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.

CO to formaldehyde transformation study on pristine and Au-modified BaTiO3(001) through DFT calculations.

CONTEXT: BaTiO3 is one of the most important ferroelectric oxides in electronic applications. Also, it has attractive properties for catalysis that could be used for reducing contamination levels, especially carbon monoxide, CO. CO is one of the main gaseous pollutants generally released from the combustion of fossil fuel. In this work, the CO transformation on pristine and Au-modified BaTiO3 perovskite for H2CO obtention is studied. The CO adsorption and hydrogenation on pristine BaTiO3 leads to formaldehyde synthesis as the most stable product through two possible routes. Furthermore, hydrogenation stages are less probable on pristine BaTiO3. On Au-modified BaTiO3 formaldehyde is the principal product too but Au adatom generates H2CO competition with HCOH. After BaTiO3 modification with Au unpaired electrons were generated. These unpaired electrons are related to the adatom reactivity. According to the obtained results, pristine and Au-modified BaTiO3 can adsorb and hydrogenate CO generating formaldehyde as the principal product. BaTiO3 modifications with Au increase the reactivity of the perovskite in the CO hydrogenation reactions. CO hydrogenation process on Au suggests that further hydrogenation stages beyond formaldehyde are possible. METHODS: The study was performed through ab initio calculations using the periodic spin-polarized Density Functional Theory (DFT) as implemented in Quantum ESPRESSO. DFT calculations were carried out using the Plane Wave self-consistent field (PWscf). Spin density difference allows us to identify reactive regions related to dangling bonds and unpaired electrons. A plane wave basis set was used to represent the electron states. Vanderbilt pseudopotentials with nonlinear core correction were used to model the ionic cores and valence electrons interaction. Exchange-correlation energies were treated within the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) parameterization.

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.

Predicting the stability and electronic structure of alkali metal aurides.

Density functional theory calculations of phonon modes predict that some compounds of the alkali metal aurides family, general formulaA2MAu6(A= K, Rb or Cs;M= Ti, Zr, Hf, Sn or Pb), have stable three-dimensional phase with a double perovskite-type structure and cubicFm3¯mspace group (K2PtCl6-type). Bader's charge analysis shows that most electron density is located within the six atoms at the octahedra vertices like double perovskite halides. However, the short spacing between Au anions enables d-orbital interactions between them. Compounds of this family, with group 4 metals only, carry conduction states around the Γ point (k= 0). On the other hand, compounds with group 14 metals possess more conduction states around all the Brillouin zone and have electron pockets in their band structures. These compounds provide further insights into the unusual anionic behavior of gold and present other alternatives for the construction of divergent nanodevices.

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.