Transition metal (Ti, Cu, Zn, Pt) single-atom modified graphene/AS2 (A = Mo, W) van der Waals heterostructures for removing airborne pollutants.

Air pollution is a worldwide issue that affects human health and the environment. The scientific community tries to control it through different approaches, from experimental to theoretical assessments. Here, we perform DFT calculations to describe CO2, NO2, and SO2 detection on a single-atom (Ti, Cu, Zn, Pt) graphene supported on 2D molybdenum disulfide (MoS2) and tungsten disulfide (WS2). Transition metal single atoms on graphene improve the monolayer reactivity by generating an effective way to remove airborne pollutants. Results indicate that SO2 and NO2 chemically adsorb on all tested transition metals, whereas CO2 stands on top of the incorporated atoms through van der Waals interactions. Since strong Ti-O interactions appear, the Ti single-atom graphene/MoS2(WS2) systems efficiently remove CO2 from the environment. Compared to pristine graphene, our proposed heterostructures improve the SO2, NO2, and CO2 adsorption energies. The heterostructures' electronic properties change once the molecules interact with the transition metals, generating sensible and selective pollutant molecule detection and removal.

Ab initio study of the adsorption of SO2 on single-atom Cu-decorated ZnO(0001) surface.

CONTEXT: The World Health Organization has cataloged sulfur dioxide (SO2) as harmful for the human health and the environment. It also contributes to generate acid rain, which affects the ecosystems. To reduce its negative effects, new strategies to control the emissions are required. New and engineered materials are investigated to detect, capture, and eradicate toxic gases from the environment. Zinc oxide is considered a promising candidate. Here, we investigate the Cu-decorated ZnO(0001) surfaces as a single-atom catalyst (SAC) to reduce SO2 by first-principles calculations. We propose a two-step reduction mechanism. First, one of the S-O bonds is broken on the pristine surface, with a calculated activation energy of 14.76 kcal/mol, 1.84 kcal/mol larger than the one obtained in the Cu SAC. In the second step, the SO reduction is viable only for Cu SAC, with calculated activation energy of 29.28 kcal/mol. Our results point that Cu SAC improves the SO2 reduction, pointing it as a potentially efficient device to eradicate such harmful pollutant from the environment. METHODS: The calculations were performed using the density functional theory, as implemented in quantum ESPRESSO package. The exchange-correlation energy was calculated within the generalized gradient approximation with the Perdew-Burke-Ernzerhof parameterization. Van der Waals dispersion-corrected interactions were considered. Spin-polarization was considered for studying dangling bonds in transition states. The minimum energy pathways were calculated by using the climbing image nudged elastic band.

Electron correlations and memory effects in ultrafast electron and hole dynamics in VO2.

By applying an approach based on time-dependent density functional theory and dynamical mean-field theory (TDDFT+DMFT) we examine the role of electron correlations in the ultrafast breakdown of the insulating M1 phase in bulk VO2. We consider the case of a spatially homogeneous ultrafast (femtosecond) laser pulse perturbation and present the dynamics of the melting of the insulating state, in particular the time-dependence of the excited charge density. The time-dependence of the chemical potential of the excited electron and hole subsystems shows that even for such short times the dynamics of the system is significantly affected by memory effects-the time-resolved electron-electron interactions. The results pave the way for obtaining a microscopic understanding of the ultrafast dynamics of strongly-correlated materials.

Studies of hydrogen sulfide and ammonia adsorption on P- and Si-doped graphene: density functional theory calculations.

Studies of hydrogen sulfide (H2S) and ammonia (NH3) adsorption on phosphorus (P) and silicon (Si) doped graphene are performed by ab initio calculations using the periodic density functional theory (DFT). The P and Si incorporation in graphene distorts the unit cell altering the bond lengths and angles. Unlike the pristine, the phosphorus-doped graphene shows a metallic behavior, and the silicon-doped graphene is a semiconductor with an energy gap of 0.25 eV. Moreover, the electronic properties of phosphorus-doped graphene may change with the adsorption of hydrogen sulfide and ammonia. However, the silicon-doped graphene only shows changes with the adsorption of hydrogen sulfide. In addition, the silicon-doped graphene exhibits chemisorption when interacting with ammonia. According to the obtained results, phosphorus-doped graphene is suitable as a gas sensor of hydrogen sulfide and ammonia, in contrast with the silicon-doped structure, which may be used as a sensor of hydrogen sulfide. Graphical Abstract Ammonia adsorption on Si-doped graphene.

Interfacial and coexistence properties of soft spheres with a short-range attractive Yukawa fluid: molecular dynamics simulations.

Molecular dynamics simulations have been carried out to obtain the interfacial and coexistence properties of soft-sphere attractive Yukawa (SAY) fluids with short attraction range, κ = 10, 9, 8, 7, 6, and 5. All our simulation results are new. These data are also compared with the recently reported results in the literature of hard-core attractive Yukawa (HAY) fluids. We show that the interfacial and coexistence properties of both potentials are different. For the surveyed systems, here we show that all coexistence curves collapse into a master curve when we rescale with their respective critical points and the surface tension curves form a single master curve when we plot γ* vs. T/T(c).

Investigating the electronic properties of silicon nanosheets by first-principles calculations.

Using first-principles total energy calculations within the density functional theory (DFT), we investigated the electronic and structural properties of graphene-like silicon sheets. Our studies were performed using the LSDA (PWC) and GGS (PBE) approaches. Two configurations were explored: one corresponding to a defect-free layer (h-Si), and the other to a layer with defects (d-Si), both of which were in the armchair geometry. These sheets contained clusters of the C(n)H(m) type. We also investigated the effects of doping with group IV-A elements. Structural stability was studied by only considering positive vibration frequencies. Results showed that both h-Si and d-Si present a corrugated structure with concavity. h-Si sheets were found to be ionic (D.M. = 0.33 Debye) with an energy gap (HOMO-LUMO) of 0.77 eV in the LSDA theory and 0.76 eV in the GGS approach, while d-Si sheets were observed to be covalent (D.M. = 2.78 D), and exhibited semimetallic electronic behavior (HOMO-LUMO gap = 0.32 eV within the LSDA theory and 0.33 eV within the GGS approach). d-Si sheets doped with one carbon or one germanium preserved the polarity of the undoped d-Si sheets, as well as their semimetallic electronic behavior. However, when the sheets were doped with two C or two Ge atoms, or with one of each atom (to give Si(52)CGeH(18)), they retained the semimetallic behavior, but they changed from having ionic character to covalent character.