The effect of mixed termination composition in Sc, Ti, and V-based MXenes.

In this study, we investigate the effect of mixed surface terminations (F, O, OH) on the properties of MC MXenes (M = Sc, Ti, V). We explore how different compositions and patterns of terminal groups affect the stability and electronic properties of these 2D materials. The bond dissociation energies and cohesion energies show a clear preference for F-terminations in ScC, while Ti- and V-based MXenes prefer O-terminations.

MnC MXene functionalized by oxygen is a semiconducting antiferromagnet and an efficient visible light absorber.

Manganese-based MXenes are promising two-dimensional materials due to the broad palette of their magnetic phases and the possibility of experimental preparation because the corresponding MAX phase was already prepared. Here, we systematically investigated geometrical conformers and spin solutions of oxygen-terminated MnC MXene and performed subsequent many-body calculations to obtain reliable electronic and optical properties. Allowing energy-lowering using the correct spin ordering supercell magnetic motifs is essential for the MnCO system.

MXene's surface functionalization patterns and their impacts on magnetism.

Two-dimensional transition metal carbides and nitrides (MXenes) are a promising group of materials with a broad palette of applications. Surface terminations are a result of MXene preparation, and post-processing can also lead to partial coverage. Despite applicability and fundamental properties being driven by termination patterns, it is not fully clear how they behave on MXene surfaces with various degrees of surface coverage.

Correction: α-FeO/TiO 3D hierarchical nanostructures for enhanced photoelectrochemical water splitting.

Correction for 'α-FeO/TiO 3D hierarchical nanostructures for enhanced photoelectrochemical water splitting' by Hyungkyu Han , , 2017, , 134-142, https://doi.org/10.1039/C6NR06908H.

Prediction of induced magnetism in 2D TiC based MXenes by manipulating the mixed surface functionalization and metal substitution computed by xTB model Hamiltonian of the DFTB method.

We employed the recently developed density functional tight binding (DFTB) method's Hamiltonian, GFN1-xTB, for modeling the mixed termination in TiC MXenes, namely three types of termination by combining -O and -OH, -O and -F, and -F and -OH. We demonstrated that the approach yields reliable predictions for the electronic and magnetic properties of such MXenes. The first highlighted result is that the mixed surface functionalization in TiCAB MXenes induces spin polarization with diverse magnetic alignments, including ferromagnetism and two types of antiferromagnetism.

Excitons, optical spectra, and electronic properties of semiconducting Hf-based MXenes.

Semiconducting MXenes are an intriguing two-dimensional (2D) material class with promising electronic and optoelectronic properties. Here, we focused on recently prepared Hf-based MXenes, namely, Hf3C2O2 and Hf2CO2. Using the first-principles calculation and excited state corrections, we proved their dynamical stability, reconciled their semiconducting behavior, and obtained fundamental gaps by using the many-body GW method (indirect 1.

Modeling size and edge functionalization of MXene-based quantum dots and their effect on electronic and magnetic properties.

In the last six years, the synthesis of MXene-based quantum dots (MXQDs) has gained widespread attention. Due to the quantum confinement effect, it is possible to significantly improve their properties compared to 2D counterparts, such as higher chemical stability and better electronic and optical properties. However, despite the growing interest in their properties, much remains unexplored.

Toward accurate modeling of structure and energetics of bulk hexagonal boron nitride.

Materials that exhibit both strong covalent and weak van der Waals interactions pose a considerable challenge to many computational methods, such as DFT. This makes assessing the accuracy of calculated properties, such as exfoliation energies in layered materials like hexagonal boron nitride (h-BN) problematic, when experimental data are not available. In this paper, we investigate the accuracy of equilibrium lattice constants and exfoliation energy calculation for various DFT-based computational approaches in bulk h-BN.

Benchmarking fundamental gap of ScC(OH) MXene by many-body methods.

ScC(OH) is a prototypical non-magnetic member of MXenes, a promising transition-metal-based 2D material family, with a direct bandgap. We provide here a benchmark of its fundamental gap Δ obtained from many-body GW and fixed-node diffusion Monte Carlo methods. Both approaches independently arrive at a similar value of Δ ∼ 1.

Electronic Nature Transition and Magnetism Creation in Vacancy-Defected TiCO MXene under Biaxial Strain: A DFTB + U Study.

The structural, electronic, and magnetic properties of vacancy defect in TiCO MXene and the effect of strain have been investigated using the density functional tight-binding (DFTB) approach including spin-polarization with Hubbard onsite correction (DFTB + U). The band gap of pure TiCO is ∼1.3 eV, which decreases to ∼0.

The electronic and optical properties of III-V binary 2D semiconductors: how to achieve high precision from accurate many-body methods.

Seven hexagonal 2D materials consisting of elements of the IIIA and VA groups (BN, BP, BAs, AlN, GaN, GaP, and GaAs) were theoretically studied using first-principles methods. Simultaneous convergence in all principal parameters of the accurate many-body perturbational GW approach and the subsequent Bethe-Salpeter equation (BSE) was necessary to achieve precise fundamental and optical gaps, exciton binding energies, and absorbance spectra. Various convergence rates of studied properties in the case of different materials were visualized and explained.

Iron Nitride Nanoparticles for Enhanced Reductive Dechlorination of Trichloroethylene.

Nitriding has been used for decades to improve the corrosion resistance of iron and steel materials. Moreover, iron nitrides (FeN) have been shown to give an outstanding catalytic performance in a wide range of applications. We demonstrate that nitriding also substantially enhances the reactivity of zerovalent iron nanoparticles (nZVI) used for groundwater remediation, alongside reducing particle corrosion.

DFTB investigations of the electronic and magnetic properties of fluorographene with vacancies and with adsorbed chemical groups.

The electronic and magnetic properties of fluorographene (CF) in the presence of F-vacancy defects and/or chemical groups (-OH, -CN, or -NH) were computationally investigated within the framework of the density functional tight-binding (DFTB) method. The current method parameterization allowed us to perform accurate electronic structure calculations (at the level of many-body methods in the particular case of CF) for hundreds of atoms in the computational cell. We show that the F-vacancy and/or chemical groups influence the magnetic structure, which depends on the number of defects and their distribution between the two sides of the graphene plane.

Lattice dynamics in the conformational environment of multilayered hexagonal boron nitride (h-BN) results in peculiar infrared optical responses.

Stacking mismatches in hexagonal boron nitride (h-BN) nanostructures affect their photonic, mechanical, and thermal properties. To access information about the stacked configuration of layered ensembles, highly sophisticated techniques like X-ray photoemission spectroscopy or electron microscopy are necessary. Here, instead, by taking advantage of the geometrical and chemical nature of h-BN, we show how simple structural models, based on shortened interplanar distances, can produce effective charge densities.

Fundamental gap of fluorographene by many-body GW and fixed-node diffusion Monte Carlo methods.

Fluorographene (FG) is a promising graphene-derived material with a large bandgap. Currently existing predictions of its fundamental gap (Δ) and optical gap (Δ) significantly vary when compared with experiment. We provide here an ultimate benchmark of Δ for FG by many-body GW and fixed-node diffusion Monte Carlo (FNDMC) methods.

A theoretical study of adsorption on iron sulfides towards nanoparticle modeling.

Surface modification of zero-valent iron (nZVI) nanoparticles, which are frequently used in the removal of chlorinated hydrocarbons from contaminated groundwater, can increase their surface stability without significant loss of reactivity. Sulfidation is a process during which thin iron sulfide phases are formed on nZVI particles. In this work, the adsorption capability of two iron sulfide minerals (mackinawite and pyrite) and ZVI with respect to two small polar molecules (H2O and H2S) and trichloroethylene (TCE) was modeled by using the quantum mechanics (QM) approach.

Optical Gaps and Excitonic Properties of 2D Materials by Hybrid Time-Dependent Density Functional Theory: Evidences for Monolayers and Prospects for van der Waals Heterostructures.

The optical properties of two-dimensional (2D) materials are accurately described by many-body methods including specifically pronounced electron-electron and electron-hole effects. Such methods are, however, computationally demanding and applicable on small computational cells only. We provide approximate optical gaps for 2D materials from time-dependent (TD) density functional theory based on a set of specific screened hybrid functionals and show that this approach effectively accounts for all important physical effects including excitons.

Highly Ordered N-Doped Carbon Dots Photosensitizer on Metal-Organic Framework-Decorated ZnO Nanotubes for Improved Photoelectrochemical Water Splitting.

In spite of having several advantages such as low cost, high chemical stability, and environmentally safe and benign synthetic as well as operational procedures, the full potential of carbon dots (CDs) is yet to be explored as photosensitizers due to the challenges associated with the fabrication of well-arrayed CDs with many other photocatalytic heterostructures. In the present study, a unique combination of metal-organic framework (MOF)-decorated zinc oxide (ZnO) 1D nanostructures as host and CDs as guest species are explored on account of their potential application in photoelectrochemical (PEC) water splitting performance. The synthetic strategy to incorporate well-defined nitrogen-doped carbon dots (N-CDs) arrays onto a zeolitic imidazolate framework-8 (ZIF-8) anchored on ZnO 1D nanostructures allows a facile unification of different components which subsequently plays a decisive role in improving the material's PEC water splitting performance.

Accurate many-body calculation of electronic and optical band gap of bulk hexagonal boron nitride.

Many-body perturbational GW approximation in conjunction with the Bethe-Salpeter equation (BSE) has been employed to calculate accurate electronic and optical band gaps of bulk hexagonal boron nitride (h-BN) in the two most important stacking configurations, AA' and AB. The carefully converged results revealed h-BN as an indirect material (indirect gap ≈ 6.1 eV) with a huge excitonic effect (≈0.

Transformations of ferrates(iv,v,vi) in liquids: Mössbauer spectroscopy of frozen solutions.

The kinetics and mechanism of ferrate(iv), (v) and (vi) transformations in water and in polar organic solvents (namely ethanol and tetrahydrofuran) have been investigated by the method of 57Fe Mössbauer spectroscopy of frozen solutions. Ethanol with a very limited amount of water under an inert atmosphere, significantly slows down the transformation reactions of ferrates(iv and v) and provides direct proof of the existence of intermediate states. Simultaneously, ethanol is oxidized to caboxylates in the close vicinity of the surface of ferrate crystallites as proven by X-ray photoelectron spectroscopy.

Sb-Doped SnO Nanorods Underlayer Effect to the α-Fe O Nanorods Sheathed with TiO for Enhanced Photoelectrochemical Water Splitting.

Here, a Sb-doped SnO (ATO) nanorod underneath an α-Fe O nanorod sheathed with TiO for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α-Fe O nanorod sheathed with TiO enhances the PEC water splitting performance. The growth of the well-defined ATO nanorods is reported as a conductive underlayer to improve α-Fe O PEC water oxidation performance.

Room temperature organic magnets derived from sp functionalized graphene.

Materials based on metallic elements that have d orbitals and exhibit room temperature magnetism have been known for centuries and applied in a huge range of technologies. Development of room temperature carbon magnets containing exclusively sp orbitals is viewed as great challenge in chemistry, physics, spintronics and materials science. Here we describe a series of room temperature organic magnets prepared by a simple and controllable route based on the substitution of fluorine atoms in fluorographene with hydroxyl groups.

Adsorption of Organic Molecules to van der Waals Materials: Comparison of Fluorographene and Fluorographite with Graphene and Graphite.

Understanding strength and nature of noncovalent binding to surfaces imposes significant challenge both for computations and experiments. We explored the adsorption of five small nonpolar organic molecules (acetone, acetonitrile, dichloromethane, ethanol, ethyl acetate) to fluorographene and fluorographite using inverse gas chromatography and theoretical calculations, providing new insights into the strength and nature of adsorption of small organic molecules on these surfaces. The measured adsorption enthalpies on fluorographite range from -7 to -13 kcal/mol and are by 1-2 kcal/mol lower than those measured on graphene/graphite, which indicates higher affinity of organic adsorbates to fluorographene than to graphene.

α-FeO/TiO 3D hierarchical nanostructures for enhanced photoelectrochemical water splitting.

We report the fabrication of 3D hierarchical hetero-nanostructures composed of thin α-FeO nanoflakes branched on TiO nanotubes. The novel α-FeO/TiO hierarchical nanostructures, synthesized on FTO through a multi-step hydrothermal process, exhibit enhanced performances in photo-electrochemical water splitting and in the photocatalytic degradation of an organic dye, with respect to pure TiO nanotubes. An enhanced separation of photogenerated charge carriers is here proposed as the main factor for the observed photo-activities: electrons photogenerated in TiO are efficiently collected at FTO, while holes are transferred to the α-FeO nanobranches that serve as charge mediators to the electrolyte.

Fluorinated graphenes as advanced biosensors - effect of fluorine coverage on electron transfer properties and adsorption of biomolecules.

Graphene derivatives are promising materials for the electrochemical sensing of diverse biomolecules and development of new biosensors owing to their improved electron transfer kinetics compared to pristine graphene. Here, we report complex electrochemical behavior and electrocatalytic performance of variously fluorinated graphene derivatives prepared by reaction of graphene with a nitrogen-fluorine mixture at 2 bars pressure. The fluorine content was simply controlled by varying the reaction time and temperature.