Machine learning and DFT investigation of CO, CO2 and CH4 adsorption on pristine and defective two-dimensional magnesene.

Adsorption study of environmentally toxic small gas molecules on two-dimensional (2D) materials plays a significant role in analyzing the performance of sensors. In this work, density functional theory (DFT) and machine learning (ML) techniques have been employed to systematically study the adsorption properties of CO, CO2, and CH4 gas molecules on the pristine and defective planar magnesium monolayer, known as magnesene (2D-Mg). The DFT analysis showed that mechanically robust 2D-Mg retains its metallicity in the presence of both mono and di-vacancy defects. Our observations have shown that 2D-Mg, whether defective or pristine, exhibits distinct adsorption behaviors towards CO, CO2, and CH4 gas molecules, including varying chemisorption and physisorption, charge transfer, and distance from the gas molecules. When analyzing the recovery time of gas molecules at room temperature, it is clear that adsorption energy has a direct correlation with the adsorption-desorption cycles, and CH4 possesses an ultra-low recovery time (15.27 ps) compared to CO2 (1.04 ns) and CO (0.90 µs) molecules. The analysis showed that defects do not have a significant impact on the work function of 2D-Mg. However, the work function decreased upon adsorption of CH4, resulting in improved sensitivity due to changes in the electronic properties. Additionally, we explored supervised ML regression models to evaluate their ability to act as a surrogate for the DFT-based adsorption energy calculation. Using both system statistics and smooth overlap of atomic position (SOAP)-based featurization, we observed that adsorption energies can be predicted with a mean absolute error of 0.10 eV.

Longitudinal Lung Function Assessment of Patients Hospitalized With COVID-19 Using 1H and 129Xe Lung MRI.

BACKGROUND: Microvascular abnormalities and impaired gas transfer have been observed in patients with COVID-19. The progression of pulmonary changes in these patients remains unclear. RESEARCH QUESTION: Do patients hospitalized with COVID-19 without evidence of architectural distortion on structural imaging exhibit longitudinal improvements in lung function measured by using 1H and 129Xe MRI between 6 and 52 weeks following hospitalization? STUDY DESIGN AND METHODS: Patients who were hospitalized with COVID-19 pneumonia underwent a pulmonary 1H and 129Xe MRI protocol at 6, 12, 25, and 51 weeks following hospital admission in a prospective cohort study between November 2020 and February 2022. The imaging protocol was as follows: 1H ultra-short echo time, contrast-enhanced lung perfusion, 129Xe ventilation, 129Xe diffusion-weighted, and 129Xe spectroscopic imaging of gas exchange. RESULTS: Nine patients were recruited (age 57 ± 14 [median ± interquartile range] years; six of nine patients were male). Patients underwent MRI at 6 (n = 9), 12 (n = 9), 25 (n = 6), and 51 (n = 8) weeks following hospital admission. Patients with signs of interstitial lung damage were excluded. At 6 weeks, patients exhibited impaired 129Xe gas transfer (RBC to membrane fraction), but lung microstructure was not increased (apparent diffusion coefficient and mean acinar airway dimensions). Minor ventilation abnormalities present in four patients were largely resolved in the 6- to 25-week period. At 12 weeks, all patients with lung perfusion data (n = 6) showed an increase in both pulmonary blood volume and flow compared with 6 weeks, although this was not statistically significant. At 12 weeks, significant improvements in 129Xe gas transfer were observed compared with 6-week examinations; however, 129Xe gas transfer remained abnormally low at weeks 12, 25, and 51. INTERPRETATION: 129Xe gas transfer was impaired up to 1 year following hospitalization in patients who were hospitalized with COVID-19 pneumonia, without evidence of architectural distortion on structural imaging, whereas lung ventilation was normal at 52 weeks.

Rational design of selenium inserted 1T/2H mixed-phase molybdenum disulfide for energy storage and pollutant degradation applications.

MoS2based materials are recognized as the promising candidate for multifunctional applications due to its unique physicochemical properties. But presence of lower number of active sites, poor electrical conductivity, and less stability of 2H and 1T MoS2inherits its practical applications. Herein, we synthesized the Se inserted mixed-phase 2H/1T MoS2nanosheets with abundant defects sites to achieve improved overall electrochemical activity. Moreover, the chalcogen insertion induces the recombination of photogenerated excitons and enhances the life of carriers. The bifunctional energy storage and photocatalytic pollutant degradation studies of the prepare materials are carried out. Fabricated symmetric solid-state supercapacitor showed an exceptional capacitance of 178 mF cm-2with an excellent energy density of 8µWh cm-2and power density of 137 mW cm-2, with remarkable capacitance retention of 86.34% after successive 8000 charge-discharge cycles. The photocatalytic dye degradation experiments demonstrate that the prepared Se incorporated 1T/2H MoS2is a promising candidate for dye degradation applications. Further, the DFT studies confirmed that the Se inserted MoS2is a promising electrode material for supercapacitor applications with higherCQdue to a larger density of states near Fermi level as compared to pristine MoS2.

From fundamental to CO2 and COCl2 gas sensing properties of pristine and defective Si2BN monolayers.

In this work, the capability of Si2BN monolayers (Si2BN-MLs) to sense CO2 and COCl2 molecules was investigated by analyzing the structural, electronic, mechanical and gas sensing properties of defect-free and defective Si2BN-ML structures. Electronic property analysis revealed that the Si2BN-ML retains its metallicity in the presence of vacancy defects. The computed vacancy formation energies of Si, B and N monovacancies are 3.25 eV, 2.27 eV and 2.55 eV, respectively, which indicate that the B monovacancy is thermodynamically more feasible. Besides, both pristine and defective Si2BN-ML structures show good mechanical stability. To validate the gas sensing properties, the adsorption energy and charge transfer were analysed, showing that both pristine and defective Si2BN-ML structures receive considerable charges from the CO2 and COCl2 molecules via a stable physisorption process. The work function analysis revealed that a minute increase <0.10 eV is responsible for the enhanced selectivity and sensitivity of Si2BN-ML structures in detecting CO2 and COCl2 molecules. The low adsorption energies of both CO2 and COCl2 gas molecules during the interaction with Si2BN-ML structures signify the possibility of a large number of adsorption-desorption cycles with an ultra-low recovery time, 0.174 ns for CO2 and 0.016 ns for COCl2, suitable for efficient gas sensing applications.

Hydrogen-induced tunable electronic and optical properties of a two-dimensional penta-Pt2N4 monolayer.

Most known two-dimensional materials lack a suitable wide-bandgap, and hydrogenation can be effectively utilized to tune the bandgap of some 2D materials. By employing density functional theory calculations, we investigate the effect of hydrogenation on the electronic and optical properties of a recently reported anisotropic penta-Pt2N4 monolayer. The results show that penta-Pt2N4 is thermally and mechanically stable after hydrogenation and also possesses anisotropic Young's modulus and Poisson's ratio. The electronic property analysis using the hybrid functional reveals that penta-Pt2N4 exhibits a bandgap of 1.10 eV, and the hydrogenation significantly enhances the bandgap to 2.70 eV. Furthermore, the hydrogenated Pt2N4 displays a strong optical absorption of up to 6.45 × 105 cm-1 in the ultraviolet region, and low absorption and low reflectivity in the visible region. Our results strongly suggest that the hydrogenated Pt2N4 has tunable electronic and optical properties for applications as a hole-transport material layer in solar cells in the visible region, and as an ultraviolet detector in the ultraviolet region of the electromagnetic spectrum.

A new planar BCN lateral heterostructure with outstanding strength and defect-mediated superior semiconducting to metallic properties.

Motivated by the recent synthesis of boron-carbon-nitride (BCN) monolayers with different atomic compositions, we propose a novel planar BCN lateral heterostructure with a combination of graphene and hexagonal boron nitride (h-BN) counterparts. Density functional theory (DFT) and classical molecular dynamics (CMD) simulations are integrated to examine the effects of defects (vacancy and Stone-Wales (SW) defects) and temperature on the physical properties of the BCN heterostructure. We found that structures with SW defects possess the lowest (4.10 eV) and those with vacancy defects possess the highest (7.32 eV) defect formation energy. DFT results show that the computed mechanical properties of the pristine and defective BCN are complementary to those of graphene, and CMD results establish that the size effect on mechanical properties is insignificant. DFT calculations also reveal that the pristine and SW defect filled BCN retain the direct semiconducting electronic characteristics, while C and B mono-vacancies interestingly make it a metallic material due to the slight overlapping of the bands at the Fermi level, and the N mono-vacancy causes a small indirect bandgap (0.08 eV). Besides, the presence of defects significantly changes the work function of BCN due to the lattice rearrangement. Herein, we argue that the defect mediated design of BCN heterostructures can provide new opportunities for plausible applications including energy conversion and storage, and high speed optical and electronic devices due to their semiconducting-metallic functionality and superior mechanical properties.

Role of Transition Metals in Layered Double Hydroxides for Differentiating the Oxygen Evolution and Nonenzymatic Glucose Sensing.

Layered double hydroxides (LDH) belong to the class of two-dimensional materials having a wide variety of applications ranging from energy storage to catalysis. Often, these materials when used for nonenzymatic electrochemical glucose sensing tend to be interfering with oxygen evolution reaction (OER), resulting in overestimation of the glucose. Herein, to address this, NiFe-based LDH were selected because of their ability to vary the metal ratios. The synthesized LDH have been characterized using various spectroscopic and microscopic techniques. Among the LDH synthesized, Ni4Fe-LDH have been able to differentiate the glucose oxidation potential and the onset potential of OER with minimum interference. The Ni4Fe-LDH sensor shows a sensitivity of 20.43 µA mM-1 cm-2 in the linear range of 0-4 mM concentrations. To further enhance the sensitivity, composites of reduced graphene oxide (rGO) have been synthesized in situ, and the Ni4Fe/rGO5 composites have shown an increased sensitivity of 176.8 µA mM-1 cm-2 attributed to the charge-transfer interactions. To understand the experimental observations, detailed computational studies have been carried out to study the effect of the electronic structure on the metal ratios of the LDH and its role in differentiating glucose sensing and the oxygen evolution reaction. Along with this, theoretical calculations are also carried out on LDH-graphene composites to study the charge-transfer interactions.

Atomistic insights into the anisotropic mechanical properties and role of ripples on the thermal expansion of h-BCN monolayers.

Monolayer boron-carbon-nitrogen (h-BCN) has been studied in comparison with graphene and hexagonal boron nitride (h-BN) using classical molecular dynamics (MD) simulations with an aim to better understand the structural and thermal behaviors and the anisotropic mechanical properties. The structural features of the simulated sample were analyzed using the pair-correlation function and a full width at half maximum (FWHM). As a hetero-structure of h-BN and graphene, the C-C bond in the h-BCN is responsible for an improved FWHM compared to graphene. Consistent with graphene and h-BN, the in-plane lattice parameter of h-BCN shows thermal contraction over a wide range of temperatures and exhibits a system size dependence. The observed thermal contraction is explained by the presence of out-of-plane bending modes excited at finite temperatures. A tensile test has been performed as a suitable means of measuring the mechanical properties of the h-BCN sheet for zigzag and armchair orientations and found that it is mechanically anisotropic and stable under various strain directions and temperatures. The fracture strength of h-BCN is affected by loading direction and temperature. We found that the Young's modulus of h-BCN is smaller than that of graphene but is higher than that of an h-BN monolayer, suggesting that h-BCN has high mechanical stiffness. Our modeling-based findings provide a guide for future experiments concerning the physical properties of this advanced composite material.

Atomistic Dynamics Investigation of the Thermomechanical Properties and Li Diffusion Kinetics in ψ-Graphene for LIB Anode Material.

A fundamental understanding of the thermomechanical properties of electrode materials and Li-ion diffusion kinetics is indispensable for designing high-performance Li-ion batteries (LIBs) with high structural stability and safety. Herein, we performed both molecular dynamics (MD) simulations and density functional theory (DFT) calculations to investigate the thermomechanical properties and Li diffusion kinetics in a two-dimensional (2D) defect-filled graphene-like membrane consisting of 5-, 6-, and 7-membered rings, called psi (ψ)-graphene. Our results reveal that ψ-graphene has a negative linear thermal expansion coefficient, a high specific heat capacity, and high elastic constants that satisfy the Born's criterion for mechanical stability, which can be elucidated as the evidence of strong anharmonicity in ψ-graphene because of the soft out-of-plane bending modes. These characteristics can help prevent the thermal runaway that can occur during overheating and prevent structural damage because of the severe volume expansion of the LIBs. In addition, the Li diffusion coefficient was estimated to be 10-9 cm2/s at 300 K with a low Li migration activation energy (<0.16 eV), which suggests favorable electrode kinetics with fast Li conduction. Our DFT calculations also show that ψ-graphene can possess a fairly good theoretical capacity (339 mA h g-1) and a lower Li diffusion barrier (<0.21 eV). Our results suggest that the new fundamental insights presented here will help to stimulate further experimental work on ψ-graphene for promising future applications as a superior electrode material for LIBs.

Assessment of the mechanical properties of monolayer graphene using the energy and strain-fluctuation methods.

Molecular statics and dynamics simulations were performed to investigate the mechanical properties of a monolayer graphene sheet using an efficient energy method and strain-fluctuation method. Using the energy method, we observed that the mechanical properties of an infinite graphene sheet are isotropic, whereas for a finite sheet, they are anisotropic. This work is the first to report the temperature-dependent elastic constants of graphene between 100 and 1000 K using the strain-fluctuation method. We found that the out-of-plane thermal excursions in a graphene membrane lead to strong anharmonic behavior, which allows large deviations from isotropic elasticity. The computed Young's modulus and Poisson's ratio of a sheet with an infinite spatial extent are 0.939 TPa and 0.223, respectively. We also found that graphene sheets with both finite and infinite spatial extent satisfy the Born elastic stability conditions. We extracted the variation in bending modulus with the system size at zero kelvin (0.83 eV) using a formula derived from the Foppl-von Karman approach. When the temperature increases, the Young's modulus of the sample decreases, which effectively reduces the longitudinal and shear wave velocities.

Directional anisotropy, finite size effect and elastic properties of hexagonal boron nitride.

Classical molecular dynamics simulations have been performed to analyze the elastic and mechanical properties of two-dimensional (2D) hexagonal boron nitride (h-BN) using a Tersoff-type interatomic empirical potential. We present a systematic study of h-BN for various system sizes. Young's modulus and Poisson's ratio are found to be anisotropic for finite sheets whereas they are isotropic for the infinite sheet. Both of them increase with system size in accordance with a power law. It is concluded from the computed values of elastic constants that h-BN sheets, finite or infinite, satisfy Born's criterion for mechanical stability. Due to the the strong in-plane sp2 bonds and the small mass of boron and nitrogen atoms, h-BN possesses high longitudinal and shear velocities. The variation of bending rigidity with system size is calculated using the Foppl-von Karman approach by coupling the in-plane bending and out-of-plane stretching modes of the 2D h-BN.

Wound Dressings During Radiotherapy for Cancer: A Survey of Practice.

BACKGROUND: Patients undergoing radiotherapy may experience changes to the skin that require dressings. Recommendations regarding radiating through wound dressings have been variable and relate to the concern regarding surface dose increase or bolus effect. OBJECTIVES: The purpose of this article is to identify current evidence and practice through literature review and a national environmental scan. METHODS: Nurses from 18 radiation oncology centers in Canada were surveyed about current practice. In-depth telephone interviews were conducted with four nurse participants to further understand the context of this issue within the nursing practice environment. FINDINGS: The integrated results of the study were reviewed with five clinical experts to make recommendations for research, practice, leadership, and policy. Implications for clinical practice included the involvement of radiation oncology nurses in the treatment planning team, development of clinical practice tools, and the relevance of the Person-Centered Nursing framework for wound management during radiotherapy.

Temperature dependent structural properties and bending rigidity of pristine and defective hexagonal boron nitride.

Structural and thermodynamical properties of monolayer pristine and defective boron nitride sheets (h-BN) have been investigated in a wide temperature range by carrying out atomistic simulations using a tuned Tersoff-type inter-atomic empirical potential. The temperature dependence of lattice parameter, radial distribution function, specific heat at constant volume, linear thermal expansion coefficient and the height correlation function of the thermally excited ripples on pristine as well as defective h-BN sheet have been investigated. Specific heat shows considerable increase beyond the Dulong-Petit limit at high temperatures, which is interpreted as a signature of strong anharmonicity present in h-BN. Analysis of the height fluctuations, ⟨h2⟩, shows that the bending rigidity and variance of height fluctuations are strongly temperature dependent and this is explained using the continuum theory of membranes. A detailed study of the height-height correlation function shows deviation from the prediction of harmonic theory of membranes as a consequence of the strong anharmonicity in h-BN. It is also seen that the variance of the height fluctuations increases with defect concentration.