investigation showed that the derivatized GABA (Fmoc-GABA) has good linearity in the range of 1–100 µg/mL, low limit of quantification (LOQ, at 1 µg/mL) and limit of detection (LOD, at 0.3 µg/mL), and good recoveries of three spiked levels (between 83.8% and 100.8% with RSDs less than 5%). Furthermore, thirty-two commercial fermented soy products in four matrices (soy sauce, soy paste, bean curd, lobster sauce) were analyzed by the proposed method for validation. As a consequence, the concentrations of GABA in these soy products were in the range of 48.4–381 mg/kg.

Facile coating strategy of Si/C composite anode for high-performance lithium-ion battery

Attributed to its high capacity by alloying with lithium, silicon is considered to be new generation of anodes that can replace graphite and receives much attention. Alleviating the electrode failure caused by volume expansion during lithiation and shrink during delihiation in silicon anodes plays a pivotal role in promoting the industrial application of silicon anodes. In this article, we proposed a facile carbon coating strategy on the surface of silicon nanospheres to buffer the stress during charge and discharge. By controlling the low molecular weight, an ethanol-soluble phenolic resin was synthesized and further self-assembled on the surface of silicon nanoparticles to form the precursor. Uniform Si/C composites were fabricated via pyrolysis. Diffraction of x-rays confirmed that the silicon retained the pristine crystalline structure. Scanning electron microscopy revealed a homogeneous wrap of the amorphous carbon layer on the superficies of the silicon. The galvanostatic charge-discharge test proved the excellent durability of Si/C anodes. Undergoing 50 cycles of galvanostatic lithiation/delithiation at 0.2C, the retention capacity was 96%, as high as 800 mAh/g. This facile but efficient strategy is compatible with large-scale production and improves the feasibility of the practical application of silicon-based anodes.

Transmission electron microscopy studies of organic–inorganic hybrid perovskites: Advances, challenges, and prospects

In the last few years, organic–inorganic hybrid perovskites (OIHPs) have attracted immense research and industry attention for their application as light absorbers in solar cells and light-emitting diodes. Characterizing OIHP materials and optoelectronic devices using transmission electron microscopy (TEM)-based techniques has played a large role in understanding their structural, compositional, and electronic properties. However, the highly energetic and electrically charged electron beam radiation used in TEM can result in damage to the pristine structure, as OIHPs are unstable and highly sensitive to electron beams. This damage potentially obscures intrinsic information and leads to a serious misunderstanding of the microscopic structure–property–performance relationship for OIHP optoelectronic devices. To address this issue, we first review the electron and ion beam-induced degradation mechanism of OIHPs, followed by a review of the development of ultra-low-dose TEM techniques that can able to minimize this damage, thus can able to obtain reliable, intrinsic structural information about OIHPs from the atomic to micrometer length scales. Finally, we suggest a protocol for appropriate TEM specimen preparation and characterization techniques. This protocol can help ensure that future TEM studies of OIHPs give reliable information, thereby enabling a deeper understanding and optimization of the performance and long-term stability of OIHP optoelectronic devices.